Human Coronavirus OC43 as a Low-Risk Model to Study COVID-19.

The coronavirus disease 2019 (COVID-19) pandemic has had irreversible and devastating impacts on every aspect of human life. To better prepare for the next similar pandemic, a clear understanding of coronavirus biology is a prerequisite. Nevertheless, the high-risk nature of the causative agent of COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), requires the use of a cumbersome biosafety level-3 (BSL-3) confinement facility. To facilitate the development of preventive and therapeutic measures against SARS-CoV-2, one of the endemic strains of low-risk coronaviruses has gained attention as a useful research alternative: human coronavirus OC43 (HCoV-OC43). In this review, its history, classification, and clinical manifestations are first summarized. The characteristics of its viral genomes, genes, and evolution process are then further explained. In addition, the host factors necessary to support the life cycle of HCoV-OC43 and the innate, as well as adaptive, immunological responses to HCoV-OC43 infection are discussed. Finally, the development of in vitro and in vivo systems to study HCoV-OC43 and its application to the discovery of potential antivirals for COVID-19 by using HCoV-OC43 models are also presented. This review should serve as a concise guide for those who wish to use HCoV-OC43 to study coronaviruses in a low-risk research setting.

Identification of brevinin-1EMa-derived stapled peptides as broad-spectrum virus entry blockers.

Based on the previously reported 13-residue antibacterial peptide analog, brevinin-1EMa (FLGWLFKVASKVL, peptide B), we attempted to design a novel class of antiviral peptides. For this goal, we synthesized three peptides with different stapling positions (B-2S, B-8S, and B-5S). The most active antiviral peptide with the specific stapling position (B-5S) was further modified in combination with either cysteine (B-5S3C, B-5S7C, and B-5S10C) or hydrophilic amino acid substitution (Bsub and Bsub-5S). Overall, B, B-5S, and Bsub-5S peptides showed superior antiviral activities against enveloped viruses such as retrovirus, lentivirus, hepatitis C virus, and herpes simplex virus with EC50 values of 1-5 µM. Murine norovirus, a non-enveloped virus, was not susceptible to the virucidal actions of these peptides, suggesting the virus membrane disruption as their main antiviral mechanisms of action. We believe that these three novel peptides could serve as promising candidates for further development of membrane-targeting antiviral drugs in the future.

Identification of novel non-nucleoside vinyl-stilbene analogs as potent norovirus replication inhibitors with a potential host-targeting mechanism.

Norovirus (NV), is the most common cause of acute gastroenteritis worldwide. To date, there is no specific anti-NV drug or vaccine to treat NV infections. In this study, we evaluated the inhibitory effect of different stilbene-based analogs on RNA genome replication of human NV (HNV) using a virus replicon-bearing cell line (HG23). Initial screening of our in-house chemical library against NV led to the identification of a hit containing stilbene scaffold 5 which on initial optimization gave us a vinyl stilbene compound 16c (EC50 = 4.4 µM). Herein we report our structure-activity relationship study of the novel series of vinyl stilbene analogs that inhibits viral RNA genome replication in a human NV-specific manner. Among these newly synthesized compounds, several amide derivatives of vinyl stilbenes exhibited potent anti-NV activity with EC50 values ranging from 1 to 2 µM. A trans-vinyl stilbenoid with an appended substituted piperazine amide (18k), exhibited potent anti-NV activity and also displayed favorable metabolic stability. Compound 18k demonstrated an excellent safety profile, the highest suppressive effect, and was selective for HNV replication via a viral RNA polymerase-independent manner. Its potential host-targeting antiviral mechanism was further supported by specific activation of heat shock factor 1-dependent stress-inducible pathway by 18k. These results suggest that 18k might be a promising lead compound for developing novel NV inhibitors with the novel antiviral mechanism.

Plant-Derived Purification, Chemical Synthesis, and In Vitro/In Vivo Evaluation of a Resveratrol Dimer, Viniferin, as an HCV Replication Inhibitor.

Oligostilbenoid compounds, a group of resveratrol multimers, display several anti-microbial activities through the neutralization of cytotoxic oxidants, and by inhibiting essential host and viral enzymes. In our previous study, we identified a series of oligostilbenoid compounds as potent hepatitis C virus (HCV) replication inhibitors. In particular, vitisin B, a resveratrol tetramer, exhibited the most dramatic anti-HCV activity (EC50 = 6 nM and CC50 > 10 µM) via the disruption of the viral helicase NS3 (IC50 = 3 nM). However, its further development as an HCV drug candidate was halted due to its intrinsic drawbacks, such as poor stability, low water solubility, and restricted in vivo absorption. In order to overcome these limitations, we focused on (+)-ε-viniferin, a resveratrol dimer, as an alternative. We prepared three different versions of (+)-ε-viniferin, including one which was extracted from the grapevine root (EVF) and two which were chemically synthesized with either penta-acetylation (SVF-5Ac) or no acetylation (SVF) using a newly established synthesis method. We confirmed their anti-HCV replication activities and minimal cytotoxicity by using genotype 1b and 2a HCV replicon cells. Their anti-HCV replication action also translated into a significant reduction of viral protein expression. Anti-HCV NS3 helicase activity by EVF was also verified in vitro. Finally, we demonstrated that SVF has improved pharmacokinetic properties over vitisin B. Overall, the favorable antiviral and pharmacokinetic properties of these three versions of viniferin warrant their further study as members of a promising new class of anti-HCV therapeutics.

Suppression of Hepatitis C Virus Genome Replication and Particle Production by a Novel Diacylglycerol Acyltransferases Inhibitor.

Diacylglycerol acyltransferases (DGATs) play a critical role in the biosynthesis of endogenous triglycerides (TGs) and formation of lipid droplets (LDs) in the liver. In particular, one member of DGATs, DGAT-1 was reported to be an essential host factor for the efficient production of hepatitis C virus (HCV) particles. By utilizing our previously characterized three different groups of twelve DGAT inhibitors, we found that one of the DGAT inhibitors, a 2-((4-adamantylphenoxy) methyl)-N-(furan-2-ylmethyl)-1H-benzo[d]imidazole-5-carboxam (10j) is a potent suppressor of both HCV genome replication and particle production. 10j was able to induce inhibition of these two critical viral functions in a mutually separate manner. Abrogation of the viral genome replication by 10j led to a significant reduction in the viral protein expression as well. Interestingly, we found that its antiviral effect did not depend on the reduction of TG biosynthesis by 10j. This suggests that the inhibitory activity of 10j against DGATs may not be directly related with its antiviral action.