Senescence and senolysis in cancer: The latest findings

Aging is a life phenomenon that occurs in most living organisms and is a major risk factor for many diseases, including cancer. Cellular senescence is a cellular trait induced by various genomic and epigenetic stresses. Senescent cells are characterized by irreversible cell growth arrest and excessive secretion of inflammatory cytokines (senescence-associated secretory phenotypes, SASP). Chronic tissue microinflammation induced by SASP contributes to the pathogenesis of a variety of age-related diseases, including cancer. Senolysis is a promising new strategy to selectively eliminate senescent cells in order to suppress chronic inflammation, suggesting its potential use as an anticancer therapy. This review summarizes recent findings on the molecular basis of senescence in cancer cells and senolysis.

Cordycepin alleviates hepatic fibrosis in association with the inhibition of glutaminolysis to promote hepatic stellate cell senescence

Cordycepin (CRD) is an active component derived from Cordyceps militaris, which possesses multiple biological activities and uses in liver disease. However, whether CRD improves liver fibrosis by regulating hepatic stellate cell (HSC) activation has remained unknown. The study aims further to clarify the activities of CRD on liver fibrosis and elucidate the possible mechanism. Our results demonstrated that CRD significantly relieved hepatocyte injury and inhibited HSC activation, alleviating hepatic fibrogenesis in the Diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate (DDC)-induced mice model. In vitro, CRD exhibited dose-dependent repress effects on HSC proliferation, migration, and pro-fibrotic function in TGF-β1-activated LX-2 and JS-1 cells. The functional enrichment analysis of RNA-seq data indicated that the pathway through which CRD alleviates HSC activation involves cellular senescence and cell cycle-related pathways. Furthermore, it was observed that CRD accumulated the number of senescence-associated a-galactosidase positive cells and the levels of senescencemarker p21, and provoked S phasearrestof activated HSC. Remarkably, CRD treatment abolished TGF-β-induced yes-associated protein (YAP) nuclear translocation that acts upstream of glutaminolysis in activated HSC. On the whole, CRD significantly inhibited glutaminolysis of activated-HSC and induced cell senescence through the YAP signaling pathway, consequently alleviating liver fibrosis, which may be a valuable supplement for treating liver fibrosis.

GLS and GOT2 as prognostic biomarkers associated with dendritic cell and immunotherapy response in breast cancer

Breast cancer is the females' most common cancer. Targeting the immune microenvironment is a new and promising treatment method for breast cancer. Nevertheless, only a small section of patients can profit by immunotherapy, and improving the ability to accurately predict the potential for immunotherapy response is still awaiting further exploration. In this study, we found that the key factors of glutamine metabolism, glutaminase 1 (GLS) and mitochondrial aspartate transaminase (GOT2), showed opposite expression patterns in breast cancer samples. Based on the expression level of GLS and GOT2, we divided the breast cancer samples into two clusters: Cluster 2 showed GLS expressed higher and GOT2 expressed lower, whereas Cluster 1 showed GOT2 expressed higher and GLS expressed lower. GSEA showed that the clusters were related to pathways of immunity. Further analysis showed that Cluster 2 was positively associated with immunity infiltration. Through WGCNA, we identified a module strongly correlated with glutamine metabolism and immunity and identified 11 dendritic cell-associated genes involved in dendritic cell development, maturation, activation and other functions. In addition, Cluster 2 also showed higher immune checkpoint gene expression, which suggest the Cluster 2 had even better response to immunotherapy. The validation dataset could also be clustered into two groups. Cluster 2 (GLS expressed higher and GOT2 expressed lower) of the validation dataset was also positively associated with dendritic cells and a better immunotherapy response. Thus, these data indicate that GLS and GOT2 are prognostic biomarkers which closely related to dendritic cells and better reacted to immunotherapy in breast cancer.

Canagliflozin reduces chemoresistance in hepatocellular carcinoma through PKM2-c-Myc complex-mediated glutamine starvation

Cisplatin (CPT) is one of the standard treatments for hepatocellular carcinoma (HCC). However, its use is limits as a monotherapy due to drug resistance, and the underlying mechanism remains unclear. To solve this problem, we tried using canagliflozin (CANA), a clinical drug for diabetes, to reduce chemoresistance to CPT, and the result showed that CANA could vigorously inhibit cell proliferation and migration independent of the original target SGLT2. Mechanistically, CANA reduced aerobic glycolysis in HCC by targeting PKM2. The downregulated PKM2 directly bound to the transcription factor c-Myc in the cytoplasm to form a complex, which upregulated the level of phosphorylated c-Myc Thr58 and promoted the ubiquitination and degradation of c-Myc. Decreased c-Myc reduced the expression of GLS1, a key enzyme in glutamine metabolism, leading to impaired glutamine utilization. Finally, intracellular glutamine starvation induced ferroptosis and sensitized HCC to CPT. In conclusion, our study showed that CANA re-sensitized HCC to CPT by inducing ferroptosis through dual effects on glycolysis and glutamine metabolism. This is a novel mechanism to increase chemosensitivity, which may provide compatible chemotherapy drugs for HCC.

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

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

Enhancing the affinity of novel GLS1 allosteric inhibitors by targeting key residue Lys320

Aim: A series of novel GLS1 irreversible allosteric inhibitors targeting Lys320 might have robust enzyme inhibitory activity and potent antitumor activity. Materials & methods: Novel GLS1 allosteric inhibitors targeting Lys320 were synthesized and their anticancer activity was assessed. Moreover, GLS1 protein was used as a model system to analyze the reactivity of these electrophilic groups in GLS1 irreversible allosteric inhibitors with other amino acids, including tyrosine, histidine, serine and threonine, using biochemical and biophysical assays. Results: AC16 exhibited robust GLS1 inhibitory activity, antiproliferative effect in vitro, good plasma stability and potential covalent addition with GLS1 K320. Conclusion: This study opens a novel avenue for the design of robust irreversible GLS1 inhibitors targeting the allosteric site K320.

An updated patent review of glutaminase inhibitors (2019-2022)

INTRODUCTION

Kidney-type glutaminase (GLS1), a key enzyme controlling the hydrolysis of glutamine to glutamate to resolve the 'glutamine addiction' of cancer cells, has been shown to play a central role in supporting cancer growth and proliferation. Therefore, the inhibition of GLS1 as a novel cancer treating strategy is of great interest.

AREAS COVERED

This review covers recent patents (2019-present) involving GLS1 inhibitors, which are mostly focused on their chemical structures, molecular mechanisms of action, pharmacokinetic properties, and potential clinical applications.

EXPERT OPINION

Currently, despite significant efforts, the search for potent GLS1 inhibitors has not resulted in the development of compounds for therapeutic applications. Most recent patents and literature focus on GLS1 inhibitors IPN60090 and DRP104, which have entered clinical trials. While other patent disclosures during this period have not generated any drug candidates, the clinical update will inform the potential of these inhibitors as promising therapeutic agents either as single or as combination interventions.

