Mesenchymal phenotype predisposes lung cancer cells to impaired proliferation and redox stress in response to glutaminase inhibition

GLS and GLS2 Glutaminase Isoenzymes in the Antioxidant System of Cancer Cells

A pathway frequently altered in cancer is glutaminolysis, whereby glutaminase (GA) catalyzes the main step as follows: the deamidation of glutamine to form glutamate and ammonium. There are two types of GA isozymes, named GLS and GLS2, which differ considerably in their expression patterns and can even perform opposing roles in cancer. GLS correlates with tumor growth and proliferation, while GLS2 can function as a context-dependent tumor suppressor. However, both isoenzymes have been described as essential molecules handling oxidant stress because of their involvement in glutathione production. We reviewed the literature to highlight the critical roles of GLS and GLS2 in restraining ROS and regulating both cellular signaling and metabolic stress due to their function as indirect antioxidant enzymes, as well as by modulating both reductive carboxylation and ferroptosis. Blocking GA activity appears to be a potential strategy in the dual activation of ferroptosis and inhibition of cancer cell growth in a ROS-mediated mechanism.

The cuproptosis-related gene glutaminase promotes alveolar macrophage copper ion accumulation in chronic obstructive pulmonary disease

Cuproptosis, a novel mode of cell death, is strongly associated with a variety of diseases. However, the contribution of cuproptosis to the onset or progression of chronic obstructive pulmonary disease (COPD), the third most common chronic cause of mortality, is not yet clear. To investigate the potential role of cuproptosis in COPD, raw datasets from multiple public clinical COPD databases (including RNA-seq, phenotype, and lung function data) were used. For further validation, mice exposed to cigarette smoke for three months were used as in vivo models, and iBMDMs (immortalized bone marrow-derived macrophages) and RAW264.7 cells stimulated with cigarette smoke extract were used as in vitro models. For the first time, the expression of the cuproptosis-related gene glutaminase (GLS) was found to be decreased in COPD, and the low expression of GLS was significantly associated with the grade of pulmonary function. In vivo experiments confirmed the decreased expression of GLS in COPD, particularly in alveolar macrophages. Furthermore, in vitro studies revealed that copper ions accumulated in alveolar macrophages, leading to a substantially decreased amount of cell activity of macrophages when stimulated with cigarette extract. In summary, we demonstrate the high potential of GLS as an avenue for diagnosis and therapy in COPD.

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.

Redox-Regulation in Cancer Stem Cells

Cancer stem cells (CSCs) represent a small subset of slowly dividing cells with tumor-initiating ability. They can self-renew and differentiate into all the distinct cell populations within a tumor. CSCs are naturally resistant to chemotherapy or radiotherapy. CSCs, thus, can repopulate a tumor after therapy and are responsible for recurrence of disease. Stemness manifests itself through, among other things, the expression of stem cell markers, the ability to induce sphere formation and tumor growth in vivo, and resistance to chemotherapeutics and irradiation. Stemness is maintained by keeping levels of reactive oxygen species (ROS) low, which is achieved by enhanced activity of antioxidant pathways. Here, cellular sources of ROS, antioxidant pathways employed by CSCs, and underlying mechanisms to overcome resistance are discussed.

Correlation between amino acid metabolism and self-renewal of cancer stem cells: Perspectives in cancer therapy

Cancer stem cells (CSCs) possess self-renewal and differentiation potential, which may be related to recurrence, metastasis, and radiochemotherapy resistance during tumor treatment. Understanding the mechanisms via which CSCs maintain self-renewal may reveal new therapeutic targets for attenuating CSC resistance and extending patient life-span. Recent studies have shown that amino acid metabolism plays an important role in maintaining the self-renewal of CSCs and is involved in regulating their tumorigenicity characteristics. This review summarizes the relationship between CSCs and amino acid metabolism, and discusses the possible mechanisms by which amino acid metabolism regulates CSC characteristics particularly self-renewal, survival and stemness. The ultimate goal is to identify new targets and research directions for elimination of CSCs.

The Epithelial-Mesenchymal Transition at the Crossroads between Metabolism and Tumor Progression

The transition between epithelial and mesenchymal phenotype is emerging as a key determinant of tumor cell invasion and metastasis. It is a plastic process in which epithelial cells first acquire the ability to invade the extracellular matrix and migrate into the bloodstream via transdifferentiation into mesenchymal cells, a phenomenon known as epithelial–mesenchymal transition (EMT), and then reacquire the epithelial phenotype, the reverse process called mesenchymal–epithelial transition (MET), to colonize a new organ. During all metastatic stages, metabolic changes, which give cancer cells the ability to adapt to increased energy demand and to withstand a hostile new environment, are also important determinants of successful cancer progression. In this review, we describe the complex interaction between EMT and metabolism during tumor progression. First, we outline the main connections between the two processes, with particular emphasis on the role of cancer stem cells and LncRNAs. Then, we focus on some specific cancers, such as breast, lung, and thyroid cancer.

