Comparative tumor initiating activity of 10-methylbenzo-[a]pyrene, 7,10-dimethylbenzo[a]pyrene and benzo[a]pyrene.

The tumor initiating activity on mouse skin of benzo[a]pyrene (BaP), 7,10-dimethylBaP, and 10-methylBaP was determined. Each compound was tested at initiating doses of 50 microgram and 100 microgram with promotion by application 3 times weekly of 2.5 microgram tetradecanoylphorbol acetate. BaP induced tumors in 40% (100 microgram) and 25% (50 microgram) of the animals. No tumors were observed in either group treated with 7,10-dimethylBaP. In the groups treated with 10-methyl-Bap, the incidence of tumor bearing animals was 20% at both doses. These results and the results of previous studies on other methylated BaP derivatives suggest that the mechanism of activation of these compounds is similar to that observed for the parent hydrocarbon and probably involves formation of an angular ring diol-epoxide or epoxide.