- NAI resistance mutations
Influenza virus neuraminidase inhibitor (NI) resistance is defined as a significantly raised IC50 (drug concentration inhibiting neuraminidase (NA) activity by 50%) value, coupled with a characterised mutation in the NA gene. The table below shows the NAI resistance mutations that have been generated and classified in vitro.
Susceptibility to NI drugs is not absolute, ranging from an alteration in susceptibility to full resistance. There are typical ranges of IC50 values that differ between influenza subtypes and between oseltamivir and zanamivir for each subtype. It is not, therefore, possible to compare subtype and drug specific data.
Influenza B viruses tend to have IC50 values 10-100 fold higher than influenza A viruses. This is normal for influenza B and this lower susceptibility does not appear to have a significant clinical impact. IC50 values for influenza B viruses tend to be higher for oseltamivir than zanamivir. IC50 values for H1N1 viruses tend to be higher for zanamivir than oseltamivir, whereas the inverse is true for H3N2 viruses where IC50 values tend to be higher for oseltamivir than zanamivir.
Furthermore, values generated by fluorescence and chemiluminescence methods should not be compared as values generated by chemiluminescence are typically lower than those for the same virus and drug in the fluorescence test. IC50 values generated from the different assay methods should not be directly compared.
Whilst there is no absolute definition of resistance, due, in part, to lack of global agreement, true resistance is usually classified as an IC50 value at least 10 times greater than the mean IC50 for similar viruses in the same influenza season.
Table: Neuraminidase inhibitor resistance mutations generated and characterised in vitro
Neuraminidase
mutationSubtype Occurrence NAI susceptibility (IC50 fold change) Reference(s) Oseltamivir Zanamivir Peramivir Functional residues R292K H3N2 In clinic R 1 H3N2 RG R (>1580) RS (2.5) RS (14) 2, 3, 4 H3N2 RG R (>30 000) RS (13) 2, 3, 4 B RG R (>300) RS (28) R (500) 5 D151E H3N2 RG RS (10) S (2) 4 R152K H3N2 RG S (1) S (2) 4 B RG R (252) RS (4.7) R (214) 5 R224K H3N2 RG R (>4000) R (>50) 4 E276D H3N2 RG R (15) R (160) 4 R371K H3N2 RG R (45) R (15) 4 Framework residues H274Y H1N1 Clinical trial R (3000) 6 H1N1 RG R (247) S R 7 H3N2 RG S S S 2 H5N1 RG R (1672) S (2) 8 N294S H1N1 RG R(113) 7 H5N1 RG R (21) RS(3) 8 E119V H3N2 Clinical trial R 9 H3N2 RG R (200) S 2, 3, 9 H3N2 RG R (18) S (0.8) S (0.7) 2 B RG R (300) S (1.9) R (531) 5 E119D H3N2 RG S (1.6) R (32) S (2.2) 2 B RG R (>300) R (>560) R (>1598) 5 E119G B In vitro R 10 B RG RS (31) R (>560) R (1598) 5 E119A B RG R (>300) R (>560) R (1598) 5
R = resistant; RS = reduced susceptibility; S = sensitive; RG = reverse genetics
All comments regarding sensitivity/resistance are as made by the authors of individual papers
Table adapted from:
Ferraris et al, 2008. J Clin Virol 41: 13-19.
Lackenby et al, 2008. Curr Opin Infect Dis21: 626-638.
References:
1. Carr J, Ives J, Kelly L, Lambkin R, Oxford J, Mendel D, Tai L, Roberts N (2002). Influenza virus carrying neuraminidase with reduced sensitivity to oseltamivir carboxylate has altered properties in vitro and is compromised for infectivity and replicative ability in vivo. Antiviral Res; 54: 79-88.
2. Zurcher T, Yates PJ, Daly J, et al. Mutations conferring zanamivir resistance in human influenza N2 neuraminidases compromise virus fitness andare not stably maintained in vitro. J Antimicrob Chemother 2006; 58: 723-732.
3. Yen H-L, Herlocher LM, Hoffman E, et al. Neuraminidase inhibitor-resistant influenza viruses may differ substantially in fitness and transmissibility. Antimicrob Agents Chemother 2005; 49: 4075-4084; 10.1128/AAc.49. 10.4075-4084.2005.
4. Yen H-L, Hoffmann E, Taylor G, et al. Importance of neuraminidase active-site residues to the neuraminidase inhibitor resistance of influenza viruses. J Virol 2006; 80: 8787-8795.
5. Jackson D, Barclay W, Zurcher T. Characterisation of recombinant influenza B viruses with key neuraminidase inhibitor resistance mutations. J Antimicrob Chemother 2005; 55:162-169
6. Ives JA, Carr JA, Mendel DB, et al. The H274Y mutation in the influenza A/H1N1 neuraminidase active site following oseltamivir phosphate treatment leave virus severely compromised both in vitro and in vivo. Antiviral Res. 2002 Aug;55(2):307-17.
7. Abed Y, Baz M, Biovin G. Impact of neuraminidase mutations conferring influenza resistance to neuraminidase inhibitors in the N1 and N2 genetic backgrounds. Antivir Ther 2006; 114: 971-976.
8. Yen HL, Ilyushina NA, Salomon R, et al. Neuraminidase inhibitor-resistant recombinant A/Vietnam/1203/04 (H5N1) influenza viruses retain their replication efficiency and pathogenicity in vitro and in vivo. J Virol 2007; 81: 12418-12426.
9. Baz M, Abed Y, McDonald J, Boivin G. Characterisation of multidrug-resistant influenza A/H3N2 viruses shed during year 1 by an immunocompromised child. Clin Infect Dis 2006; 43: 1555-61.
10. Barnett JM, Cadman A, Burrell FM, et al. In vitro selection and characterisation of influenza B/Beijing/1/87 isolates with altered susceptibility to zanamivir. Virology 1999; 265; 268-295
