THE INTERACTION OF NEURAMINIDASE AND HEMAGGLUTININ MUTATIONS IN INFLUENZA-VIRUS IN RESISTANCE TO 4-GUANIDINO-NEU5AC2EN

We have previously described a 4-guanidino-Neu5Ac2en (zanamivir)-resis tant neuraminidase (NA) variant G70C4-G, with an active site mutation Glu 119 to Gly. This variant has been found to also harbor a hemagglut inin (HA) mutation in the receptor binding site, Ser 186 to Phe. Exami nation of early passages of the G70C4-G virus revealed that this HA mu tation had arisen by the first passage. From a subsequent passage two transient variants were isolated which had each acquired a different s econd HA mutation, Ser 165 to Asn and Lys 222 to Thr. Both were highly drug resistant and drug dependent and their ability to adsorb to and penetrate cells was decreased. Comparison of drug sensitivities betwee n the variant, with the additional HA mutation at Ser 165, and viruses with either mutation alone revealed that these two HA mutations acted synergistically to increase resistance. To determine the contribution to resistance of each of the NA and HA mutations in G70C4-G, the NA m utation was separated from the HA mutation by reasserting. The NA muta tion and the HA mutation each conferred low-level resistance to zanami vir, while the two mutations interacted synergistically in the double mutant to give higher resistance in vitro. Infectivity was not adverse ly affected in the double mutant and while there was a small decrease in sensitivity to zanamivir in the mouse model, there was no detectabl e resistance to zanamivir in the ferret model. (C) 1998 Academic Press .