Abstract
Gliomas are the most common primary central nervous system tumor but the molecular mechanisms responsible for their development and progression are not completely understood. Isocitrate dehydrogenase 1 (IDH1) is the most commonly mutated gene in grade II-III glioma and secondary glioblastoma (GBM) but functional validation of this alteration has been hampered by difficulties generating autochthonous mouse models harboring mutant IDH. In this study, we used the RCAS/TVA glioma mouse model to assess the role of IDH1R132H in glioma development in the context of clinically-relevant cooperating genetic alterations in vitro and in vivo. Immortal Cdkn2a, Pten, and Atrx-deficient astrocytes expressing IDH1R132H exhibited elevated (R)-2-hydroxyglutarate (2-HG) levels, reduced NADPH, increased proliferation, and anchorage-independent growth. Cell proliferation and soft agar growth was significantly enhanced by co-expression of PDGFA. Substitution of IDH1R132H with a cell membrane-permeable [tri-fluoromethyl benzyl (TFMB)-esterified] version of (R)-2HG mimicked the phenotype observed in cells expressing IDH1R132H. Interestingly, addition of TFMB-(R)-2HG further enhanced colony formation in cells expressing IDH1R132H while treatment with the mutant IDH1 inhibitor AG-120 reduced anchorage independent growth. These data suggest that the effects of IDH1R132H are mediated by 2-HG and not loss of native IDH1 activity. Although not sufficient on its own, IDH1R132H cooperated with PDGFA and loss of Cdkn2a, Atrx, and Pten to promote glioma development in vivo. These tumors resembled proneural human mutant IDH1 GBM genetically, histologically, and functionally. Our findings support the hypothesis that IDH1R132H promotes glioma development through production of 2-HG. This model validates a role for IDH1R132H in glioma development, permits mechanistic studies that further our understanding of oncogenesis in this context, and enables rapid testing of rationale therapeutic strategies designed to combat this deadly disease.