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

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-OHE1(E-2)-1-N3Ade and 4-OHE1(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 E2 metabolism to 4-OHE1 (E-2) and 4-OCH3E1 (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 mu M E-2, whereas without the inhibitor, no increases in adducts were detected with E-2 < 10 mu M. We conclude that low COMT activity and increased formation of depurinating adducts can be critical factors leading to initiation of breast cancer. (c) 2007 Elsevier Ltd. All rights reserved.