METABOLIC-ACTIVATION AND FORMATION OF DNA-ADDUCTS OF HEXESTROL, A SYNTHETIC NONSTEROIDAL CARCINOGENIC ESTROGEN

Hexestrol (HES), a synthetic nonsteroidal estrogen, is carcinogenic in Syrian golden hamsters. The major metabolite of ICES is its catechol, 3'-OH-HES, which can be metabolically converted to the electrophilic catechol quinone, HES-3',4'-Q, by peroxidases and cytochrome P450. Sta ndard adducts were synthesized by reacting HES-3',4'-Q with dG and dA to produce the adducts 3'-OH-HES-6'(alpha,beta)-N7Gua and HES-3',4'-Q- 6'-N(6)dA, respectively. When HES-3',4'-Q was reacted with calf thymus DNA, 3'-OH-HES-6'(alpha,beta)-N7Gua was identified by HPLC and tandem mass spectrometry as the depurinating adduct, with minor amounts of s table adducts. 3'-OH-HES was bound to DNA after activation by horserad ish peroxidase, lactoperoxidase, or rat liver microsomes. The depurina ting adduct 3'-OH-HES-6'(alpha,beta)-N7Gua was identified in these sys tems at levels of 65, 41, and 11 mu mol/mol of DNA-P, respectively. Un identified stable adducts were observed in much lower amounts and were quantified by the P-32-postlabeling method. Similarly to 3'-OH-HES, t he catechol metabolites of the natural steroidal estrogens estrone (E- 1) and estradiol (E-2), namely, 2-OHE1, 4-OHE1, 2-OHE2, and 4-OHE2, ca n be oxidized to their corresponding quinones by peroxidases and cytoc hrome P450. The quinones of the carcinogenic 4-OHE1 and 4-OHE2 have ch emical and biochemical properties similar to those of HES-3',4'-Q. The results suggest that formation of HES-3',4'-Q may be a critical event in tumor initiation by HES and that HES is an excellent model compoun d to corroborate the hypothesis that estrogen-3,4-quinones are ultimat e carcinogenic metabolites of the natural steroidal estrogens E-1 and E-2.