Inhibition of Lassa virus and Ebola virus infection in host cells treated with the kinase inhibitors genistein and tyrphostin

AG1478 Elicits a Novel Anti-Influenza Function via an EGFR-Independent, GBF1-Dependent Pathway

Current options for preventing or treating influenza are still limited, and new treatments for influenza viral infection are urgently needed. In the present study, we serendipitously found that a small-molecule inhibitor (AG1478), previously used for epidermal growth factor receptor (EGFR) inhibition, demonstrated a potent activity against influenza both in vitro and in vivo. Surprisingly, the antiviral effect of AG1478 was not mediated by its EGFR inhibitory activity, as influenza virus was insensitive to EGFR blockade by other EGFR inhibitors or by siRNA knockdown of EGFR. Its antiviral activity was also interferon independent as demonstrated by a Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) knockout approach. Instead, AG1478 was found to target the Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1 (GBF1)–ADP-ribosylation factor 1 (ARF1) system by reversibly inhibiting GBF1 activity and disrupting its Golgi-cytoplasmic trafficking. Compared to known GBF1 inhibitors, AG1478 demonstrated lower cellular toxicity and better preservation of Golgi structure. Furthermore, GBF1 was found to interact with a specific set of viral proteins including M1, NP, and PA. Additionally, the alternation of GBF1 distribution induced by AG1478 treatment disrupted these interactions. Because targeting host factors, instead of the viral component, imposes a higher barrier for developing resistance, GBF1 modulation may be an effective approach to treat influenza infection.

Modulating Neurological Complications of Emerging Infectious Diseases: Mechanistic Approaches to Candidate Phytochemicals

Growing studies are revealing the critical manifestations of influenza, dengue virus (DENV) infection, Zika virus (ZIKV) disease, and Ebola virus disease (EVD) as emerging infectious diseases. However, their corresponding mechanisms of major complications headed for neuronal dysfunction are not entirely understood. From the mechanistic point of view, inflammatory/oxidative mediators are activated during emerging infectious diseases towards less cell migration, neurogenesis impairment, and neuronal death. Accordingly, the virus life cycle and associated enzymes, as well as host receptors, cytokine storm, and multiple signaling mediators, are the leading players of emerging infectious diseases. Consequently, chemokines, interleukins, interferons, carbohydrate molecules, toll-like receptors (TLRs), and tyrosine kinases are leading orchestrates of peripheral and central complications which are in near interconnections. Some of the resulting neuronal manifestations have attracted much attention, including inflammatory polyneuropathy, encephalopathy, meningitis, myelitis, stroke, Guillain-Barré syndrome (GBS), radiculomyelitis, meningoencephalitis, memory loss, headaches, cranial nerve abnormalities, tremor, and seizure. The complex pathophysiological mechanism behind the aforementioned complications urges the need for finding multi-target agents with higher efficacy and lower side effects. In recent decades, the natural kingdom has been highlighted as promising neuroprotective natural products in modulating several dysregulated signaling pathways/mediators. The present study provides neuronal manifestations of some emerging infectious diseases and underlying pathophysiological mechanisms. Besides, a mechanistic-based strategy is developed to introduce candidate natural products as promising multi-target agents in combating major dysregulated pathways towards neuroprotection in influenza, DENV infection, ZIKV disease, and EVD.

Ebola virus triggers receptor tyrosine kinase-dependent signaling to promote the delivery of viral particles to entry-conducive intracellular compartments

Filoviruses, such as the Ebola virus (EBOV) and Marburg virus (MARV), are causative agents of sporadic outbreaks of hemorrhagic fevers in humans. To infect cells, filoviruses are internalized via macropinocytosis and traffic through the endosomal pathway where host cathepsin-dependent cleavage of the viral glycoproteins occurs. Subsequently, the cleaved viral glycoprotein interacts with the late endosome/lysosome resident host protein, Niemann-Pick C1 (NPC1). This interaction is hypothesized to trigger viral and host membrane fusion, which results in the delivery of the viral genome into the cytoplasm and subsequent initiation of replication. Some studies suggest that EBOV viral particles activate signaling cascades and host-trafficking factors to promote their localization with host factors that are essential for entry. However, the mechanism through which these activating signals are initiated remains unknown. By screening a kinase inhibitor library, we found that receptor tyrosine kinase inhibitors potently block EBOV and MARV GP-dependent viral entry. Inhibitors of epidermal growth factor receptor (EGFR), tyrosine protein kinase Met (c-Met), and the insulin receptor (InsR)/insulin like growth factor 1 receptor (IGF1R) blocked filoviral GP-mediated entry and prevented growth of replicative EBOV in Vero cells. Furthermore, inhibitors of c-Met and InsR/IGF1R also blocked viral entry in macrophages, the primary targets of EBOV infection. Interestingly, while the c-Met and InsR/IGF1R inhibitors interfered with EBOV trafficking to NPC1, virus delivery to the receptor was not impaired in the presence of the EGFR inhibitor. Instead, we observed that the NPC1 positive compartments were phenotypically altered and rendered incompetent to permit viral entry. Despite their different mechanisms of action, all three RTK inhibitors tested inhibited virus-induced Akt activation, providing a possible explanation for how EBOV may activate signaling pathways during entry. In sum, these studies strongly suggest that receptor tyrosine kinases initiate signaling cascades essential for efficient post-internalization entry steps.

