Abstract 1030: IX2X2

Abstract

Abstract Introduction: Prostate cancer (PCa) is the second leading cause of cancer-related mortality in men. More than 85% of PCa and advanced aggressive castration-resistant prostate cancer (CRPC) depend on the androgen receptor (AR) for growth. AR-targeted therapeutics are the mainstay treatment option for PCa. Majority of PCa and CRPC respond to AR-LBD-binding antagonists such as enzalutamide and become refractory after a brief period of response. One of the main resistance mechanisms is the expression of AR splice variants (AR-SVs). AR-SVs lack LBD and are constitutively active, causing aggressive phenotype. Description: Rationale-based drug design was employed to synthesize selective AR irreversible covalent antagonists (SARICA). SARICAs were evaluated in AR transactivation to determine the antagonistic activity. SARICAs were incubated with purified recombinant AR activation function-1 (AF-1) protein and mass spectrometry was performed to determine their covalent binding. SARICAs were evaluated in AR-SV transactivation assay and in a Schild’s plot to determine the nature of inhibition (reversible Vs irreversible). SARICAs were tested in PCa cell line gene expression and proliferation assays and in tumor xenograft experiments. Summary: SARICAs inhibited AR transactivation in submicromolar range. Mass spectrometry with purified AF-1 protein demonstrated covalent binding of SARICAs and identified C406 and C327 as SARICA-interacting nucleophiles. Both amino acids are important for AR-V7 function and stability, making them appropriate drug targets. SARICAs inhibited the activity of AR-V7 and irreversibly inhibited AR transactivation, indicating that these covalent binders are irreversible antagonists. SARICAs selectively inhibit the proliferation and growth of AR-positive prostate cancer cells and tumors, but not AR-negative cells and tumors. Conclusion: These first-in-class AR-selective covalent molecules thus serve as chemical probes to advance our understanding of the AR-AF-1 and they potentially offer an opportunity to treat refractory cancers. Disclosure: This work was supported by an NCI grant (CA229164 and CA229164S1), a DOD grant (W81XWH2110055), and by Muirhead endowment. The SARICAs are licensed to Oncternal therapeutics, San Diego, CA. RN is a consultant to Oncternal therapeutics. Citation Format: Thamarai U. Ponnusamy, Thirumagal T. Thiyagarajan, Ramesh Narayanan. IX2X2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1030.