Deoxygenated disaccharide analogs as specific inhibitors of β1-4-galactosyltransferase 1 and selectin-mediated tumor metastasis

Abstract

The disaccharide peracetylated GlcNAcβ1-3Galβ-O-naphthalenemethanol (disaccharide 1) diminishes the formation of the glycan sialyl Lewis X (Neu5Acα2-3Galβ1-4(Fucα1-3)Glc-NAc; sLeX) 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 sLeX assembly, and (iii) generation of several glycans related to sLeX. In this report, we show that GlcNAcβ1-3Galβ-O-naphthalenemethanol binds to the acceptor site of human β1-4-galactosyltransferase much like the acceptor trisaccharide, GlcNAcβ1-2Manβ1-6Man, 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 sLeX 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, -N3, -NH2, or -OCH3 instead of the hydroxyl groups at C-3′- and C-4′-positions of the terminal N-acetylglucosamine residue also blocked sLeX formation in cells. The reduction of sLeX 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.