We're Not "DON" Yet: Optimal Dosing and Prodrug Delivery of 6-Diazo-5-oxo-L-norleucine

Glutaminase inhibition as potential cancer therapeutics: current status and future applications

Alterations in normal metabolic processes are defining features of cancer. Glutamine, an abundant amino acid in the human blood, plays a critical role in regulating several biosynthetic and bioenergetic pathways that support tumour growth. Glutaminolysis is a metabolic pathway that converts glutamine into various metabolites involved in the tricarboxylic acid (TCA) cycle and generates antioxidants that are vital for tumour cell survival. As glutaminase catalyses the initial step of this metabolic pathway, it is of great significance in cancer metabolism and tumour progression. Inhibition of glutaminase and targeting of glutaminolysis have emerged as promising strategies for cancer therapy. This review explores the role of glutaminases in cancer metabolism and discusses various glutaminase inhibitors developed as potential therapies for tumour regression.

Targeting metabolism to enhance immunotherapy within tumor microenvironment

Cancer metabolic reprogramming has been considered an emerging hallmark in tumorigenesis and the antitumor immune response. Like cancer cells, immune cells within the tumor microenvironment or premetastatic niche also undergo extensive metabolic reprogramming, which profoundly impacts anti-tumor immune responses. Numerous evidence has illuminated that immunosuppressive TME and the metabolites released by tumor cells, including lactic acid, Prostaglandin E2 (PGE2), fatty acids (FAs), cholesterol, D-2-Hydroxyglutaric acid (2-HG), adenosine (ADO), and kynurenine (KYN) can contribute to CD8+ T cell dysfunction. Dynamic alterations of these metabolites between tumor cells and immune cells can similarly initiate metabolic competition in the TME, leading to nutrient deprivation and subsequent microenvironmental acidosis, which impedes immune response. This review summarizes the new landscape beyond the classical metabolic pathways in tumor cells, highlighting the pivotal role of metabolic disturbance in the immunosuppressive microenvironment, especially how nutrient deprivation in TME leads to metabolic reprogramming of CD8+ T cells. Likewise, it emphasizes the current therapeutic targets or strategies related to tumor metabolism and immune response, providing therapeutic benefits for tumor immunotherapy and drug development in the future. Cancer metabolic reprogramming has been considered an emerging hallmark in tumorigenesis and the antitumor immune response. Dynamic alterations of metabolites between tumor cells and immune cells initiate metabolic competition in the TME, leading to nutrient deprivation and subsequent microenvironmental acidosis, which impedes immune response.

Glutamine availability regulates cDC subsets in tissue

Proliferating tumor cells take up glutamine for anabolic processes engendering glutamine deficiency in the tumor microenvironment. How this might impact immune cells is not well understood. Using multiple mouse models of soft tissue sarcomas, glutamine antagonists, as well as genetic and pharmacological inhibition of glutamine utilization, we found that the number and frequency of conventional dendritic cells (cDC) is dependent on microenvironmental glutamine levels. cDCs comprise two distinct subsets - cDC1 and cDC2, with the former subset playing a critical role in antigen cross-presentation and tumor immunity. While both subsets show dependence on Glutamine, cDC1s are particularly sensitive. Notably, glutamine antagonism did not reduce the frequency of DC precursors but decreased proliferation and survival of cDC1s. Further studies suggest a role of the nutrient sensing mTOR signaling pathway in this process. Taken together, these findings uncover glutamine dependence of cDC1s that is coopted by tumors to escape immune responses.

One Sentence Summary

Type 1 conventional dendritic cells require glutamine to maintain their number in non-lymphoid tissue.

Significance

Immune evasion is a key hallmark of cancer; however, the underlying pathways are diverse, tumor-specific and not fully elucidated. Many tumor cells avidly import glutamine to support their anabolic needs, creating a glutamine-deficient tumor microenvironment (TME). Herein, using mouse models of soft tissue sarcomas, we show that glutamine depletion in TME leads to reduced type 1 conventional dendritic cells - a cell type that is critical for adaptive immune responses. This work is a paradigm for how tumor cell metabolism can regulate anti-tumor immune responses and will be foundational to future efforts targeting glutamine metabolism for cancer immunotherapy.

Glutamine and leukemia research: progress and clinical prospects

Leukemia is an abnormal proliferation of white blood cells that occurs in bone marrow and expands through the blood. It arises from dysregulated differentiation, uncontrolled growth, and inhibition of apoptosis. Glutamine (GLN) is a "conditionally essential" amino acid that promotes growth and proliferation of leukemic cells. Recently, details about the role of GLN and its metabolism in the diagnosis and treatment of acute myeloid, chronic lymphocytic, and acute lymphoblastic leukemia have emerged. The uptake of GLN by leukemia cells and the dynamic changes of glutamine-related indexes in leukemia patients may be able to assist in determining whether the condition of leukemia is in a state of progression, remission or relapse. Utilizing the possible differences in GLN metabolism in different subtypes of leukemia may help to differentiate between different subtypes of leukemia, thus providing a basis for accurate diagnosis. Targeting GLN metabolism in leukemia requires simultaneous blockade of multiple metabolic pathways without interfering with the normal cellular and immune functions of the body to achieve effective leukemia therapy. The present review summarizes recent advances, possible applications, and clinical perspectives of GLN metabolism in leukemia. In particular, it focuses on the prospects of GLN metabolism in the diagnosis and treatment of acute myeloid leukemia. The review provides new directions and hints at potential roles for future clinical treatments and studies.

A genome-wide CRISPR screen reveals that antagonism of glutamine metabolism sensitizes head and neck squamous cell carcinoma to ferroptotic cell death

Glutamine is a conditionally essential amino acid for the growth and survival of rapidly proliferating cancer cells. Many cancers are addicted to glutamine, and as a result, targeting glutamine metabolism has been explored clinically as a therapeutic approach. Glutamine-catalyzing enzymes are highly expressed in primary and metastatic head and neck squamous cell carcinoma (HNSCC). However, the nature of the glutamine-associated pathways in this aggressive cancer type has not been elucidated. Here, we explored the therapeutic potential of a broad glutamine antagonist, DRP-104 (sirpiglenastat), in HNSCC tumors and aimed at shedding light on glutamine-dependent pathways in this disease. We observed a potent antitumoral effect of sirpiglenastat in HPV- and HPV + HNSCC xenografts. We conducted a whole-genome CRISPR screen and metabolomics analyses to identify mechanisms of sensitivity and resistance to glutamine metabolism blockade. These approaches revealed that glutamine metabolism blockade results in the rapid buildup of polyunsaturated fatty acids (PUFAs) via autophagy nutrient-sensing pathways. Finally, our analysis demonstrated that GPX4 mediates the protection of HNSCC cells from accumulating toxic lipid peroxides; hence, glutamine blockade sensitizes HNSCC cells to ferroptosis cell death upon GPX4 inhibition. These findings demonstrate the therapeutic potential of sirpiglenastat in HNSCC and establish a novel link between glutamine metabolism and ferroptosis, which may be uniquely translated into targeted glutamine-ferroptosis combination therapies.

Glutamine Metabolism and Prostate Cancer

Glutamine (Gln) is a non-essential amino acid that is involved in the development and progression of several malignancies, including prostate cancer (PCa). While Gln is non-essential for non-malignant prostate epithelial cells, PCa cells become highly dependent on an exogenous source of Gln. The Gln metabolism in PCa is tightly controlled by well-described oncogenes such as MYC, AR, and mTOR. These oncogenes contribute to therapy resistance and progression to the aggressive castration-resistant PCa. Inhibition of Gln catabolism impedes PCa growth, survival, and tumor-initiating potential while sensitizing the cells to radiotherapy. Therefore, given its significant role in tumor growth, targeting Gln metabolism is a promising approach for developing new therapeutic strategies. Ongoing clinical trials evaluate the safety and efficacy of Gln catabolism inhibitors in combination with conventional and targeted therapies in patients with various solid tumors, including PCa. Further understanding of how PCa cells metabolically interact with their microenvironment will facilitate the clinical translation of Gln inhibitors and help improve therapeutic outcomes. This review focuses on the role of Gln in PCa progression and therapy resistance and provides insights into current clinical trials.

