D-2-Hydroxyglutarate producing neo-enzymatic activity inversely correlates with frequency of the type of isocitrate dehydrogenase 1 mutations found in glioma

Background: IDH mutations frequently occur in diffuse gliomas and result in a neo-enzymatic activity that results in reduction of alpha-ketoglutarate to D-2-hydroxyglutarate. In gliomas, the frequency of IDH1 mutations in codon 132 increases in the order R132L-R132S-R132G-R132C-R132H with R132H constituting more than 90% of all IDH1 mutations. Results: We determined the levels of D-2-hydroxyglutarate in glioma tissues with IDH1 mutations. D-2-hydroxyglutarate levels increased in the order of R132H-R132C-R132S/R132G/R132L. We expressed and purified IDH1 wild type and mutant protein for biochemical characterization. Enzyme kinetics of mutant IDH protein correlated well with D-2-hydroxyglutarate production in cells with R132H exhibiting the highest and R132L the lowest KM for alpha-ketoglutarate. Addition of D-2-hydroxyglutarate to the medium of cell lines revealed an inhibitory effect at higher concentrations. Migration of LN229 increased at lower D-2-hydroxyglutarate concentrations while higher concentrations showed no effect. Conclusion: These findings may suggest natural selection against the rare IDH1R132 mutations in human glioma due to toxicity caused by high levels of D-2-hydroxyglutarate.