Abstract 4754: Androgen receptor acquires an oncogenic role in the AI resistance mechanism in breast cancer

Abstract

Abstract [Introduction] Aromatase inhibitors (AI) are the common treatment for postmenopausal estrogen receptor (ER)-positive breast cancer. However, some patients acquire resistance to AI. To investigate the mechanism of resistance, we have established several breast cancer cell lines as AI-resistant models. Recently, we have reported on AMD-EDR cells (androgen metabolite-dependent and estrogen-depletion-resistant cells) derived from MCF-7, in which ER activity depends on one of the androgen metabolites. In this study, another AI-resistant mechanism was shown by T-47D-derived AI-resistant cells, indicating the character of the AI-resistant models differ with their parental cells. [Methods] T-47D was cultured under estrogen-depleted and androgen-supplemented conditions for more than 3 months, simulating the AI treatment, which resulted in two stable variant cell lines. To examine the response of variant cell lines to estrogen and androgen, cell proliferation assay and luciferase reporter assay were performed. The mRNA and protein levels were measured by real-time PCR and western blotting. To identify the elements promoting the AI-resistance mechanism in the variant cell lines, the gene expression of variant cell line was compared with that of T-47D by microarray analysis. Immunohistchemical staining for AR and PSA was performed on 20 pairs of primary and recurrent tissue samples from AI-resistant breast cancer. [Results] The variant cell lines had neither growth response to estrogen nor expression of ER. On the other hand, androgen markedly induced the proliferation of these cell lines, and this effect was inhibited by the androgen receptor (AR) antagonist, bicalutamide. Increased expression of AR and androgen-responsive genes in the variant cell lines indicated that the AR-dependent growth pathway was enhanced. Moreover, L-dopa decarboxylase (DDC), an AR coactivator, was extremely induced, suggesting it is an enhancer of AR activity in the variant cell lines. Immunohistochemistry analysis revealed that all primary tumors did not express PSA, while two recurrent tumors did express PSA, suggesting that AR transcriptional activity is enhanced in some AI-resistant breast cancers. [Conclusion] During the AI treatment simulation these variant cell lines transformed from ER-dependent to AR-dependent, and overexpression of AR and DDC possibly enhanced the AR-mediated proliferative pathway. PSA-expression in the AI-resistance recurrent tumors suggests that AR-mediated pathway possibly plays a role in aromatase inhibitor-resistance mechanism. The AI-resistance mechanism in T-47D-derived variant cell lines was different from that in MCF-7-derived AMR-EDR cells. The fact that the character of the AI-resistant models differed with their parental cells supports the hypothesis that the intristic character of individual primary tumors contributes to diversification of AI-resistance mechanisms. Citation Format: Rika Fujii, Toru Hanamura, Toshifumi Niwa, Yuri Yamaguchi, Takanori Ishida, Hironobu Sasano, Noriaki Ohuchi, Shin-ichi Hayashi. Androgen receptor acquires an oncogenic role in the AI resistance mechanism in breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4754. doi:10.1158/1538-7445.AM2014-4754