Metabolic Reprogramming in Thyroid Cancer: Role of the Epithelial-Mesenchymal Transition

Thyroid cancer (TC) represents the most common endocrine malignancy, with an increasing incidence all over the world. Papillary TC (PTC), a differentiated TC subtype, is the most common and, even though it has an excellent prognosis following radioiodine (RAI) ablation, it shows an aggressive behavior in 20–30% of cases, becoming RAI-resistant and/or metastatic. On the other side, anaplastic thyroid carcinoma (ATC), the most undifferentiated TC, is a rare but devastating disease, indicating that progression of differentiated to undifferentiated forms of TC could be responsible for RAI-resistance and increased mortality. The epithelial-to-mesenchymal transition (EMT) plays a pivotal role in both tumor progression and resistance to therapy. Moreover, during tumor progression, cancer cells modify their metabolism to meet changed requirements for cellular proliferation. Through these metabolic changes, cancer cells may adopt cancer stem cell-like properties and express an EMT phenotype. EMT, in turn, can induce metabolic changes to which cancer cells become addicted. Here we review metabolic reprogramming in TC highlighting the role of EMT with the aim to explore a potential field to find out new therapeutic strategies for advanced-stage PTC. Accordingly, we discuss the identification of the metabolic enzymes and metabolites, critical to TC progression, which can be employed either as predicting biomarkers of tumor response to RAI therapy or possible targets in precision medicine.

Comparative transcriptional profiling of canine acanthomatous ameloblastoma and homology with human ameloblastoma

Ameloblastomas are odontogenic tumors that are rare in people but have a relatively high prevalence in dogs. Because canine acanthomatous ameloblastomas (CAA) have clinicopathologic and molecular features in common with human ameloblastomas (AM), spontaneous CAA can serve as a useful translational model of disease. However, the molecular basis of CAA and how it compares to AM are incompletely understood. In this study, we compared the global genomic expression profile of CAA with AM and evaluated its dental origin by using a bulk RNA-seq approach. For these studies, healthy gingiva and canine oral squamous cell carcinoma served as controls. We found that aberrant RAS signaling, and activation of the epithelial-to-mesenchymal transition cellular program are involved in the pathogenesis of CAA, and that CAA is enriched with genes known to be upregulated in AM including those expressed during the early stages of tooth development, suggesting a high level of molecular homology. These results support the model that domestic dogs with spontaneous CAA have potential for pre-clinical assessment of targeted therapeutic modalities against AM.

TGF-β-dependent reprogramming of amino acid metabolism induces epithelial-mesenchymal transition in non-small cell lung cancers

Epithelial–mesenchymal transition (EMT)—a fundamental process in embryogenesis and wound healing—promotes tumor metastasis and resistance to chemotherapy. While studies have identified signaling components and transcriptional factors responsible in the TGF-β-dependent EMT, whether and how intracellular metabolism is integrated with EMT remains to be fully elucidated. Here, we showed that TGF-β induces reprogramming of intracellular amino acid metabolism, which is necessary to promote EMT in non-small cell lung cancer cells. Combined metabolome and transcriptome analysis identified prolyl 4-hydroxylase α3 (P4HA3), an enzyme implicated in cancer metabolism, to be upregulated during TGF-β stimulation. Further, knockdown of P4HA3 diminished TGF-β-dependent changes in amino acids, EMT, and tumor metastasis. Conversely, manipulation of extracellular amino acids induced EMT-like responses without TGF-β stimulation. These results suggest a previously unappreciated requirement for the reprogramming of amino acid metabolism via P4HA3 for TGF-β-dependent EMT and implicate a P4HA3 inhibitor as a potential therapeutic agent for cancer.

Through metabolome and transcriptome analyses, Nakasuka et al find that TGF-β-induced epithelial–mesenchymal transition (EMT) in non-small cell lung cancer cells is associated with reprogramming of amino acid metabolism. They also identify P4HA3 as a key enzyme involved in these changes altogether providing insights into potential mechanisms of metastasis.

Targeting GLS1 to cancer therapy through glutamine metabolism

Glutamine metabolism is one of the hallmarks of cancers which is described as an essential role in serving as a major energy and building blocks supply to cell proliferation in cancer cells. Many malignant tumor cells always display glutamine addiction. The "kidney-type" glutaminase (GLS1) is a metabolism enzyme which plays a significant part in glutaminolysis. Interestingly, GLS1 is often overexpressed in highly proliferative cancer cells to fulfill enhanced glutamine demand. So far, GLS1 has been proved to be a significant target during the carcinogenesis process, and emerging evidence reveals that its inhibitors could provide a benefit strategy for cancer therapy. Herein, we summarize the prognostic value of GLS1 in multiple cancer type and its related regulatory factors which are associated with antitumor activity. Moreover, this review article highlights the remarkable reform of discovery and development for GLS1 inhibitors. On the basis of case studies, our perspectives for targeting GLS1 and development of GLS1 antagonist are discussed in the final part.

Linking Metabolic Reprogramming, Plasticity and Tumor Progression

Simple Summary

In the present review, we discuss the role of metabolic reprogramming which occurs in malignant cells. The process of metabolic reprogramming is also known as one of the “hallmarks of cancer”. Due to several reasons, including the origin of cancer, tumor microenvironment, and the tumor progression stage, metabolic reprogramming can be heterogeneous and dynamic. In this review, we provide evidence that the usage of metabolic drugs is a promising approach to treat cancer. However, because these drugs can damage not only malignant cells but also normal rapidly dividing cells, it is important to understand the exact metabolic changes which are elicited by particular drivers in concrete tissue and are specific for each stage of cancer development, including metastases. Finally, the review highlights new promising targets for the development of new metabolic drugs.

Abstract

The specific molecular features of cancer cells that distinguish them from the normal ones are denoted as “hallmarks of cancer”. One of the critical hallmarks of cancer is an altered metabolism which provides tumor cells with energy and structural resources necessary for rapid proliferation. The key feature of a cancer-reprogrammed metabolism is its plasticity, allowing cancer cells to better adapt to various conditions and to oppose different therapies. Furthermore, the alterations of metabolic pathways in malignant cells are heterogeneous and are defined by several factors including the tissue of origin, driving mutations, and microenvironment. In the present review, we discuss the key features of metabolic reprogramming and plasticity associated with different stages of tumor, from primary tumors to metastases. We also provide evidence of the successful usage of metabolic drugs in anticancer therapy. Finally, we highlight new promising targets for the development of new metabolic drugs.

