Tumor initiating activity of 5,11-dimethylchrysene and the structural requirements favoring carcinogenicity of methylated polynuclear aromatic hydrocarbons

The tumor initiating activities of 5,11-dimethylchrysene and 5-methylchrysene on mouse skin were compared. After initiating doses of 30 μg or 10 μg, with promotion by 3 times weekly applications of tetradecanoylphorbol acetate, both compounds were highly tumorigenic, inducing tumors in 70-85% of the treated animals. Since 5,12-dimethylchrysene had previously been shown to be only a weak tumor initiator, these results support the generalization that the structural requirements favoring carcinogenicity among the methylated chrysenes and other polynuclear aromatic hydrocarbons (PAH) are a bay region methyl group and a free peri position, both adjacent to an unsubstituted angular ring.