RETARDATION OF BENZO[A]PYRENE-INDUCED EPIDERMAL TUMOR-FORMATION BY THE POTENT ANTIOXIDANT 4B,5,9B,10-TETRAHYDROINDENO[1,2-B]INDOLE

The ability of the potent antioxidant, 4b,5,9b, 10-tetrahydroindeno[1, 2b]indole (THII), to inhibit tumor formation by topically-applied benz o[a]pyrene was evaluated using a complete carcinogenicity mouse skin b ioassay. THII was administered by direct application to the skin, in t he food or through the drinking water. In each case, THII increased th e average time until the appearance of tumors by 4 weeks, and also dec reased the total number of tumors compared with benzo[a]pyrene alone. These protective effects corresponded with the ability of THII to inhi bit benzo[a]pyrene- or 12-O-tetradecanoylphorbol-13-acetate-induced ep idermal ornithine decarboxylase activity, a biomarker of tissue prolif eration in skin of the treated animals. This is the first report of an antioxidant administered in food or water inhibiting chemically induc ed skin carcinogenesis.