Targeting EZH2 in advanced prostate cancer

/ABSTRACT Standard treatment of prostate cancer (PCa) with anti-androgen agents fails due to development of therapy resistance and castration-resistant prostate cancer (CRPC), a terminal disease. Enhancer of Zeste Homolog 2 (EZH2), a histone methyltransferase and catalytic subunit of Polycomb Repressive Complex 2 (PRC2), and Androgen Receptor (AR) are the two most crucial gene/chromatin regulators involved in the development and progression of advanced PCa, including CRPC. How these oncoproteins contribute to CRPC development and progression remains far from clear. Recent works by us and others show that the EZH2 regulome in CRPC goes well beyond its well-studied, canonical gene-repressive role. Specifically, EZH2 also binds AR and its constitutively active variant, AR-V7, and has a non-canonical function in activation of prostate oncogenes, which differs from the well-known PRC2:EZH2-driven canonical function related to repression of tumor- suppressive genes (TSGs). EZH2’s cryptic transactivation domain (EZH2TAD) and AR’s poly-glutamine (polyQ) and poly-glycine (polyG) motifs were identified to be important for the activation of oncogenes in AR+ PCa. To target both canonical and non-canonical oncogenic functions by EZH2, we generated EZH2 small-molecule degraders including MS177 and MS8815 using the Proteolysis Targeting Chimera (PROTAC) technology. Our extensive preliminary studies have demonstrated that MS177 effectively degrades both PRC2:EZH2 and non- PRC2 partners of EZH2 (e.g., AR/AR-V7), thus suppressing both activities of EZH2 in canonical and non-canonical oncogenic PCa cells. Importantly, our preliminary results also show that MS177 is superior to all available enzymatic inhibitors of EZH2 in cell line models of PCa including CRPC. Thus, we hypothesize that: (i) EZH2 drives a non-canonical program via EZH2TAD:ARPolyQ/G interaction for oncogene activation, which operate in parallel with the canonical PRC2:EZH2-driven repression of TSGs and that (ii) EZH2 PROTACs simultaneously repress both canonical (PRC2/EZH2) and non-canonical (EZH2/AR) oncogenic pathways, providing a novel and more effective therapeutic strategy for lethal PCa. Dissection of the mechanisms underlying EZH2-mediated oncogenesis and evaluation of the in vitro and in vivo efficacy of EZH2 PROTACs using various PCa preclinical models will have significant impact on improving treatments of lethal PCa. Towards this goal, we will further characterize such a new non-canonical oncogenic role of EZH2 in CRPC (Aim 1a) and define effects of EZH2 PROTACs on suppressing both canonical and non-canonical oncogenic activities of EZH2 (Aim 1b). We will also determine in vitro and in vivo therapeutic effects of EZH2 PROTACs by employing independent PCa models (Aim 2). Completion of the proposed research will not only provide novel mechanistic understanding of how advanced PCa develop, but also validate an innovative therapeutic strategy and generate novel lead compounds for the treatment of CRPC patients. Project Number: 1R01CA291848-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Ling Cai | Institution: DUKE UNIVERSITY, DURHAM, NC | Award Amount: $497,972 | Activity Code: R01 | Study Section: Mechanisms of Cancer Therapeutics B Study Section[MCTB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11291982