Olaparib Is a Mitochondrial Complex I Inhibitor That Kills Temozolomide-Resistant Human Glioblastoma Cells.

Glioblastoma represents the highest grade of brain tumors. Despite maximal resection surgery associated with radiotherapy and concomitant followed by adjuvant chemotherapy with temozolomide (TMZ), patients have a very poor prognosis due to the rapid recurrence and the acquisition of resistance to TMZ. Here, initially considering that TMZ is a prodrug whose activation is pH-dependent, we explored the contribution of glioblastoma cell metabolism to TMZ resistance. Using isogenic TMZ-sensitive and TMZ-resistant human glioblastoma cells, we report that the expression of O6-methylguanine DNA methyltransferase (MGMT), which is known to repair TMZ-induced DNA methylation, does not primarily account for TMZ resistance. Rather, fitter mitochondria in TMZ-resistant glioblastoma cells are a direct cause of chemoresistance that can be targeted by inhibiting oxidative phosphorylation and/or autophagy/mitophagy. Unexpectedly, we found that PARP inhibitor olaparib, but not talazoparib, is also a mitochondrial Complex I inhibitor. Hence, we propose that the anticancer activities of olaparib in glioblastoma and other cancer types combine DNA repair inhibition and impairment of cancer cell respiration.

Multi-compartment metabolomics and metagenomics reveal major hepatic and intestinal disturbances in cancer cachectic mice.

BACKGROUND: Cancer cachexia is a multifactorial syndrome characterized by multiple metabolic dysfunctions. Besides the muscle, other organs such as the liver and the gut microbiota may also contribute to this syndrome. Indeed, the gut microbiota, an important regulator of the host metabolism, is altered in the C26 preclinical model of cancer cachexia. Interventions targeting the gut microbiota have shown benefits, but mechanisms underlying the host-microbiota crosstalk in this context are still poorly understood. METHODS: To explore this crosstalk, we combined proton nuclear magnetic resonance (1 H-NMR) metabolomics in multiple compartments with 16S rDNA sequencing. These analyses were complemented by molecular and biochemical analyses, as well as hepatic transcriptomics. RESULTS: 1 H-NMR revealed major changes between control (CT) and cachectic (C26) mice in the four analysed compartments (i.e. caecal content, portal vein, liver, and vena cava). More specifically, glucose metabolism pathways in the C26 model were altered with a reduction in glycolysis and gluconeogenesis and an activation of the hexosamine pathway, arguing against the existence of a Cori cycle in this model. In parallel, amino acid uptake by the liver, with an up to four-fold accumulation of nine amino acids (q-value <0.05), was mainly used for acute phase response proteins synthesis rather than to fuel the tricarboxylic acid cycle and gluconeogenesis. We also identified a 35% reduction in hepatic carnitine levels (q-value <0.05) and a lower activation of the phosphatidylcholine pathway as potential contributors to the hepatic steatosis present in this model. Our work also reveals a reduction of different beneficial intestinal bacterial activities in cancer cachexia. We found decreased levels of two short-chain fatty acids, acetate and butyrate (72% and 88% reduction in C26 caecal content; q-value <0.001), and a reduction in aromatic amino acid metabolites, which may contribute to the altered intestinal homeostasis in these mice. A member of the Ruminococcaceae family (ASV 2) was identified as the main bacterium responsible for the drop in butyrate. Finally, we report a two-fold intestinal transit acceleration (P-value <0.001) as a key factor shaping the gut microbiota composition and activity in cancer cachexia, which together lead to a faecal loss of proteins and amino acids. CONCLUSIONS: Our work highlights new metabolic pathways potentially involved in cancer cachexia and further supports the interest of exploring the gut microbiota composition and activity, as well as intestinal transit, in cancer patients with and without cachexia.

Inflammation-induced cholestasis in cancer cachexia.

