Mutations in isocitrate dehydrogenase (IDH1/2) are common genetic abnormalities in grade II and III diffusive astrocytomas and oligodendrogliomas. In WHO grade II/III gliomas, IDH mutated tumors are highly prevalent comprising nearly 80% of all clinical cases. In glioma, IDH mutations cluster in an arginine residue at the center of the catalytic domain (IDH1 R132, IDH2 R172). Mutant IDH confers neomorphic enzymatic activity that, catalyzes alpha-ketoglutarate (alpha-KG) into 2-hydroxyglutarate (2-HG), an oncometabolite closely related to the deactivation of alpha-KG-dependent deoxygenases. Moreover, the neomorphic IDH1 mutations disrupt the redox balance by promoting reactive oxygen species (ROS) production. However, the mechanism by which IDH1-mutant cells maintain ROS homeostasis remains elusive. It is also not known whether reprogrammed ROS homeostasis establishes targetable vulnerability in IDH1-mutated cancers. In this project, we investigated ROS homeostasis in wild-type (GSC827, GSC923, GSC627, and GSC711) and IDH1-mutated cells (IDH1R132C- and IDH1R132H-transduced U87, U251; MGG152, and TS603 cells). We analyzed the stability and transcriptional activity of NRF2 in IDH1-mutated cells. The oxidative DNA damage was analyzed using NRF2-targeting small interfering RNA. Moreover, we evaluated the effect of the NRF2 inhibitor brusatol in an IDH1-mutated subcutaneous xenograft nude mouse model (control group, n=5; brusatol-treated group, n=6). All statistical tests were two-sided. Our findings showed that IDH1-mutated cells develop a dependency on the NRF2 antioxidative pathway. Genetic or pharmacologic blockade of NRF2 not only disrupted ROS homeostasis (ROS levels increased by 317% in IDH1R132C and by 286.5% in IDH1R132H cells), but also enhanced oxidative DNA damage and decreased proliferation of IDH1-mutated cells. Brusatol selectively suppressed IDH1-mutated cancer progression in vivo (final tumor volume was 761.6 mm3 in the control and 246.2 mm3 in the brusatol-treated group, P=0.021. Overall, our discovery demonstrated that IDH1 mutation reprograms ROS homeostasis in cancer cells, which leads to dependency on the NRF2 antioxidant pathway for ROS scavenging. NRF2 blockade might be a novel therapeutic approach to treat malignancies with IDH1 mutation.
