ABSTRACT
Most prostate cancers escape endocrine therapy by diverse mechanisms. One of them might be growth repression by androgen. We reported that androgen represses the growth in culture of MOP cells (a sub-line of LNCaP cells) and that of MOP cell xenografts, although tumor growth becomes androgen-independent (AI). Here we explore whether AI tumors contain androgen-responsive cells. ME carcinoma cells were established from AI tumors. The responses to androgen were examined by cell counting, DAPI labeling, flow cytometry, PSA immunoassay and tumor size follow-up. Androgen receptors (AR) were analyzed by western blotting and DNA sequencing. The pattern of responses of these cells to androgen was compared to that of MOP cells and that of JAC cells established from LNCaP-like MOP cells. R1881, a synthetic androgen: (1) repressed the growth of all the six ME cell lines obtained, MOP and JAC cells, (2) augmented the secretion of PSA, (3) induced spectacular cell bubbling/fragmentation and (4) blocked the cell cycle and induced a modest increase of apoptosis. All the androgen-repressed cells expressed the same level of mutated AR as LNCaP cells. In nude mice, the growth of ME-2 cell xenografts displayed transient androgen repression similar to that of MOP cells. In culture neither fibroblasts nor extra-cellular matrix altered the effects of R1881 on cell proliferation. These results demonstrate that androgen-independent tumors contain androgen-responsive cells. The apparent discrepancy between the responses to androgen of tumors and those of carcinoma cells in culture suggests that microenvironmental factors contribute to the androgen responsiveness of tumor cells in vivo. These modifications, albeit unspecified, could be suitable targets for restoring the androgen responsiveness of AI tumors.
Subject(s)
Androgens/pharmacology , Carcinoma/metabolism , Prostatic Neoplasms/drug therapy , Prostatic Neoplasms/pathology , Androgens/metabolism , Animals , Carcinoma/genetics , Cell Line, Tumor , Female , Fluorescent Antibody Technique, Indirect , Growth Inhibitors/metabolism , Growth Inhibitors/pharmacology , Humans , Male , Metribolone/metabolism , Metribolone/pharmacology , Mice , Mice, Nude , Neoplasm Transplantation , Prostatic Neoplasms/genetics , Time Factors , Transplantation, Heterologous , Xenograft Model Antitumor AssaysABSTRACT
The involvement of mutated androgen receptors (mut-AR) in the actions of estrogens in prostate cancer cells is controversial. This work was designed to determine the role of such receptors in the growth inhibition by estradiol (E2) and androgens of the MOP cell line, a derivative of the LNCaP cell line. Diethylstilbestrol (DES) was used as a "tool". E2 like DHT and R1881 inhibits MOP cell proliferation while DES does not. E2 and R1881 down regulate mut-AR mRNA, DES does not. E2 enhances mut-AR transcriptional activity less efficiently than R1881 while DES does not. E2 and R1881 up regulate PSA secretion in a dose-dependent manner, DES does it marginally at 10(-6)M. MOP cells express low amounts of ERalpha and ERbeta mRNA but neither DES nor E2 and R1881 do enhance ER transcriptional activity. DES and E2 bind to mut-AR with relative binding affinities which are respectively 1/175 and 1/10 that of DHT. The E2 and androgen-repressed proliferation is prevented by DES and by the anti-androgen bicalutamide. In LNCaP cells, DES prevents the androgen-enhanced proliferation. These results strongly suggest that: (a) the putative endogenous ERs are biologically inactive in MOP cells, (b) the E2-repressed proliferation results from hormone binding to mut-AR and, (c) DES is an anti-androgen in mut-AR expressing cell line.
