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단백질 분해, 아미노산 흡수 및 소화관에서의 대사. (A) 위장에 도달한 단백질은 염산과 펩신에 의해 변성 과정을 거쳐 폴리펩타이드를 생성합니다 [25]. 소장에서 췌장에서 분비된 프로테아제와 펩티다제는 폴리펩타이드의 분해 과정을 계속하여 더 작은 펩타이드와 자유 아미노산을 생성합니다. 소장의 장상피세포는 일부 펩타이드의 가수분해를 완료하는 펩티다제를 분비합니다. (B) 아미노산은 장상피세포의 아피칼 및 기저측 막에 발현된 특정 아미노산 운반체 (Solute Carriers Transporters (SLC))를 통해 장 내강에서 혈액 순환계로 이동됩니다 [11]. (C) 섭취된 아미노산과 (D) 단백질의 생체 이용률은 다중 질소 유도체나 폴리아민, 일산화질소, 단쇄 지방산, 암모니아 등 다양한 화합물의 생성에 기여할 수 있습니다.

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Amino acid metabolism in health and disease

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• Review Article
• Open access
• Published: 13 September 2023

Amino acid metabolism in health and disease

• Zhe-Nan Ling, 
• Yi-Fan Jiang, 
• Jun-Nan Ru, 
• Jia-Hua Lu, 
• Bo Ding & 
• Jian Wu 

Signal Transduction and Targeted Therapy volume 8, Article number: 345 (2023) Cite this article

•  
•  
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Abstract

Amino acids are the building blocks of protein synthesis. They are structural elements and energy sources of cells necessary for normal cell growth, differentiation and function. Amino acid metabolism disorders have been linked with a number of pathological conditions, including metabolic diseases, cardiovascular diseases, immune diseases, and cancer. In the case of tumors, alterations in amino acid metabolism can be used not only as clinical indicators of cancer progression but also as therapeutic strategies. Since the growth and development of tumors depend on the intake of foreign amino acids, more and more studies have targeted the metabolism of tumor-related amino acids to selectively kill tumor cells. Furthermore, immune-related studies have confirmed that amino acid metabolism regulates the function of effector T cells and regulatory T cells, affecting the function of immune cells. Therefore, studying amino acid metabolism associated with disease and identifying targets in amino acid metabolic pathways may be helpful for disease treatment. This article mainly focuses on the research of amino acid metabolism in tumor-oriented diseases, and reviews the research and clinical research progress of metabolic diseases, cardiovascular diseases and immune-related diseases related to amino acid metabolism, in order to provide theoretical basis for targeted therapy of amino acid metabolism.

아미노산은 

단백질 합성의 기본 단위입니다. 

이들은 

세포의 구조적 요소이자 에너지 공급원으로, 

정상적인 세포 성장, 분화 및 기능에 필수적입니다. 

아미노산 대사 장애는 

대사 질환, 심혈관 질환, 면역 질환, 암 등 

다양한 병리적 상태와 연관되어 있습니다. 

종양의 경우, 

아미노산 대사 변화는 

암 진행의 임상적 지표로 활용될 뿐만 아니라 

치료 전략으로도 활용될 수 있습니다. 

종양의 성장과 발달은 

외부 아미노산의 섭취에 의존하기 때문에, 

종양 관련 아미노산의 대사를 표적으로 삼아 

종양 세포를 선택적으로 죽이는 연구가 점점 더 증가하고 있습니다. 

또한 

면역 관련 연구는 

아미노산 대사가 

효과 T 세포와 조절 T 세포의 기능을 조절하여 

면역 세포의 기능에 영향을 미친다는 것을 확인했습니다. 

따라서 

질병과 관련된 아미노산 대사를 연구하고 

아미노산 대사 경로 내의 표적을 식별하는 것은 질병 치료에 도움이 될 수 있습니다. 

이 논문은 

종양 관련 질환에서의 아미노산 대사 연구에 주로 초점을 맞추며, 

아미노산 대사와 관련된 대사 질환, 

심혈관 질환 및 면역 관련 질환의 연구 및 임상 연구 진전을 검토하여 

아미노산 대사 표적 치료의 이론적 기반을 제공하기 위해 작성되었습니다.

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Introduction

The primary function of amino acids is to act as the monomer unit in protein synthesis and as substrates for biosynthetic reactions.1,2 Amino acid metabolism disorders have been linked to the progression of various diseases. For example, the deletion of tumor suppressor genes, such as PTEN and P53 or the activation of tumor genes, such as c-Myc and Ras, may induce changes in nutrient supply, metabolic enzymes, metabolic requirements and many other metabolic characteristics. Therapeutically targeting tumor cell metabolism have been proven effective with fewer side effects compared to some conventional treatments.3,4 Moreover, therapies targeting essential amino acids, such as dietary methionine restriction has been shown to extend lifespan in mice and rats.5,6,7,8 Tumors likely rely on external supply of nonessential amino acids.9 Therefore, restriction of these amino acids can inhibit tumor growth, demonstrating the importance of amino acid metabolism. Besides its role in cancer, amino acid metabolism has been reported as an important participant in the development of metabolic diseases such as diabetes and obesity, as well as cardiovascular diseases, autoimmune diseases and neurological diseases.10,11,12,13,14,15,16,17,18,19,20 Herein, we discussed the metabolism of amino acids in health and disease and the potential clinical application of amino acid metabolism in treating cancer and other diseases.

소개

아미노산의 주요 기능은

단백질 합성의 단위체로 작용하고

생합성 반응의 기질로 사용되는 것입니다.1,2

아미노산 대사 장애는

다양한 질병의 진행과 연관되어 있습니다.

예를 들어,

PTEN 및 P53과 같은 종양 억제 유전자의 결손이나

c-Myc 및 Ras와 같은 종양 유전자의 활성화는

영양 공급, 대사 효소, 대사 요구량 및 기타 많은 대사 특성의 변화를 유발할 수 있습니다.

종양 세포 대사 과정을 표적으로 하는 치료법은

일부 전통적인 치료법보다 부작용이 적으면서도 효과적임이 입증되었습니다.3,4

또한 필수 아미노산을 표적으로 하는 치료법,

예를 들어 식이 메티오닌 제한은

쥐와 랫트에서 수명을 연장시키는 것으로 나타났습니다.5,6,7,8

종양은

비필수 아미노산의 외부 공급에 의존할 가능성이 높습니다.9

비필수 아미노산은 단순히 단백질 합성에 필요한 20가지 아미노산 중 11가지에 불과한 것을 넘어, 종양 대사에서 다양한 중요한 역할을 수행합니다. 이러한 다양한 기능에는 거대분자 생합성의 전구체 제공, 환원-산화 상태 및 항산화 시스템 조절, 번역 후 및 에피게놈적 변형의 기질 역할 등이 포함됩니다. 이 기능적 다양성은 암 치료를 위해 비필수 아미노산 대사 경로를 표적으로 삼는 연구에 큰 관심을 불러일으켰으며, 이미 임상에서 사용 중이거나 현재 임상 시험 중인 여러 치료법의 개발을 촉진했습니다. 이 리뷰에서는 11가지 비필수 아미노산 각각이 암에서 수행하는 중요한 역할, 그들의 대사 경로가 어떻게 연결되어 있는지, 그리고 연구자들이 암 치료를 위해 비필수 아미노산 대사 경로를 표적으로 삼는 데 직면한 독특한 도전 과제를 극복하기 위해 어떻게 노력하고 있는지 논의할 것입니다.

따라서

이러한 아미노산의 제한은

종양 성장 억제를 유발하여 아미노산 대사의 중요성을 보여줍니다.

암 외에도 아미노산 대사는

당뇨병과 비만과 같은 대사 질환, 심혈관 질환, 자가면역 질환, 신경계 질환의 발생에

중요한 역할을 한다는 보고가 있습니다. 10,11,12,13,14,15,16,17,18,19,20

비만과 인슐린 저항성이 분지쇄 아미노산 및 향기족 아미노산의 혈중 농도 증가와 글리신 농도 감소와 강한 연관성이 인간 대상에서 수십 년간 인정되어 왔습니다. 검토 범위 최근 인간 대사체학 및 유전적 연구는 이러한 관찰 결과를 확인하고 확장했으며, 아미노산 균형 장애의 메커니즘을 규명하는 전임상 연구가 급증했습니다. 이 연구들은 아미노산 균형 장애가 혈당 및 지질 대사 장애와 어떻게 연결되는지, 분지쇄 아미노산(BCAA)의 증가가 인슐린 저항성, 제2형 당뇨병(T2D), 기타 심혈관 대사 질환 및 상태의 발병에 어떻게 기여할 수 있는지 밝혔습니다. 주요 결론 인간 코호트 연구에서 BCAA 및 관련 대사산물은 비만, 인슐린 저항성, T2D, 심혈관 질환의 가장 강력한 생물학적 지표 중 하나로 확립되었습니다. 비만 동물 모델에서 BCAA 제한 식이 또는 BCAA 대사 속도 제한 효소인 분지쇄 케토산 탈수소효소(BCKDH) 활성화를 통해 BCAA 및 분지쇄 케토산(BCKA) 수치를 감소시키는 것은 포도당 및 지질 균형에 명확한 유익한 효과를 보이지만, 인간 T2D 대상에서 단기 연구에서는 BCAA 제한의 효과가 상대적으로 미미합니다. 설탕이나 과당으로 풍부한 식이를 섭취한 쥐에서는 간에서 ChREBP 전사 인자가 유도되어 BCKDH 키나아제(BDK)의 발현이 증가하고 그 인산화효소(PPM1K)의 발현이 억제되어 BCKDH가 비활성화되고 주요 지질 합성 효소인 ATP-시트르산 리아제(ACLY)가 활성화됩니다. 이러한 및 기타 BCAA, 글루코스, 지방 대사 간의 새로운 연관성은 BCAA 및 관련 대사산물이 심혈관 대사 질환의 발병에 미치는 잠재적 인과적 작용을 탐구하는 지속적인 연구를 촉진하고 있습니다.

면역 체계의 잘못된 방향은 류마티스 관절염(RA)의 자가면역 조직 염증을 유발하며, 이 과정에서 사이토킨 TNF의 과도한 생산이 중요한 병리학적 사건으로 작용합니다. 자기 내성 파괴의 메커니즘은 명확하지 않지만, 관절염 관절 내 T 세포는 ATPlo 아세틸-CoAhi를 특징으로 하는 염증성 효과 세포의 독특한 대사적 특성을 나타냅니다. 본 연구에서는 이러한 자가면역 T 세포에서 미토콘드리아 아스파르트산 생산 결핍이 핵심 이상으로 확인되었습니다. 미토콘드리아 아스파르트산 부족은 대사 보조인자 니코틴아미드 아데닌 디뉴클레오티드(NAD)의 재생산을 방해하여 내소체(ER) 센서 GRP78/BiP의 ADP-데리보실화를 유발했습니다. 이로 인해 리보솜이 풍부한 ER 막이 확장되어 동시 번역적 이동과 막을 관통하는 사이토킨 TNF의 생합성이 증가했습니다. 관절염 관절에서 TNF의 주요 생산 세포는 ERrich T 세포였습니다. T 세포에 완전한 미토콘드리아를 이식하거나 외인성 아스파르트산을 보충하면 미토콘드리아에 의해 조절되는 ER 막의 확장이 회복되었으며, TNF 분비와 류마티스 조직 염증이 억제되었습니다.

본 논문에서는

건강과 질병에서의 아미노산 대사 및 암 및 기타 질환 치료에

아미노산 대사의 잠재적 임상 적용 가능성에 대해 논의했습니다.

Overview of amino acid metabolism

Amino acids are organic compounds containing amino and carboxyl groups, which can be divided into α-, β-, γ-, δ- amino acids according to the position of the functional groups of the core structure, the most important of which are the 22 alpha-amino acids that make up proteins and 20 of these amino acids are involved in protein synthesis. Amino acids are involved in biosynthesis, neurotic transmission, and other life processes.1,2 Peptide bonds link amino acids to form polypeptide chains, which undergo post-translational modifications and sometimes combine with other polypeptide chains to form proteins. Among amino acids that make up proteins, nine cannot be synthesized from other compounds and must be obtained from food; these are also essential amino acids.21,22 When amino acids are ingested by the human body from food, in addition to being used for protein and other biomolecular synthesis, they can also be oxidized to urea and carbon dioxide as energy sources through oxidative pathways.23

The oxidation pathway begins with aminotransferase-mediated deamination and transfers the amino group to alpha-ketoglutaric acid to form glutamate to enter the urea cycle. Another product, keto acid, enters the citric acid cycle to provide energy for life activities (Fig. 1).24 The uptake of amino acids by cells or organelles requires the participation of amino acid transporters (AATs). Different amino acids depend on specific AATs, but amino acids and transporters are not one-to-one matched. Multiple AATs can transport an amino acid, and the same transporter can also transport multiple substrates. In addition to serving as a channel for amino acids to enter and exit the cell, AATs also function as a probe for sensing amino acid levels and as an initiator of nutritional signals.25,26 According to the diversity of structure and function, AATs can be divided into different families, in which the solute carrier (SLC) superfamily accounts for about 20% of all membrane proteins encoded by the human genome and is the largest superfamily of membrane transporters.27 According to substrate specificity, AATs can be divided into neutral, basic, and acidic categories, and further subcategories, including sodium-dependent and sodium-independent types. Mechanistically, because amino acid concentrations in the intracellular fluid are generally higher than those in the extracellular fluid in mammalian cells, including humans, AATs transport amino acids through ion conjugation or amino acid exchange to produce sodium ions. Hydrogen or chloride cotransporters and potassium reverse transporters maintain intracellular and extracellular Na+ and K+ concentration gradients through Na+/K+-ATP pumps.28 For the specific classification, function, and mechanism of AATs in the human body, we invite readers to review the following literature.27,29,30

아미노산 대사 개요

아미노산은

아미노 그룹과 카르복실 그룹을 포함하는 유기 화합물로,

핵심 구조의 기능 그룹 위치에 따라

α-, β-, γ-, δ- 아미노산으로 분류됩니다.

이 중 가장 중요한 것은 단백질을 구성하는

22개의 알파-아미노산이며,

이 중 20개는 단백질 합성에 관여합니다.

아미노산은

생합성, 신경 전달 및 기타 생명 과정에 관여합니다.1,2

펩타이드 결합은

아미노산을 연결하여 폴리펩타이드 사슬을 형성하며,

이 사슬은 번역 후 변형을 겪거나 다른 폴리펩타이드 사슬과 결합하여

단백질을 형성합니다.

단백질을 구성하는 아미노산 중 9개는

다른 화합물로부터 합성될 수 없으며

식품으로부터 섭취해야 하며,

이는 필수 아미노산으로도 알려져 있습니다.21,22

hill mpttv

인간이 식품으로부터 아미노산을 섭취할 때,

단백질 및 기타 생체 분자 합성에 사용되는 것 외에도

산화 경로를 통해 에너지 원으로 사용되어

요산과 이산화탄소로 산화될 수 있습니다.23

산화 경로는

아미노전달효소(aminotransferase)에 의해

아미노 그룹이 탈아미노화되어

알파-케토글루타르산에 전달되어

글루타메이트를 형성한 후 요산 순환에 진입합니다.

다른 생성물인 케토산은

시트르산 순환에 진입하여 생명 활동에 필요한 에너지를 제공합니다(그림 1).24

세포나 세포 소기관이 아미노산을 흡수하려면

아미노산 운반체(AATs)의 참여가 필요합니다.

다양한 아미노산은 특정 AAT에 의존하지만,

아미노산과 운반체는 1대1로 대응하지 않습니다.

여러 AAT가 동일한 아미노산을 운반할 수 있으며,

동일한 운반체는 여러 기질을 운반할 수 있습니다.

아미노산이 세포 내외로 이동하는 통로 역할을 하는 것 외에도,

AAT는 아미노산 수준을 감지하는 센서 역할을 하고

영양 신호의 시작점으로도 기능합니다. 25,26

AATs는 세포 내 에너지 대사, 단백질 합성, 유전자 발현, 산화환원 균형, 신호 전달 경로 및 세포 및 전체 신체 수준에서의 성장 조절에 중요한 역할을 하는 막을 관통하는 단백질입니다. 생물학적 중요성 때문에 AAT의 발현 및 기능 변화는 신경퇴행성 질환, 선천성 대사 장애, 만성 신장 질환 등 다양한 질환과 연관되어 있습니다. AAT는 호르몬(예: 인슐린 및 글루카곤)의 분비 및 방출에도 참여하며, 그 기능의 변화는 당뇨병의 병리 과정과 관련이 있을 가능성이 있습니다. AAT의 조절 장애는 단백질 및 뉴클레오티드의 생합성, ATP 및 NADPH의 생성을 포함한 대사 재프로그래밍을 통해 자가포식 및 종양 세포 증식에 관여합니다. SLC1A5, SLC7A5, SLC16A4 및 SLC38A2 등 여러 AAT가 유망한 항암제 표적으로 제안되어 있습니다. 종양 세포의 AAT 발현은 운반체 특이적 양전자 방출 단층 촬영(PET) 프로브를 활용한 종양 분자 영상화에 활용될 수 있습니다. 최근 PET 연구는 다양한 종양 유전자 활성화와 AAT를 통해 매개되는 세포 대사 변화 간의 밀접한 관계를 보여주었습니다. 이 새로운 접근 방식은 종양 등급 단계 모니터링 개선, 최적의 화학 요법 요법 계획 수립, 치료에 대한 종양 반응 모니터링을 통해 향후 환자 치료 관리 최적화에 기여할 것으로 기대됩니다. 많은 AAT는 여전히 연구가 부족하며, 그들의 기능과 병리생리학적 역할을 규명하는 것은 새로운 치료 전략과 약물 발견 기회를 열어줄 수 있습니다. 암 치료제가 종종 아미노산 모방체로 구성되어 있다는 점을 고려할 때, 많은 AAT가 이러한 약물과 직접 상호작용한다는 것은 놀랍지 않습니다. 따라서 종양 세포의 AAT 발현 수준은 약물 전달을 변경함으로써 약물 효능을 결정할 수 있습니다. 이러한 지식은 미래에 암 치료 결과 예측에 도움이 될 것입니다.

구조와 기능의 다양성에 따라 AAT는

다양한 가족으로 분류될 수 있으며,

이 중 용질 운반체(SLC) 초가족은

인간 게놈에 의해编码되는 모든 막 단백질의 약 20%를 차지하며,

막 운반체 중 가장 큰 초가족입니다.27

기질 특이성에 따라 AAT는

중성, 기본, 산성 유형으로 분류되며,

추가로 나트륨 의존형과 나트륨 독립형 등 하위 분류가 있습니다.

기전적으로,

포유류 세포(인간을 포함)의 세포 내액에서 아미노산 농도는

세포 외액보다 일반적으로 높기 때문에,

AAT는 이온 결합 또는 아미노산 교환을 통해 아미노산을 수송하여

나트륨 이온을 생성합니다.

수소 또는 염화물 공수송체와 칼륨 역수송체는

Na+/K+-ATP 펌프를 통해

세포 내외의 Na+와 K+ 농도 차이를 유지합니다.28

인간 몸에서 AAT의 구체적인 분류, 기능, 및 메커니즘에 대해 자세히 알고 싶으신 독자들은

다음 문헌을 참고하시기 바랍니다.27,29,30

Fig. 1

Overview of amino acid metabolism. The human body can obtain amino acids through food digestion and absorption, tissue decomposition, internal synthesis of three ways. Amino acids in amino acid metabolism pool can be deacidified to produce amino and carbon dioxide. Or participate in the synthesis of purine, pyrimidine and other nitrogenous compounds in the transformation of metabolites; Or deamination produces α-ketoacid and NH3. According to different enzymes and pathways, α-ketoacid can produce keto bodies, or participate in oxidative energy supply or sugar and lipid synthesis; NH3 enters the urea cycle. Created with BioRender.com

아미노산 대사 개요. 

인체는 

음식의 소화 및 흡수, 

조직 분해, 

내부 합성의 

세 가지 경로를 통해 아미노산을 얻을 수 있습니다. 

아미노산 대사 풀에 존재하는 아미노산은 

탈산화 반응을 통해 아민과 이산화탄소를 생성합니다. 

또는 대사 산물의 전환 과정에서 

푸린, 피리미딘 및 기타 질소 화합물의 합성에 참여하거나, 

탈아미노화 과정을 통해 α-케토산과 NH3를 생성합니다. 

다양한 효소와 경로를 통해 α-케토산은 

케톤체를 생성하거나 산화적 에너지 공급 또는 당 및 지질 합성에 참여할 수 있으며, 

NH3는 요소 순환에 들어갑니다. 

BioRender.com에서 제작되었습니다.

In addition to being components of peptides and proteins, amino acids are involved in key pathways that maintain cell growth, metabolism, and immunity.31,32,33,34,35 For example, the mammalian target of rapamycin (mTOR) signaling pathway is a major mechanism that regulates protein synthesis.36 The mTOR system contains rapamycin-sensitive complex 1 (mTORC1) and rapamycin-insensitive complex 2 (mTORC2). mTORC1 is activated by glutamine (Gln), arginine (Arg), and Leucine (Leu), and activates protein synthesis by phosphorylation of eIF4E binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1).37,38,39 Furthermore, alanine (Ala) can regulate gluconeogenesis and glycolysis by inhibiting alanine kinase, thereby maintaining the amount of glucose produced by the starved liver.38 Arginine regulates the active state of the urea cycle by acting as an allosteric activator of N-acetyl glutamate synthetase (a mitochondrial enzyme that converts glutamate and acetyl CoA to N-acetyl glutamate).40 In terms of immunity, amino acids are involved in immune cell proliferation, differentiation and functional activation. For example, T cell activation upregulates a variety of amino acid transporters, including SLC7A5, and deletion of SLC7A5 leads to activation of the mTOR signaling pathway and upregulation of the transcription factor MYC to inhibit T cell proliferation.41 When T cells are deprived of Trp and Arg, activated T cells cannot enter the S phase, which proves that Trp and Arg are key substances for T cells to enter the cell cycle. Moreover, the depletion of Leu and isoleucine (iLe) induces T cells to enter the S-G1 phase, which then stops dividing and expires.42,43,44

In summary, amino acids are essential organic compounds for life support, as raw materials for biosynthesis and as a source of energy for life activities. The cellular uptake of amino acids requires the involvement of AATs. Transporters serve as the entry and exit channels of amino acids and act as probes for sensing amino acid concentrations and promoters of nutritional signals. In addition to being a raw material for biomass and an energy source, amino acids are also involved in key pathways in terms of cell growth, metabolism and immunity.

아미노산은

펩타이드와 단백질의 구성 요소일 뿐만 아니라

세포 성장, 대사, 면역 기능을 유지하는 핵심 경로에 관여합니다. 31,32,33,34,35

예를 들어,

포유류 라파마이신 표적 단백질 (mTOR) 신호전달 경로는

단백질 합성을 조절하는 주요 메커니즘입니다.36

mTOR 시스템은

라파마이신에 민감한 복합체 1 (mTORC1)과

라파마이신에 불감한 복합체 2 (mTORC2)를 포함합니다.

mTORC1은

글루타민(Gln), 아르기닌(Arg), 류신(Leu)에 의해 활성화되며,

eIF4E 결합 단백질 1(4E-BP1)과 리보솜 단백질 S6 키나제 1(S6K1)의 인산화를 통해

단백질 합성을 활성화합니다. 37,38,39

또한

알라닌(Ala)은

알라닌 키나아제를 억제하여 글루코네오제네시스 및 글리코lysis를 조절함으로써

굶주린 간에서 생성되는 글루코스 양을 유지합니다.38

아르기닌은

N-아세틸 글루타메이트 합성효소

(미토콘드리아 효소로 글루타메이트와 아세틸 CoA를 N-아세틸 글루타메이트로 전환함)의

알로스테릭 활성화제로 작용하여

요소 순환의 활성 상태를 조절합니다. 40

면역 측면에서

아미노산은

면역 세포의 증식, 분화 및 기능 활성화에 관여합니다.

예를 들어,

T 세포 활성화는

SLC7A5를 포함한 다양한 아미노산 운반체를 상향 조절하며,

SLC7A5의 결손은 mTOR 신호 전달 경로를 활성화하고

전사 인자 MYC를 상향 조절하여 T 세포 증식을 억제합니다.41

T 세포가

트립토판(Trp)과 아르기닌(Arg)이 결핍되면

활성화된 T 세포는 S 단계로 진입할 수 없으며,

이는 Trp와 Arg가 T 세포가 세포 주기에 진입하는 데 필수적인 물질임을 증명합니다.

또한,

류신(Leu)과 이소류신(iLe)의 고갈은

T 세포가 S-G1 단계로 진입하게 하여 분열을 중단하고 사멸하게 합니다.42,43,44

요약하면,

아미노산은 생체 유지에 필수적인 유기 화합물로,

생합성의 원료 및 생명 활동의 에너지 공급원으로 기능합니다.

아미노산의 세포 내 흡수에는

AATs의 참여가 필요합니다.

운반체는 아미노산의 출입 통로 역할을 하며,

아미노산 농도를 감지하는 센서와 영양 신호 전달의 촉진제로 작용합니다.

아미노산은

생물질의 원료와 에너지 원천으로서의 역할 외에도

세포 성장, 대사, 면역과 관련된 핵심 경로에 관여합니다.

Branched-chain amino acids (BCAAs)

BCAAs metabolism

BCAAs are a class of fatty side chain amino acids with one branch, including Leu, iLe, and valine. Three BCAAs account for 35% of the essential amino acids in muscle as essential amino acids in the human body. The breakdown process of BCAAs is similar in all species, initially forming branched-chain α-keto acids (BCKAs) via branched-chain amino acid transferase (BCATs) and transferring nitrogen to nitrogen receptors (the most common nitrogen receptor is α-ketoglutaric acid (α-KG) to form glutamate).45 The second step is an irreversible rate-limiting reaction catalyzed by branched-chain α-keto acid dehydrogenase (BCKDH), which is phosphorylated and inactivated by the specific kinase BCKDH kinase (BCKDK) and dephosphorylated and activated by Protein phosphatase 1 K (PPM1K). The products are then involved in different physiological activities through further oxidation (Fig. 2).

분지쇄 아미노산 (BCAAs)

BCAAs 대사

BCAAs는

분지된 측쇄를 가진 지방산 아미노산의 한 종류로,

류신(Leu), 이소류신(iLe), 발린(Val)을 포함합니다.

BCAAs는

인체에서 필수 아미노산의 35%를 차지하는 필수 아미노산으로,

근육에서 필수 아미노산의 주요 구성 요소입니다.

