Abstract B1: Hypoxia inducible factor (HIF) promotes reductive carboxylation by regulating citrate levels and renders VHL-deficient and hypoxic cells sensitive to glutamine deprivation

Abstract

Abstract Hypoxia is a hallmark of tumor microenvironment. We showed before that exposure of cells to hypoxia reprograms cell metabolism and directs an IDH1-mediated reductive carboxylation (RC) of glutamine-derived alpha-ketoglutarate (a-KG) for lipogenesis. In addition Von Hippel-Lindau (VHL)-deficient renal cell carcinoma cells use glutamine to generate citrate and lipids through RC of a-KG. To gain insights into the role of HIF and the molecular mechanisms underlying RC we took advantage of a panel of disease-associated VHL mutants and showed that HIF expression is necessary and sufficient for the induction of RC in human renal cell carcinoma (RCC) cells. HIF expression drastically reduces intracellular citrate levels. Feeding VHL-deficient RCC cells with acetate or citrate, or knocking-down PDK-1 and ACLY enzymes restored intracellular citrate levels and suppressed RC. These data suggest that HIF-induced low intracellular citrate levels promote the reductive flux by mass action, to maintain lipogenesis. Expression of HIF renders hypoxic and VHL-deficient cells addicted to glutamine in vitro. VHL-deficient cells displayed significantly less growth than their isogenic counterparts in media containing low glutamine concentration or in the presence of a glutaminase inhibitor. Systemic administration of a glutaminase inhibitor (BPTES) suppressed the growth of VHL-deficient human RCC cell lines as xenografts in nude mice. Lastly, we investigated whether RC occurs in vivo. We metabolically labeled mice bearing VHL-deficient tumors by infusing them with 13C-1-Glutamine for up to 6 hours and we detected the early formation of labeled citrate in the tumors; thus we showed for the first time RC in vivo. Our data provide mechanistic insights into the signaling events that mediate hypoxia-induced RC, strongly suggest that RC is an in vivo phenomenon in growing tumors and highlight potential novel therapeutic approaches for treatment of hypoxic and VHL-deficient tumors based on their metabolic signature. Citation Format: Paulo Gameiro, Ana Metelo, Rojo Pérez-Carro, Arreola Alexandra, Zongwei Wang, Kimryn W. Rathmell, Aria Olumi, Pilar López-Larrubia, Gregory Stephanopoulos, Othon Iliopoulos. Hypoxia inducible factor (HIF) promotes reductive carboxylation by regulating citrate levels and renders VHL-deficient and hypoxic cells sensitive to glutamine deprivation. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B1.