Drug Discovery
Program leader: Richard Whitley
SE-RP-015: Fusion inhibitors of H5N1 influenza
University of Alabama at Birmingham
Emerging avian influenza viruses pose an increasing threat to domestic poultry and human health. Since 2003 highly pathogenic avian influenza (HPAI) H5N1 viruses have spread to wild bird populations across Asia, Europe and Africa. In 2009, a widely spread new H1N1 influenza A virus was identified that contains segments of human, avian and swine origins. New antiviral drugs may be needed if neuraminidase inhibitors face drug resistant viruses. We hypothesize that fusion inhibitors currently under development in my lab will be potent against diverse virus strains, especially HPAI viruses, and will provide synergistic decreases in drug resistance and infectious disease when used in combination therapies. We propose the following specific aims to further develop these inhibitors:
Aim 1. Identify fusion inhibitors that are potent against diverse strains of H5N1 influenza viruses.
Our preliminary studies have identified a group of lead compounds that have EC50 values in single digit nanomoles across diverse influenza virus strains including H5N3 (vaccine strain), H3N2, H1N1 and type B. To identify potential candidates for preclinical and eventual clinical studies against HPAI H5N1 viruses, we propose to develop a library of analogs based on the initial lead. We propose to measure the inhibitory potencies of candidate compounds against diverse strains of H5N1 influenza viruses.
Aim 2. Determine the mechanisms of action of fusion protein inhibitors.
The preliminary studies showed that the fusion inhibitors we have developed alter the structure of HA. To map the binding sites of compounds, we have co-crystallized the HA protein with a bound inhibitor. However, later experiments suggested that the fusion inhibitor may interact with the lipid envelope and the transmembrane domain of the hemagglutinin. Further studies will be carried out to delineate the mechanism of action by the fusion inhibitors.
Aim 3. Determine if drug combinations that include fusion inhibitors provide advantages over existing single-agent therapies in protecting against disease and avoiding drug resistance.
A widespread use of fusion inhibitors could result in the emergence of drug-resistant viruses, similar to the acquisition of drug resistance that has been observed for neuraminidase (NA) and M2 inhibitors. We hypothesize that the use of fusion inhibitors in combination with existing NA and/or M2 inhibitors will help counteract drug resistance and decrease the severity of infectious disease. We propose to determine the efficacy of fusion inhibitors in vitro and in vivo, alone or in combination with another inhibitor. We will study the synergy provided by combination therapy against H5N1 influenza viruses.
There are no significant changes in our specific aims. In the current period, we conducted a number of studies in the mouse model of influenza virus infection using A/PR/8/34 influenza virus. The studies showed that one of the fusion inhibitors can increase the survival rate of infected mice as well as the mead time to death (MDT). The preliminary result will be confirmed with a larger number of animals in the next period. Our study also revealed that a mutation in the transmembrane region could confer drug-resistant by the mutant virus, suggesting a binding mode of interacting with the lipid envelope and the TM domain of HA. In addition, a second group of fusion inhibitors designed by use of extensive SAR studies was developed that clearly limits virus spread based on plaque assays. This group of inhibitors showed favorable pharmacokinetic properties and will be tested in our animal model in the next period.
