Abstract 1070: Dual inhibition of AR and β-catenin induces cell death in abiraterone-resistant prostate cancer

Abstract Abiraterone acetate has been clinically approved for treatment of patients with advanced-stage prostate cancer. It reduces testosterone production by blocking the enzyme cytochrome P450 17 alpha-hydroxylase. Despite exhibiting improved survival outcomes, almost all patients with advance-stage disease relapse, progressing to a more aggressive and lethal castration-resistant prostate cancer. Our pathway-related analysis and characterization of gene expression identified activation of the β-catenin pathway in abiraterone-resistant prostate cancer. Increased expression of androgen receptor (AR) and β-catenin and their crosstalk between distinct signaling pathways causes activation of AR target genes and regulatory networks for which overcoming innate or acquired resistance remains a major challenge. Here we show that co-targeting AR and β-catenin induces cell death in abiraterone-resistant prostate cancer. For these studies, we generated abiraterone-resistant C4-2B cells (C4-2B-Abi) by growing them in progressive concentration of abiraterone 5-20µM to develop resistance and maintained in 5µM abiraterone in the culture medium for >20 generations. Treatment of C4-2B-Abi cells individually with abiraterone (20µM) and ICG001 (2µM) for 72 h exhibited a partial suppressive effect in cell growth compared to C4-2B parental cell line. A combination of abiraterone and ICG001 (20µM + 2µM) exhibited marked cell growth inhibition with significant increase in G1-phase cell cycle arrest, inhibition of migration and invasion in C4-2B-Abi cells, compared to the parental counterpart. Furthermore, combination treatment led to significant reduction in cell proliferation as assessed by PCNA along with reduction in the protein expression of AR, AR-v7, CDC20, PSA, β-catenin and its downstream targets, cyclinD1 and c-Myc, which were more prominent in C4-2B-Abi cells, compared to parental C4-2B cells. Co-targeting AR and β-catenin potentiated cell death in C4-2B-Abi cells as evident by increased PARP cleavage. Together, our data identify activation of the β-catenin pathway as a major mechanism contributing to abiraterone resistance and demonstrate that combined treatment with abiraterone and ICG001 appears to be an effective regimen for treatment of abiraterone-resistant cancer cells. This opens new therapeutic modality for advance-stage castration-resistant prostate cancer patients. Citation Format: Ibrahim M. Atawia, Prem P. Kushwaha, Shiv S. Verma, Spencer Lin, Eswar Shankar, Osama Abdel-Gawad, Sanjay Gupta. Dual inhibition of AR and β-catenin induces cell death in abiraterone-resistant prostate cancer [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 1070.