Abstract LB311: Dissecting and targeting EZH2’s non-canonical oncogenic activity in cancers

Abstract

In many human cancer types, expression of Enhancer of Zeste Homolog 2 (EZH2) is well correlated with poorer outcomes. Furthermore, ∼20-25% of patients with diffuse large B-cell lymphoma (DLBCL) contain somatic mutation of EZH2 at the Tyr-646 residue within its catalytic SET domain, leading to EZH2 gain-of- function (GOF). Thus, EZH2 represents a prominent onco-target and small-molecule inhibitors targeting its enzymatic activity are under clinical evaluation, with some (i.e. tazemetostat) FDA-approved for the treatment of lymphoma and epithelial sarcoma. However, these EZH2 enzymatic inhibitors often face issues, such as ineffectiveness or resistance, and new treatment strategies targeting EZH2 are urgently needed. Traditionally, EZH2 is viewed as a catalytic subunit of Polycomb Repressive Complex 2 (PRC2), which induces trimethylation of histone H3 lysine 27 (H3K27me3) for repressing the target gene expression such as tumor-suppressive and immune-related genes. We recently have shown that EZH2’s oncogenic functions go well beyond PRC2 and its enzymatic function for H3K27me3 deposition and has the new PRC2-independent activity (non-canonical) to sustain oncogenesis. We show that the non-canonical function of EZH2 partly rely on transcriptional activation domains (tADs) of EZH2, which physically interacts with oncogene (co)activators, to turn on the oncogenic signaling. Our unpublished data point to increased Myc signaling as well as cancer metabolism enhancement such as lipid metabolism. We demonstrate such non-canonical oncogenic activity of EZH2 in blood cancers (including DLBCL) and solid tumors, which may explain why the current enzymatic inhibitors of EZH2 have rather limited antitumor effect. To develop a more effective therapeutic strategy in which both the canonical and noncanonical activities of EZH2 can be targeted, we employ the Proteolysis Targeting Chimera (PROTAC) technology and developed novel EZH2-targeted PROTAC degraders. EZH2-targeted PROTACs induced the EZH2 degradation and target the aberrant gene expression from both canonical and non-canonical activities of EZH2, leading to more effective, more consistent growth inhibition in tumors, and to a much greater degree when compared to EZH2 methyltransferase inhibitors. Collectively, this work uncovers an unexplored function of EZH2 in sustaining tumorigenesis via enhancing non-canonical oncogenic signaling. Indeed, our data support EZH2 PROTAC to be an attractive therapeutic candidate for cancer treatments. Citation Format: Arum Kim, G Greg Wang. Dissecting and targeting EZH2’s non-canonical oncogenic activity in cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited s); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2): nr LB311.