The overall objective of this proposal is to demonstrate at the molecular level the exciting and novel idea that estrogens are involved in the causation of breast and prostate cancer via a unifying mechanism that involves oxidation of endogenous 4-catechol estrogen (CE) metabolites to CE-3,4-quinones (CE-3, 4-Q) and reaction of these electrophiles with DNA. Formation of depurinating adducts that generate apurinic sites in DNA would be the critical event leading to oncogenic mutations that initiate breast and prostate cancer. To gain new, substantial evidence that the 4-CE oxidative pathway is the critical initiating event, we plan to investigate the fate of 17beta-estradiol (E2) and estrone (E1) in Syrian golden hamsters and Noble rats in relation to the induction of kidney and prostate tumors, respectively. Our approach is to identify and quantify estrogen metabolites, including CE, depurinating CE-DNA adducts, and CE-glutathione (GSH) and methoxyCE conjugates into which E1 and E2 are converted in these animals models. We will also analyze breast, prostrate and urine samples from human subjects with and without cancer. The altered amounts and altered ratios of these compounds will provide evidence on the key events leading to estrogen-induced tumor initiation. These objectives will be achieved by the following specific aims: (1) Identify and quantify the depurinating DNA adducts [4- OHE1(E2)-1-N7Gua and 4-OHE1(E2)-1-N3Ade] in the kidney and urine of male Syrian golden hamsters and the prostate of Noble rats treated with E2 at various dose levels, and compare the results with those from hamsters and rats treated with E2 plus: (a) buthionine sulfoximine (inhibitor of the synthesis of the protective GSH), (b) Ro41-0960 (competitor for the protective catechol-O-methyltransferase), (c) dicoumarol (inhibitor of the protective quinone oxidoreductase) or (d) alpha-naphthoflavone (inhibitor of cytochrome P450 1). (2) Identify and quantify the major estrogen metabolites, CE conjugates and CE adducts in human breast, prostate and urine samples obtained from subjects with and without breast or prostate cancer. From these studies, we expect to demonstrate that the pathway of oxidation of 4-CE to CE-3,4-Q and their binding to DNA to form depurinating adducts is the critical event in the initiation of breast and prostate cancer. In turn, this research will identify biomarkers that will be useful in determining cancer risk in humans.
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