Efficient induction of differentiation and growth inhibition in IDH1 mutant glioma cells by the DNMT Inhibitor Decitabine

Abstract

Mutation in the IDH1 or IDH2 genes occurs frequently in gliomas and other human malignancies. In intermediate grade gliomas, IDH1 mutation is found in over 70% of tumors. These mutations impart the mutant IDH enzyme with a neomorphic activity – the ability to synthesize 2-hydroxyglutarate (2-HG). This ability leads to a reprogramming of chromatin state, a block in differentiation, and the establishment of the glioma hypermethylator phenotype (G-CIMP). It has been hypothesized but not proven that the extensive DNA methylation that occurs in G-CIMP tumors helps maintain and “lock in” glioma cancer cells in a dedifferentiated state. Here, we tested this hypothesis by treating patient derived IDH1 mutant glioma initiating cells (GIC) with non-cytotoxic, epigenetically targeted doses of the DNMT inhibitor decitabine. Global methylome analysis of treated IDH1 mutant GICs showed that DAC treatment resulted in reversal of DNA methylation marks induced by IDH and the re-expression of genes associated with differentiation. Accordingly, treatment of IDH1 mutant glioma cells resulted in a dramatic loss of stem-like properties and efficient adoption of markers of differentiation, effects not seen in decitabine treated IDH wild-type GICs. Induction of differentiation was much more efficient than that seen following treatment with a specific inhibitor of mutant IDH enzyme (Agios). Decitabine also decreased replicative potential and tumor growth in vivo. Reexpression of polycomb regulated genes accompanied these DAC-induced phenotypes. In total, our data indicates that targeting the pathologic DNA methylation in IDH mutant cells can reverse mutant IDH induced hypermethylation and block in differentiation and promote tumor control. These findings have substantial impact for exploring new treatment strategies for patients with IDH mutant gliomas.

IDHMutation in Glioma

“…The use of DNMT inhibitors in IDH-mutated cancers is motivated by the hypothesis that the oncogenic effects of IDH mutation are driven by its effects on the methylome. Two groups 65,66 have recently studied the DNMT inhibitors decitabine and 5-azacytidine in IDH-mutant glioma cell models.…”

“…Turcan and colleagues 65 observed that the administration of decitabine to an IDH1 R132H mutant anaplastic astrocytoma cell line (TS603), while not affecting 2-HG levels, efficiently induced upregulation of differentiation genes, an effect associated with a change in methylation markers leading to reexpression of Polycombcontrolled genes. Remarkably, the differentiation effect was maintained even after drug therapy was stopped.…”

Harnessing the potential of epigenetic therapy to target solid tumors

“…Mutations in TET2 and isocitrate dehydrogenases IDH1 and IDH2 are seen in gliomas and leukemia (116)(117)(118)(119)(120)(121)(122), and IDH1 mutations in gliomas correlate with a DNA CpG island methylator phenotype (116,123). Preliminary encouraging data suggest that patients with mutations in these epigenetic regulators may particularly benefit from demethylating therapy, with preclinical studies showing decreased tumor growth and induction of tumor differentiation (124,125). More recently, mutations in the SWI/SNF chromatin remodeling complex, especially in the AT-rich interactive domain 1A (ARID1A), have also been identified in a multitude of solid cancers including pancreas, breast, ovarian, gastric, and colon (42,(126)(127)(128), although the relationship between ARID1A mutations and downstream cancer epigenome is still being elucidated.…”

Isocitrate Dehydrogenase (IDH) Mutation in Gliomas

“…Decitabine and 5-azacytidine are two very interesting DNMT inhibitors because they are well known FDA approved drugs that can pass the blood-brain barrier. Turcan et al observed that decitabine treatment promotes changes in methylation markers leading to the re-expression of differentiation genes, and long lasting differentiation effects [ 87 ]. Another group examined the impact of 5-azacytidine and a reported reversion of the G-CIMP state concomitant with the upregulation of differentiation genes and decreased tumor growth in vivo [ 88 ].…”