Chikungunya Virus: In Vitro Response to Combination Therapy With Ribavirin and Interferon Alfa 2a

Drugs targeting structural and nonstructural proteins of the chikungunya virus: A review

Chikungunya virus (CHIKV) is a single positive-stranded RNA virus of the Togaviridae family and Alphavirus genus, with a typical lipid bilayer envelope structure, and is the causative agent of human chikungunya fever (CHIKF). The U.S. Food and Drug Administration has recently approved the first chikungunya vaccine, Ixchiq; however, vaccination rates are low, and CHIKF is prevalent owing to its periodic outbreaks. Thus, developing effective anti-CHIKV drugs in clinical settings is imperative. Viral proteins encoded by the CHIKV genome play vital roles in all stages of infection, and developing therapeutic agents that target these CHIKV proteins is an effective strategy to improve CHIKF treatment efficacy and reduce mortality rates. Therefore, in the present review article, we aimed to investigate the basic structure, function, and replication cycle of CHIKV and comprehensively outline the current status and future advancements in anti-CHIKV drug development, specifically targeting nonstructural (ns) proteins, including nsP1, nsP2, nsP3, and nsP4 and structural proteins such as capsid (C), E3, E2, 6K, and E1.

Repurposed drugs in combinations exert additive anti-chikungunya virus activity: an in-vitro study

Chikungunya virus (CHIKV) infection causes chikungunya, a viral disease that currently has no specific antiviral treatment. Several repurposed drug candidates have been investigated for the treatment of the disease. In order to improve the efficacy of the known drugs, combining drugs for treatment is a promising approach. The current study was undertaken to explore the antiviral activity of a combination of repurposed drugs that were reported to have anti-CHIKV activity. We explored the effect of different combinations of six effective drugs (2-fluoroadenine, emetine, lomibuvir, enalaprilat, metyrapone and resveratrol) at their non-toxic concentrations against CHIKV under post infection treatment conditions in Vero cells. Focus-forming unit assay, real time RT-PCR, immunofluorescence assay, and western blot were used to determine the virus titre. The results revealed that the combination of 2-fluoroadenine with either metyrapone or emetine or enalaprilat exerted inhibitory activity against CHIKV under post-infection treatment conditions. The effect of these drug combinations was additive in nature compared to the effect of the individual drugs. The results suggest an additive anti-viral effect of these drug combinations against CHIKV. The findings could serve as an outline for the development of an innovative therapeutic approach in the future to treat CHIKV-infected patients.

Combination Therapy with UV-4B and Molnupiravir Enhances SARS-CoV-2 Suppression

The host targeting antiviral, UV-4B, and the RNA polymerase inhibitor, molnupiravir, are two orally available, broad-spectrum antivirals that have demonstrated potent activity against SARS-CoV-2 as monotherapy. In this work, we evaluated the effectiveness of UV-4B and EIDD-1931 (molnupiravir's main circulating metabolite) combination regimens against the SARS-CoV-2 beta, delta, and omicron BA.2 variants in a human lung cell line. Infected ACE2 transfected A549 (ACE2-A549) cells were treated with UV-4B and EIDD-1931 both as monotherapy and in combination. Viral supernatant was sampled on day three when viral titers peaked in the no-treatment control arm, and levels of infectious virus were measured by plaque assay. The drug-drug effect interaction between UV-4B and EIDD-1931 was also defined using the Greco Universal Response Surface Approach (URSA) model. Antiviral evaluations demonstrated that treatment with UV-4B plus EIDD-1931 enhanced antiviral activity against all three variants relative to monotherapy. These results were in accordance with those obtained from the Greco model, as these identified the interaction between UV-4B and EIDD-1931 as additive against the beta and omicron variants and synergistic against the delta variant. Our findings highlight the anti-SARS-CoV-2 potential of UV-4B and EIDD-1931 combination regimens, and present combination therapy as a promising therapeutic strategy against SARS-CoV-2.

Evolution and immunopathology of chikungunya virus informs therapeutic development

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, is an emerging global threat identified in more than 60 countries across continents. The risk of CHIKV transmission is rising due to increased global interactions, year-round presence of mosquito vectors, and the ability of CHIKV to produce high host viral loads and undergo mutation. Although CHIKV disease is rarely fatal, it can progress to a chronic stage, during which patients experience severe debilitating arthritis that can last from several weeks to months or years. At present, there are no licensed vaccines or antiviral drugs for CHIKV disease, and treatment is primarily symptomatic. This Review provides an overview of CHIKV pathogenesis and explores the available therapeutic options and the most recent advances in novel therapeutic strategies against CHIKV infections.

Specific sequence mutations in a long-lasting rhIFN-α2b version reduce in vitro and in vivo immunogenicity and increase in vitro protein stability

For decades, recombinant human interferon alpha (rhIFN-α2b) has been used to treat emerging and chronic viral diseases. However, rhIFN-α2b is immunogenic and has a short in vivo half-life. To solve these limitations, two long-lasting hyperglycosylated proteins with reduced immunogenicity were developed and designated as 4N-IFN(VAR1) and 4N-IFN(VAR3). Here, we continue to study the relevant characteristics of these therapeutic candidates. Thus, we demonstrated that both de-immunized IFN versions elicited significantly lower neutralizing antibody responses than the original molecule in HLA-DR1 transgenic mice, confirming our previous in vitro protein immunogenicity data. Also, we found that these biobetters exhibited remarkable stability when exposed to different physical factors that the protein product may encounter during its production process and storage, such as low pH, thermal stress, and repeated freezing/thawing cycles. Taking into consideration our previous and present results, 4N-IFN(VAR1) and 4N-IFN-4N(VAR3) appear to be valuable candidates for the treatment of human viral diseases.

