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Journal: Antiviral research


Although several clinical trials are now underway to test possible therapies, the worldwide response to the COVID-19 outbreak has been largely limited to monitoring/containment. We report here that Ivermectin, an FDA-approved anti-parasitic previously shown to have broad-spectrum anti-viral activity in vitro, is an inhibitor of the causative virus (SARS-CoV-2), with a single addition to Vero-hSLAM cells 2 hours post infection with SARS-CoV-2 able to effect ∼5000-fold reduction in viral RNA at 48 h. Ivermectin therefore warrants further investigation for possible benefits in humans.


Recent publications have brought attention to the possible benefit of chloroquine, a broadly used antimalarial drug, in the treatment of patients infected by the novel emerged coronavirus (SARS-CoV-2). The scientific community should consider this information in light of previous experiments with chloroquine in the field of antiviral research.


In 2019, a new coronavirus (2019-nCoV) infecting Humans has emerged in Wuhan, China. Its genome has been sequenced and the genomic information promptly released. Despite a high similarity with the genome sequence of SARS-CoV and SARS-like CoVs, we identified a peculiar furin-like cleavage site in the Spike protein of the 2019-nCoV, lacking in the other SARS-like CoVs. In this article, we discuss the possible functional consequences of this cleavage site in the viral cycle, pathogenicity and its potential implication in the development of antivirals.


Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has resulted in a pandemic and continues to spread around the globe at an unprecedented rate. To date, no effective therapeutic is available to fight its associated disease, COVID-19. Our discovery of a novel insertion of glycosaminoglycan (GAG)-binding motif at S1/S2 proteolytic cleavage site (681-686 (PRRARS)) and two other GAG-binding-like motifs within SARS-CoV-2 spike glycoprotein (SGP) led us to hypothesize that host cell surface GAGs may interact SARS-CoV-2 SGPs to facilitate host cell entry. Using a surface plasmon resonance direct binding assay, we found that both monomeric and trimeric SARS-CoV-2 spike bind more tightly to immobilized heparin (KD = 40 pM and 73 pM, respectively) than the SARS-CoV and MERS-CoV SGPs (500 nM and 1 nM, respectively). In competitive binding studies, the IC50 of heparin, tri-sulfated non-anticoagulant heparan sulfate, and non-anticoagulant low molecular weight heparin against SARS-CoV-2 SGP binding to immobilized heparin were 0.056 μM, 0.12 μM, and 26.4 μM, respectively. Finally, unbiased computational ligand docking indicates that heparan sulfate interacts with the GAG-binding motif at the S1/S2 site on each monomer interface in the trimeric SARS-CoV-2 SGP, and at another site (453-459 (YRLFRKS)) when the receptor-binding domain is in an open conformation. The current study serves a foundation to further investigate biological roles of GAGs in SARS-CoV-2 pathogenesis. Furthermore, our findings may provide additional basis for further heparin-based interventions for COVID-19 patients exhibiting thrombotic complications.


Cap-dependent endonuclease (CEN) resides in the PA subunit of the influenza virus and mediates the critical “cap-snatching” step of viral RNA transcription, which is considered to be a promising anti-influenza target. Here, we describe in vitro characterization of a novel CEN inhibitor, baloxavir acid (BXA), the active form of baloxavir marboxil (BXM). BXA inhibits viral RNA transcription via selective inhibition of CEN activity in enzymatic assays, and inhibits viral replication in infected cells without cytotoxicity in cytopathic effect assays. The antiviral activity of BXA is also confirmed in yield reduction assays with seasonal type A and B viruses, including neuraminidase inhibitor-resistant strains. Furthermore, BXA shows broad potency against various subtypes of influenza A viruses (H1N2, H5N1, H5N2, H5N6, H7N9 and H9N2). Additionally, serial passages of the viruses in the presence of BXA result in isolation of PA/I38T variants with reduced BXA susceptibility. Phenotypic and genotypic analyses with reverse genetics demonstrate the mechanism of BXA action via CEN inhibition in infected cells. These results reveal the in vitro characteristics of BXA and support clinical use of BXM to treat influenza.


SARS-CoV-2, a member of the coronavirus family, is responsible for the current COVID-19 worldwide pandemic. We previously demonstrated that five nucleotide analogues inhibit the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp), including the active triphosphate forms of Sofosbuvir, Alovudine, Zidovudine, Tenofovir alafenamide and Emtricitabine. We report here the evaluation of a library of nucleoside triphosphate analogues with a variety of structural and chemical features as inhibitors of the RdRps of SARS-CoV and SARS-CoV-2. These features include modifications on the sugar (2' or 3' modifications, carbocyclic, acyclic, or dideoxynucleotides) or on the base. The goal is to identify nucleotide analogues that not only terminate RNA synthesis catalyzed by these coronavirus RdRps, but also have the potential to resist the viruses' exonuclease activity. We examined these nucleotide analogues for their ability to be incorporated by the RdRps in the polymerase reaction and to prevent further incorporation. While all 11 molecules tested displayed incorporation, 6 exhibited immediate termination of the polymerase reaction (triphosphates of Carbovir, Ganciclovir, Stavudine and Entecavir; 3'-OMe-UTP and Biotin-16-dUTP), 2 showed delayed termination (Cidofovir diphosphate and 2'-OMe-UTP), and 3 did not terminate the polymerase reaction (2'-F-dUTP, 2'-NH2-dUTP and Desthiobiotin-16-UTP). The coronaviruses possess an exonuclease that apparently requires a 2'-OH at the 3'-terminus of the growing RNA strand for proofreading. In this study, all nucleoside triphosphate analogues evaluated form Watson-Crick-like base pairs. The nucleotide analogues demonstrating termination either lack a 2'-OH, have a blocked 2'-OH, or show delayed termination. Thus, these nucleotide analogues are of interest for further investigation to evaluate whether they can evade the viral exonuclease activity. Prodrugs of five of these nucleotide analogues (Cidofovir, Abacavir, Valganciclovir/Ganciclovir, Stavudine and Entecavir) are FDA-approved medications for treatment of other viral infections, and their safety profiles are well established. After demonstrating potency in inhibiting viral replication in cell culture, candidate molecules can be rapidly evaluated as potential therapies for COVID-19.


