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Evaluation of Vitamin A Analogs in Modulating Epithelial Differentiation of 13-Day Chick Embryo Metatarsal Skin Explants¹

Kettering-Meyer Laboratory [L.J.W., J.C.P., E.A.D., D.P.C.], Southern Research Institute, and the Department of Pathology [R.W.M.], University of Alabama, Birmingham, Alabama 35205

Seventeen vitamin A compounds were evaluated in organ culture for activity in altering epithelial differentiation of metatarsal skin explants from 13-day-old chick embryos. The explants keratinized in 6 to 8 days and, when cultured in the presence of ß-retinoic acid (RA), inhibition of keratinization occurred and a mucous metaplasia developed.

A cyclopentenyl analog of retinoic acid was approximately 10-fold more effective than RA in producing mucous metaplasia. Six other analogs exhibited about the same activity as RA: trimethylmethoxyphenyl analog of retinoic acid, -retinoic acid, 13-cis-retinoic acid, methyl retinoate, ethyl retinoate, and N-ethylretinamide. The following 5 vitamin A compounds were about one-fourth as effective as RA: the trimethylmethoxyphenyl analog of ethylretinamide, the phenyl analog of retinoic acid, the trimethylmethoxyphenyl analog of ethyl retinoate, ß-retinyl acetate, and retinol. The furyl analog of retinoic acid and N,N-diethylretinamide were approximately one-tenth and one-fifteenth less effective than RA in inhibiting keratinization. The analog, -retinyl acetate, was about one-hundredth as effective as RA and the pyridyl analog of retinoic acid (2.5 x 10^-5 M) did not inhibit keratinization.

Since the property of altering epithelial differentiation may be a fundamental requirement for the prophylaxis and/or treatment of malignant epithelial lesions, this system can be used to determine whether the new synthetic analogs of vitamin A are active in modulating epithelial differentiation.

¹ This investigation was supported by Contract No1-CP22064, Lung Cancer Segment, Division of Cancer Cause and Prevention, National Cancer Institute, NIH, Department of Health, Education, and Welfare.

Received 6/ 6/75. Accepted 11/21/75.