SMYD2 Promotes Hepatocellular Carcinoma Progression by Reprogramming Glutamine Metabolism via c-Myc/GLS1 Axis

Metabolic reprogramming, such as alterations in glutamine metabolism or glycolysis, is the hallmark of hepatocellular carcinoma (HCC). However, the underlying mechanisms are still incompletely elucidated. Previous studies have identified that methyltransferase SET and MYND domain-containing protein 2(SMYD2) is responsible for the pathogenesis of numerous types of cancer. Here, we innovatively uncover how SMYD2 regulates glutamine metabolism in HCC cells and promotes HCC progression. We identified that SMYD2 expression is upregulated in HCC tissues, which correlates with unfavorable clinical outcomes. Our in vitro and in vivo results showed that the depletion of SMYD2 inhibits HCC cell growth. Mechanistically, c-Myc methylation by SMYD2 increases its protein stability through the ubiquitin-proteasome system. We showed SMYD2 depletion destabilized c-Myc protein by increasing the conjugated K48-linked polyubiquitin chain. SMYD2 increased c-Myc expression and further upregulated glutaminase1 (GLS1), a crucial enzyme that catalyzes the conversion of glutamine to glutamic acid, in HCC cells. GLS1 plays an important role in SMYD2-mediated HCC progression and glutamine metabolism regulation. The knockdown of SMYD2 inhibited glutamine metabolism in HCC cells and overcame their chemoresistance to sorafenib. Collectively, our findings demonstrated a novel mechanism of how SMYD2 promotes HCC progression by regulating glutamine metabolism through the c-Myc/GLS1signaling, implicating the therapeutic potential of targeting SMYD2 in HCC patients.

Inhibition of glutaminolysis restores mitochondrial function in senescent stem cells

Mitochondrial dysfunction, a hallmark of aging, has been associated with the onset of aging phenotypes and age-related diseases. Here, we report that impaired mitochondrial function is associated with increased glutamine catabolism in senescent human mesenchymal stem cells (MSCs) and myofibroblasts derived from patients suffering from Hutchinson-Gilford progeria syndrome. Increased glutaminase (GLS1) activity accompanied by loss of urea transporter SLC14A1 induces urea accumulation, mitochondrial dysfunction, and DNA damage. Conversely, blocking GLS1 activity restores mitochondrial function and leads to amelioration of aging hallmarks. Interestingly, GLS1 expression is regulated through the JNK pathway, as demonstrated by chemical and genetic inhibition. In agreement with our in vitro findings, tissues isolated from aged or progeria mice display increased urea accumulation and GLS1 activity, concomitant with declined mitochondrial function. Inhibition of glutaminolysis in progeria mice improves mitochondrial respiratory chain activity, suggesting that targeting glutaminolysis may be a promising strategy for restoring age-associated loss of mitochondrial function.

Structure-based virtual screening discovers novel kidney-type glutaminase inhibitors

Glutaminase (GLS) serves a critical bioenergetic role for malignant tumor growth and has become a valuable therapeutic target for cancer treatment. Herein, we performed a structure-based virtual screening to discover novel GLS inhibitors and provide information for developing new GLS inhibitors. We identified critical pharmacological interactions in the GLS1 binding site by analyzing the known GLS1 inhibitors and selected potential inhibitors based on their docking score and pharmacological interactions. The inhibitory effects of compounds were further confirmed by enzymatic and cell viability assays. We treated colorectal cancer and triple-negative breast cancer cells with the selected candidates and measured the inhibitory efficacy of hit compounds on cell viability. In total, we identified three GLS1 inhibitors. The compounds identified from our structure-based virtual screening methodology exhibited great anticancer potential as a lead targeting glutamine metabolism.

GLS1 is a protective factor in patients with ovarian clear cell carcinoma and its expression does not correlate with ARID1A-mutated tumors

Targeting glutamine metabolism has emerged as a novel therapeutic strategy for several human cancers, including ovarian cancer. The primary target of this approach is the kidney isoform of glutaminase, glutaminase 1 (GLS1), a key enzyme in glutamine metabolism that is overexpressed in several human cancers. A first-in-class inhibitor of GLS1, called CB839 (Telaglenastat), has been investigated in several clinical trials, with promising results. The first clinical trial of CB839 in platinum-resistant ovarian cancer patients is forthcoming. ARID1A-mutated ovarian clear cell carcinoma (OCCC) is a relatively indolent and chemoresistant ovarian cancer histotype. In OCCC-derived cells ARID1A simultaneously drives GLS1 expression and metabolism reprograming. In ARID1A-mutated OCCC-derived mouse models, loss of ARID1A corresponds to GLS1 upregulation and increases sensitivity to GLS1 inhibition. Thus, targeting of GLS1 with CB839 has been suggested as a targeted approach for OCCC patients with tumors harboring ARID1A-mutations. Here, we investigated whether GLS1 is differentially expressed between OCCC patients whose tumors are ARID1A positive and patients whose tumors are ARID1A negative. In clinical specimens of OCCC, we found that GLS1 overexpression was not correlated with ARID1A loss. In addition, GLS1 overexpression was associated with better clinical outcomes. Our findings have implications for human trials using experimental therapeutics targeting GLS1.

Docking and Molecular Dynamics Study to Identify Novel Phytobiologics from Dracaena trifasciata against Metabolic Reprogramming in Rheumatoid Arthritis

Enhancement of glycolysis and glutaminolysis are the two most common modalities associated with metabolic reprogramming in rheumatoid arthritis (RA). This enhancement is concomitant to the upregulation of hexokinase 2 (HK2) and glutaminase 1 (GLS1). Hence, the current study was undertaken to identify potential phytobiological inhibitors against HK2 and GLS1, from Dracaena (Sansevieria) trifasciata, an indigenous ethnomedicinal plant found in Pakistan, using computational analysis. Phytobiologics from Dracaena trifasciata were assessed for their ability to co-inhibit HK2 and GLS1 via molecular docking and molecular dynamics simulations. The results underscored seven phytobiologics with promising binding affinities for both HK2 and GLS1. Molecular dynamics simulations further elucidated that all seven identified phytobiologics inhibited HK2 by forming stable complexes but only five amongst the seven had the potential to form stable complexes with GLS1 in real time, thereby implying the potential of co-inhibition for these five compounds. Compound 28MS exhibited an equally strong binding profile for both HK2 (−8.19 kcal/mol) and GLS1 (−8.99 kcal/mol). Furthermore, it exhibited a similar trend in stability during simulation for both targets. Our results serve as a primer for a more lucid understanding towards co-inhibition of HK2 and GLS1 using multiple computational approaches. The identified phytobiologics should undergo in-vitro and in-vivo validation to corroborate their therapeutic potential in RA.

The strategic roles of four enzymes in the interconnection between metabolism and oncogene activation in non-small cell lung cancer: Therapeutic implications

NSCLC is the leading cause of cancer mortality and represents a major challenge in cancer therapy. Intrinsic and acquired anticancer drug resistance are promoted by hypoxia and HIF-1α. Moreover, chemoresistance is sustained by the activation of key signaling pathways (such as RAS and its well-known downstream targets PI3K/AKT and MAPK) and several mutated oncogenes (including KRAS and EGFR among others). In this review, we highlight how these oncogenic factors are interconnected with cell metabolism (aerobic glycolysis, glutaminolysis and lipid synthesis). Also, we stress the key role of four metabolic enzymes (PFK1, dimeric-PKM2, GLS1 and ACLY), which promote the activation of these oncogenic pathways in a positive feedback loop. These four tenors orchestrating the coordination of metabolism and oncogenic pathways could be key druggable targets for specific inhibition. Since PFK1 appears as the first tenor of this orchestra, its inhibition (and/or that of its main activator PFK2/PFKFB3) could be an efficacious strategy against NSCLC. Citrate is a potent physiologic inhibitor of both PFK1 and PFKFB3, and NSCLC cells seem to maintain a low citrate level to sustain aerobic glycolysis and the PFK1/PI3K/EGFR axis. Awaiting the development of specific non-toxic inhibitors of PFK1 and PFK2/PFKFB3, we propose to test strategies increasing citrate levels in NSCLC tumors to disrupt this interconnection. This could be attempted by evaluating inhibitors of the citrate-consuming enzyme ACLY and/or by direct administration of citrate at high doses. In preclinical models, this "citrate strategy" efficiently inhibits PFK1/PFK2, HIF-1α, and IGFR/PI3K/AKT axes. It also blocks tumor growth in RAS-driven lung cancer models, reversing dedifferentiation, promoting T lymphocytes tumor infiltration, and increasing sensitivity to cytotoxic drugs.

