PTPS-09HISTONE DEMETHYLASE INHIBITION IN COMBINATION WITH RADIATION FOR DIFFUSE INTRINSIC PONTINE GLIOMAS

Abstract

INTRODUCTION: Diffuse intrinsic pontine glioma (DIPG) is a rare but uniformly fatal cancer of the brain, and often harbors oncogenic H3F3A gene mutations, resulting in replacement of lysine 27 by methionine (K27M) in the encoded histone H3.3 protein. Despite being just one of 32 genes that encode histone H3 peptides in a diploid cell, this mutation causes substantial reduction in histone H3K27 methylation in cellular chromatin, and we have recently shown that inhibition of the histone H3K27 demethylase JMJD3 acts to restore H3K27 methylation in DIPG cells, while demonstrating potent anti-tumor activity, both in cell culture and in xenograft models of DIPG. Our expression profiling of K27M DIPG treated with GSKJ4 histone H3K27 demethylase inhibitor revealed decreased transcripts from several genes whose encoded proteins are known to be involved with DNA double-strand break (DSB) repair. These results provide a basis for considering the possibility of GSKJ4 acting as a radiation enhancer, and we investigate this possibility, in association with analysis of therapeutic combination of GSKJ4 and radiation. METHOD: We examine cell growth, colony formation, and DNA DSB repair in association with GSKJ4 monotherapy and combined with radiotherapy (RT) in vitro. We use bioluminescence imaging (BLI), immunohistochemical analysis of tumors, and evaluation of survival benefit from the monotherapies and combination therapies in DIPG xenograft models. RESULTS: Mice received brainstem injection of K27M DIPG cells and are treated with vehicle, GSKJ4 (100mg/kg), RT (1Gy x 10 times), and combination of GSKJ4 + RT. BLI shows that brainstem tumor growth is inhibited by either GSKJ4 or RT monotherapy. Although this study is still ongoing, combination therapy with GSKJ4 + RT shows further reduction of tumor growth rate relative to either monotherapy. We are currently examining the effect of GSKJ4 on radiation-induced DNA DSB repair that will be reported at the meeting.