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Several epidemics of influenza have hit the headlines in recent years; they can destroy livestock farms in affected areas and generate serious economic problems in these regions.  New influenza viruses have appeared and constitute a threat to human health because they are capable of crossing the barriers from animals to man.  To contain these animal and human epidemics, the therapeutic arsenal is sadly devoid curative solutions, and indeed, new influenza vaccines need to be developed each year because the surface proteins they target can mutate rapidly.

The influenza A virus and nucleoproteins

The most recent influenza epidemics (in 2009) involved type A viruses.  The influenza A virus belongs to the orthomyxoviridae family.  Genetic information of the virus is carried by eight fragments of ribonucleic acid (RNA).  These RNA fragments are closely associated with nucleoproteins (NP).  The NP protein is well conserved and displays strong sequence homologies between the different strains of influenza virus (A, B and C).  NP interacts not only with RNA but also with viral and cellular proteins in the infected host cell. NP binds to viral polymerase to form complex structures called ribonucleoproteins (RNP).  Because of their role in replication and transcription, these RNP are essential to viral proliferation.

The Flunucleovir project or two-in-one: anti-inflammatory Naproxen displays anti-viral activity against influenza A

Working in collaboration with CNRS researchers from Grenoble in the context of the ANR project FLUNUCLEOVIR, led by an INSERM scientists, the INRA research team in the Molecular Virology and Immunology Laboratory (VIM) in Jouy-en-Josas found a much more stable, reliable target for anti-influenza activity.  Their research targeted the nucleoprotein, that prevents the assembly of RNP complexes, and their findings were obtained by means of structure-based investigations. The research was published in April 2013 in Antimicrobial Agents and Chemotherapy. The three-dimensional structure of the nucleoprotein provided the basis for the determination of new drugs that could interfere with its action. A virtual screening procedure was performed within the Sigma-Aldrich catalogue of biochemicals, and was able to identify naproxen as a potential agent.  As expected, it bound to the nucleoprotein, and impeded RNA binding. Naproxen exerts antiviral activity against the influenza A virus: further testing showed that it could reduce the viral load in cells infected with H1N1 and H3N2 influenza A viruses, and in vivo displayed a therapeutic index against influenza A that was superior to that of any other anti-inflammatory drugs. Naproxen is now one of the lead compounds for drug development, which could be improved by tweaking the molecule to boost its ability to bind to nucleoprotein. As an authorised therapeutic agent, it could be introduced as a treatment for influenza relatively rapidly.  According to Slama-Schwok, the project coordinator, and the other researchers“. . .naproxen has the advantage of inhibiting both COX-2 and the nucleoprotein of influenza A virus”.

These findings have now been patented (WO2012143141) and constitute an important step towards the development of antiviral compounds.

	3D view of the NP protein Binding of the nucleoprotein to the RNA can be blocked by the drug Naproxen, following its fixation in the RNA groove (colored blue in the picture). Detailed interactions are shown in the box. © VIM-INRA

In the future, it will be possible to increase their affinity for crucial regions in NP using rational design methods, and to develop antivirals on a “tailor-made” basis in order to enhance their efficacy.  Such compounds are currently under development.

The research team is now seeking industrial partners in order to exploit these findings.