β-Escin reduces cancer progression in aggressive MDA-MB-231 cells by inhibiting glutamine metabolism through downregulation of c-myc oncogene

BACKGROUND

The c-myc oncogene, which causes glutamine dependence in triple negative breast cancers (TNBC), is also the target of one of the signaling pathways affected by β-Escin.

METHODS AND RESULTS

We sought to determine how c-myc protein affects glutamine metabolism and the proteins, glutamine transporter alanine-serine-cysteine 2 (ASCT2) and glutaminase (GLS1), in β-Escin-treated MDA-MB-231 cells using glutamine uptake and western blot analysis. Cell viability, colony formation, migration and apoptosis were also evaluated in MDA-MB-231 cells in response to β-Escin treatment using MTS, colony forming, wound healing, and Annexin-V assay. We determined that β-Escin decreased glutamine uptake and reduced c-myc and GLS1 protein expressions and increased the expression of ASCT2. In addition, this inhibition of glutamine metabolism decreased cell proliferation, colony formation and migration, and induced apoptosis.

CONCLUSIONS

In this study, it was suggested that β-Escin inhibits glutamine metabolism via c-myc in MDA-MB-231 cells, and it is thought that as a result of interrupting the energy supply in these cells via c-myc, it results in a decrease in the carcinogenic properties of the cells. Consequently, β-Escin may be promising as a therapeutic agent for glutamine-dependent cancers.

Ginsenoside CK induces apoptosis in triple-negative breast cancer cells by targeting glutamine metabolism

Breast cancer (BC) has replaced lung cancer as the most common cancer worldwide. Ginsenoside CK (CK) can effectively inhibit triple-negative breast cancer (TNBC), the occurrence and development of which are associated with glutamine addiction. However, the connection between CK and glutamine metabolism in TNBC proliferation and the mechanism of cell death induction remains unclear. Here, we found that high glutamine-addicted TNBC cells were particularly sensitive to CK treatment. CK exerted antitumour activity against TNBC by suppressing glutamine consumption and glutamate production via downregulation of glutaminase 1 (GLS1) expression. CK treatment further decreased cellular ATP production, reduced the utilisation of amino acids associated with glutamine metabolism, and induced glutathione (GSH) depletion and reactive oxygen species (ROS) accumulation, consequently triggering apoptosis in TNBC. Furthermore, CK decreased GLS1 expression in SUM159 xenograft mouse mammary tumours and significantly inhibited tumour growth with few side effects. Together, our data provide a powerful theoretical basis for the application of CK as a glutamine metabolic inhibitor in TNBC treatment.

Dual Inhibitions on Glucose/Glutamine Metabolisms for Nontoxic Pancreatic Cancer Therapy

Glucose and glutamine are two principal nutrients in mammalian cells that provide energy and biomass for cell growth and proliferation. Especially in cancer cells, glutamine could be a main alternative for energy and biomass supply once glucose metabolism is suppressed. Therefore, single inhibition of enzymes in either glucose metabolism or glutaminolysis, though maybe efficient in vitro, is far from being satisfactory for efficient in vivo cancer therapy. Here, we proposed a new strategy for dual inhibitions on both glucose and glutamine metabolisms concurrently by silencing mutated gene Kras and glutaminase 1 (GLS1) via nanomaterial-based siKras and siGLS1 delivery, rather than conventional highly toxic chemodrugs. Such a combination therapy could overcome the challenge that glucose and glutamine are alternatives to each other in the biosynthesis and energy production for cancer cells, resulting in much elevated treatment efficacy. In addition, layered double hydroxide (LDH), the siRNA carrier, enables an enhanced gene delivery efficiency compared to the commercial transfection agent Lipofectamine 2000. Briefly, Mg-Al LDH nanosheets, loaded with siKras and siGLS1 onto their surfaces by electrostatic adsorption, could release siRNA from lysosomes into the cytoplasm via the proton sponge effect of LDH, favoring the siRNA stability and gene silencing efficiency enhancements. The thus released siRNA could downregulate the expressions of Kras, GLS1, and other enzymes involved in glucose metabolism, resulting in the downregulations of ATP and other metabolites. Such a biosafe LDH/siRNA nanomedicine is able to efficiently suppress the growth of xenografts through cancer cell proliferation suppression, displaying its great potential as a simultaneous glucose/glutamine metabolism coinhibitor for treating pancreatic cancer.

Bergenin, a PPARγ agonist, inhibits Th17 differentiation and subsequent neutrophilic asthma by preventing GLS1-dependent glutaminolysis

Bergenin is a natural PPARγ agonist that can prevent neutrophil aggregation, and often be used in clinics for treating respiratory diseases. Recent data show that Th17 cells are important for neutrophil aggregation and asthma through secreting IL-17A. In this study, we investigated the effects of bergenin on Th17 differentiation in vitro and subsequent neutrophilic asthma in mice. Naïve T cells isolated from mouse mesenteric lymph nodes were treated with IL-23, TGF-β, and IL-6 to induce Th17 differentiation. We showed that in naïve T cells under Th17-polarizing condition, the addition of bergenin (3, 10, 30 μM) concentration-dependently decreased the percentage of CD4⁺ IL-17A⁺ T cells and mRNA expression of specific transcription factor RORγt, and function-related factors IL-17A/F, IL-21, and IL-22, but did not affect the cell vitality and apoptosis. Furthermore, bergenin treatment prevented GLS1-dependent glutaminolysis in the progress of Th17 differentiation, slightly affected the levels of SLC1A5, SLC38A1, GLUD1, GOT1, and GPT2. Glutamine deprivation, the addition of glutamate (1 mM), α-ketoglutarate (1 mM), or GLS1 plasmid all significantly attenuated the above-mentioned actions of bergenin. Besides, we demonstrated that bergenin (3, 10, and 30 μM) concentration-dependently activated PPARγ in naïve T cells, whereas PPARγ antagonist GW9662 and siPPARγ abolished bergenin-caused inhibition on glutaminolysis and Th17 differentiation. Furthermore, we revealed that bergenin inhibited glutaminolysis by regulating the level of CDK1, phosphorylation and degradation of Cdh1, and APC/C-Cdh1-mediated ubiquitin-proteasomal degradation of GLS1 after activating PPARγ. We demonstrated a correlation existing among bergenin-affected GLS1-dependent glutaminolysis, PPARγ, "CDK1-APC/C-Cdh1" signaling, and Th17 differentiation. Finally, the therapeutic effect and mechanisms for bergenin-inhibited Th17 responses and neutrophilic asthma were confirmed in a mouse model of neutrophilic asthma by administration of GW9662 or GLS1 overexpression plasmid in vivo. In conclusion, bergenin repressed Th17 differentiation and then alleviated neutrophilic asthma in mice by inhibiting GLS1-dependent glutaminolysis via regulating the "CDK1-APC/C-Cdh1" signaling after activating PPARγ.

