Early antiviral activity of CYSTUS052 against H5N1 influenza virus is more efficient compared to oseltamivir

Influenza still represents a major threat to humans. The appearance of highly pathogenic avian influenza viruses of the H5N1 subtype being able to infect humans reveals the urgent need for new and efficient countermeasures against this disease. Several antiviral compounds have been developed against influenza virus, their long-term efficacy is often limited, because of their toxicity or the emergence of drug-resistant virus mutants. Moreover, neuraminidase inhibitors the most common anti-influenza agents are less effective against new H5N1 isolates. In this regard, we were able to show that a polyphenol rich plant extract from a special variety of Cistus incanus named CYSTUS052 exhibits antiviral activity against influenza viruses in vitro, in a mouse model and in clinical patents. The protective effect of CYSTUS052 appears to be mainly due to binding of the polymeric polyphenol components of the extract to the virus surface, thereby inhibiting binding of the hemagglutinin to cellular receptors. In addition, we investigated the antiviral potential of CYSTUS052 in comparison to oseltamivir against various H5N1 influenza viruses. We tested the antiviral efficacy of a single treatment with CYSTUS052 or oseltamivir, against six H5N1 viruses with avian or human origin. Using an in vitro infectivity inhibition assay we found that during the first 24 hours after infection a single treatment of CYSTUS052 is up to 100 fold more effective against these H5N1 viruses compared to oseltamivir. We conclude that CYSTUS052 given prior to infection might be an effective antiviral with prophylactic potential against influenza viruses including A/H5N1.