Growth in chikungunya virus-related research in ASEAN and South Asian countries from 1967 to 2022 following disease emergence: a bibliometric and graphical analysis

BACKGROUND

ASEAN (Association of Southeast Asian Nations) is composed of ten Southeast Asian countries bound by socio-cultural ties that promote regional peace and stability. South Asia, located in the southern subregion of Asia, includes nine countries sharing similarities in geographical and ethno-cultural factors. Chikungunya is one of the most significant problems in Southeast and South Asian countries. Much of the current chikungunya epidemic in Southeast Asia is caused by the emergence of a virus strain that originated in Africa and spread to Southeast Asia. Meanwhile, in South Asia, three confirmed lineages are in circulation. Given the positive correlation between research activity and the improvement of the clinical framework of biomedical research, this article aimed to examine the growth of chikungunya virus-related research in ASEAN and South Asian countries.

METHODS

The Scopus database was used for this bibliometric analysis. The retrieved publications were subjected to a number of analyses, including those for the most prolific countries, journals, authors, institutions, and articles. Co-occurrence mapping of terms and keywords was used to determine the current state, emerging topics, and future prospects of chikungunya virus-related research. Bibliometrix and VOSviewer were used to analyze the data and visualize the collaboration network mapping.

RESULTS

The Scopus search engine identified 1280 chikungunya-related documents published by ASEAN and South Asian countries between 1967 and 2022. According to our findings, India was the most productive country in South Asia, and Thailand was the most productive country in Southeast Asia. In the early stages of the study, researchers investigated the vectors and outbreaks of the chikungunya virus. In recent years, the development of antivirus agents has emerged as a prominent topic.

CONCLUSIONS

Our study is the first to present the growth of chikungunya virus-related research in ASEAN and South Asian countries from 1967 to 2022. In this study, the evaluation of the comprehensive profile of research on chikungunya can serve as a guide for future studies. In addition, a bibliometric analysis may serve as a resource for healthcare policymakers.

Insights into the role of the cobalt(III)-thiosemicarbazone complex as a potential inhibitor of the Chikungunya virus nsP4

Chikungunya virus (CHIKV) is the causative agent of chikungunya fever, a disease that can result in disability. Until now, there is no antiviral treatment against CHIKV, demonstrating that there is a need for development of new drugs. Studies have shown that thiosemicarbazones and their metal complexes possess biological activities, and their synthesis is simple, clean, versatile, and results in high yields. Here, we evaluated the mechanism of action (MOA) of a cobalt(III) thiosemicarbazone complex named [CoIII(L1)2]Cl based on its in vitro potent antiviral activity against CHIKV previously evaluated (80% of inhibition on replication). Furthermore, the complex has no toxicity in healthy cells, as confirmed by infecting BHK-21 cells with CHIKV-nanoluciferase in the presence of the compound, showing that [CoIII(L1)2]Cl inhibited CHIKV infection with the selective index of 3.26. [CoIII(L1)2]Cl presented a post-entry effect on viral replication, emphasized by the strong interaction of [CoIII(L1)2]Cl with CHIKV non-structural protein 4 (nsP4) in the microscale thermophoresis assay, suggesting a potential mode of action of this compound against CHIKV. Moreover, in silico analyses by molecular docking demonstrated potential interaction of [CoIII(L1)2]Cl with nsP4 through hydrogen bonds, hydrophobic and electrostatic interactions. The evaluation of ADME-Tox properties showed that [CoIII(L1)2]Cl presents appropriate lipophilicity, good human intestinal absorption, and has no toxicological effect as irritant, mutagenic, reproductive, and tumorigenic side effects.

Understanding the Biology and Immune Pathogenesis of Chikungunya Virus Infection for Diagnostic and Vaccine Development

Chikungunya virus, the causative agent of chikungunya fever, is generally characterized by the sudden onset of symptoms, including fever, rash, myalgia, and headache. In some patients, acute chikungunya virus infection progresses to severe and chronic arthralgia that persists for years. Chikungunya infection is more commonly identified in tropical and subtropical regions. However, recent expansions and epidemics in the temperate regions have raised concerns about the future public health impact of chikungunya diseases. Several underlying factors have likely contributed to the recent re-emergence of chikungunya infection, including urbanization, human travel, viral adaptation to mosquito vectors, lack of effective control measures, and the spread of mosquito vectors to new regions. However, the true burden of chikungunya disease is most likely to be underestimated, particularly in developing countries, due to the lack of standard diagnostic assays and clinical manifestations overlapping with those of other endemic viral infections in the regions. Additionally, there have been no chikungunya vaccines available to prevent the infection. Thus, it is important to update our understanding of the immunopathogenesis of chikungunya infection, its clinical manifestations, the diagnosis, and the development of chikungunya vaccines.

Applications of the hollow-fibre infection model (HFIM) in viral infection studies

Conventional cell culture systems involve growing cells in stationary cultures in the presence of growth medium containing various types of supplements. At confluency, the cells are divided and further expanded in new culture dishes. This passage from confluent monolayer to sparse cultures does not reflect normal physiological conditions and represents quite a drastic physiological change that may affect the natural cell physiobiology. Hollow-fibre bioreactors were in part developed to overcome these limitations and since their inception, they have widely been used in production of monoclonal antibodies and recombinant proteins. These bioreactors are increasingly used to study antibacterial drug effects via simulation of in vivo pharmacokinetic profiles. The use of the hollow-fibre infection model (HFIM) in viral infection studies is less well developed and in this review we have analysed and summarized the current available literature on the use of these bioreactors, with an emphasis on viruses. Our work has demonstrated that this system can be applied for viral expansion, studies of drug resistance mechanisms, and studies of pharmacokinetic/pharmacodynamic (PK/PD) of antiviral compounds. These platforms could therefore have great applications in large-scale vaccine development, and in studies of mechanisms driving antiviral resistance, since the HFIM could recapitulate the same resistance mechanisms and mutations observed in vivo in clinic. Furthermore, some dosage and spacing regimens evaluated in the HFIM system, as allowing maximal viral suppression, are in line with clinical practice and highlight this 'in vivo-like' system as a powerful tool for experimental validation of in vitro-predicted antiviral activities.

