Molecular Mechanism Underlying the Action of Influenza A Virus Fusion Inhibitor MBX2546

Influenza viruses are a major public health threat worldwide, and options for antiviral therapy are becoming limited by the emergence of drug-resistant virus strains. The influenza virus glycoprotein hemagglutinin (HA) plays critical roles in the early stage of virus infection making it a potential target for the development of anti-influenza drugs. We have identified a novel influenza virus inhibitor, MBX2546, with sulfonamide scaffolds that specifically inhibit HA-mediated viral entry. The compound has selectivity index (SI) values of >20 to 200 for different influenza virus strains; and inhibits a wide spectrum of influenza A viruses, including 2009 pandemic influenza virus A/H1N1/2009, highly pathogenic avian influenza (HPAI) virus A/H5N1, and oseltamivir-resistant A/H1N1 strains. It also exhibits large volumes of synergy with oseltamivir (36 μM(2) % at 95% confidence). Mechanism-of-action studies suggest that MBX2546 binds to HA in the stem region of the HA trimer and inhibits HA-mediated fusion. Further studies suggest that the binding of HA by MBX2546 inhibits the low-pH-induced conformational change in the HA, which is a prerequisite for membrane fusion. Mutations in MBX2546-resistant influenza A/PR/8/34 (H1N1) viruses are mapped in the HA stem region near the amino terminus of HA2. Finally, we have modeled the binding site of MBX2546 using molecular dynamics and find that the resulting structure is in good agreement with our results. Therefore, MBX2546 represents a new starting point for chemical optimization and have the potential to provide valuable future therapeutic options and research tools to study the HA-mediated entry process. It also underscores the importance of the HA stem loop region as a potential target for therapeutic intervention.