Amodiaquine, an antimalarial drug, inhibits dengue virus type 2 replication and infectivity

An RNA replicon system to investigate promising inhibitors of feline coronavirus

Feline infectious peritonitis (FIP) is a fatal feline disease, caused by a feline coronavirus (FCoV), namely feline infectious peritonitis virus (FIPV). We produced a baby hamster kidney 21 (BHK) cell line expressing a serotype I FCoV replicon RNA with a green fluorescent protein (GFP) reporter gene (BHK-F-Rep) and used it as an in vitro screening system to test different antiviral compounds. Two inhibitors of the FCoV main protease (Mpro), namely GC376 and Nirmatrelvir, as well as the nucleoside analog Remdesivir proved to be effective in inhibiting the replicon system. Different combinations of these compounds also proved to be potent inhibitors, having an additive effect when combined. Remdesivir, GC376, and Nirmatrelvir all have a 50% cytotoxic concentration (CC50) more than 200 times higher than their half-maximal inhibitory concentrations (IC50), making them important candidates for future in vivo studies as well as clinically implemented drug candidates. In addition, results were acquired with a virus infection system, where Felis catus whole fetus 4 (Fcwf-4) cells were infected with a previously described recombinant GFP-expressing FIPV (based on the laboratory-adapted serotype I FIPV strain Black) and treated with the most promising compounds. Results acquired with the replicon system were comparable to the results acquired with the virus infection system, demonstrating that we successfully implemented the FCoV replicon system for antiviral screening. We expect that this system will greatly facilitate future screens for anti-FIPV compounds and provide a non-infectious system to study and evaluate drug-resistant mutations that may emerge in the FIPV genome.IMPORTANCEFIPV is of great significance in the cat population around the world, causing 0.3%-1.4% of feline deaths in veterinary practices (2). As there are neither effective preventive measures nor approved treatment options available, there is an urgent need to identify antiviral drugs against FIPV. Our FCoV replicon system provides a valuable tool for drug discovery in vitro. Due to the lack of cell culture systems for serotype I FCoVs (the serotype most prevalent in the feline population) (2), a different system is needed to study these viruses. A viral replicon system is a valuable tool for studying FCoVs. Overall, our results demonstrate the utility of the serotype I feline coronavirus replicon system for antiviral screening as well as to study this virus in general. We propose several compounds representing promising candidates for future clinical trials and ultimately with the potential to save cats suffering from FIP.

Anti-Dengue: A Machine Learning-Assisted Prediction of Small Molecule Antivirals against Dengue Virus and Implications in Drug Repurposing

Dengue outbreaks persist in global tropical regions, lacking approved antivirals, necessitating critical therapeutic development against the virus. In this context, we developed the "Anti-Dengue" algorithm that predicts dengue virus inhibitors using a quantitative structure-activity relationship (QSAR) and MLTs. Using the "DrugRepV" database, we extracted chemicals (small molecules) and repurposed drugs targeting the dengue virus with their corresponding IC50 values. Then, molecular descriptors and fingerprints were computed for these molecules using PaDEL software. Further, these molecules were split into training/testing and independent validation datasets. We developed regression-based predictive models employing 10-fold cross-validation using a variety of machine learning approaches, including SVM, ANN, kNN, and RF. The best predictive model yielded a PCC of 0.71 on the training/testing dataset and 0.81 on the independent validation dataset. The created model's reliability and robustness were assessed using William's plot, scatter plot, decoy set, and chemical clustering analyses. Predictive models were utilized to identify possible drug candidates that could be repurposed. We identified goserelin, gonadorelin, and nafarelin as potential repurposed drugs with high pIC50 values. "Anti-Dengue" may be beneficial in accelerating antiviral drug development against the dengue virus.

Recent Trends in the Petasis Reaction: A Review of Novel Catalytic Synthetic Approaches with Applications of the Petasis Reaction

The Petasis reaction, also called the Petasis Borono-Mannich reaction, is a multicomponent reaction that couples a carbonyl derivative, an amine and boronic acids to yield substituted amines. The reaction proceeds efficiently in the presence or absence of a specific catalyst and solvent. By employing this reaction, a diverse range of chiral derivatives can easily be obtained, including α-amino acids. A broad substrate scope, high yields, distinct functional group tolerance and the availability of diverse catalytic systems constitute key features of this reaction. In this review article, attention has been drawn toward the recently reported methodologies for executing the Petasis reaction to produce structurally simple to complex aryl/allyl amino scaffolds.