Glutamine-Directed Migration of Cancer-Activated Fibroblasts Facilitates Epithelial Tumor Invasion

Tumors are complex tissues composed of transformed epithelial cells as well as cancer-activated fibroblasts (CAF) that facilitate epithelial tumor cell invasion. We show here that CAFs and other mesenchymal cells rely much more on glutamine than epithelial tumor cells; consequently, they are more sensitive to inhibition of glutaminase. Glutamine dependence drove CAF migration toward this amino acid when cultured in low glutamine conditions. CAFs also invaded a Matrigel matrix following a glutamine concentration gradient and enhanced the invasion of tumor cells when both cells were cocultured. Accordingly, glutamine directed invasion of xenografted tumors in immunocompromised mice. Stimulation of glutamine-driven epithelial tumor invasion by fibroblasts required previous CAF activation, which involved the TGFβ/Snail1 signaling axis. CAFs moving toward Gln presented a polarized Akt2 distribution that was modulated by the Gln-dependent activity of TRAF6 and p62 in the migrating front, and depletion of these proteins prevented Akt2 polarization and Gln-driven CAF invasion. Our results demonstrate that glutamine deprivation promotes CAF migration and invasion, which in turn facilitates the movement of tumor epithelial cells toward nutrient-rich territories. These results provide a novel molecular mechanism for how metabolic stress enhances invasion and metastasis. SIGNIFICANCE: Cancer-associated fibroblasts migrate and invade toward free glutamine and facilitate invasion of tumor epithelial cells, accounting for their movement away from the hostile conditions of the tumor towards nutrient-rich adjacent tissues. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/2/438/F1.large.jpg.

Metabolic Constrains Rule Metastasis Progression

Metastasis formation accounts for the majority of tumor-associated deaths and consists of different steps, each of them being characterized by a distinctive adaptive phenotype of the cancer cells. Metabolic reprogramming represents one of the main adaptive phenotypes exploited by cancer cells during all the main steps of tumor and metastatic progression. In particular, the metabolism of cancer cells evolves profoundly through all the main phases of metastasis formation, namely the metastatic dissemination, the metastatic colonization of distant organs, the metastatic dormancy, and ultimately the outgrowth into macroscopic lesions. However, the metabolic reprogramming of metastasizing cancer cells has only recently become the subject of intense study. From a clinical point of view, the latter steps of the metastatic process are very important, because patients often undergo surgical removal of the primary tumor when cancer cells have already left the primary tumor site, even though distant metastases are not clinically detectable yet. In this scenario, to precisely elucidate if and how metabolic reprogramming drives acquisition of cancer-specific adaptive phenotypes might pave the way to new therapeutic strategies by combining chemotherapy with metabolic drugs for better cancer eradication. In this review we discuss the latest evidence that claim the importance of metabolic adaptation for cancer progression.

Analysis of Epithelial-Mesenchymal Transition Metabolism Identifies Possible Cancer Biomarkers Useful in Diverse Genetic Backgrounds

Epithelial-to-mesenchymal transition (EMT) relates to many molecular and cellular alterations that occur when epithelial cells undergo a switch in differentiation generating mesenchymal-like cells with newly acquired migratory and invasive properties. In cancer cells, EMT leads to drug resistance and metastasis. Moreover, differences in genetic backgrounds, even between patients with the same type of cancer, also determine resistance to some treatments. Metabolic rewiring is essential to induce EMT, hence it is important to identify key metabolic elements for this process, which can be later used to treat cancer cells with different genetic backgrounds. Here we used a mathematical modeling approach to determine which are the metabolic reactions altered after induction of EMT, based on metabolomic and transcriptional data of three non-small cell lung cancer (NSCLC) cell lines. The model suggested that the most affected pathways were the Krebs cycle, amino acid metabolism, and glutathione metabolism. However, glutathione metabolism had many alterations either on the metabolic reactions or at the transcriptional level in the three cell lines. We identified Glutamate-cysteine ligase (GCL), a key enzyme of glutathione synthesis, as an important common feature that is dysregulated after EMT. Analyzing survival data of men with lung cancer, we observed that patients with mutations in GCL catalytic subunit (GCLC) or Glutathione peroxidase 1 (GPX1) genes survived less time than people without mutations on these genes. Besides, patients with low expression of ANPEP, GPX3 and GLS genes also survived less time than those with high expression. Hence, we propose that glutathione metabolism and glutathione itself could be good targets to delay or potentially prevent EMT induction in NSCLC cell lines.

Inhibition of the MYC-Regulated Glutaminase Metabolic Axis Is an Effective Synthetic Lethal Approach for Treating Chemoresistant Ovarian Cancers

Amplification and overexpression of the MYC oncogene in tumor cells, including ovarian cancer cells, correlates with poor responses to chemotherapy. As MYC is not directly targetable, we have analyzed molecular pathways downstream of MYC to identify potential therapeutic targets. Here we report that ovarian cancer cells overexpressing glutaminase (GLS), a target of MYC and a key enzyme in glutaminolysis, are intrinsically resistant to platinum-based chemotherapy and are enriched with intracellular antioxidant glutathione. Deprivation of glutamine by glutamine-withdrawal, GLS knockdown, or exposure to the GLS inhibitor CB-839 resulted in robust induction of reactive oxygen species in high GLS-expressing but not in low GLS-expressing ovarian cancer cells. Treatment with CB-839 rendered GLS^high cells vulnerable to the poly(ADP-ribose) polymerase (PARP) inhibitor, olaparib, and prolonged survival in tumor-bearing mice. These findings suggest consideration of applying a combined therapy of GLS inhibitor and PARP inhibitor to treat chemoresistant ovarian cancers, especially those with high GLS expression. SIGNIFICANCE: Targeting glutaminase disturbs redox homeostasis and nucleotide synthesis and causes replication stress in cancer cells, representing an exploitable vulnerability for the development of effective therapeutics. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/20/4514/F1.large.jpg.