BCAAs의 분해 과정은 모든 종에서 유사하며,

분지쇄 아미노산 전이효소(BCATs)를 통해 분지쇄 α-케토산(BCKAs)을 형성한 후

질소를 질소 수용체(가장 일반적인 질소 수용체는 α-케토글루타르산(α-KG)으로

글루타메이트를 형성합니다). 45

두 번째 단계는

분지쇄 알파-케토산 탈수소효소(BCKDH)에 의해 촉매되는 가역적 속도 제한 반응으로,

특정 키나아제인 BCKDH 키나아제(BCKDK)에 의해 인산화되어 비활성화되며,

단백질 인산화효소 1K(PPM1K)에 의해 인산화가 제거되어 활성화됩니다.

생성물은

추가 산화를 통해 다양한 생리적 활동에 참여합니다(그림 2).

Fig. 2

Glutamine and BCAA metabolism.

BCAAs can be absorbed by the cell through L-type amino acid transporter (LATs), and L-type amino acid transporter 1(LAT1) can also exchange intracellular glutamine with extracellular leucine. In cells, BCAAs are catalyzed to formα-ketoisocaproate (KIC), α-ketoisovalerate (KIV), and α-keto-β-methylvalerate (KMV). The three substances are collectively known as branched alpha-ketoacids (BCKAs). Further, BCKAs produce acetyl-CoA through an irreversible rate-limiting reaction catalyzed by branched alpha-ketoate dehydrogenase (BCKDH) and subsequent reactions. Acetyl-CoA may be involved in the TCA cycle or other amino acid synthesis. Glutamine can be transported by SLC1A5 (ASCT2), LAT1 (L-type amino acid transporter), and xCT (SLC7A11). Glutamine is involved in glutathione (GSH) synthesis and cell REDOX homeostasis regulation in cytoplasm. In the mitochondria, glutamine produces Glutamate through a reaction catalyzed by glutaminase (GLS), which participates in the TCA cycle by producing α-KG by aminotransferase (ATs) and Glutamate dehydrogenase (GLUD).

글루타민과 BCAA 대사.

BCAAs는 

L형 아미노산 운반체(LATs)를 통해 세포 내로 흡수될 수 있으며, 

L형 아미노산 운반체 1(LAT1)은

세포 내 글루타민과 세포 외 류신을 교환할 수 있습니다. 

세포 내에서 BCAA는 

α-케토이소카프로산(KIC), 

α-케토이소발레르산(KIV), 및 α-케토-β-메틸발레르산(KMV)으로 분해됩니다. 

이 세 물질은 분지형 알파-케토산(BCKAs)으로 통칭됩니다. 

또한 BCKAs는 

분지형 알파-케토산 탈수소효소(BCKDH)에 의해 촉매되는 가역적 속도 제한 반응을 통해 

아세틸-CoA를 생성하며, 

이후 반응을 통해 아세틸-CoA는 TCA 회로나 다른 아미노산 합성에 관여할 수 있습니다. 

글루타민은 

SLC1A5(ASCT2), LAT1(L-형 아미노산 운반체), 및 xCT(SLC7A11)에 의해 운반됩니다. 

글루타민은 

세포질에서 글루타티온(GSH) 합성과 세포 내 산화환원 균형 조절에 관여합니다. 

미토콘드리아에서는 

글루타민이 글루타미나제(GLS)에 의해 촉매되는 반응을 통해 글루타메이트를 생성하며, 

이는 아미노전달효소(ATs)와 글루타메이트 탈수소효소(GLUD)를 통해 α-KG를 생성하여 

TCA 회로에 참여합니다.

Created with BioRender.com. (The red blunt line represents inhibition)

Full size image

BCAAs participate in a variety of physiological processes. In terms of metabolism and signaling pathway research, BCAAs, especially Leu, are effective activators of the mTOR signaling pathway. Leu can bind to Sestrin2 (a negative regulator of mTORC1 activity) to promote mTORC1 activation,46 thereby promoting protein synthesis in the liver and other tissues.47 In addition, BCAAs also promote glycogen absorption by the liver and skeletal muscle and enhance glycogen synthesis.48 Furthermore, BCAAs are essential for the proper function of immune cells in the immune system, promoting lymphocyte proliferation and cytotoxic T-cell activation through the oxidative decomposition of dehydrogenase and decarboxylase expressed by immune cells.49

BCAAs는 다양한 생리적 과정에 참여합니다.

대사 및 신호 전달 경로 연구 측면에서 BCAAs,

특히 류신은 mTOR 신호 전달 경로의 효과적인 활성화제입니다.

류신은

mTORC1 활성의 음성 조절인자인 Sestrin2에 결합하여 mTORC1 활성화를 촉진하며,46

이로써 간 및 기타 조직에서의 단백질 합성을 촉진합니다. 47

또한 BCAAs는

간과 골격근의 글리코겐 흡수를 촉진하고 글리코겐 합성을 강화합니다.48

또한 BCAAs는

면역 체계에서 면역 세포의 정상적인 기능에 필수적이며,

면역 세포에서 발현되는 탈수소효소와 탈카복실화효소의 산화 분해를 통해

림프구 증식과 세포독성 T세포 활성화를 촉진합니다.49

BCAA in cancer

Changes in circulating levels of BCAAs have been reported in cancer patients.50,51 Recent metabonomics retrospective studies had shown that increased plasma levels of BCAAs are associated with an increased risk of pancreatic cancer, which was validated in a genetically engineered mouse model of pancreatic ductal adenocarcinoma (PDAC). This phenomenon may be caused by systematic protein breakdown to satisfy the BCAAs needed for its growth during the tumorigenic period.51 Moreover, another study suggested that KRAS mutations can promote BCAA metabolism. Although KRAS activation and P53 deletion are present in non-small cell lung cancer (NSCLC) and PDAC, the two tumors utilize BCAA differently despite the same initial events. PDAC cells tend to decompose and utilize extracellular proteins for amino acids, while NSCLC cells extract nitrogen by breaking down circulating BCAAs.52 In addition, Lei et al. found that CBP (cAMP-responsive element-binding (CREB)-binding protein) and SIRT4 in PDAC cells bind the K44 site of BCAT2 to acetylate this site, which further promotes the degradation of BCAT2 through the ubiquitin-protein pathway, reduces the metabolic rate of BCAAs in PDAC, and, in turn, inhibits the growth of tumor cells.53 In addition, KRAS and USP1 can also regulate the expression‎ of BCAT2 in PDAC through the ubiquitin-proteasome pathway: KRAS can stabilize the expression‎ of BCAT2 in PDAC by inhibiting the ubiquitination of BCAT2 by spleen tyrosine kinase (SYK) and E3 ubiquitination ligase TRIM21,54 while USP1 deubiquitinates the K229 site of BCAT2, and BCAAs promote USP1 protein expression‎ at the translation level through the GCN2-eIF2a pathway. Another study found that the expression‎ levels of USP1 and BCAT2 were consistently positively correlated in gene-edited mice and clinical samples.55 The Lei’s result further clarified why BCAAs metabolism of PDAC is lower than that of surrounding normal tissues and then turns to other ways to obtain nitrogen (Fig. 3).

BCAA와 암

암 환자에서

혈중 BCAA 수치의 변화가 보고되었습니다.50,51

최근 대사체학 기반 회고적 연구에서

혈장 내 BCAA 수치 증가가 췌장암 위험 증가와 연관되어 있으며,

이는 췌관 선암(PDAC) 유전자 변형 마우스 모델에서 검증되었습니다.

이 현상은

종양 발생 기간 동안 성장에 필요한 BCAA를 충족시키기 위해

체계적인 단백질 분해가 발생하기 때문일 수 있습니다.51

또한 다른 연구에서는 KRAS 돌연변이가 BCAA 대사 촉진을 유발할 수 있다는 제안이 있었습니다.

KRAS 활성화와 P53 결손은 비소세포 폐암(NSCLC)과 PDAC에서 모두 관찰되지만,

두 종양은 동일한 초기 사건에도 불구하고 BCAA를 다르게 활용합니다.

PDAC 세포는 아미노산을 얻기 위해 세포외 단백질을 분해하고 활용하는 반면, NSCLC 세포는 순환하는 BCAA를 분해하여 질소를 추출합니다. 52 또한 Lei 등 연구진은 PDAC 세포에서 CBP(cAMP-responsive element-binding (CREB)-binding protein)와 SIRT4가 BCAT2의 K44 부위에 결합하여 이 부위를 아세틸화하며, 이는 ubiquitin-protein 경로를 통해 BCAT2의 분해를 촉진하고 PDAC에서의 BCAA 대사 속도를 감소시켜 종양 세포의 성장을 억제한다는 사실을 발견했습니다. 53 또한 KRAS와 USP1은 PDAC에서 BCAT2의 발현을 유비퀴틴-프로테아좀 경로를 통해 조절합니다: KRAS는 비장 티로신 키나제(SYK)와 E3 유비퀴틴화 리가제 TRIM21에 의한 BCAT2의 유비퀴틴화를 억제하여 PDAC에서 BCAT2의 발현을 안정화시킵니다.54 반면 USP1은 BCAT2의 K229 부위를 데유비퀴틴화하며, BCAAs는 GCN2-eIF2a 경로를 통해 USP1 단백질 발현을 번역 수준에서 촉진합니다. 또 다른 연구에서는 유전자 편집 마우스와 임상 샘플에서 USP1과 BCAT2의 발현 수준이 일관되게 양의 상관관계를 보였다는 것이 밝혀졌습니다.55 Lei의 결과는 PDAC에서 BCAA 대사율이 주변 정상 조직보다 낮고, 이후 질소를 얻기 위해 다른 방법으로 전환되는 이유를 더욱 명확히 설명했습니다(그림 3).

Fig. 3

BCAAs metabolism in Cancer.

In pancreatic ductal adenocarcinoma (PDAC), KRAS can inhibit the ubiquitination of BCAT2 by spleen tyrosine kinase (SYK) and E3 ubiquitination ligase TRIM21, thereby stabilizing the expression‎ level of BCAT2 in PDAC cells and promoting the proliferation of tumor cells. BCAAs promote Ubiquitin Specific Peptidase 1 (USP 1) through the GCN2-eIF2a pathway and inhibit the degradation of BCAT2 by deubiquitination of the K299 site of BCAT2. This process is inhibited during the BCAAs deprivation. cAMP-responsive Elin-Binding (CREB)-binding protein (CBP) and SIRT4 compete to bind the K44 site of BCAT2, regulating the acetylation level of this site and the degradation of BCAT2. In triple-negative breast cancer, tumor cells can activate MAPK and PI3K/AKT signaling through IGF-1 and insulin signaling, and PI3K/AKT signaling can go on to activate Foxo3a, mTOR signaling, BCAT in the cytoplasm of tumor cells can also promote mitochondrial genesis and mitochondrial function by activating Foxo3a, AKT, mTOR, and Nrf2 to gain survival advantages.

BCAAs의 대사 과정과 암.
췌관 선암(PDAC)에서 KRAS는 비장 티로신 키나제(SYK)와 E3 유비퀴틴화 리가제 TRIM21을 통해 BCAT2의 유비퀴틴화를 억제함으로써 PDAC 세포 내 BCAT2의 발현 수준을 안정화시키고 종양 세포의 증식을 촉진합니다. BCAAs는 GCN2-eIF2a 경로를 통해 Ubiquitin Specific Peptidase 1 (USP 1)을 촉진하고, BCAT2의 K299 부위의 유비퀴틴화 제거를 통해 BCAT2의 분해를 억제합니다. 이 과정은 BCAAs 결핍 시 억제됩니다. cAMP 반응성 엘린 결합 단백질(CREB) 결합 단백질(CBP)과 SIRT4는 BCAT2의 K44 부위에 결합하여 이 부위의 아세틸화 수준과 BCAT2의 분해를 조절합니다. 삼중 음성 유방암에서 종양 세포는 IGF-1 및 인슐린 신호전달을 통해 MAPK 및 PI3K/AKT 신호전달을 활성화하며, PI3K/AKT 신호전달은 Foxo3a를 활성화하여 mTOR 신호전달을 촉진합니다. 종양 세포의 세포질 내 BCAT는 Foxo3a, AKT, mTOR, Nrf2를 활성화하여 미토콘드리아 생성과 기능을 촉진하여 생존 우위를 획득합니다.

Created with BioRender.com. (The red blunt line represents inhibition; The dotted line indicates that the middle step is omitted)

Increasing evidence suggests that elevated plasma BCAAs is a risk factor for pancreatic cancer. Yet, whether elevated circulating BCAAs promotes PDAC progression or PDAC produces more BCAAs. Elevated circulating BCAAs have been observed in both human and mouse models of pancreatic cancer in the early stages of progression, and blood BCAAs levels rise due to excessive protein breakdown in the tissues surrounding pancreatic cancer.51,56 Zhu et al. assessed the metabolic reprogramming in tumors and found that metabolic signals were cross-linked between PDAC and CAFs. CAFs significantly increase the catabolism of BCAAs and the secretion of BCKAs in the nutrient-poor tumor microenvironment (TME). PDAC uses BCKAs secreted by CAFs as substrates for BCAAs synthesis or increases the oxidative metabolic flux of BCKA in a BCKDH-dependent mode.57 This study suggests the feasibility of targeting BCAAs metabolism in TME mesenchymal and cancer cells for PDAC therapy (Fig. 4).

증가하는 증거는 혈장 내 분지쇄 아미노산(BCAA) 수치가 췌장암의 위험 요인임을 시사합니다. 그러나 혈중 BCAA 수치가 췌장암 진행을 촉진하는지, 아니면 췌장암이 더 많은 BCAA를 생성하는지 여부는 명확하지 않습니다. 췌장암의 초기 진행 단계에서 인간과 쥐 모델 모두에서 혈중 BCAA 수치가 증가했으며, 이는 췌장암 주변 조직에서의 과도한 단백질 분해로 인해 발생합니다.51,56 Zhu 등 연구진은 종양 내 대사 재프로그래밍을 평가했으며, PDAC와 CAF(췌장암 관련 섬유아세포) 사이에서 대사 신호가 교차 연결되어 있음을 발견했습니다. CAFs는 영양분이 부족한 종양 미세환경(TME)에서 BCAA의 분해와 BCKA 분비를 크게 증가시킵니다. PDAC는 CAFs가 분비한 BCKA를 BCAA 합성의 기질로 사용하거나 BCKDH 의존적 방식으로 BCKA의 산화적 대사 유동을 증가시킵니다.57 이 연구는 PDAC 치료를 위해 TME의 간질 세포와 암 세포에서 BCAA 대사 경로를 표적으로 삼는 가능성을 제시합니다(그림 4).

Fig. 4

BCAAs metabolism in tumor microenvironment. In triple-negative breast cancer, tumor cells can activate MAPK and PI3K/AKT signaling through IGF-1 and insulin signaling, and PI3K/AKT signaling can go on to activate Foxo3a, mTOR signaling, BCAT in the cytoplasm of tumor cells can also promote mitochondrial genesis and mitochondrial function by activating Foxo3a, AKT, mTOR, and Nrf2 to gain survival advantages. In Leukemia, the RNA-binding protein Musashi 2 (MSI2) binds to BCAT1 mRNA to promote the translation of BCAT1. BCAT1 containing CXXC motif has strong reductive and antioxidant properties, and in wild-type BCAT1 leukemia cells with CXXC motif, The number of cell surface markers CD11b, CD14, CD68, and CD36 decreased. BCKAs excretion in glioblastoma is heavily mediated by monocarboxylate transporter 1 (MCT 1), and the excreted BCKAs are phagocytic and resynthesized into BCAAs by tumor-related macrophages (TAM), but phagocytic activity of macrophages exposed to BCKAs is significantly reduced. BCAT 1 is selectively upregulated in isocitrate dehydrogenase (IDH) wild-type (WT) GBM, alpha-ketoglutaric acid (α-KG) mediates cell death in BCAT 1-deprived IDH WT GBM, and the combination of BCAT 1 inhibitor Gabapentin and α-KG induces tumor cell death.In the tumor microenvironment, CAFs upregulate the transcription of BCAT1 through SMAD5 under the influence of transforming growth factor β (TGF-β) signal, significantly increase the catabolism of BCAAs and secrete BCKAs. PDAC uses BCKAs secreted by CAFs as substrates for BCAAs synthesis or in a BCKDH-dependent mode to promote the increase of BCKA oxidative metabolic flux. Created with BioRender.com. (The red blunt line represents inhibition)

Full size image

BCAA 대사 과정은 종양 미세환경에서 중요한 역할을 합니다. 삼중음성 유방암에서 종양 세포는 IGF-1 및 인슐린 신호전달을 통해 MAPK 및 PI3K/AKT 신호전달 경로를 활성화할 수 있으며, PI3K/AKT 신호전달은 Foxo3a를 활성화하여 mTOR 신호전달을 촉진합니다. 종양 세포의 세포질에 존재하는 BCAT는 Foxo3a, AKT, mTOR, 및 Nrf2를 활성화하여 미토콘드리아 생성과 기능을 촉진함으로써 생존 우위를 획득합니다. 백혈병에서 RNA 결합 단백질 Musashi 2 (MSI2)는 BCAT1 mRNA에 결합하여 BCAT1의 번역을 촉진합니다. CXXC 모티프를 포함하는 BCAT1은 강력한 환원 및 항산화 특성을 가지고 있으며, CXXC 모티프를 가진 야생형 BCAT1 백혈병 세포에서 세포 표면 마커 CD11b, CD14, CD68, 및 CD36의 수가 감소합니다. 글리오blastoma에서 BCKAs의 배설은 단일카르복실산 운반체 1(MCT 1)에 의해 주로 매개되며, 배설된 BCKAs는 종양 관련 대식세포(TAM)에 의해 식작용을 통해 재합성되어 BCAAs로 전환됩니다. 그러나 BCKAs에 노출된 대식세포의 식작용 활성은 유의미하게 감소합니다. BCAT 1은 이소시트르산 탈수소효소(IDH) 야생형(WT) GBM에서 선택적으로 과발현되며, 알파-케토글루타르산(α-KG)은 BCAT 1 결핍 IDH WT GBM에서 세포 사멸을 매개합니다. 또한 BCAT 1 억제제 가바펜틴과 α-KG의 조합은 종양 세포 사멸을 유도합니다. 종양 미세환경에서 CAFs는 변형 성장 인자 β(TGF-β) 신호의 영향으로 SMAD5를 통해 BCAT1의 전사 발현을 증가시키며, BCAA의 분해 대사를 크게 증가시키고 BCKAs를 분비합니다. PDAC는 CAFs가 분비한 BCKAs를 BCAA 합성의 기질로 사용하거나 BCKDH 의존적 모드를 통해 BCKA 산화 대사 유동을 증가시켜 촉진합니다. BioRender.com으로 생성되었습니다. (붉은 점선은 억제를 나타냅니다)

Lung tumors show higher BCAAs uptake than PDAC. Analysis of labeled BCAAs metabolites showed more labeled α-Ketoisocaproate (α-KIC) and Leu-derived BCKAs in NSCLC cells. Meanwhile BCKDK was highly expressed in NSCLC and regulated ROS production in cells, affecting cell survival.58

Interestingly, Chi et al. found that high expression‎ of BCAAs in breast tumor tissues can reduce breast cancer N-cadherin’s expression‎ level and thus inhibit tumor metastasis.59 Shafei reported that BCAT1 inhibited the Ras/ERK pathway and activates PI3K/AKT pathway through insulin/IGF-1, ultimately promoting the expression‎ levels of FOXO3a and Nrf2 and regulating the proliferation, migration, and invasion in triple-negative breast cancer (TNBC).55 The above studies imply that breast cancers can be classified into subtypes based on their preference for BCAAs metabolism. Another study found that the subtypes of BCATs are correlated with breast cancer subtypes. BCAT1 expressed in the cytoplasm was highly expressed in human epidermal growth factor receptor 2 positive (HER2+) breast cancer, while BCAT2 expressed in the mitochondria tended to be highly expressed in estrogen receptor-positive (ER+) breast cancer. This suggests that BCATs may regulate tumors through different signaling pathways in different breast cancer subtypes.60 Similarly, BCAT1, which is highly expressed in breast cancer cells, promotes mitochondrial production and function by activating the mTOR signaling pathway and ultimately promotes breast cancer cell growth.61 The mechanism of action of BCAAs and their metabolic enzymes and metabolites in different breast cancer subtypes still needs further study (Fig. 4).

Silva et al. showed that in glioblastoma (GBM), BCKAs are heavily mediated by monocarboxylate transporter 1 (MCT 1) and that BCKAs expressed in large quantities are phagocytized and resynthesized into BCAAs by tumor-related macrophages (TAM). However, the phagocytic activity of macrophages exposed to BCKAs was significantly reduced.62 Overall, BCAAs metabolism has a key role in GBM and that metabolites of BCKAs may have a direct role in tumor immunosuppression. Moreover, recent study found that hypoxia-inducible factor (HIF)−1 and HIF-2 in GBM cells jointly mediate upregulation of the mRNA and protein expression‎ levels of the BCAAs transporter LAT 1 and the BCAAs metabolizing enzyme BCAT1, and ultimately promote the growth of cells under hypoxia conditions.63 Furthermore, BCAT 1 is selectively upregulated in isocitrate dehydrogenase (IDH) wild-type (WT) GBM, and α-ketoglutarate (α-KG) mediates cell death in BCAT 1-deficient IDH WT GBM. This argument was supported by the combination of BCAT 1 inhibitor and α-KG induced tumor cell death in patient-derived IDH WT GBM. Mechanistically, high expression‎ of BCAT1 reduces the NAD+/NADH ratio, increases mTORC1 activity, and promotes oxidative phosphorylation and nucleotide biosynthesis.64 The results of Zhang et al. illustrate the feasibility of targeting BCAAs metabolism in GBM for tumor therapy (Fig. 4).

BCATs are the first enzymes in the BCAAs metabolic pathway, including BCAT c encoded by BCAT 1 gene, mainly expressed in the cytoplasm, and BCAT m encoded by BCAT 2 gene, which is expressed in the mitochondria. BCAT 1 and BCAT 2 share a conserved sequence, the CXXC motif, which has been shown to act as a REDOX switch in BCAT enzymatic action.65 However, different isomers react differently to ROS, and the sensitivity of BCAT 2 is many orders of magnitude higher than that of BCAT 1.66 On the contrary, BCAT 1 has stronger reducing and antioxidant properties. In acute myeloid leukemia (AML), wild-type (WT) BCAT 1 can metabolize hydrogen peroxide (H2O2), while CXXC motif mutants (CXXS) and wild-type (WT) BCAT 2 cannot. In addition, AML cells overexpressing WT BCAT 1 had lower ROS, and the number of bone marrow markers (CD11b, CD14, CD68, and CD36) that marked cell differentiation on the cell surface was lower, suggesting the involvement of the BCAT 1 CXXC motif in ROS buffering and cell development in AML cells. CXXC motif affects the process of leukemogenesis mediated by ROS. Aberrant activation of BCAT 1 was similarly detected in CML. Hattori et al. revealed that the transcript of BCAT 1 is positively regulated by the oncogenic RNA binding protein Musashi 2 (MSI2), which promotes the production of BCAA in leukemia cells and the development of the disease (Fig. 4).

BCAAs metabolism is altered in various tumors such as PDAC, NSCLC, BRCA, GBM, etc. At present, even in the same type of tumor, different tumor subtypes may have different requirements for BCAAs metabolism and regulatory signaling pathways. In order to achieve precise treatment targeting BCAAs metabolism, we still need to conduct more studies on the relationship and regulatory mechanism between tumor subtypes and BCAAs-related metabolic enzymes and metabolites in the future.

폐 종양은 PDAC보다 BCAAs 흡수율이 높습니다. 표지된 BCAAs 대사산물 분석 결과, NSCLC 세포에서 표지된 α-케토이소카프로산(α-KIC)과 류신 유래 BCKAs가 더 많이 검출되었습니다. 한편 BCKDK는 NSCLC에서 고도로 발현되며 세포 내 ROS 생성을 조절하여 세포 생존에 영향을 미쳤습니다.58

흥미롭게도 Chi 등(2023)은 유방 종양 조직에서 BCAAs의 높은 발현이 유방암 N-cadherin의 발현 수준을 감소시켜 종양 전이를 억제한다는 사실을 발견했습니다. 59 Shafei는 BCAT1이 인슐린/IGF-1을 통해 Ras/ERK 경로를 억제하고 PI3K/AKT 경로를 활성화하여 FOXO3a와 Nrf2의 발현 수준을 증가시키고 삼중 음성 유방암(TNBC)의 증식, 이동, 침습을 조절한다고 보고했습니다.55 위 연구들은 유방암이 BCAA 대사 선호도에 따라 하위 유형으로 분류될 수 있음을 시사합니다. 또 다른 연구에서는 BCAT의 하위 유형이 유방암의 하위 유형과 관련이 있음을 발견했습니다. 세포질에 발현되는 BCAT1은 인간 상피 성장 인자 수용체 2 양성(HER2+) 유방암에서 고도로 발현되었으며, 미토콘드리아에 발현되는 BCAT2는 에스트로겐 수용체 양성(ER+) 유방암에서 고도로 발현되는 경향을 보였습니다. 이는 BCAT가 다양한 유방암 하위 유형에서 서로 다른 신호 전달 경로를 통해 종양을 조절할 수 있음을 시사합니다.60 마찬가지로, 유방암 세포에서 고도로 발현되는 BCAT1은 mTOR 신호 전달 경로를 활성화하여 미토콘드리아 생산과 기능을 촉진하고 최종적으로 유방암 세포의 성장을 촉진합니다.61 다양한 유방암 하위 유형에서 BCAA 및 그 대사 효소와 대사 산물의 작용 메커니즘은 추가 연구가 필요합니다(그림 4).

Silva 등(et al.)은 뇌교모세포종(GBM)에서 BCKAs가 단일카복실산 운반체 1(MCT 1)에 의해 주로 매개되며, 대량으로 발현된 BCKAs가 종양 관련 대식세포(TAM)에 의해 식작용되어 BCAAs로 재합성된다는 것을 보여주었습니다. 그러나 BCKAs에 노출된 대식세포의 식작용 활성은 유의미하게 감소했습니다.62 전반적으로 BCAAs 대사 과정은 GBM에서 핵심 역할을 하며, BCAAs 대사산물은 종양 면역 억제에 직접적인 역할을 할 수 있습니다. 또한 최근 연구에서 GBM 세포에서 저산소증 유도 인자(HIF)-1과 HIF-2가 BCAAs 운반체 LAT 1과 BCAAs 대사 효소 BCAT1의 mRNA 및 단백질 발현 수준을 공동으로 증가시켜 저산소 조건 하에서 세포 성장 촉진에 기여한다는 것이 밝혀졌습니다. 63 또한, BCAT 1은 이소시트르산 탈수소효소(IDH) 야생형(WT) GBM에서 선택적으로 상향 조절되며, α-케토글루타레이트(α-KG)는 BCAT 1 결핍 IDH WT GBM에서 세포 사멸을 매개합니다. 이 주장은 환자 유래 IDH WT GBM에서 BCAT 1 억제제와 α-KG의 조합이 종양 세포 사멸을 유도한 결과로 뒷받침되었습니다. 기전적으로, BCAT1의 고발현은 NAD+/NADH 비율을 감소시키고 mTORC1 활성을 증가시키며 산화적 인산화 및 핵산 생합성을 촉진합니다.64 Zhang 등(Zhang et al.)의 결과는 GBM에서 종양 치료를 위해 BCAA 대사 경로를 표적화하는 가능성을 보여줍니다(그림 4).

