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

Department of Biochemistry and Drug Metabolism, Hoffmann-La Roche Inc., Nutley, New Jersey 07110 [W. L., A. W. W., R. L. C., A. H. C.]; Cancer and Toxicology Program, Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 [T. J. S.]; and Section on Oxidation Mechanisms, Laboratory of Chemistry, National Institute of Arthritis, Metabolism and Digestive Diseases, NIH, Bethesda, Maryland 20014 [H. Y., D. M. J.]

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(apyrene to the backs of CD-1 mice followed by twice-weekly applications of 12-O-tetradecanoyl-phorbol-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.

¹ To whom requests for reprints should be addressed.

Received 3/29/77. Accepted 5/26/77.