Metabolic Reprogramming and Epithelial-Mesenchymal Plasticity: Opportunities and Challenges for Cancer Therapy

Metabolic reprogramming and epithelial-mesenchymal plasticity are both hallmarks of the adaptation of cancer cells for tumor growth and progression. For metabolic changes, cancer cells alter metabolism by utilizing glucose, lipids, and amino acids to meet the requirement of rapid proliferation and to endure stressful environments. Dynamic changes between the epithelial and mesenchymal phenotypes through epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are critical steps for cancer invasion and metastatic colonization. Compared to the extensively studied metabolic reprogramming in tumorigenesis, the metabolic changes in metastasis are relatively unclear. Here, we review metabolic reprogramming, epithelial-mesenchymal plasticity, and their mutual influences on tumor cells. We also review the developing treatments for targeting cancer metabolism and the impact of metabolic targeting on EMT. In summary, understanding the metabolic adaption and phenotypic plasticity will be mandatory for developing new strategies to target metastatic and refractory cancers that are intractable to current treatments.

Defining a metabolic landscape of tumours: genome meets metabolism

Cancer is a complex disease of multiple alterations occuring at the epigenomic, genomic, transcriptomic, proteomic and/or metabolic levels. The contribution of genetic mutations in cancer initiation, progression and evolution is well understood. However, although metabolic changes in cancer have long been acknowledged and considered a plausible therapeutic target, the crosstalk between genetic and metabolic alterations throughout cancer types is not clearly defined. In this review, we summarise the present understanding of the interactions between genetic drivers of cellular transformation and cancer-associated metabolic changes, and how these interactions contribute to metabolic heterogeneity of tumours. We discuss the essential question of whether changes in metabolism are a cause or a consequence in the formation of cancer. We highlight two modes of how metabolism contributes to tumour formation. One is when metabolic reprogramming occurs downstream of oncogenic mutations in signalling pathways and supports tumorigenesis. The other is where metabolic reprogramming initiates transformation being either downstream of mutations in oncometabolite genes or induced by chronic wounding, inflammation, oxygen stress or metabolic diseases. Finally, we focus on the factors that can contribute to metabolic heterogeneity in tumours, including genetic heterogeneity, immunomodulatory factors and tissue architecture. We believe that an in-depth understanding of cancer metabolic reprogramming, and the role of metabolic dysregulation in tumour initiation and progression, can help identify cellular vulnerabilities that can be exploited for therapeutic use.

Glutamine metabolism via glutaminase 1 in autosomal-dominant polycystic kidney disease

Background

Metabolism of glutamine by glutaminase 1 (GLS1) plays a key role in tumor cell proliferation via the generation of ATP and intermediates required for macromolecular synthesis. We hypothesized that glutamine metabolism also plays a role in proliferation of autosomal-dominant polycystic kidney disease (ADPKD) cells and that inhibiting GLS1 could slow cyst growth in animal models of ADPKD.

Methods

Primary normal human kidney and ADPKD human cyst-lining epithelial cells were cultured in the presence or absence of two pharmacologic inhibitors of GLS1, bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide 3 (BPTES) and CB-839, and the effect on proliferation, cyst growth in collagen and activation of downstream signaling pathways were assessed. We then determined if inhibiting GLS1 in vivo with CB-839 in the Aqp2-Cre; Pkd1fl/fl and Pkhd1-Cre; Pkd1fl/fl mouse models of ADPKD slowed cyst growth.

Results

We found that an isoform of GLS1 (GLS1-GAC) is upregulated in cyst-lining epithelia in human ADPKD kidneys and in mouse models of ADPKD. Both BPTES and CB-839 blocked forskolin-induced cyst formation in vitro. Inhibiting GLS1 in vivo with CB-839 led to variable outcomes in two mouse models of ADPKD. CB-839 slowed cyst growth in Aqp2-Cre; Pkd1fl/fl mice, but not in Pkhd1-Cre; Pkd1fl/fl mice. While CB-839 inhibited mammalian target of rapamycin (mTOR) and MEK activation in Aqp2-Cre; Pkd1fl/fl, it did not in Pkhd1-Cre; Pkd1fl/fl mice.

Conclusion

These findings provide support that alteration in glutamine metabolism may play a role in cyst growth. However, testing in other models of PKD and identification of the compensatory metabolic changes that bypass GLS1 inhibition will be critical to validate GLS1 as a drug target either alone or when combined with inhibitors of other metabolic pathways.

