Comparison of the activities of zanamivir, oseltamivir, and RWJ-270201 against clinical isolates of influenza virus and neuraminidase inhibitor-resistant variants

RWJ-270201 is a novel cyclopentane inhibitor of influenza A and B virus neuraminidases (NAs). We compared the ability of RWJ-270201 to inhibit NA activity of clinical influenza isolates and viruses with defined resistance mutations with that of zanamivir and oseltamivir carboxylate. In NA inhibition assays with influenza A viruses, the median 50% inhibitory concentration (IC50) of RWJ-270201 (approximately 0.34 nM) was comparable to that of oseltamivir carboxylate (0.45 nM) but lower than that of zanamivir (0.95 nM). For influenza B virus isolates, the IC50 of RWJ-270201 (1.36 nM) was comparable to that of zanamivir (2.7 nM) and less than that of oseltamivir carboxylate (8.5 nM). A zanamivir-resistant variant bearing a Glu119-to-Gly (Glu119 --> Gly) or Glu119 --> Ala substitution in an NA (N2) remained susceptible to RWJ-270201 and oseltamivir carboxylate. However, a zanamivir-selected variant with an Arg292 --> Lys substitution in an NA (N2) showed a moderate level of resistance to RWJ-270201 (IC50 = 30 nM) and zanamivir (IC50 = 20 nM) and a high level of resistance to oseltamivir carboxylate (IC50 > 3,000 nM). The zanamivir-resistant influenza B virus variant bearing an Arg152 --> Lys substitution was resistant to each NA inhibitor (IC50 = 100 to 750 nM). The oseltamivir-selected variant (N1) with the His274 --> Tyr substitution exhibited resistance to oseltamivir carboxylate (IC50 = 400 nM) and to RWJ-270201 (IC50 = 40 nM) but retained full susceptibility to zanamivir (IC50 = 1.5 nM). Thus, drug-resistant variants with substitutions in framework residues 119 or 274 can retain susceptibility to other NA inhibitors, whereas replacement of functional residue 152 or 292 leads to variable levels of cross-resistance. We conclude that RWJ-270201 is a potent inhibitor of NAs of wild-type and some zanamivir-resistant or oseltamivir-resistant influenza A and B virus variants.