title: Estrogen metabolism and formation of estrogen-DNA adducts in estradiol-treated MCF-10F cells. The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin induction and catechol-O-methyltransferase inhibition.
abstract: Formation of estrogen metabolites that react with DNA is thought to be a mechanism of cancer initiation by estrogens. The estrogens estrone (E(1)) and estradiol (E(2)) can form catechol estrogen (CE) metabolites, catechol estrogen quinones [E(1)(E(2))-3,4-Q], which react with DNA to form predominantly depurinating adducts. This may lead to mutations that initiate cancer. Catechol-O-methyltransferase (COMT) catalyzes an inactivation (protective) pathway for CE. This study investigated the effect of inhibiting COMT activity on the levels of depurinating 4-OHE(1)(E(2))-1-N3Ade and 4-OHE(1)(E(2))-1-N7Gua adducts in human breast epithelial cells. MCF-10F cells were treated with TCDD, a cytochrome P450 inducer, then with E(2) and Ro41-0960, a COMT inhibitor. Estrogen metabolites and depurinating DNA adducts in culture medium were analyzed by HPLC with electrochemical detection. Pre-treatment of cells with TCDD increased E(2) metabolism to 4-OHE(1)(E(2)) and 4-OCH(3)E(1)(E(2)). Inclusion of Ro41-0960 and E(2) in the medium blocked formation of methoxy CE, and depurinating adducts were observed. With Ro41-0960, more adducts were detected in MCF-10F cells exposed to 1 microM E(2), whereas without the inhibitor, no increases in adducts were detected with E(2) < or =10 microM. We conclude that low COMT activity and increased formation of depurinating adducts can be critical factors leading to initiation of breast cancer.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, USA.
authors.forename: Fang
authors.initials: F
authors.lastname: Lu
authors.forename: Muhammad
authors.initials: M
authors.lastname: Zahid
authors.forename: Muhammad
authors.initials: M
authors.lastname: Saeed
authors.forename: Ercole L
authors.initials: EL
authors.lastname: Cavalieri
authors.forename: Eleanor G
authors.initials: EG
authors.lastname: Rogan
mesh_terms: D001577:Benzophenones / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D065098:Catechol O-Methyltransferase Inhibitors; D045744:Cell Line, Tumor; D018736:DNA Adducts / Q000096:biosynthesis*; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*
chemical_list: D001577:Benzophenones; D065098:Catechol O-Methyltransferase Inhibitors; D018736:DNA Adducts; D000072317:Polychlorinated Dibenzodioxins; C071721:Ro 41-0960; D004958:Estradiol