Ebola virus (EBOV) and Marburg virus (MARV) are zoonotic pathogens that can cause severe hemorrhagic fevers in humans and non-human primates. They are members of the growing Filoviridae family that also includes three other species of Ebolaviruses known to be highly pathogenic in humans. While vaccines for EBOV are being deployed and showed high efficacy, pan-filoviral treatment is still lacking. To infect cells, EBOV requires the endosomal/lysosomal resident protein Niemann-Pick C1 (NPC1). Accordingly, viral particles require extensive trafficking within endosomal pathways for entry and delivery of the viral genome into the host cell cytoplasm. Here, we used chemical biology to reveal that EBOV triggers receptor tyrosine kinase (RTK)-dependent signaling to traffic to intracellular vesicles that contain the receptor and are conducive to entry. The characterization of host trafficking factors and signaling pathways that are potentially triggered by the virus are important as these could be targeted for antiviral therapies. In our study, we identified several RTK inhibitors, some of which are FDA-approved drugs, that potently block EBOV infection. Since all filoviruses known to date, even Měnglà virus that was recently discovered in bats in China, use NPC1 as their entry receptor, these inhibitors have the potential to be effective pan-filovirus antivirals.

Commonalities Between COVID-19 and Radiation Injury

As the multi-systemic components of COVID-19 emerge, parallel etiologies can be drawn between SARS-CoV-2 infection and radiation injuries. While some SARS-CoV-2-infected individuals present as asymptomatic, others exhibit mild symptoms that may include fever, cough, chills, and unusual symptoms like loss of taste and smell and reddening in the extremities (e.g., "COVID toes," suggestive of microvessel damage). Still others alarm healthcare providers with extreme and rapid onset of high-risk indicators of mortality that include acute respiratory distress syndrome (ARDS), multi-organ hypercoagulation, hypoxia and cardiovascular damage. Researchers are quickly refocusing their science to address this enigmatic virus that seems to unveil itself in new ways without discrimination. As investigators begin to identify early markers of disease, identification of common threads with other pathologies may provide some clues. Interestingly, years of research in the field of radiation biology documents the complex multiorgan nature of another disease state that occurs after exposure to high doses of radiation: the acute radiation syndrome (ARS). Inflammation is a key common player in COVID-19 and ARS, and drives the multi-system damage that dramatically alters biological homeostasis. Both conditions initiate a cytokine storm, with similar pro-inflammatory molecules increased and other anti-inflammatory molecules decreased. These changes manifest in a variety of ways, with a demonstrably higher health impact in patients having underlying medical conditions. The potentially dramatic human impact of ARS has guided the science that has identified many biomarkers of radiation exposure, established medical management strategies for ARS, and led to the development of medical countermeasures for use in the event of a radiation public health emergency. These efforts can now be leveraged to help elucidate mechanisms of action of COVID-19 injuries. Furthermore, this intersection between COVID-19 and ARS may point to approaches that could accelerate the discovery of treatments for both.

The upshot of Polyphenolic compounds on immunity amid COVID-19 pandemic and other emerging communicable diseases: An appraisal

Polyphenols are a large family of more than 10,000 naturally occurring compounds, which exert countless pharmacological, biological and physiological benefits for human health including several chronic diseases such as cancer, diabetes, cardiovascular, and neurological diseases. Their role in traditional medicine, such as the use of a wide range of remedial herbs (thyme, oregano, rosemary, sage, mint, basil), has been well and long known for treating common respiratory problems and cold infections. This review reports on the most highlighted polyphenolic compounds present in up to date literature and their specific antiviral perceptive properties that might enhance the body immunity facing COVID-19, and other viral infectious diseases. In fact, several studies and clinical trials increasingly proved the role of polyphenols in controlling numerous human pathogens including SARS and MERS, which are quite similar to COVID-19 through the enhancement of host immune response against viral infections by different biological mechanisms. Thus, polyphenols ought to be considered as a potential and valuable source for designing new drugs that could be used effectively in the combat against COVID-19 and other rigorous diseases.

Current status of small molecule drug development for Ebola virus and other filoviruses

The filovirus family includes some of the deadliest viruses known, including Ebola virus and Marburg virus. These viruses cause periodic outbreaks of severe disease that can be spread from person to person, making the filoviruses important public health threats. There remains a need for approved drugs that target all or most members of this virus family. Small molecule inhibitors that target conserved functions hold promise as pan-filovirus therapeutics. To date, compounds that effectively target virus entry, genome replication, gene expression, and virus egress have been described. The most advanced inhibitors are nucleoside analogs that target viral RNA synthesis reactions.

Hemorrhagic Fever-Causing Arenaviruses: Lethal Pathogens and Potent Immune Suppressors

Hemorrhagic fevers (HF) resulting from pathogenic arenaviral infections have traditionally been neglected as tropical diseases primarily affecting African and South American regions. There are currently no FDA-approved vaccines for arenaviruses, and treatments have been limited to supportive therapy and use of non-specific nucleoside analogs, such as Ribavirin. Outbreaks of arenaviral infections have been limited to certain geographic areas that are endemic but known cases of exportation of arenaviruses from endemic regions and socioeconomic challenges for local control of rodent reservoirs raise serious concerns about the potential for larger outbreaks in the future. This review synthesizes current knowledge about arenaviral evolution, ecology, transmission patterns, life cycle, modulation of host immunity, disease pathogenesis, as well as discusses recent development of preventative and therapeutic pursuits against this group of deadly viral pathogens.

