Glutaminase regulation in cancer cells: a druggable chain of events

Effects of metabolism upon immunity: Targeting myeloid-derived suppressor cells for the treatment of breast cancer is a promising area of study

Breast cancer (BC) ranks among the most prevalent malignancies affecting women, with advanced-stage patients facing an increased mortality risk. Myeloid-derived suppressor cells (MDSCs) contribute significantly to poor prognostic outcomes. Research has concentrated predominantly on the immunological mechanisms underlying MDSC functions, but a comprehensive investigation into the metabolic interactions between BC cells and MDSCs is lacking. In a hypoxic tumor microenvironment (TME), BC cells can enhance aerobic-glycolysis rates, upregulate expression of key lipid metabolism enzymes such as cluster of differentiation (CD) 36 and 5-lipoxygenase (5-LOX), accelerate glutamine (Gln) uptake, and elevate extracellular adenosine (eADO) levels, thereby fostering MDSC proliferation and amplifying immune suppression. Concurrently, alterations in the metabolic state of MDSCs also influence BC progression. To ensure adequate proliferative resources, MDSCs upregulate the pentose phosphate pathway and expedite glycolysis for energy supply while increasing the expression of fatty acid transport proteins (FATPs) such as CD36 and fatty acid transporter 2 (FATP2) to maintain intracellular lipid availability, thereby enhancing their adaptability within the TME. Furthermore, MDSCs undermine T-cell anti-tumor efficacy by depleting essential amino acids (AAs), such as arginine (Arg), tryptophan (Trp), and cysteine (Cys), required for T-cell function. This review elucidates how pharmacological agents such as metformin, liver X receptor (LXR) agonists, and 6-diazo-5-oxo-L-norleucine (DON) can augment anti-cancer treatment efficacy by targeting metabolic pathways in MDSCs. We systematically delineate the mechanisms governing interactions between BC cells and MDSCs from a metabolic standpoint while summarizing therapeutic strategies to modulate metabolism within MDSCs. Our review provides a framework for optimizing MDSC applications in BC immunotherapy.

Integrative pan-cancer analysis and experiment validation identified GLS as a biomarker in tumor progression, prognosis, immune microenvironment, and immunotherapy

Glutaminase (GLS), a crucial gene regulating glutaminolysis, has received much attention as it was found to regulate tumor metabolism and copper-induced cell death. However, its biological roles and mechanisms in human cancers remain obscure. Consequently, the integrated pan-cancer analyses and biological experiments were conducted to elucidate its oncological functions. We found GLS was differentially expressed in human cancers and upregulated GLS predicted poor survival, clinicopathological progression, and tumor heterogeneity. Single-cell analysis found GLS was closely related to various biological functions and pathways. Spatial transcriptomic analysis found GLS expression was mainly derived from tumor cells, which implies tumor cells may have a stronger ability to utilize glutamine than antitumor immune cells in the tumor microenvironment (TME). Meanwhile, we noticed GLS expression was strongly related to the infiltration of various immune cells and stromal cells, the expression of immunomodulatory genes, the activity of some conventional antitumor agents, and the therapeutic response of immunotherapy. Moreover, enrichment analyses suggested GLS was related to various metabolic reprogramming, innate and adaptive immunity suppression, and extracellular matrix remodeling. Finally, we observed GLS was highly expressed in our gastric cancer (GC) cohort. As an independent risk factor for GC prognosis, high-GLS was closely related to pathological progression. Inhibiting GLS expression in GC cells effectively prevented proliferation, migration, and invasion and triggered apoptosis. In conclusion, GLS is an underlying biomarker for oncological progression, prognosis, TME, antitumor drug sensitivity, and immunotherapy response. Targeting GLS can facilitate the implementation of individualized and combined treatment strategies.

Clinical research framework proposal for ketogenic metabolic therapy in glioblastoma

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with a universally lethal prognosis despite maximal standard therapies. Here, we present a consensus treatment protocol based on the metabolic requirements of GBM cells for the two major fermentable fuels: glucose and glutamine. Glucose is a source of carbon and ATP synthesis for tumor growth through glycolysis, while glutamine provides nitrogen, carbon, and ATP synthesis through glutaminolysis. As no tumor can grow without anabolic substrates or energy, the simultaneous targeting of glycolysis and glutaminolysis is expected to reduce the proliferation of most if not all GBM cells. Ketogenic metabolic therapy (KMT) leverages diet-drug combinations that inhibit glycolysis, glutaminolysis, and growth signaling while shifting energy metabolism to therapeutic ketosis. The glucose-ketone index (GKI) is a standardized biomarker for assessing biological compliance, ideally via real-time monitoring. KMT aims to increase substrate competition and normalize the tumor microenvironment through GKI-adjusted ketogenic diets, calorie restriction, and fasting, while also targeting glycolytic and glutaminolytic flux using specific metabolic inhibitors. Non-fermentable fuels, such as ketone bodies, fatty acids, or lactate, are comparatively less efficient in supporting the long-term bioenergetic and biosynthetic demands of cancer cell proliferation. The proposed strategy may be implemented as a synergistic metabolic priming baseline in GBM as well as other tumors driven by glycolysis and glutaminolysis, regardless of their residual mitochondrial function. Suggested best practices are provided to guide future KMT research in metabolic oncology, offering a shared, evidence-driven framework for observational and interventional studies.

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.

Glucose and glutamine drive hepatitis E virus replication

Viruses have undergone evolutionary adaptations to tune their utilization of carbon sources, enabling them to extract specific cellular substrates necessary for their replication. The lack of a reliable cell culture system and a small-animal model has hampered our understanding of the molecular mechanism of replication of hepatitis E virus (HEV) genotype 1. Our recent identification of a replicative ensemble of mutant HEV RNA libraries has allowed us to study the metabolic prerequisites for HEV replication. Initial assessments revealed increased glucose and glutamine utilization during HEV replication. Inhibition of glycolysis and glycolysis + glutaminolysis reduced the levels of HEV replication to similar levels. An integrated analysis of protein-metabolite pathways suggests that HEV replication markedly alters glycolysis, the TCA cycle, and glutamine-associated metabolic pathways. Cells supporting HEV replication showed a requirement for fructose-6-phosphate and glutamine utilization through the hexosamine biosynthetic pathway (HBP), stimulating HSP70 expression to facilitate virus replication. Observations of mannose utilization and glutamine dependence suggest a crucial role of the HBP in supporting HEV replication. Inhibition of glycolysis and HSP70 activity or knockdown of glutamine fructose-6-phosphate amidotransferase expression led to a substantial reduction in HEV RNA and ORF2 expression accompanied by a significant decrease in HSP70 levels. This study demonstrates that glucose and glutamine play critical roles in facilitating HEV replication.

