Abstract P5-09-10: Androgen receptor signal acquired oncogenic role in aromatase inhibitor resistant model of breast cancer cell

Abstract

Abstract Aromatase inhibitors (AI) are the common treatment for postmenopausal estrogen receptor (ER) positive breast cancer. However, not a few of these patients acquire resistance to AI.To investigate this molecular mechanism of resistance, we have established several breast cancer cell lines as AI resistant models. Recently, we reported on AD-EDR cells (androgen metabolite-dependent and estrogen depletion resistant cells) derived from MCF-7, in which ER activity depends on one of androgen metabolite, 5a-androstane-3β, 17β-diol (3βdiol). It is supposed that tumor heterogeneity contributes to the acquired resistance to drugs.To examine this diversity, we established another AI resistant model derived from T-47D, to compare characters of these AI resistant models from different parents. Then, we found that the androgen receptor (AR) signal acquired oncogenic role in this model in contrast to AD-EDR cells established from MCF-7. We cultured ER positive breast cancer cells, T47D-TE8, stably transfected with ERE-GFP reporter into T47D, under estrogen-depleted and androgen-supplemented conditions for more than three months, simulating the AI treatment, and established estrogen deprivation-resistant cells (TE8-EDR cells). TE8-EDR cells had little ERE-GFP activity and proliferation response to estrogen though estrogen stimulated proliferation of parental T47D-TE8. The mRNA for ER and progesterone receptor was hardly detected in TE8-EDR cells. These results suggested that they had lost the ER-mediated pathway of growth. On the contrary, Dihydrotestosterone (DHT) increased growth of T47D-TE8 cells, while it was more remarkable in TE8-EDR, and this proliferative effect was reduced by AR antagonist, bicalutamide. The mRNA expressions of AR and its target gene, PSA, were extremely increased in TE8-EDR cells. These results indicated that TE8-EDR enhanced AR-regulated pathway for growth. Increased AR expression was presumed to be one of the factors elevating AR activity. To identify other elements enhancing AR-mediated signal, we compared the gene expression of TE8-EDR cells with that of T47D-TE8 by microarray analysis. The outcome showed that the expression of some well-known androgen-related genes were increased in TE8-EDR cells. Among these genes, we focused on DDC (L-dopa decarboxylase) which has been reported as one of the AR coactivator, and its overexpression increase proliferative effect in prostate cancer cell lines.By real-time RT-PCR, we confirmed that the mRNA expression of DDC in TE8-EDR was higher over one-hundred fold than T47D-TE8. In addition, DHT-induced proliferation was cancelled by DDC inhibitor, NSD-1015. This study suggests that TE8-EDR cells shift their growth pathway from ER to AR signal, and the AR activity is enhanced by high-expression of DDC. Whereas, MCF7-derived AD-EDR cells still depends on ER signal for their proliferation. So far, few studies have shown the proliferative effects of androgen as AI resistant mechanism. Our results provide new mechanism of acquired AI-resistance in breast cancer. Moreover, the fact that the character of AI resistant models varied with their parent cells supports the hypothesis that tumor heterogeneity contributes to diversify the mechanism of acquired resistance to hormonal therapy. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-09-10.