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Abstract
Influenza A viruses (IAV) have been a major public health threat worldwide, and options for antiviral therapy become increasingly limited with the emergence of drug-resisting virus strains. New and effective anti-IAV drugs, especially for highly pathogenic influenza, with different modes of action, are urgently needed. The influenza virus glycoprotein hemagglutinin (HA) plays critical roles in the early stage of virus infection, including receptor binding and membrane fusion, making it a potential target for the development of anti-influenza drugs. In this study, we show that OA-10, a newly synthesized triterpene out of 11 oleanane-type derivatives, exhibited significant antiviral activity against four different subtypes of IAV (H1N1, H5N1, H9N2 and H3N2) replications in A549 cell cultures with EC50 ranging from 6.7 to 19.6 μM and a negligible cytotoxicity (CC50 > 640 μM). It inhibited acid-induced hemolysis in a dose-dependent manner, with an IC50 of 26 µM, and had a weak inhibition on the adsorption of H5 HA to chicken erythrocytes at higher concentrations (≥40 µM). Surface plasmon resonance (SPR) analysis showed that OA-10 interacted with HA in a dose-dependent manner with the equilibrium dissociation constants (KD) of the interaction of 2.98 × 10−12 M. Computer-aided molecular docking analysis suggested that OA-10 might bind to the cavity in HA stem region which is known to undergo significant rearrangement during membrane fusion. Our results demonstrate that OA-10 inhibits H5N1 IAV replication mainly by blocking the conformational changes of HA2 subunit required for virus fusion with endosomal membrane. These findings suggest that OA-10 could serve as a lead for further development of novel virus entry inhibitors to prevent and treat IAV infections.
Highlights
Influenza A virus (IAV), the causative agent of influenza, is a major pathogen that causes public health problem and socioeconomic burden world-wide
We found that the introduction of a disubstituted amide structure at the 17-COOH of Oleanane acid (OA) could significantly improve the selective index while maintaining their antiviral activities in vitro [27]
Inhibit H5 HA adsorption to chicken red blood cells (RBCs) with a titer at 1:16, and the settled RBCs could move when properties in the absence of H5 virus, and the positive control antisera against H5 hemagglutinin the plate was tilted (Figure 5A). These results indicated that OA-10 might have a weak interaction with (Anti-H5) could effectively inhibit H5 HA adsorption to chicken RBCs with a titer at 1:16, and the the receptor binding domain of H5 HA1, which needs further demonstration
Summary
Influenza A virus (IAV), the causative agent of influenza, is a major pathogen that causes public health problem and socioeconomic burden world-wide. With waterfowl as the primary reservoir, the virus is able to infect a wide variety of birds and mammals, including humans. Due to this trait, Viruses 2020, 12, 225; doi:10.3390/v12020225 www.mdpi.com/journal/viruses. The avian-origin H5N1 and H7N9 subtypes of influenza viruses are recent examples of animal viruses that acquired the potential to infect and cause disease in humans. In 1997 in Hongkong, six people died out of 18 confirmed human cases with HP H5N1 virus infection [3]. In 2003, novel H5N1 IAV genetic variants circulated in Southeast Asian countries, which led innumerable poultry to death and caused sporadic human infections in the following years. By the end of 2017, 860 laboratory confirmed cases of H5N1 IAV infection from 16 different countries, resulting in 454 deaths, had been reported to the
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