Targeting amino acid-metabolizing enzymes for cancer immunotherapy

Despite the immune system's role in the detection and eradication of abnormal cells, cancer cells often evade elimination by exploitation of various immune escape mechanisms. Among these mechanisms is the ability of cancer cells to upregulate amino acid-metabolizing enzymes, or to induce these enzymes in tumor-infiltrating immunosuppressive cells. Amino acids are fundamental cellular nutrients required for a variety of physiological processes, and their inadequacy can severely impact immune cell function. Amino acid-derived metabolites can additionally dampen the anti-tumor immune response by means of their immunosuppressive activities, whilst some can also promote tumor growth directly. Based on their evident role in tumor immune escape, the amino acid-metabolizing enzymes glutaminase 1 (GLS1), arginase 1 (ARG1), inducible nitric oxide synthase (iNOS), indoleamine 2,3-dioxygenase 1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and interleukin 4 induced 1 (IL4I1) each serve as a promising target for immunotherapeutic intervention. This review summarizes and discusses the involvement of these enzymes in cancer, their effect on the anti-tumor immune response and the recent progress made in the preclinical and clinical evaluation of inhibitors targeting these enzymes.

Targeting glutamine metabolism exhibits anti-tumor effects in thyroid cancer

BACKGROUND

Effective treatment for patients with advanced thyroid cancer is lacking. Metabolism reprogramming is required for cancer to undergo oncogenic transformation and rapid tumorigenic growth. Glutamine is frequently used by cancer cells for active bioenergetic and biosynthetic needs. This study aims to investigate whether targeting glutamine metabolism is a promising therapeutic strategy for thyroid cancer.

METHODS

The expression of glutaminase (GLS) and glutamate dehydrogenase (GDH) in thyroid cancer tissues was evaluated by immunohistochemistry, and glutamine metabolism-related genes were assessed using real time-qPCR and western blotting. The effects of glutamine metabolism inhibitor 6-diazo-5-oxo-l-norleucine (DON) on thyroid cancer cells were determined by CCK-8, clone formation assay, Edu incorporation assay, flow cytometry, and Transwell assay. The mechanistic study was performed by real time-qPCR, western blotting, Seahorse assay, and gas chromatography-mass spectrometer assay. The effect of DON prodrug (JHU-083) on thyroid cancer in vivo was assessed using xenograft tumor models in BALB/c nude mice.

RESULTS

GLS and GDH were over-expressed in thyroid cancer tissues, and GLS expression was positively associated with lymph-node metastasis and TNM stage. The growth of thyroid cancer cells was significantly inhibited when cultured in glutamine-free medium. Targeting glutamine metabolism with DON inhibited the proliferation of thyroid cancer cells. DON treatment did not promote apoptosis, but increased the proportion of cells in the S phase, accompanied by the decreased expression of cyclin-dependent kinase 2 and cyclin A. DON treatment also significantly inhibited the migration and invasion of thyroid cancer cells by reducing the expression of N-cadherin, Vimentin, matrix metalloproteinase-2, and matrix metalloproteinase-9. Non-essential amino acids, including proline, alanine, aspartate, asparagine, and glycine, were reduced in thyroid cancer cells treated with DON, which could explain the decrease of proteins involved in migration, invasion, and cell cycle. The efficacy and safety of DON prodrug (JHU-083) for thyroid cancer treatment were verified in a mouse model. In addition to suppressing the proliferation and metastasis potential of thyroid cancer in vivo, enhanced innate immune response was also observed in JHU-083-treated xenograft tumors as a result of decreased expression of cluster of differentiation 47 and programmed cell death ligand 1.

CONCLUSIONS

Thyroid cancer exhibited enhanced glutamine metabolism, as evidenced by the glutamine dependence of thyroid cancer cells and high expression of multiple glutamine metabolism-related genes. Targeting glutamine metabolism with DON prodrug could be a promising therapeutic option for advanced thyroid cancer.

Glutaminolysis is a Potential Therapeutic Target for Kidney Diseases

Metabolic reprogramming contributes to the progression and prognosis of various kidney diseases. Glutamine is the most abundant free amino acid in the body and participates in more metabolic processes than other amino acids. Altered glutamine metabolism is a prominent feature in different kidney diseases. Glutaminolysis converts glutamine into the TCA cycle metabolite, alpha-ketoglutarate, via a cascade of enzymatic reactions. This metabolic pathway plays pivotal roles in inflammation, maladaptive repair, cell survival and proliferation, redox homeostasis, and immune regulation. Given the crucial role of glutaminolysis in bioenergetics and anaplerotic fluxes in kidney pathogenesis, studies on this cascade could provide a better understanding of kidney diseases, thus inspiring the development of potential methods for targeted therapy. Emerging evidence has shown that targeting glutaminolysis is a promising therapeutic strategy for ameliorating kidney disease. In this narrative review, equation including keywords related to glutamine, glutaminolysis and kidney are subjected to an exhaustive search on Pubmed database, we identified all relevant articles published before 1 April, 2024. Afterwards, we summarize the regulation of glutaminolysis in major kidney diseases and its underlying molecular mechanisms. Furthermore, we highlight therapeutic strategies targeting glutaminolysis and their potential clinical applications.

Metabolic Reprogramming of Tumor-Associated Macrophages Using Glutamine Antagonist JHU083 Drives Tumor Immunity in Myeloid-Rich Prostate and Bladder Cancers

Glutamine metabolism in tumor microenvironments critically regulates antitumor immunity. Using the glutamine-antagonist prodrug JHU083, we report potent tumor growth inhibition in urologic tumors by JHU083-reprogrammed tumor-associated macrophages (TAMs) and tumor-infiltrating monocytes. We show JHU083-mediated glutamine antagonism in tumor microenvironments induced by TNF, proinflammatory, and mTORC1 signaling in intratumoral TAM clusters. JHU083-reprogrammed TAMs also exhibited increased tumor cell phagocytosis and diminished proangiogenic capacities. In vivo inhibition of TAM glutamine consumption resulted in increased glycolysis, a broken tricarboxylic acid (TCA) cycle, and purine metabolism disruption. Although the antitumor effect of glutamine antagonism on tumor-infiltrating T cells was moderate, JHU083 promoted a stem cell-like phenotype in CD8+ T cells and decreased the abundance of regulatory T cells. Finally, JHU083 caused a global shutdown in glutamine-utilizing metabolic pathways in tumor cells, leading to reduced HIF-1α, c-MYC phosphorylation, and induction of tumor cell apoptosis, all key antitumor features. Altogether, our findings demonstrate that targeting glutamine with JHU083 led to suppressed tumor growth as well as reprogramming of immunosuppressive TAMs within prostate and bladder tumors that promoted antitumor immune responses. JHU083 can offer an effective therapeutic benefit for tumor types that are enriched in immunosuppressive TAMs.

Decoding mitochondria's role in immunity and cancer therapy

The functions of mitochondria, including energy production and biomolecule synthesis, have been known for a long time. Given the rising incidence of cancer, the role of mitochondria in cancer has become increasingly popular. Activated by components released by mitochondria, various pathways interact with each other to induce immune responses to protect organisms from attack. However, mitochondria play dual roles in the progression of cancer. Abnormalities in proteins, which are the elementary structures of mitochondria, are closely linked with oncogenesis. Both the aberrant accumulation of intermediates and mutations in enzymes result in the generation and progression of cancer. Therefore, targeting mitochondria to treat cancer may be a new strategy. Several drugs aimed at inhibiting mutated enzymes and accumulated intermediates have been tested clinically. Here, we discuss the current understanding of mitochondria in cancer and the interactions between mitochondrial functions, immune responses, and oncogenesis. Furthermore, we discuss mitochondria as hopeful targets for cancer therapy, providing insights into the progression of future therapeutic strategies.

