METB-06. DOWN REGULATION OF PHOSPHOLIPID METABOLISM IS A UNIQUE HALLMARK OF MUTANT IDH1 GLIOMA CELLS

Abstract

Aberrant choline metabolism with up-regulated levels of phosphocholine (PC) and phosphoethanolamine (PE) has been recognized as a hallmark of cancer. PC and PE are crucial precursors in the synthesis of the membrane phospholipids, phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn). Interestingly, low-grade gliomas carrying the isocitrate dehydrogenase 1 (IDH1) mutation display an unusual metabolic profile with reduced PC and PE levels relative to tumors expressing the wild-type IDH1 enzyme. The goal of the current study was, therefore, to examine the mechanism behind the reduction in PC and PE levels in mutant IDH1 cells using two genetically engineered cell models, a U87 glioblastoma-based model and a normal human astrocyte (NHA) model. We used 13C-magnetic resonance spectroscopy (MRS) to quantify the flux of [1,2-13C]-choline and [1,2-13C]-ethanolamine to 13C-PC and 13C-PE in live cells assembled into a bioreactor. Our results indicated that PC and PE synthesis was reduced in mutant IDH1 cells relative to wild-type in both U87 and NHA models. The activities of choline kinase and ethanolamine kinase, the enzymes responsible for PC and PE synthesis respectively, were concomitantly reduced in mutant IDH1 cells in both models. Consistent with the fact that PC and PE are precursors in phospholipid synthesis, PtdCho and PtdEtn levels were reduced in mutant IDH1 cells relative to wild-type in both U87 and NHA models. Interestingly, cell size was not altered in mutant IDH1 cells despite the reduction in membrane phospholipids. Importantly, pharmacological inhibition of the mutant IDH1 enzyme using a specific inhibitor, AGI-5198, reversed the reduction in choline and ethanolamine kinase activity and resulted in increased PC and PE synthesis as well as increased PtdCho and PtdEtn levels in mutant IDH1 cells. Taken together, our study points to unusual remodeling of phospholipid metabolism in mutant IDH1 cells, a finding with important therapeutic implications.