Metabolic Activation and Formation of DNA Adducts of Hexestrol, a Synthetic Nonsteroidal Carcinogenic Estrogen

• Published in: Chemical research in toxicology 1998-05, Vol.11 (5), p.412-419
• Main Authors: Jan, Shyi-Tai, Devanesan, Prabu D, Stack, Douglas E, Ramanathan, Ragulan, Byun, Jaeman, Gross, Michael L, Rogan, Eleanor G, Cavalieri, Ercole L
• Format: Article
• Language: English
• Subjects: Animals; Biotransformation; Carcinogens - metabolism; Carcinogens - toxicity; Chromatography, High Pressure Liquid; Cricetinae; DNA Adducts - metabolism; Estrogens, Non-Steroidal - metabolism; Estrogens, Non-Steroidal - toxicity; Hexestrol - metabolism; Hexestrol - toxicity; In Vitro Techniques; Magnetic Resonance Spectroscopy; Mass Spectrometry; Quinones - chemistry; Quinones - metabolism; Rats; Spectrometry, Mass, Fast Atom Bombardment
• ISSN: 0893-228X; 1520-5010
• DOI: 10.1021/tx970141n

Hexestrol (HES), a synthetic nonsteroidal estrogen, is carcinogenic in Syrian golden hamsters. The major metabolite of HES 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. Standard adducts were synthesized by reacting HES-3‘,4‘-Q with dG and dA to produce the adducts 3‘-OH-HES-6‘(α,β)-N7Gua and HES-3‘,4‘-Q-6‘-N6dA, respectively. When HES-3‘,4‘-Q was reacted with calf thymus DNA, 3‘-OH-HES-6‘(α,β)-N7Gua was identified by HPLC and tandem mass spectrometry as the depurinating adduct, with minor amounts of stable adducts. 3‘-OH-HES was bound to DNA after activation by horseradish peroxidase, lactoperoxidase, or rat liver microsomes. The depurinating adduct 3‘-OH-HES-6‘(α,β)-N7Gua was identified in these systems at levels of 65, 41, and 11 μmol/mol of DNA-P, respectively. Unidentified stable adducts were observed in much lower amounts and were quantified by the 32P-postlabeling method. Similarly to 3‘-OH-HES, the catechol metabolites of the natural steroidal estrogens estrone (E1) and estradiol (E2), namely, 2-OHE1, 4-OHE1, 2-OHE2, and 4-OHE2, can be oxidized to their corresponding quinones by peroxidases and cytochrome P450. The quinones of the carcinogenic 4-OHE1 and 4-OHE2 have chemical 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 compound to corroborate the hypothesis that estrogen-3,4-quinones are ultimate carcinogenic metabolites of the natural steroidal estrogens E1 and E2.