BACKGROUND: Cancer cachexia is a debilitating metabolic syndrome contributing to cancer death. Organs other than the muscle may contribute to the pathogenesis of cancer cachexia. This work explores new mechanisms underlying hepatic alterations in cancer cachexia. METHODS: We used transcriptomics to reveal the hepatic gene expression profile in the colon carcinoma 26 cachectic mouse model. We performed bile acid, tissue mRNA, histological, biochemical, and western blot analyses. Two interventional studies were performed using a neutralizing interleukin 6 antibody and a bile acid sequestrant, cholestyramine. Our findings were evaluated in a cohort of 94 colorectal cancer patients with or without cachexia (43/51). RESULTS: In colon carcinoma 26 cachectic mice, we discovered alterations in five inflammatory pathways as well as in other pathways, including bile acid metabolism, fatty acid metabolism, and xenobiotic metabolism (normalized enrichment scores of -1.97, -2.16, and -1.34, respectively; all Padj < 0.05). The hepatobiliary transport system was deeply impaired in cachectic mice, leading to increased systemic and hepatic bile acid levels (+1512 ± 511.6 pmol/mg, P = 0.01) and increased hepatic inflammatory cytokines and neutrophil recruitment to the liver of cachectic mice (+43.36 ± 16.01 neutrophils per square millimetre, P = 0.001). Adaptive mechanisms were set up to counteract this bile acid accumulation by repressing bile acid synthesis and by enhancing alternative routes of basolateral bile acid efflux. Targeting bile acids using cholestyramine reduced hepatic inflammation, without affecting the hepatobiliary transporters (e.g. tumour necrosis factor α signalling via NFκB and inflammatory response pathways, normalized enrichment scores of -1.44 and -1.36, all Padj < 0.05). Reducing interleukin 6 levels counteracted the change in expression of genes involved in the hepatobiliary transport, bile acid synthesis, and inflammation. Serum bile acid levels were increased in cachectic vs. non-cachectic cancer patients (e.g. total bile acids, +5.409 ± 1.834 µM, P = 0.026) and were strongly correlated to systemic inflammation (taurochenodeoxycholic acid and C-reactive protein: ρ = 0.36, Padj = 0.017). CONCLUSIONS: We show alterations in bile acid metabolism and hepatobiliary secretion in cancer cachexia. In this context, we demonstrate the contribution of systemic inflammation to the impairment of the hepatobiliary transport system and the role played by bile acids in the hepatic inflammation. This work paves the way to a better understanding of the role of the liver in cancer cachexia.

Klebsiella oxytoca expands in cancer cachexia and acts as a gut pathobiont contributing to intestinal dysfunction.

Cancer cachexia is a complex multi-organ syndrome characterized by body weight loss, weakness, muscle atrophy and fat depletion. With a prevalence of 1 million people in Europe and only limited therapeutic options, there is a high medical need for new approaches to treat cachexia. Our latest results highlighted microbial dysbiosis, characterized by a bloom in Enterobacteriaceae and altered gut barrier function in preclinical models of cancer cachexia. They also demonstrated the potential of targeting the gut microbial dysbiosis in this pathology. However, the exact mechanisms underlying the gut microbiota-host crosstalk in cancer cachexia remain elusive. In this set of studies, we identified Klebsiella oxytoca as one of the main Enterobacteriaceae species increased in cancer cachexia and we demonstrated that this bacteria acts as a gut pathobiont by altering gut barrier function in cachectic mice. Moreover, we propose a conceptual framework for the lower colonization resistance to K. oxytoca in cancer cachexia that involves altered host gut epithelial metabolism and host-derived nitrate boosting the growth of the gut pathobiont. This set of studies constitutes a strong progression in the field of gut microbiota in cancer cachexia, by dissecting the mechanism of emergence of one bacterium, K. oxytoca, and establishing its role as a gut pathobiont in this severe disease.

Polyunsaturated fatty acids, polyphenols, amino acids, prebiotics: can they help to tackle cancer cachexia and related inflammation?

PURPOSE OF REVIEW: Recent studies have highlighted the importance of developing a multimodal therapeutic strategy for cancer cachectic patients. Considering the central role of metabolism and anorexia in this disease, optimized nutritional advice should be an integral part of this strategy. Current recommendations mainly focus on meeting caloric requirements. However, a few studies suggest the great potential of foods naturally enriched in nutrients presenting interesting physiological properties and the interest of using them in the management of cachectic patients. Among them, prebiotics show the capacity to control inflammation in several debilitating diseases. In this context, this review aims to summarize the most recent findings related to functional foods and nutrients and cancer cachexia, and to discuss the potential use of prebiotics in this context. RECENT FINDINGS: Even though there is a clear need for more research in the field, data from both humans and animal models support the promising benefits of functional foods and nutrients in cancer cachexia. SUMMARY: Altogether, these studies offer new insights into the potential contribution of nutrition to cancer patient management. Functional foods, by downregulating inflammatory pathways, could decrease cachexia severity and contribute to the improvement of cancer patients' quality of life.

Lactate stimulates CA IX expression in normoxic cancer cells.

Besides hypoxia, other factors and molecules such as lactate, succinate, and reactive oxygen species activate transcription factor hypoxia-inducible factor-1 (HIF-1) even in normoxia. One of the main target gene products of HIF-1 is carbonic anhydrase IX (CA IX). CA IX is overexpressed in many tumors and serves as prognostic factor for hypoxic, aggressive and malignant cancers. CA IX is also induced in normoxia in high cell density. In this study, we observed that lactate induces CA IX expression in normoxic cancer cells in vitro and in vivo. We further evidenced that participation of both HIF-1 and specificity protein 1 (SP1) transcription factors is crucial for lactate-driven normoxic induction of the CA9 gene. By inducing CA IX, lactate can facilitate the maintenance of cancer cell aggressive behavior in normoxia.

