The outbreak of an influenza pandemic as well as the continued circulation of seasonal influenza highlights the need for effective antiviral therapies. The emergence of drug-resistant strains further necessitates the development of novel antivirals that target the host factors crucial for viral replication. Area covered: This review summarizes the current understanding of the structural and functional properties of type II transmembrane serine proteases (TTSPs) as a proteolytic activator of influenza virus infection and discusses their potential as antiviral targets. It also explores the experimental evidence accumulated for inhibitors of TTSPs as novel, broad-spectrum antivirals against various influenza virus subtypes. The review also provides an overview of the properties of small molecules, proteins, and peptides that efficiently inhibit the proteolytic activation of the influenza virus. Expert opinion: TTSPs activate a wide range of influenza virus subtypes including avian influenza viruses, both in vitro and in vivo, via proteolytic cleavage of influenza hemagglutinin (HA) into infection-competent fusogenic conformation. Other viruses such as SARS-, MERS-coronaviruses and human metapneumoviruses may use the same host cell proteases for activation, implying that TTSP inhibition might be a novel strategy for developing broad-spectrum antiviral agents for respiratory viral infections.
Keywords: Influenza virus; antiviral; drug discovery; novel antiviral target; type II transmembrane serine protease.