CBIO-42DOWN REGULATION OF PYRUVATE DEHYDROGENASE ACTIVITY IS ESSENTIAL FOR CELL PROLIFERATION IN IDH1 MUTANT GLIOMA CELLS

Abstract

Somatic mutations in the isocitrate dehydrogenase 1 (IDH1) gene occur in 70-90% of low-grade gliomas. The mutation leads to the production of 2-hydroxyglutarate (2-HG), a novel “oncometabolite” that alters the epigenetic profile of DNA and inhibits cellular differentiation. Recent studies indicate that metabolic changes in IDH1 mutant cells extend beyond 2-HG production. We recently demonstrated that steady state levels of glutamate, lactate and phosphocholine were reduced in IDH1 mutant cells using two genetically engineered models, a U87 glioblastoma-based model and a normal human astrocyte (NHA) model. In this study, we explored the mechanism behind the reduction in glutamate levels in IDH1 mutant cells. We discovered that pyruvate dehydrogenase (PDH) activity was significantly reduced in U87 and NHA IDH1 mutant cells compared to wild-type cells. Reduced PDH activity was associated with increased inhibitory phosphorylation of PDH in both models. Examination of mRNA and protein levels for the pyruvate dehydrogenase kinases (PDKs) revealed that PDK3 expression was up-regulated in IDH1 mutant cells in both models. Levels of hypoxia inducible factor-1α (HIF-1α), an established regulator of PDK3 expression in cancer cells, was also higher in IDH1 mutant cells. Importantly, treatment of U87 and NHA IDH1 wild-type cells with 2-HG recapitulated the effects of the IDH1 mutation, with higher levels of HIF-1α and PDK3, and reduced PDH activity, in 2-HG treated cells. Importantly, pharmacological activation of PDH activity by treatment with dichloroacetate, a PDK inhibitor, completely abrogated the increase in clonogenicity conferred by the IDH1 mutation. Treatment of patient-derived mutant IDH1 neurosphere models (BT142 and BT54 cell lines) with dichloroacetate further confirmed that PDH activity is essential for cell proliferation. Thus, our results indicate that reversing the down regulation of PDH activity in IDH1 mutant glioma cells adversely affects their proliferation, a finding with therapeutic implications.