Discovery and Optimization of Ergosterol Peroxide Derivatives as Novel Glutaminase 1 Inhibitors for the Treatment of Triple-Negative Breast Cancer

In this study, novel ergosterol peroxide (EP) derivatives were synthesized and evaluated to assess their antiproliferative activity against four human cancer cell lines (A549, HepG2, MCF-7, and MDA-MB-231). Compound 3g exhibited the most potent antiproliferative activity, with an IC50 value of 3.20 µM against MDA-MB-231. This value was 5.4-fold higher than that of the parental EP. Bioassay optimization further identified 3g as a novel glutaminase 1 (GLS1) inhibitor (IC50 = 3.77 µM). In MDA-MB-231 cells, 3g reduced the cellular glutamate levels by blocking the glutamine hydrolysis pathway, which triggered reactive oxygen species production and induced caspase-dependent apoptosis. Molecular docking indicated that 3g interacts with the reaction site of the variable binding pocket by forming multiple interactions with GLS1. In a mouse model of breast cancer, 3g showed remarkable therapeutic effects at a dose of 50 mg/kg, with no apparent toxicity. Based on these results, 3g could be further evaluated as a novel GLS1 inhibitor for triple-negative breast cancer (TNBC) therapy.

Synergistic Effects of Glutamine Deprivation and Metformin in Acute Myeloid Leukemia

OBJECTIVE

The metabolic reprogramming of acute myeloid leukemia (AML) cells is a compensatory adaptation to meet energy requirements for rapid proliferation. This study aimed to examine the synergistic effects of glutamine deprivation and metformin exposure on AML cells.

METHODS

SKM-1 cells (an AML cell line) were subjected to glutamine deprivation and/or treatment with metformin or bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl) ethyl sulfide (BPTES, a glutaminase inhibitor) or cytarabine. Cell viability was detected by Cell Counting Kit-8 (CCK-8) assay, and cell apoptosis and reactive oxygen species (ROS) by flow cytometry. Western blotting was conducted to examine the levels of apoptotic proteins, including cleaved caspase-3 and poly(ADP-ribose) polymerase (PARP). Moreover, the human long noncoding RNA (lncRNA) microarray was used to analyze gene expression after glutamine deprivation, and results were confirmed with quantitative RT-PCR (qRT-PCR). The expression of metallothionein 2A (MT2A) was suppressed using siRNA. Cell growth and apoptosis were further detected by CCK-8 assay and flow cytometry, respectively, in cells with MT2A knockdown.

RESULTS

Glutamine deprivation or treatment with BPTES inhibited cell growth and induced apoptosis in SKM-1 cells. The lncRNA microarray result showed that the expression of MT family genes was significantly upregulated after glutamine deprivation. MT2A knockdown increased apoptosis, while proliferation was not affected in SKM-1 cells. In addition, metformin inhibited cell growth and induced apoptosis in SKM-1 cells. Both glutamine deprivation and metformin enhanced the sensitivity of SKM-1 cells to cytarabine. Furthermore, the combination of glutamine deprivation with metformin exhibited synergistic antileukemia effects on SKM-1 cells.

CONCLUSION

Targeting glutamine metabolism in combination with metformin is a promising new therapeutic strategy for AML.

Norovirus NS1/2 protein increases glutaminolysis for efficient viral replication

Viruses are obligate intracellular parasites that rely on host cell metabolism for successful replication. Thus, viruses rewire host cell pathways involved in central carbon metabolism to increase the availability of building blocks for successful propagation. However, the underlying mechanisms of virus-induced alterations to host metabolism are largely unknown. Noroviruses (NoVs) are highly prevalent pathogens that cause sporadic and epidemic viral gastroenteritis. In the present study, we uncovered several strain-specific and shared host cell metabolic requirements of three murine norovirus (MNV) strains, MNV-1, CR3, and CR6. While all three strains required glycolysis, glutaminolysis, and the pentose phosphate pathway for optimal infection of macrophages, only MNV-1 relied on host oxidative phosphorylation. Furthermore, the first metabolic flux analysis of NoV-infected cells revealed that both glycolysis and glutaminolysis are upregulated during MNV-1 infection of macrophages. Glutamine deprivation affected the viral lifecycle at the stage of genome replication, resulting in decreased non-structural and structural protein synthesis, viral assembly, and egress. Mechanistic studies further showed that MNV infection and overexpression of the non-structural protein NS1/2 increased the enzymatic activity of the rate-limiting enzyme glutaminase. In conclusion, the inaugural investigation of NoV-induced alterations to host glutaminolysis identified NS1/2 as the first viral molecule for RNA viruses that regulates glutaminolysis either directly or indirectly. This increases our fundamental understanding of virus-induced metabolic alterations and may lead to improvements in the cultivation of human NoVs.

Sirtuin 5 alleviates apoptosis and autophagy stimulated by ammonium chloride in bovine mammary epithelial cells

Ammonia (NH3) is an irritating and harmful gas that affects cell apoptosis and autophagy. Sirtuin 5 (SIRT5) has multiple enzymatic activities and regulates NH3-induced autophagy in tumor cells. In order to determine whether SIRT5 regulates NH3-induced bovine mammary epithelial cell apoptosis and autophagy, cells with SIRT5 overexpression or knockdown were generated and in addition, bovine mammary epithelial cells were treated with SIRT5 inhibitors. The results showed that SIRT5 overexpression reduced the content of NH3 and glutamate in cells by inhibiting glutaminase activity in glutamine metabolism, and reduced the ratio of ADP/ATP. The results in the SIRT5 knockdown and inhibitor groups were comparable, including increased content of NH3 and glutamate in cells by activating glutaminase activity, and an elevated ratio of ADP/ATP. It was further confirmed that SIRT5 inhibited the apoptosis and autophagy of bovine mammary epithelial cells through reverse transcription-quantitative PCR, western blot, flow cytometry with Annexin V FITC/PI staining and transmission electron microscopy. In addition, it was also found that the addition of LY294002 or Rapamycin inhibited the PI3K/Akt or mTOR kinase signal, decreasing the apoptosis and autophagy activities of bovine mammary epithelial cells induced by SIRT5-inhibited NH3. In summary, the PI3K/Akt/mTOR signal involved in NH3-induced cell autophagy and apoptosis relies on the regulation of SIRT5. This study provides a new theory for the use of NH3 to regulate bovine mammary epithelial cell apoptosis and autophagy, and provides guidance for improving the health and production performance of dairy cows.

Metabolic Rewiring in Cancer: Small Molecule Inhibitors in Colorectal Cancer Therapy

Alterations in cellular metabolism, such as dysregulation in glycolysis, lipid metabolism, and glutaminolysis in response to hypoxic and low-nutrient conditions within the tumor microenvironment, are well-recognized hallmarks of cancer. Therefore, understanding the interplay between aerobic glycolysis, lipid metabolism, and glutaminolysis is crucial for developing effective metabolism-based therapies for cancer, particularly in the context of colorectal cancer (CRC). In this regard, the present review explores the complex field of metabolic reprogramming in tumorigenesis and progression, providing insights into the current landscape of small molecule inhibitors targeting tumorigenic metabolic pathways and their implications for CRC treatment.

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.