BCAT는 BCAA 대사 경로의 첫 번째 효소로, 주로 세포질에서 발현되는 BCAT 1 유전자에 의해 암호화되는 BCAT c와 미토콘드리아에서 발현되는 BCAT 2 유전자에 의해 암호화되는 BCAT m이 있습니다. BCAT 1과 BCAT 2는 CXXC 모티프라는 보존된 서열을 공유하며, 이는 BCAT 효소 작용의 REDOX 스위치로 작용하는 것으로 밝혀졌습니다.65 그러나 다른 이성체는 ROS에 대해 다르게 반응하며, BCAT 2의 민감도는 BCAT 1보다 여러 순서대로 높습니다.66 반면 BCAT 1은 더 강한 환원 및 항산화 특성을 가지고 있습니다. 급성 골수성 백혈병(AML)에서 야생형(WT) BCAT 1은 과산화수소(H₂O₂)를 대사할 수 있지만, CXXC 모티프 돌연변이(CXXS)와 야생형(WT) BCAT 2는 그렇지 않습니다. 또한, WT BCAT 1을 과발현한 AML 세포는 ROS 수치가 낮았으며, 세포 표면에 세포 분화를 표시하는 골수 표지자(CD11b, CD14, CD68, 및 CD36)의 수가 적었습니다. 이는 BCAT 1의 CXXC 모티프가 AML 세포에서의 ROS 완충 및 세포 발달에 관여함을 시사합니다. CXXC 모티프는 ROS에 의해 매개되는 백혈병 발생 과정에 영향을 미칩니다. BCAT 1의 이상 활성화는 CML에서도 유사하게 관찰되었습니다. Hattori 등(2023)은 암유발성 RNA 결합 단백질 Musashi 2(MSI2)가 백혈병 세포에서의 BCAA 생산과 질병 진행을 촉진함으로써 BCAT 1의 전사체를 긍정적으로 조절한다는 것을 밝혔습니다(그림 4).

BCAA 대사는 PDAC, NSCLC, BRCA, GBM 등 다양한 종양에서 변화됩니다. 현재 동일한 유형의 종양에서도 종양 하위 유형에 따라 BCAA 대사 및 조절 신호 경로에 대한 요구사항이 다를 수 있습니다. BCAA 대사를 표적으로 한 정밀 치료를 달성하기 위해, 향후 종양 하위 유형과 BCAA 관련 대사 효소 및 대사산물 간의 관계 및 조절 메커니즘에 대한 추가 연구가 필요합니다.

BCAAs in disease

Metabolic disease

Existing studies point out that BCAAs and their metabolites are the strongest biomarkers of metabolic diseases such as obesity, insulin resistance, and type 2 diabetes (T2D).10 Elevated BCAAs and their metabolites are key in the early progression of metabolic diseases such as T2D.60 Each BCAA has a unique metabolic effect. Yu et al. found that a low-iLe diet can increase liver sensitivity to insulin, increase energy expenditure, and activate the FGF21-UCP1 axis; a low-valine diet has similar but more modest effects as a low-iLe diet, while the low-Leu diet has no effect. Moreover, a low-iLe diet can quickly restore the metabolic health of obese mouse models induced by a high-fat diet.67 iLe could act as a regulator of metabolic health and that a low-iLe diet can ameliorate the adverse metabolic effects of obesity. In addition, obesity could inhibit hepatic utilization of BCAAs and cause the inactivation of BCKDH by increasing the ratio of BCKDK (BCKDH kinase)/PPM1K (BCKDH dephosphorylase) in hepatocytes. This phenomenon can be reversed by BCAA diet restriction or regulating the BCKDK/PPM1K ratio in mouse models of obesity and insulin resistance. In addition, White et al. found that the transcription factor ChREBP can also promote BCKDK and inhibit PPM1K expression‎ to inhibit BCKDH activation and promote ATP citrate lyase (ACLY) activation, upregulate the lipid synthesis pathway, and induce hepatic steatosis in the obesity model of high-sugar diet.68 Another study showed that knockout of BCAT 2 in white adipose tissue (WAT) confers resistance to high-fat diet-induced obesity through browning of WAT and increased thermogenesis. Mechanistically, acetyl-CoA, a derivative of BCKAs, inhibits the interaction between PR domain-containing protein 16 (PRDM16) and peroxisome proliferator-activated receptor-γ (PPAR-γ) by acetylating the k915 site of PRDM16 to maintain WAT characteristics. When BCAT 2 is knocked down, depletion of BCKAs and its derivative acetyl-CoA promotes WAT brown steatosis and energy expenditure.69 In addition, Ma et al. also found that telmisartan, an antihypertensive drug, can directly bind to BCAT2 and inhibit its activity, thereby reducing obesity.

Recently, it was also found that valsartan, an angiotensin II inhibitor, could inhibit BCKDH-BCKDK interaction, decrease BCKDH phosphorylation, and decrease plasma BCAA concentration to increase BCKDH enzyme activity. In addition to valsartan, candesartan and irbesartan have also been found to have similar effects, suggesting that such drugs may have a similar steric structure to bind BCKDK to promote its separation from BCKDH.70 BCKDK inhibitors are also effective in attenuating insulin resistance in mouse models of obesity, and the development of a new generation of more powerful BCKDK inhibitors is important for diseases that require inhibition of BCAA catabolism.71 In addition, extra-mitochondrial localization of branched-chain α-keto acid dehydrogenase (BCKDH), a rate-limiting enzyme in BCAAs metabolism, has been reported in type 2 diabetic rat model (OLETF). This portion of BCKDH is present on the endoplasmic reticulum (ER) and interacts with AMP deaminase 3 (AMPD3), and is negatively regulated by AMPD3.72 Upregulation of AMPD3 has been reported to impair energy metabolism in OLETF hearts. This study further suggested that AMPD3 may induce cardiometabolic changes through AMPD3-BCKDH expression‎ imbalance in cardiomyocytes of diabetic individuals, providing new insights into the mechanism of the development of this disease.

BCAAs와 질환

대사 질환

기존 연구들은 BCAAs 및 그 대사산물이 비만, 인슐린 저항성, 제2형 당뇨병(T2D)과 같은 대사 질환의 가장 강력한 생물학적 지표임을 지적하고 있습니다.10 BCAAs 및 그 대사산물의 증가가 T2D와 같은 대사 질환의 초기 진행에 핵심적인 역할을 합니다.60 각 BCAA는 고유한 대사 효과를 가지고 있습니다. Yu 등 연구진은 저-iLe 식단이 간 인슐린 민감도를 증가시키고 에너지 소비를 촉진하며 FGF21-UCP1 축을 활성화한다는 사실을 발견했습니다. 저-발린 식단은 저-iLe 식단과 유사하지만 효과가 더 미미했으며, 저-류신 식단은 효과가 없었습니다. 또한, 고지방 식이로 유도된 비만 마우스 모델에서 저-iLe 식이는 대사 건강을 빠르게 회복시킬 수 있습니다.67 iLe는 대사 건강의 조절자로 작용할 수 있으며, 저-iLe 식이는 비만의 부정적인 대사 효과를 완화시킬 수 있습니다. 또한, 비만은 간에서의 BCAA 이용을 억제하고 BCKDK (BCKDH 키나제)/PPM1K (BCKDH 탈인산화효소) 비율을 증가시켜 BCKDH의 비활성화를 유발할 수 있습니다. 이 현상은 비만 및 인슐린 저항성 마우스 모델에서 BCAA 식이 제한이나 BCKDK/PPM1K 비율 조절을 통해 역전될 수 있습니다. 또한 White 등(2023)은 전사 인자 ChREBP가 BCKDK 발현을 촉진하고 PPM1K 발현을 억제하여 BCKDH 활성화를 억제하고 ATP 시트르산 리아제(ACLY) 활성화를 촉진하며, 고당분 식이 모델에서 지방 합성 경로를 활성화하고 간 지방 축적을 유발한다는 것을 발견했습니다. 68 다른 연구에서는 백색 지방 조직(WAT)에서 BCAT 2를 결손시킨 경우, WAT의 갈색화 및 열생성 증가를 통해 고지방 식이 유발 비만에 대한 저항성을 부여한다는 것이 밝혀졌습니다. 기전적으로, BCKAs의 대사산물인 아세틸-코엔자임 A는 PRDM16의 k915 부위를 아세틸화하여 PRDM16과 과산화체 증식 활성화 수용체-γ(PPAR-γ) 간의 상호작용을 억제하여 WAT의 특성을 유지합니다. BCAT 2를 노크다운하면 BCKAs와 그 유도체 아세틸-코엔자임 A의 고갈이 WAT의 갈색 지방화 및 에너지 소비를 촉진합니다.69 또한 Ma 등도 항고혈압제인 텔미사르탄이 BCAT2에 직접 결합하여 그 활성을 억제함으로써 비만을 감소시킨다는 사실을 발견했습니다.

최근에는 안지오텐신 II 억제제인 발사르탄이 BCKDH-BCKDK 상호작용을 억제하고 BCKDH 인산화를 감소시켜 혈장 BCAA 농도를 낮추며 BCKDH 효소 활성을 증가시킨다는 것이 밝혀졌습니다. 발사르탄 외에도 칸데사르탄과 이르베사르탄도 유사한 효과를 나타내며, 이러한 약물이 BCKDK에 결합하여 BCKDH로부터 분리되도록 하는 유사한 스테리크 구조를 가질 수 있음을 시사합니다.70 BCKDK 억제제는 비만 마우스 모델에서 인슐린 저항성을 완화하는 데 효과적이며, BCAA 대사 억제가 필요한 질환에 대한 새로운 세대의 더 강력한 BCKDK 억제제 개발이 중요합니다. 71 또한, BCAA 대사에서 속도 제한 효소인 분지쇄 α-케토산 탈수소효소(BCKDH)의 미토콘드리아 외 국소화가 제2형 당뇨병 쥐 모델(OLETF)에서 보고되었습니다. 이 부분의 BCKDH는 내소기관(ER)에 존재하며 AMP 탈아미노효소 3(AMPD3)와 상호작용하며, AMPD3에 의해 음성 조절됩니다.72 AMPD3의 발현 증가가 OLETF 심장에서 에너지 대사 장애를 유발한다는 보고가 있습니다. 이 연구는 AMPD3가 당뇨병 환자의 심근 세포에서 AMPD3-BCKDH 발현 불균형을 통해 심혈관 대사 변화를 유발할 수 있음을 제안했으며, 이 질환의 발병 메커니즘에 대한 새로운 통찰을 제공했습니다.

Liver and kidney disease

In patients with cirrhosis, enhanced catabolism of BCAAs, increased glutamate synthesis, and decreased circulating BCAAs levels in a hyperammonemia environment have been suggested as hallmarks of the disease and associated with increased risk of hepatic encephalopathy.73,74 Elevated circulating BCAAs have been detected in nonalcoholic fatty liver disease (NAFLD). Also, this disturbed BCAAs metabolism has a synergistic effect with the development of T2DM.75 Other studies showed that BCAAs supplementation helps restore glucose homeostasis and enhance immune system function in patients with chronic liver disease.76,77,78

In renal disease, circulating BCAAs levels are significantly decreased in patients with chronic renal failure.79,80 This phenomenon has been seen in patients with chronic kidney disease (CKD), and a phase II CKD cohort study found that plasma Leu and valine are significantly decreased in CKD patients compared with normal controls.81 This may be due to decreased BCAAs levels caused by long-term malnutrition and hemodialysis in CKD patients. Metabolic acidosis also enhances branched-chain amino acid dehydrogenase (BCKD) activity and accelerates protein breakdown. However, supplementing BCAAs and other essential amino acids to patients with chronic renal failure can help maintain protein balance and reduce uremic toxicity.82,83,84

간 및 신장 질환

간경변증 환자에게서 고암모니아 환경에서 분지쇄 아미노산(BCAA)의 분해 증가, 글루타메이트 합성 증가, 순환 BCAA 수치 감소가 질병의 특징으로 제시되었으며, 간성 뇌증 위험 증가와 연관되었습니다.73,74 비알코올성 지방간 질환(NAFLD)에서 순환 BCAA 수치 상승이 관찰되었습니다. 또한 이 BCAA 대사 장애는 제2형 당뇨병(T2DM)의 발병과 시너지 효과를 나타냅니다.75 다른 연구에서는 만성 간 질환 환자에게 BCAA 보충이 혈당 균형 회복과 면역 체계 기능 강화에 도움을 준다는 결과가 나왔습니다.76,77,78

신장 질환에서 만성 신부전 환자의 순환 BCAAs 수치는 유의미하게 감소합니다.79,80 이 현상은 만성 신장 질환(CKD) 환자에서도 관찰되었으며, CKD 코호트 연구에서 CKD 환자의 혈장 류신과 발린 수치가 정상 대조군에 비해 유의미하게 감소한 것으로 나타났습니다.81 이는 CKD 환자의 장기적인 영양 결핍과 혈액 투석으로 인한 BCAAs 수치 감소 때문일 수 있습니다. 대사성 산증은 분지쇄 아미노산 탈수소효소(BCKD) 활성을 증가시키고 단백질 분해를 가속화합니다. 그러나 만성 신부전 환자에게 BCAA 및 기타 필수 아미노산을 보충하면 단백질 균형을 유지하고 요독성 독성을 감소시키는 데 도움이 될 수 있습니다.82,83,84

Aspartate (Asp)

Aspartate metabolism

Asp is an α-amino acid used in protein synthesis that has an α-amino group, an α-carboxylic acid group, and a side-chain carboxamide.85 It is a non-essential amino acid because the body can synthesize it. Oxaloacetate is the precursor of Asp. Transaminase transfers amino groups from glutamate to oxaloacetate, producing α-ketoglutarate and Asp. In Asn synthetase-mediated enzymatic reactions, Gln provides an amino group, which combines with β-aspartate-AMP to form asparagine (Asn) and AMP.86 Asn is an amino acid necessary for brain development. Since Asp in the blood cannot directly pass through the blood-brain barrier, the development of nerve cells depends on its synthesisation in the brain. When the level of Asn synthetase in the brain is insufficient, the proliferation of brain cells will be limited or even leading to cell death.13 In turn, during catabolism, Asn is hydrolyzed by aspartase to Asp, which is then aminated with α-ketoglutarate to form glutamate and oxaloacetic acid. Then oxaloacetic acid enters the citric acid cycle (Fig. 5).86

아스파르트산 (Asp)

아스파르트산 대사

Asp는 단백질 합성에 사용되는 α-아미노산으로, α-아미노 그룹, α-카르복시산 그룹, 및 측쇄 카르복사미드를 포함합니다.85 이는 신체에서 합성될 수 있기 때문에 필수 아미노산이 아닙니다. 옥살아세테이트는 Asp의 전구체입니다. 트랜스아미나제는 글루타메이트로부터 아미노 그룹을 옥살아세테이트로 전달하여 α-케토글루타레이트와 Asp를 생성합니다. 아스파르트산 합성효소(Asn synthetase)에 의한 효소 반응에서 글루타민(Gln)은 아미노 그룹을 제공하며, 이는 β-아스파르트산-AMP와 결합하여 아스파라긴(Asn)과 AMP를 형성합니다.86 아스파라긴은 뇌 발달에 필수적인 아미노산입니다. 혈중 아스파르트산은 혈액-뇌 장벽을 직접 통과할 수 없기 때문에 신경 세포의 발달은 뇌 내에서의 합성에 의존합니다. 뇌 내 아스파르트산 합성효소(Asn synthetase)의 수준이 부족하면 뇌 세포의 증식이 제한되거나 심지어 세포 사멸로 이어질 수 있습니다.13 반면, 분해 과정에서 아스파르트산(Asn)은 아스파르타제(aspartase)에 의해 아스파르트산(Asp)으로 가수분해되며, 이는 α-케토글루타레이트와 아미노화되어 글루타메이트와 옥살아세트산으로 형성됩니다. 이후 옥살아세트산은 시트르산 회로(그림 5)로 들어갑니다.86

Fig. 5

Aspartate, Arginine and Methionine metabolism.

Aspartate aminotransferase (ASAT) catalyzes the transfer of amino groups from glutamine to oxaloacetic acid to produce aspartate and α-ketoglutaric acid. Aspartic acid is catalyzed by aspartic synthase (ASNS), and the amino group is provided by glutamine to form asparagine. Aspartic acid can participate in NAD biosynthesis by aspartic oxidase (AO). Aspartate is also involved in the synthesis of Tyrosine and Phenylalanine through its conversion to Arogenate. Aspartic acid can be transformed into Aspartate semialdehyde through aspartic kinase (AK), which further catalyzes o-phospho-l-homoserine (OPLH) to participate in Lysine, Methionine, Threonine, Synthesis of Isoleucine. Arginine in cells is catalyzed by Arginase to produce Ornithine and enter the ornithine cycle. Ornithine transcarbamylase (OTC) catalyzes the production of citrulline in mitochondria. In the cytoplasm, arginine produces citrulline and nitric oxide by nitric oxide synthase (NOS), the first step in the urea cycle. Citrulline is produced by Argininosuccinate synthase (ASS) to arginine, which is catalyzed by Argininosuccinate Lythase (ASL) to produce arginine, and the resultant fumaric acid enters the TCA cycle. In addition, ornithine in mitochondria can be converted from glutamic acid and proline. Methionine can be catalyzed by methionine adenosine transferase (MAT) to produce S-adenosine methionine (SAM). As a methyl donor, SAM participates in the methylation of histones, nucleic acids and proteins under the catalysis of methyltransferase, and produces S-homocysteine (SAH). SAH is catalyzed to produce HOMOcysteine by Adenosylhomocysteinase (AHCY), which may participate in glutathione synthesis (GSH) or in folate recycling and resynthesis of methionine via methionine synthase (MS). In the methionine remedial synthesis pathway, SAM participates in polyamine metabolism via Adenosylmethionine decarboxylase 1 (AMD1), 5,-methylthioadenosine (MTA) is produced and then phosphorylase is re-synthesized through 5-methylthioadenosine (MTAP) and the subsequent reaction. Created with BioRender.com. (The dotted line represents the intermediate process omission)

아스파르테이트, 아르기닌 및 메티오닌 대사.

아스파르테이트 아미노전달효소 (ASAT)는 글루타민으로부터 아미노 그룹을 옥살아세트산으로 전달하여 아스파르테이트와 α-케토글루타르산을 생성합니다. 아스파르테이트는 아스파르테이트 합성효소 (ASNS)에 의해 촉매되어 아스파르테이트와 글루타민으로부터 아미노 그룹을 받아 아스파라긴을 형성합니다. 아스파르테이트는 아스파르테이트 산화효소 (AO)에 의해 NAD 생합성에 참여할 수 있습니다. 아스파르테이트는 아로겐산으로 전환되어 티로신과 페닐알라닌의 합성에 관여합니다. 아스파르트산은 아스파르트산 키나아제(AK)에 의해 아스파르트산 세미알데히드로 전환되며, 이는 추가로 o-포스포-l-호모세린(OPLH)을 촉매하여 라이신, 메티오닌, 트레오닌, 이소류신 합성에 참여합니다. 세포 내 아르기닌은 아르기나아제(Arginase)에 의해 오르니틴으로 전환되어 오르니틴 순환에 참여합니다. 오르니틴 트랜스카르바밀라제(OTC)는 미토콘드리아에서 시트룰린 생성을 촉매합니다. 세포질에서는 아르기닌이 질산산화효소(NOS)에 의해 시트룰린과 질산산화물로 전환되며, 이는 요소 순환의 첫 번째 단계입니다. 시트룰린은 아르기노수신산 합성효소(ASS)에 의해 아르기닌으로 생성되며, 이는 아르기노수신산 리타제(ASL)에 의해 아르기닌으로 전환됩니다. 이 과정에서 생성된 푸마르산은 TCA 순환에 들어갑니다. 또한 미토콘드리아 내의 오르니틴은 글루탐산과 프로린으로부터 전환될 수 있습니다. 메티오닌은 메티오닌 아데노신 전이효소(MAT)에 의해 S-아데노신 메티오닌(SAM)으로 전환됩니다. 메틸 기증체로 작용하는 SAM은 메틸트랜스퍼레이즈의 촉매 작용 하에 히스톤, 핵산 및 단백질의 메틸화에 참여하며, S-호모시스테인(SAH)을 생성합니다. SAH는 아데노실호모시스테인아제(AHCY)에 의해 촉매되어 호모시스테인을 생성하며, 이는 글루타티온 합성(GSH)이나 엽산 재순환 및 메티오닌 합성효소(MS)를 통해 메티오닌 재합성에 참여할 수 있습니다. 메티오닌 보완 합성 경로에서 SAM은 아데노실메티오닌 탈카복실화효소 1(AMD1)을 통해 폴리아민 대사 과정에 참여하며, 5-메틸티오아데노신(MTA)이 생성되고 이후 5-메틸티오아데노신(MTAP)과 후속 반응을 통해 포스포릴라제가 재합성됩니다. BioRender.com으로 생성되었습니다. (점선은 중간 과정 생략을 나타냅니다)

Asp is also a metabolite of the urea cycle, carrying reduction equivalents in the malate-Asp shuttle, providing nitrogen atoms in inosine synthesis, and acting as a hydrogen acceptor in ATP synthesis. Asp is also the precursor of four essential amino acids (methionine, threonine, lysine, and isoleucine). Asp can also act as an amino acid exchange factor, becoming a medium for amino acids in and out of cells, especially histidine, arginine and serine. Asp regulates serine metabolism, nucleotide synthesis, and mTORC1 activity through amino acid exchange factor function.87

Aspartate in cancer

TP53 is a gene with the highest mutation frequency in human cancer. The protein p53 encoded by this gene inhibits the development of tumors through the regulation of the cell cycle, apoptosis, genomic stability and other pathways.88,89,90 Deng et al. reported that Asp and Asn in colon cancer cell lines could inhibit their activities by binding to LKB1 (encoding filament, threonine kinase, and direct phosphorylation of protein products to activate AMPK), thus inhibiting AMPK-mediated p53 activation.91 Activation of p53 can disrupt Asp-Asn homeostasis and promote cell senescence and cycle arrest in lymphoma and colorectal tumor models.91 Under hypoxia, Asp is a limiting factor for tumor growth. Hypoxia inhibits the electron transport chain (ETC), affecting energy and Asp synthesis. Garcia-Bermudez et al. studied the sensitivity of tumor cells to mitochondrial ETC inhibitors and found that tumor cells insensitive to ETC inhibition maintain intracellular Asp concentrations through the Asp/glutamate transporter SLC1A3, which gives tumor cells a survival advantage.92 In another study on tumor metabolism, Sullivan et al. found that Asp synthesis was a limiting factor for bladder cancer growth when oxygen was lacking in the environment. In bladder cancer cells, the poor permeability of Asp cells prevents the uptake of Asp by tumor cells from the environment. While cells have higher permeability with Asn than Asp, the activity of asparaginase in bladder cancer cells was insufficient, which could not convert Asn into Asp.93 After using guinea pig asparaginase 1 (gpASNase1) to promote the conversion of Asn to Asp in tumor cells, the growth rate of tumor cells was significantly increased, suggesting that Asp acquisition is an endogenous metabolic limitation in tumors with difficult Asp acquisition.93 It was suggested that Asp is an intrinsic limit to the growth of some tumors in vivo, and breaching this limit will promote tumor growth. The Asp-glutamate transporter SLC1A3 is closely associated with the effect of ETC inhibitors, and the SLC1A3 site is amplified in subclusters of non-glial epithelial tumors and thus against aspartic restriction.92 Sun et al. found that SLC1A3 promotes breast cancer cells to L-asparaginase (ASNase) resistance. Also, ASNase consumption of Asp and glutamate could be supplemented by SLC1A3, thus eliminating the inhibitory effect of ASNase and promoting tumor development.94 Furthermore, Xu et al. confirmed that overexpressed SLC1A3 in gastric cancer activates the PI3K/AKT pathway, upregulates the expression‎ levels of Glucose transporter 1 (GLUT1), Hexokinase 2 (HK2), and Lactate dehydrogenase A (LDHA), and promotes the growth of gastric cancer, while treatment with the PI3K/AKT inhibitor LY294002 could inhibit the growth-promoting effect of SLC1A3 overexpression‎ on gastric cancer.95 Moreover, Wong et al. found that another amino acid transporter, SLC25A22, could promote Asp synthesis, activate the AMPK pathway and reduce oxidative stress in KRAS mutant colorectal cancer (CRC) cells (Fig. 6).96 These studies have shown that AATs are potential targets for tumor metabolic reprogramming. Drugs currently being tested that target AATs are shown in (Table 1).

