Metabolism of 2S-hydroxy-3-methylcholanthrene by rat liver microsomes

Products formed in the metabolism of 2S-hydroxy-3-methylcholanthrene (2S-OH-3MC) by liver microsomes prepared from phenobarbital-treated rats were isolated by sequential use of reversed-phase and normal-phase HPLC. Metabolites of 2S-OH-3MC were characterized by UV-visible absorption, mass and circular dichroic spectra, and chiral stationary phase HPLC analyses. The metabolites that had been identified were 2S-hydroxy-3-hydroxymethylcholanthrene (2S-OH-3-OHMC), 3MC-2-one, 3MC-2-one 9,10-dihydrodiol, 8-hydroxy-2S-OH-3MC, a pair of stereoisomers 3MC (trans)-1R,2R-diol and (cis)-1S,2R-diol in a ratio of approximately 11:89, a pair of diastereomers 2S-OH-3MC 9R,10R-dihydrodiol and 2S-OH-3MC 9S,10S-dihydrodiol in a ratio of approximately 9:1, and a pair of diastereomers 2S-OH-3MC 11R,12R-dihydrodiol and 2S-OH-3MC 11S,12S-dihydrodiol in a ratio of approximately 77:23. A few tentatively identified minor metabolites were 3-OHMC trans-1R,2R-diol, 10-hydroxy-2S-OH-3MC, a 9,10-dihydrodiol derived from 3MC cis-1S,2R-diol, and a 11,12-dihydrodiol and two diastereomeric 9,10-dihydrodiols derived from 2S-OH-3-OHMC. Since the racemic 2-OH-3MC is a known potent carcinogen and 2S-OH-3MC is the most abundant metabolite of 3MC, some of the 2S-OH-3MC metabolites identified in this study may be further converted to proximate and ultimate carcinogens which may contribute to the overall carcinogenicity exhibited by 3MC.