Advances in Designing and Developing Vaccines, Drugs, and Therapies to Counter Ebola Virus

Ebola virus (EBOV), a member of the family Filoviridae, is responsible for causing Ebola virus disease (EVD) (formerly named Ebola hemorrhagic fever). This is a severe, often fatal illness with mortality rates varying from 50 to 90% in humans. Although the virus and associated disease has been recognized since 1976, it was only when the recent outbreak of EBOV in 2014-2016 highlighted the danger and global impact of this virus, necessitating the need for coming up with the effective vaccines and drugs to counter its pandemic threat. Albeit no commercial vaccine is available so far against EBOV, a few vaccine candidates are under evaluation and clinical trials to assess their prophylactic efficacy. These include recombinant viral vector (recombinant vesicular stomatitis virus vector, chimpanzee adenovirus type 3-vector, and modified vaccinia Ankara virus), Ebola virus-like particles, virus-like replicon particles, DNA, and plant-based vaccines. Due to improvement in the field of genomics and proteomics, epitope-targeted vaccines have gained top priority. Correspondingly, several therapies have also been developed, including immunoglobulins against specific viral structures small cell-penetrating antibody fragments that target intracellular EBOV proteins. Small interfering RNAs and oligomer-mediated inhibition have also been verified for EVD treatment. Other treatment options include viral entry inhibitors, transfusion of convalescent blood/serum, neutralizing antibodies, and gene expression inhibitors. Repurposed drugs, which have proven safety profiles, can be adapted after high-throughput screening for efficacy and potency for EVD treatment. Herbal and other natural products are also being explored for EVD treatment. Further studies to better understand the pathogenesis and antigenic structures of the virus can help in developing an effective vaccine and identifying appropriate antiviral targets. This review presents the recent advances in designing and developing vaccines, drugs, and therapies to counter the EBOV threat.

Antiviral activity of A771726, the active metabolite of leflunomide, against Junín virus

The aim of this study was to investigate the effect of A771726, the active metabolite of leflunomide, (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad against the infection with Junín virus (JUNV), agent of Argentine hemorrhagic fever (AHF). The treatment with non-cytotoxic concentrations of A771726 of Vero and A549 cells infected with JUNV inhibited virus replication in a dose-dependent manner, as determined by virus yield reduction assay. The antiviral effectiveness of A771726 was not importantly affected by the multiplicity of infection and the virus strain. Moreover, the combination of A771726 and ribavirin had a significantly more potent antiviral activity than each single drug treatment. Mechanistic studies showed that the main action of A771726 is exerted before 6 h of JUNV infection. Accordingly, inhibition of viral RNA synthesis was detected in treated infected cells by real time RT-PCR. The exogenous addition of uridine or orotic acid produced a partial reversal of the inhibitory effect of A771726 on infective virus production whereas a total reversion was detected on JUNV RNA synthesis, probably by restoration of the enzymatic activity of dihydroorotate dehydrogenase (DHODH) and the intracellular pyrimidine pools. In conclusion, these results suggest that the antiviral target would be viral RNA synthesis through pyrimidine depletion, but any other effect of the compound on JUNV infection cannot be excluded. This study opens the possibility of the therapeutic application of a wide spectrum host-targeted compound alone or in combination with ribavirin to combat AHF as well as other human pathogenic arenaviruses.

Flavonoids: promising natural compounds against viral infections

Flavonoids are widely distributed as secondary metabolites produced by plants and play important roles in plant physiology, having a variety of potential biological benefits such as antioxidant, anti-inflammatory, anticancer, antibacterial, antifungal and antiviral activity. Different flavonoids have been investigated for their potential antiviral activities and several of them exhibited significant antiviral properties in in vitro and even in vivo studies. This review summarizes the evidence for antiviral activity of different flavonoids, highlighting, where investigated, the cellular and molecular mechanisms of action on viruses. We also present future perspectives on therapeutic applications of flavonoids against viral infections.

Candidate medical countermeasures targeting Ebola virus cell entry

Medical countermeasures (MCMs) against virus infections ideally prevent the adsorption or entry of virions into target cells, thereby circumventing infection. Recent significant advances in elucidating the mechanism of Ebola virus (EBOV) host-cell penetration include the involvement of two-pore channels at the early stage of entry, and identification of cellular proteases for EBOV spike glycoprotein maturation and the intracellular EBOV receptor, Niemann–Pick type C1. This improved understanding of the initial steps of EBOV infection is now increasingly applied to rapid development of candidate MCMs, some of which have already entered the clinic. Candidate MCMs discussed include antibodies, small molecules and peptides that target various stages of the described EBOV cell-entry pathway. In this review, we summarize the currently known spectrum of EBOV cell-entry inhibitors, describe their mechanism of action and evaluate their potential for future development.