The roles of epigallocatechin gallate in the tumor microenvironment, metabolic reprogramming, and immunotherapy

Cancer, a disease that modern medicine has not fully understood and conquered, with its high incidence and mortality, deprives countless patients of health and even life. According to global cancer statistics, there were an estimated 19.3 million new cancer cases and nearly 10 million cancer deaths in 2020, with the age-standardized incidence and mortality rates of 201.0 and 100.7 per 100,000, respectively. Although remarkable advancements have been made in therapeutic strategies recently, the overall prognosis of cancer patients remains not optimistic. Consequently, there are still many severe challenges to be faced and difficult problems to be solved in cancer therapy today. Epigallocatechin gallate (EGCG), a natural polyphenol extracted from tea leaves, has received much attention for its antitumor effects. Accumulating investigations have confirmed that EGCG can inhibit tumorigenesis and progression by triggering apoptosis, suppressing proliferation, invasion, and migration, altering tumor epigenetic modification, and overcoming chemotherapy resistance. Nevertheless, its regulatory roles and biomolecular mechanisms in the immune microenvironment, metabolic microenvironment, and immunotherapy remain obscure. In this article, we summarized the most recent updates about the effects of EGCG on tumor microenvironment (TME), metabolic reprogramming, and anti-cancer immunotherapy. The results demonstrated EGCG can promote the anti-cancer immune response of cytotoxic lymphocytes and dendritic cells (DCs), attenuate the immunosuppression of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs), and inhibit the tumor-promoting functions of tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), and various stromal cells including cancer-associated fibroblasts (CAFs), endothelial cells (ECs), stellate cells, and mesenchymal stem/stromal cells (MSCs). Additionally, EGCG can suppress multiple metabolic reprogramming pathways, including glucose uptake, aerobic glycolysis, glutamine metabolism, fatty acid anabolism, and nucleotide synthesis. Finally, EGCG, as an immunomodulator and immune checkpoint blockade, can enhance immunotherapeutic efficacy and may be a promising candidate for antitumor immunotherapy. In conclusion, EGCG plays versatile regulatory roles in TME and metabolic reprogramming, which provides novel insights and combined therapeutic strategies for cancer immunotherapy.

Norovirus NS1/2 protein increases glutaminolysis for efficient viral replication

Viruses are obligate intracellular parasites that rely on host cell metabolism for successful replication. Thus, viruses rewire host cell pathways involved in central carbon metabolism to increase the availability of building blocks for replication. However, the underlying mechanisms of virus-induced alterations to host metabolism are largely unknown. Noroviruses (NoVs) are highly prevalent pathogens that cause sporadic and epidemic viral gastroenteritis. In the present study, we uncovered several strain-specific and shared host cell metabolic requirements of three murine norovirus (MNV) strains, the acute MNV-1 strain and the persistent CR3 and CR6 strains. While all three strains required glycolysis, glutaminolysis, and the pentose phosphate pathway for optimal infection of macrophages, only MNV-1 relied on host oxidative phosphorylation. Furthermore, the first metabolic flux analysis of NoV-infected cells revealed that both glycolysis and glutaminolysis are upregulated during MNV-1 infection of macrophages. Glutamine deprivation affected the MNV lifecycle at the stage of genome replication, resulting in decreased non-structural and structural protein synthesis, viral assembly, and egress. Mechanistic studies further showed that MNV infection and overexpression of the MNV non-structural protein NS1/2 increased the enzymatic activity of the rate-limiting enzyme glutaminase. In conclusion, the inaugural investigation of NoV-induced alterations to host glutaminolysis identified the first viral regulator of glutaminolysis for RNA viruses, which increases our fundamental understanding of virus-induced metabolic alterations.

Sijunzi Tang improves gefitinib resistance by regulating glutamine metabolism

Lung cancer is a major health concern and significant barrier to human well-being and social development. Although targeted therapy has shown remarkable progress in the treatment of lung cancer, the emergence of drug resistance has limited its clinical efficacy. Sijunzi Tang (SJZ) is a classical Chinese herbal formula known for tonifying qi and nourishing the lungs, has been recognized for its potential in lung cancer management. However, the underlying mechanism of its combined use with anti-cancer drugs remains unclear. Here, we investigated the anti-lung cancer efficacy and underlying mechanisms of the combination of gefitinib and SJZ in gefitinib-resistant human lung adenocarcinoma cells (PC-9/GR). We conducted in vitro and in vivo experiments using histopathology and targeted metabolomics approaches. Our results demonstrated that the combination of SJZ and gefitinib exhibited synergistic effects on tumor growth inhibition in PC-9/GR-bearing nude mice. Notably, the co-administration of SJZ and gefitinib synergistically promoted tumor cell apoptosis, potentially through the regulation of BAX and BCL-2 expression. Immunohistochemistry and western blot analysis found down-regulation of GLS, GS, and SLC1A5 expression in the co-administration group compared to the control and the individual treatment groups. Targeted metabolomics revealed significant alterations in the plasma glutamine metabolic markers glutamine, alanine, succinate, glutamate, and pyruvate. Of the glutamine metabolism markers measured in tumor tissues, glutamine and pyruvate demonstrated significant differences across the treatment groups. These findings suggest that administration of SJZ improves gefitinib resistance in the treatment of lung cancer without toxic effects. Moreover, SJZ may affect glutamine metabolism by regulating key targets involved in glutamine metabolism (SLC1A5, GLS, and GS) and modulating the levels of related metabolic markers, ultimately reducing gefitinib resistance.

Targeting cellular metabolism in head and neck cancer precision medicine era: A promising strategy to overcome therapy resistance

Head and neck squamous cell carcinoma (HNSCC) is among the most prevalent cancer worldwide, with the most severe impact on quality of life of patients. Despite the development of multimodal therapeutic approaches, the clinical outcomes of HNSCC are still unsatisfactory, mainly caused by relatively low responsiveness to treatment and severe drug resistance. Metabolic reprogramming is currently considered to play a pivotal role in anticancer therapeutic resistance. This review aimed to define the specific metabolic programs and adaptations in HNSCC therapy resistance. An extensive literature review of HNSCC was conducted via the PubMed including metabolic reprogramming, chemo- or immune-therapy resistance. Glucose metabolism, fatty acid metabolism, and amino acid metabolism are closely related to the malignant biological characteristics of cancer, anti-tumor drug resistance, and adverse clinical results. For HNSCC, pyruvate, lactate and almost all lipid categories are related to the occurrence and maintenance of drug resistance, and targeting amino acid metabolism can prevent tumor development and enhance the response of drug-resistant tumors to anticancer therapy. This review will provide a better understanding of the altered metabolism in therapy resistance of HNSCC and promote the development of new therapeutic strategies against HNSCC, thereby contribute to a more efficacious precision medicine.

