BET bromodomain Inhibition Potentiates Radiosensitivity by Reprograming DNA Damage Repair in H3K27M-Mutant Glioma

Diffuse intrinsic pontine glioma (DIPG) is one of the devastating childhood cancers. Radiation therapy remains the only effective treatment yet provides a 5-year survival rate of only1%. Several clinical trials have attempted to enhance radiation anti-tumor activity using radiosensitizing agents, though none have been successful in doing so. Given this, there is a critical need for identifying effective therapeutics to enhance radiation sensitivity for the treatment of DIPG. Using high-throughput radiosensitivity screening, we identified bromo- and extra-terminal domain (BET) protein inhibitors as potent radiosensitizers in DIPG. Genetic and pharmacologic inhibition of BET bromodomain activity reduced DIPG cell proliferation and enhanced radiation-induced DNA damage by inhibiting DNA repair pathways. RNA- and CUT-RUN-sequencing showed that BET bromodomain inhibitors regulate the expression of DNA repair genes mediated by H3K27acetylation at enhancers. BET bromodomain inhibitors enhanced DIPG radiation-response in patient-derived xenografts as well as genetically engineered mouse models. Together, our results highlight BET bromodomain inhibitor as a novel radiosensitizer and provide a rationale for developing combination therapy with radiation for the treatment DIPG. Overall design: Differential gene expression and H3K27Ac differential peak analyses were performed in SF8628 cells treated with AZD5153 or DMSO