LAUSR

Simple Summary While isocitrate dehydrogenases have been known for decades, their mechanisms in tumors are gradually becoming clearer. The three isocitrate dehydrogenase isoforms in human cells differ in their subcellular localization, molecular structure, cofactor requirement, and catalytic mechanism. Here, we review the role of isocitrate dehydrogenases in metabolism, provide a current overview of cancer-linked isocitrate dehydrogenases and point to future lines of research to better understand the complex biology in health and disease. Abstract The human isocitrate dehydrogenase (IDH) gene encodes for the isoenzymes IDH1, 2, and 3, which catalyze the conversion of isocitrate and α-ketoglutarate (α-KG) and are required for normal mammalian metabolism. Isocitrate dehydrogenase 1 and 2 catalyze the reversible conversion of isocitrate to α-KG. Isocitrate dehydrogenase 3 is the key enzyme that mediates the production of α-KG from isocitrate in the tricarboxylic acid (TCA) cycle. In the TCA cycle, the decarboxylation reaction catalyzed by isocitrate dehydrogenase mediates the conversion of isocitrate to α-KG accompanied by dehydrogenation, a process commonly known as oxidative decarboxylation. The formation of 6-C isocitrate from α-KG and CO2 catalyzed by IDH is termed reductive carboxylation. This IDH-mediated reversible reaction is of great importance in tumor cells. We outline the role of the various isocitrate dehydrogenase isoforms in cancer, discuss the metabolic implications of interference with IDH, summarize therapeutic interventions targeting changes in IDH expression, and highlight areas for future research.