GFPT2 expression is induced by gemcitabine administration and enhances invasion by activating the hexosamine biosynthetic pathway in pancreatic cancer

Our previous studies revealed a novel link between gemcitabine (GEM) chemotherapy and elevated glutamine-fructose-6-phosphate transaminase 2 (GFPT2) expression in pancreatic cancer (PaCa) cells. GFPT2 is a rate-limiting enzyme in the hexosamine biosynthesis pathway (HBP). HBP can enhance metastatic potential by regulating epithelial-mesenchymal transition (EMT). The aim of this study was to further evaluate the effect of chemotherapy-induced GFPT2 expression on metastatic potential. GFPT2 expression was evaluated in a mouse xenograft model following GEM exposure and in clinical specimens of patients after chemotherapy using immunohistochemical analysis. The roles of GFPT2 in HBP activation, downstream pathways, and cellular functions in PaCa cells with regulated GFPT2 expression were investigated. GEM exposure increased GFPT2 expression in tumors resected from a mouse xenograft model and in patients treated with neoadjuvant chemotherapy (NAC). GFPT2 expression was correlated with post-operative liver metastasis after NAC. Its expression activated the HBP, promoting migration and invasion. Treatment with HBP inhibitors reversed these effects. Additionally, GFPT2 upregulated ZEB1 and vimentin expression and downregulated E-cadherin expression. GEM induction upregulated GFPT2 expression. Elevated GFPT2 levels promoted invasion by activating the HBP, suggesting the potential role of this mechanism in promoting chemotherapy-induced metastasis.

Exploiting pancreatic cancer metabolism: challenges and opportunities

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive form of pancreatic cancer, known for its challenging diagnosis and limited treatment options. The focus on metabolic reprogramming as a key factor in tumor initiation, progression, and therapy resistance has gained prominence. In this review we focus on the impact of metabolic changes on the interplay among stromal, immune, and tumor cells, as glutamine and branched-chain amino acids (BCAAs) emerge as pivotal players in modulating immune cell functions and tumor growth. We also discuss ongoing clinical trials that explore metabolic modulation for PDAC, targeting mitochondrial metabolism, asparagine and glutamine addiction, and autophagy inhibition. Overcoming challenges in understanding nutrient effects on immune-stromal-tumor interactions holds promise for innovative therapeutic strategies.

Therapeutic resurgence of 6-diazo-5-oxo-l-norleucine (DON) through tissue-targeted prodrugs

The recognition that rapidly proliferating cancer cells rely heavily on glutamine for their survival and growth has renewed interest in the development of glutamine antagonists for cancer therapy. Glutamine plays a pivotal role as a carbon source for synthesizing lipids and metabolites through the TCA cycle, as well as a nitrogen source for synthesis of amino acid and nucleotides. Numerous studies have explored the significance of glutamine metabolism in cancer, providing a robust rationale for targeting this metabolic pathway in cancer treatment. The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON) has been explored as an anticancer therapeutic for nearly six decades. Initial investigations revealed remarkable efficacy in preclinical studies and promising outcomes in early clinical trials. However, further advancement of DON was hindered due to dose-limiting gastrointestinal (GI) toxicities as the GI system is highly dependent on glutamine for regulating growth and repair. In an effort to repurpose DON and mitigate gastrointestinal (GI) toxicity concerns, prodrug strategies were utilized. These strategies aimed to enhance the delivery of DON to specific target tissues, such as tumors and the central nervous system (CNS), while sparing DON delivery to normal tissues, particularly the GI tract. When administered at low daily doses, optimized for metabolic inhibition, these prodrugs exhibit remarkable effectiveness without inducing significant toxicity to normal tissues. This approach holds promise for overcoming past challenges associated with DON, offering an avenue for its successful utilization in cancer treatment.

Metabolic adaptations determine whether natural killer cells fail or thrive within the tumor microenvironment

Natural Killer (NK) cells are a top contender in the development of adoptive cell therapies for cancer due to their diverse antitumor functions and ability to restrict their activation against nonmalignant cells. Despite their success in hematologic malignancies, NK cell-based therapies have been limited in the context of solid tumors. Tumor cells undergo various metabolic adaptations to sustain the immense energy demands that are needed to support their rapid and uncontrolled proliferation. As a result, the tumor microenvironment (TME) is depleted of nutrients needed to fuel immune cell activity and contains several immunosuppressive metabolites that hinder NK cell antitumor functions. Further, we now know that NK cell metabolic status is a main determining factor of their effector functions. Hence, the ability of NK cells to withstand and adapt to these metabolically hostile conditions is imperative for effective and sustained antitumor activity in the TME. With this in mind, we review the consequences of metabolic hostility in the TME on NK cell metabolism and function. We also discuss tumor-like metabolic programs in NK cell induced by STAT3-mediated expansion that adapt NK cells to thrive in the TME. Finally, we examine how other approaches can be applied to enhance NK cell metabolism in tumors.

A redox-responsive prodrug for tumor-targeted glutamine restriction

Modulating the metabolism of cancer cells, immune cells, or both is a promising strategy to potentiate cancer immunotherapy in the nutrient-competitive tumor microenvironment. Glutamine has emerged as an ideal target as cancer cells highly rely on glutamine for replenishing the tricarboxylic acid cycle in the process of aerobic glycolysis. However, non-specific glutamine restriction may induce adverse effects in unconcerned tissues and therefore glutamine inhibitors have achieved limited success in the clinic so far. Here we report the synthesis and evaluation of a redox-responsive prodrug of 6-Diazo-5-oxo-L-norleucine (redox-DON) for tumor-targeted glutamine inhibition. When applied to treat mice bearing subcutaneous CT26 mouse colon carcinoma, redox-DON exhibited equivalent antitumor efficacy but a greatly improved safety profile, particularly, in spleen and gastrointestinal tract, as compared to the state-of-the-art DON prodrug, JHU083. Furthermore, redox-DON synergized with checkpoint blockade antibodies leading to durable cures in tumor-bearing mice. Our results suggest that redox-DON is a safe and effective therapeutic for tumor-targeted glutamine inhibition showing promise for enhanced metabolic modulatory immunotherapy. The approach of reversible chemical modification may be generalized to other metabolic modulatory drugs that suffer from overt toxicity.

Glutamine antagonist DRP-104 suppresses tumor growth and enhances response to checkpoint blockade in KEAP1 mutant lung cancer

Loss-of-function mutations in KEAP1 frequently occur in lung cancer and are associated with poor prognosis and resistance to standard of care treatment, highlighting the need for the development of targeted therapies. We previously showed that KEAP1 mutant tumors consume glutamine to support the metabolic rewiring associated with NRF2-dependent antioxidant production. Here, using preclinical patient-derived xenograft models and antigenic orthotopic lung cancer models, we show that the glutamine antagonist prodrug DRP-104 impairs the growth of KEAP1 mutant tumors. We find that DRP-104 suppresses KEAP1 mutant tumors by inhibiting glutamine-dependent nucleotide synthesis and promoting antitumor T cell responses. Using multimodal single-cell sequencing and ex vivo functional assays, we demonstrate that DRP-104 reverses T cell exhaustion, decreases Tregs, and enhances the function of CD4 and CD8 T cells, culminating in an improved response to anti-PD1 therapy. Our preclinical findings provide compelling evidence that DRP-104, currently in clinical trials, offers a promising therapeutic approach for treating patients with KEAP1 mutant lung cancer.

Exploiting the Achilles' heel of cancer: disrupting glutamine metabolism for effective cancer treatment

Cancer cells have adapted to rapid tumor growth and evade immune attack by reprogramming their metabolic pathways. Glutamine is an important nitrogen resource for synthesizing amino acids and nucleotides and an important carbon source in the tricarboxylic acid (TCA) cycle and lipid biosynthesis pathway. In this review, we summarize the significant role of glutamine metabolism in tumor development and highlight the vulnerabilities of targeting glutamine metabolism for effective therapy. In particular, we review the reported drugs targeting glutaminase and glutamine uptake for efficient cancer treatment. Moreover, we discuss the current clinical test about targeting glutamine metabolism and the prospective direction of drug development.

