Influenza A (IAV) and
influenza B (IBV) viruses are highly contagious pathogens that cause fatal respiratory disease every year, with high economic impact. In addition, IAV can cause pandemic
infections with great consequences when new viruses are introduced into humans. In this study, we evaluated 10 previously described compounds with
antiviral activity against mammarenaviruses for their ability to inhibit IAV
infection using our recently described bireporter
influenza A/Puerto Rico/8/34 (PR8) H1N1 (BIRFLU). Among the 10 tested compounds, eight (
antimycin A [AmA],
brequinar [BRQ],
6-azauridine,
azaribine,
pyrazofurin [PF],
AVN-944,
mycophenolate mofetil [MMF], and
mycophenolic acid [MPA]), but not
obatoclax or
Osu-03012, showed potent anti-influenza virus activity under posttreatment conditions [median 50% effective concentration (EC50) = 3.80 nM to 1.73 μM; selective index SI for
3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, >28.90 to 13,157.89]. AmA,
6-azauridine,
azaribine, and PF also showed potent inhibitory effect in pretreatment (EC50 = 0.14 μM to 0.55 μM; SI-MTT = 70.12 to >357.14) or cotreatment (EC50 = 34.69 nM to 7.52 μM; SI-MTT = 5.24 to > 1,441.33) settings. All of the compounds tested inhibited viral genome replication and gene transcription, and none of them affected host cellular
RNA polymerase II activities. The
antiviral activity of the eight identified compounds against BIRFLU was further confirmed with seasonal IAVs (A/California/04/2009 H1N1 and A/Wyoming/3/2003 H3N2) and an IBV (B/Brisbane/60/2008, Victoria lineage), demonstrating their broad-spectrum prophylactic and therapeutic activity against currently circulating influenza viruses in humans. Together, our results identified a new set of
antiviral compounds for the potential treatment of
influenza viral infections.IMPORTANCE Influenza viruses are highly contagious pathogens and are a major threat to human health. Vaccination remains the most effective tool to protect humans against
influenza infection. However, vaccination does not always guarantee complete protection against drifted or, more noticeably, shifted influenza viruses. Although U.S. Food and Drug Administration (FDA) drugs are approved for the treatment of
influenza infections, influenza viruses resistant to current FDA
antivirals have been reported and continue to emerge. Therefore, there is an urgent need to find novel
antivirals for the treatment of
influenza viral infections in humans, a search that could be expedited by repurposing currently approved drugs. In this study, we assessed the
influenza antiviral activity of 10 compounds previously shown to inhibit mammarenavirus
infection. Among them, eight drugs showed
antiviral activities, providing a new battery of drugs that could be used for the treatment of
influenza infections.