DIPG-44. A GAIN OF FUNCTION Ezh2 MUTATION DELAYS DIFFUSE INTRINSIC PONTINE GLIOMA PROGRESSION

BACKGROUND Diffuse Intrinsic Pontine Glioma (DIPG) remains an incurable pediatric brain cancer. The oncohistone H3K27M implicated in 80% of the cases, is also predicted to target Enhancer of Zeste Homolog 2 (Ezh2), the catalytic component of the Polycomb Repressor Complex 2 (PRC2). There are no reported mutations of Ezh2 and its function in DIPG is not fully determined. This work aims to address the role of Ezh2 in DIPG. METHODS Brainstem tumors were established by intracranial injections of Nestin;Tv-a; Ezh2Y641F/+ (NTv-a; Ezh2Y641F/+) neonatal pups using Replication Competent Avian Sarcoma leucosis virus long terminal repeat with splice acceptor (RCAS) viruses, expressing PDGF-B, p53 shRNA, and RCAS-CRE/Y. Immunohistochemical staining for Ki-67 and H3K27me3 were performed on the Discovery ULTRA (Ventana). RESULTS Ezh2 overexpression (Ezh2Y641F/+, RCAS CRE) conferred a survival advantage of approximately 10 days (n=20 mice/group, p