Glutamine Supplementation as an Anticancer Strategy: A Potential Therapeutic Alternative to the Convention

Glutamine, a multifaceted nonessential/conditionally essential amino acid integral to cellular metabolism and immune function, holds pivotal importance in the landscape of cancer therapy. This review delves into the intricate dynamics surrounding both glutamine antagonism strategies and glutamine supplementation within the context of cancer treatment, emphasizing the critical role of glutamine metabolism in cancer progression and therapy. Glutamine antagonism, aiming to disrupt tumor growth by targeting critical metabolic pathways, is challenged by the adaptive nature of cancer cells and the complex metabolic microenvironment, potentially compromising its therapeutic efficacy. In contrast, glutamine supplementation supports immune function, improves gut integrity, alleviates treatment-related toxicities, and improves patient well-being. Moreover, recent studies highlighted its contributions to epigenetic regulation within cancer cells and its potential to bolster anti-cancer immune functions. However, glutamine implementation necessitates careful consideration of potential interactions with ongoing treatment regimens and the delicate equilibrium between supporting normal cellular function and promoting tumorigenesis. By critically assessing the implications of both glutamine antagonism strategies and glutamine supplementation, this review aims to offer comprehensive insights into potential therapeutic strategies targeting glutamine metabolism for effective cancer management.

Targeting glutamine dependence with DRP-104 inhibits proliferation and tumor growth of castration-resistant prostate cancer

BACKGROUND

Prostate cancer (PCa) continues to be one of the leading causes of cancer deaths in men. While androgen deprivation therapy is initially effective, castration-resistant PCa (CRPC) often recurs and has limited treatment options. Our previous study identified glutamine metabolism to be critical for CRPC growth. The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON) blocks both carbon and nitrogen pathways but has dose-limiting toxicity. The prodrug DRP-104 is expected to be preferentially converted to DON in tumor cells to inhibit glutamine utilization with minimal toxicity. However, CRPC cells' susceptibility to DRP-104 remains unclear.

METHODS

Human PCa cell lines (LNCaP, LAPC4, C4-2/MDVR, PC-3, 22RV1, NCI-H660) were treated with DRP-104, and effects on proliferation and cell death were assessed. Unbiased metabolic profiling and isotope tracing evaluated the effects of DRP-104 on glutamine pathways. Efficacy of DRP-104 in vivo was evaluated in a mouse xenograft model of neuroendocrine PCa, NCI-H660.

RESULTS

DRP-104 inhibited proliferation and induced apoptosis in CRPC cell lines. Metabolite profiling showed decreases in the tricarboxylic acid cycle and nucleotide synthesis metabolites. Glutamine isotope tracing confirmed the blockade of both carbon pathway and nitrogen pathways. DRP-104 treated CRPC cells were rescued by the addition of nucleosides. DRP-104 inhibited neuroendocrine PCa xenograft growth without detectable toxicity.

CONCLUSIONS

The prodrug DRP-104 blocks glutamine carbon and nitrogen utilization, thereby inhibiting CRPC growth and inducing apoptosis. Targeting glutamine metabolism pathways with DRP-104 represents a promising therapeutic strategy for CRPC.

Targeting MYC induces lipid droplet accumulation by upregulation of HILPDA in clear cell renal cell carcinoma

Metabolic reprogramming is critical during clear cell renal cell carcinoma (ccRCC) tumorigenesis, manifested by accumulation of lipid droplets (LDs), organelles that have emerged as new hallmarks of cancer. Yet, regulation of their biogenesis is still poorly understood. Here, we demonstrate that MYC inhibition in ccRCC cells lacking the von Hippel Lindau (VHL) gene leads to increased triglyceride content potentiating LD formation in a glutamine-dependent manner. Importantly, the concurrent inhibition of MYC signaling and glutamine metabolism prevented LD accumulation and reduced tumor burden in vivo. Furthermore, we identified the hypoxia-inducible lipid droplet-associated protein (HILPDA) as the key driver for induction of MYC-driven LD accumulation and demonstrated that conversely, proliferation, LD formation, and tumor growth are impaired upon its downregulation. Finally, analysis of ccRCC tissue as well as healthy renal control samples postulated HILPDA as a specific ccRCC biomarker. Together, these results provide an attractive approach for development of alternative therapeutic interventions for the treatment of this type of renal cancer.

DON of Hope: Starving Pancreatic Cancer by Glutamine Antagonism

A promising approach to treat solid tumors involves disrupting their reliance on glutamine, a key component for various metabolic processes. Traditional attempts using glutamine inhibitors like 6-diazo-5-oxo-L-norleucine (DON) and CB-839 were unsuccessful, but new hope arises with DRP-104, a prodrug of DON. This compound effectively targets tumor metabolism while minimizing side effects. In a recent study published in Nature Cancer, Encarnación-Rosado and colleagues demonstrated in preclinical models that pancreatic ductal adenocarcinoma (PDAC) responds well to DRP-104, although tumors adapt through the MEK/ERK signaling pathway, which can be countered by the MEK inhibitor trametinib. In a related study, Recouvreux and colleagues found that DON is effective against pancreatic tumors, revealing that PDAC tumors upregulate asparagine synthesis in response to DON, making them susceptible to asparaginase treatment. Both studies underscore the potential of inhibiting glutamine metabolism and adaptive pathways as a promising strategy against PDAC. These findings pave the way for upcoming clinical trials utilizing DRP-104 and similar glutamine antagonists in the battle against solid tumors.

Tumor-targeted metabolic inhibitor prodrug labelled with cyanine dyes enhances immunoprevention of lung cancer

Recent progress in targeted metabolic therapy of cancer has been limited by the considerable toxicity associated with such drugs. To address this challenge, we developed a smart theranostic prodrug system that combines a fluorophore and an anticancer drug, specifically 6-diazo-5-oxo-l-norleucine (DON), using a thioketal linkage (TK). This system enables imaging, chemotherapy, photodynamic therapy, and on-demand drug release upon radiation exposure. The optimized prodrug, DON-TK-BM3, incorporating cyanine dyes as the fluorophore, displayed potent reactive oxygen species release and efficient tumor cell killing. Unlike the parent drug DON, DON-TK-BM3 exhibited no toxicity toward normal cells. Moreover, DON-TK-BM3 demonstrated high tumor accumulation and reduced side effects, including gastrointestinal toxicity, in mice. This study provides a practical strategy for designing prodrugs of metabolic inhibitors with significant toxicity stemming from their lack of tissue selectivity.

Cancer Metabolism under Limiting Oxygen Conditions

Molecular oxygen (O2) is essential for cellular bioenergetics and numerous biochemical reactions necessary for life. Solid tumors outgrow the native blood supply and diffusion limits of O2, and therefore must engage hypoxia response pathways that evolved to withstand acute periods of low O2 Hypoxia activates coordinated gene expression programs, primarily through hypoxia inducible factors (HIFs), to support survival. Many of these changes involve metabolic rewiring such as increasing glycolysis to support ATP generation while suppressing mitochondrial metabolism. Since low O2 is often coupled with nutrient stress in the tumor microenvironment, other responses to hypoxia include activation of nutrient uptake pathways, metabolite scavenging, and regulation of stress and growth signaling cascades. Continued development of models that better recapitulate tumors and their microenvironments will lead to greater understanding of oxygen-dependent metabolic reprogramming and lead to more effective cancer therapies.

Glutamine addiction in tumor cell: oncogene regulation and clinical treatment

After undergoing metabolic reprogramming, tumor cells consume additional glutamine to produce amino acids, nucleotides, fatty acids, and other substances to facilitate their unlimited proliferation. As such, the metabolism of glutamine is intricately linked to the survival and progression of cancer cells. Consequently, targeting the glutamine metabolism presents a promising strategy to inhibit growth of tumor cell and cancer development. This review describes glutamine uptake, metabolism, and transport in tumor cells and its pivotal role in biosynthesis of amino acids, fatty acids, nucleotides, and more. Furthermore, we have also summarized the impact of oncogenes like C-MYC, KRAS, HIF, and p53 on the regulation of glutamine metabolism and the mechanisms through which glutamine triggers mTORC1 activation. In addition, role of different anti-cancer agents in targeting glutamine metabolism has been described and their prospective applications are assessed.