아스파르트산(Asp)은 요소 순환의 대사산물로, 말레이트-아스파르트산 셔틀에서 환원 등가물을 운반하며, 이노신 합성에 질소 원자를 공급하고 ATP 합성에서 수소 수용체로 작용합니다. 아스파르트산은 또한 네 가지 필수 아미노산(메티오닌, 트레오닌, 라이신, 이소류신)의 전구체입니다. Asp는 아미노산 교환 인자로 작용하여 세포 내외로 아미노산을 운반하는 매개체 역할을 하며, 특히 히스티딘, 아르기닌, 세린의 이동에 관여합니다. Asp는 아미노산 교환 인자 기능을 통해 세린 대사, 뉴클레오티드 합성, mTORC1 활성을 조절합니다.87

아스파르트산과 암

TP53은 인간 암에서 가장 높은 돌연변이 빈도를 가진 유전자입니다. 이 유전자에 의해 암호화되는 단백질 p53은 세포주기, 세포사멸, 게놈 안정성 및 기타 경로를 조절하여 종양의 발병을 억제합니다.88,89,90 Deng 등(Deng et al.)은 대장암 세포주에서 아스파르트산과 아스파르트산이 LKB1(필라멘트, 트레오닌 키나아제 및 AMPK를 활성화하기 위해 단백질 제품을 직접 인산화하는 유전자)에 결합하여 AMPK 매개 p53 활성화를 억제할 수 있다고 보고했습니다. 91 p53의 활성화는 림프종 및 대장 종양 모델에서 아스파르트산-아스파르트산 균형을 방해하고 세포 노화 및 세포 주기 정지를 촉진합니다.91 저산소 조건에서 아스파르트산은 종양 성장의 제한 요인입니다. 저산소는 전자 전달 사슬(ETC)을 억제하여 에너지 및 아스파르트산 합성에 영향을 미칩니다. Garcia-Bermudez 등 연구진은 종양 세포의 미토콘드리아 ETC 억제제에 대한 감수성을 연구했으며, ETC 억제에 저항성을 보이는 종양 세포는 아스파르트산/글루타메이트 운반체 SLC1A3를 통해 세포 내 아스파르트산 농도를 유지하여 종양 세포에 생존 우위를 제공합니다.92 종양 대사 연구에서 Sullivan 등 연구진은 환경에 산소가 부족할 때 아스파르트산 합성이 방광암 성장의 제한 요인임을 발견했습니다. 방광암 세포에서 아스파르트산의 낮은 투과성은 환경으로부터 아스파르트산의 세포 내 흡수를 방해합니다. 세포는 아스파르트산보다 아스파르트산에 대한 투과성이 높지만, 방광암 세포에서의 아스파르긴아제 활성이 부족해 아스파르트산을 아스파르트산으로 전환하지 못했습니다.93 기니피그 아스파르긴아제 1(gpASNase1)을 사용해 종양 세포 내 아스파르트산으로의 전환을 촉진하자 종양 세포의 성장 속도가 유의미하게 증가했으며, 이는 아스파르트산 획득이 아스파르트산 획득이 어려운 종양에서 내인성 대사 제한 요인임을 시사합니다. 93 Asp는 일부 종양의 체내 성장에 내재된 한계이며, 이 한계를 돌파하면 종양 성장이 촉진된다는 것이 제안되었습니다. Asp-글루타메이트 운반체 SLC1A3는 ETC 억제제의 효과와 밀접하게 연관되어 있으며, SLC1A3 유전자는 비글리아 상피 종양의 하위 클러스터에서 증폭되어 아스파르트산 제한에 저항성을 보입니다.92 Sun 등 연구진은 SLC1A3가 유방암 세포의 L-아스파라긴아제 (ASNase) 저항성을 촉진한다는 사실을 발견했습니다. 또한 ASNase의 아스파르트산과 글루타메이트 소비는 SLC1A3에 의해 보완될 수 있으며, 이는 ASNase의 억제 효과를 제거하고 종양 발달을 촉진합니다.94 또한 Xu 등 연구진은 위암에서 과발현된 SLC1A3이 PI3K/AKT 경로를 활성화하고 글루코스 운반체 1(GLUT1), 헥소키나제 2(HK2), 및 젖산 탈수소효소 A(LDHA)의 발현 수준을 증가시켜 위암의 성장을 촉진하며, PI3K/AKT 억제제 LY294002로 치료 시 SLC1A3 과발현의 위암 성장 촉진 효과를 억제할 수 있음을 확인했습니다. 95 또한 Wong 등(et al.)은 다른 아미노산 운반체인 SLC25A22가 KRAS 돌연변이 대장암(CRC) 세포에서 아스파르트산(Asp) 합성을 촉진하고 AMPK 경로를 활성화하며 산화 스트레스를 감소시킨다는 것을 발견했습니다(그림 6).96 이러한 연구들은 AAT가 종양 대사 재프로그래밍의 잠재적 표적임을 보여주었습니다. AAT를 표적으로 하는 현재 테스트 중인 약물은 (표 1)에 표시되어 있습니다.

Fig. 6

Aspartate metabolism in solid tumor. The high expression‎ of SLC1A3 in tumor cells promoted the absorption of aspartate, supplemented the low aspartate state caused by ASNase, and produced resistance to ASNase therapy. SLC25A22 expressed on mitochondria can increase the intake of mitochondrial aspartate, promote mitochondrial function and reduce oxidative stress. KRAS activates NRF2-ATF4 axis through PI3K/AKT signaling pathway, promotes ASNS transcription and increases intracellular asparagine concentration. Asparagine (Asn) can bind to SRC family tyrosine kinase LCK to assist in phosphorylation of LCK at Tyr394. Enhance LCK activity and T cell receptor signaling, and promote AKT, RAS activation. Asparagine can inhibit AMPK signaling pathway activity by binding to LKB1. In T lymphocytic leukemia cells, ATF4 binds to ASNS gene promoter through ZBTB1 (Zinc Finger and BTB domain-containing protein 1), promotes ASNS transcription, increases intracellular Asparagine concentration. Created with BioRender.com. (The red blunt line represents inhibition)

Table 1 Drugs that target amino acid metabolism in clinical trials

Table 1 Drugs that target amino acid metabolism in clinical trials

From: Amino acid metabolism in health and disease

NameResearch and development codeTargetDiseasePhaseTrial registration number

AXA1125	AXA-1125		NAFLD		NCT04073368
			NASH	Phase 2	NCT04880187
			COVID-19	Phase 2	NCT05152849
BCAT 1 Inhibitor	ERG-24; ERG-245	Basigin (BSG); Branched Chain Amino Acid Transaminase 1 (BCAT1); Matrix Metallopeptidase 2 (MMP2); Matrix Metallopeptidase 9 (MMP9)	cancer/rheumatoid arthritis	Pre-clinical
BCAT2 modulator		Branched Chain Amino Acid Transaminase 2 (BCAT2)	organic acidemia/diabetes mellitus	Pre-clinical
BCKDK inhibitor		Branched Chain Keto Acid Dehydrogenase Kinase (BCKDK)	Insulin resistance; Maple glycosuria; Metabolic disorder; Type 2 diabetes	Pre-clinical
Nanvuranlat	JPH-203	L-type amino acid transporter 1 (LAT1)	Biliary tract carcinoma; Skin allergy; Solid tumor	Phase 2
4-L-[131I]iodo-phenylalanine	131I-ACD-101	L-type amino acid transporter 1 (LAT2)	glioblastoma	Phase 2	NCT03849105
QBS-10072S	QBS-10072S	L-type amino acid transporter 1 (LAT3)	Advanced solid tumor; Astrocytoma; Cholangiocarcinoma; Glioblastoma; Mesothelioma; Metastatic bladder cancer; Metastatic brain tumor; Metastatic breast cancer; Metastatic colorectal cancer; Metastatic esophageal carcinoma; Metastatic head and neck cancer; Metastatic liver cancer; Metastatic lung cancer; Metastatic ovarian cancer; Metastatic pancreatic cancer; Metastatic prostate cancer; Metastatic renal cell carcinoma; Metastatic gastric cancer; Metastatic urinary tract carcinoma; Sarcoma; Stage IV melanoma; Thymus tumor; Tongue disease; Cervical cancer	Phase 2	NCT04430842
O-(2-[18F] fluoroethyl)-L-tyrosine	TLX101-CDx	L-type amino acid transporter 1 (LAT4)	Glioblastoma; glioma	Clinical	NCT05632562; NCT03451123; NCT03216148; NCT02286531; NCT01579253; NCT01443676
4-L-[124I] iodo-L-phenylalanine	124I-ACD-101	L-type amino acid transporter 1 (LAT5)	Brain tumor	Phase 1
astatinated IPA	211At-TLX-102	L-type amino acid transporter 1 (LAT6)	Multiple myeloma	Pre-clinical
R-OKY-034F	OKY-034	L-type amino acid transporter 1 (LAT7)	Pancreatic tumor	Phase 2
[18F] AA-7	[18 F] NKO-028	L-type amino acid transporter 1 (LAT8)	Cancer; glioma	Clinical
Crisantaspase	JZP-341	Asparaginase	Acute lymphoblastic leukemia; Adenocarcinoma; Advanced solid tumor; Hematologic tumor; Metastatic colorectal cancer	Pre-clinical
L-asparaginase	ERY-001	Asparaginase	Metastatic breast cancer; Metastatic pancreatic cancer; Ductal adenocarcinoma of pancreas; Solid tumor	Phase 3	NCT05660473; NCT05631327; NCT05581030; NCT05326984; NCT05326516; NCT04956666; NCT03618238
Pegaspargase biosimilar	PF-690	Asparaginase	Acute lymphoblastic leukemia; hematoma	Pre-clinical
PJ-017	PJ-017	Asparaginase	Advanced solid tumor	Pre-clinical
Pegargiminase	ADI-PEG-20	Arginine deiminase (ADI)	Acute myelogenous leukemia; Advanced solid tumor; Glioblastoma; Glioma; Hepatocellular carcinoma; Melanoma; Mesothelioma; Metastatic pancreatic cancer; Non-small cell lung cancer; Prostate tumor; Soft tissue sarcoma; Solid tumor; Uveal melanoma	Phase 3	NCT05616624; NCT05001828; NCT04587830; NCT03449901
Pegzilarginase	AEB-1102	Arginase 1 (ARG1)	Acute myelogenous leukemia; Amino acid and protein metabolism disorders; Melanoma; Myelodysplastic syndrome; Small cell lung cancer; Uveal melanoma	New drug marketing application
Eryminase		Arginine deiminase (ADI)	Protein metabolism disorder	Pre-clinical
PFI-102	PFI-102	Peptidyl Arginine Deiminase 4 (PADI4)	Rheumatoid arthritis; Systemic lupus erythematosus	Pre-clinical
JBI-1044	JBI-1044	Peptidyl Arginine Deiminase 4 (PADI4)	Autoimmune disease; Cancer; Novel coronavirus pneumonia infection (COVID-19); Hidradenitis suppurativa; Inflammatory disease; Metastatic liver cancer; Rheumatoid arthritis; vasculitis	Pre-clinical
Arginine-depleting enzym	NEI-01		Acute myelogenous leukemia; Advanced solid tumor	Phase 1	NCT05226468
PEGylated arginine degrading enzymes	PJ-016	Arginase (ARG)	Metastatic carcinoma	Drug discovery
TNG-462	TNG-462	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Cholangiocarcinoma; Mesothelioma; Metastatic non-small cell lung cancer; Neuro-tumor; Solid tumor	Pre-clinical
AMG-193	AMG-193	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Non-small cell lung cancer	Phase 2	NCT05094336
MRTX-9768	MRTX-9768	Protein Arginine Methyltransferase 5 (PRMT5)	cancer	Pre-clinical
TNG-908	TNG-908	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Bladder cancer; Cholangiocarcinoma; Glioblastoma; Mesothelioma; Metastatic non-small cell lung cancer; Neuro-tumor; Squamous cell carcinoma	Phase 2	NCT05275478
PRT-543	PRT-543	Protein Arginine Methyltransferase 5 (PRMT5)	Acute myelogenous leukemia; Adenomatoid tumor; Advanced solid tumor; Breast tumor; Chronic granular monocytic leukemia; Diffuse large B-cell lymphoma; Hematologic tumor; Mantle cell lymphoma; Myelodysplastic syndrome; Myelofibrosis; Non-small cell lung cancer; Ovarian tumor; Spina bifida; Uveal melanoma	Phase 1	NCT03886831
PRT-811	PRT-811	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Brain tumor; Glioblastoma; Glioma; myelofibrosis	Phase 1	NCT04089449
MRTX-1719	MRTX-1719	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor	Phase 2	NCT05245500
Onametostat	JNJ-64619178	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Myelodysplastic syndrome; Non-hodgkin’s lymphoma	Phase 1	NCT03573310
PRMT-5 inhibitors	CTx-0262135	Protein Arginine Methyltransferase 5 (PRMT5)	Cancer; hematopathy	Drug discovery
SKL-27969	SKL-27969	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor	Phase 2	NCT05388435
SYHX-2001	SYHX-2001	Protein Arginine Methyltransferase 5 (PRMT5)	Acute myelogenous leukemia; Adenomatoid tumor; Advanced solid tumor; Hematologic tumor; Melanoma; Pancreatic tumor	Phase 1	NCT05407909
GSK-3226593	GSK-3226593	Protein Arginine Methyltransferase 5 (PRMT5)	Soft tissue sarcoma	Pre-clinical
SH-3765	SH-3765	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Non-hodgkin’s lymphoma	Phase 1	NCT05015309
AM-9747	AM-9747	Protein Arginine Methyltransferase 5 (PRMT5)	Cancer	Pre-clinical
PF-06939999	PF-06939999	Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Endometrial carcinoma; Metastatic bladder cancer; Metastatic esophageal carcinoma; Metastatic head and neck cancer; Metastatic non-small cell lung cancer; Squamous cell carcinoma; Cervical cancer	Phase 1	NCT03854227
AGX-323	AGX-323	Protein Arginine Methyltransferase 5 (PRMT5)	Cancer	Pre-clinical
ALG-070043	ALG-070043	Protein Arginine Methyltransferase 5 (PRMT5)	Hepatocellular carcinoma; Non-small cell lung cancer	Pre-clinical
PRT-220	PRT-220	Protein Arginine Methyltransferase 5 (PRMT5)	Graft versus host disease	Pre-clinical
OATD-02	OATD-02	Arginase 1 (ARG1); Arginase 2 (ARG2)	Advanced solid tumor; Metastatic colorectal cancer; Metastatic ovarian cancer; Metastatic pancreatic cancer; Metastatic renal cell carcinoma	Phase 1	NCT05759923
IO-112	IO-112	Arginase 1 (ARG1)	Solid tumor	Phase 1	NCT03689192
Resminostat	YHI-1001	Arginase 1 (ARG1); Histone deacetylase (HDAC); Histone Deacetylase 1 (HDAC1); Histone Deacetylase 2 (HDAC2); Histone Deacetylase 3 (HDAC3); Histone Deacetylase 6 (HDAC6)	Biliary tract tumor; Cholangiocarcinoma; Colorectal cancer; Cutaneous T-lymphoblastoma; Gallbladder tumor; Hepatocellular carcinoma; Hodgkin,s lymphoma; Mycosis fungoides; Non-small cell lung cancer; Pancreatic neoplasm; Sezary syndrome; Solid tumor	Phase 2	NCT02400788
CB-280	CB-280	Arginase (ARG)	Cystic fibrosis	Phase 1	NCT04279769
Arginase inhibitor	AZD-0011	Arginase (ARG)	Cancer	Pre-clinical
Numidargistat	INCB-01158	Arginase (ARG); T cell receptor gene (TCR)	Advanced solid tumor; Biliary tract carcinoma; Bladder cancer; Cancer; Colorectal cancer; Endometrial carcinoma; Esophageal tumor; Head and neck tumors; Lung tumor; Melanoma; Mesothelioma; Multiple myeloma; Non-small cell lung cancer; Ovarian tumor; Renal cell carcinoma; Squamous cell carcinoma; Gastric tumor; Transitional cell carcinoma	Phase 2	NCT03314935; NCT02903914
OATD-05	OATD-05	Arginase (ARG)	Cancer	Drug discovery
Pegylated, cobalt-replaced human arginase	PT-01	Arginase (ARG)	Cancer; Metastatic carcinoma; Metastatic liver cancer; Stage III melanoma; Stage IV melanoma	Phase 1	NCT04136834
Bicyclic arginase inhibitors		Arginase 1 (ARG1)	Cancer	Pre-clinical
C-0021158	C-0021158	Arginase 2 (ARG2)	Cancer	Drug discovery
Pegylated human arginase	PEG-BCT-100	Arginase (ARG)	Acute lymphoblastic leukemia; Acute myelogenous leukemia; Advanced solid tumor; Cancer; Glioma; Hepatocellular carcinoma; Hormone-resistant prostate cancer; Neuroblastoma; Renal cell carcinoma; Retinopathy; Sarcoma; Stage IV melanoma	Phase 2	NCT03455140; NCT02899286; NCT02285101; NCT02089633; NCT02089763; NCT01092091; NCT00988195
AB-474	AB-474	Arginase 1 (ARG1)	Cancer	Pre-clinical
ZB-49-0010	ZB-49-0010	Arginase 2 (ARG2)	Atherosclerosis; Cardiovascular diseases; hypertension	Pre-clinical
SCR-6920	SCR-6920	Methylthioadenosine Phosphorylase (MTAP); protein arginine N-methyltransferase (PRMT); Protein Arginine Methyltransferase 5 (PRMT5)	Advanced solid tumor; Hematologic tumor; Metastatic non-small cell lung cancer; Non-hodgkin,s lymphoma	Phase 1	NCT05528055
Telaglenastat hydrochloride	CB-839	Glutaminase (GLS)	Cervical cancer	Pre-clinical
Sirpiglenastat	DRP-104	Glutaminase (GLS)	Advanced solid tumor; Autoimmune disease; Cancer; AIDS related dementia syndrome; Inflammatory disease; Laryngeal tumor; Lung tumor; Metastatic non-small cell lung cancer; Oral tumor; Throat tumor; Squamous cell carcinoma; Urinary tract tumor	Phase 2	NCT04471415
IPN-60090	IPN-60090	Glutaminase (GLS)	Ovarian tumor	Pre-clinical
Macrocyclic glutaminase 1		Glutaminase (GLS)	Advanced solid tumor	Pre-clinical
BPTES	D-JHU-29	Glutaminase (GLS)	Breast tumor; Hematologic tumor; Pancreatic neoplasm; Rett syndrome	Pre-clinical
RP-10107	RP-10107	Glutaminase (GLS)	Solid tumor	Pre-clinical
DRP-367	DRP-367	Glutaminase (GLS)	Autoimmune disease; Cancer; Inflammatory disease	Drug discovery
Tiptuximab		Glutaminase (GLS)	Cancer; Non-small cell lung cancer	Pre-clinical
Kidney mitochondrial glutaminase inhibitors		Glutaminase (GLS)	Cancer	Pre-clinical
Sirpiglenastat	JHU-083	Glutaminase (GLS)	Advanced solid tumor; Autoimmune disease; Cancer; AIDS related dementia syndrome; Inflammatory disease; Laryngeal tumor; Lung tumor; Metastatic non-small cell lung cancer; Oral tumor; Throat tumor; Squamous cell carcinoma; Urinary tract tumor	Phase 2
xCT inhibitor		Solute Carrier Family 7 Member 11 (SLC7A11)	Ovarian tumor	Pre-clinical
Florilglutamic acid (18F)	BAY-94–9392	Solute Carrier Family 7 Member 11 (SLC7A11)	Cancer; Hepatocellular carcinoma	Phase 1
DC-10	DC-10	Solute Carrier Family 7 Member 11 (SLC7A11)	Cancer	Pre-clinical
AX-09	AX-09	Solute Carrier Family 7 Member 11 (SLC7A11)	Colorectal cancer; Metastatic breast cancer; Non-small cell lung cancer	Pre-clinical
xCT-mAb	AbX-09	Solute Carrier Family 7 Member 11 (SLC7A11)	Colorectal cancer; Metastatic breast cancer; Non-small cell lung cancer	Pre-clinical
Cysteine/cystine	PR0–071	Solute Carrier Family 7 Member 11 (SLC7A11)	Central nervous system diseases; Impulse control disorder; Obsessive compulsive disorder; Schizophrenia; trichotillomania	Phase 2
MEDI-7247	MEDI-7247	Solute Carrier Family 1 Member 5 (SLC1A5)	Hematologic malignancy	Phase 1	NCT03811652; NCT03106428
IDE-397	IDE-397	Methionine Adenosyltransferase 2A (MAT2A)	Advanced solid tumor; Metastatic bladder cancer; Metastatic esophageal carcinoma; Metastatic head and neck cancer; Metastatic non-small cell lung cancer; Metastatic pancreatic cancer; Metastatic gastric cancer	Phase 2	NCT04794699
S-95035	S-95035	Methionine Adenosyltransferase 2A (MAT2A)	Solid tumor	Pre-clinical
AG-270	AG-270	Methionine Adenosyltransferase 2A (MAT2A)	Advanced solid tumor; Lymphoma; Metastatic non-small cell lung cancer; Ductal adenocarcinoma of pancreas	Phase 1	NCT03435250
SCR-7952	SCR-7952	Methionine Adenosyltransferase 2A (MAT2A)	Cancer; Solid tumor	Pre-clinical
S-095033	S-095033	Methionine Adenosyltransferase 2A (MAT2A)	Metastatic esophageal carcinoma; Squamous cell carcinoma	Pre-clinical
Evexomostat	SDX-7320	Methionyl Aminopeptidase 2 (METAP2)	Cancer; Hepatocellular carcinoma; Idiopathic pulmonary fibrosis; Metastatic breast cancer; Metastatic colorectal cancer; Metastatic non-small cell lung cancer; Metastatic prostate cancer; Type 2 diabetes mellitus; Prostatic tumor	Phase 2	NCT05570253; NCT02743637
APL-1202	APL-1202	Methionyl Aminopeptidase 2 (METAP2)	Bladder cancer	Phase 3	NCT04813107; NCT04736394; NCT04601766; NCT04498702; NCT04490993; NCT03672240
M-8891	M-8891	Methionyl Aminopeptidase 2 (METAP2)	Advanced solid tumor; cancer	Phase 1
SDX-7195	SDX-7195	Methionyl Aminopeptidase 2 (METAP2)	Metabolic disorder	Pre-clinical	NCT04073368

Asparagine has received extensive attention as a new target for cancer treatment. Knott et al. reported that the expression‎ level of asparagine synthetase (ASNS) in breast cancer is closely related to metastatic recurrence and that inhibition of ASNS or restriction of dietary Asn can reduce tumor metastasis.97 In non-small cell lung cancer (NSCLC), activating transcription factor 4 (ATF4) can alter amino acid uptake and increase Asn synthesis through AKT and NRF2 downstream of KRAS. In addition, the use of AKT inhibitors in combination with extracellular asparagine (ASN) depletion can significantly inhibit tumor growth (Fig. 6).98

Asn also has a key role in the growth and function of immune cells. Hope et al. found that CD8+T cells hardly express asparagine synthase (ASNS) during the early stage of CD8+T cell activation and that the growth, activation, and metabolic reprogramming of CD8+T cells are disrupted in the context of Asn deprivation.99 Wu et al. also demonstrated that Asn levels are increased in activated CD8+T cells and bind to the SRC family tyrosine kinase LCK, assisting in the phosphorylation of LCK at Tyr394 and 505, enhancing LCK activity and T-cell receptor signaling.100 Asn also has a key role in hematological malignancies. Williams et al. found that activating transcription factor 4 (ATF4) binds to the ASNS gene promoter through Zinc Finger and BTB domain-containing protein 1 (ZBTB1) to promote ASNS transcription in drug-resistant T-cell leukemia. However, ZBTB1 null T-cell leukemia cells are sensitive to ASNase (Fig. 6).101 The current use of bacterial-derived L-asparaginase (ASNase) in pediatric acute lymphoblastic leukemia (ALL) has significantly improved cure rates.102 However, in solid tumors, several clinical trials have shown the occurrence of drug-related toxic side effects such as pancreatitis, neutropenia, and hypoproteinemia.103,104,105 These toxic side effects are caused, at least in part, by the synergistic activity of glutaminase in ASNase.106,107 Based on the purpose of improving the efficacy of ASNase in hematological malignancies, expanding the use of ASNase and reducing side effects, a new generation of ASNase is being developed (Tables 1, 2).

Table 2 Approved drugs targeting amino acid metabolism

Full size table

Aspartate in disease

Immune disease

Abnormal metabolism of immune cells in autoimmune diseases can promote the chemotaxis of inflammatory cells and the production of inflammatory factors. In rheumatoid arthritis (RA), overproduction of the cytokine tumor necrosis factor (TNF) is a central event in pathogenesis, and endoplasmic reticulum (ER) rich T cells are the major releasers of TNF in inflamed joints.108,109 Wu et al. found that the abundance of mitochondrial Asp in T cells in rheumatoid arthritis (RA) was decreased, which inhibited NAD+ turnover, resulting in a decrease in NAD+/NADH ratio and a reduction in ADP-ribosylation of proteins which is NAD+ dependent. The absence of ADP ribosylation of the endoplasmic reticulum (ER) chaperone BiP releases ER stress proteins, driving ER dilation and TNF production. Moreover, treating T cells in rheumatoid arthritis with exogenous NAD+ or Asp prevents ER expansion and suppresses RA inflammation.12

The treatment strategy for RA and other autoimmune diseases is to use antibodies to block cytokines or their receptors. The latest small molecule inhibitors are targeted Janus kinase (JAK) inhibitors.110 These therapeutic strategies are designed to block the downstream practice of inflammatory pathways. However, these downstream signaling pathways are widely distributed in cell types other than immune cells, which contributes to adverse events such as thrombosis.111,112 Therefore, the research on upstream inflammation in autoimmune diseases is helpful in preventing the development of the disease from the source.

아스파르테이트와 질환

면역 질환

자가면역 질환에서 면역 세포의 이상 대사 과정은 염증 세포의 화학유인 작용과 염증 인자 생산을 촉진할 수 있습니다. 류마티스 관절염(RA)에서 사이토킨인 종양 괴사 인자(TNF)의 과다 생산은 병리 발생의 핵심 사건이며, 염증성 관절에서 내소체(ER)가 풍부한 T 세포가 TNF의 주요 분비 세포입니다. 108,109 Wu 등 연구진은 류마티스 관절염(RA) 환자의 T 세포에서 미토콘드리아 아스파르테이트 농도가 감소했으며, 이는 NAD+ 회전율을 억제해 NAD+/NADH 비율을 감소시키고 NAD+ 의존적 단백질의 ADP-리보실화를 감소시켰다고 보고했습니다. 내소체(ER) 분자 접힘 보조 단백질 BiP의 ADP 리보실화가 결여되면 ER 스트레스 단백질이 방출되어 ER 확장 및 TNF 생산을 촉진합니다. 또한 류마티스 관절염의 T 세포에 외인성 NAD+ 또는 아스파르트산을 투여하면 ER 확장을 억제하고 RA 염증을 억제합니다.12

RA 및 기타 자가면역 질환의 치료 전략은 사이토카인 또는 그 수용체를 차단하는 항체를 사용하는 것입니다. 최신 소분자 억제제는 Janus kinase (JAK) 억제제를 표적으로 합니다.110 이러한 치료 전략은 염증 경로의 하류 작용을 차단하도록 설계되었습니다. 그러나 이러한 하류 신호 전달 경로는 면역 세포를 제외한 다양한 세포 유형에 널리 분포되어 있어 혈전증과 같은 부작용을 유발합니다.111,112 따라서 자가면역 질환의 상류 염증 연구는 질병의 발생을 근원에서 예방하는 데 도움이 됩니다.