Expression of GLS1 in intrahepatic cholangiocarcinoma and its clinical significance

Kidney‑type glutaminase (GLS1) plays a significant role in tumor metabolism. Our recent studies demonstrated that GLS1 was aberrantly expressed in hepatocellular carcinoma (HCC) and facilitated tumor progression. However, the roles of GLS1 in intrahepatic cholangiocarcinoma (ICC) remain largely unknown. Thus, the aim of this study was to evaluate the expression and clinical significance of GLS1 in ICC. For this purpose, combined data from the Oncomine database with those of immunohistochemistry were used to determine the expression levels of GLS1 in cancerous and non‑cancerous tissues. Second, a wound‑healing assay and Transwell assay were used to observe the effects of the knockdown and overexpression of GLS1 on the invasion and migration of ICC cells. We examined the associations between the expression of GLS1 and epithelial‑mesenchymal transition (EMT)‑related markers by western blot analysis. Finally, we examined the associations between GLS1 levels and clinicopathological factors or patient prognosis. The results revealed that GLS1 was overexpressed in different digestive system tumors, including ICC, and that GLS1 expression in ICC tissue was higher than that in peritumoral tissue. The overexpression of GLS1 in RBE cells induced metastasis and invasion. Moreover, the EMT‑related markers, E‑cadherin and Vimentin, were regulated by GLS1 in ICC cells. By contrast, the knockdown of GLS1 expression in QBC939 cells yielded opposite results. Clinically, a high expression of GLS1 in ICC samples negatively correlated with E‑cadherin expression and positively correlated with Vimentin expression. GLS1 protein expression was associated with tumor differentiation (P=0.001) and lymphatic metastasis (P=0.029). Importantly, patients with a high GLS1 expression had a poorer overall survival (OS) and a shorter time to recurrence than patients with a low GLS1 expression. Multivariate analysis indicated that GLS1 expression was an independent prognostic indicator. On the whole, the findings of this study demonstrated that GLS1 is an independent prognostic biomarker of ICC. GLS1 facilitates ICC progression and may thus prove to be a therapeutic target in ICC.

Role of Metabolic Reprogramming in Epithelial⁻Mesenchymal Transition (EMT)

Activation of epithelial–mesenchymal transition (EMT) is thought to be an essential step for cancer metastasis. Tumor cells undergo EMT in response to a diverse range of extra- and intracellular stimulants. Recently, it was reported that metabolic shifts control EMT progression and induce tumor aggressiveness. In this review, we summarize the involvement of altered glucose, lipid, and amino acid metabolic enzyme expression and the underlying molecular mechanisms in EMT induction in tumor cells. Moreover, we propose that metabolic regulation through gene-specific or pharmacological inhibition may suppress EMT and this treatment strategy may be applied to prevent tumor progression and improve anti-tumor therapeutic efficacy. This review presents evidence for the importance of metabolic changes in tumor progression and emphasizes the need for further studies to better understand tumor metabolism.

The peculiarities of cancer cell metabolism: A route to metastasization and a target for therapy

The last decade has witnessed the peculiarities of metabolic reprogramming in tumour onset and progression, and their relevance in cancer therapy. Also, it has been indicated that the metastatic process may depend on the metabolic rewiring and adaptation of cancer cells to the pressure of tumour microenvironment and limiting nutrient availability. The present review gatherers the existent knowledge on the influence of tumour microenvironment and metabolic routes driving metastasis. A focus will be given to glycolysis, fatty acid metabolism, glutaminolysis, and amino acid handling. In addition, the role of metabolic waste driving metastasization will be explored. Finally, we discuss the status of cancer treatment approaches targeting metabolism. This knowledge revision will highlight the critical metabolic targets in metastasis and the chemicals already used in preclinical studies and clinical trials, providing clues that would be further exploited in medicinal chemistry research.

Targeting glutaminase 1 attenuates stemness properties in hepatocellular carcinoma by increasing reactive oxygen species and suppressing Wnt/beta-catenin pathway

Background

Hepatocellular carcinoma (HCC) is an aggressive malignant disease with poor prognosis. Recent advances suggest the existence of cancer stem cells (CSCs) within liver cancer, which are considered to be responsible for tumor relapse, metastasis, and chemoresistance. However, novel therapeutic approaches for eradicating CSCs are yet to be established. Here, we aimed to identify the role of glutaminase 1 (GLS1) in stemness, and the feasibility that GLS1 serves as a therapeutic target for elimination CSCs as well as the possible mechanism.

Methods

Publicly-available data from the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) was mined to unearth the association between GLS1 and stemness phenotype. Using big data, human tissues and multiple cell lines, we gained a general picture of GLS1 expression in HCC progression. We generated stable cell lines by lentiviral-mediated overexpression or CRISPR/Cas9-based knockout. Sphere formation assays and colony formation assays were employed to analyze the relationship between GLS1 and stemness. A series of bioinformatics analyses and molecular experiments including qRT-PCR, immunoblotting, flow cytometry, and immunofluorescence were employed to investigate the role of GLS1 in regulating stemness in vitro and in vivo.

Findings

We observed GLS1 (both KGA and GAC isoform) is highly expressed in HCC, and that high expression of GAC predicts a poor prognosis. GLS1 is exclusively expressed in the mitochondrial matrix. Upregulation of GLS1 is positively associated with advanced clinicopathological features and stemness phenotype. Targeting GLS1 reduced the expression of stemness-related genes and suppressed CSC properties in vitro. We further found GLS1 regulates stemness properties via ROS/Wnt/β-catenin signaling and that GLS1 knockout inhibits tumorigenicity in vivo.

Interpretation

Targeting GLS1 attenuates stemness properties in HCC by increasing ROS accumulation and suppressing Wnt/β-catenin pathway, which implied that GLS1 could serve as a therapeutic target for elimination of CSCs.

