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Journal: Antiviral research


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.


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


Receptor recognition is a major determinant of the host range, cross-species infections, and pathogenesis of the severe acute respiratory syndrome coronavirus (SARS-CoV). A defined receptor-binding domain (RBD) in the SARS-CoV spike protein specifically recognizes its host receptor, angiotensin-converting enzyme 2 (ACE2). This article reviews the latest knowledge about how RBDs from different SARS-CoV strains interact with ACE2 from several animal species. Detailed research on these RBD/ACE2 interactions has established important principles on host receptor adaptations, cross-species infections, and future evolution of SARS-CoV. These principles may apply to other emerging animal viruses, including the recently emerged Middle East respiratory syndrome coronavirus (MERS-CoV). This paper forms part of a series of invited articles in Antiviral Research on “From SARS to MERS: 10years of research on highly pathogenic human coronaviruses”.

Concepts: Immune system, Protein, Bacteria, Virus, Severe acute respiratory syndrome, SARS coronavirus, Coronavirus, Nidovirales


The dengue fever virus (DENV) and the yellow fever virus (YFV) are members of the genus flavivirus in the family Flaviviridae. An estimated 50 to 100 million cases of DENV infections occur each year and approximately half a million patients require hospitalization. There is no vaccine or effective antiviral treatment available. There is an urgent need for potent and safe inhibitors of DENV replication; ideally such compounds should have broad-spectrum activity against flaviviruses. We here report on the in vitro activity of 3',5'di-O-trityluridine on flavivirus replication. The compound results in a dose-dependent inhibition of (i) DENV- and YFV-induced cytopathic effect (CPE) (EC50 values in the low micromolar range for the 4 DENV serotypes), (ii) RNA replication (DENV-2 EC50= 1.5 μM; YFV-17D EC50= 0.83 μM) and (iii) viral antigen production. Antiviral activity was also demonstrated in DENV subgenomic replicons (which do not encode the structural viral proteins) (EC50= 2.3 μM), indicating that the compound inhibits intracellular events of the viral replication cycle. Preliminary data indicate that the molecule may inhibit the viral RNA-dependent RNA polymerase.

Concepts: Virus, RNA, Malaria, Yellow fever, RNA polymerase, Fever, Dengue fever, Flaviviridae


The aim of the present study was to evaluate the ability of the iminosugar drug UV-4 to provide in vivo protection from lethal dengue virus (DENV) challenge. This study utilized a well-described model of dengue hemorrhagic fever / dengue shock syndrome (DHF/DSS)-like lethal disease in AG129 mice lacking the type I and II interferon receptors. Herein, we present UV-4 as a potent iminosugar for controlling DENV infection and disease in this mouse model. Specifically, administration of UV-4 reduced mortality, as well as viremia and viral RNA in key tissues, and cytokine storm. In addition, UV-4 treatment can be delayed, and it does not alter the anti-DENV antibody response. These results have set the foundation for development of UV-4 as a DENV-specific antiviral in phase I human clinical trials.

Concepts: Immune system, Cytokine, Virus, Interferon, Ribavirin, Fever, Dengue fever, Viral hemorrhagic fever


PURPOSE: To develop spray dried mucoadhesive and pH-sensitive microspheres (MS) based on polymethacrylate salt intended for vaginal delivery of tenofovir (a model HIV microbicide) and assess their critical biological responses. METHODS: The formulation variables and process parameters are screened and optimized using a 2(4-1) fractional factorial design. The MS are characterized for size, zeta potential, yield, encapsulation efficiency, Carr’s index, drug loading, in vitro release, cytotoxicity, inflammatory responses and mucoadhesion. RESULTS: The optimal MS formulation has an average size of 4.73 μm, Zeta potential of -26.3 mV, 68.9% yield, encapsulation efficiency of 88.7%, Carr’s index of 28.3 and drug loading of 2% (w/w). The MS formulation can release 90% of its payload in the presence of simulated human semen. At a concentration of 1 mg/ml, the MS are noncytotoxic to vaginal endocervical/epithelial cells and Lactobacillus crispatus when compared to control media. There is also no statistically significant level of inflammatory cytokine (IL1-α, IL-1β, IL-6, IL-8, and IP-10) release triggered by MS. The mucoadhesive property of MS formulation is 2-fold higher than that of 1% HEC gel formulation. CONCLUSION: These data suggest the promise of using such MS as an alternative controlled microbicide delivery template by intravaginal route for HIV prevention.

Concepts: Childbirth, Sexual intercourse, Statistical significance, Colloid, Semen, Drying, Statistical theory, Pre-ejaculate


Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans and a member of the genus Orthohepevirus in the family Hepeviridae. HEV infections are the common cause of acute hepatitis but can also take chronic courses. Ribavirin is the treatment of choice for most patients and type I interferon (IFN) has been evaluated in a few infected transplantation patients in vivo. However, no effective and specific treatments against HEV infections are currently available. In this study, we evaluated the natural compound silvestrol, isolated from the plant Aglaia foveolata, and known for its specific inhibition of the DEAD-box RNA helicase eIF4A in state-of-the-art HEV experimental model systems. Silvestrol blocked HEV replication of different subgenomic replicons in a dose-dependent manner at low nanomolar concentrations and acted additive to ribavirin (RBV). In addition, HEV p6-based full length replication and production of infectious particles was reduced in the presence of silvestrol. A pangenotypic effect of the compound was further demonstrated with primary isolates from four different human genotypes in HEV infection experiments of hepatocyte-like cells derived from human embryonic and induced pluripotent stem cells. In vivo, HEV RNA levels rapidly declined in the feces of treated mice while no effect was observed in the vehicle treated control animals. In conclusion, silvestrol could be identified as pangenotypic HEV replication inhibitor in vitro with additive effect to RBV and further demonstrated high potency in vivo. The compound therefore may be considered in future treatment strategies of chronic hepatitis E in immunocompromised patients.


Enterovirus 71 (EV71), a member of Picornaviridae, is one of the major pathogens of human hand, foot and mouth disease. EV71 mainly infects children and causes severe neurological complications and even death. The pathogenesis of EV71 infection is largely unknown, and no clinically approved vaccine or effective treatment is available to date. Here we described a novel bioluminescence imaging approach for EV71 detection. In this approach, a plasmid-based reporter was constructed to express the fusion protein AmN(Q/G)BC, a split firefly luciferase mutant, which can be specifically cleaved by EV71 protease 3C(pro). Upon cleavage, the splitting fusion protein restores luciferase activity. Our test confirmed that AmN(Q/G)BC was specifically cleaved by 3C(pro) and EV71 and restored the luciferase activity to a degree that corresponds to the 3C(pro) and virus doses in cells and mice. The anti-EV71 effect of GW5074 and U0126, two mitogen-activated protein kinase (MAPK) inhibitors, was evaluated using this approach to validate its application of screening anti-EV71 agents. We found that the AmN(Q/G)BC reporter efficiently monitors the inhibitory effect of GW5074 and U0126 on EV71 infection under in vitro and in vivo conditions. The data from AmN(Q/G)BC reporter were consistent with western blotting and histopathology examination. Taken together, this real-time imaging approach can quantitatively monitor the efficacy of anti-EV71 agents and is valuable for anti-EV71 drug screening and evaluation, especially, under in vivo conditions.

Concepts: Signal transduction, Enzyme, In vivo, In vitro, Mitogen-activated protein kinase, Protein kinases, Firefly, Bioluminescence