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.