Integration of Global Analyses of Host Molecular Responses with Clinical Data To Evaluate Pathogenesis and Advance Therapies for Emerging and Re-emerging Viral Infections

Outbreaks associated with emerging and re-emerging viral pathogens continue to increase in frequency and are associated with an increasing burden to global health. In light of this, there is a need to integrate basic and clinical research for investigating the connections between molecular and clinical pathogenesis and for therapeutic development strategies. Here, we will discuss this approach with a focus on the emerging viral pathogens Middle East respiratory syndrome coronavirus (MERS-CoV), Ebola virus (EBOV), and monkeypox virus (MPXV) from the context of clinical presentation, immunological and molecular features of the diseases, and OMICS-based analyses of pathogenesis. Furthermore, we will highlight the role of global investigations of host kinases, the kinome, for investigating emerging and re-emerging viral pathogens from the context of characterizing cellular responses and identifying novel therapeutic targets. Lastly, we will address how increased integration of clinical and basic research will assist treatment and prevention efforts for emerging pathogens.

Integrated Computational Approach for Virtual Hit Identification against Ebola Viral Proteins VP35 and VP40

The Ebola virus (EBOV) has been recognised for nearly 40 years, with the most recent EBOV outbreak being in West Africa, where it created a humanitarian crisis. Mortalities reported up to 30 March 2016 totalled 11,307. However, up until now, EBOV drugs have been far from achieving regulatory (FDA) approval. It is therefore essential to identify parent compounds that have the potential to be developed into effective drugs. Studies on Ebola viral proteins have shown that some can elicit an immunological response in mice, and these are now considered essential components of a vaccine designed to protect against Ebola haemorrhagic fever. The current study focuses on chemoinformatic approaches to identify virtual hits against Ebola viral proteins (VP35 and VP40), including protein binding site prediction, drug-likeness, pharmacokinetic and pharmacodynamic properties, metabolic site prediction, and molecular docking. Retrospective validation was performed using a database of non-active compounds, and early enrichment of EBOV actives at different false positive rates was calculated. Homology modelling and subsequent superimposition of binding site residues on other strains of EBOV were carried out to check residual conformations, and hence to confirm the efficacy of potential compounds. As a mechanism for artefactual inhibition of proteins through non-specific compounds, virtual hits were assessed for their aggregator potential compared with previously reported aggregators. These systematic studies have indicated that a few compounds may be effective inhibitors of EBOV replication and therefore might have the potential to be developed as anti-EBOV drugs after subsequent testing and validation in experiments in vivo.

Apigenin inhibits African swine fever virus infection in vitro

African swine fever virus (ASFV) is one of the most devastating diseases of domestic pigs for which no effective vaccines are available. Flavonoids, natural products isolated from plants, have been reported to have significant in vitro and in vivo antiviral activity against different viruses. Here, we tested the antiviral effect of five flavonoids on the replication of ASFV in Vero cells. Our results showed a potent, dose-dependent anti-ASFV effect of apigenin in vitro. Time-of-addition experiments revealed that apigenin was highly effective at the early stages of infection. Apigenin reduced the ASFV yield by more than 99.99 % when it was added at 1 hpi. The antiviral activity of apigenin was further investigated by evaluation of ASFV protein synthesis and viral factories. This flavonoid inhibited ASFV-specific protein synthesis and viral factory formation. ASFV-infected cells continuously treated with apigenin did not display a cytopathic effect. Further studies addressing the use of apigenin in vivo are needed.

Cellular minichromosome maintenance complex component 5 (MCM5) is incorporated into HIV-1 virions and modulates viral replication in the newly infected cells

The post-entry events of HIV-1 infection occur within reverse transcription complexes derived from the viral cores entering the target cell. HIV-1 cores contain host proteins incorporated from virus-producing cells. In this report, we show that MCM5, a subunit of the hexameric minichromosome maintenance (MCM) DNA helicase complex, associates with Gag polyprotein and is incorporated into HIV-1 virions. The progeny virions depleted of MCM5 demonstrated reduced reverse transcription in newly infected cells, but integration and subsequent replication steps were not affected. Interestingly, increased packaging of MCM5 into the virions also led to reduced reverse transcription, but here viral replication was impaired. Our data suggest that incorporation of physiological amounts of MCM5 promotes aberrant reverse transcription, leading to partial incapacitation of cDNA, whereas increased MCM5 abundance leads to reduced reverse transcription and infection. Therefore, MCM5 has the properties of an inhibitory factor that interferes with production of an integration-competent cDNA product.

Ethnomedical and ethnobotanical investigations on the response capacities of Guinean traditional health practioners in the management of outbreaks of infectious diseases: The case of the Ebola virus epidemic

ETHNOPHARMACOLOGICAL RELEVANCE

The recent outbreak of Ebola virus infections has mostly remained confined to the West African countries Guinea-Conakry, Sierra-Leone and Liberia. Due to intense national and international mobilizations, a significant reduction in Ebola virus transmission has been recorded. While international efforts focus on new vaccines, medicines and diagnostics, no coherent national or international approach exists to integrate the potential of the traditional health practitioners (THPs) in the management of infectious diseases epidemics. Nevertheless, the first contact of most of the Ebola infected patients is with the THPs since the symptoms are similar to those of common traditionally treated diseases or symptoms such as malaria, hemorrhagic syndrome, typhoid or other gastrointestinal diseases, fever and vomiting.

