Abstract 1864: Differential effects of the isoflavone genistein on androgen receptor expression and cell proliferation comparing prostate cancer cells with mutant and wild type androgen receptor

Abstract

Abstract In advanced prostate cancer, cells become androgen independent and therefore resistant to androgen ablation therapy. One mechanism by which prostate cancer bypasses androgen ablation therapy is acquisition of androgen receptor (AR) mutations some of which render it promiscuous enabling activation by a broad group of steroids such as estrogen, progesterone, and even anti-androgens. Genistein, an exogenous steroid (phytoestrogen) and isoflavone found in soy, has estrogenic activity. Most studies have shown that genistein has anti-proliferative effects on prostate cancer cells without regard for the status of the AR. It has been suggested that activation of the mutant AR (MT-AR) by genistein could lead to increased cellular proliferation. Previous studies examining genistein's effect on AR expression used prostate cell lines (i.e. LNCaP) with ARs carrying the promiscuous T877A mutation, without comparison to cells with wild type (WT) AR. Genistein does not bind WT-AR, and thus, may not have the same effect on AR expression as it does in the presence of MT-AR. We set out to compare the effects of genistein in the presence of WT-AR versus MT-AR, using human prostate cancer cell lines with WT-AR (LAPC-4) and MT-AR (LNCaP). Cells were treated with increasing concentrations (0, 0.5, 1, 10, 25, and 50 μM) of genistein. Real time PCR, Western blot analysis, PSA luciferase assay, cell counting by hemocytometer, and MTS proliferation assays were used to determine levels of AR mRNA, protein, transcriptional activity, and cell proliferation, respectively. Genistein caused an androgen-independent biphasic changes in AR mRNA, protein levels, and transcriptional activity, and in cell proliferation in LNCaP cells, which reached a maximum at 1μM of genistein (40-45% increase in AR protein and mRNA expression, 42% increase in PSA luciferase activity, and 2-fold increase in cell proliferation compared to controls). These effects reversed at a concentration of 10 μM. In contrast, in LAPC-4 cells AR mRNA and protein levels and transcriptional activity as well as cell proliferation decreased linearly with increasing dose of genistein, without showing the stimulatory bi-phasic trend observed in LNCaP cells. These decreases were significant, beginning at 1 μM genistein, at which concentration AR mRNA was reduced by 30%, protein expression by 22%, PSA luciferase activity by 40%, and cell proliferation by 56%. These results demonstrate that at physiological concentrations, genistein can exert a mitogenic effect in the presence of MT-AR. Our findings highlight the significance of promiscuous mutations such as T877A for the AR response to genistein treatment and indicate that men with advanced prostatic cancers which carry such AR mutations could be adversely affected by genistein. (Supported in part by Grant No. CA116195) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1864. doi:10.1158/1538-7445.AM2011-1864