The NA inhibitors oseltamivir carboxylate (oseltamivir; Hoffman-La Roche) and zanamivir (GlaxoSmithKline) were prepared in sterile distilled water and stored in aliquots at − 30 °C until use.
Inhibition of NA enzyme activity by the 2 NA inhibitors was assessed in the fluorescence-based NA inhibition assay using the NA-Fluor Influenza Neuraminidase Assay Kit (Applied Biosystems, ThermoFisher) as previously described [15 (link)]. IC50 values, defined as the concentration of drug required to reduce enzyme activity by 50%, were calculated using GraphPad Prism 5 software. The IC50 values reported are the means (±SD) of IC50 values measured for at least 2 independent tests with 2 duplicates for each sample. Interpretation of IC50 values (obtained by comparing the test virus with the drug-sensitive reference virus) was performed using the WHO AVWG criteria for influenza A viruses: a < 10-fold increase in IC50 represents normal inhibition, a 10~100-fold increase represents reduced inhibition, while a > 100-fold increase is highly reduced inhibition.
Inhibition of NA enzyme activity by the 2 NA inhibitors was assessed in the fluorescence-based NA inhibition assay using the NA-Fluor Influenza Neuraminidase Assay Kit (Applied Biosystems, ThermoFisher) as previously described [15 (link)]. IC50 values, defined as the concentration of drug required to reduce enzyme activity by 50%, were calculated using GraphPad Prism 5 software. The IC50 values reported are the means (±SD) of IC50 values measured for at least 2 independent tests with 2 duplicates for each sample. Interpretation of IC50 values (obtained by comparing the test virus with the drug-sensitive reference virus) was performed using the WHO AVWG criteria for influenza A viruses: a < 10-fold increase in IC50 represents normal inhibition, a 10~100-fold increase represents reduced inhibition, while a > 100-fold increase is highly reduced inhibition.
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