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 (IC(50)) 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 IC(50) 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 (IC(50) = 30 nM) and
zanamivir (IC(50) = 20 nM) and a high level of resistance to
oseltamivir carboxylate (IC(50) > 3,000 nM). The
zanamivir-resistant influenza B virus variant bearing an Arg152-->Lys substitution was resistant to each NA inhibitor (IC(50) = 100 to 750 nM). The
oseltamivir-selected variant (N1) with the His274-->Tyr substitution exhibited resistance to
oseltamivir carboxylate (IC(50) = 400 nM) and to
RWJ-270201 (IC(50) = 40 nM) but retained full susceptibility to
zanamivir (IC(50) = 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.