[SIZE=-1]Journal of Virology, November 2007, p. 12418-12426, Vol. 81, No. 22
0022-538X/07/$08.00+0 doi:10.1128/JVI.01067-07
Copyright ? 2007, American Society for Microbiology. All Rights Reserved.[/SIZE]
Neuraminidase Inhibitor-Resistant Recombinant A/Vietnam/1203/04 (H5N1) Influenza Viruses Retain Their Replication Efficiency and Pathogenicity In Vitro and In Vivo<sup>
</sup>
Hui-Ling Yen,<sup>
</sup> Natalia A. Ilyushina,<sup>
</sup> Rachelle Salomon, Erich Hoffmann, Robert G. Webster, and Elena A. Govorkova<sup>*</sup> Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-2794
Received 17 May 2007/ Accepted 29 August 2007
<!-- ABS --> Effective antiviral drugs are essential for early control of<sup> </sup>an influenza pandemic. It is therefore crucial to evaluate the<sup> </sup>possible threat posed by neuraminidase (NA) inhibitor-resistant<sup> </sup>influenza viruses with pandemic potential. Four NA mutations<sup> </sup>(E119G, H274Y, R292K, and N294S) that have been reported to<sup> </sup>confer resistance to NA inhibitors were each introduced into<sup> </sup>recombinant A/Vietnam/1203/04 (VN1203) H5N1 influenza virus.<sup> </sup>For comparison, the same mutations were introduced into recombinant<sup> </sup>A/Puerto Rico/8/34 (PR8) H1N1 influenza virus. The E119G and<sup> </sup>R292K mutations significantly compromised viral growth in vitro,<sup> </sup>but the H274Y and N294S mutations were stably maintained in<sup> </sup>VN1203 and PR8 viruses. In both backgrounds, the H274Y and N294S<sup> </sup>mutations conferred resistance to oseltamivir carboxylate (50%<sup> </sup>inhibitory concentration [IC<sub>50</sub>] increases, >250-fold and<sup> </sup>>20-fold, respectively), and the N294S mutation reduced susceptibility<sup> </sup>to zanamivir (IC<sub>50</sub> increase, >3.0-fold). Although the H274Y<sup> </sup>and N294S mutations did not compromise the replication efficiency<sup> </sup>of VN1203 or PR8 viruses in vitro, these mutations slightly<sup> </sup>reduced the lethality of PR8 virus in mice. However, the VN1203<sup> </sup>virus carrying either the H274Y or N294S mutation exhibited<sup> </sup>lethality similar to that of the wild-type VN1203 virus. The<sup> </sup>different enzyme kinetic parameters (V<sub>max</sub> and K<sub>m</sub>) of avian-like<sup> </sup>VN1203 NA and human-like PR8 NA suggest that resistance-associated<sup> </sup>NA mutations can cause different levels of functional loss in<sup> </sup>NA glycoproteins of the same subtype. Our results suggest that<sup> </sup>NA inhibitor-resistant H5N1 variants may retain the high pathogenicity<sup> </sup>of the wild-type virus in mammalian species. Patients receiving<sup> </sup>NA inhibitors for H5N1 influenza virus infection should be closely<sup> </sup>monitored for the emergence of resistant variants.
0022-538X/07/$08.00+0 doi:10.1128/JVI.01067-07
Copyright ? 2007, American Society for Microbiology. All Rights Reserved.[/SIZE]
Neuraminidase Inhibitor-Resistant Recombinant A/Vietnam/1203/04 (H5N1) Influenza Viruses Retain Their Replication Efficiency and Pathogenicity In Vitro and In Vivo<sup>
Hui-Ling Yen,<sup>
Received 17 May 2007/ Accepted 29 August 2007
<!-- ABS --> Effective antiviral drugs are essential for early control of<sup> </sup>an influenza pandemic. It is therefore crucial to evaluate the<sup> </sup>possible threat posed by neuraminidase (NA) inhibitor-resistant<sup> </sup>influenza viruses with pandemic potential. Four NA mutations<sup> </sup>(E119G, H274Y, R292K, and N294S) that have been reported to<sup> </sup>confer resistance to NA inhibitors were each introduced into<sup> </sup>recombinant A/Vietnam/1203/04 (VN1203) H5N1 influenza virus.<sup> </sup>For comparison, the same mutations were introduced into recombinant<sup> </sup>A/Puerto Rico/8/34 (PR8) H1N1 influenza virus. The E119G and<sup> </sup>R292K mutations significantly compromised viral growth in vitro,<sup> </sup>but the H274Y and N294S mutations were stably maintained in<sup> </sup>VN1203 and PR8 viruses. In both backgrounds, the H274Y and N294S<sup> </sup>mutations conferred resistance to oseltamivir carboxylate (50%<sup> </sup>inhibitory concentration [IC<sub>50</sub>] increases, >250-fold and<sup> </sup>>20-fold, respectively), and the N294S mutation reduced susceptibility<sup> </sup>to zanamivir (IC<sub>50</sub> increase, >3.0-fold). Although the H274Y<sup> </sup>and N294S mutations did not compromise the replication efficiency<sup> </sup>of VN1203 or PR8 viruses in vitro, these mutations slightly<sup> </sup>reduced the lethality of PR8 virus in mice. However, the VN1203<sup> </sup>virus carrying either the H274Y or N294S mutation exhibited<sup> </sup>lethality similar to that of the wild-type VN1203 virus. The<sup> </sup>different enzyme kinetic parameters (V<sub>max</sub> and K<sub>m</sub>) of avian-like<sup> </sup>VN1203 NA and human-like PR8 NA suggest that resistance-associated<sup> </sup>NA mutations can cause different levels of functional loss in<sup> </sup>NA glycoproteins of the same subtype. Our results suggest that<sup> </sup>NA inhibitor-resistant H5N1 variants may retain the high pathogenicity<sup> </sup>of the wild-type virus in mammalian species. Patients receiving<sup> </sup>NA inhibitors for H5N1 influenza virus infection should be closely<sup> </sup>monitored for the emergence of resistant variants.