HIF1A and glioma: Kucharzewska et al. reported decreased levels of metabolites produced by the TCA cycle in U87 glioma cells cultured under hypoxic conditions, along with significantly increased concentrations of 2-hydroxyglutarate (2HG), an oncometabolite [231] synthesized from α-KG by the IDH1 and IDH2 mutant forms expressed in some gliomas and secondary GBMs [234]; decreased levels of α-KG negatively regulate the stability of HIF1α [235].