Glutamine metabolism in breast cancer and possible therapeutic targets

Cancer is characterized by metabolic reprogramming, which is a hot topic in tumor treatment research. Cancer cells alter metabolic pathways to promote their growth, and the common purpose of these altered metabolic pathways is to adapt the metabolic state to the uncontrolled proliferation of cancer cells. Most cancer cells in a state of nonhypoxia will increase the uptake of glucose and produce lactate, called the Warburg effect. Increased glucose consumption is used as a carbon source to support cell proliferation, including nucleotide, lipid and protein synthesis. In the Warburg effect, pyruvate dehydrogenase activity decreases, thereby disrupting the TCA cycle. In addition to glucose, glutamine is also an important nutrient for the growth and proliferation of cancer cells, an important carbon bank and nitrogen bank for the growth and proliferation of cancer cells, providing ribose, nonessential amino acids, citrate, and glycerin necessary for cancer cell growth and proliferation and compensating for the reduction in oxidative phosphorylation pathways in cancer cells caused by the Warburg effect. In human plasma, glutamine is the most abundant amino acid. Normal cells produce glutamine via glutamine synthase (GLS), but the glutamine synthesized by tumor cells is insufficient to meet their high growth needs, resulting in a "glutamine-dependent phenomenon." Most cancers have an increased glutamine demand, including breast cancer. Metabolic reprogramming not only enables tumor cells to maintain the reduction-oxidation (redox) balance and commit resources to biosynthesis but also establishes heterogeneous metabolic phenotypes of tumor cells that are distinct from those of nontumor cells. Thus, targeting the metabolic differences between tumor and nontumor cells may be a promising and novel anticancer strategy. Glutamine metabolic compartments have emerged as promising candidates, especially in TNBC and drug-resistant breast cancer. In this review, the latest discoveries of breast cancer and glutamine metabolism are discussed, novel treatment methods based on amino acid transporters and glutaminase are discussed, and the relationship between glutamine metabolism and breast cancer metastasis, drug resistance, tumor immunity and ferroptosis are explained, which provides new ideas for the clinical treatment of breast cancer.

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.

Alone and together: current approaches to targeting glutaminase enzymes as part of anti-cancer therapies

Metabolic reprogramming is a major hallmark of malignant transformation in cancer, and part of the so-called Warburg effect, in which the upregulation of glutamine catabolism plays a major role. The glutaminase enzymes convert glutamine to glutamate, which initiates this pathway. Inhibition of different forms of glutaminase (KGA, GAC, or LGA) demonstrated potential as an emerging anti-cancer therapeutic strategy. The regulation of these enzymes, and the molecular basis for their inhibition, have been the focus of much recent research. This review will explore the recent progress in understanding the molecular basis for activation and inhibition of different forms of glutaminase, as well as the recent focus on combination therapies of glutaminase inhibitors with other anti-cancer drugs.

Recent progress of amino acid transporters as a novel antitumor target

Glutamine transporters transport different amino acids for cell growth and metabolism. In tumor cells, glutamine transporters are often highly expressed and play a crucial role in their growth. By inhibiting the amino acid transport of these transporters, the growth of cancer cells can be inhibited. In recent years, more and more attention has been paid to the study of glutamine transporter. In this article, the differences between the ASC system amino acid transporter 2 (ASCT2), L-type amino acid transporter 1 (LAT1), and the cystine–glutamate exchange (xCT) transporters research progress on the mechanism of action and corresponding small molecule inhibitors are summarized. This article introduces 62 related small molecule inhibitors of different transporters of ASCT2, LAT1, and xCT. These novel chemical structures provide ideas for the research and design of targeted inhibitors of glutamine transporters, as well as important references and clues for the design of new anti-tumor drugs.

Hormone-Glutamine Metabolism: A Critical Regulatory Axis in Endocrine-Related Cancers

The endocrine-related cancers and hormones are undoubtedly highly interconnected. How hormones support or repress tumor induction and progression has been extensively profiled. Furthermore, advances in understanding the role of glutamine metabolism in mediating tumorigenesis and development, coupled with these in-depth studies on hormone (e.g., estrogen, progesterone, androgen, prostaglandin, thyroid hormone, and insulin) regulation of glutamine metabolism, have led us to think about the relationship between these three factors, which remains to be elucidated. Accordingly, in this review, we present an updated overview of glutamine metabolism traits and its influence on endocrine oncology, as well as its upstream hormonal regulation. More importantly, this hormone/glutamine metabolism axis may help in the discovery of novel therapeutic strategies for endocrine-related cancer.

New Avenues of Heme Synthesis Regulation

During erythropoiesis, there is an enormous demand for the synthesis of the essential cofactor of hemoglobin, heme. Heme is synthesized de novo via an eight enzyme-catalyzed pathway within each developing erythroid cell. A large body of data exists to explain the transcriptional regulation of the heme biosynthesis enzymes, but until recently much less was known about alternate forms of regulation that would allow the massive production of heme without depleting cellular metabolites. Herein, we review new studies focused on the regulation of heme synthesis via carbon flux for porphyrin synthesis to post-translations modifications (PTMs) that regulate individual enzymes. These PTMs include cofactor regulation, phosphorylation, succinylation, and glutathionylation. Additionally discussed is the role of the immunometabolite itaconate and its connection to heme synthesis and the anemia of chronic disease. These recent studies provide new avenues to regulate heme synthesis for the treatment of diseases including anemias and porphyrias.

Targeting mTORC2/HDAC3 Inhibits Stemness of Liver Cancer Cells Against Glutamine Starvation

Cancer cells are addicted to glutamine. However, cancer cells often suffer from glutamine starvation, which largely results from the fast growth of cancer cells and the insufficient vascularization in the interior of cancer tissues. Herein, based on clinical samples, patient-derived cells (PDCs), and cell lines, it is found that liver cancer cells display stem-like characteristics upon glutamine shortage due to maintaining the stemness of tumor initiating cells (TICs) and even promoting transformation of non-TICs into stem-like cells by glutamine starvation. Increased expression of glutamine synthetase (GS) is essential for maintaining and promoting stem-like characteristics of liver cancer cells during glutamine starvation. Mechanistically, glutamine starvation activates Rictor/mTORC2 to induce HDAC3-mediated deacetylation and stabilization of GS. Rictor is significantly correlated with the expression of GS and stem marker OCT4 at tumor site, and closely correlates with poor prognosis of hepatocellular carcinomas. Inhibiting components of mTORC2-HDAC3-GS axis decrease TICs and promote xenografts regression upon glutamine-starvation therapy. Collectively, the data provides novel insights into the role of Rictor/mTORC2-HDAC3 in reprogramming glutamine metabolism to sustain stemness of cancer cells. Targeting Rictor/HDAC3 may enhance the efficacy of glutamine-starvation therapy and limit the rapid growth and malignant progression of tumors.

Zeolitic imidazolate framework-based nanoparticles for the cascade enhancement of cancer chemodynamic therapy by targeting glutamine metabolism

The reprogrammed amino acid metabolism maintains the powerful antioxidant defense and DNA damage repair capacity of cancer cells, which could promote their escape from reactive oxygen species (ROS)-induced damage and inevitably diminish the efficacy of ROS-based therapies. Herein, we propose a strategy to enhance the effect of chemodynamic therapy (CDT) via glutaminolysis-targeted inhibition for cancer cells dependent on abnormal glutamine metabolism. To screen optimum drugs targeting glutamine metabolism, transcriptomic analysis is performed to identify predictive biomarkers. Eventually, telaglenastat (CB-839) is used to block mitochondrial glutaminase 1 (GLS 1) in basal-like breast cancer and loaded into the developed iron-doped zeolitic imidazolate frameworks (ZIF(Fe) NPs) to form ZIF(Fe)&CB nanoparticles, which are able to co-deliver Fe²⁺ and CB-839 into the tumor. CB-839 induced-glutaminolysis inhibition not only reduces intracellular antioxidants (glutathione, taurine) to amplify Fe²⁺-induced oxidative stress, but also decreases nucleotide pools (e.g., adenosine, dihydroorotate) to incur the deficiency of building blocks for DNA damage repair, thereby promoting the cell-killing effect of CDT. In vivo assessments further confirm the enhanced anticancer performance and good biocompatibility of ZIF(Fe)&CB nanoparticles. This study provides a promising strategy for the development and improvement of ROS-based anticancer nanosystems.