A sulfonamide chalcone inhibited dengue virus with a potential target at the SAM-binding site of viral methyltransferase

Dengue infection is a global health problem as climate change facilitates the spread of mosquito vectors. Infected patients could progress to severe plasma leakage and hemorrhagic shock, where current standard treatment remains supportive. Previous reports suggested that several flavonoid derivatives inhibited mosquito-borne flaviviruses. This work aimed to explore sulfonamide chalcone derivatives as dengue inhibitors and to identify molecular targets. We initially screened 27 sulfonamide chalcones using cell-based antiviral and cytotoxic screenings. Two potential compounds, SC22 and SC27, were identified with DENV1-4 EC50s in the range of 0.71-0.94 and 3.15-4.46 μM, and CC50s at 14.63 and 31.02 μM, respectively. The compounds did not show any elevation in ALT or Cr in C57BL/6 mice on the 1st, 3rd, and 7th days after being administered intraperitoneally with 50 mg/kg SC22 or SC27 in a single dose. Moreover, the SAM-binding site of NS5 methyltransferase was a potential target of SC27 identified by computational and enzyme-based assays. The main target of SC22 was in a late stage of viral replication, but the exact target molecule had yet to be identified. In summary, a sulfonamide chalcone, SC27, was a potential DENV inhibitor that targeted viral methyltransferase. Further investigation should be the study of the structure-activity relationship of SC27 derivatives for higher potency and lower toxicity.

The 8-bromobaicalein alleviated chikungunya-induced musculoskeletal inflammation and reduced the viral load in healthy adult mice

Chikungunya virus is a re-emerging arbovirus that has caused epidemic outbreaks in recent decades. Patients in older age groups with high viral load and severe immunologic response during acute infection are likely to develop chronic arthritis and severe joint pain. Currently, no antiviral drug is available. Previous studies suggested that a flavone derivative, 8-bromobaicalein, was a potential dengue and Zika replication inhibitor in a cell-based system targeting flaviviral polymerase. Here we characterized that 8-bromobaicalein inhibited chikungunya virus replication with EC50 of 0.49 ± 0.11 µM in Vero cells. The molecular target predicted at viral nsP1 methyltransferase using molecular binding and fragment molecular orbital calculation. Additionally, oral administration of 250 mg/kg twice daily treatment alleviated chikungunya-induced musculoskeletal inflammation and reduced viral load in healthy adult mice. Pharmacokinetic analysis indicated that the 250 mg/kg administration maintained the compound level above EC99.9 for 12 h. Therefore, 8-bromobaicalein should be a potential candidate for further development as a pan-arboviral drug.

Vector-Transmitted Flaviviruses: An Antiviral Molecules Overview

Flaviviruses cause numerous pathologies in humans across a broad clinical spectrum with potentially severe clinical manifestations, including hemorrhagic and neurological disorders. Among human flaviviruses, some viral proteins show high conservation and are good candidates as targets for drug design. From an epidemiological point of view, flaviviruses cause more than 400 million cases of infection worldwide each year. In particular, the Yellow Fever, dengue, West Nile, and Zika viruses have high morbidity and mortality-about an estimated 20,000 deaths per year. As they depend on human vectors, they have expanded their geographical range in recent years due to altered climatic and social conditions. Despite these epidemiological and clinical premises, there are limited antiviral treatments for these infections. In this review, we describe the major compounds that are currently under evaluation for the treatment of flavivirus infections and the challenges faced during clinical trials, outlining their mechanisms of action in order to present an overview of ongoing studies. According to our review, the absence of approved antivirals for flaviviruses led to in vitro and in vivo experiments aimed at identifying compounds that can interfere with one or more viral cycle steps. Still, the currently unavailability of approved antivirals poses a significant public health issue.

Novel Potent Autophagy Inhibitor Ka-003 Inhibits Dengue Virus Replication

Every year, dengue virus (DENV) affects millions of people. Currently, there are no approved drugs for the treatment of DENV infection. Autophagy is a conserved degradation process that was shown to be induced by DENV infection and required for optimal DENV replication. The modulation of autophagy is, therefore, considered an attractive target to treat DENV infection. This study carried out a high-content image screen analysis using Crispr-Cas9 GFP-LC3 knocked-in HeLa cells of a compound library synthesized from or inspired by natural products and their biocongener precursors to discover novel autophagy inhibitors. The screen identified Ka-003 as the most effective compound for decreasing the number of autophagic vacuoles inside cells upon autophagy induction. Ka-003 could inhibit autophagy in a dose-dependent manner at low micromolar concentrations. More importantly, Ka-003 demonstrated the concentration-dependent inhibition of DENV production in Crispr-Cas9 GFP-LC3 knocked-in THP-1 monocytes. The core structure of Ka-003, which is a methyl cyclohexene derivative, resembles those found in mulberry plants, and could be synthetically prepared in a bioinspired fashion. Taken together, data indicate that Ka-003 hampered autophagy and limited DENV replication. The low cytotoxicity of Ka-003 suggests its therapeutic potential, which warrants further studies for the lead optimization of the compound for dengue treatment.

