Potential and action mechanism of favipiravir as an antiviral against Junin virus

Mode of antiviral action of the galactose-specific lectin, AJLec, on the Junin virus propagation

Junin virus (JUNV), a member of Arenaviridae, is the causative agent of Argentine hemorrhagic fever (AHF). Available AHF treatments are limited; therefore, development of effective and safe treatments is required. Thus, in this study, novel lectins were examined for anti-JUNV activity. To evaluate JUNV propagation, a recombinant Junin virus vaccine strain (r3Candid #1/ZsGreen) containing the ZsGreen gene as a marker in the viral genome was used. The anti-JUNV effects of four types of marine organism-derived lectins collected in Japan, including the Nagasaki Prefecture, were examined. AJLec, which was extracted from the Sea Anemone Anthopleura japonica, reduced the number of infected cells and viral production. Infection and infection-surrogate assays revealed that incubation of AJLec with viruses and cells before infection, and maintaining it during infection, was required to exhibit full antiviral activity. Moreover, the anti-JUNV activity of AJLec was suppressed by the addition of lactose; hence, the anti-JUNV activity of AJLec was a result of its galactose recognition. This indicates the importance of galactose on the surface of the Junin virion and the cell membrane for entry into cells. Overall, these results provide new insights into the anti-JUNV activity of AJLec. Particularly, the potential of lectins as new antiviral agents that inhibit pathogenic arenavirus replication and propagation is promising.

SARS-CoV-2 Omicron subvariants progressively adapt to human cells with altered host cell entry

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant exhibits high transmissibility with a strong immune escape ability and causes frequent large-scale global infections by producing predominant subvariants. Here, using human upper/lower airway and intestinal cells, we examined the previously dominant BA.1-BA.5 and BA.2.75 subvariants, together with the recently emerged XBB/BQ lineages, in comparison to the former Delta variant. We observed a tendency for each virus to demonstrate higher growth capability than the previously dominant subvariants. Unlike human bronchial and intestinal cells, nasal epithelial cells accommodated the efficient entry of certain Omicron subvariants, similar to the Delta variant. In contrast to the Delta's reliance on cell-surface transmembrane protease serine 2, all tested Omicron variants depended on endosomal cathepsin L. Moreover, S1/S2 cleavage of early Omicron spikes was less efficient, whereas recent viruses exhibit improved cleavage efficacy. Our results show that the Omicron variant progressively adapts to human cells through continuous endosome-mediated host cell entry.IMPORTANCESARS-CoV-2, the causative agent of coronavirus disease 2019, has evolved into a number of variants/subvariants, which have generated multiple global waves of infection. In order to monitor/predict virological features of emerging variants and determine appropriate strategies for anti-viral development, understanding conserved or altered features of evolving SARS-CoV-2 is important. In this study, we addressed previously or recently predominant Omicron subvariants and demonstrated the gradual adaptation to human cells. The host cell entry route, which was altered from the former Delta variant, was conserved among all tested Omicron subvariants. Collectively, this study revealed both changing and maintained features of SARS-CoV-2 during the Omicron variant evolution.

Treatment of highly virulent mammarenavirus infections-status quo and future directions

INTRODUCTION

Mammarenaviruses are negative-sense bisegmented enveloped RNA viruses that are endemic in Africa, the Americas, and Europe. Several are highly virulent, causing acute human diseases associated with high case fatality rates, and are considered to be significant with respect to public health impact or bioterrorism threat.

AREAS COVERED

This review summarizes the status quo of treatment development, starting with drugs that are in advanced stages of evaluation in early clinical trials, followed by promising candidate medical countermeasures emerging from bench analyses and investigational animal research.

EXPERT OPINION

Specific therapeutic treatments for diseases caused by mammarenaviruses remain limited to the off-label use of ribavirin and transfusion of convalescent sera. Progress in identifying novel candidate medical countermeasures against mammarenavirus infection has been slow in part because of the biosafety and biosecurity requirements. However, novel methodologies and tools have enabled increasingly efficient high-throughput molecular screens of regulatory-agency-approved small-molecule drugs and led to the identification of several compounds that could be repurposed for the treatment of infection with several mammarenaviruses. Unfortunately, most of them have not yet been evaluated in vivo. The most promising treatment under development is a monoclonal antibody cocktail that is protective against multiple lineages of the Lassa virus in nonhuman primate disease models.

