EXTH-25. EXPLOITING EPIGENETIC DYSREGULATION IN ISOCITRATE DEHYDROGENASE MUTANT GLIOMA VIA THE USE OF HISTONE DEACETYLASE INHIBITORS

Abstract

Abstract Isocitrate dehydrogenase 1/2 mutations (IDHmut) define a unique subtype of glioma that exhibits profound epigenetic dysregulation through DNA and histone hypermethylation. Though IDHmutgliomas are less aggressive than their IDH wildtype (IDHwt) counterparts, these tumors are still incurable and are invariably fatal. New treatments are therefore needed. Histone deacetylase (HDAC) enzymes compose a class of epigenetic drug targets already used in the clinic to treat other malignancies, but their potential against gliomas, specifically IDHmutgliomas, have not been extensively studied. We previously showed that IDHwt gliomas are more sensitive than IDHwt gliomas to the cytotoxic and antiproliferative effects mediated by the FDA-approved HDAC inhibitor panobinostat, and that this sensitivity was associated with a greater increase in histone acetylation in IDHmut glioma cultures. Follow-up RNA-Seq showed that panobinostat more greatly affected gene expression in IDHmut glioma cells, with 1999 significant differentially expressed genes showing a 10% or greater change in gene expression in IDHmut cells compared to 388 genes for IDHwt counterparts. This included the known HDAC target and cell-cycle inhibitor CDKN1A, with panobinostat causing a 1.9-fold greater upregulation of CDKN1A in IDHmut cells than IDHwt cells (p= 0.045). In immunocompromised mice intracranially engrafted with IDHmut or IDHwt glioma, 15 mg/kg intraperitoneally-administered panobinostat was detectable after 6 hours within the intracerebral tumors via mass spectrometry at a concentration of 52.4 ng/g (150.1 nM), and extended the survival of IDHmut glioma-engrafted mice (Median: 4 days; Mean: 9.4 days), but not IDHwt glioma-engrafted mice (IDHmut: logrank p= 0.044; IDHwt: logrank p= 0.18). These results suggest that HDAC inhibition via panobinostat may be an effective therapy to treat IDHmutglioma patients. Ongoing studies, including ChIP-Seq, will determine specific sites of histone acetylation and HDACs that are responsible for the greater sensitivity of IDHmut gliomas to HDAC inhibition.