The Expression of Glutaminases and their Association with Clinicopathological Parameters in the Head and Neck Cancers

BACKGROUND

The increased glutamine metabolism is a characteristic feature of cancer cells. The interconversion between glutamine and glutamate is catalyzed by two glutaminase isoforms, GLS1 and GLS2, which appear to have different roles in different types of cancer. We investigated for the first time the protein expression of GLS1 and GLS2, and their correlation with advanced clinicopathological parameters in head and neck cancers.

METHOD

Consecutive slides from a tissue microarray comprised of 80 samples ranging from normal to metastatic, were stained immunohistochemically for GLS1, GLS2, HIF-1α or CD147. Following analysis by two expert pathologists we carried out statistical analysis of the scores.

RESULTS

GLS1 and GLS2 are upregulated at protein level in head and neck tumours compared to normal tissues and this increased expression correlated positively (GLS1) and negatively (GLS2) with tumor grade, indicating a shift of expression between GLS enzyme isoforms based on tumor differentiation. Increased expression of GLS1 was associated with high CD147 expression; and elevated GLS2 expression was associated with both high CD147 and high HIF-1α expressions. The correlation of the GLS1 and GLS2 with HIF-1α or CD147 was strongly associated with more advanced clinicopathological parameters.

CONCLUSION

The increased expression of GLS1 and GLS2 may be explored as a new treatment for head and neck cancers.

Blockade of glutamine-dependent cell survival augments antitumor efficacy of CPI-613 in head and neck cancer

BACKGROUND

Alterations in metabolism are one of the emerging hallmarks of cancer cells and targeting dysregulated cancer metabolism provides a new approach to developing more selective therapeutics. However, insufficient blockade critical metabolic dependencies of cancer allows the development of metabolic bypasses, thus limiting therapeutic benefits.

METHODS

A series of head and neck squamous cell carcinoma (HNSCC) cell lines and animal models were used to determine the efficacy of CPI-613 and CB-839 when given alone or in combination. Glutaminase 1 (GLS1) depletion was achieved by lentiviral shRNAs. Cell viability and apoptosis were determined in HNSCC cells cultured in 2D culture dish and SeedEZ™ 3D scaffold. Molecular alterations were examined by Western blotting and immunohistochemistry. Metabolic changes were assessed by glucose uptake, lactate production, glutathione levels, and oxygen consumption rate.

RESULTS

We show here that HNSCC cells display strong addiction to glutamine. CPI-613, a novel lipoate analog, redirects cellular activity towards tumor-promoting glutaminolysis, leading to low anticancer efficacy in HNSCC cells. Mechanistically, CPI-613 inhibits the tricarboxylic acid cycle by blocking the enzyme activities of pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, which upregulates GLS1 and eventually promotes the compensatory role of glutaminolysis in cancer cell survival. Most importantly, the addition of a GLS1 inhibitor CB-839 to CPI-613 treatment abrogates the metabolic dependency of HNSCC cells on glutamine, achieving a synergistic anticancer effect in glutamine-addicted HNSCC.

CONCLUSIONS

These findings uncover the critical role of GLS1-mediated glutaminolysis in CPI-613 treatment and suggest that the CB-839 and CPI-613 combination may potentiate synergistic anticancer activity for HNSCC therapeutic gain.

Targeting glutamine metabolism and autophagy: the combination for prostate cancer radiosensitization

Radiotherapy is one of the curative mainstays of prostate cancer; however, its efficacy is often diminished by tumor radioresistance. Depending on the stage of disease, tumors can relapse in approximately 50% of patients with prostate cancer after radiotherapy. Nevertheless, the mechanisms that drive tumor cell survival are not fully characterized, and reliable molecular prognostic markers of prostate cancer radioresistance are missing. Similar to other tumor entities, prostate cancer cells are heterogeneous in their capability to maintain tumor growth. The populations of cancer stem cells (CSCs) with self-renewal and differentiation properties are responsible for tumor development and recurrence after treatment. Eradication of these CSC populations is of utmost importance for efficient tumor cure. In a recently published study, we showed that prostate cancer cells could be radiosensitized by glutamine deprivation, resulting in DNA damage, oxidative stress, epigenetic modifications, and depletion of CSCs. Conversely, prostate cancer cells with resistance to glutamine depletion show an activation of ATG-mediated macroautophagy/autophagy as a survival strategy to withstand radiation-induced damage. Thus, a combination of targeting glutamine metabolism and autophagy blockade lead to more efficient prostate cancer radiosensitization.

Abbreviations: ATG5: autophagy related 5; CSCs: cancer stem cells; GLS: glutaminase; TCA cycle: tricarboxylic acid cycle

Simultaneous inhibition of PFKFB3 and GLS1 selectively kills KRAS-transformed pancreatic cells

Activating mutations of the oncogenic KRAS in pancreatic ductal adenocarcinoma (PDAC) are associated with an aberrant metabolic phenotype that may be therapeutically exploited. Increased glutamine utilization via glutaminase-1 (GLS1) is one such feature of the activated KRAS signaling that is essential to cell survival and proliferation; however, metabolic plasticity of PDAC cells allow them to adapt to GLS1 inhibition via various mechanisms including activation of glycolysis, suggesting a requirement for combinatorial anti-metabolic approaches to combat PDAC. We investigated whether targeting the glycolytic regulator 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3) in combination with GLS1 can selectively prevent the growth of KRAS-transformed cells. We show that KRAS-transformation of pancreatic duct cells robustly sensitizes them to the dual targeting of GLS1 and PFKFB3. We also report that this sensitivity is preserved in the PDAC cell line PANC-1 which harbors an activating KRAS mutation. We then demonstrate that GLS1 inhibition reduced fructose-2,6-bisphosphate levels, the product of PFKFB3, whereas PFKFB3 inhibition increased glutamine consumption, and these effects were augmented by the co-inhibition of GLS1 and PFKFB3, suggesting a reciprocal regulation between PFKFB3 and GLS1. In conclusion, this study identifies a novel mutant KRAS-induced metabolic vulnerability that may be targeted via combinatorial inhibition of GLS1 and PFKFB3 to suppress PDAC cell growth.

