Targeted inhibition of tumor-specific glutaminase diminishes cell-autonomous tumorigenesis

Efficacy of Dual Inhibition of Glycolysis and Glutaminolysis for Therapy of Renal Lesions in Tsc2+/- Mice

Tuberous sclerosis is caused by mutations in the TSC1 or TSC2 gene and characterized by development of tumors in multiple organs including the kidneys. TSC-associated tumors exhibit somatic loss of the second allele of the TSC genes, leading to aberrant activation of the mechanistic target of rapamycin (mTOR) signaling pathway. Activation of mTOR complex 1 (mTORC1) causes addiction to glucose and glutamine in Tsc1^−/−or Tsc2^−/− mouse embryonic fibroblasts (MEFs). Blocking of glutamine anaplerosis in combination with glycolytic inhibition causes significant cell death in Tsc2^−/− but not Tsc2^+/+ MEFs. In this study, we tested efficacy of dual inhibition of glycolysis with 3-BrPA and glutaminolysis with CB-839 for renal tumors in Tsc2^+/− mice. Following 2 months of treatment of Tsc2^+/− mice from the age of 12 months, combination of 3-BrPA and CB-839 significantly reduced overall size and cellular areas of all renal lesions (cystic/papillary adenomas and solid carcinomas), but neither alone did. Combination of 3-BrPA and CB-839 inhibited mTORC1 and the proliferation of tumor cells but did not increase apoptosis. However, combination of 3-BrPA and CB-839 was not as efficacious as rapamycin alone or rapamycin in combination with either 3-BrPA or CB-839 for renal lesions of Tsc2^+/− mice. Consistently, rapamycin alone or rapamycin in combination with either 3-BrPA or CB-839 had stronger inhibitory effects on mTORC1 and proliferation of tumor cells than combination of 3-BrPA and CB-839. We conclude that combination of 3-BRPA and CB-839 may not offer a better therapeutic strategy than rapamycin for TSC-associated tumors.

Metabolic Regulation of Epithelial to Mesenchymal Transition: Implications for Endocrine Cancer

The last few decades have witnessed an outstanding advancement in our understanding of the hallmarks of endocrine cancers. This includes the epithelial to mesenchymal transition (EMT), a process that alters the morphology and functional characteristics of carcinoma cells. The mesenchymal stem cell like phenotype produced by EMT allows the dislocation of cancer cells from the primary tumor site with inheritance of motility, metastatic and invasive properties. A fundamental driver thought to initiate and propagate EMT is metabolic reprogramming that occur during these transitions. Though there remains a paucity of data regarding the alterations that occur during EMT in endocrine cancers, the contribution of deregulated metabolism is a prominent feature. This mini review focuses on metabolic reprogramming events that occur in cancer cells and in particular those of endocrine origin. It highlights the main metabolic reprogramming outcomes of EMT, encompassing glycolysis, mitochondria oxidative phosphorylation and function, glutamine and lipid metabolism. Comprehending the metabolic changes that occur during EMT will help formulate potential bioenergetic targets as therapies for endocrine cancer metastasis.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

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.

Overview of the Development of Glutaminase Inhibitors: Achievements and Future Directions

It has been demonstrated that glutamine metabolism has become the main energy and building blocks supply for the growth and viability of a potentially large subset of malignant tumors. The glutamine metabolism often depends upon mitochondrial glutaminase (GLS) activity, which converts glutamine to glutamate and serves as a significant role for bioenergetic processes. Thus, recently, the GLS has become a key target for small molecule therapeutic intervention. Numerous medicinal chemistry studies are currently aimed at the design of novel and potent inhibitors for GLS, however, to date, only one compound (named CB-839) have entered clinical trials for the treatment of advanced solid tumors and hematological malignancies. The perspective summarizes the progress in the discovery and development of GLS inhibitors, including the potential binding site, biochemical techniques for inhibitor identification, and approaches for identifying small-molecule inhibitors, as well as future therapeutic perspectives in glutamine metabolism are also put forward in order to provide reference and rational for the drug discovery of novel and potent glutamine metabolism modulators.

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.

Emerging roles of Myc in stem cell biology and novel tumor therapies

The pathophysiological roles and the therapeutic potentials of Myc family are reviewed in this article. The physiological functions and molecular machineries in stem cells, including embryonic stem (ES) cells and induced pluripotent stem (iPS) cells, are clearly described. The c-Myc/Max complex inhibits the ectopic differentiation of both types of artificial stem cells. Whereas c-Myc plays a fundamental role as a "double-edged sword" promoting both iPS cells generation and malignant transformation, L-Myc contributes to the nuclear reprogramming with the significant down-regulation of differentiation-associated genetic expression. Furthermore, given the therapeutic resistance of neuroendocrine tumors such as small-cell lung cancer and neuroblastoma, the roles of N-Myc in difficult-to-treat tumors are discussed. N-Myc and p53 exhibit the co-localization in the nucleus and alter p53-dependent transcriptional responses which are necessary for DNA repair, anti-apoptosis, and lipid metabolic reprogramming. NCYM protein stabilizes N-Myc, resulting in the stimulation of Oct4 expression, while Oct4 induces both N-Myc and NCYM via direct transcriptional activation of N-Myc, [corrected] thereby leading to the enhanced metastatic potential. Importantly enough, accumulating evidence strongly suggests that c-Myc can be a promising therapeutic target molecule among Myc family in terms of the biological characteristics of cancer stem-like cells (CSCs). The presence of CSCs leads to the intra-tumoral heterogeneity, which is mainly responsible for the therapeutic resistance. Mechanistically, it has been shown that Myc-induced epigenetic reprogramming enhances the CSC phenotypes. In this review article, the author describes two major therapeutic strategies of CSCs by targeting c-Myc; Firstly, Myc-dependent metabolic reprogramming is closely related to CD44 variant-dependent redox stress regulation in CSCs. It has been shown that c-Myc increases NADPH production via enhanced glutaminolysis with a finely-regulated mechanism. Secondly, the dormancy of CSCs due to FBW7-depedent c-Myc degradation pathway is also responsible for the therapeutic resistance to the conventional anti-tumor agents, the action points of which are largely dependent on the operation of the cell cycle. That is why the loss-of-functional mutations of FBW7 gene are expected to trigger "awakening" of dormant CSCs in the niche with c-Myc up-regulation. Collectively, although the further research is warranted to develop the effective anti-tumor therapeutic strategy targeting Myc family, we cancer researchers should always catch up with the current advances in the complex functions of Myc family in highly-malignant and heterogeneous tumor cells to realize the precision medicine.

Nuclear factor-κB p65 regulates glutaminase 1 expression in human hepatocellular carcinoma

Background

Glutaminase (GLS), the key enzyme that catalyzes glutamine catabolism, facilitates the production of energy, building blocks, and factors resisting stresses. Two isoforms of GLS have been identified: GLS1 and GLS2. Elevated GLS1 contributes to tumorigenesis and tumor progression. This study investigates the molecular mechanism by which GLS1 is regulated in human hepatocellular carcinoma (HCC).

