The broad objective of this application is to investigate the biochemical and molecular mechanisms of retinoid-induced teratogenesis. Natural and synthetic retinoids are useful in the treatment of various dermatological diseases, including basal cell carcinoma, keratoacanthoma and melanoma. Retinoids have been recommended as chemopreventive agents for lung, breast and urinary bladder cancer. All-trans-retinoic acid (Retin-A) has been suggested as an effective anti-wrinkling agent to prevent aging of skin. One of the major undesirable effects of retinoid therapy is their inherent teratological hazard. A number of human malformations have been reported following retinoid use. In this previous grant (HD 21399) the structure-activity relationship of a large number of synthetic retinoids was investigated. The hamster was shown to be a good model for retinoid-induced terata in humans. Synthetic retinoids showed a range of teratogenic potency over four orders of magnitude. This variation, although described by their molecular characteristics, can not be explained on the basis of their pharmacokinetic parameters or placental permeability. A qualitative relationship was observed between teratogenic potency and binding affinity or retinoids to hamster fetal cellular retinoic acid binding protein (CRABP). The extension of these studies to human embryonic CRABP and characterization of retinoid binding to nuclear retinoic acid receptors (RARs) is now proposed. A large number of synthetic retinoids have been procured and arrangements have been made to obtain human embryonal tissue (obtained from life- threatening ectopic pregnancies and collected under an NIH program). The cDNA clones for different nuclear RARs have been obtained. Investigations will be conducted in the hamster model and to a limited extent on human tissues; data would be compared to each other. Binding affinities of retinoids to human CRABP and to hamster and human RARs will be determined. For retinoids modified at the acidic terminal, their free acid congeners will be used. Presence and amount of different nuclear RARs will be investigated in different tissues at different gestational age in embryos of both species by measuring the amount of specific mRNA, by in situ hybridization, and by immunocytochemistry with monoclonal antibodies. Age- and tissue-specific distribution of RARs will be related to distribution of CRABP and different retinoids. Finally, the induction of RARbeta will be investigated after retinoid exposure since the respective gene has a promoter region for its own product. Results are expected to provide a better understanding of retinoid-induced teratogenesis and a possible identification of chemicals with reduced teratogenic potential.