The combination of pleconaril, rupintrivir, and remdesivir efficiently inhibits enterovirus infections in vitro, delaying the development of drug-resistant virus variants

Enteroviruses are a significant global health concern, causing a spectrum of diseases from the common cold to more severe conditions like hand-foot-and-mouth disease, meningitis, myocarditis, pancreatitis, and poliomyelitis. Current treatment options for these infections are limited, underscoring the urgent need for effective therapeutic strategies. To find better treatment option we analyzed toxicity and efficacy of 12 known broad-spectrum anti-enterovirals both individually and in combinations against different enteroviruses in vitro. We identified several novel, synergistic two-drug and three-drug combinations that demonstrated significant inhibition of enterovirus infections in vitro. Specifically, the triple-drug combination of pleconaril, rupintrivir, and remdesivir exhibited remarkable efficacy against echovirus (EV) 1, EV6, EV11, and coxsackievirus (CV) B5, in human lung epithelial A549 cells. This combination surpassed the effectiveness of single-agent or dual-drug treatments, as evidenced by its ability to protect A549 cells from EV1-induced cytotoxicity across seven passages. Additionally, this triple-drug cocktail showed potent antiviral activity against EV-A71 in human intestinal organoids. Thus, our findings highlight the therapeutic potential of the pleconaril-rupintrivir-remdesivir combination as a broad-spectrum treatment option against a range of enterovirus infections. The study also paves the way towards development of strategic antiviral drug combinations with virus family coverage and high-resistance barriers.

Favipiravir Analogues as Inhibitors of SARS-CoV-2 RNA-Dependent RNA Polymerase, Combined Quantum Chemical Modeling, Quantitative Structure-Property Relationship, and Molecular Docking Study

Our study was motivated by the urgent need to develop or improve antivirals for effective therapy targeting RNA viruses. We hypothesized that analogues of favipiravir (FVP), an inhibitor of RNA-dependent RNA polymerase (RdRp), could provide more effective nucleic acid recognition and binding processes while reducing side effects such as cardiotoxicity, hepatotoxicity, teratogenicity, and embryotoxicity. We proposed a set of FVP analogues together with their forms of triphosphate as new SARS-CoV-2 RdRp inhibitors. The main aim of our study was to investigate changes in the mechanism and binding capacity resulting from these modifications. Using three different approaches, QTAIM, QSPR, and MD, the differences in the reactivity, toxicity, binding efficiency, and ability to be incorporated by RdRp were assessed. Two new quantum chemical reactivity descriptors, the relative electro-donating and electro-accepting power, were defined and successfully applied. Moreover, a new quantitative method for comparing binding modes was developed based on mathematical metrics and an atypical radar plot. These methods provide deep insight into the set of desirable properties responsible for inhibiting RdRp, allowing ligands to be conveniently screened. The proposed modification of the FVP structure seems to improve its binding ability and enhance the productive mode of binding. In particular, two of the FVP analogues (the trifluoro- and cyano-) bind very strongly to the RNA template, RNA primer, cofactors, and RdRp, and thus may constitute a very good alternative to FVP.

Molecular docking, molecular dynamics and binding free energy based identification of novel potential multitarget inhibitors of Nipah virus

Nipah virus (NiV) is one of the most common viral diseases affecting the brain and nervous system of the body. To date, there is no significant antiviral drug specifically designed to inhibit NiV. In the last ten years, there has been a significant increase in interest in multitarget drug development. Therefore, the reported work focuses on designing a multitarget inhibitor for NiV. Among the twelve designed compounds, five exhibited better drug-likeness and ADMET properties, hence being selected for further analysis. In a molecular docking study, these compounds possessed better binding affinity as compared to Favipiravir. The RMSD of these compounds was ≤2Å and the number of H-bonds signified the better stability of the complexes formed. The ΔGbind of C4, C6 and C7 was found to be comparatively higher than the other screened compounds, revealing their greater ability to bind efficiently with NiV-G, NiV-F and NiV-N receptors, respectively. Therefore, based on molecular docking, molecular dynamics, and MM/PBSA analysis, these compounds can act as potential inhibitors of multitargets of NiV.Communicated by Ramaswamy H. Sarma.

Molnupiravir Revisited-Critical Assessment of Studies in Animal Models of COVID-19

Molnupiravir, a prodrug known for its broad antiviral activity, has demonstrated efficacy in animal models of COVID-19, prompting clinical trials, in which initial results indicated a significant effect against the disease. However, subsequent clinical studies did not confirm these findings, leading to the refusal of molnupiravir for permanent market authorization in many countries. This report critically assessed 22 studies published in 18 reports that investigated the efficacy of molnupiravir in animal models of COVID-19, with the purpose of determining how well the design of these models informed human studies. We found that the administered doses of molnupiravir in most studies involving animal COVID-19 models were disproportionately higher than the dose recommended for human use. Specifically, when adjusted for body surface area, over half of the doses of molnupiravir used in the animal studies exceeded twice the human dose. Direct comparison of reported drug exposure across species after oral administration of molnupiravir indicated that the antiviral efficacy of the dose recommended for human use was underestimated in some animal models and overestimated in others. Frequently, molnupiravir was given prophylactically or shortly after SARS-CoV-2 inoculation in these models, in contrast to clinical trials where such timing is not consistently achieved. Furthermore, the recommended five-day treatment duration for humans was exceeded in several animal studies. Collectively, we suggest that design elements in the animal studies under examination contributed to a preference favoring molnupiravir, and thus inflated expectations for its efficacy against COVID-19. Addressing these elements may offer strategies to enhance the clinical efficacy of molnupiravir for the treatment of COVID-19. Such strategies include dose increment, early treatment initiation, administration by inhalation, and use of the drug in antiviral combination therapy.