Methods

Online databases were investigated to search for factors that co-overexpress with GLS1. siRNA knockdown or chemical compounds were utilized to manipulate the activation or inactivation of nuclear factor-κB (NF-κB) p65 signaling. Both the mRNA and protein levels of GLS1 were detected. The biological and clinical importance of p65-GLS1 in HCC was also demonstrated.

Results

NF-κB p65 regulates GLS1 expression in HCC cells. Knockdown or suppression of GLS1 compromises HCC cell proliferation. Elevated GLS1 expression correlates with neoplasm histological grade, and the dysregulation of p65-GLS1 is associated with poor prognosis in human HCC patients.

Conclusion

GLS1 can be developed as a diagnostic and therapeutic target for human HCC.

MYC-induced metabolic stress and tumorigenesis

The MYC oncogene is commonly altered across human cancers. Distinct from the normal MYC proto-oncogene, which is under tight transcriptional, translational, and post-translational control, deregulated oncogenic MYC drives imbalanced, non-linear amplification of transcription that results in oncogenic 'stress.' The term 'stress' had been a euphemism for our lack of mechanistic understanding, but synthesis of many studies over the past decade provides a more coherent picture of oncogenic MYC driving metastable cellular states, particularly altered metabolism, that activate and depend on cellular stress response pathways to allow for continued growth and survival. Both deregulated metabolism and these stress response pathways represent vulnerabilities that can be exploited therapeutically.

Cooperative STAT/NF-κB signaling regulates lymphoma metabolic reprogramming and aberrant GOT2 expression

Knowledge of stromal factors that have a role in the transcriptional regulation of metabolic pathways aside from c-Myc is fundamental to improvements in lymphoma therapy. Using a MYC-inducible human B-cell line, we observed the cooperative activation of STAT3 and NF-κB by IL10 and CpG stimulation. We show that IL10 + CpG-mediated cell proliferation of MYC^low cells depends on glutaminolysis. By ¹³C- and ¹⁵N-tracing of glutamine metabolism and metabolite rescue experiments, we demonstrate that GOT2 provides aspartate and nucleotides to cells with activated or aberrant Jak/STAT and NF-κB signaling. A model of GOT2 transcriptional regulation is proposed, in which the cooperative phosphorylation of STAT3 and direct joint binding of STAT3 and p65/NF-κB to the proximal GOT2 promoter are important. Furthermore, high aberrant GOT2 expression is prognostic in diffuse large B-cell lymphoma underscoring the current findings and importance of stromal factors in lymphoma biology.

Metabolic rewiring of cancer cells can be driven by both extrinsic and intrinsic factors. Here the authors show that microenvironmental factors induce metabolic rewiring of B-cell lymphoma through activation of STAT3 and NF-ΚB resulting in upregulation of the aminotransferase GOT2 and glutamine addiction.

Hedgehog-YAP Signaling Pathway Regulates Glutaminolysis to Control Activation of Hepatic Stellate Cells

BACKGROUND & AIMS

Cirrhosis results from accumulation of myofibroblasts derived from quiescent hepatic stellate cells (Q-HSCs); it regresses when myofibroblastic HSCs are depleted. Hedgehog signaling promotes transdifferentiation of HSCs by activating Yes-associated protein 1 (YAP1 or YAP) and inducing aerobic glycolysis. However, increased aerobic glycolysis alone cannot meet the high metabolic demands of myofibroblastic HSCs. Determining the metabolic processes of these cells could lead to strategies to prevent progressive liver fibrosis, so we investigated whether glutaminolysis (conversion of glutamine to alpha-ketoglutarate) sustains energy metabolism and permits anabolism when Q-HSCs become myofibroblastic, and whether this is controlled by hedgehog signaling to YAP.

METHODS

Primary HSCs were isolated from C57BL/6 or Smo^flox/flox mice; we also performed studies with rat and human myofibroblastic HSCs. We measured changes of glutaminolytic genes during culture-induced primary HSC transdifferentiation. Glutaminolysis was disrupted in cells by glutamine deprivation or pathway inhibitors (bis-2-[5-phenylacetamido-1,2,4-thiadiazol-2-yl] ethyl sulfide, CB-839, epigallocatechin gallate, and aminooxyacetic acid), and effects on mitochondrial respiration, cell growth and migration, and fibrogenesis were measured. Hedgehog signaling to YAP was disrupted in cells by adenovirus expression of Cre-recombinase or by small hairpin RNA knockdown of YAP. Hedgehog and YAP activity were inhibited by incubation of cells with cyclopamine or verteporfin, and effects on glutaminolysis were measured. Acute and chronic liver fibrosis were induced in mice by intraperitoneal injection of CCl₄ or methionine choline-deficient diet. Some mice were then given injections of bis-2-[5-phenylacetamido-1,2,4-thiadiazol-2-yl] ethyl sulfide to inhibit glutaminolysis, and myofibroblast accumulation was measured. We also performed messenger RNA and immunohistochemical analyses of percutaneous liver biopsies from healthy human and 4 patients with no fibrosis, 6 patients with mild fibrosis, and 3 patients with severe fibrosis.

RESULTS

Expression of genes that regulate glutaminolysis increased during transdifferentiation of primary Q-HSCs into myofibroblastic HSCs, and inhibition of glutaminolysis disrupted transdifferentiation. Blocking glutaminolysis in myofibroblastic HSCs suppressed mitochondrial respiration, cell growth and migration, and fibrogenesis; replenishing glutaminolysis metabolites to these cells restored these activities. Knockout of the hedgehog signaling intermediate smoothened or knockdown of YAP inhibited expression of glutaminase, the rate-limiting enzyme in glutaminolysis. Hedgehog and YAP inhibitors blocked glutaminolysis and suppressed myofibroblastic activities in HSCs. In livers of patients and of mice with acute or chronic fibrosis, glutaminolysis was induced in myofibroblastic HSCs. In mice with liver fibrosis, inhibition of glutaminase blocked accumulation of myofibroblasts and fibrosis progression.

CONCLUSIONS

Glutaminolysis controls accumulation of myofibroblast HSCs in mice and might be a therapeutic target for cirrhosis.

Exploiting Metabolic Vulnerabilities of Cancer with Precision and Accuracy

Links between oncogenic drivers and cancer cell metabolism have emerged over the past several decades, indicating that constitutive oncogenic growth signaling can render cancers susceptible to metabolic interventions. While significant progress has been achieved in the identification of metabolic vulnerabilities of cancer cells, the complexity of the tumor microenvironment (TME) and the dynamic nature of organismal circadian metabolism challenge the precision of targeting cancer metabolism. Here current progress in the areas of cancer metabolism and TME metabolism is reviewed, highlighting how cancer metabolism can be accurately and precisely targeted.