Neurological disease

Asparagine synthesis disorder (ASD) is a newly discovered neurological disorder associated with mutations in the ASNS gene on chromosome 7q2. ASD seriously impacts early neurodevelopment, leading to intellectual disability, developmental delay, intractable seizures, progressive brain atrophy and respiratory defects.13,14,15,16,17,18 Currently, the disease can only be diagnosed by DNA sequencing, and only a subset of individuals have detectable reductions in Asn levels in serum and cerebrospinal fluid, hindering the use of this test for initial screening. Because Asn does not actively accumulate in the brain due to the blood-brain barrier, reduced activity of ASNS in the brain is thought to contribute to the disease.13,14 So far, 15 ASD-related mutations have been reported, some of which disrupt the protein structure and reduce the substrate binding ability and catalytic efficiency of ASNS. For example, R49Q is a mutation located in the Gln-binding pocket of the N-terminal domain, and this mutation causes the loss of hydrogen bonds not only to the second β-sheet but also to Gln. Moreover, G289A and T337I mutations are located proximal to the ATP-binding pocket of the C-terminal domain, G289A would cause steric conflict with Ser293, and T337I would cause a hydrophobic patch on the protein surface and reduce protein solubility.16

In terms of treatment, dietary Asp supplementation has not been as effective as expected, and artificially elevated blood Asn may affect the absorption of other amino acids due to competition for cotransporters.113,114 Current treatments are only partially effective, and further understanding of the disease’s mechanism are needed to develop effective drugs.

In neurological diseases, functional defects in N-methyl-D-aspartate receptors (NMDARs) are the major defects that cause neural signaling disorders. NMDARs are a class of glutamate and ion channel receptors. NMDA receptor signaling is mediated by Ca2+ permeability and the C-terminal domain of GluN2 subunit-associated network signaling and scaffold proteins. Mutations in NDMARs subunits are associated with neurodevelopmental disorders.115,116 D-aspartate (D-Asp) has been shown to influence the signaling of NMDARs by acting as an agonist to bind to the agonist site of NMDARs and activate this glutamate receptor. D-Asp is present in the cytoplasm, peroxisome and extracellular neurons. Endogenous D-Asp is converted from L-Asp by racemization in the central nervous system and endocrine system.117 Several preclinical studies have shown that D-Asp is associated with the NMDA-dependent phenotype associated with schizophrenia (Sch). In a D-Asp oxidase knockout mouse model, treatment with D-Asp significantly alleviated phencyclidine-induced cortico-limbic thalamic dysfunction and reduced neuronal prepulse deficits induced by psychotropic drugs (amphetamine and MK-801).118,119 Sacchi et al. found that extracellular D-Asp and L-Glu levels were increased in the prefrontal cortex of olanzapine-treated mice but not in a D-Asp oxidase knockout mouse model. Regulation of D-Asp metabolism in the central nervous system may have an impact on olanzapine treatment in patients with drug-resistant schizophrenia (TRS).120 Currently, research on D-Asp as a treatment for TRS disease is still in its early stages, and animal experiments are ongoing.

신경계 질환

아스파라긴 합성 장애(ASD)는 7q2 염색체에 위치한 ASNS 유전자 변이와 관련된 새롭게 발견된 신경계 질환입니다. ASD는 초기 신경 발달에 심각한 영향을 미쳐 지적 장애, 발달 지연, 치료가 어려운 발작, 진행성 뇌 위축 및 호흡 장애를 유발합니다.13,14,15,16,17,18 현재 이 질환은 DNA 시퀀싱을 통해만 진단 가능하며, 혈청 및 뇌척수액에서 아스파라긴 수치 감소가 검출되는 환자는 일부에 불과해 초기 선별 검사로 활용하기 어렵습니다. 아스파르트산은 혈액-뇌 장벽으로 인해 뇌에 적극적으로 축적되지 않기 때문에, 뇌에서의 ASNS 활성 감소가 질환에 기여할 것으로 추정됩니다.13,14 현재까지 ASD와 관련된 15개의 돌연변이가 보고되었으며, 이 중 일부는 ASNS의 단백질 구조를 파괴하고 기질 결합 능력 및 촉매 효율성을 감소시킵니다. 예를 들어, R49Q는 N-말단 도메인의 글루타민 결합 포켓에 위치한 돌연변이로, 이 돌연변이는 두 번째 베타 시트뿐만 아니라 글루타민과의 수소 결합을 상실시킵니다. 또한 G289A와 T337I 돌연변이는 C-말단 도메인의 ATP 결합 부근에 위치하며, G289A는 Ser293과의 공간적 충돌을 유발하고, T337I는 단백질 표면에 친수성 패치를 형성하여 단백질 용해도를 감소시킵니다.16

치료 측면에서 아스파르트산(Asp) 보충은 기대만큼 효과적이지 않았으며, 혈중 아스파르트산(Asn)을 인위적으로 증가시키면 코트랜스포터 경쟁으로 인해 다른 아미노산의 흡수에도 영향을 미칠 수 있습니다.113,114 현재 치료법은 부분적으로만 효과적이며, 효과적인 약물을 개발하기 위해 질병의 메커니즘에 대한 추가적인 이해가 필요합니다.

신경학적 질환에서 N-메틸-D-아스파르테이트 수용체(NMDARs)의 기능적 결함은 신경 신호 전달 장애를 유발하는 주요 결함입니다. NMDARs는 글루타메이트 및 이온 채널 수용체의 한 종류입니다. NMDA 수용체 신호전달은 Ca2+ 투과성과 GluN2 서브유닛과 연관된 C말단 도메인의 신호전달 네트워크 및 스캐폴드 단백질을 통해 매개됩니다. NDMARs 서브유닛의 돌연변이는 신경발달 장애와 연관되어 있습니다.115,116 D-아스파르트산(D-Asp)은 NMDARs의 작용제 부위에 결합하여 이 글루타메이트 수용체를 활성화하는 작용제로 작용함으로써 NMDARs의 신호전달에 영향을 미치는 것으로 밝혀졌습니다. D-Asp는 세포질, 과산화체 및 세포외 신경세포에 존재합니다. 내인성 D-Asp는 중추 신경계와 내분비계에서 L-Asp로부터 라세미화 과정을 통해 전환됩니다.117 여러 전임상 연구에서 D-Asp가 정신분열증(Sch)과 관련된 NMDA 의존성 표현형과 연관되어 있음을 보여주었습니다. D-Asp 산화효소 결손 마우스 모델에서 D-Asp 투여는 페니클리딘 유발성 피질-한계-시상 기능 장애를 유의미하게 완화했으며, 정신활성 약물(암페타민 및 MK-801)에 의해 유발된 신경세포 사전 자극 결핍을 감소시켰습니다. 118,119 Sacchi 등(Sacchi et al.)은 올란자핀 투여 마우스의 전전두엽 피질에서 세포외 D-Asp 및 L-Glu 수치가 증가했지만, D-Asp 산화효소 결손 마우스 모델에서는 증가하지 않았음을 발견했습니다. 중추 신경계에서의 D-Asp 대사 조절은 약물 저항성 정신분열증(TRS) 환자의 올란자핀 치료에 영향을 미칠 수 있습니다.120 현재 TRS 질환의 치료제로서 D-Asp에 대한 연구는 초기 단계에 있으며, 동물 실험이 진행 중입니다.

Glutamine (Gln)

Glutamine metabolism

Gln is an α-amino acid used in protein synthesis. It is structurally similar to glutamate, but the carboxylic acid group of the side chain is replaced by an amide. Gln is a non-essential amino acid obtained from food121 and the most consumed amino acid and is involved in synthesizing all nonessential amino acids (NEAAs) and proteins.9 Muscle tissue produces the most Gln in the human body, accounting for about 90% of all synthesized Gln. The brain and lungs can also release a small amount of Gln. Although the liver can also synthesize Gln, its main function is to regulate the large amount of Gln absorbed from the intestine. Gut cells, kidney cells, activated immune cells, and various tumor cells are the most urgent consumers of Gln.122,123,124 Gln enters the cell via the amino acid transporter ASCT2/SLC1A5 and is converted to glutamate in the mitochondria by a deamination reaction involving glutaminase (GLS). Glutamate is then catalyzed by glutamate dehydrogenase (GDH) or glutamate transaminase, or aspartate transaminase (TAs) to produce α-ketoglutarate (α-KG). α-KG is an intermediate product of the TCA cycle (Fig. 5). Under hypoxia or mitochondrial dysfunction, α-KG can be converted to citrate by Isocitrate dehydrogenase (IDH 2) catalyzed carboxylation reaction, which is used for the synthesis of amino acids and fatty acids and the production of reducing agent NADPH.125,126,127

Glutamine in cancer

Tumor cells are urgent consumers of Gln. The signaling molecules Akt, Ras, and AMPK can induce lactate production by activating glycolysis to cause the Warburg effect, prompting tumor cells to meet energy demand through Gln metabolism. Gln metabolism is regulated by oncogenes/tumor suppressor genes such as c-Myc and p53 in various tumors.128 The oncogene c-Myc upregulates Gln metabolism through transcriptional activation of GLS and SLC1A5 genes. Mukha et al. reported that GLS-driven Gln metabolism is a regulator of radiotherapy tolerance in prostate cancer (PCa) and that high expression‎ of GLS 1 and c-MYC, key regulators of Gln, are significantly associated with reduced progression-free survival in prostate cancer patients treated with radiotherapy. Gln metabolism can maintain prostate cancer stem cells (CSCs) through α-KG-dependent chromatin dioxygenase. Inhibition of Gln metabolism reduces the frequency of CSCs population in vivo and the rate of tumor growth in mouse models.129 Amaya et al. found that signal transducers and activators of transcription 3 (STAT3) promote MYC expression‎ in tumor cells in AML, which in turn regulates the transcription of amino acid transporter SLC1A5, promotes Gln metabolism in AML cells, and oxidative phosphorylation (OXPHOS) of leukemia stem cells (LSCs). Small-molecule inhibitors of STAT3 selectively kill AML stem cells and preserve normal hematopoietic cells.130 In addition, Tajan et al. found that in colon cancer, Gln deprivation stimulates p53 activation and promotes the expression‎ of the aspartate/glutamate transporter SLC1A3, thereby promoting glutamate, Gln and nucleotide synthesis, maintaining electron transport chain and tricarboxylic acid cycle activity. Loss of SLC1A3 reduces tumor cell resistance to Gln starvation and inhibits tumor cell growth.131 In addition, it has been shown that tumor cells with high expression‎ of cystine/glutamate anti-transporter SLC7A11/xCT are highly dependent on Gln metabolism. In the absence of amino acids such as cystine, cells promote translation of ATF4 via the general control non-repressor 2 (GCN2) -eukaryotic initiation factor (eIF2a) signaling pathway, which promotes transcription of genes involved in amino acid metabolism and stress response, including SLC7A11, enabling cells to cope with amino acid starvation.132 In lung cancer, the RNA-binding protein RBMS1 was reported to interact directly with eIF3d to promote SLC7A11 translation (Fig. 7).133 Because tumor cells exchange intracellular glutamate for extracellular cystine through SLC7A11, intracellular glutamate is consumed, which causes cells to absorb more Gln and activate glutaminase to supplement intracellular glutamate, making cells with high expression‎ of SLC7A11 become Gln-dependent. In triple-negative breast cancer (TNBC), cells with high SLC7A11 expression‎ consume more Gln and are more sensitive to Gln starvation compared to other breast cancer cells.134 SLC7A11 is also highly expressed in lung, PDAC, renal, and liver cancers.135,136,137 Moreover, Badgley et al. found that deletion of SLC7A11 has no effect on normal pancreatic tissue development in mice but severely impairs KRAS-driven PDAC growth.137 The non-necessity of SLC7A11 under physiological conditions and the high expression‎ of SLC7A11 in tumors make SLC7A11 a promising target for cancer therapy (Table 1).

글루타민(Gln)

글루타민 대사

Gln은 단백질 합성에 사용되는 α-아미노산입니다. 글루타메이트와 구조적으로 유사하지만, 측쇄의 카르복시산 그룹이 아미드 그룹으로 대체되어 있습니다. 글루타민은 식품으로부터 섭취되는 비필수 아미노산이며, 가장 많이 소비되는 아미노산으로 모든 비필수 아미노산(NEAAs)과 단백질 합성에 관여합니다.9 인간 몸에서 글루타민은 주로 근육 조직에서 생성되며, 전체 합성된 글루타민의 약 90%를 차지합니다. 뇌와 폐도 소량의 글루타민을 방출할 수 있습니다. 간도 글루타민을 합성할 수 있지만, 주요 기능은 장에서 흡수된 대량의 글루타민을 조절하는 것입니다. 장 세포, 신장 세포, 활성화된 면역 세포, 다양한 종양 세포는 글루타민의 가장 긴급한 소비자입니다.122,123,124 글루타민은 아미노산 운반체 ASCT2/SLC1A5를 통해 세포로 들어가 글루타미나제(GLS)에 의한 탈아미노 반응을 통해 미토콘드리아에서 글루타메이트로 전환됩니다. 글루타메이트는 글루타메이트 탈수소효소(GDH) 또는 글루타메이트 트랜스아미나제, 아스파르테이트 트랜스아미나제(TAs)에 의해 α-케토글루타레이트(α-KG)로 전환됩니다. α-KG는 TCA 회로의 중간 대사산물입니다(그림 5). 저산소 상태나 미토콘드리아 기능 장애 시 α-KG는 이소시트르산 탈수소효소(IDH 2)에 의해 촉매되는 카복실화 반응을 통해 시트르산으로 전환됩니다. 이 과정은 아미노산 및 지방산 합성 및 환원제 NADPH 생산에 사용됩니다.125,126,127

글루타민과 암

종양 세포는 글루타민의 급격한 소비자입니다. 신호 전달 분자 Akt, Ras, 및 AMPK는 글리코lysis를 활성화하여 젖산 생성을 유도해 워버그 효과를 일으키며, 이는 암 세포가 글루타민 대사 통해 에너지 요구를 충족시키도록 합니다. 글루타민 대사는 c-Myc 및 p53과 같은 종양 유전자/종양 억제 유전자에 의해 다양한 암에서 조절됩니다.128 종양 유전자 c-Myc는 GLS 및 SLC1A5 유전자의 전사 활성화를 통해 글루타민 대사를 증가시킵니다. Mukha 등 연구진은 GLS에 의해 조절되는 글루타민 대사가 전립선 암(PCa)의 방사선 치료 내성 조절자임을 보고했으며, 글루타민의 주요 조절인자인 GLS 1과 c-MYC의 고발현이 방사선 치료를 받은 전립선 암 환자의 무진행 생존 기간 감소와 유의미하게 연관되어 있음을 확인했습니다. 글루타민 대사는 α-KG 의존성 염색질 디옥시게나제를 통해 전립선 암 줄기세포(CSCs)를 유지합니다. 글루타민 대사 억제는 생체 내 CSCs 인구 빈도와 마우스 모델에서의 종양 성장 속도를 감소시킵니다.129 Amaya 등 연구진은 급성 골수성 백혈병(AML)에서 신호 전달 및 전사 활성화 인자 3(STAT3)이 종양 세포에서 MYC 발현을 촉진하며, 이는 다시 아미노산 운반체 SLC1A5의 전사를 조절하여 AML 세포에서의 글루타민 대사 및 백혈병 줄기세포(LSCs)의 산화적 인산화(OXPHOS)를 촉진한다는 사실을 발견했습니다. STAT3의 소분자 억제제는 AML 줄기 세포를 선택적으로 사멸시키고 정상 혈액 생성 세포를 보존합니다.130 또한 Tajan 등 연구진은 대장암에서 글루타민 결핍이 p53 활성화를 자극하고 아스파르트산/글루타메이트 운반체 SLC1A3의 발현을 촉진하여 글루타메이트, 글루타민 및 뉴클레오티드 합성을 촉진하며 전자 전달 사슬과 트리카르복실산 회로 활성을 유지한다는 것을 발견했습니다. SLC1A3의 상실은 종양 세포의 글루타민 결핍에 대한 저항성을 감소시키고 종양 세포의 성장을 억제합니다.131 또한, 시스테인/글루타메이트 항운반체 SLC7A11/xCT의 고발현을 보이는 종양 세포는 글루타민 대사 의존성이 높다는 것이 밝혀졌습니다. 시스테인과 같은 아미노산이 결핍된 상태에서 세포는 일반적 제어 비억제자 2(GCN2)-유전자 발현 인자(eIF2a) 신호 경로를 통해 ATF4의 번역을 촉진하여 아미노산 대사 및 스트레스 반응과 관련된 유전자(SLC7A11 포함)의 전사를 촉진하여 아미노산 결핍에 대응합니다. 132 폐암에서 RNA 결합 단백질 RBMS1이 eIF3d와 직접 상호작용하여 SLC7A11 번역을 촉진한다는 보고가 있습니다(그림 7). 133 종양 세포는 SLC7A11을 통해 세포 내 글루타메이트를 세포 외 시스테인과 교환합니다. 이 과정에서 세포 내 글루타메이트가 소모되어 세포가 더 많은 글루타민을 흡수하고 글루타민아제를 활성화하여 세포 내 글루타메이트를 보충하게 됩니다. 이로 인해 SLC7A11 발현이 높은 세포는 글루타민 의존성이 높아집니다. 삼중 음성 유방암(TNBC)에서 SLC7A11 발현이 높은 세포는 다른 유방암 세포에 비해 글루타민을 더 많이 소비하며 글루타민 결핍에 더 민감합니다.134 SLC7A11은 폐, PDAC, 신장, 간 암에서도 고발현됩니다. 135,136,137 또한 Badgley 등(et al.)은 SLC7A11의 결실이 쥐의 정상 췌장 조직 발달에는 영향을 미치지 않지만 KRAS에 의해 유도된 PDAC 성장에 심각한 장애를 초래한다는 것을 발견했습니다.137 생리적 조건 하에서 SLC7A11의 필수성이 없으며 종양에서 SLC7A11의 높은 발현은 SLC7A11을 암 치료의 유망한 표적으로 만들며(표 1).

Fig. 7

Glutamine metabolism in tumor.

GCN5L1 (general control of amino acid synthesis 5 like 1) in mitochondria can promote the acetylation and inactivation of GLS, thus inhibiting the activation of mTORC1 and cell proliferation. GOT2 catalyzes the production of α-KG (α-ketoglutaric acid) from glutamate. When the expression‎ level of GOT2 is decreased, the participation of Glu in the synthesis of GSH increases and Glu is sensitive to the glutaminase inhibitor CB-839. Treatment with CB-839 increased ROS (reactive oxygen species) levels and promoted the activation of 5-FU through the NRF2 (Nuclear factor erythroid 2-related factor 2)-UPP1 (Uridine phosphorylase 1) axis. SASP(Sulfasalazine) reduces intracellular glutamate and extracellular cystine exchange by inhibiting SLC7A11. Glutamine deprivation increases the expression‎ of SLC1A3 on the surface of colon cancer cells by stimulating p53. In glutamine depletion environment, T cells secreted less Granzyme B and IFN-γ, and their function was inhibited. Acute myeloid leukemia (AML) cells promote SLC1A5 transcription via the STAT3-MYC axis. RNA-binding protein RBMS1 in lung cancer promotes SLC7A11 translation by binding to eIF3d. Created with BioRender.com. (The red blunt line represents inhibition)

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Glutaminase, which hydrolyzes Gln to glutamate, is a key enzyme in Gln metabolism. The expression‎ of glutaminase is tissue-specific. Glutaminase is actively expressed in periportal liver cells, renal epithelial cells, and the central nervous system, which is used to synthesize urea and neurotransmitters. Four isoforms of human glutaminase are divided into two highly active renal glutaminase types encoded by GLS1 and two low active hepatic glutaminase types encoded by GLS2.138 The heterogeneity of GLS1 and GLS2 expression‎ in different tumors indicates that malignant cells have different requirements for Gln metabolism. Zhang et al. found that general control of amino acid synthesis 5 like 1 (GCN5L1) in mitochondria of liver cancer cells can promote the acetylation and inactivation of GLS1 and GLS2 isomers, thus inhibiting mTORC1 activation and cell proliferation. In a mouse model of hepatocellular carcinoma induced by diethylnitrosamine (DEN), liver GCN5L1 knockout increased DEN sensitivity in the model. In addition, hepatoma cells with low expression‎ of glutamic oxalacetic transaminase 2 (GOT2) showed sensitivity to the glutaminase inhibitor CB-839. Specifically, hepatoma cells with low expression‎ of GOT2 showed a high dependence on Gln metabolism by increasing Gln metabolism, nucleotide synthesis, and glutathione synthesis to support cellular antioxidants (Fig. 7).139 Interestingly, in prostate cancer treated with androgen deprivation therapy, Xu et al. found that although androgen deprivation therapy inhibited the expression‎ of renal glutaminase (KGA) in the GLS1 subtype, the expression‎ of glutaminase C (GAC) was upregulated in tumor cells, which is an androgen-independent GLS1 subtype with stronger enzymatic activity. This switch leads to increased Gln utilization by tumor cells and promotes tumor proliferation and metastasis. Therapeutic approaches inhibiting GAC may increase the efficacy of castration-resistant prostate cancer.140 In clear-cell ovarian cancer (OCCC), the glutaminase inhibitor CB-839 inhibited ARID1A (AT-rich interactive domain-containing protein 1A) -mutated PDX tumor growth. ARID1A is a member of the SWI/SNF family, and the inhibition of GLS1 by SWI/SNF is weakened in OCCC with ARID1A mutation, which promotes Gln utilization and metabolism IN tumor cells.141 SWI/SNF mutations are present in nearly 25% of cancers, which led us to wonder whether other SWI/ SNF-mutated tumors are also sensitive to glutaminase inhibitors.142,143

Best et al. reported that LKB1 mutation in KRAS mutant lung adenocarcinoma confers a glutamate enriched phenotype in TME, and this feature was associated with CD8+T cell activation against PD-1, whereas treatment with the glutaminase inhibitor CB-839 inhibited CD8+T cell expansion and activation. Their data suggested that glutaminase inhibitors could inhibit CD8+T cells activated by PD-1 immunotherapy in lung adenocarcinoma.144 Morevoer, Zhao et al. reported that CB-839 could promote the production of reactive oxygen species (ROS) in colorectal cancer cells, cause nuclear translocation of Nrf2, and subsequently upregulate the expression‎ of uridine phosphorylase 1 (UPP1), which promotes the activation of 5-fluorouracil (5-FU).145 Existing preclinical and clinical experiment data show that Gln inhibitor CB-839 joint capecitabine can effectively treat type PI3KCA mutations in colorectal cancer (NCT02861300).

A randomized, double-blind, controlled phase II trial in advanced renal cell carcinoma (RCC) demonstrated synergistic anticancer effects with the combination of the glutaminase inhibitor telaglenastat (CB-839) and the mTOR inhibitor everolimus (TelaE), which was well tolerated by patients previously treated with TKIs. Also, TelaE could improve progression-free survival (PFS) compared with placebo plus everolimus (PboE).146 Another phase I b clinical trial also showed good tolerability and clinical activity of TelaE or telaglenastat combined with cabozantinib (TelaC) in treating RCC.147

Glutamine in disease

Pancreatitis

Gln can be used as a nutritional supplement for a variety of diseases. Several meta-analyses found that Gln supplementation can reduce the mortality, complication rate, and total length of hospital stay for patients with severe pancreatitis.148,149,150,151 A randomized, double-blind, placebo-controlled clinical study showed that supplementation of Gln to the low fermentable oligo-monosaccharides and polyols (FODMAP) diet improves irritable bowel syndrome (IBS) symptoms.152 In terms of promoting wound healing, Arribas-Lopez et al. found that arginine and Gln supplementation could positively affect wound healing, and Gln supplementation significantly affected nitrogen balance in patients and reduced the length of hospital stay and mortality.153 However, Gln supplementation does not seem to significantly affect the prognosis of burn patients. Moreover, in a double-blind, randomized, placebo-controlled trial enrolling 1200 patients, survival to hospital discharge was 40 days in the Gln-supplementation group versus 38 days in the placebo group. Mortality was 17.2% in the Gln group, which was not significantly different from 16.2% in the placebo group, and Gln supplementation did not reduce the length of hospital stay.154 In their study, Heyland et al. showed the benefits and risks of Gln supplementation, while clinical trials in burns and other diseases have shown conflicting results. The benefits and risks of Gln supplementation in various diseases still need more data from clinical trials.

Cardiovascular disease

In cardiovascular disease, Myc and Myc-related factor X (Max) upregulate the Gln transporters SLC1A5 and SLC7A5 and mitochondrial malate in pulmonary hypertension, thereby promoting glutaminolysis-induced right ventricular hypertrophy.19 Under oxidative stress, the glutathione (GSH) level in cardiomyocytes decreases by 60–70%, and the levels of Gln, glutamate and α-ketoglutarate (α-KG) also decrease significantly, while the enzyme activity of GLS, which converts Gln to glutamate, is enhanced. However, inhibition of GLS activity can reduce ATP and GSH levels produced by cardiomyocytes under oxidative stress conditions.

T2DM is a major risk factor for the development of cardiovascular disease. Dysregulation of skeletal muscle metabolism in diabetes affects insulin sensitivity and glucose homeostasis. Dollet et al. found that Gln is a key amino acid in the regulation of glucose stability and insulin sensitivity, and the level of Gln affects the inflammatory response of skeletal muscle and regulates the expression‎ of the adaptive protein GRB10, an insulin signaling inhibitor. Moreover, the systemic elevation of Gln improves insulin sensitivity and restores glucose homeostasis in mouse models of obesity.155

The anthracycline antibiotic doxorubicin (DOX) is a widely used anti-tumor drug in solid malignant tumors; yet, this therapy may lead to serious cardiotoxicity due to free radicals and oxidative stress. Gln supplementation significantly reduced cardiac lipid peroxide levels and increased peroxidase and glutathione levels, protecting cardiac function in DOX-treated rat models.156,157

Drugs targeting cardiac Gln metabolism are being developed. Oridinon (Ori), a natural terpenoid derived from the plant Isodon rubescens (Hemsl.), can increase cardiac Gln levels and inhibit the decline of ATP/ADP ratio, protecting cardiomyocytes and reducing infarct size in a rat model of myocardial injury.158

Severe acute respiratory syndrome

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of coronavirus disease 2019 (COVID-19). The disease is spread through close person-to-person contact or respiratory secretions from infected people. Risk factors for COVID-19 include cardiovascular disease and diabetes, and such high-risk groups exhibit common metabolic features of low levels of Gln, NAD+, and overproduction of hyaluronic acid (HA).159,160,161 Levels of Gln and NAD+ cause dysregulation of SIRT1, a key negative regulator of the Hyaluronan synthase 2 (HAS2) gene.162 These metabolic alterations eventually lead to the overproduction of HA and Plasminogen activator inhibitor 1 (PAI-1) and the expansion of Tregs and myeloid-derived suppressor cells (MDSCs) populations. Therefore, Gln deficiency has led to immune dysfunction and HA overproduction in people at high risk of COVID-19. HA can activate STAT3 through PAI-1.163 Due to dysregulation of SIRT1, STAT3, and O-GlcNacylation induce hyaluronic acid storm through activation of HAS2. In addition, although SARS-CoV-2 vaccines have significantly reduced COVID-19 cases, cells are placed under intense oxidative stress conditions after SARS-CoV-2 infection, which promotes the consumption of Gln to synthesize glutathione.164 This process exacerbates Gln deficiency in high-risk populations and may induce metabolic dysfunction. At the same time, it can also cause STAT3 pathway inactivation and PAI-1 activation, leading to severe complications of COVID-19 in some people. Small clinical trials have shown that Gln supplementation reduces post-infection severity in patients with COVID-19.165,166 However, this part of the study needs to be expanded to more accurately assess the value of Gln in the treatment of COVID-19.