Targeting pancreatic cancer metabolic dependencies through glutamine antagonism

Pancreatic ductal adenocarcinoma (PDAC) cells use glutamine (Gln) to support proliferation and redox balance. Early attempts to inhibit Gln metabolism using glutaminase inhibitors resulted in rapid metabolic reprogramming and therapeutic resistance. Here, we demonstrated that treating PDAC cells with a Gln antagonist, 6-diazo-5-oxo-L-norleucine (DON), led to a metabolic crisis in vitro. In addition, we observed a profound decrease in tumor growth in several in vivo models using sirpiglenastat (DRP-104), a pro-drug version of DON that was designed to circumvent DON-associated toxicity. We found that extracellular signal-regulated kinase (ERK) signaling is increased as a compensatory mechanism. Combinatorial treatment with DRP-104 and trametinib led to a significant increase in survival in a syngeneic model of PDAC. These proof-of-concept studies suggested that broadly targeting Gln metabolism could provide a therapeutic avenue for PDAC. The combination with an ERK signaling pathway inhibitor could further improve the therapeutic outcome.

Glutamine mimicry suppresses tumor progression through asparagine metabolism in pancreatic ductal adenocarcinoma

In pancreatic ductal adenocarcinoma (PDAC), glutamine is a critical nutrient that drives a wide array of metabolic and biosynthetic processes that support tumor growth. Here, we elucidate how 6-diazo-5-oxo-L-norleucine (DON), a glutamine antagonist that broadly inhibits glutamine metabolism, blocks PDAC tumor growth and metastasis. We find that DON significantly reduces asparagine production by inhibiting asparagine synthetase (ASNS), and that the effects of DON are rescued by asparagine. As a metabolic adaptation, PDAC cells upregulate ASNS expression in response to DON, and we show that ASNS levels are inversely correlated with DON efficacy. We also show that L-asparaginase (ASNase) synergizes with DON to affect the viability of PDAC cells, and that DON and ASNase combination therapy has a significant impact on metastasis. These results shed light on the mechanisms that drive the effects of glutamine mimicry and point to the utility of cotargeting adaptive responses to control PDAC progression.

Pro-905, a Novel Purine Antimetabolite, Combines with Glutamine Amidotransferase Inhibition to Suppress Growth of Malignant Peripheral Nerve Sheath Tumor

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive soft-tissue sarcomas that arise from neural tissues and carry a poor prognosis. Previously, we found that the glutamine amidotransferase inhibitor JHU395 partially impeded tumor growth in preclinical models of MPNST. JHU395 inhibits de novo purine synthesis in human MPNST cells and murine tumors with partial decreases in purine monophosphates. On the basis of prior studies showing enhanced efficacy when glutamine amidotransferase inhibition was combined with the antimetabolite 6-mercaptopurine (6-MP), we hypothesized that such a combination would be efficacious in MPNST. Given the known toxicity associated with 6-MP, we set out to develop a more efficient and well-tolerated drug that targets the purine salvage pathway. Here, we report the discovery of Pro-905, a phosphoramidate protide that delivered the active nucleotide antimetabolite thioguanosine monophosphate (TGMP) to tumors over 2.5 times better than equimolar 6-MP. Pro-905 effectively prevented the incorporation of purine salvage substrates into nucleic acids and inhibited colony formation of human MPNST cells in a dose-dependent manner. In addition, Pro-905 inhibited MPNST growth and was well-tolerated in both human patient-derived xenograft (PDX) and murine flank MPNST models. When combined with JHU395, Pro-905 enhanced the colony formation inhibitory potency of JHU395 in human MPNST cells and augmented the antitumor efficacy of JHU395 in mice. In summary, the dual inhibition of the de novo and purine salvage pathways in preclinical models may safely be used to enhance therapeutic efficacy against MPNST.

The immunometabolic ecosystem in cancer

Our increased understanding of how key metabolic pathways are activated and regulated in malignant cells has identified metabolic vulnerabilities of cancers. Translating this insight to the clinics, however, has proved challenging. Roadblocks limiting efficacy of drugs targeting cancer metabolism may lie in the nature of the metabolic ecosystem of tumors. The exchange of metabolites and growth factors between cancer cells and nonmalignant tumor-resident cells is essential for tumor growth and evolution, as well as the development of an immunosuppressive microenvironment. In this Review, we will examine the metabolic interplay between tumor-resident cells and how targeted inhibition of specific metabolic enzymes in malignant cells could elicit pro-tumorigenic effects in non-transformed tumor-resident cells and inhibit the function of tumor-specific T cells. To improve the efficacy of metabolism-targeted anticancer strategies, a holistic approach that considers the effect of metabolic inhibitors on major tumor-resident cell populations is needed.

The O-GlcNAc dichotomy: when does adaptation become pathological?

O-Linked attachment of β-N-acetylglucosamine (O-GlcNAc) on serine and threonine residues of nuclear, cytoplasmic, and mitochondrial proteins is a highly dynamic and ubiquitous post-translational modification that impacts the function, activity, subcellular localization, and stability of target proteins. Physiologically, acute O-GlcNAcylation serves primarily to modulate cellular signaling and transcription regulatory pathways in response to nutrients and stress. To date, thousands of proteins have been revealed to be O-GlcNAcylated and this number continues to grow as the technology for the detection of O-GlcNAc improves. The attachment of a single O-GlcNAc is catalyzed by the enzyme O-GlcNAc transferase (OGT), and their removal is catalyzed by O-GlcNAcase (OGA). O-GlcNAcylation is regulated by the metabolism of glucose via the hexosamine biosynthesis pathway, and the metabolic abnormalities associated with pathophysiological conditions are all associated with increased flux through this pathway and elevate O-GlcNAc levels. While chronic O-GlcNAcylation is well associated with cardiovascular dysfunction, only until recently, and with genetically modified animals, has O-GlcNAcylation as a contributing mechanism of cardiovascular disease emerged. This review will address and critically evaluate the current literature on the role of O-GlcNAcylation in vascular physiology, with a view that this pathway can offer novel targets for the treatment and prevention of cardiovascular diseases.

Telomerase reverse transcriptase induces targetable alterations in glutathione and nucleotide biosynthesis in glioblastomas

Telomerase reverse transcriptase (TERT) is essential for glioblastoma (GBM) proliferation. Delineating metabolic vulnerabilities induced by TERT can lead to novel GBM therapies. We previously showed that TERT upregulates glutathione (GSH) pool size in GBMs. Here, we show that TERT acts via the FOXO1 transcription factor to upregulate expression of the catalytic subunit of glutamate-cysteine ligase (GCLC), the rate-limiting enzyme of de novo GSH synthesis. Inhibiting GCLC using siRNA or buthionine sulfoximine (BSO) reduces synthesis of 13 C-GSH from [U- 13 C]-glutamine and inhibits clonogenicity. However, GCLC inhibition does not induce cell death, an effect that is associated with elevated [U- 13 C]-glutamine metabolism to glutamate and pyrimidine nucleotide biosynthesis. Mechanistically, GCLC inhibition activates MYC and leads to compensatory upregulation of two key glutamine-utilizing enzymes i.e., glutaminase (GLS), which generates glutamate from glutamine, and CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, dihydroorotatase), the enzyme that converts glutamine to the pyrimidine nucleotide precursor dihydroorotate. We then examined the therapeutic potential of inhibiting GLS and CAD in combination with GCLC. 6-diazo-5-oxy-L-norleucin (DON) is a potent inhibitor of glutamine-utilizing enzymes including GLS and CAD. The combination of BSO and DON suppresses GSH and pyrimidine nucleotide biosynthesis and is synergistically lethal in GBM cells. Importantly, in vivo stable isotope tracing indicates that combined treatment with JHU-083 (a brain-penetrant prodrug of DON) and BSO abrogates synthesis of GSH and pyrimidine nucleotides from [U- 13 C]-glutamine and induces tumor shrinkage in mice bearing intracranial GBM xenografts. Collectively, our studies exploit a mechanistic understanding of TERT biology to identify synthetically lethal metabolic vulnerabilities in GBMs.

SIGNIFICANCE

Using in vivo stable isotope tracing, metabolomics, and loss-of-function studies, we demonstrate that TERT expression is associated with metabolic alterations that can be synergistically targeted for therapy in glioblastomas.

