Abstract LB-288: An allosteric PRC2 inhibitor targeting the H3K27me3 binding pocket of EED

Polycomb repressive complex 2 ( PRC2) consists of three core subunits, EZH2, EED and SUZ12and plays pivotal roles in transcriptional regulation through its histone H3K27 methyltransferase activity. Dysregulation of PRC2is observed in multiple human cancers, for example, the catalytic subunit EZH2is overexpressed in a wide range of human cancers and gain-of-function mutations of EZH2within its catalytic site have been reported in human B-cell lymphoma, parathyroid carcinomaand melanoma. Small molecule inhibitors that compete with the cofactor S-adenosylmethionine (SAM) have been reported and showed anti-lymphoma efficacy in pre-clinical studies. EED within the PRC2complex allosterically activate the enzymatic activity by binding to tri-methylated H3K27 (H3K27me3). Here we report the discovery of EED226, a potent and selective PRC2inhibitor directly binding to the H3K27me3 binding pocket of EED. EED226 induces conformational change upon binding EED leading to loss of PRC2activity. EED226 shows similar activity as SAM-competitive inhibitors in blocking H3K27 methylation of PRC2target genes and inducing regression of human lymphoma xenograft tumors. Interestingly, EED226 also effectively inhibits PRC2containing mutant EZH2protein resistant to SAM-competitive inhibitors. Together, we show EED226 inhibits PRC2activity via an allosteric mechanism and offers opportunity for treatment of PRC2-dependent cancers. Citation Format: Wei Qi, Kehao Zhao, Justin Gu, Ying Huang, Youzhen Wang, Hailong Zhang, Man Zhang, Jeff Zhang, Zhengtian Yu, Ling Li, Lin Teng, Shannon Chuai, Chao Zhang, Mengxi Zhao, HoMan Chan, Zijun Chen, Douglas Fang, FeiQi, Leying Feng, Lijian Feng, Yuan Gao, Hui Ge, Xinjian Ge, Andreas Lingel, Guobin Li, Ying Lin, Yueqin Liu, Fangjun Luo, Minlong Shi, Long Wang, Zhaofu Wang, Yanyan Yu, Jue Zeng, Chenhui Zeng, Lijun Zhang, Qiong Zhang, Shaolian Zhou, Counde Oyang, Peter Atadja, En Li. An allosteric PRC2inhibitor targeting the H3K27me3 binding pocket of EED [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-288. doi:10.1158/1538-7445.AM2017-LB-288