Spectral characterization of fluorescently labeled catechol estrogen 3,4-quinone-derived N7 guanine adducts and their identification in rat mammary gland tissue.
The oxidation of carcinogenic 4-hydroxycatechol estrogens (CE) of estrone (E1) and estradiol (E2) to catechol estrogen 3,4-quinones (CE-3,4-Q) results in electrophilic intermediates that covalently bind to DNA to form depurinating adducts [Cavalieri et al. (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 10937]. These DNA adducts, 4-OHE1-1-N7Gua and 4-OHE2-1-N7Gua, are nonfluorescent. To utilize laser-excited fluorescence methods, the catechol estrogen-derived metabolites and adducts were labeled with a fluorescent marker. The 4-OHEi-1-N7Gua adduct standards (i = 1, 2) and 4-OHEi metabolites have been derivatized with 1-pyrenesulfonyl chloride and investigated by low-temperature spectroscopy under non-line-narrowing and line-narrowing conditions. Molecular modeling studies assisted in interpretation of the fluorescence spectra; energetically favored structures of the 4-OHE2-1-N7Gua-dipyrene adduct and 4-OHE2-dipyrene metabolite reveal unique conformations which, in agreement with fluorescence data, show a significant pi-pi interaction of pyrene labels with guanine and/or the aromatic ring of catechol estrogen. The conformation obtained for the 4-OHE2-1-N7Gua-dipyrene adduct appears to be conducive to mixing of its pipi state with pyrene-guanine charge-transfer states, consistent with the experimentally observed strong electron-phonon coupling. Non-line-narrowed and line-narrowed spectra obtained at 77 and 4.2 K, respectively, are shown to distinguish 4-OHE2-1-N7Gua-dipyrene adducts from 4-OHE2-dipyrene metabolites. These standards have subsequently been used for the spectroscopic identification of depurinating DNA adducts formed in a tissue culture experiment where rat mammary gland tissue was treated with the estrogen quinone E2-3,4-Q. The depurinating adduct formed is 4-OHE2-1-N7Gua.
Jankowiak
R
R
Ames Laboratory-USDOE, Iowa State University, Ames, Iowa 50011, USA. jankowiak@ameslab.gov
Zamzow
D
D
Stack
D E
DE
Todorovic
R
R
Cavalieri
E L
EL
Small
G J
GJ
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000737:chemistry; D002393:Estrogens, Catechol / Q000737:chemistry*; D005260:Female; D008321:Mammary Glands, Animal / Q000737:chemistry*; D008958:Models, Molecular; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley
D002393:Estrogens, Catechol; C116356:catechol estrogen 3,4-quinone; D004247:DNA