Abstract 315: Potential role of androgen receptor in aromatase inhibitor resistance

Abstract

Abstract Clinical assessment of breast cancer tumors has shown that androgen receptor (AR) is expressed in more than 75% of cases, independent of molecular subtype. Specifically, clinical studies have shown that estrogen receptor (ER) and AR discordance correlates with endocrine resistance. Preclinical studies show that downregulation of ER results in a lack of estrogen mediated growth which is concurrent with upregulation of AR and its mediated gene targets. In addition, forced expression of AR was shown to induce resistance to tamoxifen, even when estrogen receptor was still expressed. Furthermore, ER positive breast cancer cells made resistant to tamoxifen express higher levels of AR and show sensitivity to abiraterone acetate. Together, these results implicate AR in endocrine resistance and suggest AR as a potential therapeutic target in a subset of these endocrine resistant cancers. The aim of this study was to better understand the role of AR in aromatase inhibitor (AI) resistance through the use of cell lines made resistant to AI through xenograft mouse modeling. In this study, MCF7 cells, MCF7 cells transfected with the human aromatase gene (MCF7Ca), and their aromatase inhibitor (AI) resistant counterparts, were analyzed for changes in AR and ER expression by qPCR and Western blot. Sensitivity of these cells to AR targeting agents was assessed by MTT assay. MCF7Ca cells displayed decreased expression of AR and increased expression of ER when compared to MCF7 cells. AI-resistant cell lines displayed modulation of ER and AR expression when compared to their AI-sensitive counterparts. Upregulation of AR was accompanied with increased AR transcriptional activity, as demonstrated by increased expression of PSA. Treatment of AI-resistant cells with AR targeting agents displayed increased sensitivity when compared to AI-sensitive cells. Together, these results suggest that upregulation of AR may contribute to AI-resistance, and that targeting AR in AI-resistant breast cancer may have therapeutic relevance. Citation Format: Caleb Hunt, Sarah E. Lock, Cynthia E. Shannon, Nichole M. Varela-Gonzalez, Randolph K. Larsen, Amanda J. Schech. Potential role of androgen receptor in aromatase inhibitor resistance. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 315.