Mutant isocitrate dehydrogenase in cancer: Structural biology, small-molecule inhibitors, and future drug discovery strategies.

Isocitrate dehydrogenase (IDH) enzymes convert isocitrate to α-ketoglutarate. When IDH1 or IDH2 is mutated, the enzyme gains a new function, and the oncometabolite D-2-hydroxyglutarate (D-2-HG) accumulates. Its epigenetic and metabolic effects depend on the tumor context. This review classifies mutant IDH inhibitors by chemical scaffold and relates their binding in the allosteric pocket to structure-activity trends, isoform selectivity, brain penetration, and clinical outcome. Mutant IDH1, mutant IDH2, pan-IDH, and covalent inhibitors are compared, with lessons from successful and failed clinical candidates. Resistance is treated separately: secondary mutations, isoform switching, metabolic adaptation, rational combinations, proteolysis-targeting chimera (PROTAC) degraders, and biomarkers. Since reduced 2-HG indicates target engagement rather than clinical benefit, design priorities for the next generation of IDH-directed agents are outlined.