Abstract IA19: Targeting the PRC2 complex through EED for anti-cancer therapy

Abstract

Abstract The Polycomb Repressive Complex-2 (PRC2) plays important roles in regulating gene expression through its histone H3 lysine methyl transferase activity. Dysregulation of PRC2 is observed in multiple cancers. For example, gain of function mutations of the EZH2 catalytic subunit of PRC2 have been reported in B-cell lymphomas, melanoma and parathyroid carcinoma. Components of the complex are also overexpressed in a number of cancers. The PRC2-complex have therefore become a major target for anti-cancer drug discovery. We and others, have reported anti-tumor activity of small molecular weight agents targeting the SAM-binding pocket of EZH2 in preclinical models and a number of EZH2 inhibitors ore showing promising activity in clinical trials. EED and SUZ12 are two additional components of the PRC2 core complex required for regulation of its catalytic function. High resolution structures and other reports have showed that binding of EED to tri-methylated histone H3 Lysine 27 (H3K27Me3) further stimulates the catalytic effect of EZh2. This suggests that small molecular weight compounds binding to and interfering with the EED stimulatory effect on Ezh2 may be able to modulate PRC2 activity. Following this possibility, we launched a comprehensive effort to discover non-catalytic site PRC2 binders. The discovery and characterization of EED226, a highly potent and selective EED-binding inhibitor of PRC2 will be presented. Data will be presented to demonstrate that EED226 inhibits PRC2 function via a distinct allosteric mechanism by binding to the H3K27Me3 binding pocket of EED. Furthermore, EED226 potently inhibits cellular H3K27Me3 levels, modulates target gene expression similar to the SAM competitive Ezh2 inhibitors and inhibits the proliferation of cell lines carrying mutant Ezh2. Oral administration of EED226 to EZH2-mutant tumor bearing mice leads to profound tumor regression. Our data therefore demonstrates that the multi-subunit PRC2 complex can be targeted at non-catalytic binding pockets to achieve anti-tumor activity. Some unique features of the anti-tumor activity achieved through targeting PRC2 will be discussed. Citation Format: Peter W. Atadja. Targeting the PRC2 complex through EED for anti-cancer therapy [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr IA19.