Introduction: Recent efforts have revealed IDH1 mutation not only results in marked accumulation of 2-hydroxyglutarate (2-HG), it generates genomic chromatin alterations, altered HIF activity and reprogrammed metabolic flux. We characterized the metabolic perturbations caused by heterozygous mutant IDH1 by comparing endogenous IDH1 mutant glioma cells treated with direct inhibitors of mutant IDH1 (IDH1i) to control cells without treatment, with the overall aim of identifying novel metabolic therapeutic targets.
Experimental Procedures: We tested the effect of IDH1i on the in vitro and in vivo phenotype of a panel of patient-derived endogenous IDH1 mutant solid cancer cells (including gliomas, melanoma, and sarcomas). We then assessed the effect of IDH1i on the metabolome of endogenous IDH1 mutant glioma cells using liquid chromatography-mass spectrometry. We further investigated specifically perturbed metabolic pathways using lentiviral knockdown and overexpression systems.
Results: We found that IDH1i exposure and the resulting 2-HG depletion had a mixed effect in 12 endogenous mutant IDH1 lines studied both in vitro or in vivo, including an orthotopic glioma xenograft model. For 10 of 12 lines, IDH1i treatment had no demonstrable effect on proliferation or survival, while 2 lines displayed growth inhibition after IDH1i treatment. However, no significant changes were detected in the genomic DNA methylation profiles or the global levels of histone tail marks including H3K4me3, H3K9me2, H3K9me3 and H3K27me3 in IDH1 mutant glioma lines, even after inhibition of mutant IDH1 for 12 months in vitro. Broader metabolite profiling revealed that inhibition of mutant IDH1 significantly altered levels of the canonical metabolite NAD+. We tested the effect of NAD+ depletion using NAD+ biosynthesis inhibitors, and found that endogenously mutant IDH1 cells were highly dependent on NAD+ for survival, whereas proliferation and survival of IDH1/2 wild-type cancer cells were unaffected by NAD+ depletion. Using an inducible mutant IDH1 expression system we discovered that mutant IDH1 reduced intracellular NAD+ levels, rendering mutant IDH1 cells susceptible to further NAD+ depletion. Lack of sufficient NAD+ induced metabolic crisis with reduced ATP levels in IDH1 mutant cells, triggering the intracellular energy sensor AMPK and autophagy. In vivo, NAD+ depletion significantly extended the survival of mice bearing IDH1 mutant xenograft tumors, including intracerebral gliomas.
Conclusions: Although most IDH1 mutant cell lines derived from solid cancers were resistant to direct IDH1 inhibition, a subset of IDH1 mutant cancers were found to be sensitive. Mutant IDH1 reprograms metabolism and renders cancer cells highly dependent on NAD+ for survival. This metabolic addiction presents a potential opportunity for metabolically targeted therapeutic development.
Citation Format: Andrew S. Chi, Kensuke Tateishi, Wakimoto Hiroaki, Tracy T. Batchelor, Anthony J. Iafrate, Daniel P. Cahill. Metabolic addiction in IDH1 mutant cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2675.