Synergistic Effect of Zinc-Chitosan Nanoparticles and Hydroxychloroquine to Inhibit Buffalo Coronavirus

Zinc ions can hinder the synthesis of proteins required for accomplishing several stages of the viral life cycle. The intracellular zinc concentration can be increased by using zinc ionophores which transport zinc ions into the cells and hinder viral replication. (Hydroxy)chloroquine is an example of a zinc ionophore, but both zinc and (hydroxy)chloroquine can be toxic to the host organism. The nanocarriers may serve as camouflage to evade the adverse effects of drugs, chemicals, and nanoparticles on the host. We formulated ZnO nanoparticles with flower-like morphology (ZnONFs). It was further decorated with chitosan along with hydroxychloroquine (as a zinc ionophore) (CHCZnO NPs). We have chosen the cationic polymer chitosan since it is biocompatible, biodegradable and binds easily with the cells, and enhances the transport of drugs across cell membranes. The formulation was investigated for size, shape, surface charge, and interaction of chemicals used. We evaluated the formulations for cytotoxicity, and biocompatibility in embryonated chicks and their efficacy against bovine coronavirus (BCoV) isolated from a buffalo calf, and pneumo-enteric coronaviruses isolated from a buffalo calf with promising results in comparison to ZnONFs/hydroxychloroquine alone. Furthermore, we elucidate the mechanism underlying the lysosomotropic effect of various formulations on Vero cells infected with the buffalo coronavirus.

Chloroquine chaos and COVID-19: Smart delivery perspectives through pH sensitive polymers/micelles and ZnO nanoparticles

The global pandemic of COVID-19 had a consequential impact on our lives. (Hydroxy)chloroquine, a well-known drug for treatment or prevention against malaria and chronic inflammatory conditions, was also used for COVID patients with reported potential efficacy. Although it was well tolerated, however in some cases, it produced severe side effects, including grave cardiac issues. The variable reports on the administration of (hydroxy)chloroquine in COVID19 patients led to chaos. This drug is a well-known zinc ionophore, besides possessing antiviral effects. Zinc ionophores augment the intracellular Zn²⁺ concentration by facilitating the zinc ions into the cells and subsequently impair virus replication. Zinc oxide nanoparticles (ZnO NPs) have been reported to possess antiviral activity. However, the adverse effects of both components are also reported. We discussed in depth their possible mechanism as antiviral and smart delivery perspectives through pH-sensitive polymers/ micelles and ZnO NPs.

Amodiaquine derivatives as inhibitors of severe fever with thrombocytopenia syndrome virus (SFTSV) replication

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral infection caused by a bandavirus in the family of Phenuiviridae, commonly known as SFTS virus (SFTSV). We have previously isolated SFTSV from blood samples of SFTS patients and established an antiviral assay system to identify selective inhibitors of SFTSV in vitro. Using the assay system, the antimalarial agent amodiaquine was identified as a selective inhibitor of SFTSV replication. However, due to its insufficient antiviral activity, 98 amodiaquine derivatives were newly synthesized and examined for their anti-SFTSV activity. Among the derivatives, some compounds showed selective inhibitory effect on SFTSV replication in vitro. The 50% effective concentration (EC₅₀) and cytotoxic concentration (CC₅₀) of the most active compound (C-90) were 2.6 ± 0.6 and >50 μM, respectively. This EC₅₀ value was comparable to or slightly better than that of favipiravir (4.1 ± 0.6 μM). On the other hand, pharmacokinetic studies in vivo revealed that C-90 was poor in its oral bioavailability in mice. Therefore, we further designed and synthesized derivatives and obtained 2 compounds with selective anti-SFTSV activity in vitro and improved pharmacokinetics in vivo.

Antiviral Treatment Options for Severe Fever with Thrombocytopenia Syndrome Infections

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus that produces severe fever with thrombocytopenia syndrome (SFTS). It is widespread in Japan, South Korea, and Central and Eastern China. The epidemic has developed rapidly through China in recent years. SFTS cases have been reported in 25 provinces in China, mainly distributed in rural areas in mountainous and hilly areas. The infection has a high case fatality rate and no specific treatments or vaccinations. Therefore, early diagnosis and treatment of SFTS infection is important to survival and disease control. In this article, we provide an overview on different aspects of SFTS with an emphasis on management, to explore the current treatment and prophylactic measures further.

