DDDR-26. IDENTIFICATION OF MODULATORS OF IDH INHIBITOR SENSITIVITY IN<i>IDH</i>-MUTATED DIFFUSE GLIOMAS

Abstract Driver mutations in IDH1 and IDH2 characterize a substantial proportion of lower-grade diffuse gliomas in adults. Mutated IDH molecules cause the accumulation of D-2-hydroxyglutarate (D-2-HG), which perturbs many cellular functions, including metabolism, epigenetic regulation, and the ability to differentiate. This is notably associated with DNA and histone hyper-methylation. Recently, the newly developed IDH inhibitor, vorasidenib, was shown to delay tumor progression and the need for additional treatment in the groundbreaking INDIGO clinical trial. Nevertheless, the responses to vorasidenib were variable between patients, and so far have been established only for less aggressive disease. In addition, it is unclear to what extent vorasidenib can cause tumor regression. This highlights the need to identify molecules and pathways that control IDH inhibitor sensitivity. Towards this goal, we generated a new mouse model that combines Idh1R132H and Trp53 loss-of-function, targeted to oligodendrocyte progenitors. All the mutant mice develop diffuse gliomas that recapitulate the cardinal features of the corresponding human disease. We established multiple cell lines from these tumors, which retained expression of mutant IDH. The cells robustly produced D-2-HG, which was concentration-dependently suppressed by vorasidenib. Accordingly, vorasidenib could lower DNA methylation, and induce the expression of mature glial cell markers. To identify determinants of vorasidenib sensitivity, we performed genome-wide loss-of-function CRISPR/Cas9 functional genomics screens. In those experiments, targeting genes associated with astrocyte differentiation or Notch signaling enhanced cell fitness in the presence of vorasidenib, consistent with the anticipated effects of the drug on inducing cell differentiation. Conversely, vorasidenib-treated cells were more sensitive to the loss of regulators of cell growth and metabolism, and of some epigenetic regulators. These studies point to strategies that may enhance the efficacy of IDH inhibitors for the treatment of IDH mutated gliomas.