Traditionally sex hormones are recognized as non-genotoxic carcinogens that induce neoplastic transformation epigenetically via enhancement of cell proliferation in target tissues. We have obtained recent evidence that estrogens, per se or via metabolic conversion, can cause genetic damage in vivo and hence may act as tumor initiators in the prostate. A rat model with features of the human prostatic cancer is used as an experimental model of study. Treatment of intact Noble (NBL) rats with testosterone (T) and estradiol- 17beta (E2beta) consistently induced a 100% dysplasia and adenocarcinoma in the dorsolateral lobe (DLP) of the rat gland. Dysplasia was however, not induced when rats were exposed to T, DHT or E2beta alone. We observed that the induction of dysplasia was preceded by the drastic increase in DLP mitotic activity and type II estrogen receptor level. More recently, we found a significant increase in DNA-strand breaks and lipid peroxidation exclusively in DLPs harboring the dysplasia. We therefore conclude that, in addition to mitogenic action, the sex steroids may have direct genotoxicity in this prostatic lobe. We hypothesize that the synergism between genetic and epigenetic action of the sex hormones provides the mechanistic basis of tumor initiation and promotion which eventually leads to neoplastic transformation and tumor formation in rat DLP. In this application we propose the following specific aims to evaluate the relateive importance of the genotoxic and mitogenic action of sex hormones in prostatic carcinogenesis in NBL rats: 1) to ascertain if E2beta is the component in the E2beta treatment that actually induces DNA damage in the rat DLP; 20 to evaluate whether the T + E2beta-induced DNA damage in the rat DLP is a primary event induced by E2beta genotoxicity and not a secondary phenomenon caused by cell proliferation; 3) to determine whether the occurrence of increase in DNA damage precedes the appearance of cell proliferation and dysplasia and thereby provides evidence that genetic-damage is an event likely involved in tumor initiation; 40 to examine if catechol estrogens (CEs) formation is the metabolic step responsible for the conversion of E2beta to DNA- reactive products in the DLP, but not in the VP, of the rat gland and to determine whether prostatic CE formation activity in NBL rats is higher than that found in Sprague-Dawley (SD) rats. This difference may then explain the difference in cancer susceptibility of the two rat strains; 5) to assess the effectiveness of T + diethylstilbestrol (DES, a synthetic estrogen with known genotoxicity) treatment in inducing DNA damage, cell proliferation and dysplasia in the two major prostatic lobes, VP and DLP, of the rat gland. Data from this study are expected to identify the principal roles of sex- hormones in prostatic carcinogenesis and help shape our views on the mechanisms of hormonal carcinogenesis in, not just the prostate, but other hormone-sensitive tissues as well. This study also offers the prospect of using DNA damage and enhancement of cell proliferation as short-term and points from assessing the caner risk of a sex hormone.