Identification of Montelukast as flavivirus NS2B-NS3 protease inhibitor by inverse virtual screening and experimental validation

Flavivirus, such as Dengue Virus (DENV) and Zika virus (ZIKV), infects millions of people and cause the death of thousands of people every year. Despite many efforts, there is no approved anti-flaviviral treatment available. In particular, some antiflavivirus compounds were investigated the cellular activities of DENV and ZIKV, but lacking the exploration of specific target enzyme, thereby resulting in the hindrance of structure-based drug design. One example is Montlukast, which was found to inhibit the replicon replication in DENV and ZIKV infected cells, with EC₅₀ values as 1.03 μM (DENV) and 1.14 μM (ZIKV), while the underlying mechanism remains unclear. In our study, the inhibitory mechanisms of Montelukast against the replicon replication of DENV and ZIKV infected cells were studied by using in silico approaches including inverse virtual screening (IVS), molecular dynamics (MD) simulations and binding free energy calculation, and validated through in vitro protease assay, confirming Montelukast could bind to NS2B-NS3 proteases of DENV and ZIKV as a competitive inhibitor (IC₅₀ for DENV: 25.65 μM, for ZIKV: 15.57 μM). Moreover, Montelukast has no potential off-target effect on NS2B-NS3 protease from thrombin and trypsin inhibitory assay. Overall, Montelukast may be used as a potential candidate to block NS2B-NS3 protease as well as lead for structural modification.

Dengue virus replication enhances labile zinc pools by modulation of ZIP8

Zinc‐dependent viral proteins rely on intracellular zinc homeostasis for successful completion of infectious life‐cycle. Here, we report that the intracellular labile zinc levels were elevated at early stages of dengue virus (DENV) infection in hepatic cells and this increase in free zinc was abolished in cells infected with UV‐inactivated virus or with a DENV replication inhibitor implicating a role for zinc homeostasis in viral RNA replication. This change in free zinc was mediated by zinc transporter, ZIP8, as siRNA‐mediated knockdown of ZIP8 resulted in abrogation of increase in free zinc levels leading to significant reduction in DENV titers suggesting a crucial role for ZIP8 in early stages of DENV replication. Furthermore, elevated free zinc levels correlated with high copy numbers of dengue genome in peripheral blood leukocytes obtained from dengue patients compared to healthy controls suggesting a critical role for zinc homeostasis in dengue infection.

Can Antimalarial Phytochemicals be a Possible Cure for COVID-19? Molecular Docking Studies of Some Phytochemicals to SARS-CoV-2 3C-like Protease

OBJECTIVE

To evaluate the efficacy of reported anti-malarial phytochemicals as lead compounds for possible drug development against COVID-19.

METHODS

An in silico approach was used in this study to determine through molecular docking the binding affinities and site of binding of these phytochemicals to the 3C-like protease of COVID-19 which is considered as the main protease of the virus.

RESULTS

A number of anti-malarial phytochemicals like apigenin-7-O-glucoside, decurvisine, luteolin-7-O-glucoside, sargabolide J, and shizukaols A, B, F, and G showed predicted high binding energies with G values of -8.0 kcal/mol or higher. Shizukaols F and B demonstrated the best binding energies of -9.5 and -9.8, respectively. The acridone alkaloid 5-hydroxynoracronycine also gave a predicted high binding energy of -7.9 kcal/mol.

CONCLUSION

This is for the first time that decursivine and several shizukaols were reported as potential anti-viral agents. These compounds merit further studies to determine whether they can be effective drug candidates against COVID-19.

Broad spectrum anti-coronavirus activity of a series of anti-malaria quinoline analogues

In this study, a series of 10 quinoline analogues was evaluated for their in vitro antiviral activity against a panel of alpha- and beta-coronaviruses, including the severe acute respiratory syndrome coronaviruses 1 and 2 (SARS-CoV-1 and SARS-CoV-2), as well as the human coronaviruses (HCoV) 229E and OC43. Chloroquine and hydroxychloroquine were the most potent with antiviral EC₅₀ values in the range of 0.12-12 μM. Chloroquine displayed the most favorable selectivity index (i.e. ratio cytotoxic versus antiviral concentration), being 165 for HCoV-OC43 in HEL cells. Potent anti-coronavirus activity was also observed with amodiaquine, ferroquine and mefloquine, although this was associated with substantial cytotoxicity for mefloquine. Primaquine, quinidine, quinine and tafenoquine only blocked coronavirus replication at higher concentrations, while piperaquine completely lacked antiviral and cytotoxic effects. A time-of-addition experiment in HCoV-229E-infected HEL cells revealed that chloroquine interferes with viral entry at a post-attachment stage. Using confocal microscopy, no viral RNA synthesis could be detected upon treatment of SARS-CoV-2-infected cells with chloroquine. The inhibition of SARS-CoV-2 replication by chloroquine and hydroxychloroquine coincided with an inhibitory effect on the autophagy pathway as visualized by a dose-dependent increase in LC3-positive puncta. The latter effect was less pronounced or even absent with the other quinolines. In summary, we showed that several quinoline analogues, including chloroquine, hydroxychloroquine, amodiaquine, ferroquine and mefloquine, exhibit broad anti-coronavirus activity in vitro.

