Evaluation of Small Molecule Combinations against Respiratory Syncytial Virus In Vitro

Respiratory syncytial virus (RSV) is a major pathogen that causes severe lower respiratory tract infection in infants, the elderly and the immunocompromised worldwide. At present no approved specific drugs or vaccines are available to treat this pathogen. Recently, several promising candidates targeting RSV entry and multiplication steps are under investigation. However, it is possible to lead to drug resistance under the long-term treatment. Therapeutic combinations constitute an alternative to prevent resistance and reduce antiviral doses. Therefore, we tested in vitro two-drug combinations of fusion inhibitors (GS5806, Ziresovir and BMS433771) and RNA-dependent RNA polymerase complex (RdRp) inhibitors (ALS8176, RSV604, and Cyclopamine). The statistical program MacSynergy II was employed to determine synergism, additivity or antagonism between drugs. From the result, we found that combinations of ALS8176 and Ziresovir or GS5806 exhibit additive effects against RSV in vitro, with interaction volume of 50 µM²% and 31 µM²% at 95% confidence interval, respectively. On the other hand, all combinations between fusion inhibitors showed antagonistic effects against RSV in vitro, with volume of antagonism ranging from −50 µM² % to −176 µM² % at 95% confidence interval. Over all, our results suggest the potentially therapeutic combinations in combating RSV in vitro could be considered for further animal and clinical evaluations.

Broad-Spectrum Coronavirus Fusion Inhibitors to Combat COVID-19 and Other Emerging Coronavirus Diseases

In the past 17 years, three novel coronaviruses have caused severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and the coronavirus disease 2019 (COVID-19). As emerging infectious diseases, they were characterized by their novel pathogens and transmissibility without available clinical drugs or vaccines. This is especially true for the newly identified COVID-19 caused by SARS coronavirus 2 (SARS-CoV-2) for which, to date, no specific antiviral drugs or vaccines have been approved. Similar to SARS and MERS, the lag time in the development of therapeutics is likely to take months to years. These facts call for the development of broad-spectrum anti-coronavirus drugs targeting a conserved target site. This review will systematically describe potential broad-spectrum coronavirus fusion inhibitors, including antibodies, protease inhibitors, and peptide fusion inhibitors, along with a discussion of their advantages and disadvantages.

Membrane Fusion and Infection of the Influenza Hemagglutinin

The influenza virus is a major health concern associated with an estimated 5000 to 30,000 deaths every year (Reed et al. 2015) and a significant economic impact with the development of treatments, vaccinations and research (Molinari et al. 2007). The entirety of the influenza genome is comprised of only eleven coding genes. An enormous degree of variation in non-conserved regions leads to significant challenges in the development of inclusive inhibitors for treatment. The fusion peptide domain of the influenza A hemagglutinin (HA) is a promising candidate for treatment since it is one of the most highly conserved sequences in the influenza genome (Heiny et al. 2007), and it is vital to the viral life cycle. Hemagglutinin is a class I viral fusion protein that catalyzes the membrane fusion process during cellular entry and infection. Impediment of the hemagglutinin's function, either through incomplete post-translational processing (Klenk et al. 1975; Lazarowitz and Choppin 1975) or through mutations (Cross et al. 2001), leads to non-infective virus particles. This review will investigate current research on the role of hemagglutinin in the virus life cycle, its structural biology and mechanism as well as the central role of the hemagglutinin fusion peptide (HAfp) to influenza membrane fusion and infection.

New influenza A Virus Entry Inhibitors Derived from the Viral Fusion Peptides

Influenza A viral (IAV) fusion peptides are known for their important role in viral-cell fusion process and membrane destabilization potential which are compatible with those of antimicrobial peptides. Thus, by replacing the negatively or neutrally charged residues of FPs with positively charged lysines, we synthesized several potent antimicrobial peptides derived from the fusogenic peptides (FPs) of hemagglutinin glycoproteins (HAs) of IAV. The biological screening identified that in addition to the potent antibacterial activities, these positively charged fusion peptides (pFPs) effectively inhibited the replication of influenza A viruses including oseltamivir-resistant strain. By employing pseudovirus-based entry inhibition assays including H5N1 influenza A virus (IAV), and VSV-G, the mechanism study indicated that the antiviral activity may be associated with the interactions between the HA2 subunit and pFP, of which, the nascent pFP exerted a strong effect to interrupt the conformational changes of HA2, thereby blocking the entry of viruses into host cells. In addition to providing new peptide “entry blockers”, these data also demonstrate a useful strategy in designing potent antibacterial agents, as well as effective viral entry inhibitors. It would be meaningful in treatment of bacterial co-infection during influenza pandemic periods, as well as in our current war against those emerging pathogenic microorganisms such as IAV and HIV.