IRE1α RNase-dependent lipid homeostasis promotes survival in Myc-transformed cancers

Myc activation is a primary oncogenic event in many human cancers; however, these transcription factors are difficult to inhibit pharmacologically, suggesting that Myc-dependent downstream effectors may be more tractable therapeutic targets. Here, we show that Myc overexpression induces endoplasmic reticulum (ER) stress and engages the inositol-requiring enzyme 1α (IRE1α)/X-box binding protein 1 (XBP1) pathway through multiple molecular mechanisms in a variety of c-Myc- and N-Myc-dependent cancers. In particular, Myc-overexpressing cells require IRE1α/XBP1 signaling for sustained growth and survival in vitro and in vivo, dependent on elevated stearoyl-CoA-desaturase 1 (SCD1) activity. Pharmacological and genetic XBP1 inhibition induces Myc-dependent apoptosis, which is alleviated by exogenous unsaturated fatty acids. Of note, SCD1 inhibition phenocopies IRE1α RNase activity suppression in vivo. Furthermore, IRE1α inhibition enhances the cytotoxic effects of standard chemotherapy drugs used to treat c-Myc-overexpressing Burkitt's lymphoma, suggesting that inhibiting the IRE1α/XBP1 pathway is a useful general strategy for treatment of Myc-driven cancers.

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.

Targeting the hexosamine biosynthetic pathway and O-linked N-acetylglucosamine cycling for therapeutic and imaging capabilities in diffuse large B-cell lymphoma

The hexosamine biosynthetic pathway (HBP) requires two key nutrients glucose and glutamine for O-linked N-acetylglucosamine (O-GlcNAc) cycling, a post-translational protein modification that adds GlcNAc to nuclear and cytoplasmic proteins. Increased GlcNAc has been linked to regulatory factors involved in cancer cell growth and survival. However, the biological significance of GlcNAc in diffuse large B-cell lymphoma (DLBCL) is not well defined. This study is the first to show that both the substrate and the endpoint O-GlcNAc transferase (OGT) enzyme of the HBP were highly expressed in DLBCL cell lines and in patient tumors compared with normal B-lymphocytes. Notably, high OGT mRNA levels were associated with poor survival of DLBCL patients. Targeting OGT via small interference RNA in DLBCL cells inhibited activation of GlcNAc, nuclear factor kappa B (NF-κB), and nuclear factor of activated T-cells 1 (NFATc1), as well as cell growth. Depleting both glucose and glutamine in DLBCL cells or treating them with an HBP inhibitor (azaserine) diminished O-GlcNAc protein substrate, inhibited constitutive NF-κB and NFATc1 activation, and induced G0/G1 cell-cycle arrest and apoptosis. Replenishing glucose-and glutamine-deprived DLBCL cells with a synthetic glucose analog (ethylenedicysteine-N-acetylglucosamine [ECG]) reversed these phenotypes. Finally, we showed in both in vitro and in vivo murine models that DLBCL cells easily take up radiolabeled technetium-99m-ECG conjugate. These findings suggest that targeting the HBP has therapeutic relevance for DLBCL and underscores the imaging potential of the glucosamine analog ECG in DLBCL.

Glutamine Synthetase: Localization Dictates Outcome

Glutamine synthetase (GS) is the adenosine triphosphate (ATP)-dependent enzyme that catalyses the synthesis of glutamine by condensing ammonium to glutamate. In the circulatory system, glutamine carries ammonia from muscle and brain to the kidney and liver. In brain reduction of GS activity has been suggested as a mechanism mediating neurotoxicity in neurodegenerative disorders. In cancer, the delicate balance between glutamine synthesis and catabolism is a critical event. In vitro evidence, confirmed in vivo in some cases, suggests that reduced GS activity in cancer cells associates with a more invasive and aggressive phenotype. However, GS is known to be highly expressed in cells of the tumor microenvironment, such as fibroblasts, adipocytes and immune cells, and their ability to synthesize glutamine is responsible for the acquisition of protumoral phenotypes. This has opened a new window into the complex scenario of the tumor microenvironment, in which the balance of glutamine consumption versus glutamine synthesis influences cellular function. Since GS expression responds to glutamine starvation, a lower glutamine synthesizing power due to the absence of GS in cancer cells might apply a metabolic pressure on stromal cells. This event might push stroma towards a GS-high/protumoral phenotype. When referred to stromal cells, GS expression might acquire a ‘bad’ significance to the point that GS inhibition might be considered a conceivable strategy against cancer metastasis.

Pharmacological blockade of ASCT2-dependent glutamine transport leads to antitumor efficacy in preclinical models

The unique metabolic demands of cancer cells underscore potentially fruitful opportunities for drug discovery in the era of precision medicine. However, therapeutic targeting of cancer metabolism has led to surprisingly few new drugs to date. The neutral amino acid glutamine serves as a key intermediate in numerous metabolic processes leveraged by cancer cells, including biosynthesis, cell signaling, and oxidative protection. Herein we report the preclinical development of V-9302, a competitive small molecule antagonist of transmembrane glutamine flux that selectively and potently targets the amino acid transporter ASCT2. Pharmacological blockade of ASCT2 with V-9302 resulted in attenuated cancer cell growth and proliferation, increased cell death, and increased oxidative stress, which collectively contributed to antitumor responses in vitro and in vivo. This is the first study, to our knowledge, to demonstrate the utility of a pharmacological inhibitor of glutamine transport in oncology, representing a new class of targeted therapy and laying a framework for paradigm-shifting therapies targeting cancer cell metabolism.

Expression of glutamine metabolism-related proteins in thyroid cancer

PURPOSE

This study aimed to investigate the expression of glutamine metabolism-related protein in tumor and stromal compartments among the histologic subtypes of thyroid cancer.

RESULTS

GLS1 and GDH expression in tumor and stromal compartments were the highest in AC than in other subtypes. Tumoral ASCT2 expression was higher in MC but lower in FC (p < 0.001). In PTC, tumoral GLS1 and tumoral GDH expression was higher in the conventional type than in the follicular variant (p = 0.043 and 0.001, respectively), and in PTC with BRAF V600E mutation than in PTC without BRAF V600E mutation (p<0.001). Stromal GDH positivity was the independent factor associated with short overall survival (hazard ratio: 21.48, 95% confidence interval: 2.178-211.8, p = 0.009).

METHODS

We performed tissue microarrays with 557 thyroid cancer cases (papillary thyroid carcinoma [PTC]: 344, follicular carcinoma [FC]: 112, medullary carcinoma [MC]: 70, poorly differentiated carcinoma [PDC]: 23, and anaplastic carcinoma [AC]: 8) and 152 follicular adenoma (FA) cases. We performed immunohistochemical staining of glutaminolysis-related proteins (glutaminase 1 [GLS1], glutamate dehydrogenase [GDH], and amino acid transporter-2 [ASCT-2]).