Drug Repurposing: A Strategy for Discovering Inhibitors against Emerging Viral Infections

BACKGROUND

Viral diseases are responsible for several deaths around the world. Over the past few years, the world has seen several outbreaks caused by viral diseases that, for a long time, seemed to possess no risk. These are diseases that have been forgotten for a long time and, until nowadays, there are no approved drugs or vaccines, leading the pharmaceutical industry and several research groups to run out of time in the search for new pharmacological treatments or prevention methods. In this context, drug repurposing proves to be a fast and economically viable technique, considering the fact that it uses drugs that have a well-established safety profile. Thus, in this review, we present the main advances in drug repurposing and their benefit for searching new treatments against emerging viral diseases.

METHODS

We conducted a search in the bibliographic databases (Science Direct, Bentham Science, PubMed, Springer, ACS Publisher, Wiley, and NIH's COVID-19 Portfolio) using the keywords "drug repurposing", "emerging viral infections" and each of the diseases reported here (CoV; ZIKV; DENV; CHIKV; EBOV and MARV) as an inclusion/exclusion criterion. A subjective analysis was performed regarding the quality of the works for inclusion in this manuscript. Thus, the selected works were those that presented drugs repositioned against the emerging viral diseases presented here by means of computational, high-throughput screening or phenotype-based strategies, with no time limit and of relevant scientific value.

RESULTS

291 papers were selected, 24 of which were CHIKV; 52 for ZIKV; 43 for DENV; 35 for EBOV; 10 for MARV; and 56 for CoV and the rest (72 papers) related to the drugs repurposing and emerging viral diseases. Among CoV-related articles, most were published in 2020 (31 papers), updating the current topic. Besides, between the years 2003 - 2005, 10 articles were created, and from 2011 - 2015, there were 7 articles, portraying the outbreaks that occurred at that time. For ZIKV, similar to CoV, most publications were during the period of outbreaks between the years 2016 - 2017 (23 articles). Similarly, most CHIKV (13 papers) and DENV (14 papers) publications occur at the same time interval. For EBOV (13 papers) and MARV (4 papers), they were between the years 2015 - 2016. Through this review, several drugs were highlighted that can be evolved in vivo and clinical trials as possible used against these pathogens showed that remdesivir represent potential treatments against CoV. Furthermore, ribavirin may also be a potential treatment against CHIKV; sofosbuvir against ZIKV; celgosivir against DENV, and favipiravir against EBOV and MARV, representing new hopes against these pathogens.

CONCLUSION

The conclusions of this review manuscript show the potential of the drug repurposing strategy in the discovery of new pharmaceutical products, as from this approach, drugs could be used against emerging viral diseases. Thus, this strategy deserves more attention among research groups and is a promising approach to the discovery of new drugs against emerging viral diseases and also other diseases.

Chloroquine Analogs: An Overview of Natural and Synthetic Quinolines as Broad Spectrum Antiviral Agents

SARS-CoV-2, a positive single-stranded RNA enveloped coronavirus, currently poses a global health threat. Drugs with quinoline scaffolds have been studied to repurpose their useful broad-spectrum properties into treating various diseases, including viruses. Preliminary studies on the quinoline medications, chloroquine and hydroxychloroquine, against SARS-CoV-2, have shown to be a potential area of interest for drug development due to their ability to prevent viral entry, act as anti-inflammatory modulators, and inhibit key enzymes allowing reduced viral infectivity. In addition to Chloroquine and Hydroxychloroquine, we discussed analogs of the drugs to understand the quinoline scaffold's potential antiviral mechanisms. The heterocyclic scaffold of quinoline can be modified in many ways, primarily through the modification of its substituents. We studied these different synthetic derivatives to understand properties that could enhance its antiviral specificity thoroughly. Chloroquine and its analogs can act on various stages of the viral life cycle, pre and post entry. In this study, we reviewed chloroquine and its synthetic and natural analogs for their antiviral properties in a variety of viruses. Furthermore, we reviewed the compound's potential abilities to attenuate symptoms associated with viral infections. Natural compounds that share scaffolding to chloroquine can act as antivirals or attenuate symptoms through the stimulation of the host immune system or reduction of oxidative stress. Furthermore, we discuss perspectives of the drug's repurposing due to its ability to inhibit the beta-hematin formation and to be a Zinc Ionophore.

