Tumor initiation by 7,12-dimethylbenz[a]anthracene in dermal melanocytes of hamster: inhibition through 7,8-benzoflavone.

Initiation of dermal melanocytes by 7,12-dimethylbenz[a]-anthracene (DMBA) in the dorsal skin of Syrian golden hamsters was investigated for its sensitivity to inhibition by 7,8-benzoflavone (BF). Initiation was carried out by a single intragastric application of DMBA (50 mg/kg body weight) and melanoma development pursued with or without subsequent promotion through repeated topical administration of 12-O-tetradecanoylphorbol-13-acetate (40 nmol/animal, 3 X weekly). A single intragastric application of BF (200 mg/kg body weight) 2 h prior to DMBA resulted in a suppression of melanoma yields by approximately 70%. Further, there were indications that BF generally causes a decrease of melanoma rates and an increase of survival rates. The study provides a first mechanistic concept for melanoma initiation by DMBA. It shows that metabolic activation of DMBA (i) is prerequisite to initiation and (ii) has a similar molecular basis as in other target cells of DMBA, the essential pathway including the cytochrome P-448-dependent monooxygenase system.