Retinoic acid and its analogues have generated much interest because of their potential utility as cancer chemopreventive agents. Although promising compounds, a major impediment to fully exploiting these polyenes lies in the uncertainty concerning the mechanism(s) by which they modulate cellular differentiation. Currently, the most accepted hypothesis holds that the cellular retinoid acid-binding protein(s) (CRABP) mediate retinoid action by a steroid hormone-like mechanism of action. Some inconsistencies remain with this model leaving open questions about the actual mechanism of retinoic acid action.
Specific aims for this chemical program are the synthesis of probes of the nature and role of the CRABP or other retinoid receptors. Four investigations are described: 1) the synthesis of electrophilic affinity labels for the active site of the CRABP, 2) the synthesis of photo-affinity labels to be used as in 1) above, 3) the preparation of retinoic acid-containing affinity matrices to expedite chromatographic purification of the CRABP(s), and 4) the preparation of improved antigenic forms of retinoic acid.
Aims of the biological studies will be: 1) preliminary evaluation of the affinity and specificity of the CRABP affinity probes followed by determination of any specific covalent modifications of the CRABP(s), 2) study of the pharmacological activity of these agents, particularly as long-acting retinoid agonists or antagonists, 3) demonstration of the utility of an affinity chromatography purification of the CRABP, and 4) development of a retinoid-specific radioimmunoassay. Demonstration of utility of any of the above research probes should generate interest in longer-range studies in this area. These studies would investigate the physico-chemical nature of the CRABP's and the transport and localization of retinoids by the CRABP's which should lead to a much better understanding of the mechanism of retinoid action.
