EFFECTS OF WEAK OR NON-CARCINOGENIC POLYCYCLIC-HYDROCARBONS ON 7, 12-DIMETHYLBENZ[ALPHA]ANTHRACENE AND BENZO[ALPHA]PYRENE SKIN TUMOR-INITIATION

Benzo[e]pyrene (B[e]P) inhibited 7,12-dimethylbenz[a]anthracene (DMBA) skin tumor-initiation in mice by 84%, whereas pyrene and fluoranthene inhibited DMBA initiation by 50 and 34%, respectively. However, B[e]P, pyrene and fluoranthene had either no significant effect or a slight enhancing effect on benzo[a]pyrene (B[a]P) skin tumor-initiation. In addition, B[e]P had essentially no effect on the initiating ability of (±)B[a]P-7β,8α-diol-9α,10α-epoxide. As a tumor-initiator, B[e]P was found to have very weak activity at a 252 μg/level (0.4 papillomas/mouse at 40 weeks) and no activity at 100 μg. When given at a dose of 100 μg twice weekly, B[e]P induced 2.1 papillomas/mouse at 30 weeks, and 25% of the mice had carcinomas at 40 weeks. However, B[e]P carcinogenic activity is weak when compared to B[a]P, which can induce a comparable tumor response at a dose of 5 μg twice weekly. When B[e]P was tested as a tumor promoter at a dose of 100 μg twice weekly after DMBA initiation, it induced 4.5 papillomas/mouse at 30 weeks and a 45% carcinoma incidence at 40 weeks, which was approximately twice as effective as B[e]P alone. The data show that B[e]P is a very weak tumor initiator, a weak complete carcinogen, a moderate tumor promoter, possibly a weak co-tumor-initiator when given with B[a]P, and a potent anti-tumor-initiator when given with DMBA. The anti-tumor initiating and co-tumor-initiating effects of B[e]P appear to be related to its ability to modify the conversion of the tumor initiator into an electrophilic intermediate(s) which are capable of covalently binding to DNA. In addition, B[e]P induced epidermal cellular proliferation which may be related to its promoting ability. © 1979 Elsevier/North-Holland Scientific Publishers Ltd., All rights reserved.