Comparisonof the Skin Tumor-initiatingActivitiesof Dihydrodiolsand Diol-Epoxidesof VariousPolycyclicAromatic Hydrocarbons1

†̃ †̃bay-region' â€d̃iol-epoxides of PAH are important in their car cinogenic activity. A bay region occurs in PAH when an angu larly fused benzo ring is present (Chart 1). There is now direct evidence from tumorigenicity studies that bay-region diol epoxides of B(a)P (2, 14, 15, 22, 23) and BA (18, 25, 26) are ultimate carcinogenic metabolites. In addition, recent studies have shown that certain benzo-ring dihydrodiols (im mediate precursors of bay-region diol-epoxides) of the car cinogens B(a)P, BA, 7-MBA, 7,12-dimethylbenz(a)anthracene, DB(a,h)A, and chrysene are tumorigenic in mice (1, 3, 4, 14, i 5, 18—20,22—26). In this study, we compare the skin tumor-initiating activities in mice of dihydrodiols and diol-epoxides of 7-MBA, DB(a,h)A, DB(a,c)A, chrysene, and B(e)P (Chart 1). Our results show that 7-MBA 3,4-dihydrodiol and chrysene i ,2-dihydrodiol are more potent than the corresponding parent hydrocarbon, whereas B(e)P 9,10-dihydroaiol was approximately the same, and DB(a,h)A 3,4-dihydrodiol is less active. In general, the bay region diol-epoxides of the above hydrocarbons were very weak skin tumor initiators.