Mechanism of metabolic activation and DNA adduct formation by the human carcinogen diethylstilbestrol: The defining link to natural estrogens

Abstract

Diethylstilbestrol (DES) is a human carcinogen, based on sufficient epidemiological evidence. DES is mainly metabolized to its catechol, 3 0 -hydroxyDES (3 0 -OH-DES), which can further oxidize to DES-3 0 ,4 0 -quinone (DES-3 0 ,4 0 -Q). Similarly to estradiol-3,4-quinone, the reaction of DES-3 0 ,4 0 -Q with DNA would form the depurinating 3 0 -OH-DES-6 0 -N3Ade and 3 0 -OH-DES-6 0 -N7Gua adducts. To prove this hypothesis, synthesis of DES-3 0 ,4 0 -Q by oxidation of 3 0 -OH-DES with Ag 2 O was tried; this failed due to instantaneous formation of a spiro-quinone. Oxidation of 3 0 -OH-DES by lactoperoxidase or tyrosinase in the presence of DNA led to the formation of 3 0 -OH-DES-6 0 -N3Ade and 3 0 -OH-DES-6 0 -N7Gua adducts. These adducts were tentatively identified by LC-MS/MS as 3 0 -OH-DIES with DNA did not produce any depurinating adducts, due to the dienic chain being perpendicular to the phenyl planes, which impedes the intercalation of DIES into the DNA. Enzymic oxidation of 3 0 -OH-DES suggests that the catechol of DES intercalates into DNA and is then oxidized to its quinone to yield N3Ade and N7Gua adducts. These results suggest that the common denominator of tumor initiation by the synthetic estrogen DES and the natural estrogen estradiol is formation of their catechol quinones, which react with DNA to afford the depurinating N3Ade and N7Gua adducts. ' 2008 Wiley-Liss, Inc.Key words: DES catechol quinone; depurinating DES-DNA adducts; metabolic activation of DES Diethylstilbestrol (DES), a potent synthetic estrogen, was obtained in 1938 and thereafter used to prevent spontaneous abortions and premature deliveries.1 In 1971 an association was found between prenatal exposure to DES and clear cell adenocarcinoma of the vagina and cervix in young women.2 Evidence for a causal relationship between transplacental exposure to DES and clear cell adenocarcinoma is conclusive.3-5 Furthermore, it was later reported that women who took DES during pregnancy had a higher incidence of breast cancer.6,7 More recently, it was found that women exposed to DES prenatally also have a higher incidence of breast cancer after age 40. 8,9 The natural estrogens estradiol (E 2 ) and estrone (E 1 ) are metabolically oxidized to their respective catechols, and the catechols are subsequently oxidized to their quinones, in particular the E 1 (E 2 )-3,4-quinones (Q). We have proposed and demonstrated that reaction of the E 1 (E 2 )-3,4-Q with DNA is the first critical step in the initiation of cancer.10-13 The depurinating adducts 4-OHE 1 (E 2 )-1-N3Ade and 4-OHE 1 (E 2 )-1-N7Gua, as well as the resulting apurinic sites in the DNA, are formed in this reaction. These apurinic sites generate mutations that we think can lead to cancer initiation. 13-15The same mechanism of metabolic activation and reaction with DNA has been demonstrated for the synthetic estrogen hexestrol (HES). 16,17 The catechol quinone of HES has chemical and biochemical properties similar to those of E 1 (E 2 )-3,4-Q; namely, it forms analogous depurinating N3Ade...

Characterization of UDP-Glucuronosyltransferases Involved in Glucuronidation of Diethylstilbestrol in Human Liver and Intestine

“…The purified metabolites were stored at −20°C before dissolving in methanol-d 4 (Euriso-Top, Saint-Aubin, France) for NMR analysis. Chemical shifts were given on δ scale and referenced to tetramethylsilane (TMS) at 0 ppm for 1 H NMR (500 MHz) and 13 C NMR (125 MHz). Screening of UGTs with DES Glucuronidation Activity.…”

Prediction of embryotoxic potential using the ReProGlo stem cell-based Wnt reporter assay

“…Prenatal exposure to DES does apparently not cause teratogenic effects in rats [60]. DES undergoes oxidative metabolism to a quinone [61], which is able to form DNA adducts. Again, this metabolite which is probably not formed in ES cells does not explain the cytotoxic effects seen in the ReProGlo assay.…”

The etiology and prevention of breast cancer

“…The specificity of the crucial mutations derives from the preliminary intercalating physical complex between the estrogens and DNA before formation of a covalent bond between them. This has been demonstrated by studying the mechanism of cancer initiation by the human carcinogen diethylstilbestrol [22]. …”

“…This mechanism of activation has been demonstrated to occur with benzene [13,14], naphthalene [15,16], estrone (E 1 ) and estradiol (E 2 ) [17–21], diethylstilbestrol [22], hexestrol [20,23,24] and possibly bisphenol A [25] (Fig. 1).…”