St3Gal-II Inhibitors

Chemical inhibitors of St3Gal-II include a range of compounds that interfere with the enzyme's ability to sialylate glycoproteins and glycolipids. Benzyl-α-GalNAc is a competitive inhibitor, resembling the natural substrates of St3Gal-II and thus blocking the active site of the enzyme. This prevents the transfer of sialic acid to its intended targets. Similarly, PUGNAc causes an accumulation of O-GlcNAc-modified proteins that compete with the substrates of St3Gal-II, effectively reducing the enzyme's sialylation activity. Swainsonine and Deoxymannojirimycin both target glycan-processing enzymes upstream of St3Gal-II, specifically inhibiting Golgi alpha-mannosidase II and mannosidase, respectively. This results in an altered N-glycan processing path, which impedes the access of St3Gal-II to its natural substrates, leading to its functional inhibition.

Further, Castanospermine and Celgosivir, both glucosidase inhibitors, disrupt the proper folding and processing of glycoproteins, which are essential for St3Gal-II action. The misfolded glycoproteins are not suitable substrates for St3Gal-II, leading to a decrease in its sialylation function. Kifunensine, by inhibiting mannosidase I, leads to an accumulation of high-mannose type glycans, which are not optimal substrates for St3Gal-II. NB-DNJ, also known as Miglustat, inhibits glucosylceramide synthase, potentially resulting in a decreased synthesis of glycosphingolipids, thus reducing the pool of substrates available for St3Gal-II. Salacinol and Deoxynojirimycin also inhibit glucosidases, leading to the accumulation of misfolded glycoproteins and reduced St3Gal-II functionality. Fumonisin B1, by inhibiting ceramide synthase, decreases the levels of glycosphingolipids, which are substrates for St3Gal-II, thus indirectly inhibiting the enzyme. Lastly, AMP-DNM targets N-acetylglucosaminyltransferases and, while it does not directly inhibit St3Gal-II, it can alter glycan structures on glycoproteins, thereby reducing the availability of suitable substrates for St3Gal-II and functionally inhibiting the enzyme.