Pan-Cancer Metabolic Signature Predicts Co-Dependency on Glutaminase and De Novo Glutathione Synthesis Linked to a High-Mesenchymal Cell State

The enzyme glutaminase (GLS1) is currently in clinical trials for oncology, yet there are no clear diagnostic criteria to identify responders. The evaluation of 25 basal breast lines expressing GLS1, predominantly through its splice isoform GAC, demonstrated that only GLS1-dependent basal B lines required it for maintaining de novo glutathione synthesis in addition to mitochondrial bioenergetics. Drug sensitivity profiling of 407 tumor lines with GLS1 and gamma-glutamylcysteine synthetase (GCS) inhibitors revealed a high degree of co-dependency on both enzymes across indications, suggesting that redox balance is a key function of GLS1 in tumors. To leverage these findings, we derived a pan-cancer metabolic signature predictive of GLS1/GCS co-dependency and validated it in vivo using four lung patient-derived xenograft models, revealing the additional requirement for expression of GAC above a threshold (log₂RPKM + 1 ≥ 4.5, where RPKM is reads per kilobase per million mapped reads). Analysis of the pan-TCGA dataset with our signature identified multiple indications, including mesenchymal tumors, as putative responders to GLS1 inhibitors.

Microenvironmental regulation of cancer cell metabolism: implications for experimental design and translational studies

Cancers have an altered metabolism, and there is interest in understanding precisely how oncogenic transformation alters cellular metabolism and how these metabolic alterations can translate into therapeutic opportunities. Researchers are developing increasingly powerful experimental techniques to study cellular metabolism, and these techniques have allowed for the analysis of cancer cell metabolism, both in tumors and in ex vivo cancer models. These analyses show that, while factors intrinsic to cancer cells such as oncogenic mutations, alter cellular metabolism, cell-extrinsic microenvironmental factors also substantially contribute to the metabolic phenotype of cancer cells. These findings highlight that microenvironmental factors within the tumor, such as nutrient availability, physical properties of the extracellular matrix, and interactions with stromal cells, can influence the metabolic phenotype of cancer cells and might ultimately dictate the response to metabolically targeted therapies. In an effort to better understand and target cancer metabolism, this Review focuses on the experimental evidence that microenvironmental factors regulate tumor metabolism, and on the implications of these findings for choosing appropriate model systems and experimental approaches.

N-terminal phosphorylation of glutaminase C decreases its enzymatic activity and cancer cell migration

The mitochondrial phosphate-activated glutaminase C (GAC) is produced by the alternative splicing of the GLS gene. Compared to the other GLS isoform, the kidney-type glutaminase (KGA), GAC is more enzymatically efficient and of particular importance for cancer cell growth. Although its catalytic mechanism is well understood, little is known about how post-translational modifications can impact GAC function. Here, we identified by mass spectrometry a phosphorylated serine at the GLS N-terminal domain (at position 95) and investigated its role on regulating GAC activity. The ectopic expression of the phosphomimetic mutant (GAC.S95D) in breast cancer cells, compared to wild-type GAC (GAC.WT), led to decreased glutaminase activity, glutamine uptake, glutamate release and intracellular glutamate levels, without changing GAC sub-cellular localization. Interestingly, cells expressing the GAC.S95D mutant, compared to GAC.WT, presented decreased migration and vimentin level, an epithelial-to-mesenchymal transition marker. These results reveal that GAC is post-translationally regulated by phosphorylation, which affects cellular glutamine metabolism and glutaminase-related cell phenotype.

Lkb1 deficiency confers glutamine dependency in polycystic kidney disease

Polycystic kidney disease (PKD) is a common genetic disorder characterized by the growth of fluid-filled cysts in the kidneys. Several studies reported that the serine-threonine kinase Lkb1 is dysregulated in PKD. Here we show that genetic ablation of Lkb1 in the embryonic ureteric bud has no effects on tubule formation, maintenance, or growth. However, co-ablation of Lkb1 and Tsc1, an mTOR repressor, results in an early developing, aggressive form of PKD. We find that both loss of Lkb1 and loss of Pkd1 render cells dependent on glutamine for growth. Metabolomics analysis suggests that Lkb1 mutant kidneys require glutamine for non-essential amino acid and glutathione metabolism. Inhibition of glutamine metabolism in both Lkb1/Tsc1 and Pkd1 mutant mice significantly reduces cyst progression. Thus, we identify a role for Lkb1 in glutamine metabolism within the kidney epithelia and suggest that drugs targeting glutamine metabolism may help reduce cyst number and/or size in PKD.

Polycystic kidney disease (PKD) is characterized by the formation of large fluid-filled cysts. Here Flowers and colleagues show that loss of Lkb1, downregulated in PKD, renders kidney cells dependent on glutamine for growth, and suggest that inhibition of glutamine metabolism may prevent cyst development in PKD.

Cell death-based treatment of neuroblastoma

Neuroblastoma (NB) is the most common solid childhood tumor outside the brain and causes 15% of childhood cancer-related mortality. The main drivers of NB formation are neural crest cell-derived sympathoadrenal cells that undergo abnormal genetic arrangements. Moreover, NB is a complex disease that has high heterogeneity and is therefore difficult to target for successful therapy. Thus, a better understanding of NB development helps to improve treatment and increase the survival rate. One of the major causes of sporadic NB is known to be MYCN amplification and mutations in ALK (anaplastic lymphoma kinase) are responsible for familial NB. Many other genetic abnormalities can be found; however, they are not considered as driver mutations, rather they support tumor aggressiveness. Tumor cell elimination via cell death is widely accepted as a successful technique. Therefore, in this review, we provide a thorough overview of how different modes of cell death and treatment strategies, such as immunotherapy or spontaneous regression, are or can be applied for NB elimination. In addition, several currently used and innovative approaches and their suitability for clinical testing and usage will be discussed. Moreover, significant attention will be given to combined therapies that show more effective results with fewer side effects than drugs targeting only one specific protein or pathway.