Glutamine metabolism inhibition has dual immunomodulatory and antibacterial activities against Mycobacterium tuberculosis

As one of the most successful human pathogens, Mycobacterium tuberculosis (Mtb) has evolved a diverse array of determinants to subvert host immunity and alter host metabolic patterns. However, the mechanisms of pathogen interference with host metabolism remain poorly understood. Here we show that a glutamine metabolism antagonist, JHU083, inhibits Mtb proliferation in vitro and in vivo. JHU083-treated mice exhibit weight gain, improved survival, a 2.5 log lower lung bacillary burden at 35 days post-infection, and reduced lung pathology. JHU083 treatment also initiates earlier T-cell recruitment, increased proinflammatory myeloid cell infiltration, and a reduced frequency of immunosuppressive myeloid cells when compared to uninfected and rifampin-treated controls. Metabolomic analysis of lungs from JHU083-treated Mtb-infected mice reveals citrulline accumulation, suggesting elevated nitric oxide (NO) synthesis, and lowered levels of quinolinic acid which is derived from the immunosuppressive metabolite kynurenine. JHU083-treated macrophages also produce more NO potentiating their antibacterial activity. When tested in an immunocompromised mouse model of Mtb infection, JHU083 loses its therapeutic efficacy suggesting the drug's host-directed effects are likely to be predominant. Collectively, these data reveal that JHU083-mediated glutamine metabolism inhibition results in dual antibacterial and host-directed activity against tuberculosis.

Participation of protein metabolism in cancer progression and its potential targeting for the management of cancer

Cancer malignancies may broadly be described as heterogeneous disorders manifested by uncontrolled cellular growth/division and proliferation. Tumor cells utilize metabolic reprogramming to accomplish the upregulated nutritional requirements for sustaining their uncontrolled growth, proliferation, and survival. Metabolic reprogramming also called altered or dysregulated metabolism undergoes modification in normal metabolic pathways for anabolic precursor's generation that serves to continue biomass formation that sustains the growth, proliferation, and survival of carcinogenic cells under a nutrition-deprived microenvironment. A wide range of dysregulated/altered metabolic pathways encompassing different metabolic regulators have been described; however, the current review is focused to explain deeply the metabolic pathways modifications inducing upregulation of proteins/amino acids metabolism. The essential modification of various metabolic cycles with their consequent outcomes meanwhile explored promising therapeutic targets playing a pivotal role in metabolic regulation and is successfully employed for effective target-specific cancer treatment. The current review is aimed to understand the metabolic reprogramming of different proteins/amino acids involved in tumor progression along with potential therapeutic perspective elucidating targeted cancer therapy via these targets.

The role of bone marrow microenvironment (BMM) cells in acute myeloid leukemia (AML) progression: immune checkpoints, metabolic checkpoints, and signaling pathways

Acute myeloid leukemia (AML) comprises a multifarious and heterogeneous array of illnesses characterized by the anomalous proliferation of myeloid cells in the bone marrow microenvironment (BMM). The BMM plays a pivotal role in promoting AML progression, angiogenesis, and metastasis. The immune checkpoints (ICs) and metabolic processes are the key players in this process. In this review, we delineate the metabolic and immune checkpoint characteristics of the AML BMM, with a focus on the roles of BMM cells e.g. tumor-associated macrophages, natural killer cells, dendritic cells, metabolic profiles and related signaling pathways. We also discuss the signaling pathways stimulated in AML cells by BMM factors that lead to AML progression. We then delve into the roles of immune checkpoints in AML angiogenesis, metastasis, and cell proliferation, including co-stimulatory and inhibitory ICs. Lastly, we discuss the potential therapeutic approaches and future directions for AML treatment, emphasizing the potential of targeting metabolic and immune checkpoints in AML BMM as prognostic and therapeutic targets. In conclusion, the modulation of these processes through the use of directed drugs opens up new promising avenues in combating AML. Thereby, a comprehensive elucidation of the significance of these AML BMM cells' metabolic and immune checkpoints and signaling pathways on leukemic cells can be undertaken in the future investigations. Additionally, these checkpoints and cells should be considered plausible multi-targeted therapies for AML in combination with other conventional treatments in AML. Video Abstract.

Screening in serum-derived medium reveals differential response to compounds targeting metabolism

A challenge for screening new anticancer drugs is that efficacy in cell culture models is not always predictive of efficacy in patients. One limitation of standard cell culture is a reliance on non-physiological nutrient levels, which can influence cell metabolism and drug sensitivity. A general assessment of how physiological nutrients affect cancer cell response to small molecule therapies is lacking. To address this, we developed a serum-derived culture medium that supports the proliferation of diverse cancer cell lines and is amenable to high-throughput screening. We screened several small molecule libraries and found that compounds targeting metabolic enzymes were differentially effective in standard compared to serum-derived medium. We exploited the differences in nutrient levels between each medium to understand why medium conditions affected the response of cells to some compounds, illustrating how this approach can be used to screen potential therapeutics and understand how their efficacy is modified by available nutrients.

Tumor microenvironmental nutrients, cellular responses, and cancer

Over the last two decades, the rapidly expanding field of tumor metabolism has enhanced our knowledge of the impact of nutrient availability on metabolic reprogramming in cancer. Apart from established roles in cancer cells themselves, various nutrients, metabolic enzymes, and stress responses are key to the activities of tumor microenvironmental immune, fibroblastic, endothelial, and other cell types that support malignant transformation. In this article, we review our current understanding of how nutrient availability affects metabolic pathways and responses in both cancer and "stromal" cells, by dissecting major examples and their regulation of cellular activity. Understanding the relationship of nutrient availability to cellular behaviors in the tumor ecosystem will broaden the horizon of exploiting novel therapeutic vulnerabilities in cancer.

Differential Effects of Glutamine Inhibition Strategies on Antitumor CD8 T Cells

Activated T cells undergo metabolic reprogramming to meet anabolic, differentiation, and functional demands. Glutamine supports many processes in activated T cells, and inhibition of glutamine metabolism alters T cell function in autoimmune disease and cancer. Multiple glutamine-targeting molecules are under investigation, yet the precise mechanisms of glutamine-dependent CD8 T cell differentiation remain unclear. We show that distinct strategies of glutamine inhibition by glutaminase-specific inhibition with small molecule CB-839, pan-glutamine inhibition with 6-diazo-5-oxo-l-norleucine (DON), or by glutamine-depleted conditions (No Q) produce distinct metabolic differentiation trajectories in murine CD8 T cells. T cell activation with CB-839 treatment had a milder effect than did DON or No Q treatment. A key difference was that CB-839-treated cells compensated with increased glycolytic metabolism, whereas DON and No Q-treated cells increased oxidative metabolism. However, all glutamine treatment strategies elevated CD8 T cell dependence on glucose metabolism, and No Q treatment caused adaptation toward reduced glutamine dependence. DON treatment reduced histone modifications and numbers of persisting cells in adoptive transfer studies, but those T cells that remained could expand normally upon secondary Ag encounter. In contrast, No Q-treated cells persisted well yet demonstrated decreased secondary expansion. Consistent with reduced persistence, CD8 T cells activated in the presence of DON had reduced ability to control tumor growth and reduced tumor infiltration in adoptive cell therapy. Overall, each approach to inhibit glutamine metabolism confers distinct effects on CD8 T cells and highlights that targeting the same pathway in different ways can elicit opposing metabolic and functional outcomes.

Metabolic Heterogeneity, Plasticity, and Adaptation to "Glutamine Addiction" in Cancer Cells: The Role of Glutaminase and the GTωA [Glutamine Transaminase-ω-Amidase (Glutaminase II)] Pathway

Many cancers utilize l-glutamine as a major energy source. Often cited in the literature as "l-glutamine addiction", this well-characterized pathway involves hydrolysis of l-glutamine by a glutaminase to l-glutamate, followed by oxidative deamination, or transamination, to α-ketoglutarate, which enters the tricarboxylic acid cycle. However, mammalian tissues/cancers possess a rarely mentioned, alternative pathway (the glutaminase II pathway): l-glutamine is transaminated to α-ketoglutaramate (KGM), followed by ω-amidase (ωA)-catalyzed hydrolysis of KGM to α-ketoglutarate. The name glutaminase II may be confused with the glutaminase 2 (GLS2) isozyme. Thus, we recently renamed the glutaminase II pathway the "glutamine transaminase-ω-amidase (GTωA)" pathway. Herein, we summarize the metabolic importance of the GTωA pathway, including its role in closing the methionine salvage pathway, and as a source of anaplerotic α-ketoglutarate. An advantage of the GTωA pathway is that there is no net change in redox status, permitting α-ketoglutarate production during hypoxia, diminishing cellular energy demands. We suggest that the ability to coordinate control of both pathways bestows a metabolic advantage to cancer cells. Finally, we discuss possible benefits of GTωA pathway inhibitors, not only as aids to studying the normal biological roles of the pathway but also as possible useful anticancer agents.

