Author:

Abstract:

Influenza is a highly contagious infectious disease that affects millions of people every year. In the twentieth century, influenza caused more fatalities in Europe than any other infectious disease. Current vaccines against influenza virus require annual updating due to continuous variation of the viral antigens. Thus, anti-influenza virus drugs are vital as a first line of defense. At present, two classes of antivirals are available: the neuraminidase inhibitors oseltamivir and zanamivir, and the M2 proton channel blockers amantadine and rimantadine. For both drug classes, viral resistance is an emerging concern and, hence, novel antiviral agents with an alternative mode of action and favorable resistance profile are urgently needed. A promising new target is the influenza virus PA endonuclease, which performs the "cap-snatching" reaction during viral mRNA synthesis, and is essential for virus replication. The crystal structure of the N-terminal part of PA (PA-Nter) containing the catalytic endonuclease domain, was recently revealed, enabling structure-based development of PA inhibitors. Our group synthesized and evaluated several analogues of the natural compound Flutimide (a fungus-derived influenza virus endonuclease inhibitor with a 2,6-diketo-Δ3-piperazine motif). Using an enzymatic PA endonuclease activity assay, we show that these compounds block the enzymatic activity of PA-Nter. Theoretical calculations are also undertaken for providing a structural rationale for the interaction between the synthesized analogues and the viral protein and a number of molecular interactions contributing to binding affinity and specificity were elucidated. Theoretical results are supported by biochemical analyses of the enzymatic activity inhibition. Overall, our data reveal exciting strategies for the design and optimization of novel influenza virus inhibitors that target the viral PA endonuclease.