In silico and in vitro screening of licensed antimalarial drugs for repurposing as inhibitors of hepatitis E virus

ABSTRACT

Hepatitis E virus (HEV) infection is emerging in Cameroon and represents one of the most common causes of acute hepatitis and jaundice. Moreover, earlier reports showed evidence of falciparum malaria/HEVcoexistence. Although the Sofosbuvir/Ribavirin combination was recently proposed in the treatment of HEV-infected patients, no specific antiviral drug has been approved so far, thereby urging the search for new therapies. Fortunately, drug repurposing offers a good alternative to this end. In this study, we report the in silico and in vitro activities of 8 licensed antimalarial drugs and two anti-hepatitis C virus agents used as references (Sofosbuvir, and Ribavirin), for repurposing as antiviral inhibitors against HEV. Compounds were docked against five HEV-specific targets including the Zinc-binding non-structural protein (6NU9), RNA-dependent RNA polymerase (RdRp), cryoEM structure of HEV VLP, genotype 1 (6LAT), capsid protein ORF-2, genotype 3 (2ZTN), and the E2s domain of genotype 1 (3GGQ) using the iGEMDOCK software and their pharmacokinetic profiles and toxicities were predicted using ADMETlab2.0. Their in vitro effects were also assessed on a gt 3 p6Gluc replicon system using the luciferase reporter assay. The docking results showed that Sofosbuvir had the best binding affinities with 6NU9 (- 98.22 kcal/mol), RdRp (- 113.86 kcal/mol), 2ZTN (- 106.96 kcal/mol), while Ribavirin better collided with 6LAT (- 99.33 kcal/mol). Interestingly, Lumefantrine showed the best affinity with 3GGQ (-106.05 kcal/mol). N-desethylamodiaquine and Amodiaquine presented higher binding scores with 6NU9 (- 93.5 and - 89.9 kcal/mol respectively vs - 80.83 kcal/mol), while Lumefantrine had the greatest energies with RdRp (- 102 vs - 84.58), and Pyrimethamine and N-desethylamodiaquine had stronger affinities with 2ZTN compared to Ribavirin (- 105.17 and - 102.65 kcal/mol vs - 96.04 kcal/mol). The biological screening demonstrated a significant (P < 0.001) antiviral effect on replication with 1 µM N-desethylamodiaquine, the major metabolite of Amodiaquine. However, Lumefantrine showed no effect at the tested concentrations (1, 5, and 10 µM). The biocomputational analysis of the pharmacokinetic profile of both drugs revealed a low permeability of Lumefantrine and a specific inactivation by CYP3A2 which might partly contribute to the short half-time of this drug. In conclusion, Amodiaquine and Lumefantrine may be good antimalarial drug candidates for repurposing against HEV. Further in vitro and in vivo experiments are necessary to validate these predictions.

GRAPHIC ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40203-021-00093-y.

DrugRepV: a compendium of repurposed drugs and chemicals targeting epidemic and pandemic viruses

Viruses are responsible for causing various epidemics and pandemics with a high mortality rate e.g. ongoing SARS-CoronaVirus-2 crisis. The discovery of novel antivirals remains a challenge but drug repurposing is emerging as a potential solution to develop antivirals in a cost-effective manner. In this regard, we collated the information of repurposed drugs tested for antiviral activity from literature and presented it in the form of a user-friendly web server named ‘DrugRepV’. The database contains 8485 entries (3448 unique) with biological, chemical, clinical and structural information of 23 viruses responsible to cause epidemics/pandemics. The database harbors browse and search options to explore the repurposed drug entries. The data can be explored by some important fields like drugs, viruses, drug targets, clinical trials, assays, etc. For summarizing the data, we provide overall statistics of the repurposed candidates. To make the database more informative, it is hyperlinked to various external repositories like DrugBank, PubChem, NCBI-Taxonomy, Clinicaltrials.gov, World Health Organization and many more. ‘DrugRepV’ database (https://bioinfo.imtech.res.in/manojk/drugrepv/) would be highly useful to the research community working to develop antivirals.

