Regulation of distribution, amount and ligand affinity of sugar receptors in human colon carcinoma cells by treatment with sodium butyrate, retinoic acid and phorbol ester.

Human colon carcinoma cells were treated with non-toxic levels of sodium butyrate, retinoic acid or phorbol ester, eliciting characteristic growth inhibition and morphological changes. Since protein-carbohydrate interactions are supposedly involved in regulatory processes and can serve within targeted drug delivery, the capacity to bind components of the carbohydrate chains of cellular glycoconjugates was monitored for such cells in relation to the type of the medium additive. The pattern of binding of a panel of neoglycoproteins was significantly altered for fixed cells, depending on the type of putative maturation factor. Quantitation of cell surface sugar receptors at a non-saturating concentration of neoglycoenzyme, employed as carbohydrate ligand-exposing probe, led to a similar conclusion. Up to six-fold increases were determined for individual probes. Binding studies with varying concentrations of neoglycoenzymes in the case of four ligands revealed that the receptor density, but not the affinity was significantly affected. Biochemical analyses corroborated this result by demonstrating mainly quantitative differences after affinity chromatography of detergent extracts from the four types of cell pellet. By showing the inhibitory potency of neoglycoprotein-conjugated liposomes in the cell binding assay with neoglycoenzymes, a perspective is indicated, of how the different effects of the differentiation-inducing agents might be beneficially exploited in targeted drug delivery.