Emergence of Marburg virus: a global perspective on fatal outbreaks and clinical challenges

The Marburg virus (MV), identified in 1967, has caused deadly outbreaks worldwide, the mortality rate of Marburg virus disease (MVD) varies depending on the outbreak and virus strain, but the average case fatality rate is around 50%. However, case fatality rates have varied from 24 to 88% in past outbreaks depending on virus strain and case management. Designated a priority pathogen by the National Institute of Allergy and Infectious Diseases (NIAID), MV induces hemorrhagic fever, organ failure, and coagulation issues in both humans and non-human primates. This review presents an extensive exploration of MVD outbreak evolution, virus structure, and genome, as well as the sources and transmission routes of MV, including human-to-human spread and involvement of natural hosts such as the Egyptian fruit bat (Rousettus aegyptiacus) and other Chiroptera species. The disease progression involves early viral replication impacting immune cells like monocytes, macrophages, and dendritic cells, followed by damage to the spleen, liver, and secondary lymphoid organs. Subsequent spread occurs to hepatocytes, endothelial cells, fibroblasts, and epithelial cells. MV can evade host immune response by inhibiting interferon type I (IFN-1) synthesis. This comprehensive investigation aims to enhance understanding of pathophysiology, cellular tropism, and injury sites in the host, aiding insights into MVD causes. Clinical data and treatments are discussed, albeit current methods to halt MVD outbreaks remain elusive. By elucidating MV infection's history and mechanisms, this review seeks to advance MV disease treatment, drug development, and vaccine creation. The World Health Organization (WHO) considers MV a high-concern filovirus causing severe and fatal hemorrhagic fever, with a death rate ranging from 24 to 88%. The virus often spreads through contact with infected individuals, originating from animals. Visitors to bat habitats like caves or mines face higher risk. We tailored this search strategy for four databases: Scopus, Web of Science, Google Scholar, and PubMed. we primarily utilized search terms such as "Marburg virus," "Epidemiology," "Vaccine," "Outbreak," and "Transmission." To enhance comprehension of the virus and associated disease, this summary offers a comprehensive overview of MV outbreaks, pathophysiology, and management strategies. Continued research and learning hold promise for preventing and controlling future MVD outbreaks. GRAPHICAL ABSTRACT.

Calcium Influx Regulates the Replication of Several Negative-Strand RNA Viruses Including Severe Fever with Thrombocytopenia Syndrome Virus

Negative-strand RNA viruses (NSVs) represent one of the most threatening groups of emerging viruses globally. Severe fever with thrombocytopenia syndrome virus (SFTSV) is a highly pathogenic emerging virus that was initially reported in 2011 from China. Currently, no licensed vaccines or therapeutic agents have been approved for use against SFTSV. Here, L-type calcium channel blockers obtained from a U.S. Food and Drug Administration (FDA)-approved compound library were identified as effective anti-SFTSV compounds. Manidipine, a representative L-type calcium channel blocker, restricted SFTSV genome replication and exhibited inhibitory effects against other NSVs. The result from the immunofluorescent assay suggested that manidipine inhibited SFTSV N-induced inclusion body formation, which is believed to be important for the virus genome replication. We have shown that calcium possesses at least two different roles in regulating SFTSV genome replication. Inhibition of calcineurin, the activation of which is triggered by calcium influx, using FK506 or cyclosporine was shown to reduce SFTSV production, suggesting the important role of calcium signaling on SFTSV genome replication. In addition, we showed that globular actin, the conversion of which is facilitated by calcium from filamentous actin (actin depolymerization), supports SFTSV genome replication. We also observed an increased survival rate and a reduction of viral load in the spleen in a lethal mouse model of SFTSV infections after manidipine treatment. Overall, these results provide information regarding the importance of calcium for NSV replication and may thereby contribute to the development of broad-scale protective therapies against pathogenic NSVs. IMPORTANCE SFTS is an emerging infectious disease and has a high mortality rate of up to 30%. There are no licensed vaccines or antivirals against SFTS. In this article, L-type calcium channel blockers were identified as anti-SFTSV compounds through an FDA-approved compound library screen. Our results showed the involvement of L-type calcium channel as a common host factor for several different families of NSVs. The formation of an inclusion body, which is induced by SFTSV N, was inhibited by manidipine. Further experiments showed that SFTSV replication required the activation of calcineurin, a downstream effecter of the calcium channel. In addition, we identified that globular actin, the conversion of which is facilitated by calcium from filamentous actin, supports SFTSV genome replication. We also observed an increased survival rate in a lethal mouse model of SFTSV infection after manidipine treatment. These results facilitate both our understanding of the NSV replication mechanism and the development of novel anti-NSV treatment.