Inhibition of Chikungunya Virus Infection by 4-Hydroxy-1-Methyl-3-(3-morpholinopropanoyl)quinoline-2(1H)-one (QVIR) Targeting nsP2 and E2 Proteins

The re-emergence of Chikungunya virus (CHIKV) infection in humans with no approved antiviral therapies or vaccines is one of the major problems with global significance. In the present investigation, we screened 80 in-house quinoline derivatives for their anti-CHIKV activity by computational techniques and found 4-hydroxy-1-methyl-3-(3-morpholinopropanoyl)quinoline-2(1H)-one (QVIR) to have potential binding affinities with CHIKV nsP2 and E2 glycoproteins. QVIR was evaluated in vitro for its anti-CHIKV potential. QVIR showed strong inhibition of CHIKV infection with an EC₅₀ (50% effective concentration) value of 2.2 ± 0.49 μM without significant cytotoxicity (CC₅₀ > 200 μM) and was chosen for further elucidation of its antiviral mechanism. The infectious viral particle formation was abolished by approximately 72% at a QVIR concentration of 20 μM during infection in the BHK-21 cell line, and the CHIKV RNA synthesis was diminished by 84% for nsP2 as well as 74% for E2, whereas the levels of viral proteins were decreased by 69.9% for nsP2 and 53.9% for E2. Flow cytometry analysis confirmed a huge decline in the expression of viral nsP2 and E2 proteins by 71.84 and 67.7%, respectively. Time of addition experiments indicated that QVIR inhibited viral infection at early and late stages of viral replication cycle, and the optimal inhibition was observed at 16 h post infection. The present study advocates for the first time that QVIR acts as a substantial and potent inhibitor against CHIKV and might be as an auspicious novel drug candidate for the development of therapeutic agents against CHIKV infections.

Chloroquine and Sulfadoxine Derivatives Inhibit ZIKV Replication in Cervical Cells

Despite the severe morbidity caused by Zika fever, its specific treatment is still a challenge for public health. Several research groups have investigated the drug repurposing of chloroquine. However, the highly toxic side effect induced by chloroquine paves the way for the improvement of this drug for use in Zika fever clinics. Our aim is to evaluate the anti-Zika virus (ZIKV) effect of hybrid compounds derived from chloroquine and sulfadoxine antimalarial drugs. The antiviral activity of hybrid compounds (C-Sd1 to C-Sd7) was assessed in an in-vitro model of human cervical and Vero cell lines infected with a Brazilian (BR) ZIKV strain. First, we evaluated the cytotoxic effect on cultures treated with up to 200 µM of C-Sds and observed CC₅₀ values that ranged from 112.0 ± 1.8 to >200 µM in cervical cells and 43.2 ± 0.4 to 143.0 ± 1.3 µM in Vero cells. Then, the cultures were ZIKV-infected and treated with up to 25 µM of C-Sds for 48 h. The treatment of cervical cells with C-Sds at 12 µM induced a reduction of 79.8% ± 4.2% to 90.7% ± 1.5% of ZIKV-envelope glycoprotein expression in infected cells as compared to 36.8% ± 2.9% of infection in vehicle control. The viral load was also investigated and revealed a reduction of 2- to 3-logs of ZIKV genome copies/mL in culture supernatants compared to 6.7 ± 0.7 × 10⁸ copies/mL in vehicle control. The dose-response curve by plaque-forming reduction (PFR) in cervical cells revealed a potent dose-dependent activity of C-Sds in inhibiting ZIKV replication, with PFR above 50% and 90% at 6 and 12 µM, respectively, while 25 µM inhibited 100% of viral progeny. The treatment of Vero cells at 12 µM led to 100% PFR, confirming the C-Sds activity in another cell type. Regarding effective concentration in cervical cells, the EC₅₀ values ranged from 3.2 ± 0.1 to 5.0 ± 0.2 µM, and the EC₉₀ values ranged from 7.2 ± 0.1 to 11.6 ± 0.1 µM, with selectivity index above 40 for most C-Sds, showing a good therapeutic window. Here, our aim is to investigate the anti-ZIKV activity of new hybrid compounds that show highly potent efficacy as inhibitors of ZIKV in-vitro infection. However, further studies will be needed to investigate whether these new chemical structures can lead to the improvement of chloroquine antiviral activity.

Beyond the Surface: Endocytosis of Mosquito-Borne Flaviviruses

Flaviviruses are a group of positive-sense RNA viruses that are primarily transmitted through arthropod vectors and are capable of causing a broad spectrum of diseases. Many of the flaviviruses that are pathogenic in humans are transmitted specifically through mosquito vectors. Over the past century, many mosquito-borne flavivirus infections have emerged and re-emerged, and are of global importance with hundreds of millions of infections occurring yearly. There is a need for novel, effective, and accessible vaccines and antivirals capable of inhibiting flavivirus infection and ameliorating disease. The development of therapeutics targeting viral entry has long been a goal of antiviral research, but most efforts are hindered by the lack of broad-spectrum potency or toxicities associated with on-target effects, since many host proteins necessary for viral entry are also essential for host cell biology. Mosquito-borne flaviviruses generally enter cells by clathrin-mediated endocytosis (CME), and recent studies suggest that a subset of these viruses can be internalized through a specialized form of CME that has additional dependencies distinct from canonical CME pathways, and antivirals targeting this pathway have been discovered. In this review, we discuss the role and contribution of endocytosis to mosquito-borne flavivirus entry as well as consider past and future efforts to target endocytosis for therapeutic interventions.