Development and Application of Treatment for Chikungunya Fever

The development and application of treatment for Chikungunya fever (CHIKF) remains complicated as there is no current standard treatment and many barriers to research exist. Chikungunya virus (CHIKV) causes serious global health implications due to its socioeconomic impact and high morbidity rates. In research, treatment through natural and pharmaceutical techniques is being evaluated for their efficacy and effectiveness. Natural treatment options, such as homeopathy and physiotherapy, give patients a variety of options for how to best manage acute and chronic symptoms. Some of the most used pharmaceutical therapies for CHIKV include non-steroidal anti-inflammatory drugs (NSAIDS), methotrexate (MTX), chloroquine, and ribavirin. Currently, there is no commercially available vaccine for chikungunya, but vaccine development is crucial for this virus. Potential treatments need further research until they can become a standard part of treatment. The barriers to research for this complicated virus create challenges in the efficacy and equitability of its research. The rising need for increased research to fully understand chikungunya in order to develop more effective treatment options is vital in protecting endemic populations globally.

DeepVir: Graphical Deep Matrix Factorization for In Silico Antiviral Repositioning-Application to COVID-19

This study formulates antiviral repositioning as a matrix completion problem wherein the antiviral drugs are along the rows and the viruses are along the columns. The input matrix is partially filled, with ones in positions where the antiviral drug has been known to be effective against a virus. The curated metadata for antivirals (chemical structure and pathways) and viruses (genomic structure and symptoms) are encoded into our matrix completion framework as graph Laplacian regularization. We then frame the resulting multiple graph regularized matrix completion (GRMC) problem as deep matrix factorization. This is solved by using a novel optimization method called HyPALM (Hybrid Proximal Alternating Linearized Minimization). Results of our curated RNA drug-virus association data set show that the proposed approach excels over state-of-the-art GRMC techniques. When applied to in silico prediction of antivirals for COVID-19, our approach returns antivirals that are either used for treating patients or are under trials for the same.

Treatment of Respiratory Viral Coinfections

With the advent of rapid multiplex PCR, physicians have been able to test for multiple viral pathogens when a patient presents with influenza-like illness. This has led to the discovery that many respiratory infections are caused by more than one virus. Antiviral treatment of viral coinfections can be complex because treatment of one virus will affect the time course of the other virus. Since effective antivirals are only available for some respiratory viruses, careful consideration needs to be given on the effect treating one virus will have on the dynamics of the other virus, which might not have available antiviral treatment. In this study, we use mathematical models of viral coinfections to assess the effect of antiviral treatment on coinfections. We examine the effect of the mechanism of action, relative growth rates of the viruses, and the assumptions underlying the interaction of the viruses. We find that high antiviral efficacy is needed to suppress both infections. If high doses of both antivirals are not achieved, then we run the risk of lengthening the duration of coinfection or even of allowing a suppressed virus to replicate to higher viral titers.

Development of highly stable and de-immunized versions of recombinant alpha interferon: Promising candidates for the treatment of chronic and emerging viral diseases

Human interferon alpha (hIFN-α) administration constitutes the current FDA approved therapy for chronic Hepatitis B and C virus infections. Additionally, hIFN-α treatment efficacy was recently demonstrated in patients with COVID-19. Thus, hIFN-α constitutes a therapeutic alternative for those countries where vaccination is inaccessible and for people who did not respond effectively to vaccination. However, hIFN-α2b exhibits a short plasma half-life resulting in the occurrence of severe side effects. To optimize the cytokine's pharmacokinetic profile, we developed a hyperglycosylated IFN, referred to as GMOP-IFN.

Given the significant number of reports showing neutralizing antibodies (NAb) formation after hIFN-α administration, here we applied the DeFT (De-immunization of Functional Therapeutics) approach to develop functional, de-immunized versions of GMOP-IFN. Two GMOP-IFN variants exhibited significantly reduced ex vivo immunogenicity and null antiproliferative activity, while preserving antiviral function. The results obtained in this work indicate that the new de-immunized GMOP-IFN variants constitute promising candidates for antiviral therapy.

Antivirals against the Chikungunya Virus

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that has re-emerged in recent decades, causing large-scale epidemics in many parts of the world. CHIKV infection leads to a febrile disease known as chikungunya fever (CHIKF), which is characterised by severe joint pain and myalgia. As many patients develop a painful chronic stage and neither antiviral drugs nor vaccines are available, the development of a potent CHIKV inhibiting drug is crucial for CHIKF treatment. A comprehensive summary of current antiviral research and development of small-molecule inhibitor against CHIKV is presented in this review. We highlight different approaches used for the identification of such compounds and further discuss the identification and application of promising viral and host targets.

