Comparison of the inhibitory effects of retinoids on 12-O-tetradecanoylphorbol-13-acetate-promoted tumor formation in CD-1 and Sencar mice.

Linear regression analysis of the dose levels of retinoids required to inhibit the formation of papillomas by 50% in mouse dorsal epidermis topically treated with 7,12-dimethylbenz[a]anthracene (DMBA) (200 nmol) and then promoted 2 weeks later with twice-weekly applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) (8.5 nmol) indicated that there was a good correlation (r = 0.9095, P less than 0.02) between retinoid inhibitory activities in the CD-1 mouse at 20 weeks after the start of promotion and in the Sencar mouse after 12 weeks of promotion. The ID50 values (nmol) determined were as follows: all-trans-retinoic acid (RA) (3.5, CD-1; 17, Sencar); 4-[2-(5,6,7,8-tetrahydro-5,5,8,8- tetramethyl-2-naphthalenyl)-1E-propen-1-yl]benzoic acid (0.14, CD-1; 0.71, Sencar); 4-[1-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl- 2-naphthalenyl)- 1E-propen-2-yl]benzoic acid (0.54, CD-1; 1.9, Sencar); 6-[1-(4-carboxyphenyl)-1E-propen-2-yl]- 3,4- dihydro-4,4-dimethyl-2H-1-benzothiopyran (3.0 CD-1; 11, Sencar); 7-[1-(4-carboxyphenyl)-1E-propen-2-yl)- 3,4-dihydro- 4,4-dimethyl-2H-1-benzothiopyran (1.5, CD-1; 0.4, Sencar); 2-[1-(4-carboxyphenyl)-1E-propen-2-yl]- 4,5,6,7-tetrahydro-4,4- dimethyl-benzo[b]thiophene (0.30, CD-1; 2.3, Sencar).