Discovery of novel Glutaminase allosteric inhibitors through drug repurposing and comparative MMGB/PBSA and molecular dynamics simulation

GLS1 enzymes (Glutaminase C (GAC) and kidney-type Glutaminase (KGA)) are gaining prominence as a target for tumor treatment including lung, breast, kidney, prostate, and colorectal. To date, several medicinal chemistry studies are being conducted to develop new and effective inhibitors against GLS1 enzymes. Telaglenastat, a drug that targets the allosteric site of GLS1, has undergone clinical trials for the first time for the therapy of solid tumors and hematological malignancies. A comprehensive computational investigation is performed to get insights into the inhibition mechanism of the Telaglenastat. Some novel inhibitors are also proposed against GLS1 enzymes using the drug repurposing approach using 2D-fingerprinting virtual screening method against 2.4 million compounds, application of pharmacokinetics, Molecular Docking, and Molecular Dynamic (MD) Simulations. A TIP3P water box of 10 Å was defined to solvate both enzymes to improve MD simulation reliability. The dynamics results were validated further by the MMGB/PBSA binding free energy method, RDF, and AFD analysis. Results of these computational analysis revealed a stable binding affinity of Telaglenastat, as well as an FDA approved drug Astemizole (IC₅₀ ∼ 0.9 nM) and a novel para position oriented methoxy group containing Chembridge compound (Chem-64284604) that provides an effective inhibitory action against GAC and KGA.

Succinate receptor 1 inhibits mitochondrial respiration in cancer cells addicted to glutamine

Cancer cells display metabolic alterations to meet the bioenergetic demands for their high proliferation rates. Succinate is a central metabolite of the tricarboxylic acid (TCA) cycle, but was also shown to act as an oncometabolite and to specifically activate the succinate receptor 1 (SUCNR1), which is expressed in several types of cancer. However, functional studies focusing on the connection between SUCNR1 and cancer cell metabolism are still lacking. In the present study, we analyzed the role of SUCNR1 for cancer cell metabolism and survival applying different signal transduction, metabolic and imaging analyses. We chose a gastric, a lung and a pancreatic cancer cell line for which our data revealed functional expression of SUCNR1. Further, presence of glutamine (Gln) caused high respiratory rates and elevated expression of SUCNR1. Knockdown of SUCNR1 resulted in a significant increase of mitochondrial respiration and superoxide production accompanied by an increase in TCA cycle throughput and a reduction of cancer cell survival in the analyzed cancer cell lines. Combination of SUCNR1 knockdown and treatment with the chemotherapeutics cisplatin and gemcitabine further increased cancer cell death. In summary, our data implicates that SUCNR1 is crucial for Gln-addicted cancer cells by limiting TCA cycle throughput, mitochondrial respiration and the production of reactive oxygen species, highlighting its potential as a pharmacological target for cancer treatment.

The potential role of exosomal circRNAs in the tumor microenvironment: insights into cancer diagnosis and therapy

Exosomes are multifunctional regulators of intercellular communication by carrying various messages under both physiological and pathological status of cancer patients. Accumulating studies have identified the presence of circular RNAs (circRNAs) in exosomes with crucial regulatory roles in diverse pathophysiological processes. Exosomal circRNAs derived from donor cells can modulate crosstalk with recipient cells locally or remotely to enhance cancer development and propagation, and play crucial roles in the tumor microenvironment (TME), leading to significant enhancement of tumor immunity, metabolism, angiogenesis, drug resistance, epithelial mesenchymal transition (EMT), invasion and metastasis. In this review, we describe the advances of exosomal circRNAs and their roles in modulating cancer hallmarks, especially those in the TME. Moreover, clinical application potential of exosomal circRNAs in cancer diagnosis and therapy are highlighted, bridging the gap between basic knowledge and clinical practice.

The Neglected Liaison: Targeting Cancer Cell Metabolic Reprogramming Modifies the Composition of Non-Malignant Populations of the Tumor Microenvironment

Metabolic reprogramming is a well-known hallmark of cancer, whereby the development of drugs that target cancer cell metabolism is gaining momentum. However, when establishing preclinical studies and clinical trials, it is often neglected that a tumor mass is a complex system in which cancer cells coexist and interact with several types of microenvironment populations, including endothelial cells, fibroblasts and immune cells. We are just starting to understand how such populations are affected by the metabolic changes occurring in a transformed cell and little is known about the impact of metabolism-targeting drugs on the non-malignant tumor components. Here we provide a general overview of the links between cancer cell metabolism and tumor microenvironment (TME), particularly focusing on the emerging literature reporting TME-specific effects of metabolic therapies.

Role of glutamine and its metabolite ammonia in crosstalk of cancer-associated fibroblasts and cancer cells

Cancer-associated fibroblasts (CAFs), the most abundant cells in the tumor microenvironment, play an indispensable role in cancer initiation, progression, metastasis, and metabolism. The limitations of traditional treatments can be partly attributed to the lack of understanding of the role of the tumor stroma. For this reason, CAF targeting is gradually gaining attention, and many studies are trying to overcome the limitations of tumor treatment with CAF as a breakthrough. Glutamine (GLN) has been called a “nitrogen reservoir” for cancer cells because of its role in supporting anabolic processes such as fuel proliferation and nucleotide synthesis, but ammonia is a byproduct of the metabolism of GLN and other nitrogenous compounds. Moreover, in some studies, GLN has been reported as a fundamental nitrogen source that can support tumor biomass. In this review, we discuss the latest findings on the role of GLN and ammonia in the crosstalk between CAFs and cancer cells as well as the potential therapeutic implications of nitrogen metabolism.

More Than Meets the Eye Regarding Cancer Metabolism

In spite of the continuous improvement in our knowledge of the nature of cancer, the causes of its formation and the development of new treatment methods, our knowledge is still incomplete. A key issue is the difference in metabolism between normal and cancer cells. The features that distinguish cancer cells from normal cells are the increased proliferation and abnormal differentiation and maturation of these cells, which are due to regulatory changes in the emerging tumour. Normal cells use oxidative phosphorylation (OXPHOS) in the mitochondrion as a major source of energy during division. During OXPHOS, there are 36 ATP molecules produced from one molecule of glucose, in contrast to glycolysis which provides an ATP supply of only two molecules. Although aerobic glucose metabolism is more efficient, metabolism based on intensive glycolysis provides intermediate metabolites necessary for the synthesis of nucleic acids, proteins and lipids, which are in constant high demand due to the intense cell division in cancer. This is the main reason why the cancer cell does not "give up" on glycolysis despite the high demand for energy in the form of ATP. One of the evolving trends in the development of anti-cancer therapies is to exploit differences in the metabolism of normal cells and cancer cells. Currently constructed therapies, based on cell metabolism, focus on the attempt to reprogram the metabolic pathways of the cell in such a manner that it becomes possible to stop unrestrained proliferation.