GLS-driven glutamine catabolism contributes to prostate cancer radiosensitivity by regulating the redox state, stemness and ATG5-mediated autophagy

Radiotherapy is one of the curative treatment options for localized prostate cancer (PCa). The curative potential of radiotherapy is mediated by irradiation-induced oxidative stress and DNA damage in tumor cells. However, PCa radiocurability can be impeded by tumor resistance mechanisms and normal tissue toxicity. Metabolic reprogramming is one of the major hallmarks of tumor progression and therapy resistance. Specific metabolic features of PCa might serve as therapeutic targets for tumor radiosensitization and as biomarkers for identifying the patients most likely to respond to radiotherapy. The study aimed to characterize a potential role of glutaminase (GLS)-driven glutamine catabolism as a prognostic biomarker and a therapeutic target for PCa radiosensitization. Methods: We analyzed primary cell cultures and radioresistant (RR) derivatives of the conventional PCa cell lines by gene expression and metabolic assays to identify the molecular traits associated with radiation resistance. Relative radiosensitivity of the cell lines and primary cell cultures were analyzed by 2-D and 3-D clonogenic analyses. Targeting of glutamine (Gln) metabolism was achieved by Gln starvation, gene knockdown, and chemical inhibition. Activation of the DNA damage response (DDR) and autophagy was assessed by gene expression, western blotting, and fluorescence microscopy. Reactive oxygen species (ROS) and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) were analyzed by fluorescence and luminescence probes, respectively. Cancer stem cell (CSC) properties were investigated by sphere-forming assay, CSC marker analysis, and in vivo limiting dilution assays. Single circulating tumor cells (CTCs) isolated from the blood of PCa patients were analyzed by array comparative genome hybridization. Expression levels of the GLS1 and MYC gene in tumor tissues and amino acid concentrations in blood plasma were correlated to a progression-free survival in PCa patients. Results: Here, we found that radioresistant PCa cells and prostate CSCs have a high glutamine demand. GLS-driven catabolism of glutamine serves not only for energy production but also for the maintenance of the redox state. Consequently, glutamine depletion or inhibition of critical regulators of glutamine utilization, such as GLS and the transcription factor MYC results in PCa radiosensitization. On the contrary, we found that a combination of glutamine metabolism inhibitors with irradiation does not cause toxic effects on nonmalignant prostate cells. Glutamine catabolism contributes to the maintenance of CSCs through regulation of the alpha-ketoglutarate (α-KG)-dependent chromatin-modifying dioxygenase. The lack of glutamine results in the inhibition of CSCs with a high aldehyde dehydrogenase (ALDH) activity, decreases the frequency of the CSC populations in vivo and reduces tumor formation in xenograft mouse models. Moreover, this study shows that activation of the ATG5-mediated autophagy in response to a lack of glutamine is a tumor survival strategy to withstand radiation-mediated cell damage. In combination with autophagy inhibition, the blockade of glutamine metabolism might be a promising strategy for PCa radiosensitization. High blood levels of glutamine in PCa patients significantly correlate with a shorter prostate-specific antigen (PSA) doubling time. Furthermore, high expression of critical regulators of glutamine metabolism, GLS1 and MYC, is significantly associated with a decreased progression-free survival in PCa patients treated with radiotherapy. Conclusions: Our findings demonstrate that GLS-driven glutaminolysis is a prognostic biomarker and therapeutic target for PCa radiosensitization.

GLS1 depletion inhibited colorectal cancer proliferation and migration via redox/Nrf2/autophagy-dependent pathway

Cancer cells can metabolize glutamine to replenish TCA cycle intermediates for cell survival. Glutaminase (GLS1) is over-expressed in multiple cancers, including colorectal cancer (CRC). However, the role of GLS1 in colorectal cancer development has not yet fully elucidated. In this study, we found that GLS1 levels were significantly increased in CRC cells. Knockdown of GLS1 by shRNAs as well as GLS1 inhibitor BPTES decreased DLD1 and SW480 cell proliferation, colony formation and migration. Knockdown of GLS1 as well as BPTES induced reactive oxygen species (ROS) production, down-regulation of GSH/GSSG ratio, an decrease in Nrf2 protein expression and an increase in cytoplasmic Nrf2 protein expression in DLD1 and SW480 cells. Furthermore, Knockdown of GLS1 as well as BPTES inhibited autophagy pathway, antioxidant NAC and Nrf2 activator could reversed inhibition of GLS1-mediated an decrease in autophagic flux in DLD1 and SW480 cells. Depletion of GLS1-induced inhibition of DLD1 and SW480 CRC cell proliferation, colony formation and migration was reversed by autophagy inducer rapamycin. These results suggest that targeting GLS1 might be a new potential therapeutic target for the treatment of CRC.

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.

Mechanism of miR-455-3 in suppressing epithelial-mesenchymal transition and angiogenesis of non-small cell lung cancer cells

The tumor-suppressing role of miR-455-3p has been reported in lung cancer, but the working mechanism remains to be fully elucidated. This study aims to explore the possible mechanism of miR-455-3p in regulating epithelial-mesenchymal transition (EMT) progression and angiogenesis in non-small cell lung cancer (NSCLC) cells.The expressions of miR-455-3p, HSF1, GLS1, and EMT-related proteins (E-cadherin, N-cadherin, vimentin, and Snail-1) in both NSCLC tissues and cell lines were determined by RT-qPCR and western blot. After cell transfection, cell proliferation and angiogenesis ability on NSCLC cells were assessed by MTT and tube formation assay. The binding of miR-455-3p with HSF1 was measured by luciferase reporter gene assay, while the interaction between HSF1 and GLS1 was determined by co-immunoprecipitation assay (Co-IP).HSF1 was highly expressed in NSCLC tissues and cells. Inhibition of HSF1 expression or overexpression of miR-455-3p in NSCLC cells can suppress cell proliferation, angiogenesis ability, and EMT progression. miR-455-3p was found to negatively regulate HSF1 expression. Co-transfection of miR-455-3p overexpression and HSF1 inhibition in NSCLC cells showed that miR-455-3p can partially counteract the effect of HSF1 in NSCLC cells. HSF1 can interact with GLS1 and elevate the expression of GLS1. GLS1 can partially abolish the suppressive effect of miR-455-3p in NSCLC cells.miR-455-3p can bind HSF1 to suppress the GLS1 in NSCLC cells, therefore suppressing EMT progression and angiogenesis of NSCLC cells.

Silencing of miR-23a attenuates hydrogen peroxide (H2O2) induced oxidative damages in ARPE-19 cells by upregulating GLS1: an in vitro study

BACKGROUND

Oxidative damages contributes to age-related macular degeneration (AMD) caused vision blindness, but the molecular mechanisms are still largely unknown.

OBJECTIVES

This study managed to investigate this issue by conducting in vitro experiments.

METHODS

Oxidative stress were evaluated by L-012 dye, DHE staining and MDA assay. CCK-8 and colony formation assay were conducted to examine cell proliferation. Cell death was evaluated by trypan blue staining and Annexin V-FITC/PI double staining method through flow cytometry (FCM). The binding sites of miR-23a and GLS1 mRNA were predicted by online miRDB database and validated by dual-luciferase reporter gene system. Real-Time qPCR for miR-23a levels and Western Blot for protein expressions.

RESULTS

The retinal pigment epithelial (RPE) cells (ARPE-19) were subjected to hydrogen peroxide (H2O2) stimulation to simulate AMD progression in vitro, and we identified a novel miR-23a/glutaminase-1 (GLS1) pathway that regulated H2O2 induced oxidative damages in ARPE-19 cells. Mechanistically, H2O2 induced oxidative stress, inhibited cell proliferation and induced cell death in ARPE-19 cells in a dose- and time-dependent manner. Also, H2O2 stimulation hindered cell invasion, migration and glutamine uptake in ARPE-19 cells. Interestingly, we proved that H2O2 increased miR-23a levels, while downregulated glutaminase-1 (GLS1) in ARPE-19 cells, and miR-23a targeted 3' untranslated region (3'UTR) of GLS1 mRNA for GLS1 degradation. Finally, our data suggested that silencing miR-23a upregulated GLS1 to reverse the detrimental effects of H2O2 treatment on ARPE-19 cells.

