Abstract 7215: Targeting EZH2 in castration-resistance prostate cancer using a novel PROTAC

Abstract Background: EZH2, a core subunit of the Polycomb Repressive Complex 2 (PRC2), is significantly upregulated in advanced Prostate Cancer (PCa), especially in Castration-Resistant Prostate Cancer (CRPC). However, enzymatic inhibitors of EZH2, such as EPZ-6438, have shown limited efficacy in PCa, while EZH2 knockdown has previously shown to lead to cellular senescence and major growth suppression, warranting the development of Proteolysis Targeting Chimera (PROTAC) to degrade all EZH2 proteins. Methods: Medicinal chemistry was utilized to develop a plethora of EZH2 PROTACs. Mass spectrometry and western blotting were used to assess target protein levels. RNA-seq and H3K27me3 ChIP-seq analyses were performed in PCA cells to evaluate transcriptional and histone modification changes. Senescence staining and flow cytometry were used to evaluate cellular senescence and analyze cell cycle progression. Cell proliferation was assessed in vitro using CellTiter-Glo and live-cell proliferation assays. In vivo efficacy was evaluated using 22Rv1 and VCaP xenograft mouse models. Results: Among several EZH2 PROTAC degraders, 6272 was chosen as the lead candidate due to its high specificity and efficiency in degrading EZH2. We showed that 6272 significantly inhibited 22Rv1 and VCaP cell proliferation compared to EPZ-6438, although this effect was not observed in LNCaP cells. RNA-seq analysis revealed that 6272 readily induced cellular senescence pathways, such as CDKN1A (p21) expression, in 22Rv1 and VCaP, but not LNCaP cells. Further, ChIP-seq showed no changes in H3K27me3 at the CDKN1A gene locus, indicating that 6272 regulates these genes in a catalytic function-independent manner. Lastly, we confirmed that 6272 also significantly reduced 22Rv1 and VCaP xenograft tumor growth. Conclusion: In this study, we developed a novel EZH2 PROTAC with superior efficacy compared to EPZ-6438 in suppressing some prostate cancer cells via rapidly promoting cellular senescence. Citation Format: Qi Chu, Wanqing Xie, Galina Gritsina, Xiaodong Lu, Ka Wing Fong, Zhiquan Lei, Hongshun Shi, Lourdes Brea, Jonathan Zhao, Gary Schiltz, Jindan Yu. Targeting EZH2 in castration-resistance prostate cancer using a novel PROTAC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7215.