Abstract 6059: Discovery of ETS-007, a first-in-class degrader targeting N-terminal domain of androgen receptor derived from AR liquid-liquid phase separation inhibitor

Abstract Patients with advanced prostate cancer inevitably acquire resistance to anti-androgen therapies, and progress to lethal castration-resistant prostate cancer (CRPC). The resistance mechanisms involve AR gene amplification and overexpression, constitutively active ligand-independent splice variants such as AR-V7, and the mutations in the AR ligand-binding domain (LBD). Our previous study has shown that the AR N-terminal domain (NTD) is responsible for AR liquid-liquid phase separation (LLPS) capability, which is essential for AR/AR-V7 transcriptional activity. We conducted a compound library screening using an AR LLPS phenotypic assay and identified ET0516 as a hit to specifically inhibit AR LLPS and its downstream gene expression, indicating that inhibition of AR. LLPS through targeting its NTD is a feasible approach to overcome the resistance to current anti-androgens therapy. Here we report the identification of a novel AR degrader, ETS-007 which is originated and evolved from internal LLPS phenotypic screening, that effectively degrades both AR and AR-V7 proteins with DC50 of single-digit nM by inducing a protein-protein interaction between AR NTD and an E3 ligase complex. ETS-007 induced AR and AR-V7 polyubiquitination, followed by degradation which could be blocked by the protease inhibitor MG132. ETS-007 significantly inhibited cell proliferation in AR and/or AR-V7 positive cell lines, e. g. LNCaP and 22RV1, and downregulated the androgen responsive genes such as PSA and TMPRSS2. Compared with enzalutamide and ARV-110, ETS-007 could block transcriptional activities of AR-V7, and AR mutants in luciferase report assay. Oral administration of ETS-007 in an enzalutamide-resistant 22RV1 xenograft model led to intratumoral AR-V7 degradation and concomitant decrease in PSA protein levels, resulting in a remarkable tumor regression. Taken together, our findings provide preclinical evidence that ETS-007 as a potent AR-NTD degrader derived from our LLPS platform can effectively block the transcriptional activities of both AR and AR-V7 for the treatment of metastatic CRPC. Citation Format: Yingjie Li, Mingyue Fei, Yingke Miao, Lijian Feng, Xiaofei Fan, Jinping Li, Yaozhong Chen, Ming Xu, Wenqi Cui, Qiangang Zheng, Jidong Zhu. Discovery of ETS-007, a first-in-class degrader targeting N-terminal domain of androgen receptor derived from AR liquid-liquid phase separation inhibitor abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6059.