CONCLUSIONS

In general, analysis of the data suggested that miR-23a ablation upregulated GLS1 to attenuate H2O2 stimulation induced oxidative damages in ARPE-19 cells in vitro, and this study broadened our knowledge in this field, which might help to provide novel theranostic signatures for AMD.

SIRT7-mediated modulation of glutaminase 1 regulates TGF-β-induced pulmonary fibrosis

In the current work we show that the profibrotic actions of TGF-β are mediated, at least in part, through a metabolic maladaptation in glutamine metabolism and how the inhibition of glutaminase 1 (GLS1) reverses pulmonary fibrosis. GLS1 was found to be highly expressed in fibrotic vs normal lung fibroblasts and the expression of profibrotic targets, cell migration, and soft agar colony formation stimulated by TGF-β required GLS1 activity. Moreover, knockdown of SMAD2 or SMAD3 as well as inhibition of PI3K, mTORC2, and PDGFR abrogated the induction of GLS1 by TGF-β. We further demonstrated that the NAD-dependent protein deacetylase, SIRT7, and the FOXO4 transcription factor acted as endogenous brakes for GLS1 expression, which are inhibited by TGF-β. Lastly, administration of the GLS1 inhibitor CB-839 attenuated bleomycin-induced pulmonary fibrosis. Our study points to an exciting and unexplored connection between epigenetic and transcriptional processes that regulate glutamine metabolism and fibrotic development in a TGF-β-dependent manner.

NUDT21 suppresses the growth of small cell lung cancer by modulating GLS1 splicing

The mRNA precursor 3'-end modification factor NUDT21 is a major regulator of 3'UTR shortening and an important component of pre-mRNA cleavage and polyadenylation. However, its role in pathologic progress of small cell lung cancer (SCLC) remains unclear. In this study, we observed that NUDT21 expression is downregulated in SCLC tissues. Hypoxia-induced down-regulation of NUDT21 through HIF-1α. NUDT21 shRNA transduction promotes proliferation and inhibits apoptosis of A549 cells. NUDT21 inhibition also promotes tumor growth in a mouse xenograft model. Furthermore, we clarified that HIF-1α mediated NUDT21 downregulation which altered the expression patterns of two isoforms of GLS1, GAC and KGA. These results link the hypoxic tumor environments to aberrant glutamine metabolism which is important for cellular energy in SCLC cells. Therefore, NUDT21 could be considered as a potential target for the treatment of SCLC.

Targeting Hepatic Glutaminase 1 Ameliorates Non-alcoholic Steatohepatitis by Restoring Very-Low-Density Lipoprotein Triglyceride Assembly

Non-alcoholic steatohepatitis (NASH) is characterized by the accumulation of hepatic fat in an inflammatory/fibrotic background. Herein, we show that the hepatic high-activity glutaminase 1 isoform (GLS1) is overexpressed in NASH. Importantly, GLS1 inhibition reduces lipid content in choline and/or methionine deprivation-induced steatotic mouse primary hepatocytes, in human hepatocyte cell lines, and in NASH mouse livers. We suggest that under these circumstances, defective glutamine fueling of anaplerotic mitochondrial metabolism and concomitant reduction of oxidative stress promotes a reprogramming of serine metabolism, wherein serine is shifted from the generation of the antioxidant glutathione and channeled to provide one-carbon units to regenerate the methionine cycle. The restored methionine cycle can induce phosphatidylcholine synthesis from the phosphatidylethanolamine N-methyltransferase-mediated and CDP-choline pathways as well as by base-exchange reactions between phospholipids, thereby restoring hepatic phosphatidylcholine content and very-low-density lipoprotein export. Overall, we provide evidence that hepatic GLS1 targeting is a valuable therapeutic approach in NASH.

Antiapoptotic properties of MALT1 protease are associated with redox homeostasis in ABC-DLBCL cells

Mucosa-associated lymphoid tissue lymphoma translocation protein-1 (MALT1) protease presents crucial antiapoptotic properties in activated B cell-like diffuse large B-cell lymphoma (ABC-DLBCL); however, the mechanism is unclear. Here, we reported that inhibition of MALT1 protease in ABC-DLBCL cells led to cell apoptosis, along with elevated mitochondrial reactive oxygen species production and a reduced oxygen consumption rate. These alterations induced by MALT1 protease inhibition were associated with reduced expression of glutaminase (GLS1) and glutathione levels. We further show that MALT1 protease was required for the activation and nuclear translocation of c-Jun, which functions as a transcription factor of the GLS1 gene by binding directly to its promoter region. Taken together, MALT1 protease maintained mitochondrial redox homeostasis and mitochondrial bioenergetics through the MALT1-c-Jun-GLS1-coupled metabolic pathway to defend against apoptosis in ABC-DLBCL cells, which raises exciting possibilities regarding targeting of the MALT1-c-Jun-GLS1 axis as a potential therapeutic strategy against ABC-DLBCL.

GLS1 Mutant Mice Display Moderate Alterations of Hippocampal Glutamatergic Neurotransmission Associated with Specific Adaptive Behavioral Changes

Significant alterations in glutamatergic neurotransmission have been reported in major depressive disorder (MDD) that could underlie psychiatric traits. Studies were mainly interested in synaptic dysfunction in the prefrontal cortex, a key structure involved in depressive-like behavior, however hippocampus has been shown to be important in MDD. As cognitive deficits such as hippocampus-memory process were observed in MDD, we investigated in a mild hypoglutamatergic model behaviors related to depression and memory, synaptic transmission parameters and glutamatergic state specifically in the hippocampus. We thus characterized these phenotypes in adult male mice partially depleted in glutaminase type 1 or GLS1 (GLS1 HET), the enzyme responsible for glutamate synthesis in neurons, that we previously characterized as displaying moderate lower levels of glutamate in brain. We showed that GLS1 mutant mice display AMPA-R-mediated response deficits after prolonged repetitive stimulation with electrophysiological recording and inability to sustain glutamate release by microdialysis experiments with no consequences on behavioral spatial learning performances. However, their ability to escape from unpleasant but repeated escapable condition was attenuated whereas they were more immobile in the unescapable situation in the FST during re-test. These results show that GLS1 mutant mice display moderate impairments of hippocampal glutamatergic neurotransmission and moderate changes in adaptive behaviors that have been shown to participate to the development of depressive-like state.

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.

Activation of p53 by costunolide blocks glutaminolysis and inhibits proliferation in human colorectal cancer cells

Colorectal cancer is a leading cause of cancer-related death. Glutaminolysis has been suggested as a therapeutic target for cancer. Costunolide is a natural sesquiterpene lactone showing potent antitumor activity. Our studies were aimed at evaluating how costunolide affected glutaminolysis leading to proliferation inhibition in human colorectal cancer cells. Costunolide suppressed viability and proliferation of HCT116 cells concentration-dependently, but did not apparently affect human intestinal epithelial cells. Costunolide at 20 μM reduced viability and proliferation of HCT116 cells time-dependently. Costunolide also repressed phosphorylation of mTOR and its downstream kinases p70S6K and 4E-BP1. Examinations of glutaminolysis metabolites showed that costunolide increased intracellular glutamine levels, but decreased intracellular levels of glutamate, α-ketoglutarate (α-KG), and ATP in HCT116 cells, suggesting costunolide blockade of glutaminolysis. Furthermore, costunolide inhibited promoter activity of glutaminase 1 (GLS1), the first rate-limiting enzyme in glutaminolysis, and reduced mRNA and protein expression of GLS1 in HCT116 cells, The GLS1 inhibitor BPTES, similar to costunolide, significantly reduced intracellular levels of α-KG and ATP and inhibited proliferation in HCT116 cells. Finally, costunolide increased phosphorylation and nuclear translocation of p53 in HCT116 cells. Both p53 inhibitor pifithrin-α and p53 siRNA significantly rescued costunolide suppression of GLS1 promoter activity and expression in HCT116 cells. These data in aggregate suggested that activation of p53 was required for costunolide inhibition of GLS1 resulting in blockade of glutaminolysis and inhibition of proliferation in colorectal cancer cells, which was a novel mechanism underlying the antitumor activity of costunolide against colorectal cancer.