CONCLUSION

Glutamine metabolism-related protein expression differed among the histologic subtypes of thyroid cancer.

Glutamate Dehydrogenase as a Neuroprotective Target Against Neurodegeneration

Regulation of glutamate metabolism via glutamate dehydrogenase (GDH) might be the promising therapeutic approach for treating neurodegenerative disorders. In the central nervous system, glutamate functions both as a major excitatory neurotransmitter and as a key intermediate metabolite for neurons. GDH converts glutamate to α-ketoglutarate, which serves as a TCA cycle intermediate. Dysregulated GDH activity in the central nervous system is highly correlated with neurological disorders. Indeed, studies conducted with mutant mice and allosteric drugs have shown that deficient or overexpressed GDH activity in the brain can regulate whole body energy metabolism and affect early onset of Parkinson's disease, Alzheimer's disease, temporal lobe epilepsy, and spinocerebellar atrophy. Moreover, in strokes with excitotoxicity as the main pathophysiology, mice that overexpressed GDH exhibited smaller ischemic lesion than mice with normal GDH expression. In additions, GDH activators improve lesions in vivo by increasing α-ketoglutarate levels. In neurons exposed to an insult in vitro, enhanced GDH activity increases ATP levels. Thus, in an energy crisis, neuronal mitochondrial activity is improved and excitotoxic risk is reduced. Consequently, modulating GDH activity in energy-depleted conditions could be a sound strategy for maintaining the mitochondrial factory in neurons, and thus, protect against metabolic failure.

Inhibition of Glycolysis and Glutaminolysis: An Emerging Drug Discovery Approach to Combat Cancer

Cancer cells have a very different metabolism from that of normal cells from which they are derived. Their metabolism is elevated, which allows them to sustain higher proliferative rate and resist some cell death signals. This phenomenon, known as the "Warburg effect", has become the focus of intensive efforts in the discovery of new therapeutic targets and new cancer drugs. Both glycolysis and glutaminolysis pathways are enhanced in cancer cells. While glycolysis is enhanced to satisfy the increasing energy demand of cancer cells, glutaminolysis is enhanced to provide biosynthetic precursors for cancer cells. It was recently discovered that there is a tyrosine phosphorylation of a specific isoform of pyruvate kinase, the M2 isoform, that is preferentially expressed in all cancer cells, which results in the generation of pyruvate through a unique enzymatic mechanism that is uncoupled from ATP production. Pyruvate produced through this unique enzymatic mechanism is converted primarily into lactic acid, rather than acetyl-CoA for the synthesis of citrate, which would normally then enter the citric acid cycle. Inhibition of key enzymes in glycolysis and glutaminolysis pathways with small molecules has provided a novel but emerging area of cancer research and has been proven effective in slowing the proliferation of cancer cells, with several inhibitors being in clinical trials. This review paper will cover recent advances in the development of chemotherapeutic agents against several metabolic targets for cancer therapy, including glucose transporters, hexokinase, pyruvate kinase M2, glutaminase, and isocitrate dehydrogenase.

Digital gene expression analysis in the gills of Ruditapes philippinarum exposed to short- and long-term exposures of ammonia nitrogen

Previous study revealed severe toxic effects of ammonia nitrogen on Ruditapes philippinarum including lysosomal instability, disturbed metabolic profiles, gill tissues with damaged structure, and variation of neurotransmitter concentrations. However, the underlying molecular mechanism was not fully understood yet. In the present study, digital gene expression technology (DGE) was applied to globally screen the key genes and pathways involved in the responses to short- and long-term exposures of ammonia nitrogen. Results of DGE analysis indicated that short-term duration of ammonia exposure affected pathways in Dorso-ventral axis formation, Notch signaling, thyroid hormone signaling and protein processing in endoplasmic reticulum. The long-term exposure led to DEGs significantly enriched in gap junction, immunity, signal and hormone transduction, as well as key substance metabolism pathways. Functional research of significantly changed DEGs suggested that the immunity of R. philippinarum was weakened heavily by toxic effects of ammonia nitrogen, as well as neuro-transduction and metabolism of important substances. Taken together, the present study provides a molecular support for the previous results of the detrimental toxicity of ammonia exposure in R. philippinarum, further work will be performed to investigate the specific genes and their certain functions involved in ammonia toxicity to molluscs.

Metabolic Profiles Associated With Metformin Efficacy in Cancer

Metformin is one of the most commonly prescribed medications for the treatment of type 2 diabetes. Numerous reports have suggested potential anti-cancerous and cancer preventive properties of metformin, although these findings vary depending on the intrinsic properties of the tumor, as well as the systemic physiology of patients. These intriguing studies have led to a renewed interest in metformin use in the oncology setting, and fueled research to unveil its elusive mode of action. It is now appreciated that metformin inhibits complex I of the electron transport chain in mitochondria, causing bioenergetic stress in cancer cells, and rendering them dependent on glycolysis for ATP production. Understanding the mode of action of metformin and the consequences of its use on cancer cell bioenergetics permits the identification of cancer types most susceptible to metformin action. Such knowledge may also shed light on the varying results to metformin usage that have been observed in clinical trials. In this review, we discuss metabolic profiles of cancer cells that are associated with metformin sensitivity, and rationalize combinatorial treatment options. We use the concept of bioenergetic flexibility, which has recently emerged in the field of cancer cell metabolism, to further understand metabolic rearrangements that occur upon metformin treatment. Finally, we advance the notion that metabolic fitness of cancer cells increases during progression to metastatic disease and the emergence of therapeutic resistance. As a result, sophisticated combinatorial approaches that prevent metabolic compensatory mechanisms will be required to effectively manage metastatic disease.

Targeting KRAS Mutant CMS3 Subtype by Metabolic Inhibitors

Cancer cells rewire their metabolism in order to boost growth, survival, proliferation, and chemoresistance. The common event of this aberrant metabolism is the increased glucose uptake and fermentation of glucose to lactate. This phenomenon is observed even in the presence of O₂ and completely functioning mitochondria. This is known as the "Warburg Effect" and it is a hallmark in cancer. Up to 40% of all CRC's are known to have a mutated (abnormal) KRAS gene, found at differing frequencies in all consensus molecular subtypes (CMS). CMS3 colon cancer molecular subtype contains the so-called 'metabolic tumours' which represents 13% of total CR cases. These tumours display remarkable metabolic deregulation, often showing KRAS mutations (68%). Unfortunately, patients harbouring mutated KRAS are unlikely to benefit from anti-EGFR therapies. Moreover, it remains unclear that patients with KRAS wild-type CRC will definitely respond to such therapies. Although some clinically designed-strategies to modulate KRAS aberrant activation have been designed, all attempts to target KRAS have failed in the clinical assays and KRAS has been assumed to be invulnerable to chemotherapeutic attack. Quest for metabolic inhibitors with anti-tumour activity may constitute a novel and hopeful approach in order to handle KRAS dependent chemoresistance in colon cancer.