Differential Aspartate Usage Identifies a Subset of Cancer Cells Particularly Dependent on OGDH

Although aberrant metabolism in tumors has been well described, the identification of cancer subsets with particular metabolic vulnerabilities has remained challenging. Here, we conducted an siRNA screen focusing on enzymes involved in the tricarboxylic acid (TCA) cycle and uncovered a striking range of cancer cell dependencies on OGDH, the E1 subunit of the alpha-ketoglutarate dehydrogenase complex. Using an integrative metabolomics approach, we identified differential aspartate utilization, via the malate-aspartate shuttle, as a predictor of whether OGDH is required for proliferation in 3D culture assays and for the growth of xenograft tumors. These findings highlight an anaplerotic role of aspartate and, more broadly, suggest that differential nutrient utilization patterns can identify subsets of cancers with distinct metabolic dependencies for potential pharmacological intervention.

Glutaminase is essential for the growth of triple-negative breast cancer cells with a deregulated glutamine metabolism pathway and its suppression synergizes with mTOR inhibition

Tumor cells display fundamental changes in metabolism and nutrient uptake in order to utilize additional nutrient sources to meet their enhanced bioenergetic requirements. Glutamine (Gln) is one such nutrient that is rapidly taken up by tumor cells to fulfill this increased metabolic demand. A vital step in the catabolism of glutamine is its conversion to glutamate by the mitochondrial enzyme glutaminase (GLS). This study has identified GLS a potential therapeutic target in breast cancer, specifically in the basal subtype that exhibits a deregulated glutaminolysis pathway. Using inducible shRNA mediated gene knockdown, we discovered that loss of GLS function in triple-negative breast cancer (TNBC) cell lines with a deregulated glutaminolysis pathway led to profound tumor growth inhibition in vitro and in vivo. GLS knockdown had no effect on growth and metabolite levels in non-TNBC cell lines. We rescued the anti-tumor effect of GLS knockdown using shRNA resistant cDNAs encoding both GLS isoforms and by addition of an α-ketoglutarate (αKG) analog thus confirming the critical role of GLS in TNBC. Pharmacological inhibition of GLS with the small molecule inhibitor CB-839 reduced cell growth and led to a decrease in mammalian target of rapamycin (mTOR) activity and an increase in the stress response pathway driven by activating transcription factor 4 (ATF4). Finally, we found that GLS inhibition synergizes with mTOR inhibition, which introduces the possibility of a novel therapeutic strategy for TNBC. Our study revealed that GLS is essential for the survival of TNBC with a deregulated glutaminolysis pathway. The synergistic activity of GLS and mTOR inhibitors in TNBC cell lines suggests therapeutic potential of this combination for the treatment of vulnerable subpopulations of TNBC.

Studies on the Interaction of the Histone Demethylase KDM5B with Tricarboxylic Acid Cycle Intermediates

Methylation of lysine-4 of histone H3 (H3K4men) is an important regulatory factor in eukaryotic transcription. Removal of the transcriptionally activating H3K4 methylation is catalyzed by histone demethylases, including the Jumonji C (JmjC) KDM5 subfamily. The JmjC KDMs are Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenases, some of which are associated with cancer. Altered levels of tricarboxylic acid (TCA) cycle intermediates and the associated metabolites D- and L-2-hydroxyglutarate (2HG) can cause changes in chromatin methylation status. We report comprehensive biochemical, structural and cellular studies on the interaction of TCA cycle intermediates with KDM5B, which is a current medicinal chemistry target for cancer. The tested TCA intermediates were poor or moderate KDM5B inhibitors, except for oxaloacetate and succinate, which were shown to compete for binding with 2OG. D- and L-2HG were moderate inhibitors at levels that might be relevant in cancer cells bearing isocitrate dehydrogenase mutations. Crystallographic analyses with succinate, fumarate, L-malate, oxaloacetate, pyruvate and D- and L-2HG support the kinetic studies showing competition with 2OG. An unexpected binding mode for oxaloacetate was observed in which it coordinates the active site metal via its C-4 carboxylate rather than the C-1 carboxylate/C-2 keto groups. Studies employing immunofluorescence antibody-based assays reveal no changes in H3K4me3 levels in cells ectopically overexpressing KDM5B in response to dosing with TCA cycle metabolite pro-drug esters, suggesting that the high levels of cellular 2OG may preclude inhibition. The combined results reveal the potential for KDM5B inhibition by TCA cycle intermediates, but suggest that in cells, such inhibition will normally be effectively competed by 2OG.

Environmental cystine drives glutamine anaplerosis and sensitizes cancer cells to glutaminase inhibition

Many mammalian cancer cell lines depend on glutamine as a major tri-carboxylic acid (TCA) cycle anaplerotic substrate to support proliferation. However, some cell lines that depend on glutamine anaplerosis in culture rely less on glutamine catabolism to proliferate in vivo. We sought to understand the environmental differences that cause differential dependence on glutamine for anaplerosis. We find that cells cultured in adult bovine serum, which better reflects nutrients available to cells in vivo, exhibit decreased glutamine catabolism and reduced reliance on glutamine anaplerosis compared to cells cultured in standard tissue culture conditions. We find that levels of a single nutrient, cystine, accounts for the differential dependence on glutamine in these different environmental contexts. Further, we show that cystine levels dictate glutamine dependence via the cystine/glutamate antiporter xCT/SLC7A11. Thus, xCT/SLC7A11 expression, in conjunction with environmental cystine, is necessary and sufficient to increase glutamine catabolism, defining important determinants of glutamine anaplerosis and glutaminase dependence in cancer.

