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Metabolic alterations are established as a hallmark of cancer. Such hallmark changes in cancer metabolism are characterized by reprogramming of energy-producing pathways and increases in the generation of biosynthetic intermediates to meet the needs of rapidly proliferating tumor cells. Various metabolic phenotypes such as aerobic glycolysis, increased glutamine consumption, and lipolysis have also been associated with the process of metastasis. However, in addition to the energy and biosynthetic alterations, a number of secondary functions of enzymes and metabolites are emerging that specifically contribute to metastasis. Here, we describe atypical intracellular roles of metabolic enzymes, extracellular functions of metabolic enzymes, roles of metabolites as signaling molecules, and epigenetic regulation mediated by altered metabolism, all of which can affect metastatic progression. We highlight how some of these mechanisms are already being exploited for therapeutic purposes, and discuss how others show similar potential.
Human cytochrome P450 (P450) family 4 enzymes are involved in the metabolism of fatty acids and the bioactivation of carcinogenic arylamines and toxic natural products, e.g., 4-ipomeanol. These and other drug-metabolizing P450s are redox sensitive, showing a loss of activity resulting from preincubation with HO and recovery with mild reducing agents [Albertolle, M. W., et al. (2017) J. Biol. Chem. 292, 11230-11242]. The inhibition is due to sulfenylation of the heme-thiolate ligand, as determined by chemopreoteomics and spectroscopy. This phenomenon may have implications for chemical toxicity and observed disease-drug interactions, in which the decreased metabolism of P450 substrates occurs in patients with inflammatory diseases (e.g., influenza and autoimmunity). Human P450 1A2 was determined to be redox insensitive. To determine the mechanism underlying the differential redox sensitivity, molecular dynamics (MD) simulations were employed using the crystal structure of rabbit P450 4B1 (Protein Data Bank entry 5T6Q ). In simulating either the thiolate (Cys-S) or the sulfenic acid (Cys-SOH) at the heme ligation site, MD revealed Gln-451 in either an "open" or "closed" conformation, respectively, between the cytosol and heme-thiolate cysteine. Mutation to either an isosteric leucine (Q451L) or glutamate (Q451E) abrogated the redox sensitivity, suggesting that this "open" conformation allows for reduction of the sulfenic acid and religation of the thiolate to the heme iron. In summary, MD simulations suggest that Gln-451 in P450 4B1 adopts conformations that may stabilize and protect the heme-thiolate sulfenic acid; mutating this residue destabilizes the interaction, producing a redox insensitive enzyme.
Hepatocyte lipotoxicity is characterized by aberrant mitochondrial metabolism, which predisposes cells to oxidative stress and apoptosis. Previously, we reported that translocation of calcium from the endoplasmic reticulum to mitochondria of palmitate-treated hepatocytes activates anaplerotic flux from glutamine to α-ketoglutarate (αKG), which subsequently enters the citric acid cycle (CAC) for oxidation. We hypothesized that increased glutamine anaplerosis fuels elevations in CAC flux and oxidative stress following palmitate treatment. To test this hypothesis, primary rat hepatocytes or immortalized H4IIEC3 rat hepatoma cells were treated with lipotoxic levels of palmitate while modulating anaplerotic pathways leading to αKG. We found that culture media supplemented with glutamine, glutamate, or dimethyl-αKG increased palmitate lipotoxicity compared with media that lacked these anaplerotic substrates. Knockdown of glutamate-oxaloacetate transaminase activity significantly reduced the lipotoxic effects of palmitate, whereas knockdown of glutamate dehydrogenase (Glud1) had no effect on palmitate lipotoxicity. C flux analysis of H4IIEC3 cells co-treated with palmitate and the pan-transaminase inhibitor aminooxyacetic acid confirmed that reductions in lipotoxic markers were associated with decreases in anaplerosis, CAC flux, and oxygen consumption. Taken together, these results demonstrate that lipotoxic palmitate treatments enhance anaplerosis in cultured rat hepatocytes, causing a shift to aberrant transaminase metabolism that fuels CAC dysregulation and oxidative stress.
© 2019 Egnatchik et al.
Many tumors increase uptake and dependence on glucose, cystine or glutamine. These basic observations on cancer cell metabolism have opened multiple new diagnostic and therapeutic avenues in cancer research. Recent studies demonstrated that smoking could induce the expression of xCT (SLC7A11) in oral cancer cells, suggesting that overexpression of xCT may support lung tumor progression. We hypothesized that overexpression of xCT occurs in lung cancer cells to satisfy the metabolic requirements for growth and survival. Our results demonstrated that 1) xCT was highly expressed at the cytoplasmic membrane in non-small cell lung cancer (NSCLC), 2) the expression of xCT was correlated with advanced stage and predicted a worse 5-year survival, 3) targeting xCT transport activity in xCT overexpressing NSCLC cells with sulfasalazine decreased cell proliferation and invasion in vitro and in vivo and 4) increased dependence on glutamine was observed in xCT overexpressed normal airway epithelial cells. These results suggested that xCT regulate metabolic requirements during lung cancer progression and be a potential therapeutic target in NSCLC.
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.
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 or substantially reduced the amount of intracellular glutamate through decreased expression of and , respectively, genes that encode proteins that promote glutamine uptake and metabolism. The regulatory DNA elements of both and contain TEAD binding sites and were bound by TEAD4 in an EphA2-dependent manner. In patient breast cancer tissues, expression positively correlated with that of and , as well as that of and Although high expression of 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.
Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
Decreasing glucagon action lowers the blood glucose and may be useful therapeutically for diabetes. However, interrupted glucagon signaling leads to α cell proliferation. To identify postulated hepatic-derived circulating factor(s) responsible for α cell proliferation, we used transcriptomics/proteomics/metabolomics in three models of interrupted glucagon signaling and found that proliferation of mouse, zebrafish, and human α cells was mTOR and FoxP transcription factor dependent. Changes in hepatic amino acid (AA) catabolism gene expression predicted the observed increase in circulating AAs. Mimicking these AA levels stimulated α cell proliferation in a newly developed in vitro assay with L-glutamine being a critical AA. α cell expression of the AA transporter Slc38a5 was markedly increased in mice with interrupted glucagon signaling and played a role in α cell proliferation. These results indicate a hepatic α islet cell axis where glucagon regulates serum AA availability and AAs, especially L-glutamine, regulate α cell proliferation and mass via mTOR-dependent nutrient sensing.
Copyright © 2017 Elsevier Inc. All rights reserved.
PURPOSE - This study aimed to study whether cancer cells possess distinguishing metabolic features compared with surrounding normal cells, such as increased glutamine uptake. Given this, quantitative measures of glutamine uptake may reflect critical processes in oncology. Approximately, 10 % of patients with colorectal cancer (CRC) express BRAF , which may be actionable with selective BRAF inhibitors or in combination with inhibitors of complementary signaling axes. Non-invasive and quantitative predictive measures of response to these targeted therapies remain poorly developed in this setting. The primary objective of this study was to explore 4-[F]fluoroglutamine (4-[F]F-GLN) positron emission tomography (PET) to predict response to BRAF-targeted therapy in preclinical models of colon cancer.
PROCEDURES - Tumor microarrays from patients with primary human colon cancers (n = 115) and CRC liver metastases (n = 111) were used to evaluate the prevalence of ASCT2, the primary glutamine transporter in oncology, by immunohistochemistry. Subsequently, 4-[F]F-GLN PET was evaluated in mouse models of human BRAF -expressing and BRAF wild-type CRC.
RESULTS - Approximately 70 % of primary colon cancers and 53 % of metastases exhibited positive ASCT2 immunoreactivity, suggesting that [F]4-F-GLN PET could be applicable to a majority of patients with colon cancer. ASCT2 expression was not associated selectively with the expression of mutant BRAF. Decreased 4-[F]F-GLN predicted pharmacological response to single-agent BRAF and combination BRAF and PI3K/mTOR inhibition in BRAF -mutant Colo-205 tumors. In contrast, a similar decrease was not observed in BRAF wild-type HCT-116 tumors, a setting where BRAF-targeted therapies are ineffective.
CONCLUSIONS - 4-[F]F-GLN PET selectively reflected pharmacodynamic response to BRAF inhibition when compared with 2-deoxy-2[F]fluoro-D-glucose PET, which was decreased non-specifically for all treated cohorts, regardless of downstream pathway inhibition. These findings illustrate the utility of non-invasive PET imaging measures of glutamine uptake to selectively predict response to BRAF-targeted therapy in colon cancer and may suggest further opportunities to inform colon cancer clinical trials using targeted therapies against MAPK activation.
Dysregulation of receptor tyrosine kinases (RTK) contributes to cellular transformation and cancer progression by disrupting key metabolic signaling pathways. The EPHA2 RTK is overexpressed in aggressive forms of breast cancer, including the HER2(+) subtype, and correlates with poor prognosis. However, the role of EPHA2 in tumor metabolism remains unexplored. In this study, we used in vivo and in vitro models of HER2-overexpressing breast cancer to investigate the mechanisms by which EPHA2 ligand-independent signaling promotes tumorigenesis in the absence of its prototypic ligand, ephrin-A1. We demonstrate that ephrin-A1 loss leads to upregulated glutamine metabolism and lipid accumulation that enhanced tumor growth. Global metabolic profiling of ephrin-A1-null, HER2-overexpressing mammary tumors revealed a significant increase in glutaminolysis, a critical metabolic pathway that generates intermediates for lipogenesis. Pharmacologic inhibition of glutaminase activity reduced tumor growth in both ephrin-A1-depleted and EPHA2-overexpressing tumor allografts in vivo Mechanistically, we show that the enhanced proliferation and glutaminolysis in the absence of ephrin-A1 were attributed to increased RhoA-dependent glutaminase activity. EPHA2 depletion or pharmacologic inhibition of Rho, glutaminase, or fatty acid synthase abrogated the increased lipid content and proliferative effects of ephrin-A1 knockdown. Together, these findings highlight a novel, unsuspected connection between the EPHA2/ephrin-A1 signaling axis and tumor metabolism, and suggest potential new therapeutic targets in cancer subtypes exhibiting glutamine dependency. Cancer Res; 76(7); 1825-36. ©2016 AACR.
©2016 American Association for Cancer Research.
Herein, we report the discovery of 2-amino-4-bis(aryloxybenzyl)aminobutanoic acids as novel inhibitors of ASCT2(SLC1A5)-mediated glutamine accumulation in mammalian cells. Focused library development led to two novel ASCT2 inhibitors that exhibit significantly improved potency compared with prior art in C6 (rat) and HEK293 (human) cells. The potency of leads reported here represents a 40-fold improvement over our most potent, previously reported inhibitor and represents, to our knowledge, the most potent pharmacological inhibitors of ASCT2-mediated glutamine accumulation in live cells. These and other compounds in this novel series exhibit tractable chemical properties for further development as potential therapeutic leads.
Copyright © 2015 Elsevier Ltd. All rights reserved.