Arginine (Arg)

Arginine metabolism

Arginine, also known as L-arginine, is a raw material for protein synthesis and an intermediate product of the urea and nitric oxide cycles.40,167 Arginine is classified as a conditionally essential amino acid, and its requirement depends on developmental stage and health status. In humans, small intestinal epithelial cells convert Gln and glutamate to citrulline, which is then transported by the circulatory system to renal proximal tubular cells, where arginine is synthesized by arginine-succinate synthetase and arginine-succinate lyase in the urea cycle. Arginine synthesis is impaired when small intestine and kidney function is impaired, thus creating a dietary requirement for arginine. In other cell types, arginine synthesis by citrulline is very low but dramatically increases when inducible nitric oxide synthase (NOS) increases (Fig. 5). Under these conditions, citrulline, a byproduct of nitric oxide synthesis, can recover arginine via the arginine-citrulline pathway.168 Arginine is important for cell division, wound healing, and immune function.169,170,171 Arginine from proteins can be catalyzed by PAD enzymes to citrulline, a process called citrullination, which is part of the normal immune process. Another type of post-translational modification is methylation by arginine methyltransferases (PRMTs), in which arginine can be methylated to either monomethylated arginine or dimethylated arginine. Arginine methyltransferases can be divided into three following classes: Type I PRMTs (PRMT1, PRMT2, PRMT3, PRMT4, PRMT6, and PRMT8) catalyze the production of asymmetric dimethylarginine; Type II PRMTs (PRMT5 and PRMT9) catalyze the formation of symmetrical dimethylarginine; Type III PRMTs are currently the only known PRMT7, which produces only monomethylarginine.172 Arginine methylation usually occurs in the glycine and arginine-rich "GAR motif". Many arginine-methylated proteins have been shown to interact with DNA or RNA, and the arginine residue acts as an important hydrogen donor for the phosphate backbone.173,174 In addition, arginine methylation also affects protein–protein interactions involved in various cellular processes such as protein trafficking, signal transduction and transcriptional regulation.173

Arginine in cancer

Citrulline and aspartate can be converted to arginine in normal cells by arginine-succinate synthetase 1 (ASS1) and arginine-succinate lyase (ASL) in the urea cycle.175 Arginine-succinate synthetase 1 (ASS1) transcriptional repression occurs in various tumors, creating a dependence on external arginine and enabling arginine-deprivation therapy. Use of the arginine-depleting agent pegylated arginine deiminase ADI-PEG20 in GBM can increase nitric oxide (NO) synthesis and produce cytotoxic pernitrite, increasing the sensitivity of tumor cells to ionizing radiation and significantly enhancing the effect of radiotherapy on GBM.176 The combination of ADI with Palomid 529 or chloroquine showed a synergistic tumor inhibition effect in vitro. Combination with suberoylanilide hydroxamic acid (SAHA) can effectively control the growth of GBM xenografts.177 ASS1 is downregulated in hepatocellular carcinoma (HCC); therefore, arginine dystrophy is also present. Treatment of HCC cells with ADI-PEG20 downregulates the key enzymes of pyrimidine synthesis in the TCA cycle, carbamoyl phosphate synthetase 2, thymine synthase (TS), aspartate transcarbamylase and dihydrooratase (CAD) and malate dehydrogenase 1 (MDH-1) activities, making tumor cells more susceptible to 5-fluorouracil (5-FU). The effect of this synergistic treatment is ASS-dependent, and the activity of the enzymes mentioned above can be restored by transfection of ASS, eliminating the sensitivity of tumor cells to ADI-PEG20 combined with 5-FU treatment.178 Meanwhile, arginine deprivation promotes GCN2-dependent cycle arrest in HCC cells, and inhibition of GCN2 in arginine-deprived HCC cells promotes cellular senescence and increases the efficacy of senolytic compounds (Fig. 8).179 Ass-deficient prostate and pancreatic cancers have also been shown to be sensitive to ADI-PEG20, and ADI-PEG20 promotes cell death by inducing autophagy and apoptosis.180,181

Fig. 8

Arginine metabolism in tumor cells. Arginine depletion can increase the phosphorylation level of GCN2 in hepatocellular cancer cells, activate GCN, increase the expression‎ level of SLC7A11 and increase the uptake of arginine. Activated GCN2 can also be mediated by p21 cell cycle arrest; GCN2 also increases protein synthesis by activating mTORC1 via sestrin. ARG2 in the mitochondria of melanoma cells increases transfer-promoting gene transcription via the p66SC-H2O2-Stat3 axis. Myeloid cells can promote intracellular p38 and ARG1 transcription by receiving tumor cell-derived CSF and activation of STAT3. In addition, low pH of tumor microenvironment also promoted ARG1 transcription through H+ activation of intracellular cAMP-CREB axis. IL-6 and IL-8 promote ARG1 transcription by activating the PI3K/AKT pathway. The arginine metabolism of myeloid cells with high expression‎ of ARG1 was enhanced, and the arginine metabolism of T cells was inhibited, and the tumor immunity was inhibited. Created with BioRender.com. (The red blunt line represents inhibition)

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The arginase isoenzymes arginase1 (ARG1) and arginase2 (ARG2) are abnormally upregulated in various cancers. ARG1 is mainly expressed in the cytoplasm of hepatocytes and plays a role in the urea cycle. In contrast, ARG2 is expressed in mitochondria of multiple tissues, with the most abundant expression‎ in the kidney and prostate, and mediates arginine/ornithine balance.182,183 In neuroblastoma, overexpression‎ of ARG1 can increase AKT and ERK phosphorylation and promote cell proliferation.184 In gastric cancer, serum factors IL-6 and IL-8 can stimulate CD45+CD33lowCD11bdim MDSCs to express ARG1 and ultimately inhibit CD8+ T cell function through the PI3K-AKT signaling pathway (Fig. 8).185 GM-CSF derived from breast cancer tumor cells can promote ARG1 expression‎ in tumor-infiltrating myeloid cells through STAT3 and p38 MAPK signaling pathways, enhance the function of tumor-infiltrating myeloid cells, and promote the development of immunosuppressive TME (Fig. 8).186 Studies have also found that the expression‎ level of ARG2 in malignant thyroid tumors is significantly higher than that in normal tissues, and ARG2 inhibition can reduce the expression‎ level of AKT and promote tumor cell apoptosis.187

In head and neck squamous cell carcinoma (HNSCC), phosphorylated STAT3 can directly bind to the ARG1 promoter region of MDSCs to promote transcription, thereby contributing to the immunosuppressive effect of MDSCs.188 ARG2 has also been reported to promote melanoma tumor metastasis through the H2O2-STAT3 pathway (Fig. 8).189 Multiple tissue-derived tumor samples show a large number of Arg1-positive myeloid cells in the tumor microenvironment. In cancer patients, ARG1 is increased while L-Arginine is decreased in plasma samples. Administration of CB-1158 (a small molecule inhibitor of arginase) can slow tumor growth rates, block myeloid cell-mediated suppression of T-cell proliferation, and increase the number of tumor-infiltrating CD8+ T cells and NK cells in mouse models of multiple tumors.190 Piceatannol (PIC), another natural arginase inhibitor, can effectively inhibit TGF-β1 /TGF-β receptor type 1 (TGF-βR1) signaling pathway, limit M2-type macrophage polarization to regulate TME and inhibit CRC progression and metastasis.191 These results suggest that ARG is a potential target for tumor metabolism. Arginase inhibitors have been developed and experimentally eval‎uated in various tumors.

Protein arginine methyltransferases (PRMTs)

PRMTs are SAM-dependent enzymes that catalyze the mono- and di-methylation of peptidyl arginine residues. Many studies have shown that the activity of PRMTs is related to cancer stem cells (CSCs), which can self-renew and generate differentiated progeny. This is an important factor leading to tumor drug resistance, metastasis and recurrence. PRMT5 is highly expressed in breast cancer and chronic myeloid leukemia (CML) stem cells, and the knockdown of PRMT5 or the use of PRMT5 inhibitors can significantly impair the self-renewal capacity of CSCs.192,193 PRMT5 can also promote DVL3 expression‎, thereby driving Wnt/β-catenin signaling.192 In addition, PRMT1 is a key regulatory molecule that maintains the pluripotent state of progenitor cells.194 PRMT7 can promote the transcription of Oct4, c-Myc, Nanog, and Klf4 by regulating the histone methylation of miR-24-2 and miR-221 promoters and inhibiting the expression‎ of miRNA.195,196 PRMT8 can also maintain ES cell diversity by inducing SOX2 expression‎.197 In breast cancer, arginine 21 (R21) and lysine 108 (K108) on mitochondrial ribosomal protein S23 (MRPS23) are methylated by methyltransferase 7 (PRMT7) and SET-domain-containing protein 6 (SETD6), respectively. Methylation of R21 promotes the polyubiquitination and degradation of MRPS23, which inhibits mitochondrial phosphorylation (OXPHOS) and increases ROS levels, thereby promoting breast cancer cell metastasis. On the other hand, K108 methylation cooperates with R21 methylation to maintain low levels of OXPHOS, which favors breast cancer cell survival.198 The use of the PRMTs inhibitor MS023 in TNBC induces an interferon response and exerts an antitumor effect.199 In GBM, PRMT2 participates in oncogene transcription by mediating H3R8me2a modification.200 PRMT5 expression‎ levels are elevated and associated with poor patient prognosis. Also, PRMT5 knockdown impairs the self-renewal ability of GBM cells and promotes apoptosis.201,202 Administration of the PRMT6 inhibitor EPZO20411 can inhibit the arginine methylation of chromatin condensation regulator 1 (RCC1), block the tyrosine kinase 2 (CK2) -PRMT6-RCC1 signaling axis, inhibit the proliferation of glioblastoma stem cells (GSCs) and increase their sensitivity to radiotherapy.203 Targeting PRMT7 reduces glycine decarboxylase expression‎, leading to the reprogramming of glycine metabolism and production of methylglyoxal, impairing the self-renewal capacity of leukemia stem cells (LSCs) and slowing the progression of leukemia.204 Similarly, administration of the PRMT5 inhibitor PJ-68 in a CML mouse model with high expression‎ of PRMT5 LSCs could deplete DVL3, thereby inhibiting Wnt/β-catenin signaling and significantly prolonging the survival time of a retroviral BCR-ABL-driven CML mouse model.193 These studies prove that PRMTs are potential targets for cancer therapy, and several PRMTs inhibitors are currently in clinical trials (Table 1).

Arginine in disease

Wound healing

In the process of wound healing, arginine participates in the response of inflammatory factors through the arginine-NO pathway. In addition, ornithine and urea produced by arginase degradation of arginine are essential during this process and have a key role in the synthesis of collagen and polyamines.171,205,206 Arginine can promote fibroblast proliferation through GPRC6A-ERK1/2 and PI3K/Akt signaling pathways.207 Arginine can also increase monocyte migration and proinflammatory factor production in peripheral blood during the early stages of inflammation.208 In the later stage of inflammation, arginine can also inhibit the activity of immune cells and regulate immune status. In myeloid cells, activated nitric oxide synthase (NOS) and NO inhibit T lymphocyte function by interfering with IL-2.209 In summary, arginine and its metabolites are essential for wound healing and are involved in multiple stages of wound healing, including collagen formation, cell proliferation, and immune regulation.

Dietary arginine supplementation is the most convenient way and has multiple benefits for wound healing. Arginine supplementation enhances the body’s DNA synthesis.210 In colitis models, arginine supplements inhibit the expression‎ of inflammatory factors and chemokines, suppress the inflammatory response, and promote the repair of injured tissues.211 Patients undergoing trauma/hemorrhagic shock have difficulty achieving wound healing due to reduced collagen synthesis. On the contrary, arginine supplementation significantly alleviates the above problems and increases wound strength.212 During diabetic wound healing, arginine supplementation can reverse the insufficient synthesis of NO and restore the concentration of NO in damaged tissues, promoting wound healing.213 Arginine has also been used to mitigate the risk of pressure ulcers, and supplementation of arginine in patients at high risk for pressure ulcers can significantly accelerate pressure ulcer healing.214

Alzheimer’s disease (AD)

Alzheimer’s disease (AD) is characterized by senile plaques and neurofibrillary tangles (NFTs) caused by amyloid-β and phosphorylated tau deposition. Advanced glycation end products (AGEs) modify proteins to cause their dysfunction. Glycosylation of the AMPK-γ subunit inhibits AMPK function, and arginine treatment protects AMPK-γ from glycosylation and increases AMPK phosphorylation in a mouse model of AD, thereby ameliorating AD disease.215 In patients with mild AD/cognitive impairment (MCI), a combination of L-arginine, HMG-CoA inhibitor simvastatin, and tetrahydrobiopterin to enhance the endothelial nitric oxide synthase (eNOS) pathway modestly increases cerebral blood flow and improves cognition.216 In addition, PRMT4-catalyzed asymmetric dimethylarginine (ADMA) has been reported to bind to NOS as a ligand, leading to NOS dysfunction, resulting in decreased cerebral blood flow and aggravating AD, which can be reversed by inhibition of PRMT4.217

Lung disease

Asthma is a variable, recurrent, long-term inflammatory disease of the respiratory tract. Imbalances in the metabolism of Arg and nitric oxide have been implicated in the pathophysiology of asthma. An analysis of plasma metabolic mass spectrometry in children with asthma showed that Arg, Lys, and Met levels were significantly decreased in the susceptible asthma group compared to the non-susceptible asthma group.218 Althoff et al. also showed significant increases in serum concentrations of asymmetric dimethylarginine (ADMA), enhanced inhibition of NOS, enhanced catabolism of Arg, increased levels of ornithine (Orn) and proline (Pro), and decreased Arg/Orn ratio in patients with asthma and obstructive sleep apnea (OSA).219 A controlled trial conducted by Liao et al. showed that adding L-Arginine to labeled asthma medications did not significantly reduce asthma exacerbations.220 This may be due to a marked increase in the activity of arginase induced by IL-4 and IL-13 and a marked increase in the downstream product putreamine in allergen-stimulated lungs.221 The addition of L-citrulline (a precursor of the L-arginine cycle and NO synthesis) to medications in obese asthmatic patients may assist in asthma control and improve fractional NO excretion (FeNO) levels.222

In chronic obstructive pulmonary disease (COPD), monocytes in lung tissue induce the transcription of PRMT7 through the NF-κB/RelA signaling pathway. High expression‎ of PRMT7 promotes the methylation of RAP1A regulatory element histones and regulates monocyte adhesion and migration. Decreased expression‎ of PRMT7 reduces monocyte recruitment to sites of lung injury.223

Cardiovascular diseases

Patients with hypercholesterolemia and vascular disease commonly have elevated asymmetric dimethylarginine (ADMA), which is associated with impaired NO synthesis and an early marker of endothelial dysfunction.20 ADMA is an endogenous nitric oxide synthase (NOS) inhibitor that can significantly reduce the synthesis of vasodilator NO, leading to the development of cardiovascular disease. The abnormal activity of PRMTs results in increased ADMA and MMA, which increases the risk of cardiovascular disease. Loss of PRMT7 in the heart reduces symmetrical dimethylation of β-catenin, enhances Wnt-β-catenin signaling, and promotes myocardial hypertrophy.224 PRMT1 is the main enzyme that catalyzes ADMA. It regulates gene activation by regulating histone methylation modification in the promoter region of myocartin. Ablation of PRMT1 can downregulate the expression‎ of contractile genes such as myocartin and significantly reduce the contractility of the aorta and the traction force of vascular smooth muscle cells (VSMCs).225 Administration of the PRMT4 inhibitor TP-064 in a mouse model of atherosclerotic cardiovascular disease can induce a decrease in monocyte tumor necrosis factor-α (TNF-α) secretion, downregulate the gene expression‎ of the glycogen metabolism-related protein G6pc in the liver, and reduce plasma triglyceride levels, exerting regulatory effects from inflammatory and metabolic pathways.226

Inhibitors targeting PRMTs are being developed and experimentally tested. Arg methylase inhibitors (AMIs), symmetric sulfonated urea, specifically inhibit PRMT activity and, in a rat model, cyclooxygenase-2 (COX-2) expression‎ and suppress inflammation.227 MS023, another selective PRMT type I inhibitor, reduced ADMA, increased MAA and SDMA levels, and shifted PRMTs activity from type I to type II/III in cells treated with MS023.228

Methionine (Met)

Methionine metabolism

Met is an essential amino acid and a precursor of other amino acids such as cysteine (Cys) and taurine, as well as S-adenosyl-L-methionine (SAM) and glutathione (GSH). The backbone of Met biosynthesis is mainly derived from aspartate.229

Aspartate is first converted to homoserine through the reduction reaction of the β-aspartate semialdehyde terminal. The intermediate aspartate semialdehyde can be condensation with pyruvate to participate in the Lys biosynthesis pathway, and homoserine itself can also participate in threonine biosynthesis. The homoserine hydroxyl group is then activated by phosphate, succinyl, or acetyl groups, and the hydroxyl group is then replaced by cysteine, methyl thiol, or hydrogen sulfide by displacement reactions. It reacts with Cys under the catalysis of cystathionine-γ-synthetase to produce cystathionine, which is cleaved by cystathionine-β-lyase to form homocysteine. In reaction with free hydrogen sulfide, homocysteine is formed under the catalysis of O-acetyl-homoserine aminocarboxypropyl transferase. The reaction with methanethiol yields Met directly.229 Cysteine and homocysteine can be interconverted through the sulfur transfer pathway. This pathway includes both forward and reverse. The forward pathway is present in bacteria such as Escherichia coli and Bacillus subtilis and can transfer sulfhydryl groups from cysteine to homocysteine.230,231 The reverse pathway exists in organisms, including humans, to transfer sulfhydryl groups from homocysteine to cysteine.232 Even though Met is classified as an essential amino acid because of the reverse sulfur conversion pathway in humans, cysteine does not fall into this category.

In catabolism, Met is catalyzed by Met adenosine transferase (MAT) to SAM. As a methyl donor, SAM participates in various methyl transfer reactions and is converted to S-adenosylhomocysteine (SAH) in the reaction. Met can increase the intracellular concentration of glutathione, promote cellular REDOX regulation, and protect cells by binding to oxidative metabolites (Fig. 5).233

Methionine in cancer

Met, as an essential amino acid, has an important role in tumor growth and metabolism. In addition to exogenous supply, the Met salvage pathway is the only Met source. This pathway requires the activity of methyladenosine phosphorylase (MTAP) as well as Met synthase (MS).234 MTAP is located in the periphery of the tumor suppressor cyclin-dependent kinase inhibitor 2 A (CDNK2A), and the co-deletion of the two genes occurs in ~15% of cancers and results in a highly aggressive tumor with a poor prognosis. These enzymes are often downregulated in malignant tumors, resulting in a strong dependence of the cells on Met intake from the external environment.234,235 In addition, Met is broken down by the Met cycle, in which Met adenosine transferase 2A (MAT2A) is upregulated and highly active in tumors.236 MAT2A has been proposed as a lethal target in MTAP null tumors. In the absence of MTAP, the substrate methyl thionyl adenosine (MTA) accumulates and acts as a selective inhibitor of PRMT5 to inhibit PRMT5 methylation activity,237 whereas MAT2A can produce the PRMT5 substrate SAM,238 allowing PRMT5 to exert its oncogenic effect. Valosin-Containing Protein P97/P47 Complex-Interacting Protein 1 (VCIP135) binds and stabilizes MAT2A in response to folate signaling in HCC and promotes tumor formation and progression in DEN/high-fat diet (HFD)—induced HCC mouse models (Fig. 9).239 Treatment with MAT2A inhibitors AG-24152 and AG-270 significantly reduces SAM levels, inhibits PRMT5 activity, and causes DNA damage and mitotic defects in tumor cells. Also, AG-270 showed a synergistic antiproliferative effect with the anti-mitotic drug taxane in vitro and in vivo.240 It has also been shown that MTA accumulation and secretion occur in MTAP-deficient GBM, but no significant MTA accumulation was detected in vivo because the stromal cells in the TME express WTAP and consume the MTA emitted by tumor cells and increase the activity of PRMT5. PRMT5 inhibitors GSK591 and ly-283 caused a broad inhibition of transcriptome splicing in GBM cells, particularly affecting the products of cell cycle genes and prolonged survival in the PDX mouse model.241

Fig. 9

Methionine metabolism in tumor cells. In hepatocellular carcinoma, valosin-containing protein P97/P47 complex-interacting protein 1 (VCIP135) responded to folic acid signals to bind and stabilize MAT2A. In MTAP deficient cells, the MTAP substrate, MTA, accumulates and inhibits PRMT5 activity. Tumor cells can increase methionine intake through high expression‎ of SLC43A2, competitive consumption of methionine in the environment, resulting in methionine deficiency in T cells. T cell methionine restriction can inhibit the normal methylation in cells, resulting in the transcription of STAT5 gene obstruction, affecting T cell survival and function. On the other hand, methionine metabolism inhibited PD-L1 and V-domain Ig suppressor of T cell activation (VISTA) immune checkpoint translation. Created with BioRender.com. (The red blunt line represents inhibition)

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Because of its central role in methylation, Met is considered a candidate target for tumor therapy driven by ten-eleven translocation (TET), isocitrate dehydrogenase (IDH) proteins, methyltransferases, and other phenotypic modifiers. Anti-tumor effects of the Met-free diet were first reported in Walker-256 sarcoma-bearing Sprague-Dawley rats.242 Met restricted diet can reduce N6-methyladenosine (m6A) methylation and immune checkpoint translation, such as PD-L1 and V-domain Ig suppressor of T cell activation (VISTA) in tumor cells. In addition, it increases the number of tumor-infiltrating CD8+ T cells to inhibit tumor immune escape (Fig. 9).243 In AML, the level of H3K36me3 changes most dramatically before and after Met deprivation, and inhibition of STED2, the H3K36-specific methyltransferase, can reproduce most of the cytotoxic phenotypes produced by Met deprivation.244 In addition, tumor cells can consume a large amount of Met in the environment by highly expressing Met transporter SLC43A2, which can inhibit the Met metabolism of T cells in the microenvironment, resulting in the loss of dimethylation of histone H3K79me2 lysine 79 in T cells, low expression‎ of STAT5, and inhibition of T cell function. Met supplementation or inhibition of SLC43A2 expression‎ in tumor cells can reverse the above-mentioned functional suppression of

T cells and activate tumor immunity (Fig. 9).245

The hepatocyte nuclear factor 4α (HNF4α) regulates sulfur amino acid (SAA) metabolism in the liver. Knocking down HNF4α in hepatocellular carcinoma impairs SAA metabolism, increases tumor cell tolerance to Met deprivation and sorafenib, and promotes tumor EMT. In contrast, restoring SAA metabolism alleviated the tumor phenotype resulting from HNF4α deficiency.246 These studies suggest that Met starvation not only suppresses tumor cell metabolism but also involves immune cells and that tumor cells themselves have complex preferential pathways to regulate Met metabolism. Therefore, more precise and focused treatment methods should be developed for tumor cell Met metabolism. Targeting STED2 and SLC43A2 provides new insights.

Methionine in disease

Fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a disease caused by abnormal metabolic pathways leading to the accumulation of triglycerides (TG) in the liver. Obesity and T2D mellitus are strong risk factors for NAFLD. HFD and Met and choline-deficient diet (MCD) can mimic human diseases’ histological and metabolic abnormalities and are commonly used to establish NAFLD mouse models. When eval‎uating the differences in the construction of the NALFD/NASH model between the two methods, it was found that the MCD diet could spontaneously lead to liver fibrosis within 2–4 weeks and significantly affect the expression‎ of genes involved in liver fibrosis pathways. This effect of HFD was not observed until 24 weeks after insulin resistance, which resulted in less liver fibrosis.247 Clinical data show that Met levels are reduced in the early stages of NAFLD and that higher Met intake is inversely associated with fibrosis risk. Methyl donor supplementation reduces hepatic fat accumulation by activating the AMPK signaling pathway to increase fatty acid consumption.248 Also, SAM has a key role in regulating liver homeostasis, and reduced levels of SAM synthesis have been detected in various chronic liver injuries, such as NAFLD.249 SAM can alleviate fat accumulation and oxidative stress by promoting mitochondrial fatty acid β-oxidation and releasing TG.249

In alcoholic liver disease, long-term alcohol intake increases the levels of homocysteine and SAH, decreases the SAM/SAH ratio, and directly affects cellular methylation levels.250,251 At the same time, ethanol can directly affect the activities of MAT, BHMT, and other enzymes, interfere with Met metabolism, inhibit GSH formation, and weaken the antioxidant capacity of cells.252 SAM supplementation reverses GSH depletion, reduces mitochondrial DNA damage, and ameliorates steatosis and hepatocyte necrosis in ethanol-fed models.253,254 Moreover, betaine can similarly mitigate ethanol-induced liver injury by improving ethanol-induced fatty acid synthesis by targeting FA synthetases, peroxisome activator receptor γ (PPAR γ) coactivator 1, and hepatic sterol regulatory element binding protein (SREBP) − 1c.255 Methionine adenosyl-transferase α1 (MATα1) synthesizes SAM in the liver. As a transcription factor, MATα1 negatively regulates cytochrome P450 2E1 (CYP2E1) at the mRNA level. On the other hand, MATα1 directly interacts with CYP2E1 to promote the methylation of CYP2E1 at R379 site and degradation through the proteasome pathway. Patients with ALD have reduced levels of MATα1 and a reduced hepatocyte methylation/CYP2E1 ratio. MATα1 KO hepatocytes can also be detected with reduced methylation/CYP2E1 ratio, reduced mitochondrial membrane potential, increased ROS content, and are sensitive to ethanol and TNF-α-induced mitochondrial dysfunction.256 In addition, ethanol could activate kinase CK2 to phosphorylate MATα1 at Ser114, promote its interaction with PIN1 isomerase, inhibit MATα1 localization in mitochondria, and promote ethanol-induced mitochondrial dysfunction and fat accumulation. Blocking the interaction between PIN-1 and MATα1 reversed the alcohol-induced cytotoxic phenotype.257

Kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic disease characterized by the enlargement of renal cysts. In the ADPKD model, the levels of Met and SAM are increased, which induces the expression‎ of Mettl3. Also, Mettl3 can increase c-Myc and Avpr2 mRNA modification, activate c-Myc and cAMP pathways, and accelerate cyst growth. A Met restricted diet may slow the progression of ADPKD.258 Kidney injury markers clusterin and cystatin c significantly decreased in the methionine restriction (MR) mouse injury model. Compared with the normal feeding model, the kidney inflammation genes such as Emr1, Nos2, and Tnfa were downregulated, and the degree of basophil aggregation was lower in the MR model. The renal fibrosis genes Fn1, Serpine1, Tgfb1, and Col1a1 were downregulated, and the degree of fibrosis was milder.259

Diabetes

Elevated levels of circulating Met, acetyl-aspartate, and Asn can be detected in T2DM and diabetic kidney disease (DKD). Also, elevated circulating Met levels can be used to predict the risk of developing diabetes.260 Met metabolism regulates Cys and endogenous hydrogen sulfide (H2S) levels. H2S inhibits glucose-induced insulin release in pancreatic β cells and insulin-stimulated glucose uptake in adipose tissue. Cystathionine γ-lyase (CSE) is a key enzyme in H2S synthesis, and the use of CSE inhibitors increases glucose uptake by adipocytes.261 MR can enhance insulin-stimulated phosphorylation of AKT and S6 and activate PI3K/AKT signaling pathway. Meanwhile, MR can also downregulate genes involved in an inflammatory response and immune cell infiltration, such as chemokine receptor (CCRs), chemokine ligand 7 (CCL7), IL-1β, IL-6, IFN-γ, and TNF-α.262 In summary, Met restriction (MR) can alleviate diabetes by interfering with glucose homeostasis, increasing insulin sensitivity and inflammatory response.