MATERIALS AND METHODS

In an ethnomedical survey conducted in the 4 main Guinean regions contacts were established with a total of 113 THPs. The socio-demographic characteristics, the professional status and the traditional perception of Ebola Virus Disease (EVD) were recorded.

RESULTS

The traditional treatment of the main symptoms was based on 47 vegetal recipes which were focused on the treatment of diarrhea (22 recipes), fever (22 recipes), vomiting (2 recipes), external antiseptic (2 recipes), hemorrhagic syndrome (2 recipes), convulsion and dysentery (one recipe each). An ethnobotanical survey led to the collection of 54 plant species from which 44 identified belonging to 26 families. The most represented families were Euphorbiaceae, Caesalpiniaceae and Rubiaceae. Literature data on the twelve most cited plant species tends to corroborate their traditional use and to highlight their pharmacological potential.

CONCLUSIONS

It is worth to document all available knowledge on the traditional management of EVD-like symptoms in order to evaluate systematically the anti-Ebola potential of Guinean plant species.

Calcium Regulation of Hemorrhagic Fever Virus Budding: Mechanistic Implications for Host-Oriented Therapeutic Intervention

Hemorrhagic fever viruses, including the filoviruses (Ebola and Marburg) and arenaviruses (Lassa and Junín viruses), are serious human pathogens for which there are currently no FDA approved therapeutics or vaccines. Importantly, transmission of these viruses, and specifically late steps of budding, critically depend upon host cell machinery. Consequently, strategies which target these mechanisms represent potential targets for broad spectrum host oriented therapeutics. An important cellular signal implicated previously in EBOV budding is calcium. Indeed, host cell calcium signals are increasingly being recognized to play a role in steps of entry, replication, and transmission for a range of viruses, but if and how filoviruses and arenaviruses mobilize calcium and the precise stage of virus transmission regulated by calcium have not been defined. Here we demonstrate that expression of matrix proteins from both filoviruses and arenaviruses triggers an increase in host cytoplasmic Ca²⁺ concentration by a mechanism that requires host Orai1 channels. Furthermore, we demonstrate that Orai1 regulates both VLP and infectious filovirus and arenavirus production and spread. Notably, suppression of the protein that triggers Orai activation (Stromal Interaction Molecule 1, STIM1) and genetic inactivation or pharmacological blockade of Orai1 channels inhibits VLP and infectious virus egress. These findings are highly significant as they expand our understanding of host mechanisms that may broadly control enveloped RNA virus budding, and they establish Orai and STIM1 as novel targets for broad-spectrum host-oriented therapeutics to combat these emerging BSL-4 pathogens and potentially other enveloped RNA viruses that bud via similar mechanisms.

Filoviruses (Ebola and Marburg viruses) and arenaviruses (Lassa and Junín viruses) are high-priority pathogens that hijack host proteins and pathways to complete their replication cycles and spread from cell to cell. Here we provide genetic and pharmacological evidence to demonstrate that the host calcium channel protein Orai1 and ER calcium sensor protein STIM1 regulate efficient budding and spread of BSL-4 pathogens Ebola, Marburg, Lassa, and Junín viruses. Our findings are of broad significance as they provide new mechanistic insight into fundamental, immutable, and conserved mechanisms of hemorrhagic fever virus pathogenesis. Moreover, this strategy of targeting highly conserved host cellular protein(s) and mechanisms required by these viruses to complete their life cycle should elicit minimal drug resistance.

Antiherpes evaluation of soybean isoflavonoids

The antiviral effects of soybean isoflavonoids have been investigated recently, especially those of genistein. It has been reported that this isoflavone is able to inhibit herpes simplex virus (HSV) replication, which is associated with skin and epithelial mucosa infections. The treatment of these infections with antiherpes drugs has resulted in the emergence of resistant viral strains. Based on this evidence, the aim of this study was to investigate the anti-HSV effects of soybean isoflavonoids: daidzein, genistein, glycitein, and coumestrol. Genistein and coumestrol inhibited HSV-1 (KOS and 29R strains, which are acyclovir sensitive and acyclovir resistant, respectively) and HSV-2 (333 strain) replication, whereas no antiviral effects were detected for daidzein and glycitein. The mechanisms of action were evaluated by different methodological strategies. Coumestrol affected the early stages of viral infection, and both compounds were able to reduce HSV-1 protein expression, as well as HSV-2 cell-to-cell spread.

Ebola virus outbreak, updates on current therapeutic strategies

Filoviruses are enveloped negative‐sense single‐stranded RNA viruses, which include Ebola and Marburg viruses, known to cause hemorrhagic fever in humans with a case fatality of up to 90%. There have been several Ebola virus outbreaks since the first outbreak in the Democratic Republic of Congo in 1976 of which, the recent 2013–2015 epidemic in Guinea, Liberia, and Sierra Leone is the largest in recorded history. Within a few months of the start of the outbreak in December 2013, thousands of infected cases were reported with a significant number of deaths. As of March 2015, according to the Centers for Disease Control and Prevention, there have been nearly 25 000 suspected cases, with 15 000 confirmed by laboratory testing, and over 10 000 deaths. The large number of cases and the high mortality rate, combined with the lack of effective Food and Drug Administration‐approved treatments, necessitate the development of potent and safe therapeutic measures to combat the current and future outbreaks. Since the beginning of the outbreak, there have been considerable efforts to develop and characterize protective measures including vaccines and antiviral small molecules, and some have proven effective in vitro and in animal models. Most recently, a cocktail of monoclonal antibodies has been shown to be highly effective in protecting non‐human primates from Ebola virus infection. In this review, we will discuss what is known about the nature of the virus, phylogenetic classification, genomic organization and replication, disease transmission, and viral entry and highlight the current approaches and efforts, in the development of therapeutics, to control the outbreak. Copyright © 2015 John Wiley & Sons, Ltd.