Antiviral Evaluation of UV-4B and Interferon-Alpha Combination Regimens against Dengue Virus

Dengue virus (DENV) is a flavivirus associated with clinical manifestations ranging in severity from self-limiting dengue fever, to the potentially life threatening condition, severe dengue. There are currently no approved antiviral therapies for the treatment of DENV. Here, we evaluated the antiviral potential of four broad-spectrum antivirals, UV-4B, interferon-alpha (IFN), sofosbuvir (SOF), and favipiravir (FAV) against DENV serotype 2 as mono- and combination therapy in cell lines that are physiologically relevant to human infection. Cell lines derived from human liver (HUH-7), neurons (SK-N-MC), and skin (HFF-1) were infected with DENV and treated with UV-4B, IFN, SOF, or FAV. Viral supernatant was sampled daily and infectious viral burden was quantified by plaque assay on Vero cells. Drug effect on cell proliferation in uninfected and infected cells was also assessed. UV-4B inhibited DENV in HUH-7, SK-N-MC, and HFF-1 cells yielding EC₅₀ values of 23.75, 49.44, and 37.38 µM, respectively. Clinically achievable IFN concentrations substantially reduced viral burden in HUH-7 (EC₅₀ = 102.7 IU/mL), SK-N-MC (EC₅₀ = 86.59 IU/mL), and HFF-1 (EC₅₀ = 163.1 IU/mL) cells. SOF potently inhibited DENV in HUH-7 cells but failed to produce the same effect in SK-N-MC and HFF-1 cells. Finally, FAV provided minimal suppression in HUH-7 and SK-N-MC cells, but was ineffective in HFF-1 cells. The two most potent anti-DENV agents, UV-4B and IFN, were also assessed in combination. UV-4B + IFN treatment enhanced antiviral activity in HUH-7, SK-N-MC, and HFF-1 cells relative to monotherapy. Our results demonstrate the antiviral potential of UV-4B and IFN against DENV in multiple physiologically relevant cell types.

A computational approach to aid clinicians in selecting anti-viral drugs for COVID-19 trials

The year 2020 witnessed a heavy death toll due to COVID-19, calling for a global emergency. The continuous ongoing research and clinical trials paved the way for vaccines. But, the vaccine efficacy in the long run is still questionable due to the mutating coronavirus, which makes drug re-positioning a reasonable alternative. COVID-19 has hence fast-paced drug re-positioning for the treatment of COVID-19 and its symptoms. This work builds computational models using matrix completion techniques to predict drug-virus association for drug re-positioning. The aim is to assist clinicians with a tool for selecting prospective antiviral treatments. Since the virus is known to mutate fast, the tool is likely to help clinicians in selecting the right set of antivirals for the mutated isolate. The main contribution of this work is a manually curated database publicly shared, comprising of existing associations between viruses and their corresponding antivirals. The database gathers similarity information using the chemical structure of drugs and the genomic structure of viruses. Along with this database, we make available a set of state-of-the-art computational drug re-positioning tools based on matrix completion. The tools are first analysed on a standard set of experimental protocols for drug target interactions. The best performing ones are applied for the task of re-positioning antivirals for COVID-19. These tools select six drugs out of which four are currently under various stages of trial, namely Remdesivir (as a cure), Ribavarin (in combination with others for cure), Umifenovir (as a prophylactic and cure) and Sofosbuvir (as a cure). Another unanimous prediction is Tenofovir alafenamide, which is a novel Tenofovir prodrug developed in order to improve renal safety when compared to its original counterpart (older version) Tenofovir disoproxil. Both are under trail, the former as a cure and the latter as a prophylactic. These results establish that the computational methods are in sync with the state-of-practice. We also demonstrate how the drugs to be used against the virus would vary as SARS-Cov-2 mutates over time by predicting the drugs for the mutated strains, suggesting the importance of such a tool in drug prediction. We believe this work would open up possibilities for applying machine learning models to clinical research for drug-virus association prediction and other similar biological problems.

Combination Regimens of Favipiravir Plus Interferon Alpha Inhibit Chikungunya Virus Replication in Clinically Relevant Human Cell Lines

Chikungunya virus (CHIKV) is an alphavirus associated with a broad tissue tropism for which no antivirals or vaccines are approved. This study evaluated the antiviral potential of favipiravir (FAV), interferon-alpha (IFN), and ribavirin (RBV) against CHIKV as mono- and combination-therapy in cell lines that are clinically relevant to human infection. Cells derived from human connective tissue (HT-1080), neurons (SK-N-MC), and skin (HFF-1) were infected with CHIKV and treated with different concentrations of FAV, IFN, or RBV. Viral supernatant was sampled daily and the burden was quantified by plaque assay on Vero cells. FAV and IFN were the most effective against CHIKV on various cell lines, suppressing the viral burden at clinically achievable concentrations; although the degree of antiviral activity was heavily influenced by cell type. RBV was not effective and demonstrated substantial toxicity, indicating that it is not a feasible candidate for CHIKV. The combination of FAV and IFN was then assessed on all cell lines. Combination therapy enhanced antiviral activity in HT-1080 and SK-N-MC cells, but not in HFF-1 cells. We developed a pharmacokinetic/pharmacodynamic model that described the viral burden and inhibitory antiviral effect. Simulations from this model predicted clinically relevant concentrations of FAV plus IFN completely suppressed CHIKV replication in HT-1080 cells, and considerably slowed down the rate of viral replication in SK-N-MC cells. The model predicted substantial inhibition of viral replication by clinical IFN regimens in HFF-1 cells. Our results highlight the antiviral potential of FAV and IFN combination regimens against CHIKV in clinically relevant cell types.