Amino acid metabolism in the tumor microenvironment (TME)

Over recent years, more and more studies have shown that amino acids in different cells in the TME and their interactions affect tumor immunity and therapeutic effect. Amino acids, transporters, and metabolites participate in tumor immunity through metabolic reprogramming. In addition, specific amino acid deficiency or the immunosuppressive effect of certain amino acid metabolism can damage the function of immune cells, including effector T cells, in the tumor microenvironment. The function of T cells is closely related to the effect of immunotherapy, chemotherapy and other tumor treatments.263,264 This section will present the current advances in amino acid metabolism and immunity.

BCAA

BCAAs have an important role in supporting immune cell function as carbon backbone providers in immune cells. A deficiency of BCAA impairs the immune function of lymphocytes and leukocytes.265 Leu depletion in T cells leads to restricted mTORC1 signaling and inhibits T-cell activation. A reduction in IFN-γ and IL-2 release from T cells was detected when T cells were co-stimulated with anti-CD3 and anti-CD28 using the Leu analog N-acetyl-Leu amide (NALA).266,267 Also, BCAA supplementation can increase CD8+ T cells to upregulate glucose transporter GLUT 1 in a FoxO1-dependent manner, increase glucose uptake and utilization, and enhance the antitumor activity of CD8+ T cells, having a synergistic role with anti-PD-1 therapy.268

There is a subset of immunomodulatory B cells in the TME with TGF-β1 as the main regulatory feature and expressing Leu-tRNA-synthase 2 (LARS2). This subpopulation of LARS B cells shows a preference for Leu metabolism, which can be induced by a Leu diet to promote mitochondrial NAD+ production and oxidative metabolism and recruit NAD+-dependent protein deacetylase SIRTUIN-1 (SIRT1) to participate in the regulation of LARS B cells. Depletion of LARS B cell subsets by LARS gene ablation or Leu depletion can inhibit immune escape in CRC.269

BCAA uptake is dependent on the type I amino acid transporter LAT, and mutations in SLC7A5 and SLC3A2, members of the LAT family, impair BCAA uptake by T cells and inhibit the proliferation and differentiation of Th1, Th17, and CTL cells.41 Slc3a2-dependent BCAA metabolism also has a key role in the physiological activities of Foxp3+ Treg cells, and either BCAA deprivation or SLC3A2 mutation can induce impaired activation of the mTORC1 pathway in Treg cells and inhibit the immunosuppressive function of Treg cells.270 Interestingly, a study on the correlation between amino acid metabolism and the immune microenvironment in LUAD (Lung adenocarcinoma) patients found that SLC7A5 expression‎ was downregulated in various T cells, especially in effector T cells. However, high expression‎ of SLC7A5 in tumor cells predicts reduced expression‎ of immune-related genes, reduced immune cell infiltration, and poor efficacy of immunotherapy.271 Another bioinformatics analysis for breast cancer reached a similar conclusion.272 In addition, BCAT isoenzymes may serve as markers of tumor TME status. In non-malignant T cells, such as activated CD4+ T cells and CTL cells, BCAT c accounts for 50% of the total BCAT expression‎ level, whereas this proportion is upregulated to 60% in T-cell lymphomas. Consistent with this phenomenon, the expression‎ level of BCAT m is decreased in tumor tissues.273 In malignant gliomas, BCAT c gene expression‎ has been reported to be positively correlated with M2-type macrophages and Treg markers,274 and GBM cells with high BCAT c expression‎ can excrete BCKAs through monocarboxylate transporter 1 (MCT1). Increased uptake of BCKAs by M1 macrophages inhibits the phagocytic capacity of M1 macrophages and may therefore produce immunosuppression.275 However, positive correlations between BCAT c gene expression‎ levels and infiltration levels of CTL, CD4+ T cells, macrophages, and dendritic cells have also been reported in colorectal and squamous cell carcinomas.276

Aspartate

As a nonessential amino acid, cells can supplement Asp via the de novo synthetic pathway. The aspartate synthesis pathway requires the mitochondrial ETC to provide electron acceptors.92 Thus, aspartate is a limiting factor for growth under hypoxic conditions. When ETC is limited, cells rely on the amino acid transporter SLC1A3 for Asp uptake from the environment. Inadequate mitochondrial Asp production is an important cause of T cell dysfunction, and lack of aspartate inhibits nicotinamide purine dinucleotide (NADH) production, causing ER expansion and TNF release.12 In addition, Asp can promote the activation of hypoxia-inducible factor HIF-1α and inflammasome in M1 macrophages and increase the production of Asn and other metabolites. At the same time, Asn can also promote IL-1β secretion by M1 macrophages.277 Inhibition of aspartate aminotransferase in macrophages inhibits nitric oxide and IL-6 production by M1-type macrophages.278 However, in T cells, Asn can enhance the antitumor effect of CD8+ T cells by binding to the SRC family protein tyrosinase LCK and assisting LCK to phosphorylate at Tyr394 and 505, thereby enhancing the activity of Lck starved T cell receptor signaling pathway.100 In helper T cell 1 (Th 1), the electron transport chain complex I, the apple-aspartate shuttle, and citrate are required for aspartate synthesis and helper T cell proliferation.279

Glutamine

Gln is the most abundant and versatile amino acid in the body. In general, the requirement for Gln by immune cells is similar to that of glucose.280 Gln can promote the proliferation of immune cells by activating ERK, JNK, and other proteins and increasing the transcription of cell proliferation genes.125 In addition, Gln can promote the expression‎ of lymphocyte surface markers such as CD25 and CD71 and increase the production of cytokines such as IFN-γ and TNF-α.281,282,283 In the TME, Gln metabolic reprogramming is essential for the survival of tumor cells and immune cells, and there is competition for Gln uptake. For example, studies have found that triple-negative breast cancer (TNBC) competes for Gln uptake in the environment, limiting Gln metabolism in tumor-infiltrating T cells and inhibiting anti-tumor responses. In contrast, in models with GLS mutations, glutamate metabolism in tumor cells is restricted, which increases Gln concentration in the microenvironment and T-cell uptake and antitumor activity.284 A similar phenomenon has been observed in Gln-dependent clear cell renal carcinoma (RCC), which competitively depletes environmental Gln, causing local Gln depletion and IL-23 release from tumor-infiltrating macrophages, which further activates Treg function to suppress tumor immunity.285 Based on the above phenomena, researchers have developed therapeutic ideas to target Gln metabolism in tumor cells, increase the concentration of Gln in TME, and promote Gln metabolism in tumor-infiltrating cells.

Administration of the Gln synthetase inhibitor CB-839 promotes the differentiation and cytokine secretion of CD4+ Th 1 cells as well as CD8+ T cells while inhibiting the differentiation and co-function of Th 17 cells.286 This suggests that T cell subsets are heterogeneous for Gln metabolism.287 The currently developed JHU-083 is a prodrug of 6-Diazo-5-oxo-L-norLeu (L-DON) generation glutaminase inhibitor that selectively activates L-DON in the TME.288 Existing studies have demonstrated that L-DON and JHU-083 can extensively inhibit Gln metabolizing enzymes and activate AMPK and c-Myc to inhibit glycolysis, thereby stopping tumor metabolic activity, alleviating hypoxia, and increasing the concentration of Gln and glucose in TME.289 At the same time, the promotion of CD8+ T cell activation and recruitment and significant inhibition of MDSCs generation and recruitment were observed in models treated with L-DON and JHU-083.290

V-9302, an inhibitor of Gln transporter SLC1A5, increases intracellular ROS and autophagosome production. A preclinical study showed that V-9302 could selectively block Gln uptake by TNBC cells, promote the activation of CD4+ T cells and CD8+ T cells, and reduce the level of Treg in a TNBC mouse model. Interestingly, CD8+ T cells compensatory upregulate the Gln transporter ATB+/SLC6A14 to maintain their Gln uptake requirement after treatment with V-9302, but this phenomenon was not observed in tumor cells.284 In addition, PD-L1 upregulation was observed in tumor cells after V-9302 treatment, and the combination of V-9302 and anti-PD-1 antibody showed greater anti-tumor efficacy than either drug alone.291,292

Arginine

Accumulating evidence has shown that arginine has an important role in regulating the function of immune cells. Human Burkitt B lymphocytes require an adequate arginine concentration for proliferation and maturation.293 Supplementation of the diet of high-risk surgical patients with an immune-enhancing diet (IED) containing arginine reduces the incidence of infection and increases macrophage phagocytosis, IL-2 expression‎, and CD4+ T cell numbers.294,295 However, some clinical trials have shown no benefit,296,297 so the value of arginine supplementation needs to be further tested. Although the effect of arginine supplementation remains to be tested, many studies have demonstrated that the downregulation of TCR receptor complex subunit CD3ζ in T cells cultured under arginine-restricted conditions leads to the restriction of T cell proliferation.298,299,300 However, the addition of citrulline, a precursor for arginine synthesis, can promote the expression‎ of this molecule by prolonging the half-life of CD3ζ.301 In addition, arginase 1 (Arg1) administration to activated T cells leading to arginine starvation can block T cell glycolysis.302 Myeloid cells can activate their own Arg 1 expression‎ in response to tumor-derived GM-CSF stimulation through activation of STAT3, p38, and cAMP signaling pathways, and Arg 1-expressing myeloid cells depleting environmental arginine inhibits T cell function.186 However, T cells have a mechanism to combat arginine deficiency: when confronted with arginine deficiency caused by Arg1-expressing myeloid cells, T cells increase arginine biosynthesis by up-regulating ASS1 expression‎.303

Arginase 2 (Arg 2) is a regulator of activated T cells, and Arg 2-deficient or Arg2−/− CD8+ T cells exhibit enhanced cytotoxicity and synergistic effect with anti-PD-1 antibody in inhibiting tumor growth.304 In melanoma, Tregs expressing Arg 2 were detected, and Arg 2 inhibited mTOR activity and enhanced the immunosuppressive activity of Tregs.305 At the therapeutic level, therapeutic vaccines targeting Arg 1 have been shown to activate antitumor immunity in a variety of syngeneic mouse tumor models such as lung cancer, melanoma, and colon cancer, and the combination of Arg 1 vaccine with anti-PD-1 antibody can increase T cell infiltration, inhibit myeloid cell function, and increase the ratio of tumor-infiltrating M1/M2 macrophages.306 A similar conclusion was reached in the study of arginase inhibitor CB-1158. CB-1158 could block myeloid cell-mediated inhibition of T cell proliferation, increase the number of tumor-infiltrating CD8+ T cells and NK cells, and increase the expression‎ of inflammatory factors and interferon-α, thereby changing the immune microenvironment to promote inflammation and reduce tumor immune escape, inhibiting tumor cell proliferation.190

On the other hand, arginine methylases (PRMTS) are widely expressed enzymes that catalyze the arginine methylation of proteins. Among them, type I PRMTs (PRMT1, PRMT2, PRMT3, PRMT4, PRMT6, and PRMT8) catalyze asymmetric dimethylated arginine to regulate DNA damage and transcriptional regulation, which is closely related to the occurrence and development of tumors. Applying type I PRMT inhibitor GSK3368715 can inhibit PRMTS-mediated epigenetic modification of IFN genes, increase the response of IFN genes to immune signals, and reduce the expression‎ of VEGF in immunosuppressive cells. In anti PD-1 resistant T cell rejection models, the application of type I PRMT inhibitors PT1001B or GSK3368715 can increase the number of tumor-infiltrating T cells and increase the efficacy of anti-PD-1 therapy.307,308

Methionine

Met metabolism is involved in a variety of cellular functions, including REDOX, methylation, and immune regulation. A second group of innate lymphoid cells (ILC2s) has a key role in type II immune response. Met metabolism is critical for regulating the function of ILC2s. Blockade of Met metabolism or loss of STAT3 significantly inhibits ILC2s function.309 Recently, Met restricted diet (MRD) has been reported to have an important role in anti-tumor immune regulation. MRD inhibited SAM-induced m6A methylation and translation of immune checkpoints such as PD-L1 and V-domain Ig suppressor of T cell activation (VISTA) in various mouse tumor models such as colorectal cancer and sarcoma. It also increased the number and toxicity of tumor-infiltrating T cells and enhanced antitumor immune responses.243 Moreover, inhibition of m6A-specific binding protein YTHDF1 can enhance tumor immunity like MRD.243 In EBV (Epstein-Barr virus)-infected tumors such as Burkitt’s lymphoma, Met metabolism helps shape B-cell immortalization required to regulate EBV-latent genes. The passage of MRD impairs Epstein-Barr virus-driven B-cell immortalization and exposes EBV antigens on the surface of Burkitt’s lymphoma.310

Tregs are characterized by high Met uptake and SAM use. Met metabolism is also essential for Treg survival after IL-2 deprivation, and solute carrier protein SLC43A2 plays a key role in Met uptake and maintenance of Treg growth activity.311 High expression‎ of SLC43A2 and high activity of Met adenosine transferase 2A (MAT2A) in tumor cells imply vigorous Met metabolism and competitive inhibition of Met metabolism, STAT5 expression‎ levels, and antitumor immune function in CD8+ T cells.245,312 Meanwhile, TAMs with high MAT2A expression‎ also showed strong Met metabolic activity, increased histone H3K4 methylation level and receptor-interacting serine/threonine protein kinase 1 (RIPK1) gene expression‎.313 Several therapeutic approaches targeting Met metabolism, including Met restriction, MAT2A inhibitors IDE397 and AG-270, are in clinical trials, and their therapeutic effects need to be verified.

In summary, how to specifically inhibit the amino acid metabolism of tumor cells and immunosuppressive cells in the microenvironment, and enhance the amino acid metabolism of anti-tumor immune cells such as CD8+ T cells, is an urgent problem to be solved. One idea is to enhance the activity of amino acid metabolism of CAR-T cells by adding cytokines that promote the expression‎ of transporters related to amino acid metabolism, such as SLC1A5, SLC3A2 and SLC7A5, or directly importing transcripts encoding these AATs into T cells. Furthermore, developing small molecule inhibitors targeting BCAA transporters in tumor cells and immunosuppressive cells allows CD8+ T cells to obtain amino acid metabolic advantages in the immune microenvironment and enhance the anti-tumor effect.

Targeted therapies and clinical research of AA metabolism (tentative)

In the above modules, we introduced the mechanisms of amino acids, related metabolic enzymes, and metabolites related to the occurrence and development of diseases. In addition, investigators are exploring therapeutic strategies to address this metabolic feature of the disease. Therefore, this section focused on the progress of clinical trials for treating amino acid metabolism in diseases.

AXA1125 and AXA1957 are oral endogenous modulator (EMM) compositions. AXA1125 contains five amino acids (Leu, iLe, valine, arginine, and Gln) in specific ratios and the amino acid precursor N-acetylcysteine (NAC), while AXA1957 is composed of five amino acids, Leu, iLe, arginine, Gln, and serine, as well as carnitine and NAC. A multicenter, single-blind, placebo-controlled, randomized clinical study (NCT04073368) assessed the effect of AXA1125 and AXA1957 on nonalcoholic fatty liver disease (NAFLD). Patients were treated with 16 weeks and magnetic resonance imaging (MRI)-proton density fat fraction [MRI-PDFF] and homeostasis model assessment of insulin resistance [HOMA-IR]) and homeostasis model assessment of insulin resistance (HOMA-IR) fibro-inflammation markers (alanine aminotransferase [ALT], corrected T1 [cT1], keratin-18 [K-18] M65, and N-terminal type III collagen pro-peptide [Pro-C3]) was applied. The results showed that the biological activity of AXA1125 was greater in patients with T2D, compared with placebo. The MRI-PDFF (−31.2% vs.−8.3%), ALT (−34.6% vs. −13.9%) and cT1 (−105.1% vs. −42.7 ms) of AXA1125 decreased more significantly. By week 16, a larger proportion of AXA1125-treated subjects (35–40%) than those in the placebo group (8–25%) reached clinically relevant thresholds for MRI-PDFF reductions of ≥30%, ALT reductions of ≥17 IU/L, and cT1 reductions of ≥80 ms.

Moreover, a phenotypic study on human primary macrophages and stellate cells suggested that AXA1125 can inhibit lipopolysaccharide (LPS)-induced TNF-α expression‎ in M1 macrophages and increase the secretion of anti-inflammatory chemokine C-C motif ligands by M2 macrophages, as well as reduced Pro-C3 and HSP47 expression‎ in HSC.314,315 Both compositions have demonstrated multi-target activity in NAFLD and are worthy of further continuing clinical trials.316

Another Phase 2 study eval‎uating AXA1125 for the treatment of fatigue after COVID-19 infection has been completed, and a clinical study eval‎uating the safety, efficacy, and tolerability of AXA1125 in the treatment of nonalcoholic steatohepatitis (NASH) is ongoing.

BCAT

The use of BCAT1 Inhibitor 2 in the NAFLD model can inhibit the activation of JNK and AKT signaling pathways and BCL2/Bax/Caspase axis induced by oleic acid, alleviate lipid accumulation, and inhibit mitochondrial ROS formation and apoptosis.317 However, BCAT Inhibitor is currently in preclinical studies, and their clinical value has yet to be verified (Table 1).

Branched chain keto acid dehydrogenase kinase (BCKDK)

Sodium phenylbutyrate targets BCKDK and is an accelerator of BCAA catabolism. In clinical trials on insulin resistance and type 2 diabetes, phenylbutyrate could significantly improve peripheral insulin sensitivity (ΔRd:13.2 ± 1.8 vs. 9.6 ± 1.8 µmol/kg/min, p = 0.02). Plasma BCAA levels and glucose levels were also decreased (Table 1).318

LAT1

The amino acid transporter LAT1 (SLC3A2/SLC7A5) is a kind of cancer cell-specific transporter expressed in various sources of cancer, and the high expression‎ level of LAT1 is closely related to the poor prognosis of patients. α-methyl aromatic amino acids are LAT1 specific, and 18F-labeled 3-fluoro-l-α-methyl-tyrosine (FAMT) has been used as LAT1 specific probe for cancer detection. JPH-203, a LAT1-specific inhibitor designed based on LAT1 ligands, has a strong affinity and does not show obvious toxicity in preclinical studies. In phase I clinical trials, JPH-203 showed excellent inhibition of solid tumors and was well tolerated.319 Phase II clinical trials are currently underway. In addition to JPH-203, other drugs currently in preclinical and clinical trials targeting LAT1 include IPA-131, QBS-10072S, TLX101-CDx, 124I-ACD-101, 211At-TLX-102, OKY-034, [18F] NKO-028 (Table 1).320,321

ASNase

Asn is a mature target for amino acid depletion therapy in tumors. Most compounds that target tumor metabolism (methotrexate, 5-fluorouracil) fail to distinguish between tumor tissue and rapidly differentiating epithelial tissue (skin, bone marrow),4,322 whereas therapies targeting the specific amino acid dependence of tumor cells are cell-selective, such as leukemic blasts that are selectively dependent on Asn, the use of bacterial-derived ASNase in pediatric ALL has significantly improved the cure rate.102 Pegaspargase and Calaspargase pegol are two ASNase-targeted drugs that have shown good results in treating hematological tumors. In a controlled study, patients (1–21 years of age) with newly diagnosed ALL or lymphoblastic lymphoma were given pegaspargase (2500 IU/M2, once induction, 15 doses every 2 weeks starting at week 7) or calaspargase pegol (2500 IU/M2, once induction, 10 doses every 3 weeks starting at week 7). Both drugs showed significant antitumor activity, with serum asparaginase activity (SAA) ≥ 0.1 UI/ml (considered therapeutic) in ≥95% of patients in both groups after 18 days of treatment and 25 days after treatment. More patients receiving calaspargase pegol had SAA ≥ 0.1 UI/ml (88% vs. 17%; p < 0.001). Moreover, in 230 patients, 99% of those receiving pegaspargase and 95% of those receiving calaspargase and pegol achieved complete remission. In terms of prognosis, the 5-year event-free survival (EFS) was 84.9% (SE ± 3.4%) for pegaspargase and 88.1% (SE ± 3.0%) for calaspargase pegol. Treatment with both drugs achieved similar nadir SAA and survival outcomes. Therefore, it is considered that the dosing strategy can be further optimized (Table 1).323

In addition to the above two drugs, asparaginase-targeting drugs include OP-01, JZP-458, ERY-001, and PF-690. JZP-458 was well tolerated in phase I clinical trials.324 More recently, the drug has been approved for phase II/III clinical experiments showing good effectiveness and safety (NCT04145531) (Tables 1, 2).325

Argininase

The presence of arginine-succinate synthetase 1 (ASS1) deficienct tumors is arginine-dependent, thus enabling arginine-deprivation therapy. Pegylated arginase has potential arginine degradation and antitumor activity. After intravenous administration of pegylated arginase, arginine can be metabolized to ornithine and urea, reducing plasma arginine levels. Pegylated arginine arginase (PEG-BCT-100) showed promising tumor suppressive activity, survival advantage, and safety against advanced HCC in phase I clinical trials of combination chemotherapy (oxaliplatin and capecitabine).326 A phase II clinical trial is currently underway (NCT03455140). However, there is a bottleneck in this therapy. Externally introduced arginase analogs can inhibit T cells’ antitumor activity by reducing the arginine level in the tumor microenvironment, just as the tumor or immunosuppressive cells expressing arginase 1 can. An alternative therapeutic approach that has been developed on the basis of this problem is the use of arginase-1 peptide vaccines that activate T cells to target and recognize cells expressing arginase 1. Recent clinical trials showed good safety of arginase 1 peptide vaccine in patients with refractory solid tumors (NCT03689192).327 yet, its effectiveness remains to be further tested (Table 1).

Arginine deiminase (ADI)

ADI is an enzyme that catalyzes the interconversion of arginine and citrulline. As an arginine degradation tool, its analogs were investigated in treating tumors with arginine-succinate synthetase (ASS1) mutations and/or arginine-succinate lyase (ASL). Pegylated arginine deiminase (ADI-PEG-20), which duplicates arginine and increases tumor stress and cytotoxicity, increased the number of tumor-infiltrating T cells in phase I studies and was safe in combination with anti-PD-1 antibody, but with an increased risk of neutropenia.328 ADI-PEG-20, in combination with pemetrexed and cisplatin (ADIPEMCIS), was well tolerated in another phase I study of recurrent high-grade glioma (HGG) (NCT02029690).329 The role of ADI-PEG-20 in HGG warrants further investigation. In hepatocellular carcinoma (HCC) studies, ADI-PEG-20 has been shown in early clinical trials to make HCC animal models and patients more sensitive to FOLFOX chemotherapy through arginine depletion. However, a recent large global, multicenter phase II study of HCC showed that ADI-PRG-20 combined with 5-fluorouracil, leucovorin, and oxaliplatin (mFOLFOX6) was associated with an ORR of 9.3% versus 8.15% with FOLFOX4. There was a significant difference in PFS (3.8 months vs. 2.93 months), although the improvement in OS (14.4 months vs. 6.4 months) was exciting. Still, authors suggested that it is more likely to be due to the short median follow-up time and the high proportion of Censored patients. Limited treatment efficacy and low response rates with this combination led to the early termination of the study. Despite the early termination of the trial, it is interesting to note that 13 of 140 patients had a median duration of response of 10.2 months, indicating that these patients benefited from combination therapy and that exploring the mechanisms of this benefit should be the focus of future research.239 Another phase II/III study eval‎uating ADI-PEG-20 for cisplatin and pemetrexed in patients with malignant pleural mesothelioma is ongoing and has completed recruitment (NCT02709512) (Table 1).

Arginine methyltransferases (PRMTs)

Type I PRMTs catalyze asymmetric dimethylation of arginine, which is associated with cancer. The overexpression‎ of arginine methyltransferase 5 (PRMT5) in solid and hematological tumors leads to the elevation of the methylation level of arginine residues on functionally related proteins in tumor cells, which affects cell cycle regulation, mRNA splicing, cell differentiation, signal transduction, and other physiological processes. Current studies are exploring PRMT5 inhibitors as a treatment for PRMT5-dependent tumors. The PRMT5 inhibitor PF-06939999 inhibited the proliferation of non-small cell lung cancer (NSCLC) in cells and animal models and dose-dependent reduced symmetrical dimethylarginine (SDMA) levels.330 Another PRMT5 inhibitor, JNJ-64619178, has shown long-term PRMT5 inhibition and potent anti-tumor effect in lung, pancreatic, and hematological tumors. A phase I clinical trial is ongoing to eval‎uate JNJ-64619178 in advanced solid tumors (NCT03573310). GSK3368715 is a reversible type I PRMTs inhibitor that synergistically inhibits tumor growth when combined with PRMT5 inhibitors. Metabolite 2-methylthiophosphate is an endogenous inhibitor of PRMT5. Deletion of the key catalytic enzyme methylthioadenosine phosphorylase (MTAP) gene is associated with the sensitivity of GSK3368715,331 and a current phase II clinical study of GSK3368715 in breast cancer has been enrolled (NCT04676516) (Table 1).