Targeting Glutamine Metabolism for Cancer Treatment

Rapidly proliferating cancer cells require energy and cellular building blocks for their growth and ability to maintain redox balance. Many studies have focused on understanding how cancer cells adapt their nutrient metabolism to meet the high demand of anabolism required for proliferation and maintaining redox balance. Glutamine, the most abundant amino acid in plasma, is a well-known nutrient used by cancer cells to increase proliferation as well as survival under metabolic stress conditions. In this review, we provide an overview of the role of glutamine metabolism in cancer cell survival and growth and highlight the mechanisms by which glutamine metabolism affects cancer cell signaling. Furthermore, we summarize the potential therapeutic approaches of targeting glutamine metabolism for the treatment of numerous types of cancer.

Teaching the basics of reactive oxygen species and their relevance to cancer biology: Mitochondrial reactive oxygen species detection, redox signaling, and targeted therapies

Reactive oxygen species (ROS) have been implicated in tumorigenesis (tumor initiation, tumor progression, and metastasis). Of the many cellular sources of ROS generation, the mitochondria and the NADPH oxidase family of enzymes are possibly the most prevalent intracellular sources. In this article, we discuss the methodologies to detect mitochondria-derived superoxide and hydrogen peroxide using conventional probes as well as newly developed assays and probes, and the necessity of characterizing the diagnostic marker products with HPLC and LC-MS in order to rigorously identify the oxidizing species. The redox signaling roles of mitochondrial ROS, mitochondrial thiol peroxidases, and transcription factors in response to mitochondria-targeted drugs are highlighted. ROS generation and ROS detoxification in drug-resistant cancer cells and the relationship to metabolic reprogramming are discussed. Understanding the subtle role of ROS in redox signaling and in tumor proliferation, progression, and metastasis as well as the molecular and cellular mechanisms (e.g., autophagy) could help in the development of combination therapies. The paradoxical aspects of antioxidants in cancer treatment are highlighted in relation to the ROS mechanisms in normal and cancer cells. Finally, the potential uses of newly synthesized exomarker probes for in vivo superoxide and hydrogen peroxide detection and the low-temperature electron paramagnetic resonance technique for monitoring oxidant production in tumor tissues are discussed.

Lipid Metabolism and Lipid Droplets in Pancreatic Cancer and Stellate Cells

Pancreatic ductal adenocarcinoma (PDAC) is projected to become the second deadliest cancer by 2030, and the overall 5-year survival rate is currently less than 7%. Cancer cells frequently exhibit reprogramming of their metabolic activity. It is increasingly recognized that aberrant de novo lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of various cancers, including pancreatic cancer. In this review, the current knowledge about lipid metabolism and lipid droplets in pancreatic cancer is discussed. In the first part, molecular mechanisms of lipid metabolism and roles of enzymes involved in lipid metabolism which are relevant for pancreatic cancer research are presented. Further, preclinical studies and clinical trials with drugs/inhibitors targeting cancer metabolic systems in cancer are summarized. An increase of our knowledge in lipid metabolism in pancreatic cancer cells and in tumor stroma is important for developing novel strategies of future individualized therapies of pancreatic cancer.

The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ

Malignant tumors reprogram cellular metabolism to support cancer cell proliferation and survival. Although most cancers depend on a high rate of aerobic glycolysis, many cancer cells also display addiction to glutamine. Glutamine transporters and glutaminase activity are critical for glutamine metabolism in tumor cells. We found that the receptor tyrosine kinase EphA2 activated the TEAD family transcriptional coactivators YAP and TAZ (YAP/TAZ), likely in a ligand-independent manner, to promote glutamine metabolism in cells and mouse models of HER2-positive breast cancer. Overexpression of EphA2 induced the nuclear accumulation of YAP and TAZ and increased the expression of YAP/TAZ target genes. Inhibition of the GTPase Rho or the kinase ROCK abolished EphA2-dependent YAP/TAZ nuclear localization. Silencing YAP or TAZ substantially reduced the amount of intracellular glutamate through decreased expression of SLC1A5 and GLS, respectively, genes that encode proteins that promote glutamine uptake and metabolism. The regulatory DNA elements of both SLC1A5 and GLS contain TEAD binding sites and were bound by TEAD4 in an EphA2-dependent manner. In patient breast cancer tissues, EphA2 expression positively correlated with that of YAP and TAZ, as well as that of GLS and SLC1A5 Although high expression of EphA2 predicted enhanced metastatic potential and poor patient survival, it also rendered HER2-positive breast cancer cells more sensitive to glutaminase inhibition. The findings define a previously unknown mechanism of EphA2-mediated glutaminolysis through YAP/TAZ activation in HER2-positive breast cancer and identify potential therapeutic targets in patients.

Metabolic Alterations in Cancer and Their Potential as Therapeutic Targets

Otto Warburg's discovery in the 1920s that tumor cells took up more glucose and produced more lactate than normal cells provided the first clues that cancer cells reprogrammed their metabolism. For many years, however, it was unclear as to whether these metabolic alterations were a consequence of tumor growth or an adaptation that provided a survival advantage to these cells. In more recent years, interest in the metabolic differences in cancer cells has surged, as tumor proliferation and survival have been shown to be dependent upon these metabolic changes. In this educational review, we discuss some of the mechanisms that tumor cells use for reprogramming their metabolism to provide the energy and nutrients that they need for quick or sustained proliferation and discuss the potential for therapeutic targeting of these pathways to improve patient outcomes.

Multifaceted Roles of Glutathione and Glutathione-Based Systems in Carcinogenesis and Anticancer Drug Resistance

SIGNIFICANCE

Glutathione is the most abundant antioxidant molecule in living organisms and has multiple functions. Intracellular glutathione homeostasis, through its synthesis, consumption, and degradation, is an intricately balanced process. Glutathione levels are often high in tumor cells before treatment, and there is a strong correlation between elevated levels of intracellular glutathione/sustained glutathione-mediated redox activity and resistance to pro-oxidant anticancer therapy. Recent Advances: Ample evidence demonstrates that glutathione and glutathione-based systems are particularly relevant in cancer initiation, progression, and the development of anticancer drug resistance.

CRITICAL ISSUES

This review highlights the multifaceted roles of glutathione and glutathione-based systems in carcinogenesis, anticancer drug resistance, and clinical applications.