Current and Promising Antivirals Against Chikungunya Virus

Chikungunya virus (CHIKV) is the causative agent of chikungunya fever (CHIKF) and is categorized as a(n) (re)emerging arbovirus. CHIKV has repeatedly been responsible for outbreaks that caused serious economic and public health problems in the affected countries. To date, no vaccine or specific antiviral therapies are available. This review gives a summary on current antivirals that have been investigated as potential therapeutics against CHIKF. The mode of action as well as possible compound targets (viral and host targets) are being addressed. This review hopes to provide critical information on the in vitro efficacies of various compounds and might help researchers in their considerations for future experiments.

Antiviral Strategies against Arthritogenic Alphaviruses

Alphaviruses are members of the Togaviridae family that are mainly transmitted by arthropods such as mosquitoes. In the last decades, several alphaviruses have re-emerged, causing outbreaks worldwide. One example is the re-emergence of chikungunya virus (CHIKV) in 2004, which caused massive epidemics in the Indian Ocean region after which the virus dramatically spread to the Americas in late 2013. Besides CHIKV, other alphaviruses, such as the Ross River virus (RRV), Mayaro virus (MAYV), and Venezuelan equine encephalitis virus (VEEV), have emerged and have become a serious public health concern in recent years. Infections with the Old World alphaviruses (e.g., CHIKV, RRV) are primarily associated with polyarthritis and myalgia that can persist for months to years. On the other hand, New World alphaviruses such as VEEV cause mainly neurological disease. Despite the worldwide (re-)emergence of these viruses, there are no antivirals or vaccines available for the treatment or prevention of infections with alphaviruses. It is therefore of utmost importance to develop antiviral strategies against these viruses. We here provided an overview of the reported antiviral strategies against arthritogenic alphaviruses. In addition, we highlighted the future perspectives for the development and the proper use of such antivirals.

An approximate solution of the interferon-dependent viral kinetics model of influenza

The analysis of viral kinetics models is mostly achieved by numerical methods. We present an approach via a Magnus expansion that allows us to give an approximate solution to the interferon-dependent viral infection model of influenza which is compared with numerical results. The time of peak viral load is calculated from the approximation and stays within 10% in the studied range of interferon (IFN) efficacy ϵ ∈ [0, 1000]. We utilize our solution to interpret the effect of varying IFN efficacy, suggesting a competition between virions and interferon that can cause an additional peak in the usually exponential increase in the viral load.

Antiviral drug discovery against arthritogenic alphaviruses: Tools and molecular targets

Alphaviruses are (mainly) arthropod-borne viruses that belong to the family of the Togaviridae. Based on the disease they cause, alphaviruses are divided into an arthritogenic and an encephalitic group. Arthritogenic alphaviruses such as the chikungunya virus (CHIKV), the Ross River virus (RRV) and the Mayaro virus (MAYV) have become a serious public health concern in recent years. Epidemics are associated with high morbidity and the infections cause in many patients debilitating joint pain that can persist for months to years. The recent (2013-2014) introduction of CHIKV in the Americas resulted in millions of infected persons. Massive outbreaks of CHIKV and other arthritogenic alphaviruses are likely to occur in the future. Despite the worldwide (re-)emergence of these viruses, there are no antivirals or vaccines available for the treatment or prevention of infections with alphaviruses. It is therefore of utmost importance to develop antiviral strategies against these viruses. We here review the possible molecular targets in the replication cycle of these viruses for the development of antivirals. In addition, we provide an overview of the currently available in vitro systems and mouse infection models that can be used to assess the potential antiviral effect against these viruses.

Antiviral Effect of Lithium Chloride and Diammonium Glycyrrhizinate on Porcine Deltacoronavirus In Vitro

Porcine deltacoronavirus (PDCoV) is an emerging global swine virus that has a propensity for interspecies transmission. It was identified in Hong Kong in 2012. Given that neither specific antiviral drugs nor vaccines are available for newly emerging porcine deltacoronavirus, searching for effective antiviral drugs is a high priority. In this study, lithium chloride (LiCl) and diammonium glycyrrhizinate (DG), which are host-acting antivirals (HAAs), were tested against PDCoV. We found that LiCl and DG inhibited PDCoV replication in LLC-PK1 cells in a dose-dependent manner. The antiviral effects of LiCl and DG occurred at the early stage of PDCoV replication, and DG also inhibited virus attachment to the cells. Moreover, both drugs inhibited PDCoV-induced apoptosis in LLC-PK1 cells. This study suggests LiCl and DG as new drugs for the treatment of PDCoV infection.

Antiviral activity of nobiletin against chikungunya virus in vitro

BACKGROUND

Chikungunya virus (CHIKV), a highly contagious re-emerging virus, is transmitted by infected mosquitoes. CHIKV is prevalent in tropical countries and is continuing to creep farther north into temperate areas. CHIKV is responsible for induction of chikungunya fever (CF) and severe joint stiffness with the capability of developing into bilateral and systemic arthralgia or even encephalitis. Despite the high morbidity rate, no approved antiviral drug is available. Therefore, an anti-CHIKV therapy is necessary to control this disease. In this study, we screened four flavonoids for anti-CHIKV activities: nobiletin, phlorizin, resveratrol and oxyresveratrol.

METHODS

We performed MTT, Viral ToxGlo^TM and lactate dehydrogenase (LDH) assays to assess the viability of CHIKV-infected host cells. Plaque assay and immunofluorescent assay were utilized to evaluate the levels of viral production in quantification and qualification, respectively.

RESULTS

We first confirmed that nobiletin can maintain the cellular survival of infected cells without inducing significant toxicity to host cells. Nobiletin suppressed virus-induced cell death and viral production. Also, the antiviral efficacy of nobiletin can last for at least 48 h during infection. More importantly, nobiletin inhibited CHIKV infection during the translation/replication stages and viral entry, making nobiletin a potential clinical antiviral agent in prophylaxis and post-exposure treatment.