Reverse genetics systems as tools for the development of novel therapies against filoviruses

Filoviruses cause severe hemorrhagic fevers with case fatality rates of up to 90%, for which no antivirals are currently available. Their categorization as biosafety level 4 agents restricts work with infectious viruses to a few maximum containment laboratories worldwide, which constitutes a significant obstacle for the development of countermeasures. Reverse genetics facilitates the generation of recombinant filoviruses, including reporter-expressing viruses, which have been increasingly used for drug screening and development in recent years. Further, reverse-genetics based lifecycle modeling systems allow modeling of the filovirus lifecycle without the need for a maximum containment laboratory and have recently been optimized for use in high-throughput assays. The availability of these reverse genetics-based tools will significantly improve our ability to find novel antivirals against filoviruses.

Crimean-Congo hemorrhagic fever virus entry into host cells occurs through the multivesicular body and requires ESCRT regulators

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne bunyavirus causing outbreaks of severe disease in humans, with a fatality rate approaching 30%. There are no widely accepted therapeutics available to prevent or treat the disease. CCHFV enters host cells through clathrin-mediated endocytosis and is subsequently transported to an acidified compartment where the fusion of virus envelope with cellular membranes takes place. To better understand the uptake pathway, we sought to identify host factors controlling CCHFV transport through the cell. We demonstrate that after passing through early endosomes in a Rab5-dependent manner, CCHFV is delivered to multivesicular bodies (MVBs). Virus particles localized to MVBs approximately 1 hour after infection and affected the distribution of the organelle within cells. Interestingly, blocking Rab7 activity had no effect on association of the virus with MVBs. Productive virus infection depended on phosphatidylinositol 3-kinase (PI3K) activity, which meditates the formation of functional MVBs. Silencing Tsg101, Vps24, Vps4B, or Alix/Aip1, components of the endosomal sorting complex required for transport (ESCRT) pathway controlling MVB biogenesis, inhibited infection of wild-type virus as well as a novel pseudotyped vesicular stomatitis virus (VSV) bearing CCHFV glycoprotein, supporting a role for the MVB pathway in CCHFV entry. We further demonstrate that blocking transport out of MVBs still allowed virus entry while preventing vesicular acidification, required for membrane fusion, trapped virions in the MVBs. These findings suggest that MVBs are necessary for infection and are the sites of virus-endosome membrane fusion.

Crimean-Congo hemorrhagic fever virus (CCHFV) is the cause of a severe, often fatal disease in humans. While it has been demonstrated that CCHFV cell entry depends on clathrin-mediated endocytosis, low pH, and early endosomes, the identity of the endosomes where virus penetrates into cell cytoplasm to initiate genome replication is unknown. Here, we showed that CCHFV was transported through early endosomes to multivesicular bodies (MVBs). We also showed that MVBs were likely the last organelle virus encountered before escaping into the cytoplasm. Our work has identified new cellular factors essential for CCHFV entry and potential novel targets for therapeutic intervention against this pathogen.

Small-molecule probes targeting the viral PPxY-host Nedd4 interface block egress of a broad range of RNA viruses

Budding of filoviruses, arenaviruses, and rhabdoviruses is facilitated by subversion of host proteins, such as Nedd4 E3 ubiquitin ligase, by viral PPxY late (L) budding domains expressed within the matrix proteins of these RNA viruses. As L domains are important for budding and are highly conserved in a wide array of RNA viruses, they represent potential broad-spectrum targets for the development of antiviral drugs. To identify potential competitive blockers, we used the known Nedd4 WW domain-PPxY interaction interface as the basis of an in silico screen. Using PPxY-dependent budding of Marburg (MARV) VP40 virus-like particles (VLPs) as our model system, we identified small-molecule hit 1 that inhibited Nedd4-PPxY interaction and PPxY-dependent budding. This lead candidate was subsequently improved with additional structure-activity relationship (SAR) analog testing which enhanced antibudding activity into the nanomolar range. Current lead compounds 4 and 5 exhibit on-target effects by specifically blocking the MARV VP40 PPxY-host Nedd4 interaction and subsequent PPxY-dependent egress of MARV VP40 VLPs. In addition, lead compounds 4 and 5 exhibited antibudding activity against Ebola and Lassa fever VLPs, as well as vesicular stomatitis and rabies viruses (VSV and RABV, respectively). These data provide target validation and suggest that inhibition of the PPxY-Nedd4 interaction can serve as the basis for the development of a novel class of broad-spectrum, host-oriented antivirals targeting viruses that depend on a functional PPxY L domain for efficient egress.

