Mutagenicity of chrysene, its methyl and benzo derivatives, and their interactions with cytochromes P-450 and the Ah-receptor; relevance to their carcinogenic potency.

The genotoxicity in the Ames test of chrysene, of its six methyl and of two benzo-derivatives, and their ability to induce rat hepatic CYP1A and epoxide hydrolase activities, and stimulate their own bioactivation were determined. The primary objective is to provide a rationale for the higher carcinogenic potency of 5-methylchrysene when compared to that of the parent compound and the other methyl isomers. In the presence of Aroclor 1254-induced hepatic microsomes chrysene, its 5- and 4-methyl derivatives and to a lesser extent the 2- and 3-methyl derivatives and benzo[c]chrysene elicited a positive mutagenic response. Chrysene, all derivatives studied and especially benzo[c]chrysene were potent inducers of rat hepatic CYP1A1 activity as exemplified by the O-deethylation of ethoxyresorufin (30-180-fold when activities are expressed per nmol of total cytochrome P-450). All compounds studied displaced [3H]TCDD from the cytosolic Ah receptor at a concentration of 10(-10)-10(-9) M. Benzo[c]chrysene and to a lesser extent 6-methylchrysene were the only compounds capable of stimulating epoxide hydrolase activity, but the effect was modest. None of the compounds studied could induce its own activation to mutagens in the Ames test. The present findings indicate that the higher carcinogenic potency of 5-methylchrysene cannot be related to its mutagenic potential or its ability to enhance its own activation through induction of CYP1A1 and epoxide hydrolase activities.