METABOLIC PLASTICITY AND HETEROGENEITY IN IDH1(MUT) CELL LINES PRODUCES RESISTANCE TO GLUTAMINASE INHIBITION BY CB839

Abstract BACKGROUND Mutant IDH1 (IDH1mut) gliomas have characteristic genetic and metabolic profiles and exhibit phenotype that is distinct from their wild-type counterparts. The glutamine/glutamate pathway has been hypothesized as a selective therapeutic target in IDH1mut gliomas. However, little information exists on the contribution of this pathway to the formation of D-2-hydroxyglutarate (D-2HG), a hallmark of IDHmut cells, and the metabolic consequences of inhibiting this pathway. METHODS We employed an untargeted metabolic profiling approach in order to detect metabolic changes arising from glutaminase (GLS) inhibition treatment. Subsequently, 13C metabolic tracing analysis through a combined Nuclear Magnetic Resonance and Liquid Chromatography-Mass Spectrometry approach, we explored the fate of glutamine and glucose under treatment with CB839 a glutaminase-GLS-inhibitor and their respective contributions to D-2HG formation. RESULTS AND CONCLUSIONS The effects of CB839 on cellular proliferation differed among the cell lines tested, leading to designations of GLS-inhibition super-sensitive, -sensitive or -resistant. Our data indicates a decrease in the production of downstream metabolites of glutamate, including those involved in the TCA cycle, when treating the sensitive cells with CB839 (glutaminase -GLS- inhibitor). Notably, CB839-sensitive IDH1mutcells respond to GLS inhibition by upregulating glycolysis and lactate production. In contrast, CB839-resistantIDH1mut cell lines do not rely only on glutamine for the sustenance of TCA cycle. In these cells, glucose contribution to TCA is enough to compensate the downregulation of glutamine-derived TCA metabolites. This investigation reveals that the glutamine/glutamate pathway contributes differentially to D-2HG in a cell-line dependent fashion on a panel of IDHmut cell lines. Further, these results demonstrate that there is a heterogeneous landscape of IDH1mut metabolic phenotypes. This underscores the importance of detailed metabolic profiling of IDH1mut patients prior to the decision to target glutamine/glutamate pathway clinically.