The effects of promoter treatments prior to initiation on subsequent promotion by mezerein were examined in SENCAR mice. Groups of mice received two applications of various complete as well as first and second stage promoters given at various time intervals prior to initiation ranging from 3 days to 10 weeks. The mice were then initiated with 2 μg of 7,12-dimethylbenz[a]anthracene (DMBA) followed 2 weeks later by twice-weekly treatments with 2 μg of mezerein. The papilloma response in mice, receiving pretreatments with 2 μgof 12-O-tetradecanoylphorbol-13-acetate (TPA) either 3 days, 1, 2, 3 or 5 weeks before initiation, was similar to that seen when TPA was given after initiation during stage I of promotion followed by stage II of promotion with mezerein (4-5 papillomas per mouse in allgroups). Surprisingly, pretreatment with the stage II promoter, mezerein (2 μg), either 2 or 5 weeks prior to initiation, also gave papilloma responses similar to that induced with the standard two-stage promotion protocol (4.7 and 6.4 papillomas per mouse, respectively). The papilloma response was less than that in the standard two-stage promotion protocol when pretreatments with the stage I promoter A23187 (80 μg/mouse) were given either 2 or 5 weeks before initiation (2.6 and 2.3 papillomas per mouse, respectively). However, a repeat experiment (currently in progress) with a higher dose of A23187 (160 μg/mouse) given 2 weeks prior to initiation indicates that it is more effective than the 80 μg dose. When the time interval between pretreatment and initiation was increased to 10 weeks, the papilloma response with TPA and A23187 pretreatment was reduced to below two papillomas per mouse and with mezerein pretreatment to below three papillomas per mouse, indicating the effect was reversible. Histological changes in epidermis of mice which received two applications of these compounds correlated with the tumor response. In this regard, treatment with two applications of TPA and mezerein resulted in an epidermal hyperplasia of similar magnitude (epidermal thickness of 53.5 ± 1.5 and 50.0 ± 1.1 μm, respectively). The hyperplasia produced by treatment with two applications of 80 μg A23187 (39.4 ± 1.8 μm) was significantly less. The ability of pretreatments with benzoyl peroxide (20 mg) and chrysarobin (50μg) to affect the subsequent promoting activity of mezerein was also examined. Pretreatmentsat2 or 5 weeks before initiation with these com pounds resulted in a tumor response upon subsequent promotion with mezerein similar to the groups of mice which received acetone prior to initiation (1-2 papillomas per mouse). These results indicate that the ability to enhance promotion with mezerein by pretreatments prior to initiation is not a general property of all classes of skin tumor promoters. The time-course for reversibility of this effect and the correlation with induced hyperplasia support the hypothesis that TPA, mezerein and A23187 can effect what has been operationally referred to as stage I promotion prior to Initiation.
ASJC Scopus subject areas
- Cancer Research