IMPORTANCE

There is an urgent and unmet need for the development of safe and effective therapeutics against biodefense and high-priority pathogens, including filoviruses (Ebola and Marburg) and arenaviruses (e.g., Lassa and Junin) which cause severe hemorrhagic fever syndromes with high mortality rates. We along with others have established that efficient budding of filoviruses, arenaviruses, and other viruses is critically dependent on the subversion of host proteins. As disruption of virus budding would prevent virus dissemination, identification of small-molecule compounds that block these critical viral-host interactions should effectively block disease progression and transmission. Our findings provide validation for targeting these virus-host interactions as we have identified lead inhibitors with broad-spectrum antiviral activity. In addition, such inhibitors might prove useful for newly emerging RNA viruses for which no therapeutics would be available.

A host-oriented inhibitor of Junin Argentine hemorrhagic fever virus egress

There are currently no U.S. Food and Drug Administration (FDA)-approved vaccines or therapeutics to prevent or treat Argentine hemorrhagic fever (AHF). The causative agent of AHF is Junin virus (JUNV); a New World arenavirus classified as a National Institute of Allergy and Infectious Disease/Centers for Disease Control and Prevention category A priority pathogen. The PTAP late (L) domain motif within JUNV Z protein facilitates virion egress and transmission by recruiting host Tsg101 and other ESCRT complex proteins to promote scission of the virus particle from the plasma membrane. Here, we describe a novel compound (compound 0013) that blocks the JUNV Z-Tsg101 interaction and inhibits budding of virus-like particles (VLPs) driven by ectopic expression of the Z protein and live-attenuated JUNV Candid-1 strain in cell culture. Since inhibition of the PTAP-Tsg101 interaction inhibits JUNV egress, compound 0013 serves as a prototype therapeutic that could reduce virus dissemination and disease progression in infected individuals. Moreover, since PTAP l-domain-mediated Tsg101 recruitment is utilized by other RNA virus pathogens (e.g., Ebola virus and HIV-1), PTAP inhibitors such as compound 0013 have the potential to function as potent broad-spectrum, host-oriented antiviral drugs.

IMPORTANCE

There are currently no FDA-approved vaccines or therapeutics to prevent or treat Argentine hemorrhagic fever (AHF). The causative agent of AHF is Junin virus (JUNV); a New World arenavirus classified as an NIAID/CDC category A priority pathogen. Here, we describe a prototype therapeutic that blocks budding of JUNV and has the potential to function as a broad-spectrum antiviral drug.

Could the Ebola virus matrix protein VP40 be a drug target?

Filoviruses are filamentous lipid-enveloped viruses and include Ebola (EBOV) and Marburg, which are morphologically identical but antigenically distinct. These viruses can be very deadly with outbreaks of EBOV having clinical fatality as high as 90%. In 2012 there were two separate Ebola outbreaks in the Democratic Republic of Congo and Uganda that resulted in 25 and 4 fatalities, respectively. The lack of preventive vaccines and FDA-approved therapeutics has struck fear that the EBOV could become a pandemic threat. The Ebola genome encodes only seven genes, which mediate the entry, replication, and egress of the virus from the host cell. The EBOV matrix protein is VP40, which is found localized under the lipid envelope of the virus where it bridges the viral lipid envelope and nucleocapsid. VP40 is effectively a peripheral protein that mediates the plasma membrane binding and budding of the virus prior to egress. A number of studies have demonstrated specific deletions or mutations of VP40 to abrogate viral egress but to date pharmacological inhibition of VP40 has not been demonstrated. This editorial highlights VP40, which is the most abundantly expressed protein of the virus and discusses VP40 as a potential therapeutic target.

Sodium hydrogen exchangers contribute to arenavirus cell entry

Several arenaviruses, chiefly Lassa virus (LASV), cause hemorrhagic fever (HF) disease in humans and pose a great public health concern in the regions in which they are endemic. Moreover, evidence indicates that the worldwide-distributed prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen of clinical significance. The limited existing armamentarium to combat human-pathogenic arenaviruses underscores the importance of developing novel antiarenaviral drugs, a task that would be facilitated by the identification and characterization of virus-host cell factor interactions that contribute to the arenavirus life cycle. A genome-wide small interfering RNA (siRNA) screen identified sodium hydrogen exchanger 3 (NHE3) as required for efficient multiplication of LCMV in HeLa cells, but the mechanisms by which NHE activity contributed to the life cycle of LCMV remain unknown. Here we show that treatment with the NHE inhibitor 5-(N-ethyl-N-isopropyl) amiloride (EIPA) resulted in a robust inhibition of LCMV multiplication in both rodent (BHK-21) and human (A549) cells. EIPA-mediated inhibition was due not to interference with virus RNA replication, gene expression, or budding but rather to a blockade of virus cell entry. EIPA also inhibited cell entry mediated by the glycoproteins of the HF arenaviruses LASV and Junin virus (JUNV). Pharmacological and genetic studies revealed that cell entry of LCMV in A549 cells depended on actin remodeling and Pak1, suggesting a macropinocytosis-like cell entry pathway. Finally, zoniporide, an NHE inhibitor being explored as a therapeutic agent to treat myocardial infarction, inhibited LCMV propagation in culture cells. Our findings indicate that targeting NHEs could be a novel strategy to combat human-pathogenic arenaviruses.

