In vitro efficacy of anti-influenza active compounds against clinical isolates with high growth capability

Highly replicative influenza viruses have been linked to elevated nasopharyngeal viral load in patients, while in murine model these viruses are associated with amplified cytokine responses, and greater severity. In the present study, five anti-influenza agents-including four neuraminidase inhibitors (zanamivir, laninamivir, peramivir, and oseltamivir acid) and one polymerase acidic endonuclease inhibitor (baloxavir acid)-were evaluated against both a laboratory strain (PR8) and four clinical isolates lacking known resistance mutations. Madin-Darby Canine Kidney (MDCK) and A549 human lung epithelial cells were inoculated at 1x10⁵ and 3x10⁵ virus copies/mL, respectively, and exposed to varying concentrations of the drug for 72 hours. Subsequent analysis measured viral loads and infectious units. Both classes of antiviral drugs demonstrated substantial activity, particularly against strains that proliferate rapidly in vitro. While all tested anti-influenza drugs reduced viral particles production by approximately 50% in clinical isolates, achieving 90% suppression with neuraminidase inhibitors was limited to the PR8 laboratory strain. In A549 cell cultures, PR8 showed a 90% reduction in viral particles production with any of the compounds; however, neuraminidase inhibitors typically had diminished impact on clinical isolates. Notably, baloxavir acid consistently achieved robust suppression in both the PR8 strain and clinical isolates in MDCK and A549 cell lines. The present study finds that antiviral drugs can significantly impact highly replicative influenza viruses, but do not always suppress them to undetectable levels. Effectiveness varies by the epidemic strains, likely due to unknown genetic factors. Further research is needed to identify these traits and improve diagnosis and treatment.