Marked Differences in the Tumor-initiating Activity of Optically Pure (+)- and (−)-trans-7,8-Dihydroxy-7,8-dihydrobenzo(a)pyrene on Mouse Skin

The ability of optically pure (+)-and (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene to initiate skin tumors in mice was determined with a two-stage tumorigenesis system. A single application of 50 to 200 nmoles of (+)-or (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene to the backs of CD-1 mice followed by twice-weekly applications of 12-0-tetradecanoylphorbol-13-acetate revealed that the (-)-enantiomer was 5-to 10-fold more potent than was the (+)-enantiomer as a tumor initiator at the three dosage levels tested. When the tumor-initiating activities of the (+)-and (-)-enantiomers of trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene were compared to the activity of benzo(a)pyrene at an equimolar dose, the (-)-enantiomer was more active while the (+)-enantiomer was considerably less active. This is the first report of differences in the carcinogenic activity between optical enantiomers.