The generation of glycosyltransferase inhibitors as probe molecules for biological systems is a long-standing problem. One hurdle is the charged natures of glycosyltransferase substrates, which makes it difficult to target these enzymes in cells using inhibitors that are substrate analogues. To circumvent this problem we have developed a rational approach to inhibition of certain glycosyltransferases within cells using a metabolite feeding approach. As proof of concept we have designed and prepared a nucleotide sugar analog that inhibits the human glycosyltransferase responsible for the reversible post-translational modification of nucleocytoplasmic proteins with O-linked N-acetylglucosamine residues (O-GlcNAc). Feeding of a GlcNAc analogue to cells leads to its transformation, by cellular biosynthetic enzymes, into an analogue of UDP-GlcNAc. This UDP-GlcNAc analogue blocks the action of O-GlcNAc transferase in cells, leading to decreased O-GlcNAc levels. More recently we have demonstrated the generality of this approach by blocking the cellular action of fucosyltransferases, leading to decreased cell surface levels of the blood-group antigen Sialyl Lewis X and impaired selectin-mediated cell adhesion. Here we report an overview of this approach and discuss our recent findings on the exploitation of metabolic pathways to inhibit glycosyltransferases within cells.
