Neuraminidase inhibitors (NAIs) play a major role for managing influenza virus
infections. The widespread
oseltamivir resistance among 2007-2008 seasonal A(H1N1) viruses and community outbreaks of
oseltamivir-resistant A(H1N1)pdm09 strains highlights the need for additional anti-influenza virus agents.
Laninamivir is a novel long-lasting NAI that has demonstrated in vitro activity against
influenza A and B viruses, and its
prodrug (
laninamivir octanoate) is in phase II clinical trials in the United States and other countries. Currently, little information is available on the mechanisms of resistance to
laninamivir. In this study, we first performed
neuraminidase (NA) inhibition assays to determine the activity of
laninamivir against a set of influenza A viruses containing NA mutations conferring resistance to one or many other NAIs. We also generated
drug-resistant A(H1N1) and A(H3N2) viruses under in vitro
laninamivir pressure.
Laninamivir demonstrated a profile of susceptibility that was similar to that of
zanamivir. More specifically, it retained activity against
oseltamivir-resistant H275Y and N295S A(H1N1) variants and the E119V A(H3N2) variant. In vitro,
laninamivir pressure selected the E119A NA substitution in the A/Solomon Islands/3/2006 A(H1N1) background, whereas E119K and G147E NA changes along with a K133E
hemagglutinin (HA) substitution were selected in the A/Quebec/144147/2009 A(H1N1)pdm09 strain. In the A/Brisbane/10/2007 A(H3N2) background, a large NA deletion accompanied by S138A/P194L HA substitutions was selected. This H3N2 variant had altered receptor-binding properties and was highly resistant to
laninamivir in plaque reduction assays. Overall, we confirmed the similarity between
zanamivir and
laninamivir susceptibility profiles and demonstrated that both NA and HA changes can contribute to
laninamivir resistance in vitro.