MDA-MB-231 breast cancer cells fuel osteoclast metabolism and activity: A new rationale for the pathogenesis of osteolytic bone metastases.

Recent progress in dissecting the molecular paracrine circuits of cancer and stromal cells in bone metastases (BM) are offering new options to improve current merely palliative approach. The study of tumor-stroma metabolic interplay may further ameliorate this scenario. In this context, we demonstrated that highly glycolytic MDA-MB-231 cancer cells, that form osteolytic BM in vivo, release a large amount of lactate at a significantly higher level than MCF7 cells. Thus, we speculated that lactate released from carcinoma cells is uptaken and metabolically used by osteoclasts, the key players of osteolysis associated with BM. First, we demonstrated that the release of lactate at the bone site is mediated by monocarboxylate transporter 4 (MCT4), as revealed by immunostaining and MCT4 localization at the plasma membrane of tumor cells in mouse model of BM and in human tissue sections of BM. Then, we showed that in vitro lactate is uptaken by osteoclasts to be used as a fuel for the oxidative metabolism of osteoclasts, ultimately enhancing Type I collagen resorption. The passive transport of lactate into osteoclasts was mediated by MCT1: MCT1 expression is significantly upregulated during osteoclast differentiation and Type I collagen resorption is significantly impaired when osteoclasts are treated with 7-(N-benzyl-N-methylamino)-2-oxo-2H-chromene-3-carboxylic acid, an MCT-1 inhibitor. Together, these data demonstrate that lactate released by glycolytic breast carcinoma cells in the bone microenvironment promotes the formation of osteolytic lesions, and provide the rationale for further studies on the use of MCT1 targeting as a novel therapeutic approach in advanced cancer patients with BM.

Ffar2 expression regulates leukaemic cell growth in vivo.

BACKGROUND: Activation of free fatty acid receptor 2 (FFAR2) by microbiota-derived metabolites (e.g., propionate) reduces leukaemic cell proliferation in vitro. This study aims to test whether Ffar2 expression per se also influences leukaemia cell growth in vivo. METHODS: Bcr-Abl-expressing BaF cells were used as a leukaemia model and the role of Ffar2 was evaluated in Balb/c mice after lentiviral shRNA transduction. RESULTS: Our data formally establish that reduced leukaemic cell proliferation is associated with increased Ffar2 expression in vivo and in vitro. Going beyond association, we point out that decreasing Ffar2 expression fosters cancer cell growth in vitro and in vivo. CONCLUSIONS: Our data demonstrate the role of Ffar2 in the control of leukaemic cell proliferation in vivo and indicate that a modulation of Ffar2 expression through nutritional tools or pharmacological agents may constitute an attractive therapeutic approach to tackle leukaemia progression in humans.

Glutamine activates STAT3 to control cancer cell proliferation independently of glutamine metabolism.

Cancer cells can use a variety of metabolic substrates to fulfill the bioenergetic and biosynthetic needs of their oncogenic program. Besides bioenergetics, cancer cell metabolism also directly influences genetic, epigenetic and signaling events associated with tumor progression. Many cancer cells are addicted to glutamine, and this addiction is observed in oxidative as well as in glycolytic cells. Although both oxidative and bioreductive glutamine metabolism can contribute to cancer progression and glutamine can further serve to generate peptides (including glutathione) and proteins, we report that glutamine promotes the proliferation of cancer cells independently of its use as a metabolic fuel or as a precursor of glutathione. Extracellular glutamine activates transcription factor signal transducer and activator of transcription 3 (STAT3), which is necessary and sufficient to mediate the proliferative effects of glutamine on glycolytic and oxidative cancer cells. Glutamine also activates transcription factors hypoxia-inducible factor-1, mammalian target of rapamycin and c-Myc, but these factors do not mediate the effects of glutamine on cancer cell proliferation. Our findings shed a new light on the anticancer effects of l-asparaginase that possesses glutaminase activity and converts glutamine into glutamate extracellularly. Conversely, cancer resistance to treatments that block glutamine metabolism could arise from glutamine-independent STAT3 reactivation.

Energy metabolism in osteoclast formation and activity.

