Cancer-associated IDH1 mutations produce 2-hydroxyglutarate

Mutations in the enzyme cytosolic isocitrate dehydrogenase 1 (IDH1) are a common feature of a major subset of primary human brain cancers. These mutations occur at a single amino acid residue of the IDH1 active site, resulting in loss of the enzyme’s ability to catalyse conversion of isocitrate to α-ketoglutarate. However, only a single copy of the gene is mutated in tumours, raising the possibility that the mutations do not result in a simple loss of function. Here we show that cancer-associated IDH1 mutations result in a new ability of the enzyme to catalyse the NADPH-dependent reduction of α-ketoglutarate to R(-)-2-hydroxyglutarate (2HG). Structural studies demonstrate that when arginine 132 is mutated to histidine, residues in the active site are shifted to produce structural changes consistent with reduced oxidative decarboxylation of isocitrate and acquisition of the ability to convert α-ketoglutarate to 2HG. Excess accumulation of 2HG has been shown to lead to an elevated risk of malignant brain tumours in patients with inborn errors of 2HG metabolism. Similarly, in human malignant gliomas harbouring IDH1 mutations, we find markedly elevated levels of 2HG. These data demonstrate that the IDH1 mutations result in production of the onco-metabolite 2HG, and indicate that the excess 2HG which accumulates in vivo contributes to the formation and malignant progression of gliomas. A high percentage of human glioblastomas has been found to harbour mutations in the metabolic enzyme cytosolic isocitrate dehydrogenase 1 (IDH1). The predominant R132H mutation is now shown to act as a gain-of-function mutation, enabling IDH1 to convert α-ketoglutarate to 2-hydroxyglutarate (2-HG). Human glioblastoma samples with IDH1 mutations indeed contain elevated levels of 2-HG. Future work will be directed at understanding the mechanisms by which 2-HG can contribute to tumorigenesis. Mutations in the enzyme cytosolic isocitrate dehydrogenase 1 (IDH1) are commonly found in glioblastomas, a major subset of primary human brain cancers. However, only a single copy of the gene is mutated, suggesting that the mutation does not result in a simple loss of function. Here, IDH1 mutations are shown to act in a gain-of-function manner, resulting in a new ability of the enzyme to catalyse α-ketoglutarate to R(-)-2-hydroxyglutarate, an onco-metabolite.