CONCLUSIONS

In this study, our results provided a strategy to develop anti-chikungunya agents by utilizing natural compounds. Also, we believe that nobiletin can be a potential antiviral agent against CHIKV infection worthy of being further investigated as a remedial candidate in vivo.

The effectiveness of antiviral agents with broad-spectrum activity against chikungunya virus varies between host cell lines

Chikungunya virus (CHIKV) is a mosquito-borne virus that has recently emerged in the Western Hemisphere. Approved antiviral therapies or vaccines for the treatment or prevention of CHIKV infections are not available. This study aims to evaluate the antiviral activity of commercially available broad-spectrum antivirals against CHIKV. Due to host cell-specific variability in uptake and intracellular processing of drug, we evaluated the antiviral effects of each agent in three cell lines. Antiviral activities of ribavirin (RBV), interferon-alfa (IFN-α) and favipiravir (FAV) were assessed in CHIKV-infected Vero, HUH-7, and A549 cells. CHIKV-infected cells were treated with increasing concentrations of each agent for three days and viral burden was quantified by plaque assay on Vero cells. Cytotoxic effects of RBV, FAV and IFN-α were also evaluated. Antiviral activity differed depending on the cell line used for evaluation. RBV had the greatest antiviral effect in HUH-7 cells (EC₅₀ = 2.575 µg/mL); IFN-α was most effective in A549 cells (EC₅₀ = 4.235 IU/mL); and FAV in HUH-7 cells (EC₅₀ = 20.00 μg/mL). The results of our study show FAV and IFN-α are the most promising candidates, as their use led to substantial reductions in viral burden at clinically achievable concentrations in two human-derived cell lines. FAV is an especially attractive candidate for further investigation due to its oral bioavailability. These findings also highlight the importance of cell line selection for preclinical drug trials.

Atovaquone Inhibits Arbovirus Replication through the Depletion of Intracellular Nucleotides

Arthropod-borne viruses represent a significant public health threat worldwide, yet there are few antiviral therapies or prophylaxes targeting these pathogens. In particular, the development of novel antivirals for high-risk populations such as pregnant women is essential to prevent devastating disease such as that which was experienced with the recent outbreak of Zika virus (ZIKV) in the Americas. One potential avenue to identify new and pregnancy-acceptable antiviral compounds is to repurpose well-known and widely used FDA-approved drugs. In this study, we addressed the antiviral role of atovaquone, an FDA Pregnancy Category C drug and pyrimidine biosynthesis inhibitor used for the prevention and treatment of parasitic infections. We found that atovaquone was able to inhibit ZIKV and chikungunya virus virion production in human cells and that this antiviral effect occurred early during infection at the initial steps of viral RNA replication. Moreover, we were able to complement viral replication and virion production with the addition of exogenous pyrimidine nucleosides, indicating that atovaquone functions through the inhibition of the pyrimidine biosynthesis pathway to inhibit viral replication. Finally, using an ex vivo human placental tissue model, we found that atovaquone could limit ZIKV infection in a dose-dependent manner, providing evidence that atovaquone may function as an antiviral in humans. Taken together, these studies suggest that atovaquone could be a broad-spectrum antiviral drug and a potential attractive candidate for the prophylaxis or treatment of arbovirus infection in vulnerable populations, such as pregnant women and children.IMPORTANCE The ability to protect vulnerable populations such as pregnant women and children from Zika virus and other arbovirus infections is essential to preventing the devastating complications induced by these viruses. One class of antiviral therapies may lie in known pregnancy-acceptable drugs that have the potential to mitigate arbovirus infections and disease, yet this has not been explored in detail. In this study, we show that the common antiparasitic drug atovaquone inhibits arbovirus replication through intracellular nucleotide depletion and can impair ZIKV infection in an ex vivo human placental explant model. Our study provides a novel function for atovaquone and highlights that the rediscovery of pregnancy-acceptable drugs with potential antiviral effects can be the key to better addressing the immediate need for treating viral infections and preventing potential birth complications and future disease.

Emergence and treatment of chikungunya arthritis

PURPOSE OF REVIEW

To review the emergence, clinical features, pathogenesis, and treatment of acute chikungunya (CHIK) fever and chronic CHIK arthritis.

RECENT FINDINGS

Since 2004, CHIK, an arboviral infection, has spread throughout the world, infecting millions of people. The illness occurs in two phases: an acute viremic infection followed by chronic arthritis. In less developed countries, there are limited resources and effective treatment. For acutely ill CHIK fever patients, management is symptomatic. The treatment of chronic CHIK arthritis should be determined by an understanding of pathogenesis. Is chronic CHIK arthritis a persistent viral infection or a postinfectious inflammatory process? Multiple proinflammatory cytokines, chemokines, and growth factors have been identified in chronic CHIK arthritis. Attempts to isolate CHIK virus from synovial fluid have been unsuccessful. Given pathogenetic similarities (as well as differences) compared with rheumatoid arthritis and the painful, disabling nature of the arthritis, it is not surprising that disease-modifying antirheumatic drugs such as methotrexate have begun to be used.

SUMMARY

CHIK infection has emerged with major arthritic epidemics for which evidence-based therapy is limited. But there is an opportunity to improve the treatment of chronic CHIK arthritis and, from this disease, to gain understanding of the pathogenesis and treatment of inflammatory arthritis more generally.

