IDENTIFICATION OF 3-ALPHA-HYDROXY-CYPROTERONE ACETATE AS A METABOLITE OF CYPROTERONE-ACETATE IN THE BILE OF FEMALE RATS AND THE POTENTIAL OF THIS AND OTHER ALREADY KNOWN OR PUTATIVE METABOLITES TO FORM DNA-ADDUCTS IN-VITRO

Cyproterone acetate (CPA) is a synthetic steroid hormone used in the therapy of prostate cancer in men and different forms of acne and hirsutism in women. CPA has been shown by P-32-postlabeling analysis to bind covalently to hepatic DNA of rats in vivo and in vitro, A prerequisite for DNA adduct formation of CPA is metabolic activation of the drug to a reactive intermediate, In the present study bile was collected from [H-3]CPA-treated female rats and, following chromatographic separation of bile extracts, fractions of the eluate were examined for the presence of reactive metabolites which were able to form adducts with calf thymus DNA in vitro. The formation of adducts was detected by P-32-postlabeling analysis. One major metabolite of CPA present in the bile extracts was isolated and, following a thorough structural elucidation by mass spectrometry and H-1-NMR, this metabolite was identified as 3 alpha-hydroxy-cyproterone acetate (3 alpha-OH-CPA). This metabolite was able to form the same major adduct in vitro which has been observed before in CPA-treated rats in vivo and in rat hepatocytes in vitro. A number of already known or putative metabolites of CPA were available as authentic standards and these were also examined for their propensity to form adducts in vitro. A positive result was obtained for 3-O-acetyl-cyproterone acetate, which formed the same major adduct as 3 alpha-OH-CPA. However, the presence of this putative metabolite in rat bile could not be demonstrated, Besides 3 alpha-OH-CPA, additional reactive metabolites of CPA were present in the bile extracts, however, since these were only minor components, their chemical structures could not be elucidated.