circNFIX facilitates hepatocellular carcinoma progression by targeting miR-3064-5p/HMGA2 to enhance glutaminolysis

Hepatocellular carcinoma (HCC) is acknowledged to be a fatal malignant cancer around the world. Circular RNAs (circRNAs) function as crucial regulators in the pathological procession of HCC. Here, we elucidated the biological function of a novel circRNA, circNFIX, in HCC tumorigenesis. qRT-PCR was performed to determine the expressions of circNFIX, miR-3064-5p, and HMGA2. circNFIX stability was evaluated after treatment with ribonuclease R. The growth and invasion of HCC cells were assessed by CCK8 and transwell assays. Protein levels were measured by Western blotting. The levels of glutaminolysis metabolites were evaluated by commercial kits. Dual-luciferase report assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay were performed for validating the interaction between miR-3064-5p and circNFIX/HMGA2. Tumor growth in vivo was detected using xenograft assay. Our results showed that circNFIX was remarkably up-regulated in HCC and was associated with a poor survival. Knockdown of circNFIX repressed proliferation, invasion and glutaminolysis of HCC cells. Moreover, circNFIX directly sponged miR-3064-5p to release HMGA2 expression, and thus conferred the malignant development of HCC. In conclusion, circNFIX serves as a competing endogenous RNA to accelerate HCC progression via regulating miR-3064-5p/HMGA2 axis, suggesting a therapeutic strategy for HCC intervention.

Review and Prospect of Tissue-agnostic Targeted Strategies in Anticancer Therapies

Due to the increasing prevalence of cancer year by year, and the complexity and refractory nature of the disease itself, it is required to constantly innovate the development of new cancer treatment schemes. At the same time, the understanding of cancers has deepened, from the use of chemotherapy regimens with high toxicity and side effects, to the popularity of targeted drugs with specific targets, to precise treatments based on tumor characteristics rather than traditional anatomical location classification. In precision medicine, in the view of the specific cancer diseases and their biological characteristics, there is a great potential to develop tissue-agnostic targeted therapy with broad-spectrum anticancer significance. The present review has discussed tissue-agnostic targeted therapy based on the biological and genetic characteristics of cancers, expounded its theoretical basis and strategies for drug development. In addition, the feasible drug targets, FDA-approved drugs, as well as drug candidates in clinical trials have also been summarized. In conclusion, the "tissue-agnostic targeted therapy" is a breakthrough in anticancer therapies.

The expression of miR-513c and miR-3163 was downregulated in tumor tissues compared with normal adjacent tissue of patients with breast cancer

BACKGROUND

Breast cancer (BC) is the most invasive cancer with different subtypes that its metabolism is unique compared with normal cells. Glutamine is considered critical nutrition that many cancer cells, particularly BC cells, are dependent on it for growth and proliferation. Therefore, targeting glutamine metabolism, especially enzymes that are related to this pathway, can be beneficial to design anti-cancer agents. Recent evidence has shown that microRNAs (miRNAs), with a short length and single-strand properties, play a prominent role in regulating the genes related to glutamine metabolism, which may control the development of cancer.

METHODS

In silico analysis confirmed that miR-513c and miR-3163 might be involved in glutamine metabolism. The expression level of these two miRNAs was evaluated in eighty BC tissues and normal adjacent tissues. Furthermore, GSE38167, GSE38867, GSE42128, GSE45666, and GSE53179 were employed from gene expression omnibus (GEO). The Limma package was utilized to identify differentially expressed miRNAs (DEMs) of mentioned datasets to evaluate miR-513c and miR-3163 expression. Further, in silico analysis was utilized to predict the potential biological processes and molecular pathways of miR-513c and miR-3163, based on their target genes.

RESULTS

In silico studies revealed top categories of biological processes and cellular pathways that might play a critical role in metabolism reprogramming and cancer development and were target genes for miR-513c and miR-3163. The current study showed that miR-513c (p value = 0.02062 and FC =  - 2.3801) and miR-3163 (p value = 0.02034 and FC =  - 2.3792) were downregulated in tumor tissues compared to normal adjacent tissues. The analysis of GEO microarray datasets showed that miR-513c was downregulated in GSE38167, GSE38867, GSE42128, GSE45666 and GSE53179, whereas there was a significant downregulation of miR-3163 in only two studies, including GSE38867 and GSE42128 that they were in accordance with our experimental results. Furthermore, the subgroup analysis did not show any substantial relationship between expression levels of these two miRNAs and factors such as age, family history of cancer, and abortion history.

CONCLUSION

MiR-513c and miR-3163 were downregulated in BC tissues, which might serve as tumor suppressors. They are suggested as potential therapeutic targets for patients with BC.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

Glutaminolysis dynamics during astrocytoma progression correlates with tumor aggressiveness

Background

Glioblastoma is the most frequent and high-grade adult malignant central nervous system tumor. The prognosis is still poor despite the use of combined therapy involving maximal surgical resection, radiotherapy, and chemotherapy. Metabolic reprogramming currently is recognized as one of the hallmarks of cancer. Glutamine metabolism through glutaminolysis has been associated with tumor cell maintenance and survival, and with antioxidative stress through glutathione (GSH) synthesis.

Methods

In the present study, we analyzed the glutaminolysis-related gene expression levels in our cohort of 153 astrocytomas of different malignant grades and 22 non-neoplastic brain samples through qRT-PCR. Additionally, we investigated the protein expression profile of the key regulator of glutaminolysis (GLS), glutamate dehydrogenase (GLUD1), and glutamate pyruvate transaminase (GPT2) in these samples. We also investigated the glutathione synthase (GS) protein profile and the GSH levels in different grades of astrocytomas. The differential gene expressions were validated in silico on the TCGA database.

Results

We found an increase of glutaminase isoform 2 gene (GLSiso2) expression in all grades of astrocytoma compared to non-neoplastic brain tissue, with a gradual expression increment in parallel to malignancy. Genes coding for GLUD1 and GPT2 expression levels varied according to the grade of malignancy, being downregulated in glioblastoma, and upregulated in lower grades of astrocytoma (AGII–AGIII). Significant low GLUD1 and GPT2 protein levels were observed in the mesenchymal subtype of GBM.

Conclusions

In glioblastoma, particularly in the mesenchymal subtype, the downregulation of both genes and proteins (GLUD1 and GPT2) increases the source of glutamate for GSH synthesis and enhances tumor cell fitness due to increased antioxidative capacity. In contrast, in lower-grade astrocytoma, mainly in those harboring the IDH1 mutation, the gene expression profile indicates that tumor cells might be sensitized to oxidative stress due to reduced GSH synthesis. The measurement of GLUD1 and GPT2 metabolic substrates, ammonia, and alanine, by noninvasive MR spectroscopy, may potentially allow the identification of IDH1^mut AGII and AGIII progression towards secondary GBM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40170-021-00255-8.