FUTURE DIRECTIONS

The evidence summarized here underscores the important role played by glutathione and the glutathione-based systems in carcinogenesis and anticancer drug resistance. Future studies should address mechanistic questions regarding the distinct roles of glutathione in different stages of cancer development and cancer cell death. It will be important to study how metabolic alterations in cancer cells can influence glutathione homeostasis. Sensitive approaches to monitor glutathione dynamics in subcellular compartments will be an indispensible step. Therapeutic perspectives should focus on mechanism-based rational drug combinations that are directed against multiple redox targets using effective, specific, and clinically safe inhibitors. This new strategy is expected to produce a synergistic effect, prevent drug resistance, and diminish doses of single drugs. Antioxid. Redox Signal. 27, 1217-1234.

Identification of cellular genes and pathways important for tumorigenicity of hepatocellular carcinoma cell lines by proteomic profiling

Hepatocellular carcinoma (HCC) is the most commonly diagnosed malignancy of the liver. A more thorough understanding of HCC pathogenesis will provide novel targets for development of cancer drugs to effectively treat HCC. To further this goal, we carried out a proteomic profiling of HCC cell lines Huh-7.4 and Huh-7.5. These two cell lines were derived from subgenomic HCV RNA-replicating Huh-7 cells upon clearance of HCV RNA by antiviral drug treatment. Initially, the tumorigenicity of each cell line was determined and compared in parallel in the same immunedeficient mice. Strikingly, the Huh-7.4 cell line was able to induce tumors, whereas the Huh-7.5 cell line failed to do so, providing unique model systems for identifying cellular genes and pathways important for HCC development and progression. Subsequently, one-dimensional LC-MS/MS proteomic and bioinformatics analyses were performed in the hope of identifying unique cellular genes and pathways responsible for HCC tumorigenicity. Interestingly, a total of 130 cellular genes were found to be significantly up- or downregulated between these two cell lines (r>3 fold, P<0.001). Also, EIF (EIF2&4), mTOR/p70S6K, ERK5, and EGFR signaling pathways were significantly different. Overall, these results provide significant new information to shed light on the underlying biological processes involved in HCC development and progression.

MYC and tumor metabolism: chicken and egg

Transcription factors of the MYC family are deregulated in the majority of all human cancers. Oncogenic levels of MYC reprogram cellular metabolism, a hallmark of cancer development, to sustain the high rate of proliferation of cancer cells. Conversely, cells need to modulate MYC function according to the availability of nutrients, in order to avoid a metabolic collapse. Here, we review recent evidence that the multiple interactions of MYC with cell metabolism are mutual and review mechanisms that control MYC levels and function in response to metabolic stress situations. The main hypothesis we put forward is that regulation of MYC levels is an integral part of the adaptation of cells to nutrient deprivation. Since such mechanisms would be particularly relevant in tumor cells, we propose that-in contrast to growth factor-dependent controls-they are not disrupted during tumorigenesis and that maintaining flexibility of expression is integral to MYC's oncogenic function.

Glutamine deficiency induces DNA alkylation damage and sensitizes cancer cells to alkylating agents through inhibition of ALKBH enzymes

Driven by oncogenic signaling, glutamine addiction exhibited by cancer cells often leads to severe glutamine depletion in solid tumors. Despite this nutritional environment that tumor cells often experience, the effect of glutamine deficiency on cellular responses to DNA damage and chemotherapeutic treatment remains unclear. Here, we show that glutamine deficiency, through the reduction of alpha-ketoglutarate, inhibits the AlkB homolog (ALKBH) enzymes activity and induces DNA alkylation damage. As a result, glutamine deprivation or glutaminase inhibitor treatment triggers DNA damage accumulation independent of cell death. In addition, low glutamine-induced DNA damage is abolished in ALKBH deficient cells. Importantly, we show that glutaminase inhibitors, 6-Diazo-5-oxo-L-norleucine (DON) or CB-839, hypersensitize cancer cells to alkylating agents both in vitro and in vivo. Together, the crosstalk between glutamine metabolism and the DNA repair pathway identified in this study highlights a potential role of metabolic stress in genomic instability and therapeutic response in cancer.

Cancer cells residing within the intratumoral microenvironment are subject to severe glutamine shortages. Herein, we provide mechanistic insight by which glutamine deficiency leads to cellular sensitivity to alkylating agents. We find that glutamine deficiency inhibits the DNA repair activity of the ALKBH enzymes, leading to accumulation of DNA alkylation damage and thereby increasing cellular sensitivity to alkylating agents. This study provides a critical molecular basis to combine glutaminase inhibitors with alkylating agents for more effective treatment of cancers. These findings extend our understanding of the role of metabolic stress, in particular glutamine deficiency, in tumor development and therapeutic response.

Deciphering metabolic rewiring in breast cancer subtypes

Metabolic reprogramming, an emerging hallmark of cancer, is observed in breast cancer. Breast cancer cells rewire their cellular metabolism to meet the demands of survival, proliferation, and invasion. However, breast cancer is a heterogeneous disease, and metabolic rewiring is not uniform. Each subtype of breast cancer displays distinct metabolic alterations. Here, we focus on unique metabolic reprogramming associated with subtypes of breast cancer, as well as common features. Therapeutic opportunities based on subtype-specific metabolic alterations are also discussed. Through this discussion, we aim to provide insight into subtype-specific metabolic rewiring and vulnerabilities that have the potential to better guide therapy and improve outcomes for patients.

Selenite inhibits glutamine metabolism and induces apoptosis by regulating GLS1 protein degradation via APC/C-CDH1 pathway in colorectal cancer cells

Glutaminolysis is important for metabolism and biosynthesis of cancer cells, and GLS is essential in the process. Selenite is widely regarded as a chemopreventive agent against cancer risk. Emerging evidence suggests that it also has chemotherapeutic potential in various cancer types, but the mechanism remains elusive. We demonstrate for the first time that supranutritional dose of selenite suppresses glutaminolysis by promoting GLS1 protein degradation and apoptosis. Mechanistically, selenite promotes association of APC/C-CDH1 with GLS1 and leads to GLS1 degradation by ubiquitination, this process is related to induction of PTEN expression. In addition, GLS1 expression is increased in human colorectal cancer tissues compared with normal mucosae. Our data provide a novel mechanistic explanation for the anti-cancer effect of selenite from a perspective of cell metabolism. Moreover, our results indicate that glutaminolysis especially GLS1 could be an attractive therapeutic target in colorectal cancer.