Cancer cells need to consume certain nutrients in order to grow, and some cancer drugs work by affecting the ability of the cells to use these nutrients. For decades researchers have grown cancer cells in petri dishes with standard nutrient formulations (also known as tissue culture), but the nutrients available to cancer cells in tissue culture are not the same as those found in the body.

Cancer cells growing in tissue culture consume large amounts of a nutrient called glutamine. These cells die when exposed to a class of drugs called glutaminase inhibitors that prevent them from processing glutamine. However, when these same cancer cells grow as tumors in animals, they process less glutamine and are not affected by glutaminase inhibitors. So what differences are there between growing cancer cells in tumors and tissue culture that explain this different reliance on glutamine?

Muir et al. reasoned that changing the levels of nutrients available to cancer cells might change what these cells consume, and so grew human cancer cells in cow serum (which has a similar nutrient content to blood in humans and other mammals). Indeed, these cells consumed less glutamine and responded to glutaminase inhibitors in a way that is similar to how tumors in the body respond to these drugs. Comparing the nutrient content of cow serum and typical tissue culture formulations revealed that high levels of the nutrient cystine cause the cells to rely more on glutamine.

The results presented by Muir et al. suggest that cancer cells in tumors could be made to consume more glutamine and that this would make them sensitive to glutaminase inhibitors – a possibility that will be studied in future work. Exposing cultured cancer cells to nutrient levels closer to those found in the body may also better predict how tumor cells use nutrients and respond to some treatments.

Metabolic reprogramming and epithelial-to-mesenchymal transition in cancer

Several lines of evidence indicate that during transformation epithelial cancer cells can acquire mesenchymal features via a process called epithelial-to-mesenchymal transition (EMT). This process endows cancer cells with increased invasive and migratory capacity, enabling tumour dissemination and metastasis. EMT is associated with a complex metabolic reprogramming, orchestrated by EMT transcription factors, which support the energy requirements of increased motility and growth in harsh environmental conditions. The discovery that mutations in metabolic genes such as FH, SDH and IDH activate EMT provided further evidence that EMT and metabolism are intertwined. In this review, we discuss the role of EMT in cancer and the underpinning metabolic reprogramming. We also put forward the hypothesis that, by altering chromatin structure and function, metabolic pathways engaged by EMT are necessary for its full activation.

Glutaminase inhibitor compound 968 inhibits cell proliferation and sensitizes paclitaxel in ovarian cancer

Our overall goal was to investigate the anti-tumor activity of the glutaminase 1 (GLS1) Inhibitor compound 968 in ovarian cancer cells. The human ovarian cancer cell lines, HEY, SKOV3 and IGROV-1 were used. Cell proliferation was assessed by MTT assay after treatment with compound 968. Cell cycle progression and Annexin V expression were evaluated using Cellometer. Western blotting was performed to determine changes in GLS1, cellular stress and cell cycle checkpoints. Reactive oxygen species (ROS) and glutamate dehydrogenase (GDH) activity were assessed by ELISA assay. Compound 968 significantly inhibited cell proliferation and the expression of GLS1 in a dose-dependent manner in all three ovarian cancer cell lines. Compound 968 induced G1 phase cell cycle arrest and apoptosis. Treatment with compound 968 increased ROS levels and induced the protein expression of calnexin, binding immunoglobulin protein (BiP) and protein kinase RNA-like endoplasmic reticulum kinase (PERK). Deprivation of glutamine increased the sensitivity of cells to paclitaxel, and compound 968 sensitized cells to the anti-proliferative effects of paclitaxel. Compound 968 inhibited cell growth in ovarian cancer cells through induction of G1 phase cell cycle arrest, apoptosis and cellular stress, suggesting that targeting GLS1 provide a novel therapeutic strategy for ovarian cancer.

Glutaminolysis as a target for cancer therapy

Cancer cells display an altered metabolic circuitry that is directly regulated by oncogenic mutations and loss of tumor suppressors. Mounting evidence indicates that altered glutamine metabolism in cancer cells has critical roles in supporting macromolecule biosynthesis, regulating signaling pathways, and maintaining redox homeostasis, all of which contribute to cancer cell proliferation and survival. Thus, intervention in these metabolic processes could provide novel approaches to improve cancer treatment. This review summarizes current findings on the role of glutaminolytic enzymes in human cancers and provides an update on the development of small molecule inhibitors to target glutaminolysis for cancer therapy.

Metabolic changes associated with tumor metastasis, part 2: Mitochondria, lipid and amino acid metabolism

Metabolic alterations are a hallmark of cancer controlling tumor progression and metastasis. Among the various metabolic phenotypes encountered in tumors, this review focuses on the contributions of mitochondria, lipid and amino acid metabolism to the metastatic process. Tumor cells require functional mitochondria to grow, proliferate and metastasize, but shifts in mitochondrial activities confer pro-metastatic traits encompassing increased production of mitochondrial reactive oxygen species (mtROS), enhanced resistance to apoptosis and the increased or de novo production of metabolic intermediates of the TCA cycle behaving as oncometabolites, including succinate, fumarate, and D-2-hydroxyglutarate that control energy production, biosynthesis and the redox state. Lipid metabolism and the metabolism of amino acids, such as glutamine, glutamate and proline are also currently emerging as focal control points of cancer metastasis.