Revealing the Potential Application of EC-Synthetic Retinoid Analogues in Anticancer Therapy

(1) Background and Aim: All-trans retinoic acid (ATRA) induces differentiation and inhibits growth of many cancer cells. However, resistance develops rapidly prompting the urgent need for new synthetic and potent derivatives. EC19 and EC23 are two synthetic retinoids with potent stem cell neuro-differentiation activity. Here, these compounds were screened for their in vitro antiproliferative and cytotoxic activity using an array of different cancer cell lines. (2) Methods: MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, AV/PI (annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI)), cell cycle analysis, immunocytochemistry, gene expression analysis, Western blotting, measurement of glutamate and total antioxidant concentrations were recruited. (3) Results: HepG2, Caco-2, and MCF-7 were the most sensitive cell lines; HepG2 (ATRA; 36.2, EC19; 42.2 and EC23; 0.74 µM), Caco-2 (ATRA; 58.0, EC19; 10.8 and EC23; 14.7 µM) and MCF-7 (ATRA; 99.0, EC19; 9.4 and EC23; 5.56 µM). Caco-2 cells were selected for further biochemical investigations. Isobologram analysis revealed the combined synergistic effects with 5-fluorouracil with substantial reduction in IC50. All retinoids induced apoptosis but EC19 had higher potency, with significant cell cycle arrest at subG0-G1, -S and G2/M phases, than ATRA and EC23. Moreover, EC19 reduced cellular metastasis in a transwell invasion assay due to overexpression of E-cadherin, retinoic acid-induced 2 (RAI2) and Werner (WRN) genes. (4) Conclusion: The present study suggests that EC-synthetic retinoids, particularly EC19, can be effective, alone or in combinations, for potential anticancer activity to colorectal cancer. Further in vivo studies are recommended to pave the way for clinical applications.

STK11/LKB1 Mutations in NSCLC Are Associated with KEAP1/NRF2-Dependent Radiotherapy Resistance Targetable by Glutaminase Inhibition

PURPOSE

Radiotherapy with or without chemotherapy is a mainstay of treatment for locally advanced non-small cell lung cancer (NSCLC), but no predictive markers are currently available to select patients who will benefit from these therapies. In this study, we investigated the association between alterations in STK11/LKB1, the second most common tumor suppressor in NSCLC, and response to radiotherapy as well as potential therapeutic approaches to improve outcomes.

EXPERIMENTAL DESIGN

We conducted a retrospective analysis of 194 patients with stage I-III NSCLC, including 164 stage III patients bearing mutant or wild-type STK11/LKB1 treated with radiotherapy, and assessed locoregional recurrence (LRR), distant metastasis rates, disease-free survival (DFS), and overall survival (OS), and we investigated the causal role of LKB1 in mediating radiotherapy resistance using isogenic pairs of NSCLC cell lines with LKB1 loss or gain.

RESULTS

In stage III patients, with 4 years median follow-up, STK11/LKB1 mutations were associated with higher LRR (P = 0.0108), and shorter DFS (HR 2.530, P = 0.0029) and OS (HR 2.198, P = 0.0263). LKB1 loss promoted relative resistance to radiotherapy, which was dependent on the KEAP1/NRF2 pathway for redox homeostasis. Suppression of the KEAP1/NRF2 pathway via KEAP1 expression, or pharmacologic blockade of glutaminase (GLS) 1 sensitized LKB1-deficient tumors to radiotherapy.

CONCLUSIONS

These data provide evidence that LKB1 loss is associated with LRR and poor clinical outcomes in patients with NSCLC treated with radiotherapy and that targeting the KEAP1/NRF2 pathway or GLS inhibition are potential approaches to radiosensitize LKB1-deficient tumors.

Metabolic Reprogramming of Cancer by Chemicals that Target Glutaminase Isoenzymes

BACKGROUND

Metabolic reprogramming of tumours is a hallmark of cancer. Among the changes in the metabolic network of cancer cells, glutaminolysis is a key reaction altered in neoplasms. Glutaminase proteins control the first step in glutamine metabolism and their expression correlates with malignancy and growth rate of a great variety of cancers. The two types of glutaminase isoenzymes, GLS and GLS2, differ in their expression patterns and functional roles: GLS has oncogenic properties and GLS2 has been described as a tumour suppressor factor.

RESULTS

We have focused on glutaminase connections with key oncogenes and tumour suppressor genes. Targeting glutaminase isoenzymes includes different strategies aimed at deactivating the rewiring of cancer metabolism. In addition, we found a long list of metabolic enzymes, transcription factors and signalling pathways dealing with glutaminase. On the other hand, a number of chemicals have been described as isoenzyme-specific inhibitors of GLS and/or GLS2 isoforms. These molecules are being characterized as synergic and therapeutic agents in many types of tumours.

CONCLUSION

This review states the metabolic pathways that are rewired in cancer, the roles of glutaminase isoforms in cancer, as well as the metabolic circuits regulated by glutaminases. We also show the plethora of anticancer drugs that specifically inhibit glutaminase isoenzymes for treating several sets of cancer.

Discovery and optimization of withangulatin A derivatives as novel glutaminase 1 inhibitors for the treatment of triple-negative breast cancer

To develop novel GLS1 inhibitors as effective therapeutic agents for triple-negative breast cancer (TNBC), 25 derivatives were synthesized from the natural inhibitor withangulatin A (IC₅₀ = 18.2 μM). Bioassay optimization identified a novel and selective GLS1 inhibitor 7 (IC₅₀ = 1.08 μM). In MDA-MB-231 cells, 7 diminished cellular glutamate levels by blocking glutaminolysis pathway, further triggering the generation of reactive oxygen species to induce caspase-dependent apoptosis. Molecular docking indicated that 7 interacted with a new reacting site of allosteric binding pocket by forming various interactions in GLS1. The intraperitoneal administration of 7 at a dose of 50 mg/kg exhibited remarkable therapeutic effects and no apparent toxicity in the MDA-MB-231 xenograft model, indicating its potential as a novel GLS1 inhibitor for treatment of TNBC.

Discovery of IPN60090, a Clinical Stage Selective Glutaminase-1 (GLS-1) Inhibitor with Excellent Pharmacokinetic and Physicochemical Properties

Inhibition of glutaminase-1 (GLS-1) hampers the proliferation of tumor cells reliant on glutamine. Known glutaminase inhibitors have potential limitations, and in vivo exposures are potentially limited due to poor physicochemical properties. We initiated a GLS-1 inhibitor discovery program focused on optimizing physicochemical and pharmacokinetic properties, and have developed a new selective inhibitor, compound 27 (IPN60090), which is currently in phase 1 clinical trials. Compound 27 attains high oral exposures in preclinical species, with strong in vivo target engagement, and should robustly inhibit glutaminase in humans.

Metabolic Signaling Cascades Prompted by Glutaminolysis in Cancer

Simple Summary

Within the last few years, accumulating evidences suggest the involvement of altered metabolisms in human diseases including cancer. Metabolism is defined as the sum of biochemical processes in living organisms that produce and consume energy. Tumor growth requires restructuring of cellular metabolism to meet the increasing demand for building blocks to support the ever-increasing cancer cell numbers. The principle of perturbed metabolism in tumors is known for 50–60 years, it regains greater appreciation within the last few years with the realization that there is interdependency between metabolism and all aspects of cellular function including regulation and control of cell growth. Tumor cells do not need stimulation signals from the surrounding environment to promote cell proliferation; in some cases, the tumor cells can generate their own growth signals. In order to support the continuous tumor cell growth even under stressful conditions, a change in metabolism is necessary to fulfill the continuous demand for energy and building blocks. A better understanding of the relationship between tumor environment and altered cell metabolisms will provide valuable insights to design innovative approaches to limit the supply of energy and macromolecules for the treatment of cancer including melanoma.

