PDTB-10. INHIBITION OF RADIATION-INDUCED DNA DAMAGE REPAIR MEDIATED CHROMATIN MODIFICATION BY HISTONE H3 DEMETHYLASE INHIBITOR IN PEDIATRIC BRAINSTEM GLIOMA

Abstract

Diffuse intrinsic pontine glioma (DIPG) is among the most devastating childhood cancers, and virtually all patients die within two years after diagnosis. Since these tumors occur in the brainstem, there are no surgical options for providing relief to patients, the only therapeutic modality routinely used in the treatment of DIPG is radiation. Radiation often provides transient relief from DIPG symptoms, but cancer recurrence and patient demise is inevitable. Identifying efficacious therapeutics to enhance the radiation effect is desperately needed. We have recently shown that inhibition of the histone H3K27 demethylase JMJD3 acts to restore H3K27 methylation in DIPG harboring H3K27M mutation, while demonstrating potent anti-tumor activity, both in vitro and in vivo. Our expression profiling of K27M DIPG treated with GSKJ4 JMJD3 demethylase inhibitor revealed several decreases in the genes encoded proteins involved with DNA double-strand break (DSB) repair. We investigate the hypothesis that GSKJ4 may inhibits radiation-induced DNA repair by chromatin modification, in association with analysis of therapeutic combination of GSKJ4 and radiation. DNA damage repair is evaluated by western blotting, DNA repair assay, and immunocytochemistry of DSB markers gH2AX and 53BP1. MNase digestion and FAIRE-seq will analyze nucleosome assembly and transcriptional activity in cellular chromatin. Clonogenic survival assays assess the response to radiation in combination with GSKJ4. In vivo response to radiation therapy (RT) and combination of RT + GSKJ4 were measured by bioluminescence imaging and animal survival. GSKJ4 sustained high levels of gH2AX and 53BP1 in irradiated cells treated with GSKJ4 and increase clonogenic death compared to cells exposed to radiation alone. GSKJ4 + RT combination therapy shows further reduction of tumor growth rate and increase of animal survival relative to either monotherapy. We are currently examining the effect of GSKJ4 on chromatin modification in DIPG, which will be reported at the meeting.