EED226, an allosteric PRC2 inhibitor, modulates gene transcription in EZH2 mutant lymphoma cell Karpas422 through PRC2 inhibition

Polycomb repressive complex (PRC) 2, containing minimally EZH2, EED and Suz12, is the H3 lysine 27 methyltransferase playing pivotal roles in transcriptional regulation. EZH2 is the catalytic subunit, and H3K27me3 activates PRC2 through binding EED to propagate the repressive mark. Cofactor SAM-competitive (SAM-C) PRC2 inhibitors (PRC2is) have been discovered to treat lymphoma and rhabdoid tumors. Here we report the discovery of EED226, a potent and selective PRC2i directly binding to the H3K27me3 pocket of EED. Upon binding, EED226 induces conformational change in EED protein. Interestingly, it inhibits both the basal and the H3K27me3-stimulated PRC2 activities. Furthermore, EED226 selectively pulled down the endogenous PRC2 complex from human cell lysates, specifically modulates H3K27 methylation and target genes similarly as SAM-C PRC2 inhibitors, and effectively regresses human lymphoma xenograft tumor in mouse. More importantly, EED226 potently inhibits the SAM-C inhibitor-resistant PRC2 and synergizes with SAM-C PRC2i in cell proliferation blocking. Together, EED226 is an inhibitor of PRC2 with a novel mechanism and represent a potential complementary strategy for PRC2-targeted cancer therapy. The dataset includes gene expression profiling of DLBCL cell line Karpas422 at 1 day, 2 days, 3 days, and 6 days after DMSO or EZH2 inhibitor (5 uM) treatment with biological triplicates.