Osteoclastogenesis and osteolysis are energy-consuming processes supported by high metabolic activities. In human osteoclasts derived from the fusion of monocytic precursors, we found a substantial increase in the number of mitochondria with differentiation. In mature osteoclasts, mitochondria were also increased in size, rich of cristae and arranged in a complex tubular network. When compared with immature cells, fully differentiated osteoclasts showed higher levels of enzymes of the electron transport chain, a higher mitochondrial oxygen consumption rate and a lower glycolytic efficiency, as evaluated by extracellular flux analysis and by the quantification of metabolites in the culture supernatant. Thus, oxidative phosphorylation appeared the main bioenergetic source for osteoclast formation. Conversely, we found that bone resorption mainly relied on glycolysis. In fact, osteoclast fuelling with galactose, forcing cells to depend on Oxidative Phosphorylation by reducing the rate of glycolysis, significantly impaired Type I collagen degradation, whereas non-cytotoxic doses of rotenone, an inhibitor of the mitochondrial complex I, enhanced osteoclast activity. Furthermore, we found that the enzymes associated to the glycolytic pathway are localised close to the actin ring of polarised osteoclasts, where energy-demanding activities associated with bone degradation take place. In conclusion, we demonstrate that the energy required for osteoclast differentiation mainly derives from mitochondrial oxidative metabolism, whereas the peripheral cellular activities associated with bone matrix degradation are supported by glycolysis. A better understanding of human osteoclast energy metabolism holds the potential for future therapeutic interventions aimed to target osteoclast activity in different pathological conditions of bone.

Lactate Dehydrogenase B Controls Lysosome Activity and Autophagy in Cancer.

Metabolic adaptability is essential for tumor progression and includes cooperation between cancer cells with different metabolic phenotypes. Optimal glucose supply to glycolytic cancer cells occurs when oxidative cancer cells use lactate preferentially to glucose. However, using lactate instead of glucose mimics glucose deprivation, and glucose starvation induces autophagy. We report that lactate sustains autophagy in cancer. In cancer cells preferentially to normal cells, lactate dehydrogenase B (LDHB), catalyzing the conversion of lactate and NAD(+) to pyruvate, NADH and H(+), controls lysosomal acidification, vesicle maturation, and intracellular proteolysis. LDHB activity is necessary for basal autophagy and cancer cell proliferation not only in oxidative cancer cells but also in glycolytic cancer cells.

Monocarboxylate transporters in the brain and in cancer.

Monocarboxylate transporters (MCTs) constitute a family of 14 members among which MCT1-4 facilitate the passive transport of monocarboxylates such as lactate, pyruvate and ketone bodies together with protons across cell membranes. Their anchorage and activity at the plasma membrane requires interaction with chaperon protein such as basigin/CD147 and embigin/gp70. MCT1-4 are expressed in different tissues where they play important roles in physiological and pathological processes. This review focuses on the brain and on cancer. In the brain, MCTs control the delivery of lactate, produced by astrocytes, to neurons, where it is used as an oxidative fuel. Consequently, MCT dysfunctions are associated with pathologies of the central nervous system encompassing neurodegeneration and cognitive defects, epilepsy and metabolic disorders. In tumors, MCTs control the exchange of lactate and other monocarboxylates between glycolytic and oxidative cancer cells, between stromal and cancer cells and between glycolytic cells and endothelial cells. Lactate is not only a metabolic waste for glycolytic cells and a metabolic fuel for oxidative cells, but it also behaves as a signaling agent that promotes angiogenesis and as an immunosuppressive metabolite. Because MCTs gate the activities of lactate, drugs targeting these transporters have been developed that could constitute new anticancer treatments. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Lactate promotes glutamine uptake and metabolism in oxidative cancer cells.

Oxygenated cancer cells have a high metabolic plasticity as they can use glucose, glutamine and lactate as main substrates to support their bioenergetic and biosynthetic activities. Metabolic optimization requires integration. While glycolysis and glutaminolysis can cooperate to support cellular proliferation, oxidative lactate metabolism opposes glycolysis in oxidative cancer cells engaged in a symbiotic relation with their hypoxic/glycolytic neighbors. However, little is known concerning the relationship between oxidative lactate metabolism and glutamine metabolism. Using SiHa and HeLa human cancer cells, this study reports that intracellular lactate signaling promotes glutamine uptake and metabolism in oxidative cancer cells. It depends on the uptake of extracellular lactate by monocarboxylate transporter 1 (MCT1). Lactate first stabilizes hypoxia-inducible factor-2α (HIF-2α), and HIF-2α then transactivates c-Myc in a pathway that mimics a response to hypoxia. Consequently, lactate-induced c-Myc activation triggers the expression of glutamine transporter ASCT2 and of glutaminase 1 (GLS1), resulting in improved glutamine uptake and catabolism. Elucidation of this metabolic dependence could be of therapeutic interest. First, inhibitors of lactate uptake targeting MCT1 are currently entering clinical trials. They have the potential to indirectly repress glutaminolysis. Second, in oxidative cancer cells, resistance to glutaminolysis inhibition could arise from compensation by oxidative lactate metabolism and increased lactate signaling.