title: Formation of the depurinating N3adenine and N7guanine adducts by reaction of DNA with hexestrol-3',4'-quinone or enzyme-activated 3'-hydroxyhexestrol. Implications for a unifying mechanism of tumor initiation by natural and synthetic estrogens.
abstract: The nonsteroidal synthetic estrogen hexestrol (HES), which is diethylstilbestrol hydrogenated at the C-3-C-4 double bond, is carcinogenic. Its major metabolite is the catechol, 3'-OH-HES, which can be metabolically converted to the catechol quinone, HES-3',4'-Q. Study of HES was undertaken with the scope to substantiate evidence that natural catechol estrogen-3,4-quinones are endogenous carcinogenic metabolites. HES-3',4'-Q was previously shown to react with deoxyguanosine to form the depurinating adduct 3'-OH-HES-6'-N7Gua by 1,4-Michael addition [Jan S-T, Devanesan PD, Stack DE, Ramanathan R, Byun J, Gross ML, et al. Metabolic activation and formation of DNAadducts of hexestrol,a synthetic nonsteroidal carcinogenic estrogen. Chem Res Toxicol 1998;11:412-9.]. We report here formation of the depurinating adduct 3'-OH-HES-6'-N3Ade by reaction of HES-3',4'-Q with Ade by 1,4-Michael addition. The structure of the N3Ade adduct was established by NMR and MS. We also report here formation of the depurinating 3'-OH-HES-6'-N7Gua and 3'-OH-HES-6'-N3Ade adducts by reaction of HES-3',4'-Q with DNA or by activation of 3'-OH-HES by tyrosinase, lactoperoxidase, prostaglandin H synthase or 3-methylcholanthrene-induced rat liver microsomes in the presence of DNA. The N3Ade adduct was released instantaneously from DNA, whereas the N7Gua adduct was released with a half-life of approximately 3 h. Much lower (<1%) levels of unidentified stable adducts were detected in the DNA from these reactions. These results are similar to those obtained by reaction of endogenous catechol estrogen-3,4-quinones with DNA. The similarities extend to the instantaneously-depurinating N3Ade adducts and relatively slowly-depurinating N7Gua adducts. The endogenous estrogens, estrone and estradiol, their 4-catechol estrogens and HES are carcinogenic in the kidney of Syrian golden hamsters. These results suggest that estrone (estradiol)-3,4-quinones and HES-3',4'-Q are the ultimate carcinogenic metabolites of the natural and synthetic estrogens, respectively. Reaction of the electrophilic quinones by 1,4-Michael addition with DNA at the nucleophilic N-3 of Ade and N-7 of Gua is suggested to be the major critical step in tumor initiation by these compounds.
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: Muhammad
authors.initials: M
authors.lastname: Saeed
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Gunselman
authors.forename: Sheila
authors.initials: S
authors.lastname: Higginbotham
authors.forename: Eleanor
authors.initials: E
authors.lastname: Rogan
authors.forename: Ercole
authors.initials: E
authors.lastname: Cavalieri
mesh_terms: D002273:Carcinogens / Q000737:chemistry / Q000633:toxicity*; D004247:DNA / Q000737:chemistry*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000737:chemistry*; D004967:Estrogens / Q000737:chemistry / Q000633:toxicity*; D006147:Guanine / Q000737:chemistry*; D006589:Hexestrol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000633:toxicity*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002273:Carcinogens; D004967:Estrogens; C500989:hexestrol-3',4'-quinone; D006589:Hexestrol; D004958:Estradiol; D006147:Guanine; C047287:3'-hydroxyhexestrol; D004247:DNA