Fig. 1: Reactions catalysed by wild-type and cancer cell harbouring IDH1/2 variants.

a Wild-type (wt) IDH1/2 catalyses the NADP⁺-dependent oxidation of d-isocitrate to 2OG; cancer-associated IDH1/2 variants additionally catalyse NADPH-dependent 2OG reduction to d-2HG. b IDH inhibitors bind at the dimer interface. Active site and overall views of superimposed structures of homodimeric wt IDH1 (pale cyan, PDB 1T0L)¹² and R132H IDH1 (pale orange/orange, PDB 3INM)¹³. The active site contains the cofactor (NADP⁺ for wt IDH1; NADPH for R132H IDH1), the substrate (isocitrate for wt IDH1; 2OG for R132H IDH1) and inhibitory Ca²⁺ positioned to coordinate to the substrate; Mg²⁺, which is required for catalysis, likely binds in a related manner. The dimer interface where potent R132H IDH1 inhibitors bind is indicated by a purple dotted box. The active site and the dimer interface are linked through a proposed ‘regulatory’ α10 (orange, residues N271–G286); the metal ion and allosteric inhibitors bind on opposite faces of α10 (D275 and D279 from which are involved in metal chelation). Five R132H IDH1 allosteric inhibitor structures superimposed at the dimer interface: GSK321 (teal, PDB 5DE1)¹⁷, BAY-1436032 analogue (navy, PDB 5LGE)¹⁸, Vorasidenib (green, PDB 6ADG)⁵⁸, Novartis IDH889 (purple, PDB 5TQH)⁵⁹ and Sanofi 1 (dark grey, PDB 4UMX)²⁷. c Conversion of dl-isocitrate and NADP⁺ catalysed by R132H IDH1, as monitored by ¹H NMR (700 MHz) spectroscopy. Isocitrate is converted to 2HG via 2OG. Conditions: 50 mM Tris-D₁₁-HCl, pH 7.5 in 90% H₂O/10% D₂O (v/v), 2 µM R132H IDH1, 1.5 mM dl-isocitrate, 500 µM NADP⁺ and 10 mM MgCl₂. Initially, NADP⁺ (teal) is converted to NADPH (blue) during the conversion of isocitrate (yellow-green) to 2OG (pink). As R132H IDH1 also catalyses the conversion of 2OG (pink) to 2HG (orange), NADPH is consumed to regenerate NADP⁺.