Syncarcinogenic effect of the environmental pollutants cyclopenteno[cd]pyrene and benzo[a]pyrene in mouse skin

Benzo[a]pyrene (BP) and cyclopenteno[cd]pyrene (CPEP) are widespreadenvironmental pollutants. CPEP is a relatively potent carcinogenin mouse skin with an activity second only to BP among environmentalaromatic hydrocarbons. We have studied the combined applicationof BP and CPEP on mouse skin to determine their possible synergisticcarcinogenic effect. Nine-week-old female Swiss mice in groupsof 30 were treated on the back with high (H), medium (M) andlow (L) doses, respectively, of 20 (H), 6.6 (M) or 2.2 (L) nmolBP or 200 (H), 66.6 (M) or 22.2 (L) nmol CPEP in 50 µlacetone twice weekly for 48 weeks. Other groups received BP-H+ CPEP-H, BP-M + CPEP-M, BP-L + CPEP-L, BP-H + CPEP-L, BP-M+ CPEP-L, BP-L + CPEP-H, or BP-L + CPEP-M. A significant, 3-to 7-fold syncarcinogenic effect occurred when BP-M + CPEP-Mwere administered together. A smaller, but significant, synergisticeffect (1.2- to 3.8-fold) was also observed when BP-M + CPEP-Lor BP-L + CPEP-M was applied. Because of the syncarcinogeniceffect of BP and CPEP, their abundance in engine emissions andambient air samples may present a major source of carcinogenicrisk.