Methylation-dependent Tissue Factor Suppression Contributes to the Reduced Malignancy of IDH1-mutant Gliomas

Purpose: Gliomas with isocitrate dehydrogenase 1 mutations (IDH1 ^mut ) are less aggressive than IDH1 wild-type (IDH1 ^wt ) gliomas and have global genomic hypermethylation. Yet it is unclear how specific hypermethylation events contribute to the IDH1 ^mut phenotype. Previously, we showed that the gene encoding the procoagulant tissue factor (TF), F3, is among the most hypermethylated and downregulated genes in IDH1 ^mut gliomas, correlating with greatly reduced thrombosis in patients with IDH1 ^mut glioma. Because TF also increases the aggressiveness of many cancers, the current study explored the contribution of TF suppression to the reduced malignancy of IDH1 ^mut gliomas. Experimental Design: TF expression was manipulated in patient-derived IDH1 ^mut and IDH1 ^wt glioma cells, followed by evaluation of in vitro and in vivo behavior and analyses of cell signaling pathways. Results: A demethylating agent, decitabine, increased F3 transcription and TF-dependent coagulative activity in IDH1 ^mut cells, but not in IDH1 ^wt cells. TF induction enhanced the proliferation, invasion, and colony formation of IDH1 ^mut cells, and increased the intracranial engraftment of IDH1 ^mut GBM164 from 0% to 100% (P ¼ 0.0001). Conversely, TF knockdown doubled the median survival of mice engrafted with IDH1 ^wt /EGFRvIII ^amp GBM6, and caused complete regression of IDH1 ^wt /EGFR ^amp GBM12 (P ¼ 0.001). In vitro and in vivo effects were linked to activation of receptor tyrosine kinases (RTK) by TF through a Src-dependent intracellular pathway, even when extracellular RTK stimulation was blocked. TF stimulated invasion predominately through upregulation of b-catenin. Conclusions: These data show that TF suppression is a component of IDH1 ^mut glioma behavior, and that it may therefore be an attractive target against IDH1 ^wt gliomas.