IDH1‐mutated gliomas rely on anaplerosis of glutamate and lactate whereas IDH1 wild‐type gliomas rely on glycolysis and acetate anaplerosis

Abstract

IntroductionHotspot mutations in isocitrate dehydrogenase 1 (IDH1MUT) initiate low grade glioma (LGG) and secondary glioblastoma and induce neomorphic activity that converts α‐ketoglutarate (α‐KG) to the oncometabolite D‐2‐hydroxyglutarate (D‐2HG). This causes metabolic rewiring and stress that is not fully understood. In vitro studies suggest that this stress is relieved via glutaminolysis, providing cells with α‐KG via activities of glutaminase (GLS) and glutamate dehydrogenase (GLUD). We previously postulated that IDH1MUT gliomas directly use glutamate as a shortcut.ResultsTo test this hypothesis, we first showed by in silico analysis of 269 IDH1 wild‐type (IDH1WT) and 408 IDH1MUT gliomas, obtained from the The Cancer Genome Atlas (TCGA) database, that IDH1WT gliomas have high expression levels of genes encoding for enzymes that are involved in glycolysis and acetate anaplerosis. On the other hand, the tricarboxylic acid (TCA) cycle, rather than glycolytic lactate production, is the predominant metabolic pathway in IDH1MUT gliomas and is driven by lactate and glutamate anaplerosis to facilitate production of α‐KG, and ultimately D‐2‐HG. Secondly, we confirmed these findings by a novel technique of quantitative targeted next‐generation sequencing of RNAs encoding for 104 metabolic enzymes, on a cohort of 66 clinical gliomas. Preferential glutamate processing in IDH1MUT gliomas was confirmed by in situ enzyme activity mapping experiments in clinical gliomas of known IDH status. We functionally validated these findings in a set of glioma xenografts with and without the endogenous IDH1R132H mutation, indicating that IDH1MUT gliomas depend on glutamatolysis, rather than glutaminolysis. We show that transcript levels in our xenocraft models are in good agreement with our in silico analysis of the TCGA database. Finally, we confirmed the glutamate dependency of IDH1MUT gliomas by in vivo magnetic resonance spectroscopic imaging, whereas IDH1WT gliomas showed high lactate levels.ConclusionsWe show that IDH1WT gliomas have a typical Warburg phenotype and rely on acetate anaplerosis whereas IDH1MUT gliomas are glutamate and lactate dependent. This metabolic rewiring in IDH1MUT glioma, enables targeting of glutaminolysis rather than direct inhibition of IDH1MUT for therapy. It diminishes the supply of glutamate‐derived α‐KG and directly inhibits the production of D‐2HG and simultaneously worsen the redox status of the glioma cells by inhibiting NAD(P)H production by GLUD. A candidate drug to inhibit GLUD is epigallocatechin‐3‐gallate gallate, a component of green tea that is currently receiving high interest as anticancer agent.Support or Funding InformationThis work was supported by Dutch Cancer Society grant UvA 2014‐6839 (KL, MK) and by Stichting StopHersentumoren (CNAMvdH). RJM was supported by an AMC PhD scholarship. THP was supported by EFRO/GO project Ultrasense NMR.