Spectrum of candidate molecules against Chikungunya virus - an insight into the antiviral screening platforms

INTRODUCTION

Chikungunya disease has undergone a phenomenal transition in its status from being recognized as a sporadic infection to acquiring a global prominence over the last couple of decades. The causative agent behind the explosive epidemics worldwide is the re-emerging pathogen, Chikungunya virus (CHIKV). Areas covered: The current review discusses all the possible avenues of antiviral research towards combating CHIKV infection. Aspects of antiviral drug discovery such as antiviral targets, candidate molecules screened, and the various criteria to be a potential inhibitor are all discussed at length. Existing antiviral drug screening tools for CHIKV and their applications are thoroughly described. Clinical trial status of agents with therapeutic potential has been updated with special mention of candidate molecules under patent approval. Databases such as PubMed, Google Scholar, ScienceDirect, Google Patent, and Clinical Trial Registry platforms were referred. Expert opinion: The massive outbreaks of Chikungunya viral disease in the recent past and the serious health concerns imposed thereby, have driven the search for effective therapeutics. The greatest challenge being the non-availability of robust, reproducible, cost-effective and biologically accurate assay models. Nevertheless, there is a need to identify good models mimicking the appropriate microenvironment of an infectious setting.

Beyond Members of the Flaviviridae Family, Sofosbuvir Also Inhibits Chikungunya Virus Replication

Chikungunya virus (CHIKV) causes a febrile disease associated with chronic arthralgia, which may progress to neurological impairment. Chikungunya fever (CF) is an ongoing public health problem in tropical and subtropical regions of the world, where control of the CHIKV vector, Aedes mosquitos, has failed. As there is no vaccine or specific treatment for CHIKV, patients receive only palliative care to alleviate pain and arthralgia. Thus, drug repurposing is necessary to identify antivirals against CHIKV. CHIKV RNA polymerase is similar to the orthologue enzyme of other positive-sense RNA viruses, such as members of the Flaviviridae family. Among the Flaviviridae, not only is hepatitis C virus RNA polymerase susceptible to sofosbuvir, a clinically approved nucleotide analogue, but so is dengue, Zika, and yellow fever virus replication. Here, we found that sofosbuvir was three times more selective in inhibiting CHIKV production in human hepatoma cells than ribavirin, a pan-antiviral drug. Although CHIKV replication in human induced pluripotent stem cell-derived astrocytes was less susceptible to sofosbuvir than were hepatoma cells, sofosbuvir nevertheless impaired virus production and cell death in a multiplicity of infection-dependent manner. Sofosbuvir also exhibited antiviral activity in vivo by preventing CHIKV-induced paw edema in adult mice at a dose of 20 mg/kg of body weight/day and prevented mortality in a neonate mouse model at 40- and 80-mg/kg/day doses. Our data demonstrate that a prototypic alphavirus, CHIKV, is also susceptible to sofosbuvir. As sofosbuvir is a clinically approved drug, our findings could pave the way to it becoming a therapeutic option against CF.

Host target-based approaches against arboviral diseases

In the 20th century, socioeconomic and environmental changes facilitated the reintroduction of mosquitoes in developing cities, resulting in the reinsertion of mosquito-borne viral diseases and the dispersal of their causative agents on a worldwide scale. Recurrent outbreaks of arboviral diseases are being reported, even in regions without a previous history of arboviral disease transmission. Of note, arboviral infections represented approximately 30% of all emerging vector-borne diseases in the last decade. Therapeutic strategies against infectious viral diseases include the use of different classes of molecules that act directly on the pathogen and/or act by optimizing the host immune response. Drugs targeting the virus usually provide amelioration of symptoms by suppressing and controlling the infection. However, it is limited by the short-window of effectiveness, ineffectiveness against latent viruses, development of drug-resistant mutants and toxic side effects. Disease may also be a consequence of an excessive, uncontrolled or misplaced inflammatory response, treatments that interfere in host immune response are interesting options and can be used isolated or in combination with virus-targeted therapies. The use of host-targeted therapies requires specific knowledge regarding host immune patterns that may trigger dengue virus (DENV), chikungunya virus (CHIKV) or Zika virus (ZIKV) disease.

Antiviral Effects of Clinically-Relevant Interferon-α and Ribavirin Regimens against Dengue Virus in the Hollow Fiber Infection Model (HFIM)

Dengue virus (DENV) is the most prevalent mosquito-borne viral illness in humans. Currently, there are no therapeutic agents available to prevent or treat DENV infections. Our objective was to fill this unmet medical need by evaluating the antiviral activity of interferon-α (IFN) and ribavirin (RBV) as a combination therapy against DENV. DENV-infected Vero and Huh-7 cells were exposed to RBV and/or IFN, and the viral burden was quantified over time by plaque assay. Drug-drug interactions for antiviral effect were determined by fitting a mathematical model to the data. We then assessed clinically-relevant exposures of IFN plus RBV using the hollow fiber infection model (HFIM) system. RBV monotherapy was only effective against DENV at toxic concentrations in Vero and Huh-7 cells. IFN, as a single agent, did inhibit DENV replication at physiological concentrations and viral suppression was substantial in Huh-7 cells (Half maximal effective concentration (EC₅₀) = 58.34 IU/mL). As a combination therapy, RBV plus IFN was additive for viral suppression in both cell lines; however, enhancement of antiviral activity at clinically-achievable concentrations was observed only in Huh-7 cells. Finally, clinical exposures of RBV plus IFN suppressed DENV replication by 99% even when treatment was initiated 24 h post-infection in the HFIM. Further evaluation revealed that the antiviral effectiveness of the combination regimen against DENV is mostly attributed to activity associated with IFN. These findings suggest that IFN is a potential therapeutic strategy for the treatment of DENV.