Angiogenesis revisited from a metabolic perspective: role and therapeutic implications of endothelial cell metabolism

Endothelial cell (EC) metabolism has lately emerged as a novel and promising therapeutic target to block vascular dysregulation associated with diseases like cancer and blinding eye disease. Glycolysis, fatty acid oxidation (FAO) and, more recently, glutamine/asparagine metabolism emerged as key regulators of EC metabolism, able to impact angiogenesis in health and disease. ECs are highly glycolytic as they require ATP and biomass for vessel sprouting. Notably, a regulator of the glycolytic pathway, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3, controls vessel sprouting during the angiogenic switch and its inhibition in tumour ECs leads to vessel normalization, thereby reducing metastasis and ameliorating chemotherapy. Moreover, FAO promotes EC proliferation through DNA synthesis, and plays an essential role in lymphangiogenesis via epigenetic regulation of histone acetylation. Pathological angiogenesis was decreased upon blockade of carnitine palmitoyltransferase 1, a regulator of FAO in ECs. More recently, metabolism of glutamine, in conjunction with asparagine, was reported to maintain EC sprouting through TCA anaplerosis, redox homeostasis, mTOR activation and endoplasmic stress control. Inactivation or blockade of glutaminase 1, which hydrolyses glutamine into ammonia and glutamate, impairs angiogenesis in health and disease, while silencing of asparagine synthetase reduces vessel sprouting in vitro. In this review, we summarize recent insights into EC metabolism and discuss therapeutic implications of targeting EC metabolism.

Heat Shock Factor 1 Epigenetically Stimulates Glutaminase-1-Dependent mTOR Activation to Promote Colorectal Carcinogenesis

Heat shock factor 1 (HSF1) generally exhibits its properties under stress conditions. In tumors, HSF1 has a pleiotropic feature in regulating growth, survival, and aggressiveness of cancer cells. In this study, we found HSF1 was increased in colorectal cancer (CRC) and had a positive correlation with shorter disease-free survival (DFS). Knockdown of HSF1 in CRC cells attenuated their growth while inhibiting mTOR activation and glutamine metabolism. HSF1 inhibited the expression of microRNA137 (MIR137), which targeted GLS1 (glutaminase 1), thus stimulating GLS1 protein expression to promote glutaminolysis and mTOR activation. HSF1 bound DNA methyltransferase DNMT3a and recruited it to the promoter of lncRNA MIR137 host gene (MIR137HG), suppressing the generation of primary MIR137. The chemical inhibitor of HSF1 also reduced cell growth, increased apoptosis, and impaired glutamine metabolism in vitro. Moreover, both chemical inhibition and genetic knockout of HSF1 succeeded in increasing MIR137 expression, reducing GLS1 expression, and alleviating colorectal tumorigenesis in azoxymethane (AOM)/dextran sulfate sodium (DSS) mice. In conclusion, HSF1 expression was increased and associated with poor prognosis in CRC. By recruiting DNMT3a to suppress the expression of MIR137 that targets GLS1 mRNA, HSF1 stimulated GLS1-dependent mTOR activation to promote colorectal carcinogenesis. Therefore, targeting HSF1 to attenuate glutaminolysis and mTOR activation could be a promising approach for CRC treatment.

Kr-POK (ZBTB7c) regulates cancer cell proliferation through glutamine metabolism

Kr-POK (ZBTB7c) is a kidney cancer-related POK transcription factor that not only represses transcription of CDKN1A but also increases expression of FASN. However, precisely how Kr-POK affects cell metabolism by controlling gene expression in response to an energy source in rapidly proliferating cells remains unknown. In this study, we characterized the molecular and functional features of Kr-POK in the context of tumor growth and glutamine metabolism. We found that cells expressing Kr-POK shRNA exhibited more severe cell death than control cells in glucose-deprived medium, and that knockdown of Kr-POK decreased glutamine uptake. Glutamine is critical for tumor cell proliferation. Glutaminase (GLS1), which is activated by p-STAT1, catalyzes the initial reaction in the pathway of glutaminolysis. Kr-POK interacts with PIAS1 to disrupt the interaction between PIAS1 and p-STAT1, and free p-STAT1 can activate GLS1 transcription through an interaction with p300. Kr-POK can be also sumoylated by PIAS1, facilitating Kr-POK degradation by the ubiquitin-mediated proteasomal pathway. Finally, we showed that repression of Kr-POK inhibited tumor growth in vivo in a xenograft model by repressing GLS1 expression. Taken together, our data reveal that Kr-POK activates GLS1 transcription and increases glutamine uptake to support rapid cancer cell proliferation.

Dlx-2 and glutaminase upregulate epithelial-mesenchymal transition and glycolytic switch

Most cancer cells depend on enhanced glucose and glutamine (Gln) metabolism for growth and survival. Oncogenic metabolism provides biosynthetic precursors for nucleotides, lipids, and amino acids; however, its specific roles in tumor progression are largely unknown. We previously showed that distal-less homeobox-2 (Dlx-2), a homeodomain transcription factor involved in embryonic and tumor development, induces glycolytic switch and epithelial-mesenchymal transition (EMT) by inducing Snail expression. Here we show that Dlx-2 also induces the expression of the crucial Gln metabolism enzyme glutaminase (GLS1), which converts Gln to glutamate. TGF-β and Wnt induced GLS1 expression in a Dlx-2-dependent manner. GLS1 shRNA (shGLS1) suppressed in vivo tumor metastasis and growth. Inhibition of Gln metabolism by shGLS1, Gln deprivation, and Gln metabolism inhibitors (DON, 968 and BPTES) prevented Dlx-2-, TGF-β-, Wnt-, and Snail-induced EMT and glycolytic switch. Finally, shDlx-2 and Gln metabolism inhibition decreased Snail mRNA levels through p53-dependent upregulation of Snail-targeting microRNAs. These results demonstrate that the Dlx-2/GLS1/Gln metabolism axis is an important regulator of TGF-β/Wnt-induced, Snail-dependent EMT, metastasis, and glycolytic switch.

Blockage of glutaminolysis enhances the sensitivity of ovarian cancer cells to PI3K/mTOR inhibition involvement of STAT3 signaling

The PI3K/Akt/mTOR axis in ovarian cancer is frequently activated and implicated in tumorigenesis. Specific targeting of this pathway is therefore an attractive therapeutic approach for ovarian cancer. However, ovarian cancer cells are resistant to PP242, a dual inhibitor of mTORC1 and mTORC2. Interestingly, blockage of GLS1 with a selective inhibitor, CB839, or siRNA dramatically sensitized the PP242-induced cell death, as evident from increased PARP cleavage. The anti-cancer activity of CB-839 and PP242 was abrogated by the addition of the TCA cycle product α-ketoglutarate, indicating the critical function of GLS1 in ovarian cancer cell survival. Finally, glutaminolysis inhibition activated apoptosis and synergistically sensitized ovarian cancer cells to priming with the mTOR inhibitor PP242. GLS1 inhibition significantly reduced phosphorylated STAT3 expression in ovarian cancer cells. These findings show that targeting glutamine addiction via GLS1 inhibition offers a potential novel therapeutic strategy to overcome resistance to PI3K/Akt/mTOR inhibition.