An escalating pandemic by the novel SARS-CoV-2 virus is impacting global health and effective therapeutic options are urgently needed. We evaluated the in vitro antiviral effect of compounds that were previously reported to inhibit coronavirus replication and compounds that are currently under evaluation in clinical trials for SARS-CoV-2 patients. We report the antiviral effect of remdesivir, lopinavir, homorringtonine, and emetine against SARS-CoV-2 virus in Vero E6 cells with the estimated 50% effective concentration at 23.15 μM, 26.63 μM, 2.55 μM and 0.46 μM, respectively. Ribavirin or favipiravir that are currently evaluated under clinical trials showed no inhibition at 100 μM. Synergy between remdesivir and emetine was observed, and remdesivir at 6.25 μM in combination with emetine at 0.195 μM may achieve 64.9% inhibition in viral yield. Combinational therapy may help to reduce the effective concentration of compounds below the therapeutic plasma concentrations and provide better clinical benefits.


ASP2151 (amenamevir) is a helicase-primase complex inhibitor with antiviral activity against herpes simplex virus (HSV)-1, HSV-2, and varicella-zoster virus (VZV). To assess combination therapy of ASP2151 with existing antiherpes agents against HSV-1, HSV-2, and VZV, we conducted in vitro and in vivo studies of two-drug combinations. The combination activity effect of ASP2151 with nucleoside analogs acyclovir (ACV), penciclovir (PCV), or vidarabine (VDB) was tested via plaque-reduction assay and MTS assay, and the data were analyzed using isobolograms and response surface modeling. In vivo combination therapy of ASP2151 with valaciclovir (VACV) was studied in an HSV-1-infected zosteriform spread mouse model. The antiviral activity of ASP2151 combined with ACV and PCV against ACV-susceptible HSV-1, HSV-2, and VZV showed a statistically significant synergistic effect (P<0.05). ASP2151 with VDB was observed to have additive effects against ACV-susceptible HSV-2 and synergistic effects against VZV. In the mouse model of zosteriform spread, the inhibition of disease progression via combination therapy was more potent than that of either drugs as monotherapy (P<0.05). These results indicate that the combination therapies of ASP2151 with ACV and PCV have synergistic antiherpes effects against HSV and VZV infections and may be feasible in case of severe disease, such as herpes encephalitis or in patients with immunosuppression.

Concepts: Virus, Herpes simplex virus, Herpesviridae, Herpes simplex, Encephalitis, Virus latency, Herpes zoster, Alphaherpesvirinae


We designed a series of epitope proteins containing the G-H loops of three topotypes of foot-and-mouth disease virus (FMDV) serotype O and promiscuous artificial Th sites and selected one epitope protein (designated as B4) with optimal immunogenicity and cross-reactivity. Three out of five pigs immunized intramuscularly with this B4 were protected against virulent FMDV challenge after a single inoculation, while all pigs co-immunized with B4 and polyinosinic-cytidylic acid [poly (I: C)] conferred complete protection following FMDV challenge. Additionally, we demonstrated that all pigs co-immunized with B4 and poly (I: C) elicited FMDV-specific neutralizing antibodies, total IgG antibodies, typeIinterferon (IFN-α/β) and cytokines IFN-γ. In contrast, some pigs immunized with B4 alone produced parameters mentioned above, while some not, suggesting that poly (I: C) reduced animal-to-animal variations in both cellular and humoral responses often observed in association with epitope-based vaccines and up-regulated T-cell immunity often poorly observed in protein-based vaccines. We propose that poly (I: C) is an effective adjuvant for this epitope-based vaccine of FMDV. This combination could yield an effective and safe candidate vaccine for the control and eradication of FMD in pigs.

Concepts: Immune system, Antibody, Protein, Vaccination, Immunology, Smallpox, Aphthovirus, Foot-and-mouth disease


Sequential sampling from animals challenged with highly pathogenic organisms, such as haemorrhagic fever viruses, is required for many pharmaceutical studies. Using the guinea pig model of Ebola virus infection, a catheterized system was used which had the benefits of allowing repeated sampling of the same cohort of animals, and also a reduction in the use of sharps at high biological containment. Levels of a PS-targeting antibody (Bavituximab) were measured in Ebola-infected animals and uninfected controls. Data showed that the pharmacokinetics were similar in both groups, therefore Ebola virus infection did not have an observable effect on the half-life of the antibody.

Concepts: Immune system, Bacteria, Organism, Microbiology, Virus, Biological warfare, Ebola, Viral hemorrhagic fever