INHIBITORS OF PROCESSING AND LYSOSOMAL GLYCOSIDASES

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Glycosidases have essential functions in mammalian cells in at least several capacities. In one capacity, they are essential for the processing of the oligosaccharide chain of cell surface and secretory glycoproteins. These processing reactions are necessary for the formation of the complex types of glycoproteins that may function as cell surface receptors for many important biological molecules or interactions. In another capacity, glycosidases are critical to lysosomal function and serve to degrade various complex carbohydrates such as proteoglycans, glycolipids and glycoproteins. Absence or alteration of certain lysosomal glycosidases leads to storage diseases such as Hurlers or Hunters syndromes as examples of mucopolysaccharidosis, or Gauchers or Tay Sachs as examples of mucolipodosis. Recently, we found that the plant alkaloid swainsonine was a potent inhibitor of glycoprotein processing when given to cells in culture, and prevented the formation of normal complex oligosaccharides. The compound was shown by other workers to inhibit the processing mannosidase II and probably results in the formation of a hybrid type of oligosaccharide. Swainsonine also inhibits lysosomal Alpha-mannosidase and causes symptoms of Alpha-mannosidosis in animals that ingest it. Since swainsonine is a trihydroxylated indolizidine, it seems likely that other stereoisomers of this compound would inhibit other glycosidases involved in glycoprotein processing or lysosomal function. These stereoisomers would be valuable tools for studying glycoprotein processing and causing the formation of altered glycoproteins, or they might be valuable for inhibiting lysosomal glycosidases and mimicing lysosomal storage diseases. This idea is strengthened by our recent finding that a tetrahydroxylated alkaloid, castanospermine, is a potent inhibitor of Beta-glucosidase and also of Beta-glucocerebrosidase. Thus, we will synthesize swainsonine and its various stereoisomers and will test these synthetic isomers on a number of glycosidases to see which ones are inhibited. We will also test these isomers on several mammalian cell systems to determine their effect on glycoprotein processing. We will also complete the biological studies on swainsonine and castanospermine to determine how they inhibit glycoprotein processing. These studies will be done in cell culture.