Genetic Pharmacotherapy as an Early CNS Drug Development Strategy: Testing Glutaminase Inhibition for Schizophrenia Treatment in Adult Mice

Genetic pharmacotherapy is an early drug development strategy for the identification of novel CNS targets in mouse models prior to the development of specific ligands. Here for the first time, we have implemented this strategy to address the potential therapeutic value of a glutamate-based pharmacotherapy for schizophrenia involving inhibition of the glutamate recycling enzyme phosphate-activated glutaminase. Mice constitutively heterozygous for GLS1, the gene encoding glutaminase, manifest a schizophrenia resilience phenotype, a key dimension of which is an attenuated locomotor response to propsychotic amphetamine challenge. If resilience is due to glutaminase deficiency in adulthood, then glutaminase inhibitors should have therapeutic potential. However, this has been difficult to test given the dearth of neuroactive glutaminase inhibitors. So, we used genetic pharmacotherapy to ask whether adult induction of GLS1 heterozygosity would attenuate amphetamine responsiveness. We generated conditional floxGLS1 mice and crossed them with global CAG^ERT2cre∕+ mice to produce GLS1 iHET mice, susceptible to tamoxifen induction of GLS1 heterozygosity. One month after tamoxifen treatment of adult GLS1 iHET mice, we found a 50% reduction in GLS1 allelic abundance and glutaminase mRNA levels in the brain. While GLS1 iHET mice showed some recombination prior to tamoxifen, there was no impact on mRNA levels. We then asked whether induction of GLS heterozygosity would attenuate the locomotor response to propsychotic amphetamine challenge. Before tamoxifen, control and GLS1 iHET mice did not differ in their response to amphetamine. One month after tamoxifen treatment, amphetamine-induced hyperlocomotion was blocked in GLS1 iHET mice. The block was largely maintained after 5 months. Thus, a genetically induced glutaminase reduction—mimicking pharmacological inhibition—strongly attenuated the response to a propsychotic challenge, suggesting that glutaminase may be a novel target for the pharmacotherapy of schizophrenia. These results demonstrate how genetic pharmacotherapy can be implemented to test a CNS target in advance of the development of specific neuroactive inhibitors. We discuss further the advantages, limitations, and feasibility of the wider application of genetic pharmacotherapy for neuropsychiatric drug development.

Elevated expression of glutaminase confers glucose utilization via glutaminolysis in prostate cancer

Cancer cells reprogram their metabolism towards aerobic glycolysis and elevated glutaminolysis, which contributes to the aggressive phenotype. Understanding how these metabolic pathways are regulated may provide critical targets for therapeutic intervention. Glutaminase (GLS1) is a key enzyme that converts glutamine to glutamate. In this study, we show the loss of GLS1 function by RNA interference or inhibitor diminished the rates of glucose utilization, growth and invasiveness of prostate cancer cells. We propose that GLS1 positively regulates glucose uptake in addition to glutaminolysis. Further, GLS1 involves the transcriptional repression of thioredoxin interacting protein (TXNIP), which is a potent negative regulator of glucose uptake and aerobic glycolysis. Most importantly, we provided direct evidence that elevated GLS1 expression was highly correlated with the tumor stage and progression in prostate cancer patients. Together, we defined a key role for GLS1 in coupling glutaminolysis of the TCA cycle with elevated glucose uptake and consequently the growth of prostate cancer cells. These data extends the role of GLS1 in regulating cell metabolism and the clinical utility of GLS1 inhibitors in the restriction of essential nutrients.

ErbB2 activation upregulates glutaminase 1 expression which promotes breast cancer cell proliferation

Active glutamine utilization is critical for tumor cell proliferation. Glutaminolysis represents the first and rate-limiting step of glutamine utilization and is catalyzed by glutaminase (GLS). Activation of ErbB2 is one of the major causes of breast cancers, the second most common cause of death for women in many countries. However, it remains unclear whether ErbB2 signaling affects glutaminase expression in breast cancer cells. In this study, we show that MCF10A-NeuT cell line has higher GLS1 expression at both mRNA and protein levels than its parental line MCF10A, and knockdown of ErbB2 decreases GLS1 expression in MCF10A-NeuT cells. We further show that in these cells, ErbB2-mediated upregulation of GLS1 is not correlated to c-Myc expression. Moreover, activation of neither PI3K-Akt nor MAPK pathway is sufficient to upregulate GLS1 expression. Interestingly, inhibition of NF-κB blocks ErbB2-stimulated GLS1 expression, whereas stimulation of NF-κB is sufficient to enhance GLS1 levels in MCF10A cells, suggesting a PI3K-Akt-independent activation of NF-κB upregulates GLS1 in ErbB2-positive breast cancer cells. Finally, knockdown or inhibition of GLS1 significantly decreased the proliferation of breast cancer cells with high GLS1 levels. Taken together, our data indicate that ErbB2 activation promotes GLS1 expression via a PI3K-Akt-independent NF-κB pathway in breast cancer cells, identifying another oncogenic signaling pathway which stimulates GLS1 expression, and thus promoting glutamine utilization in cancer cells. These findings, if validated by in vivo model, may facilitate the identification of novel biochemical targets for cancer prevention and therapy.

Availability of the key metabolic substrates dictates the respiratory response of cancer cells to the mitochondrial uncoupling

Active glycolysis and glutaminolysis provide bioenergetic stability of cancer cells in physiological conditions. Under hypoxia, metabolic and mitochondrial disorders, or pharmacological treatment, a deficit of key metabolic substrates may become life-threatening to cancer cells. We analysed the effects of mitochondrial uncoupling by FCCP on the respiration of cells fed by different combinations of Glc, Gal, Gln and Pyr. In cancer PC12 and HCT116 cells, a large increase in O2 consumption rate (OCR) upon uncoupling was only seen when Gln was combined with either Glc or Pyr. Inhibition of glutaminolysis with BPTES abolished this effect. Despite the key role of Gln, addition of FCCP inhibited respiration and induced apoptosis in cells supplied with Gln alone or Gal/Gln. For all substrate combinations, amplitude of respiratory responses to FCCP did not correlate with Akt, Erk and AMPK phosphorylation, cellular ATP, and resting OCR, mitochondrial Ca(2+) or membrane potential. However, we propose that proton motive force could modulate respiratory response to FCCP by regulating mitochondrial transport of Gln and Pyr, which decreases upon mitochondrial depolarisation. As a result, an increase in respiration upon uncoupling is abolished in cells, deprived of Gln or Pyr (Glc). Unlike PC12 or HCT116 cells, mouse embryonic fibroblasts were capable of generating pronounced response to FCCP when deprived of Gln, thus exhibiting lower dependence on glutaminolysis. Overall, the differential regulation of the respiratory response to FCCP by metabolic environment suggests that mitochondrial uncoupling has a potential for substrate-specific inhibition of cell function, and can be explored for selective cancer treatment.