Synthesis of a Ganglioside GM3Position Isomer,N-Acetylneuraminosyl-(α(2→6)-lactosyl-β(1→1)-ceramide

Design, synthesis and biological evaluation of new ganglioside GM3 analogues as potential agents for cancer therapy

Ganglioside GM3 is well known as a tumor-associated carbohydrate antigen on several types of tumors. Many studies have demonstrated that GM3 plays roles in cells proliferation, adhesion, motility and differentiation, which is involved in the process of cancer development. In the present study, we developed methods to synthesize GM3 analogues conveniently. By enzymatic hydrolysis and chemical procedures, two novel analogues and two known analogues were synthesized, containing lactose and glucosamine. Then anti-proliferation and anti-migration activities were evaluated by cytotoxicity assays and wound healing tests, and the data demonstrated that these analogues exhibited anticancer activities. Based on our previous studies, the structure-activity relationships were discussed. This study could provide valuable sight to find new antitumor agents for cancer therapy.

Inhibition of influenza virus infections by sialylgalactose-binding peptides selected from a phage library

Influenza virus hemagglutinin recognizes sialyloligosaccharides of glycoproteins and glycolipids as cell surface receptors in the initial stage of the infection process. We demonstrate that pentadecapeptides that bind to a sialylgalactose structure (Neu5Ac-Gal) inhibited the infection of cells by influenza virus. The pentadecapeptides were identified through affinity selection from a phage-displayed random peptide library using a monolayer of the ganglioside Neu5Acalpha2-3Galbeta1-4Glcbeta1-1'Cer (GM3). The peptides were found to have affinity for GM3, and alanine scanning showed seven amino acid residues that contribute to carbohydrate recognition. The binding of peptides to the cell surface was significantly inhibited in the presence of sialic acid or by the digestion of cell surface sialyl residues by neuraminidase. Plaque assays indicated that a molecular assembly of alkylated peptides inhibited the infection of Madin-Darby canine kidney cells by influenza virus. Carbohydrate-binding peptides that inhibit carbohydrate-virus interaction showed inhibitory activity. These results may lead to a new approach to the design of antiviral drugs.

Surface Plasmon Resonance Study of Carbohydrate−Carbohydrate Interaction between Various Gangliosides and Gg3-Carrying Polystyrene

Carbohydrate-carbohydrate interactions between Gg3 trisaccharide-carrying polystyrene (PN(Gg3)) and monolayers of several glycosphingolipids (GSLs) were quantitatively investigated by surface plasmon resonance techniques. PN(Gg3) was adsorbed onto a GM3 monolayer strongly and specifically with an apparent affinity constant of K(a) = 2.5 x 10(6) M(-1), and the apparent affinity constants onto GSLs decreased in the following order: GM3 > LacCer > (KDN)GM3 approximately GlcCer > GM2 approximately GD3 approximately GM4 > GM1 approximately 2,6-isoGM3 > ceramide. These results suggest that PN(Gg3) recognizes not only some specified portions of GM3 but also the trisaccharide as a whole. On the other hand, PN(Lac) and PN(Cel) were bound to GSLs less strongly (K(a) approximately 10(4) M(-1)) and less selectively. The kinetic analysis revealed that the selectivity in the adsorption of PN(Gg3) onto the GM3 monolayer is dominated by the faster adsorption rate.

Interaction between complement proteins C5b-7 and erythrocyte membrane sialic acid

The initial phase of membrane attack by complement is the interaction between C5b6, C7, and the cell membrane that leads to the insertion of C5b-7. Here we investigate the role of sialic acid residues in the assembly of C5b-7 intermediates on erythrocyte cell membranes. We find that C5b6 binds to glycophorin, whereas C5 or C6 does not bind, and desialylation of the glycophorin abolishes C5b6 binding. Complement lysis is inhibited by either masking glycophorin sialic acid with F(ab) fragments of an mAb, or by removal of the sialylated region of glycophorin by mild trypsinization. Gangliosides inhibit C5b-7 deposition when added to the aqueous phase. Asialogangliosides and synthetic gangliosides lacking the carboxylic acid residue have no inhibitory activity. We conclude that C5b6 binds to sialylated molecules on the erythrocyte surface. We propose a new model of membrane attack in which C5b6 initially binds to membranes via ionic forces. C7 then binds to C5b6, disrupting the ionic interaction and leading to the exposure of hydrophobic domains. Sialic acid is known to inhibit complement activation. Thus, these findings reveal a paradoxical role for sialic acid in complement attack; the presence of sialic acid inhibits the generation of C5b6, but once the membrane attack pathway is initiated, sialic acid enhances complement lysis.