Selection of Influenza A and B Viruses for Resistance to 4‐Guanidino‐Neu5Ac2en in Cell Culture

The reassortant influenza viruses, A/NWS-G70c with N9 neuraminidase (NA) and B/HK/8/73 (HG) with B/Lee/40 NA, were selected for resistance to 4-guanidino-Neu5Ac2en (4-GuDANA) by passaging the virus in stepwise increases in the concentration of 4-GuDANA. In the NA of resistant viruses, the absolutely conserved Glu 119, which lies in a pocket beneath the active site of the enzyme and interacts with the guanidinium moiety of 4-GuDANA, was changed to Gly. The mutant NA was >200-fold more resistant to 4-GuDANA than was the wild-type enzyme. During 72 h in cell culture, resistant A and B viruses displayed much less NA activity than did wild-type viruses but did undergo multicycle replication. While emergence of resistance to 4-GuDANA has not been observed in vivo, these results demonstrate that the development of resistance is possible and can be mediated by a single amino acid change in the active site of the viral NA.