Cell entry of Lassa virus induces tyrosine phosphorylation of dystroglycan

The extracellular matrix (ECM) receptor dystroglycan (DG) serves as a cellular receptor for the highly pathogenic arenavirus Lassa virus (LASV) that causes a haemorrhagic fever with high mortality in human. In the host cell, DG provides a molecular link between the ECM and the actin cytoskeleton via the adapter proteins utrophin or dystrophin. Here we investigated post-translational modifications of DG in the context of LASV cell entry. Using the tyrosine kinase inhibitor genistein, we found that tyrosine kinases are required for efficient internalization of virus particles, but not virus-receptor binding. Engagement of cellular DG by LASV envelope glycoprotein (LASV GP) in human epithelial cells induced tyrosine phosphorylation of the cytoplasmic domain of DG. LASV GP binding to DG further resulted in dissociation of the adapter protein utrophin from virus-bound DG. This virus-induced dissociation of utrophin was affected by genistein treatment, suggesting a role of receptor tyrosine phosphorylation in the process.

Arenaviruses and lethal mutagenesis. Prospects for new ribavirin-based interventions

Lymphocytic choriomeningitis virus (LCMV) has contributed to unveil some of the molecular mechanisms of lethal mutagenesis, or loss of virus infectivity due to increased mutation rates. Here we review these developments, and provide additional evidence that ribavirin displays a dual mutagenic and inhibitory activity on LCMV that can be relevant to treatment designs. Using 5-fluorouracil as mutagenic agent and ribavirin either as inhibitor or mutagen, we document an advantage of a sequential inhibitor-mutagen administration over the corresponding combination treatment to achieve a low LCMV load in cell culture. This advantage is accentuated in the concentration range in which ribavirin acts mainly as an inhibitor, rather than as mutagen. This observation reinforces previous theoretical and experimental studies in supporting a sequential inhibitor-mutagen administration as a possible antiviral design. Given recent progress in the development of new inhibitors of arenavirus replication, our results suggest new options of ribavirin-based anti-arenavirus treatments.

Animal models, prophylaxis, and therapeutics for arenavirus infections

Arenaviruses are enveloped, bipartite negative single-stranded RNA viruses that can cause a wide spectrum of disease in humans and experimental animals including hemorrhagic fever. The majority of these viruses are rodent-borne and the arenavirus family can be divided into two groups: the Lassa-Lymphocytic choriomeningitis serocomplex and the Tacaribe serocomplex. Arenavirus-induced disease may include characteristic symptoms ranging from fever, malaise, body aches, petechiae, dehydration, hemorrhage, organ failure, shock, and in severe cases death. Currently, there are few prophylactic and therapeutic treatments available for arenavirus-induced symptoms. Supportive care and ribavirin remain the predominant strategies for treating most of the arenavirus-induced diseases. Therefore, efficacy testing of novel therapeutic and prophylactic strategies in relevant animal models is necessary. Because of the potential for person-to-person spread, the ability to cause lethal or debilitating disease in humans, limited treatment options, and potential as a bio-weapon, the development of prophylactics and therapeutics is essential. This article reviews the current arenavirus animal models and prophylactic and therapeutic strategies under development to treat arenavirus infection.

Host cell factors as antiviral targets in arenavirus infection

Among the members of the Arenaviridae family, Lassa virus and Junin virus generate periodic annual outbreaks of severe human hemorrhagic fever (HF) in endemic areas of West Africa and Argentina, respectively. Given the human health threat that arenaviruses represent and the lack of a specific and safe chemotherapy, the search for effective antiviral compounds is a continuous demanding effort. Since diverse host cell pathways and enzymes are used by RNA viruses to fulfill their replicative cycle, the targeting of a host process has turned an attractive antiviral approach in the last years for many unrelated virus types. This strategy has the additional benefit to reduce the serious challenge for therapy of RNA viruses to escape from drug effects through selection of resistant variants triggered by their high mutation rate. This article focuses on novel strategies to identify inhibitors for arenavirus therapy, analyzing the potential for antiviral developments of diverse host factors essential for virus infection.

Therapeutics for filovirus infection: traditional approaches and progress towards in silico drug design

INTRODUCTION

Ebolaviruses and marburgviruses cause severe and often lethal human hemorrhagic fevers. As no FDA-approved therapeutics are available for these infections, efforts to discover new therapeutics are important, especially because these pathogens are considered biothreats and emerging infectious diseases. All methods for discovering new therapeutics should be considered, including compound library screening in vitro against virus and in silico structure-based drug design, where possible, if sufficient biochemical and structural information is available.

AREAS COVERED

This review covers the structure and function of filovirus proteins, as they have been reported to date, as well as some of the current antiviral screening approaches. The authors discuss key studies mapping small-molecule modulators that were found through library and in silico screens to potential sites on viral proteins or host proteins involved in virus trafficking and pathogenesis. A description of ebolavirus and marburgvirus diseases and available animal models is also presented.

EXPERT OPINION

To discover novel therapeutics with potent efficacy using sophisticated computational methods, more high-resolution crystal structures of filovirus proteins and more details about the protein functions and host interaction will be required. Current compound screening efforts are finding active antiviral compounds, but an emphasis on discovery research to investigate protein structures and functions enabling in silico drug design would provide another avenue for finding antiviral molecules. Additionally, targeting of protein-protein interactions may be a future avenue for drug discovery since disrupting catalytic sites may not be possible for all proteins.