Abstract

Aberrant glutamatergic signaling has been implicated in altered metabolic activity and the demand to synthesize biomass in several types of cancer including melanoma. In the last decade, there has been a significant contribution to our understanding of metabolic pathways. An increasing number of studies are now emphasizing the importance of glutamate functioning as a signaling molecule and a building block for cancer progression. To that end, our group has previously illustrated the role of glutamatergic signaling mediated by metabotropic glutamate receptor 1 (GRM1) in neoplastic transformation of melanocytes in vitro and spontaneous development of metastatic melanoma in vivo. Glutamate, the natural ligand of GRM1, is one of the most abundant amino acids in humans and the predominant excitatory neurotransmitter in the central nervous system. Elevated levels of glutaminolytic mitochondrial tricarboxylic acid (TCA) cycle intermediates, especially glutamate, have been reported in numerous cancer cells. Herein, we highlight and critically review metabolic bottlenecks that are prevalent during tumor evolution along with therapeutic implications of limiting glutamate bioavailability in tumors.

Allosteric kidney-type glutaminase (GLS) inhibitors with a mercaptoethyl linker

A series of allosteric kidney-type glutaminase (GLS) inhibitors possessing a mercaptoethyl (SCH₂CH₂) linker were synthesized in an effort to further expand the structural diversity of chemotypes derived from bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES), a prototype allosteric inhibitor of GLS. BPTES analog 3a with a mercaptoethyl linker between the two thiadiazole rings was found to potently inhibit GLS with an IC₅₀ value of 50 nM. Interestingly, the corresponding derivative with an n-propyl (CH₂CH₂CH₂) linker showed substantially lower inhibitory potency (IC₅₀ = 2.3 μM) while the derivative with a dimethylsulfide (CH₂SCH₂) linker showed no inhibitory activity at concentrations up to 100 μM, underscoring the critical role played by the mercaptoethyl linker in the high affinity binding to the allosteric site of GLS. Additional mercaptoethyl-linked compounds were synthesized and tested as GLS inhibitors to further explore SAR within this scaffold including derivatives possessing a pyridazine as a replacement for one of the two thiadiazole moiety.

Glutaminase Inhibition on NSCLC Depends on Extracellular Alanine Exploitation

Non-small-cell lung cancer (NSCLC) cell lines vary in their sensitivity to glutaminase inhibitors, so it is important to identify the metabolic assets underling their efficacy in cancer cells. Even though specific genetic lesions such as in KRAS and LKB1 have been associated with reliance on glutamine for their metabolic needs, we found no distinction between glutaminase inhibitor CB-839 sensitivity and resistant phenotypes in NSCLC cells with or without these genetic alterations. We demonstrated the close relationship between environmental alanine uptake and catabolism. This response depended on the individual cell’s ability to employ alanine aminotransferase (GPT2) to compensate the reduced glutamate availability. It may, therefore, be useful to determine GPT2 levels to predict which NSCLC patients would benefit most from glutaminase inhibitor treatment.

Circ_0016418 promotes melanoma development and glutamine catabolism by regulating the miR-605-5p/GLS axis

BACKGROUND

Malignant melanoma is a skin cancer with a high rate of metastasis. Numerous circular RNAs (circRNAs) have been shown to play vital roles in melanoma. This research aimed to investigate the role and molecular basis of circ_0016418 in melanoma progression.

METHODS

The abundanced of circ_0016418, miR-605-5p and glutaminase (GLS) were measured using quantitative real-time polymerase chain reaction or western blot analysis. Cell proliferation was evaluated using Cell Counting Kit-8 (CCK-8) assay and colony formation assay. Cell migration and invasion were assessed by transwell assay. Cell cycle and apoptosis were monitored by flow cytometry. The levels of glutamine consumption and glutamate were examined using commercial kits. The interaction among circ_0016418, miR-605-5p and GLS was verified with the dual-luciferase reporter assay. A xenograft model was used to analyze tumor growth in vivo.

RESULTS

Circ_0016418 and GLS were up-regulated, while miR-605-5p was down-regulated in melanoma tissues and cells. Circ_0016418 silencing hindered cell proliferation, metastasis, and glutamine catabolism and promoted cell cycle arrest and apoptosis in A375 and A875 cells. Circ_0016418 modulated melanoma progression and glutamine catabolism through sponging miR-605-5p. Also, miR-605-5p inhibited melanoma progression and glutamine catabolism by targeting GLS. Moreover, circ_0016418 depletion blocked tumor growth in vivo.

CONCLUSION

Knockdown of circ_0016418 suppressed melanoma development and glutamine catabolism by modulating the miR-605-5p/GLS pathway.

The progress and development of GLUT1 inhibitors targeting cancer energy metabolism

A major difference between glucose metabolism in cancer cells and normal cells is that glucose in cancer cells is preferably converted to lactate in aerobic conditions rather than oxidized in mitochondria. This process is called aerobic glycolysis, known as the 'Warburg effect'. In this review, we focus on the energy-metabolism characteristics between tumor and normal cells, analyzing the regulation mechanism of energy metabolism based on glycolysis, and summarizing two targets on the upstream proteins of glycolysis, including glucose transporter (GLUT) and hexokinase. In addition, we proposed the risks and limitations of GLUT1-based drug research and summarized the current research progress of representative drugs, including natural and synthetic GLUT1 inhibitors. This will provide guidance for designing and synthesizing small molecule drugs targeting GLUT1 in glycolysis.

The activation loop and substrate-binding cleft of glutaminase C are allosterically coupled

The glutaminase C (GAC) isoform of mitochondrial glutaminase is overexpressed in many cancer cells and therefore represents a potential therapeutic target. Understanding the regulation of GAC activity has been guided by the development of spectroscopic approaches that measure glutaminase activity in real time. Previously, we engineered a GAC protein (GAC(F327W)) in which a tryptophan residue is substituted for phenylalanine in an activation loop to explore the role of this loop in enzyme activity. We showed that the fluorescence emission of Trp-327 is enhanced in response to activator binding, but quenched by inhibitors of the BPTES class that bind to the GAC tetramer and contact the activation loop, thereby constraining it in an inactive conformation. In the present work, we took advantage of a tryptophan substitution at position 471, proximal to the GAC catalytic site, to examine the conformational coupling between the activation loop and the substrate-binding cleft, separated by ∼16 Å. Comparison of glutamine binding in the presence or absence of the BPTES analog CB-839 revealed a reciprocal relationship between the constraints imposed on the activation loop position and the affinity of GAC for substrate. Binding of the inhibitor weakened the affinity of GAC for glutamine, whereas activating anions such as P_i increased this affinity. These results indicate that the conformations of the activation loop and the substrate-binding cleft in GAC are allosterically coupled and that this coupling determines substrate affinity and enzymatic activity and explains the activities of CB-839, which is currently in clinical trials.