Abstract 609: Triptolide inhibits ovarian cancer growth by enhancing EZH2 degradation

Abstract Ovarian cancer is a lethal gynecological tumor, typically diagnosed at an advanced stage and associated with limited treatment options. The Enhancer of Zeste Homolog 2 (EZH2) is a crucial methyltransferase that serves as a catalytic subunit of the Polycomb Repressive Complex 2 (PRC2), alongside other core subunits (EED, SUZ12, and RbAp46/48). EZH2 contributes to ovarian cancer progression through both its catalytic and non-catalytic functions, making it a promising therapeutic target. Data from the TCGA database and the Human Protein Atlas indicate that EZH2 mRNA and protein levels are elevated in ovarian cancer tissues compared to normal ovary tissues, correlating with poor prognosis in patients. This provides a rationale for targeting EZH2 in ovarian cancer treatment. However, traditional EZH2 enzyme inhibitors only block its catalytic function and are ineffective against ovarian cancer driven by its non-catalytic functions. EZH2 degraders can effectively inhibit both functions. To identify phytochemicals that promote EZH2 degradation, we screened and identified 20 candidates that can directly or indirectly modulate EZH2 expression. Western blot analysis revealed that Triptolide (TPL, 1 µM) significantly degrades EZH2 protein. TPL is a diterpene compound extracted from the roots, leaves, flowers, and fruits of Tripterygium wilfordii, known for its anti-inflammatory and anti-tumor properties. However, its role in regulating EZH2 in ovarian cancer has not been previously reported. Our western blot results showed that TPL significantly degrades EZH2 and other core PRC2 subunits (EED and SUZ12) in a concentration-dependent manner, with a half-degradation concentration (DC50) as low as 25 nM in the ovarian cancer cell line A2780. The degradation effect of TPL on EZH2 and PRC2 increased with longer exposure times. Further experiments indicated that TPL induces degradation of EZH2 or the PRC2 complex via the ubiquitin-proteasome pathway. A biotin-labeled TPL probe, Biotin-TPL, used in a pull-down assay, confirmed the interaction between TPL and EZH2. Additionally, TPL effectively inhibits the proliferation of ovarian cancer cells in a time- and concentration-dependent manner, with IC50 values in low nanomolar range. Colony formation and 3D cell spheroid formation assays demonstrated that TPL (3.7-33.3 nM) significantly reduces colony formation in A2780 and ES-2 ovarian cancer cells, as well as the formation of ovarian cancer 3D cell spheroids. RNA-seq data and subsequent validation experiments showed that TPL can inhibit signaling pathways regulated by EZH2's non-catalytic functions. Collectively, these findings suggest that TPL may inhibit ovarian cancer growth by degrading the EZH2/PRC2 complex and modulating the signaling pathways associated with EZH2’s non-catalytic functions. Acknowledgements: This work was supported by National Natural Science Foundation of China (82304454). Citation Format: Yongxia Zhu, Qing Tang, Hongtao Xiao, Ningyu Wang. Triptolide inhibits ovarian cancer growth by enhancing EZH2 degradation [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 609.