Targeted inhibition of glutaminase as a potential new approach for the treatment of NF1 associated soft tissue malignancies

Many cancer cells rely on glutamine as the source of carbon molecules to feed the biosynthetic pathways and are often addicted to glutaminolysis. Inhibitors of glutaminase activity have gained attention in the last few years due to their anti-proliferative effect and ability to induce apoptosis in some cancers. Although it is a promising therapeutic approach, its efficacy or the role played by glutamine in modulating cell proliferation in NF1 associated tumors has never been studied. We report for the first time, a strong correlation between the NF1 status of tumor cells and increased sensitivity to glutamine deprivation and glutaminase inhibition. Soft-tissue cell lines null for NF1 were highly dependent on glutamine for proliferation and showed decreased mTORC1 and Ras activity in response to glutaminase inhibition. Re-addition of glutamine or intermediary metabolite such as glutamate to the media restored mTORC1 and Ras activity. SiRNA mediated NF1 knockdown in wild-type NF1 cell line shows increased sensitivity to glutaminase inhibition. Conversely, NF1 overexpression in NF1 null cell lines results in reduced sensitivity to glutaminase inhibition, and restores mTORC1 signaling and Ras activity. These findings provide new insights into the role played by glutamine metabolism in NF1 associated tumors and strongly warrant further investigation as a potential therapy in the NF1 disease setting.

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.

Targeting Metabolism for Cancer Therapy

Metabolic reprogramming contributes to tumor development and introduces metabolic liabilities that can be exploited to treat cancer. Chemotherapies targeting metabolism have been effective cancer treatments for decades, and the success of these therapies demonstrates that a therapeutic window exists to target malignant metabolism. New insights into the differential metabolic dependencies of tumors have provided novel therapeutic strategies to exploit altered metabolism, some of which are being evaluated in preclinical models or clinical trials. Here, we review our current understanding of cancer metabolism and discuss how this might guide treatments targeting the metabolic requirements of tumor cells.

Altered Metabolism of Leukemic Cells: New Therapeutic Opportunity

The cancer metabolic program alters bioenergetic processes to meet the higher demands of tumor cells for biomass production, nucleotide synthesis, and NADPH-balancing redox homeostasis. It is widely accepted that cancer cells mostly utilize glycolysis, as opposed to normal cells, in which oxidative phosphorylation is the most employed bioenergetic process. Still, studies examining cancer metabolism had been overlooked for many decades, and it was only recently discovered that metabolic alterations affect both the oncogenic potential and therapeutic response. Since most of the published works concern solid tumors, in this comprehensive review, we aim to summarize knowledge about the metabolism of leukemia cells. Leukemia is a malignant disease that ranks first and fifth in cancer-related deaths in children and adults, respectively. Current treatment has reached its limits due to toxicity, and there has been a need for new therapeutic approaches. One of the possible scenarios is improved use of established drugs and another is to introduce new druggable targets. Herein, we aim to describe the complexity of leukemia metabolism and highlight cellular processes that could be targeted therapeutically and enhance the effectiveness of current treatments.

Treatment of Pancreatic Cancer Patient-Derived Xenograft Panel with Metabolic Inhibitors Reveals Efficacy of Phenformin

Purpose: To identify effective metabolic inhibitors to suppress the aggressive growth of pancreatic ductal adenocarcinoma (PDAC), we explored the in vivo antitumor efficacy of metabolic inhibitors, as single agents, in a panel of patient-derived PDAC xenograft models (PDX) and investigated whether genomic alterations of tumors correlate with the sensitivity to metabolic inhibitors.Experimental Design: Mice with established PDAC tumors from 6 to 13 individual PDXs were randomized and treated, once daily for 4 weeks, with either sterile PBS (vehicle) or the glutaminase inhibitor bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES), transaminase inhibitor aminooxyacetate (AOA), pyruvate dehydrogenase kinase inhibitor dichloroacetate (DCA), autophagy inhibitor chloroquine (CQ), and mitochondrial complex I inhibitor phenformin/metformin.Results: Among the agents tested, phenformin showed significant tumor growth inhibition (>30% compared with vehicle) in 5 of 12 individual PDXs. Metformin, at a fivefold higher dose, displayed significant tumor growth inhibition in 3 of 12 PDXs similar to BPTES (2/8 PDXs) and DCA (2/6 PDXs). AOA and CQ had the lowest response rates. Gene set enrichment analysis conducted using the baseline gene expression profile of pancreatic tumors identified a gene expression signature that inversely correlated with phenformin sensitivity, which is in agreement with the phenformin gene expression signature of NIH Library of Integrated Network-based Cellular Signatures (LINCS). The PDXs that were more sensitive to phenformin showed a baseline reduction in amino acids and elevation in oxidized glutathione. There was no correlation between phenformin response and genetic alterations in KRAS, TP53, SMAD4, or PTENConclusions: Phenformin treatment showed relatively higher antitumor efficacy against established PDAC tumors, compared with the efficacy of other metabolic inhibitors and metformin. Phenformin treatment significantly diminished PDAC tumor progression and prolonged tumor doubling time. Overall, our results serve as a foundation for further evaluation of phenformin as a therapeutic agent in pancreatic cancer. Clin Cancer Res; 23(18); 5639-47. ©2017 AACR.

Glutaminase inhibition in multiple myeloma induces apoptosis via MYC degradation

Multiple Myeloma (MM) is an incurable hematological malignancy affecting millions of people worldwide. As in all tumor cells both glucose and more recently glutamine have been identified as important for MM cellular metabolism, however there is some dispute as to the role of glutamine in MM cell survival. Here we show that the small molecule inhibitor compound 968 effectively inhibits glutaminase and that this inhibition induces apoptosis in both human multiple myeloma cell lines (HMCLs) and primary patient material. The HMCL U266 which does not express MYC was insensitive to both glutamine removal and compound 968, but ectopic expression of MYC imparted sensitivity. Finally, we show that glutamine depletion is reflected by rapid loss of MYC protein which is independent of MYC transcription and post translational modifications. However, MYC loss is dependent on proteasomal activity, and this loss was paralleled by an equally rapid induction of apoptosis. These findings are in contrast to those of glucose depletion which largely affected rates of proliferation in HMCLs, but had no effects on either MYC expression or viability. Therefore, inhibition of glutaminolysis is effective at inducing apoptosis and thus serves as a possible therapeutic target in MM.

Cancer Hallmarks and MicroRNAs: The Therapeutic Connection

Human cancers are characterized by a number of hallmarks, including sustained proliferative signaling, evasion of growth suppressors, activated invasion and metastasis, replicative immortality, angiogenesis, resistance to cell death, and evasion of immune destruction. As microRNAs (miRNAs) are deregulated in virtually all human cancers, they show involvement in each of the cancer hallmarks as well. In this chapter, we describe the involvement of miRNAs in cancer from a cancer hallmarks and targeted therapeutics point of view. As no miRNA-based cancer therapeutics are available to date, and the only clinical trial on miRNA-based cancer therapeutics (MRX34) was terminated prematurely due to serious adverse events, we are focusing on protein-coding miRNA targets for which targeted therapeutics in oncology are already approved by the FDA. For each of the cancer hallmarks, we selected major protein-coding players and describe the miRNAs that target them.

