Sterically hindered analogues of diacylglycerols. Synthesis, binding to the phorbol ester receptor and metabolism in A549 human lung carcinoma cells

Abstract

The 5 following compounds were synthesized in order to investigate the relationship between structure and ability of glyceride-type molecules to bind to the phorbol ester receptor: one dioctanoyl cyclohexane-1,2,4-triol, 2 isomeric methyl analogues of 1,2-dioctanoyl-sn-glycerol (diC8), one dimethyl and one cyclohexyl analogue of diC8. Their ability to compete with 3H-labelled phorbol-12,13-dibutyrate [( 3H]PDBu) for specific binding sites in intact A549 human-derived lung carcinoma cells and in a cytosolic cell extract was compared with that of diC8 and 12-O-tetradecanoylphorbol-13-acetate (TPA). The affinity of diC8 for the phorbol ester receptor was much weaker than that of TPA. The analogues in turn were less able than diC8 to compete with [3H]PDBu for receptor sites. Like diC8 and unlike TPA, the synthesized compounds inhibited cell growth only at those concentrations at which cytotoxicity was also apparent. DiC8 and its methyl and dimethyl derivates, but not the cyclohexyl derivative or the cyclohexanetriol diester, were metabolically removed from cellular incubates as measured by gas liquid chromatography. The results suggest that the binding of glyceride-type molecules to the phorbol ester receptor exhibits stringent specificity and that the design of novel potent agonists of phorbol esters might require the placement of the molecular features of diacylglycerols important for biological activity into a molecular framework which is more complicated than glycerol.