The emergence of the 2009 H1N1 pandemic swine influenza A virus is a good example of how this viral infection can impact health systems around the world in a very short time. The continuous zoonotic circulation and reassortment potential of influenza A viruses (IAV) in nature represents an enormous public health threat to humans. Beside vaccination antivirals are needed to efficiently control spreading of the disease. In the present work we investigated whether the MEK inhibitor U0126, targeting the intracellular Raf/MEK/ERK signaling pathway, is able to suppress propagation of the 2009 pandemic IV H1N1v (v=variant) as well as highly pathogenic avian influenza viruses (HPAIV) in cell culture and also in vivo in the mouse lung. U0126 showed antiviral activity in cell culture against all tested IAV strains including oseltamivir resistant variants. Furthermore, we were able to demonstrate that treatment of mice with U0126 via the aerosol route led to (i) inhibition of MEK activation in the lung (ii) reduction of progeny IAV titers compared to untreated controls (iii) protection of IAV infected mice against a 100× lethal viral challenge. Moreover, no adverse effects of U0126 were found in cell culture or in the mouse. Thus, we conclude that U0126, by inhibiting the cellular target MEK, has an antiviral potential not only in vitro in cell culture, but also in vivo in the mouse model.
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