Deoxygenated Disaccharide Analogs as Specific Inhibitors of beta 1-4-Galactosyltransferase 1 and Selectin-mediated Tumor Metastasis

The disaccharide peracetylated GlcNAc beta 1-3Gal beta-O-naphthalenemethanol (disaccharide 1) diminishes the formation of the glycan sialyl Lewis X (Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3)Glc-NAc, sLe(X)) in tumor cells. Previous studies showed that the mechanism of action of disaccharide 1 involves three steps: (i) deacetylation by carboxyesterases, (ii) action as a biosynthetic intermediate for downstream enzymes involved in sLe(X) assembly, and (iii) generation of several glycans related to sLe(X). In this report, we show that GlcNAc beta 1-3Gal beta-O-naphthalenemethanol binds to the acceptor site of human beta 1-4-galactosyltransferase much like the acceptor trisaccharide, GlcNAc beta 1-2Man beta 1-6Man, which is present on N-linked glycans. The 4'-deoxy analog, in which the acceptor hydroxyl group was replaced by -H, did not act as a substrate but instead acted as a competitive inhibitor of the enzyme. The acetylated form of this compound inhibited sLe(X) formation in U937 monocytic leukemia cells, suggesting that it had inhibitory activity in vivo as well. A series of synthetic acetylated analogs of 1 containing -H, -F, -N-3, -NH2, or -OCH3 instead of the hydroxyl groups at C-3'- and C-4'-positions of the terminal N-acetylglucosamine residue also blocked sLe(X) formation in cells. The reduction of sLe(X) by the 4'-deoxy analog also diminished experimental tumor metastasis by Lewis lung carcinoma in vivo. These data suggest that nonsubstrate disaccharides have therapeutic potential through their ability to bind to glycosyltransferases in vivo and to alter glycan-dependent pathologic processes.

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