Glutaminase (GLS)

GLS supports tumor Gln synthesis. In preclinical studies, telaglenastat (CB-839), a Gln synthetase inhibitor, promoted the function of CD4+ Th 1 cells and CD8+ T cells, and inhibited the function of Th 17 cells.286 It also induced the regression of PI3KCA-mutant tumors in xenograft models in combination with 5-fluorouracil (5-FU).145 Telaglenastat, a glutaminase inhibitor, was also eval‎uated in combination with everolimus (TelaE) in a phase I trial of advanced/metastatic renal cell carcinoma (mRCC), and TelaE therapy was well tolerated in patients previously treated with TKIs and checkpoint inhibitors (NCT03163667). The median PFS was improved compared with placebo (PboE) (3.8 months vs. 1.9 months).146 Currently, a phase II trial eval‎uating telaglenastat in cervical, prostate, and metastatic cancer is underway (NCT04824937; NCT05521997).

Another glutaminase inhibitor, JHU-083, extensively inhibits Gln-metabolizing enzymes and increases the concentrations of Gln and glucose in the TME by inhibiting glycolysis, relieving the hypoxic state.289 In addition, CD8+ T cell activation and recruitment were increased in the JHU-083 treatment model, and MDSCs generation and recruitment were significantly inhibited.290 A phase I/II trial is currently underway to eval‎uate the efficacy of JHU-083 in advanced solid tumors (NCT04471415) (Table 1).

SLC1A5

The amino acid transporter SLC1A5 (ASCT 2) is highly expressed in various tumor tissues and is associated with poor prognosis of cancer. MEDI7247 is a novel antibody-drug coupling compound (ADC) that couples an ASCT 2 human monoclonal antibody site to a dimer of peroxbenzodiazepine (PBD). In preclinical studies, the drug has shown strong anti-tumor activity and survival advantage in AML, DLBCL, cALL, and Burkitt lymphoma tumor models.332 Currently, phase I trials have been completed to eval‎uate the efficacy of MEDI7247 in treating ASCT2-positive hematological malignancies and advanced solid tumors (NCT03106428; NCT03811652). Another Gln transporter SLC1A5 inhibitor, V-9302, selectively blocked Gln uptake by TNBC cells, promoted the activation of CD4+ and CD8+ T cells, and reduced Treg levels in a TNBC mouse model (Table 1).284

MAT2A

Methylthioadenosine phosphorylase (MTAP)-deficient tumors account for ~15% of solid tumors, including ~15% of NSCLC, 28% of esophageal cancer, 26% of bladder cancer, and 10% of esophagogastric cancer. In MTAP null tumors, inhibition of Met adenosine transferase 2A (MAT2A) inhibits Met synthesis of SAM, thereby inhibiting tumor growth. MAT2A has been proposed as a therapeutic target in tumors with MTAP gene deletion.333 AG-270 is an oral selective MAT2A inhibitor that selectively inhibits the proliferation of MTAP null cells and effectively reduces the level of SAM in tumor cells in tissue and xenograft tumor models.334 A phase I study is ongoing to eval‎uate AG-270 in advanced solid tumors and lymphomas (NCT03435250). IDE-397 is another MAT2A inhibitor with low hepatotoxicity and high solubility that has shown potent modulation of SAM and symmetric dimethyarginine (SDMA) in preclinical studies. A phase I study to eval‎uate IDE-397 in solid tumors is currently underway (NCT04794699) (Table 1).

METAP

Met aminopeptidase (METAP) is a kind of cytoplasmic enzyme, metal catalytic protein hydrolysis N end Met residue in the newborn. This enzyme has a key role in angiogenesis and is essential for progressing diseases such as solid tumors and rheumatoid arthritis.335,336 First reported as the first reversible METAP inhibitor (METAPi) in 2003, LAF389 is a natural benzimide compound with dual METAP 1i and METAP 2i activities.337 Although all cell types responded to this inhibitor in vitro and showed promising therapeutic effects in vivo,337 phase I clinical trials for treating advanced solid tumors ultimately failed due to cardiovascular toxicity and wide variability in patient responses.338 A-357300, which was subsequently developed, has shown anticancer activity in mouse models of cancer, sarcoma, and nervous system tumors,339,340 and another candidate, METAPi A-800141, which was selected based on affinity selection based on mass spectrometry, has better selectivity and efficacy than A-357300.341,342 A-800141 has demonstrated anti-angiogenic and anti-tumor activity in multiple xenograft models, including neuroblastoma, colon cancer, prostate cancer, and B-cell lymphoma.343 Evexomostat (SDX-7320), which irreversibly binds METAP2 and regulates insulin, leptin, and adiponectin downstream, was one of the first drugs developed for cancer patients with metabolic complications. The efficacy of evexomostat in inhibiting the angiogenic proteins FGF (Fibroblast growth factors) and VEGF (Vascular endothelial growth factor) was validated in a phase I clinical trial in advanced solid tumors (NCT02743637). Enrollment is ongoing for phase II trials eval‎uating Evexomostat in metastatic breast cancer and in patients with diabetes (NCT05455619; NCT05570253) (Table 1).

Conclusion and future perspective

Amino acids metabolism affects multiple levels of cell metabolism and many cell processes, from protein synthesis to epigenetic regulation. These physiological processes are closely related to maintaining cell homeostasis and normal function. Thus, abnormal amino acid metabolism can contribute to disease development.344 Herein, we discussed physiological, and metabolic patterns of BCAAs, Asp, Gln, Arg, Met metabolism, and the role of various amino acids and their related enzymes and products in disease.

BCAA includes Leu, iLe, and valine, and all three amino acids participate in the citric acid cycle by producing acyl-CoA derivatives via branched-chain amino acid transferase (BCAT), branched-chain α-keto acid dehydrogenase (BCKDH), which in a subsequent series of reactions produce acetyl-CoA.45 BCAA has an important role in tumor and metabolic diseases as an essential amino acid. For example, in PDAC and NSCLC, which share the same genetic mutation background (KRAS and p53 mutations), BCAA requirements are high but significantly different. Yet, the exact difference in BCAA requirement between tumors is still not fully understood. Existing evidence suggests that CBP and SIRT4 can promote the ubiquitin-proteasome degradation of BCAT2 by acetylation of BCAT2 at the K44 site in PDAC.53 This reveals a novel BCAA metabolism inhibition mode in the context of KRAS inhibition of BCAT2 ubiquitination degradation, explaining the preference for PDAC amino acid metabolism. However, on the other hand, studies on the interaction of different cells in the microenvironment have found that CAFs cells have a high metabolism of BCAA and provide BCKA to PDAC cells to assist tumor cells in BCAA metabolism.57 In addition, the phagocytic activity of macrophages exposed to BCKA is inhibited.275 This provides an idea for treating PDAC by targeting the BCAA metabolism of CAF cells in the tumor environment and also proves that the tumor and various cells in the environment communicate with each other as a whole. Subsets with different preferences for BCAA metabolism have also been found in breast cancer, and further studies are needed to determine whether this is due to differences in tumor cells or the involvement of other cells in the microenvironment.55,59 BCAA metabolism is equally important for the function of proinflammatory CD4+ and CD8+ T cells and immunosuppressive regulatory Treg cells,41,265,266,267,268,269,270,271,272 which plays key role in metabolic diseases, liver and kidney diseases.10,11,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,345,346 Currently, drugs targeting BCAA uptake-dependent amino acid transporter LAT1 and metabolic enzymes BCAT and BCKDK are in trials.317,318,319,320,321,347

Aspartate is a nonessential amino acid, but it is also an intrinsic limiting factor in the growth of some tumors.92,93 The transamination product of Asp, asparagine (Asn), is more permeable than Asp, but when cellular asparaginase activity is inhibited, Asn cannot be converted to Asp.93 Bladder cancer cells lack asparaginase, leading to dysfunction in converting Asn to Asp. Under hypoxia, the mitochondrial ETC is inhibited, and energy synthesis and Asp synthesis are limited, which leads to the dependence of tumor cells on the environmental uptake of Asp. The amino acid transporter SLC1A3 has an important role in maintaining Asp concentrations inside tumor cells and antagonizing the therapeutic effects of ASNase.94 SLC1A3 inhibitors can promote cell cycle arrest and apoptosis and counteract SLC1A3-induced ASNase resistance.94 Moreover, SLC1A3 is mainly expressed in brain tissue, and its high expressions in some solid tumors, such as clear cell renal cell carcinoma, papillary renal cell carcinoma, hepatocellular carcinoma and gastric adenocarcinoma, may make SLC1A3 inhibitors a solution to ASNase resistance. Another glutaminase inhibitor, JHU-083, extensively inhibits Gln-metabolizing enzymes and increases the concentrations of Gln and glucose in the TME by inhibiting glycolysis, relieving the hypoxic state.289 One limitation of ASNase therapy, which promotes tumor cell death by systematically lowering the asparagine concentration, is that it impairs ASN requirements in normal immune cells.99,100 This may explain the immune-related side effects of ASNase drugs and limit the application of ASNase in cancer treatment. Therefore, limiting Asn metabolism in tumor cells and immunosuppressive cells in the TME and protecting and promoting Asn metabolism in anti-tumor immune cells should be a problem to be solved. In treating solid tumors, developing more tumor-targeting ASNase is one aspect, and the SLC1A3 inhibitor mentioned earlier also provides an idea to solve this problem.

Gln is extensively consumed by intestinal, renal, immune, and tumor cells.122,123,124 The key Gln-regulated enzyme GLS and the amino acid transporter SLC1A5 are regulated by the oncogene c-Myc.128 Meanwhile, SLC1A5 expression‎ was also regulated by STAT3 in AML cells. Gln depletion therapy can inhibit Gln metabolism in tumor cells, but in colon cancer, it has been observed that Gln depletion promotes the expression‎ of the aspartate/glutamate transporter SLC1A3 in tumor cells, increasing the intracellular glutamate concentration and promotes Gln synthesis.131 In addition, the cystine/glutamate antiporter SLC7A11/xCT also has an important role in cellular Gln metabolism. Because SLC7A11 exchanges intracellular glutamate with extracellular cystine, the intracellular glutamate concentration decreases, which leads to more Gln uptake and increased glutaminase activity and making these cells dependent on external Gln. According to the TCGA database, The expression‎ levels of SLC7A11 mRNA in Cervical cancer (CESC), Cholangiocarcinoma (CHOL), Colonic adenocarcinoma (COAD), Esophagus cancer (ESCA), Head and neck squamous cell carcinoma (HNSC), chromophobe kidney cell carcinoma (KICH), Clear cell carcinoma of kidney (KIRC), Papillary cell carcinoma of the kidney (KIRP), Liver cell carcinoma (LIHC), Lung adenocarcinoma (LUAD), Squamous cell carcinoma of the lung (LUSC), Adenocarcinoma of the pancreas (PAAD), Rectum adenocarcinoma (READ), Sarcoma (SARC), Cutaneous melanoma (SKCM), Stomach adenocarcinoma (STAD), and Endometrial carcinoma of the flesh (UCEC) were significantly higher than those in adjacent normal tissues. These features suggest that SLC7A11 may serve as a promising target for cancer metabolism. Glutaminase (GLS), as a key enzyme in tubular aminamide metabolism, has also received extensive attention. CB-839, an inhibitor targeting GLS, has shown good tumor inhibition activity, tolerance, and safety in preclinical studies and phase I clinical trials in solid tumors.145,146,286

Cells lacking arginine-succinate synthetase 1 (ASS1) are arginine-dependent. ASS1 expression‎ is downregulated in CHOL, GBM, KICH, KIRC, KIRP, and LIHC tumor categories, suggesting the feasibility of arginine depletion therapy. Analogs targeting arginase and arginine deiminase, the enzymes involved in arginine depletion, have been developed. Using the arginine deiminase analog ADI-PEG-20 in hepatocellular carcinoma and glioblastoma has demonstrated antitumor activity in vitro and in xenograft models and demonstrated safety and efficacy in a phase I clinical trial.328 Although setbacks occurred in the phase II study, the combination of ADI-PEG-20 and mFOLFOX6 chemotherapy regimen did not show a significant therapeutic advantage for hepatocellular carcinoma,239 but there are a small number of subjects who benefit from this regimen. Studying the mechanism of benefit in this group of subjects to seek the precision of treatment should be the next problem to be solved. Pegylated arginase PEG-BCT-100 combined with oxaliplatin and capecitabine has shown satisfactory therapeutic efficacy and safety in phase I clinical trials in solid tumors.326 In addition, the role of arginine methyltransferase (PRMT) in the regulation of tumorigenesis and development has also received extensive attention, and a variety of PRMT inhibitors have shown good anti-tumor activity in vitro and animal models, and a variety of drugs targeting type I PRMT and PRMT5 have been tested.330,331

The status of Met as an essential amino acid and its role in the transmethylation process predestines the cells’ dependence on Met metabolism. Methythioadenosine phosphorylase (MTAP) gene deletion occurs in ~15% of solid tumors, including 15% of NSCLC, 28% of esophageal cancer, 26% of bladder cancer, and 10% of esophagogastric cancer. For tumor cells deficient in methythioadenosine phosphorylase (MTAP), Met depletion and inhibition of the key enzyme MAT2A in the Met metabolism pathway are possible therapeutic strategies. MAT2A inhibitors AG-270 and IDE-397 have demonstrated significant antitumor activity both in vitro and in animal models, and phase I clinical trials are currently underway.240,333,334

Currently, amino acid metabolism-targeted therapy still faces many challenges. Adipocytes and bone marrow stromal cells in the TME can promote the resistance of tumor cells to ASNase treatment by supplying Gln and cysteine to leukemia cells,348,349 and cancer-associated fibroblasts can secrete Asp to promote solid tumor growth.57,350 Many lines of evidence have found that tumor resistance is caused by cells and the external environment in which the cells are located. The efficacy of a drug also depends on its ability to reach the tumor site. When the drug fails to reach the tumor site, it fails to induce tumor cell death successfully. In addition, immune and allergic reactions to non-human enzymes can compromise therapy and harm patients.344,351 Therefore, a comprehensive understanding of the metabolism-dependent characteristics of various tumor types and their microenvironment is needed. Decoding the metabolic requirements of amino acids in different tissues and understanding how to target the metabolism and metabolic pathways of these amino acids is indispensable for improving the level of cancer treatment.

결론 및 미래 전망

아미노산 대사는

단백질 합성부터 에피제네틱 조절에 이르는

세포 대사 및 다양한 세포 과정의 다중 수준에 영향을 미칩니다.

이러한 생리적 과정은 세

포 항상성 유지와 정상 기능과 밀접하게 연관되어 있습니다.

따라서

아미노산 대사의 이상은 질병 발병에 기여할 수 있습니다.344

본 연구에서는

BCAA, 아스파르트산(Asp), 글루타민(Gln), 아르기닌(Arg), 메티오닌(Met)의

대사 패턴 및 다양한 아미노산과 관련 효소 및 대사 산물이 질병에 미치는 역할을 논의했습니다.

BCAA는

Leu, iLe, valine으로 구성되며,

이 세 아미노산은 분지 사슬 아미노산 전이효소(BCAT)와 분지 사슬 α-케토산 탈수소효소(BCKDH)를 통해

아실-CoA 유도체를 생성함으로써 시트르산 회로에 참여합니다.

이 과정은 후속 반응을 통해

아세틸-CoA를 생성합니다.45

BCAA는

필수 아미노산으로서 종양 및 대사 질환에서 중요한 역할을 합니다.

예를 들어,

동일한 유전적 변이 배경(KRAS 및 p53 변이)을 공유하는 PDAC와 NSCLC에서 BCAA 요구량은 높지만 유의미하게 다릅니다. 그러나 종양 간 BCAA 요구량의 정확한 차이는 아직 완전히 이해되지 않았습니다. 기존 연구 결과는 PDAC에서 CBP와 SIRT4가 BCAT2의 K44 부위 아세틸화를 통해 BCAT2의 유비퀴틴-프로테아좀 분해를 촉진한다는 것을 보여줍니다.53 이는 KRAS에 의한 BCAT2 유비퀴틴화 분해 억제 맥락에서 새로운 BCAA 대사 억제 메커니즘을 밝히며, PDAC의 아미노산 대사 선호성을 설명합니다. 그러나另一方面, 미세환경 내 다양한 세포 간의 상호작용 연구에서는 CAFs 세포가 BCAA 대사율이 높으며 PDAC 세포에 BCKA를 공급해 종양 세포의 BCAA 대사를 돕는 것으로 나타났습니다.57 또한 BCKA에 노출된 대식세포의 식작용 활성이 억제됩니다. 275 이는 종양 환경에서 CAF 세포의 BCAA 대사 표적을 통해 PDAC를 치료하는 방법을 제시하며, 종양과 환경 내 다양한 세포가 전체적으로 상호작용한다는 것을 증명합니다. 유방암에서도 BCAA 대사 선호도가 다른 하위 집합이 발견되었으며, 이는 종양 세포의 차이 또는 미세환경 내 다른 세포의 관여 여부를 확인하기 위해 추가 연구가 필요합니다. 55,59 BCAA 대사는 염증성 CD4+ 및 CD8+ T 세포와 면역 억제성 조절 Treg 세포의 기능에 동일하게 중요하며,41,265,266,267,268,269,270,271,272 대사 질환, 간 및 신장 질환에서 핵심 역할을 합니다. 10,11,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,345,346 Currently, drugs targeting BCAA uptake-dependent amino acid transporter LAT1 and metabolic enzymes BCAT and BCKDK are in trials. 317,318,319,320,321,347

아스파르테이트는

필수 아미노산이 아니지만

일부 종양의 성장에 내재적 제한 요인으로 작용합니다.92,93

아스파르테이트의 트랜스아미노화 산물인 아스파라긴(Asn)은

아스파르테이트보다 세포 내 투과성이 높지만,

세포 내 아스파라긴아제 활성이 억제되면

Asn이 아스파르테이트로 전환되지 않습니다.93

방광암 세포는 아스파라긴아제를 결핍하여 Asn을 아스파르테이트로 전환하는 기능이 장애를 일으킵니다. 저산소 상태에서 미토콘드리아 전자전달계(ETC)가 억제되어 에너지 합성과 아스파르트산 합성이 제한되며, 이는 종양 세포가 환경으로부터 아스파르트산을 흡수하는 것에 의존하게 됩니다. 아미노산 운반체 SLC1A3는 종양 세포 내 아스파르트산 농도를 유지하는 데 중요한 역할을 하며, ASNase의 치료 효과를 방해합니다.94 SLC1A3 억제제는 세포 주기 정지와 아포토시를 촉진하고 SLC1A3에 의한 ASNase 저항성을 억제합니다. 94 또한 SLC1A3는 주로 뇌 조직에서 발현되며, 투명세포 신세포암, 유두상 신세포암, 간세포암, 위 선암 등 일부 고형 종양에서 높은 발현을 보여 SLC1A3 억제제가 ASNase 저항성에 대한 해결책이 될 수 있습니다. 또 다른 글루타민아제 억제제인 JHU-083은 글루코네오겐시스 억제를 통해 글루코네오겐시스 효소를 광범위하게 억제하고 TME 내 글루코네오겐시스 농도를 증가시켜 저산소 상태를 완화합니다. 289 ASNase 치료의 한 한계는 아스파라긴 농도를 체계적으로 낮추어 종양 세포 사멸을 촉진하지만, 정상 면역 세포의 ASN 요구량을 저해한다는 점입니다.99,100 이는 ASNase 약물의 면역 관련 부작용을 설명하고 ASNase의 암 치료 적용을 제한할 수 있습니다. 따라서 종양 세포와 TME 내 면역 억제 세포에서의 아스파라긴 대사 억제와 항종양 면역 세포에서의 아스파라긴 대사 보호 및 촉진은 해결해야 할 문제입니다. 고형 종양 치료에서 종양 표적형 ASNase 개발은 한 측면이며, 앞서 언급된 SLC1A3 억제제도 이 문제를 해결하는 아이디어를 제공합니다.

글루타민(Gln)은

장, 신장, 면역, 종양 세포에서 광범위하게 소비됩니다.122,123,124

글루타민 조절 효소 GLS와 아미노산 운반체 SLC1A5는

종양 유전자 c-Myc에 의해 조절됩니다.128

한편, AML 세포에서 SLC1A5 발현은 STAT3에 의해 조절되었습니다.

글루타민 고갈 치료는

종양 세포의 글루타민 대사를 억제하지만,

대장암에서는 글루타민 고갈이 종양 세포에서

아스파르트산/글루타메이트 운반체 SLC1A3의 발현을 촉진하여

세포 내 글루타메이트 농도를 증가시키고 글루타민 합성을 촉진한다는 것이 관찰되었습니다.131

또한 시스테인/글루타메이트 항운반체 SLC7A11/xCT도 세포 내 글루타민 대사에서 중요한 역할을 합니다. SLC7A11은 세포 내 글루타메이트와 세포 외 시스테인을 교환하여 세포 내 글루타메이트 농도를 감소시키며, 이는 글루타민 섭취 증가와 글루타미나제 활성 증가를 유발하여 이러한 세포가 외부 글루타민에 의존하게 만듭니다. TCGA 데이터베이스에 따르면, SLC7A11 mRNA 발현 수준은 자궁경부암 (CESC), 담관암 (CHOL), 대장 선암 (COAD), 식도암 (ESCA), 두경부 편평상피암(HNSC), 크로모포브 신세포암(KICH), 신세포암(KIRC), 신세포암(KIRP), 간세포암(LIHC), 폐 선암(LUAD), 폐 편평상피암(LUSC), 췌장 선암(PAAD), 직장 선암(READ), 육종 (SARC), 피부 흑색종 (SKCM), 위 선암 (STAD), 및 자궁 내막 암 (UCEC)은 인접한 정상 조직에 비해 유의미하게 높았습니다. 이러한 특징은 SLC7A11이 암 대사 분야의 유망한 표적 역할을 할 수 있음을 시사합니다. 글루타미나제 (GLS)는 관상 아미노산 대사에서 핵심 효소로, 광범위한 관심을 받고 있습니다. GLS를 표적으로 하는 억제제인 CB-839는 고형 종양에서 전임상 연구 및 제1상 임상 시험에서 우수한 종양 억제 활성, 내약성, 및 안전성을 보여주었습니다.145,146,286

아르기닌-수크신산 합성효소 1(ASS1)이 결핍된 세포는

아르기닌에 의존적입니다.

ASS1 발현은

CHOL, GBM, KICH, KIRC, KIRP, LIHC 종양 분류에서 하향 조절되어

아르기닌 고갈 치료의 가능성을 시사합니다.

아르기닌 고갈에 관여하는 효소인 아르기나제와 아르기닌 디이미나제를 표적하는 아날로그가 개발되었습니다.

아르기닌 디이미나제 아날로그 ADI-PEG-20을 간세포암과 뇌교모세포종에 적용한 결과, 체외 및 이종 이식 모델에서 항종양 활성을 보여주었으며, 제1상 임상 시험에서 안전성과 효능을 입증했습니다. 328 제2상 연구에서 장애물이 발생했지만, ADI-PEG-20과 mFOLFOX6 화학요법 요법의 조합은 간세포암에 대해 유의미한 치료적 우위를 보여주지 않았습니다.239 그러나 이 요법으로부터 혜택을 받은 소수의 환자가 있습니다. 이 환자 그룹에서 혜택의 메커니즘을 연구하여 치료의 정밀도를 추구하는 것이 다음 해결해야 할 문제입니다. Pegylated arginase PEG-BCT-100과 옥살리플라틴, 카페시타빈의 조합은 고형 종양에서 제1상 임상 시험에서 만족스러운 치료 효과와 안전성을 보여주었습니다. 326 또한, 아르기닌 메틸전달효소(PRMT)가 종양 발생 및 발달 조절에 미치는 역할도 광범위한 관심을 받고 있으며, 다양한 PRMT 억제제가 체외 및 동물 모델에서 우수한 항종양 활성을 보여주었으며, 유형 I PRMT 및 PRMT5를 표적으로 하는 다양한 약물이 테스트되었습니다.330,331

메티오닌(Met)이

필수 아미노산으로서의 지위와 트랜스메틸화 과정에서의 역할은

세포가 메티오닌 대사 과정에 의존하도록 결정합니다.

메티오티오아데노신 포스포릴레이스(MTAP) 유전자 결손은

고형암의 약 15%에서 발생하며,

이 중 비소세포폐암(NSCLC)의 15%,

식도암의 28%,

방광암의 26%,

식도위암의 10%에서 관찰됩니다.

메틸티오아데노신 포스포릴레이스(MTAP)가 결핍된 종양 세포에서 메틸 부족과 메틸 대사 경로의 핵심 효소 MAT2A의 억제는 가능한 치료 전략입니다. MAT2A 억제제 AG-270과 IDE-397은 체외 실험과 동물 모델에서 유의미한 항종양 활성을 보여주었으며, 현재 1상 임상 시험이 진행 중입니다.240,333,334

현재 아미노산 대사 표적 치료는

여전히 많은 도전 과제에 직면해 있습니다.

종양 미세환경(TME)

내 지방세포와 골수 간질 세포는

백혈병 세포에 글루타민(Gln)과 시스테인을 공급하여

ASNase 치료에 대한 종양 세포의 저항성을 촉진할 수 있습니다.348,349

또한 암 관련 섬유아세포는

아스파르트산(Asp)을 분비하여 고형 종양의 성장을 촉진할 수 있습니다.57,350

많은 연구 결과는

종양 저항성이 세포 자체와 세포가 위치한 외부 환경에 의해 유발된다는 것을 보여주었습니다.

약물의 효능은

약물이 종양 부위에 도달하는 능력에 달려 있습니다.

약물이 종양 부위에 도달하지 못하면

종양 세포 사멸을 성공적으로 유도하지 못합니다.

또한

비인간 효소에 대한 면역 및 알레르기 반응은

치료 효과를 저해하고 환자에게 해를 입힐 수 있습니다.344,351

따라서

다양한 종양 유형과 그 미세환경의 대사 의존적 특성을 포괄적으로 이해하는 것이 필요합니다.

다양한 조직에서 아미노산의 대사 요구사항을 해독하고

이러한 아미노산의 대사 및 대사 경로를 표적화하는 방법을 이해하는 것은

암 치료 수준을 향상시키는 데 필수적입니다.

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