KDM6 Enzymes are the Mechanistic Targets of Mutant IDH that Dictate Replication Stress Sensitivity

Cancer-associated isocitrate dehydrogenase (IDH) mutations sensitize gliomas to replication stress, although the underlying mechanisms are unclear. IDH-mutant enzymes synthesize (R)-2-hydroxyglutarate (R2HG), which broadly inhibits 2-oxoglutarate-dependent enzymes. We performed forward genetic screens targeting all 2-oxoglutarate-dependent enzymes and discovered that KDM6 histone demethylases play a vital role in protecting cells from replication stress. Genetic or R2HG-mediated repression of KDM6 catalytic activity sensitized glioma cells to disparate replication stress-inducing drugs, including Ataxia-telangiectasia and Rad3-related (ATR) and dihydroorotate dehydrogenase (DHODH) inhibitors. This liability is generalizable because KDM6A loss-of-function mutations commonly observed in urothelial carcinomas sensitized bladder cancer cells to DHODH inhibition, thereby phenocopying IDH mutations in glioma. To exploit these oncogene-induced replication stress vulnerabilities, we developed an effective, on-target, and well-tolerated DHODH inhibitor, GLIO-1, that is poised for clinical translation. Collectively, we reveal KDM6 activity as a fundamental determinant of replication stress sensitivity and nominate pan-cancer, mechanism-based biomarkers of ATR and DHODH inhibitor efficacy. STATEMENT OF SIGNIFICANCEWe discovered that the KDM6 enzymes are the mechanistic targets of R2HG that mediate mutant IDH-induced replication stress hypersensitivity. We report a promising new DHODH inhibitor, GLIO-1, and nominate KDM6 and IDH mutations as predictive biomarkers for the antitumor effects of GLIO-1 and other replication stress inducers.