Small molecule inhibitors for cancer metabolism: promising prospects to be explored

BACKGROUND

Abnormal metabolism is the main hallmark of cancer, and cancer metabolism plays an important role in tumorigenesis, metastasis, and drug resistance. Therefore, studying the changes of tumor metabolic pathways is beneficial to find targets for the treatment of cancer diseases. The success of metabolism-targeted chemotherapy suggests that cancer metabolism research will provide potential new targets for the treatment of malignant tumors.

PURPOSE

The aim of this study was to systemically review recent research findings on targeted inhibitors of tumor metabolism. In addition, we summarized new insights into tumor metabolic reprogramming and discussed how to guide the exploration of new strategies for cancer-targeted therapy.

CONCLUSION

Cancer cells have shown various altered metabolic pathways, providing sufficient fuel for their survival. The combination of these pathways is considered to be a more useful method for screening multilateral pathways. Better understanding of the clinical research progress of small molecule inhibitors of potential targets of tumor metabolism will help to explore more effective cancer treatment strategies.

Immunometabolism: a new dimension in immunotherapy resistance

Immune checkpoint inhibitors (ICIs) have demonstrated unparalleled clinical responses and revolutionized the paradigm of tumor treatment, while substantial patients remain unresponsive or develop resistance to ICIs as a single agent, which is traceable to cellular metabolic dysfunction. Although dysregulated metabolism has long been adjudged as a hallmark of tumor, it is now increasingly accepted that metabolic reprogramming is not exclusive to tumor cells but is also characteristic of immunocytes. Correspondingly, people used to pay more attention to the effect of tumor cell metabolism on immunocytes, but in practice immunocytes interact intimately with their own metabolic function in a way that has never been realized before during their activation and differentiation, which opens up a whole new frontier called immunometabolism. The metabolic intervention for tumor-infiltrating immunocytes could offer fresh opportunities to break the resistance and ameliorate existing ICI immunotherapy, whose crux might be to ascertain synergistic combinations of metabolic intervention with ICIs to reap synergic benefits and facilitate an adjusted anti-tumor immune response. Herein, we elaborate potential mechanisms underlying immunotherapy resistance from a novel dimension of metabolic reprogramming in diverse tumor-infiltrating immunocytes, and related metabolic intervention in the hope of offering a reference for targeting metabolic vulnerabilities to circumvent immunotherapeutic resistance.

Glutamine antagonist DRP-104 suppresses tumor growth and enhances response to checkpoint blockade in KEAP1 mutant lung cancer

Loss-of-function mutations in KEAP1 frequently occur in lung cancer and are associated with resistance to standard of care treatment, highlighting the need for the development of targeted therapies. We have previously shown that KEAP1 mutant tumors have increased glutamine consumption to support the metabolic rewiring associated with NRF2 activation. Here, using patient-derived xenograft models and antigenic orthotopic lung cancer models, we show that the novel glutamine antagonist DRP-104 impairs the growth of KEAP1 mutant tumors. We find that DRP-104 suppresses KEAP1 mutant tumor growth by inhibiting glutamine-dependent nucleotide synthesis and promoting anti-tumor CD4 and CD8 T cell responses. Using multimodal single-cell sequencing and ex vivo functional assays, we discover that DRP-104 reverses T cell exhaustion and enhances the function of CD4 and CD8 T cells culminating in an improved response to anti-PD1 therapy. Our pre-clinical findings provide compelling evidence that DRP-104, currently in phase 1 clinical trials, offers a promising therapeutic approach for treating patients with KEAP1 mutant lung cancer. Furthermore, we demonstrate that by combining DRP-104 with checkpoint inhibition, we can achieve suppression of tumor intrinsic metabolism and augmentation of anti-tumor T cell responses.

Targeting Glutamine Metabolism as an Attractive Therapeutic Strategy for Acute Myeloid Leukemia

OPINION STATEMENT

Relapse after chemotherapy and hematopoietic stem cell transplantation leads to adverse prognosis for acute myeloid leukemia (AML) patients. As a "conditionally essential amino acid," glutamine contributes to the growth and proliferation of AML cells. Glutamine-target strategies as new treatment approaches have been widely explored in AML treatment to improve outcome. Glutamine-target strategies including depletion of systemic glutamine and application of glutamine uptake inhibitors, glutamine antagonists/analogues, and glutaminase inhibitors. Because glutamine metabolism involved in multiple pathways in cells and each pathway of glutamine metabolism has many regulatory factors, therefore, AML therapy targeting glutamine metabolism should focus on how to inhibit multiple metabolic pathways without affecting normal cells and host immune to achieve effective treatment for AML.

Crosstalk between arginine, glutamine, and the branched chain amino acid metabolism in the tumor microenvironment

Arginine, glutamine, and the branched chain amino acids (BCAAs) are a focus of increased interest in the field of oncology due to their importance in the metabolic reprogramming of cancer cells. In the tumor microenvironment (TME), these amino acids serve to support the elevated biosynthetic and energy demands of cancer cells, while simultaneously maintaining the growth, homeostasis, and effector function of tumor-infiltrating immune cells. To escape immune destruction, cancer cells utilize a variety of mechanisms to suppress the cytotoxic activity of effector T cells, facilitating T cell exhaustion. One such mechanism is the ability of cancer cells to overexpress metabolic enzymes specializing in the catabolism of arginine, glutamine, and the BCAAs in the TME. The action of such enzymes supplies cancer cells with metabolic intermediates that feed into the TCA cycle, supporting energy generation, or providing precursors for purine, pyrimidine, and polyamine biosynthesis. Armed with substantial metabolic flexibility, cancer cells redirect amino acids from the TME for their own advantage and growth, while leaving the local infiltrating effector T cells deprived of essential nutrients. This review addresses the metabolic pressure that cancer cells exert over immune cells in the TME by up-regulating amino acid metabolism, while discussing opportunities for targeting amino acid metabolism for therapeutic intervention. Special emphasis is given to the crosstalk between arginine, glutamine, and BCAA metabolism in affording cancer cells with metabolic dominance in the TME.

Mitochondrial remodeling in colorectal cancer initiation, progression, metastasis, and therapy: A review

Colorectal cancer (CRC) is a major health concern with multifactorial pathophysiology representing intense therapeutic challenges. It is well known that deregulation of spatiotemporally-controlled signaling pathways and their metabolic reprogramming effects play a pivotal role in the development and progression of CRC. As such, the mitochondrial role in CRC initiation gained a lot of attention recently, as it is considered the powerhouse that regulates the bioenergetics in CRC. In addition, the crosstalk between microRNAs (miRNAs) and mitochondrial dysfunction has become a newfangled passion for deciphering CRC molecular mechanisms. This review sheds light on the relationship between different signaling pathways involved in metabolic reprogramming and their therapeutic targets, alterations in mitochondrial DNA content, mitochondrial biogenesis, and mitophagy, and the role of polymorphisms in mitochondrial genes as well as miRNAs regulating mitochondrial proteins in CRC initiation, progression, metastasis, and resistance to various therapies.

