Targeting chordoma via an isocitrate dehydrogenase-1-dependent susceptibility to redox metabolism

Chordomas are rare cancers that arise along the axial skeleton. Alterations in metabolism are a hallmark of cancer, and we sought to identify metabolic vulnerabilities in chordoma. We discovered that the tricarboxylic acid (TCA)-related enzyme isocitrate dehydrogenase-1 (IDH1) was expressed highly in bulk and single-cell patient-derived chordomas and was associated with worse survival outcomes. IDH1 catalyzes the conversion of isocitrate and nicotinamide adenine dinucleotide phosphate (NADP+) to alpha-ketoglutarate (⍺-KG) and NADPH. This critical reaction influences TCA cycle metabolism, regulates epigenetic pathways, and affects redox balance. Both IDH1 knockdown and treatment with an inhibitor targeting IDH1 were toxic to chordoma cells. An integrated analysis of the transcriptomic, chromatin, and metabolomic responses on IDH1 inhibition converged on deregulated glutathione metabolism. IDH1 inhibition was associated with increased expression and enrichment of activating H3K27ac at NRF2 (nuclear factor erythroid 2-related factor 2) signature genes including those in the glutathione biosynthetic pathway. This was accompanied by reduction of both NADPH/NADP+ and reduced/oxidized glutathione (GSH/GSSG) ratios. Importantly, IDH1 inhibitor-driven toxicity was rescued via media supplementation with the antioxidant N-acetylcysteine, suggesting that IDH1 inhibition in chordomas creates a redox-dependent metabolic vulnerability. Finally, IDH1 inhibitor treatment reduced tumor growth in two independent chordoma mouse xenograft models. Our findings suggest a potential therapeutic avenue for further exploration in chordoma.