Recent developments on Junin virus, a causative agent for Argentine haemorrhagic fever

Junin virus consists of ribonucleic acid as the genome and is responsible for a rapidly changing tendency of the virus. The virus is accountable for ailments in the human body and causes Argentine Haemorrhagic Fever (AHF). The infection is may be transmitted through contact between an infected animal/host and a person, and later between person to person. Prevention of outbreaks of AHF in humans can be a tough practice, as their occurrence is infrequent and unpredictable. In this review, recent information from the past 5 years available on the Junin virus including the risk of its emergence, infectious agents, its pathogenesis in humans, available diagnostic and therapeutic approaches, and disease management has been summarised. Altogether, this article would be highly significant in understanding the mechanistic basis behind virus interaction and other processes during the life cycle. Currently, no specific therapeutic options are available to treat the Junin virus infection. The information covered in this review could be important for finding possible treatment options for Junin virus infections.

Atypical Mutational Spectrum of SARS-CoV-2 Replicating in the Presence of Ribavirin

We report that ribavirin exerts an inhibitory and mutagenic activity on SARS-CoV-2-infecting Vero cells, with a therapeutic index higher than 10. Deep sequencing analysis of the mutant spectrum of SARS-CoV-2 replicating in the absence or presence of ribavirin indicated an increase in the number of mutations, but not in deletions, and modification of diversity indices, expected from a mutagenic activity. Notably, the major mutation types enhanced by replication in the presence of ribavirin were A→G and U→C transitions, a pattern which is opposite to the dominance of G→A and C→U transitions previously described for most RNA viruses. Implications of the inhibitory activity of ribavirin, and the atypical mutational bias produced on SARS-CoV-2, for the search for synergistic anti-COVID-19 lethal mutagen combinations are discussed.

Topoisomerase II as a Novel Antiviral Target against Panarenaviral Diseases

Although many arenaviruses cause severe diseases with high fatality rates each year, treatment options are limited to off-label use of ribavirin, and a Food and Drug Administration (FDA)-approved vaccine is not available. To identify novel therapeutic candidates against arenaviral diseases, an RNA polymerase I-driven minigenome (MG) expression system for Lassa virus (LASV) was developed and optimized for high-throughput screening (HTS). Using this system, we screened 2595 FDA-approved compounds for inhibitors of LASV genome replication and identified multiple compounds including pixantrone maleate, a topoisomerase II inhibitor, as hits. Other tested topoisomerase II inhibitors also suppressed LASV MG activity. These topoisomerase II inhibitors also inhibited Junin virus (JUNV) MG activity and effectively limited infection by the JUNV Candid #1 strain, and siRNA knockdown of both topoisomerases (IIα and IIβ) restricted JUNV replication. These results suggest that topoisomerases II regulate arenavirus replication and can serve as molecular targets for panarenaviral replication inhibitors.

Severe mammarenaviral disease in guinea pigs effectively treated by an orally bioavailable fusion inhibitor, alone or in combination with favipiravir

Infections by pathogenic New World mammarenaviruses (NWM)s, including Junín virus (JUNV), can result in a severe life-threatening viral hemorrhagic fever syndrome. In the absence of FDA-licensed vaccines or antivirals, these viruses are considered high priority pathogens. The mammarenavirus envelope glycoprotein complex (GPC) mediates pH-dependent fusion between viral and cellular membranes, which is essential to viral entry and may be vulnerable to small-molecule inhibitors that disrupt this process. ARN-75039 is a potent fusion inhibitor of a broad spectrum of pseudotyped and native mammarenaviruses in cell culture and Tacaribe virus infection in mice. In the present study, we evaluated ARN-75039 against pathogenic JUNV in the rigorous guinea pig infection model. The compound was well-tolerated and had favorable pharmacokinetics supporting once-per-day oral dosing in guinea pigs. Importantly, significant protection against JUNV challenge was observed even when ARN-75039 was withheld until 6 days after the viral challenge when clinical signs of disease are starting to develop. We also show that ARN-75039 combination treatment with favipiravir, a viral polymerase inhibitor, results in synergistic activity in vitro and improves survival outcomes in JUNV-challenged guinea pigs. Our findings support the continued development of ARN-75039 as an attractive therapeutic candidate for treating mammarenaviral hemorrhagic fevers, including those associated with NWM infection.