Genetically Programmable Vesicles for Enhancing CAR-T Therapy against Solid Tumors

Chimeric antigen receptor-T (CAR-T) cell therapy has shown remarkable success in eradicating hematologic malignancies; however, its efficacy in treating solid tumors has always been limited due to the presence of an immune-suppressive tumor microenvironment (TME). Here, genetically programmable cellular vesicles expressing high-affinity anti-programmed death-ligand 1 single chain variable fragment (anti-PD-L1 scFv) loaded with glutamine antagonist (D@aPD-L1 NVs) are developed to metabolically dismantle the immunosuppressive TME and enhance the efficiency of anti-mesothelin CAR-T cells in orthotopic lung cancer. As anti-PD-L1 scFv can specifically bind to the programmed death-ligand 1 (PD-L1) on tumor cells, D@aPD-L1 NVs enable the targeted delivery of glutamine antagonists to the tumor site and address the upregulation of PD-L1 on tumor cells, which prevents the premature exhaustion of CAR-T cells. More importantly, D@aPD-L1 NVs effectively reduce the number of immunosuppressive cells and promote the recruitment of inflammatory cells and the secretion of inflammatory cytokines in tumor tissues. These unique features of D@aPD-L1 NVs improve the infiltration and effector functions of CAR-T cells, which ultimately enhance the anti-tumor ability and long-term memory immunity of CAR-T cells. The findings support that D@aPD-L1 NVs act as a promising drug to strengthen the effectiveness of CAR-T cells against solid tumors.

The combination of immunotherapy and a glutamine metabolism inhibitor represents an effective therapeutic strategy for advanced and metastatic murine pancreatic adenocarcinoma

Despite constant advances in cancer research, the treatment of pancreatic adenocarcinoma remains extremely challenging. The intratumoral immunotherapy approach that was developed by our research group and was based on a combination of mannan-BAM, TLR ligands, and anti-CD40 antibody (MBTA) showed promising therapeutic effects in various murine tumor models, including a pancreatic adenocarcinoma model (Panc02). However, the efficacy of MBTA therapy in the Panc02 model was negatively correlated with tumor size at the time of therapy initiation. Here, we aimed to further improve the outcome of MBTA therapy in the Panc02 model using the glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON). The combination of intratumoral MBTA therapy and intraperitoneal administration of DON resulted in the complete elimination of advanced Panc02 subcutaneous tumors (140.8 ± 46.8 mm3) in 50% of treated animals and was followed by development of long-term immune memory. In the bilateral Panc02 subcutaneous tumor model, we observed a significant reduction in tumor growth in both tumors as well as prolonged survival of treated animals. The appropriate timing and method of administration of DON were also addressed to maximize its therapeutic effects and minimize its side effects. In summary, our findings demonstrate that the intraperitoneal application of DON significantly improves the efficacy of intratumoral MBTA therapy in both advanced and bilateral Panc02 subcutaneous tumor murine models.

The Hexosamine Biosynthesis Pathway: Regulation and Function

The hexosamine biosynthesis pathway (HBP) produces uridine diphosphate-N-acetyl glucosamine, UDP-GlcNAc, which is a key metabolite that is used for N- or O-linked glycosylation, a co- or post-translational modification, respectively, that modulates protein activity and expression. The production of hexosamines can occur via de novo or salvage mechanisms that are catalyzed by metabolic enzymes. Nutrients including glutamine, glucose, acetyl-CoA, and UTP are utilized by the HBP. Together with availability of these nutrients, signaling molecules that respond to environmental signals, such as mTOR, AMPK, and stress-regulated transcription factors, modulate the HBP. This review discusses the regulation of GFAT, the key enzyme of the de novo HBP, as well as other metabolic enzymes that catalyze the reactions to produce UDP-GlcNAc. We also examine the contribution of the salvage mechanisms in the HBP and how dietary supplementation of the salvage metabolites glucosamine and N-acetylglucosamine could reprogram metabolism and have therapeutic potential. We elaborate on how UDP-GlcNAc is utilized for N-glycosylation of membrane and secretory proteins and how the HBP is reprogrammed during nutrient fluctuations to maintain proteostasis. We also consider how O-GlcNAcylation is coupled to nutrient availability and how this modification modulates cell signaling. We summarize how deregulation of protein N-glycosylation and O-GlcNAcylation can lead to diseases including cancer, diabetes, immunodeficiencies, and congenital disorders of glycosylation. We review the current pharmacological strategies to inhibit GFAT and other enzymes involved in the HBP or glycosylation and how engineered prodrugs could have better therapeutic efficacy for the treatment of diseases related to HBP deregulation.

Targeting glutaminase 1 (GLS1) by small molecules for anticancer therapeutics

Glutaminase-1 (GLS1) is a critical enzyme involved in several cellular processes, and its overexpression has been linked to the development and progression of cancer. Based on existing research, GLS1 plays a crucial role in the metabolic activities of cancer cells, promoting rapid proliferation, cell survival, and immune evasion. Therefore, targeting GLS1 has been proposed as a promising cancer therapy strategy, with several GLS1 inhibitors currently under development. To date, several GLS1 inhibitors have been identified, which can be broadly classified into two types: active site and allosteric inhibitors. Despite their pre-clinical effectiveness, only a few number of these inhibitors have advanced to initial clinical trials. Hence, the present medical research emphasizes the need for developing small molecule inhibitors of GLS1 possessing significantly high potency and selectivity. In this manuscript, we aim to summarize the regulatory role of GLS1 in physiological and pathophysiological processes. We also provide a comprehensive overview of the development of GLS1 inhibitors, focusing on multiple aspects such as target selectivity, in vitro and in vivo potency and structure-activity relationships.

Role and therapeutic targeting of glutamine metabolism in non‑small cell lung cancer (Review)

The Warburg effect indicates that cancer cells survive through glycolysis under aerobic conditions; as such, the topic of cancer metabolism has aroused interest. It is requisite to further explore cancer metabolism, as it helps to simultaneously explain the process of carcinogenesis and guide therapy. The flexible metabolism of cancer cells, which is the result of metabolic reprogramming, can meet the basic needs of cells, even in a nutrition-deficient environment. Glutamine is the most abundant non-essential amino acid in the circulation, and along with glucose, comprise the two basic nutrients of cancer cell metabolism. Glutamine is crucial in non-small cell lung cancer (NSCLC) cells and serves an important role in supporting cell growth, activating signal transduction and maintaining redox homeostasis. In this perspective, the present review aims to provide a new therapeutic strategy of NSCLC through inhibiting the metabolism of glutamine. This review not only summarizes the significance of glutamine metabolism in NSCLC cells, but also enumerates traditional glutamine inhibitors along with new targets. It also puts forward the concept of combination therapy and patient stratification with the aim of comprehensively showing the effect and prospect of targeted glutamine metabolism in NSCLC therapy. This review was completed by searching for keywords including 'glutamine', 'NSCLC' and 'therapy' on PubMed, and screening out articles.

Controlling the confounding effect of metabolic gene expression to identify actual metabolite targets in microsatellite instability cancers

BACKGROUND

The metabolome is the best representation of cancer phenotypes. Gene expression can be considered a confounding covariate affecting metabolite levels. Data integration across metabolomics and genomics to establish the biological relevance of cancer metabolism is challenging. This study aimed to eliminate the confounding effect of metabolic gene expression to reflect actual metabolite levels in microsatellite instability (MSI) cancers.

METHODS

In this study, we propose a new strategy using covariate-adjusted tensor classification in high dimensions (CATCH) models to integrate metabolite and metabolic gene expression data to classify MSI and microsatellite stability (MSS) cancers. We used datasets from the Cancer Cell Line Encyclopedia (CCLE) phase II project and treated metabolomic data as tensor predictors and data on gene expression of metabolic enzymes as confounding covariates.

RESULTS

The CATCH model performed well, with high accuracy (0.82), sensitivity (0.66), specificity (0.88), precision (0.65), and F1 score (0.65). Seven metabolite features adjusted for metabolic gene expression, namely, 3-phosphoglycerate, 6-phosphogluconate, cholesterol ester, lysophosphatidylethanolamine (LPE), phosphatidylcholine, reduced glutathione, and sarcosine, were found in MSI cancers. Only one metabolite, Hippurate, was present in MSS cancers. The gene expression of phosphofructokinase 1 (PFKP), which is involved in the glycolytic pathway, was related to 3-phosphoglycerate. ALDH4A1 and GPT2 were associated with sarcosine. LPE was associated with the expression of CHPT1, which is involved in lipid metabolism. The glycolysis, nucleotide, glutamate, and lipid metabolic pathways were enriched in MSI cancers.

CONCLUSIONS

We propose an effective CATCH model for predicting MSI cancer status. By controlling the confounding effect of metabolic gene expression, we identified cancer metabolic biomarkers and therapeutic targets. In addition, we provided the possible biology and genetics of MSI cancer metabolism.