Anti-estrogens act as chemo-preventatives in prostate cancer progression.

B152

It is known that the steroid hormones testosterone (T) and estradiol (E2) are associated with prostate cancer (PRCA) progression. It has previously been demonstrated that the anti-estrogen, Toremifene, prevents PRCA progression in men. However, it is unknown which estrogen receptors (ERs) are present within the prostate and if other clinically used anti-estrogens may affect human PRCA progression. The objectives of these experiments were to determine which ERs are present within prostate and prostate cancer tissues and to evaluate the role of the clinically relevant anti-estrogen, Keoxifene hydrochloride, in HUMAN PRCA progression utilizing the SVM+BPH-1 tissue recombination model. Tissue recombinants were grown in untreated mice and in mice treated with T+E₂, T+E₂+Keoxifene hydrochloride (25 mg), or T only for two months and then plasma and tissues were collected. Plasma levels of T were within normal ranges of men whereas E2 concentrations were approximately 3-fold higher then typically found in men. No differences in T or E2 were observed between T+E2 and T+E2+Keoxifene hydrochloride treated groups. To determine which ERs were present within tissue recombinants rtPCR, Western analyses, and immunohistochemistry were performed. Through rtPCR analysis both ER-alpha and ER-beta were detected within BPH-1 cells derived from non-tumorigenic (BPH-1-NT) and tumorigenic (BPH-1-TD) tissue recombinants. Both BPH-1-NT and BPH-1-TD contained ER-alpha protein of variable molecular weights (including 66, 63, 36 kd), however these cells were negative for the membrane ER, GPR30, as determined by Western blotting. Immunohistochemistry demonstrated that in tissue recombinants grown in untreated animals ER-alpha was present primarily within the stroma whereas ER-beta was present within the epithelium. In T+E₂-treated mice, tissue recombinants developed into large invasive tumors that metastasized, whereas tissue recombinants in T+E₂+ Keoxifene hydrochloride, T only, or untreated mice were small and non-invasive with significantly (P<0.05) lessened wet weights. The histopathology of T+E₂-treated mice was determined to be cancerous, whereas tissue recombinants from T+E₂+Keoxifene hydrochloride, T only, and untreated mice contained organized epithelial structures surrounded by a thick muscular stroma. To evaluate the effects of Keoxifene hydrochloride on malignant transformation of the epithelium, BPH-1 cells were isolated from the above described groups. BPH-1-isolates from each group were purified and regrown (100,000 cells) without stroma or hormones in new hosts and only BPH-1-TD were tumorigenic, whereas little growth was observed in BPH-1 cells isolated from tissue recombinants grown in untreated, T-treated, or T+E2+Keoxifene hydrochloride treated groups. These data suggest that anti-estrogens do act as chemo-preventatives in HUMAN PRCA progression. These data also suggest that multiple isoforms of ER-alpha and/or ER-beta may be key chemo-preventative targets of anti-estrogens.