MONOMERIC INHIBITORS OF INFLUENZA NEURAMINIDASE ENHANCE THE HEMAGGLUTINATION INHIBITION ACTIVITIES OF POLYACRYLAMIDES PRESENTING MULTIPLE C-SIALOSIDE GROUPS

Background: Influenza Viruses use hemagglutinin (HA) arrays to bind to sialic acid moieties on the surface of cells; crosslinking of erythro cytes by this mechanism leads to hemagglutination. A number of synthet ic polymers containing multiple sialic acid (Neu5Ac) groups as side ch ains are potent inhibitors of this process. Inhibition may be due to t wo mechanisms: polyvalent binding of the inhibitor's multiple Neu5Ac s ide chains to multiple HA sites on the viral surface, or steric stabil ization of the viral particle by a layer of the adsorbed, water-swolle n polymer, which prevents adhesion to the erythrocyte. The balance bet ween these two effects is not yet known. Results: Polyacrylamides with multiple C-sialosides (PA(Neu5Ac)) were 2-20 fold more effective as i nhibitors of virally mediated hemagglutination when assayed in the pre sence of Neu2en-NH2, a potent monomeric inhibitor of influenza neurami nidase (NA). The ability of monomeric inhibitors of NA to enhance the inhibition of hemagglutination in this assay correlated with the affin ity of the monomer for NA. Conclusions: Wie propose that inhibitors of NA act by competing with the C-sialosides of PA(Neu5Ac) for binding t o the active sites of the NA. Competitive displacement of Neu5Ac cause s an expansion of the layer of polymeric gel adsorbed to the virus, en hancing its inhibitory effect. This study provides an example of syner gy between two Ligands directed toward the active sites of two differe nt proteins, and reinforces the conclusion that steric stabilization i s important for the activity of polyvalent inhibitors.