Metabolism of the carcinogen (³H)6-nitrochrysene in the preweanling mouse: Identification of 6-aminochrysene-1, 2-dihydrodiol as the probable proximate carcinogenic metabolite

6-Nitrochrysene (NC) is a potent lung and liver carcinogen when administered in multiple doses to preweanling mice. We have investigated both the in vitro metabolism of (³H)NC by 9000 g supernatants (S9) prepared from the livers of preweanling mice and the in vivo metabolism of (³H)NC in these animals. The in vitro covalent binding of primary metabolites of NC to DNA after further reductive and/or oxidative metabolism was then examined in an attempt to define the metabolic activation pathway responsible for the formation of carcinogen-DNA adducts in NC-treated preweanling mice. NC-1,2-dihydrodiol, NC-9, 10-dihydrodiol, 6-aminochrysene (AC), and several unidentified compounds were found in ethyl acetate extracts of incubations containing (³H)NC and liver S9 from 1-or 8-day-old BLU: Ha mice. Comparison of the in vivo metabolism of NC in 1-day-old animals and 8-day-old animals which had been treated with NC on day 1 indicated that the formation of AC and the two NC dihydrodiols was greater in the younger animals. Further metabolism of NC-1, 2-dihydridiol by S9 from 8-day-old mice yielded AC-1,2-dihydrodiol as a major product. Incubation of AC-1,2-dihydrodiol, calf thymus DNA and liver microsomes from 3-methylcholanthrene-induced rats yielded a single major adduct that was chromatographically and chemically identical to the major adduct formed in (³HJNC-and (³H)-AC-treated preweanling mice. The results indicated that the major DNA adduct found in vivo is derived from the further metabolism of the proximate carcinogen AC-1, 2-dihydrodiol.