Drug-induced amino acid deprivation as strategy for cancer therapy

Cancer is caused by uncontrollable growth of neoplastic cells, leading to invasion of adjacent and distant tissues resulting in death. Cancer cells have specific nutrient(s) auxotrophy and have a much higher nutrient demand compared to normal tissues. Therefore, different metabolic inhibitors or nutrient-depleting enzymes have been tested for their anti-cancer activities. We review recent available laboratory and clinical data on using various specific amino acid metabolic pathways inhibitors in treating cancers. Our focus is on glutamine, asparagine, and arginine starvation. These three amino acids are chosen due to their better scientific evidence compared to other related approaches in cancer treatment. Amino acid-specific depleting enzymes have been adopted in different standard chemotherapy protocols. Glutamine starvation by glutaminase inhibitior, transporter inhibitor, or glutamine depletion has shown to have significant anti-cancer effect in pre-clinical studies. Currently, glutaminase inhibitor is under clinical trial for testing anti-cancer efficacy. Clinical data suggests that asparagine depletion is effective in treating hematologic malignancies even as a single agent. On the other hand, arginine depletion has lower toxicity profile and can effectively reduce the level of pro-cancer biochemicals in patients as shown by ours and others’ data. This supports the clinical use of arginine depletion as anti-cancer therapy but its exact efficacy in various cancers requires further investigation. However, clinical application of these enzymes is usually hindered by common problems including allergy to these foreign proteins, off-target cytotoxicity, short half-life and rapidly emerging chemoresistance. There have been efforts to overcome these problems by modifying the drugs in different ways to circumvent these hindrance such as (1) isolate human native enzymes to reduce allergy, (2) isolate enzyme isoforms with higher specificities and efficiencies, (3) pegylate the enzymes to reduce allergy and prolong the half-lives, and (4) design drug combinations protocols to enhance the efficacy of chemotherapy by drug synergy and minimizing resistance. These improvements can potentially lead to the development of more effective anti-cancer treatment with less adverse effects and higher therapeutic efficacy.

MYC is a positive regulator of choline metabolism and impedes mitophagy-dependent necroptosis in diffuse large B-cell lymphoma

The activation of oncogenes can reprogram tumor cell metabolism. Here, in diffuse large B-cell lymphoma (DLBCL), serum metabolomic analysis revealed that oncogenic MYC could induce aberrant choline metabolism by transcriptionally activating the key enzyme phosphate cytidylyltransferase 1 choline-α (PCYT1A). In B-lymphoma cells, as a consequence of PCYT1A upregulation, MYC impeded lymphoma cells undergo a mitophagy-dependent necroptosis. In DLBCL patients, overexpression of PCYT1A was in parallel with an increase in tumor MYC, as well as a decrease in serum choline metabolite phosphatidylcholine levels and an International Prognostic Index, indicating intermediate-high or high risk. Both in vitro and in vivo, lipid-lowering alkaloid berberine (BBR) exhibited an anti-lymphoma activity through inhibiting MYC-driven downstream PCYT1A expression and inducing mitophagy-dependent necroptosis. Collectively, PCYT1A was upregulated by MYC, which resulted in the induction of aberrant choline metabolism and the inhibition of B-lymphoma cell necroptosis. Referred as a biomarker for DLBCL progression, PCYT1A can be targeted by BBR, providing a potential lipid-modifying strategy in treating MYC-High lymphoma.

Compensatory metabolic networks in pancreatic cancers upon perturbation of glutamine metabolism

Pancreatic ductal adenocarcinoma is a notoriously difficult-to-treat cancer and patients are in need of novel therapies. We have shown previously that these tumours have altered metabolic requirements, making them highly reliant on a number of adaptations including a non-canonical glutamine (Gln) metabolic pathway and that inhibition of downstream components of Gln metabolism leads to a decrease in tumour growth. Here we test whether recently developed inhibitors of glutaminase (GLS), which mediates an early step in Gln metabolism, represent a viable therapeutic strategy. We show that despite marked early effects on in vitro proliferation caused by GLS inhibition, pancreatic cancer cells have adaptive metabolic networks that sustain proliferation in vitro and in vivo. We use an integrated metabolomic and proteomic platform to understand this adaptive response and thereby design rational combinatorial approaches. We demonstrate that pancreatic cancer metabolism is adaptive and that targeting Gln metabolism in combination with these adaptive responses may yield clinical benefits for patients.

The MYC mRNA 3'-UTR couples RNA polymerase II function to glutamine and ribonucleotide levels

Deregulated expression of MYC enhances glutamine utilization and renders cell survival dependent on glutamine, inducing "glutamine addiction". Surprisingly, colon cancer cells that express high levels of MYC due to WNT pathway mutations are not glutamine-addicted but undergo a reversible cell cycle arrest upon glutamine deprivation. We show here that glutamine deprivation suppresses translation of endogenous MYC via the 3'-UTR of the MYC mRNA, enabling escape from apoptosis. This regulation is mediated by glutamine-dependent changes in adenosine-nucleotide levels. Glutamine deprivation causes a global reduction in promoter association of RNA polymerase II (RNAPII) and slows transcriptional elongation. While activation of MYC restores binding of MYC and RNAPII function on most promoters, restoration of elongation is imperfect and activation of MYC in the absence of glutamine causes stalling of RNAPII on multiple genes, correlating with R-loop formation. Stalling of RNAPII and R-loop formation can cause DNA damage, arguing that the MYC 3'-UTR is critical for maintaining genome stability when ribonucleotide levels are low.

The glutamate/cystine antiporter SLC7A11/xCT enhances cancer cell dependency on glucose by exporting glutamate

Cancer cells with specific genetic alterations may be highly dependent on certain nutrients for survival, which can inform therapeutic strategies to target these cancer-specific metabolic vulnerabilities. The glutamate/cystine antiporter solute carrier family 7 member 11 (SLC7A11, also called xCT) is overexpressed in several cancers. Contrasting the established pro-survival roles of SLC7A11 under other stress conditions, here we report the unexpected finding that SLC7A11 overexpression enhances cancer cell dependence on glucose and renders cancer cells more sensitive to glucose starvation-induced cell death and, conversely, that SLC7A11 deficiency by either knockdown or pharmacological inhibition promotes cancer cell survival upon glucose starvation. We further show that glucose starvation induces SLC7A11 expression through ATF4 and NRF2 transcription factors and, correspondingly, that ATF4 or NRF2 deficiency also renders cancer cells more resistant to glucose starvation. Finally, we show that SLC7A11 overexpression decreases whereas SLC7A11 deficiency increases intracellular glutamate levels because of SLC7A11-mediated glutamate export and that supplementation of α-ketoglutarate, a key downstream metabolite of glutamate, fully restores survival in SLC7A11-overexpressing cells under glucose starvation. Together, our results support the notion that both glucose and glutamate have important roles in maintaining cancer cell survival and uncover a previously unappreciated role of SLC7A11 to promote cancer cell dependence on glucose. Our study therefore informs therapeutic strategies to target the metabolic vulnerability in tumors with high SLC7A11 expression.