Current Strategies for Inhibition of Chikungunya Infection

Increasing incidences of Chikungunya virus (CHIKV) infection and co-infections with Dengue/Zika virus have highlighted the urgency for CHIKV management. Failure in developing effective vaccines or specific antivirals has fuelled further research. This review discusses updated strategies of CHIKV inhibition and provides possible future directions. In addition, it analyzes advances in CHIKV lifecycle, drug-target development, and potential hits obtained by in silico and experimental methods. Molecules identified with anti-CHIKV properties using traditional/rational drug design and their potential to succeed in subsequent stages of drug development have also been discussed. Possibilities of repurposing existing drugs based on their in vitro findings have also been elucidated. Probable modes of interference of these compounds at various stages of infection, including entry and replication, have been highlighted. The use of host factors as targets to identify antivirals against CHIKV has been addressed. While most of the earlier antivirals were effective in the early phases of the CHIKV life cycle, this review is also focused on drug candidates that are effective at multiple stages of its life cycle. Since most of these antivirals require validation in preclinical and clinical models, the challenges regarding this have been discussed and will provide critical information for further research.

Chikungunya Arthritis: Implications of Acute and Chronic Inflammation Mechanisms on Disease Management

In the past decade, arboviruses-arthropod-borne viruses-have been the focus of public health institutions worldwide following a spate of devastating outbreaks. Chikungunya virus, an arbovirus that belongs to the alphavirus genus, is a reemerging arthritogenic virus that has caused explosive outbreaks since 2006, notably on Réunion Island, and more recently in the Caribbean, South America, India, and Southeast Asia. The severity of arthritic disease caused by chikungunya virus has prompted public health authorities in affected countries to develop specific guidelines to tackle this pathogen. Chikungunya virus disease manifests first as an acute stage of severe joint inflammation and febrile illness, which later progresses to a chronic stage, during which patients may experience debilitating and persisting articular pain for extended periods. This review aims to provide a broad perspective on current knowledge of chikungunya virus pathogenesis by identifying key clinical and experimental studies that have contributed to our understanding of chikungunya virus to date. In addition, the review explores the practical aspects of treatment and management of both acute and chronic chikungunya virus based on clinical experience during chikungunya virus outbreaks. Finally, recent findings on potential therapeutic solutions-from antiviral agents to immunomodulators-are reviewed to provide both viral immunologists and clinical rheumatologists with a balanced perspective on the nature of a reemerging arboviral disease of significant public health concern, and insight into future therapeutic approaches to better address the treatment and management of chikungunya virus.

Zika Virus Replication Is Substantially Inhibited by Novel Favipiravir and Interferon Alpha Combination Regimens

Zika virus (ZIKV) is a major public health concern due to its overwhelming spread into the Americas. Currently, there are neither licensed vaccines nor antiviral therapies available for the treatment of ZIKV. We aimed to identify and rationally optimize effective therapeutic regimens for ZIKV by evaluating the antiviral potentials of the approved broad-spectrum antiviral agents favipiravir (FAV), interferon alpha (IFN), and ribavirin (RBV) as single agents and in combinations. For these studies, Vero cells were infected with ZIKV in the presence of increasing concentrations of FAV, IFN, or/and RBV for 4 days. Supernatants were harvested daily, and the viral burden was quantified by a plaque assay on Vero cells. The time course of the viral burden during treatment in vitro was characterized by a novel translational, mechanism-based model, which was subsequently used to rationally optimize combination dosage regimens. The combination regimen of FAV plus IFN provided the greatest extent of viral inhibition without cytotoxicity, reducing the viral burden by 4.4 log₁₀ PFU/ml at concentrations of 250 μM FAV and 100 IU/ml IFN. Importantly, these concentrations are achievable in humans. The translational, mechanism-based model yielded unbiased and reasonably precise curve fits. Simulations with the model predicted that clinically relevant regimens of FAV plus IFN would markedly reduce viral burdens in humans, resulting in at least a 10,000-fold reduction in the amount of the virus during the first 4 days of treatment. These findings highlight the substantial promise of rationally optimized combination dosage regimens of FAV plus IFN, which should be further investigated to combat ZIKV.

Vaccine and Therapeutic Options To Control Chikungunya Virus

Beginning in 2004, chikungunya virus (CHIKV) went from an endemic pathogen limited to Africa and Asia that caused periodic outbreaks to a global pathogen. Given that outbreaks caused by CHIKV have continued and expanded, serious consideration must be given to identifying potential options for vaccines and therapeutics. Currently, there are no licensed products in this realm, and control relies completely on the use of personal protective measures and integrated vector control, which are only minimally effective. Therefore, it is prudent to urgently examine further possibilities for control. Vaccines have been shown to be highly effective against vector-borne diseases. However, as CHIKV is known to rapidly spread and generate high attack rates, therapeutics would also be highly valuable. Several candidates are currently being developed; this review describes the multiple options under consideration for future development and assesses their relative advantages and disadvantages.

Evaluation of a range of mammalian and mosquito cell lines for use in Chikungunya virus research

Chikungunya virus (CHIKV) is becoming an increasing global health issue which has spread across the globe and as far north as southern Europe. There is currently no vaccine or anti-viral treatment available. Although there has been a recent increase in CHIKV research, many of these in vitro studies have used a wide range of cell lines which are not physiologically relevant to CHIKV infection in vivo. In this study, we aimed to evaluate a panel of cell lines to identify a subset that would be both representative of the infectious cycle of CHIKV in vivo, and amenable to in vitro applications such as transfection, luciferase assays, immunofluorescence, western blotting and virus infection. Based on these parameters we selected four mammalian and two mosquito cell lines, and further characterised these as potential tools in CHIKV research.