Histologic changes induced in SENCAR skin following a single treatment with
chrysarobin (1,8-dihydroxy-3-methyl-9-anthrone) exhibited differences in time course from that observed with 12-O-tetradecanoylphorbol-13-acetate (TPA). Although not significantly different, maximum elevations in epidermal thickness, total number of nucleated epidermal cells, and dark basal keratinocytes (DCs) induced by 220 nmol
chrysarobin occurred at 96 h
after treatment, while those induced by 3.4 nmol TPA occurred at 48 h. Both compounds elicited comparable inflammatory responses. Twice-weekly applications of
chrysarobin for 2.5 weeks induced a moderate
hyperplasia, increase in total nucleated epidermal cells, and increased DCs at 48 and 96 h after the last treatment, with a higher value for these parameters occurring at 48 h. Interestingly, the magnitude of these changes was similar to that observed after a single application. In contrast, twice-weekly applications of TPA induced a dramatic, potentiated induction of epidermal
hyperplasia and DCs. Once-weekly applications of
chrysarobin led to a potentiated induction of both
hyperplasia and DCs compared to the twice-weekly treatment regimen and also more effectively promoted epidermal
papillomas in previously initiated SENCAR mice. Skin sections from mice treated with
chrysarobin displayed overt signs of epidermal toxicity including altered basal cell morphology and a decreased number of basal cells per 125 micron of basement membrane.
Hyperplasia induced by multiple but not single treatments with
chrysarobin and TPA correlated quantitatively with their
papilloma promoting activity. In addition, the data suggest that epidermal toxicity may play a role in
tumor promotion by
anthrones.