Repurposing Approved Drugs for Guiding COVID-19 Prophylaxis: A Systematic Review

The SARS-CoV-2 outbreak originally appeared in China in December 2019 and became a global pandemic in March 2020. This infectious disease has directly affected public health and the world economy. Several palliative therapeutic treatments and prophylaxis strategies have been used to control the progress of this viral infection, including pre-(PrEP) and post-exposure prophylaxis. On the other hand, research groups around the world are still studying novel drug prophylaxis and treatment using repurposing approaches, as well as vaccination options, which are in different pre-clinical and clinical testing phases. This systematic review evaluated 1,228 articles from the PubMed and Scopus indexing databases, following the Kitchenham bibliographic searching protocol, with the aim to list drug candidates, potentially approved to be used as new options for SARS-CoV-2 prophylaxis clinical trials and medical protocols. In searching protocol, we used the following keywords: "Covid-19 or SARS-CoV-2" or "Coronavirus or 2019 nCoV," "prophylaxis," "prophylactic," "pre-exposure," "COVID-19 or SARS-CoV-2 Chemoprophylaxis," "repurposed," "strategies," "clinical," "trials," "anti-SARS-CoV-2," "anti-covid-19," "Antiviral," "Therapy prevention in vitro," in cells "and" human testing. After all protocol steps, we selected 60 articles that included: 15 studies with clinical data, 22 studies that used in vitro experiments, seven studies using animal models, and 18 studies performed with in silico experiments. Additionally, we included more 22 compounds between FDA approved drugs and drug-like like molecules, which were tested in large-scale screenings, as well as those repurposed approved drugs with new mechanism of actions. The drugs selected in this review can assist clinical studies and medical guidelines on the rational repurposing of known antiviral drugs for COVID-19 prophylaxis.

Repurposing Sigma-1 Receptor Ligands for COVID-19 Therapy?

Outbreaks of emerging infections, such as COVID-19 pandemic especially, confront health professionals with the unique challenge of treating patients. With no time to discover new drugs, repurposing of approved drugs or in clinical development is likely the only solution. Replication of coronaviruses (CoVs) occurs in a modified membranous compartment derived from the endoplasmic reticulum (ER), causes host cell ER stress and activates pathways to facilitate adaptation of the host cell machinery to viral needs. Accordingly, modulation of ER remodeling and ER stress response might be pivotal in elucidating CoV-host interactions and provide a rationale for new therapeutic, host-based antiviral approaches. The sigma-1 receptor (Sig-1R) is a ligand-operated, ER membrane-bound chaperone that acts as an upstream modulator of ER stress and thus a candidate host protein for host-based repurposing approaches to treat COVID-19 patients. Sig-1R ligands are frequently identified in in vitro drug repurposing screens aiming to identify antiviral compounds against CoVs, including severe acute respiratory syndrome CoV-2 (SARS-CoV-2). Sig-1R regulates key mechanisms of the adaptive host cell stress response and takes part in early steps of viral replication. It is enriched in lipid rafts and detergent-resistant ER membranes, where it colocalizes with viral replicase proteins. Indeed, the non-structural SARS-CoV-2 protein Nsp6 interacts with Sig-1R. The activity of Sig-1R ligands against COVID-19 remains to be specifically assessed in clinical trials. This review provides a rationale for targeting Sig-1R as a host-based drug repurposing approach to treat COVID-19 patients. Evidence gained using Sig-1R ligands in unbiased in vitro antiviral drug screens and the potential mechanisms underlying the modulatory effect of Sig-1R on the host cell response are discussed. Targeting Sig-1R is not expected to reduce dramatically established viral replication, but it might interfere with early steps of virus-induced host cell reprogramming, aid to slow down the course of infection, prevent the aggravation of the disease and/or allow a time window to mature a protective immune response. Sig-1R-based medicines could provide benefit not only as early intervention, preventive but also as adjuvant therapy.

Broad-Spectrum Flavivirus Inhibitors: a Medicinal Chemistry Point of View

Infections by flaviviruses, such as Dengue, West Nile, Yellow Fever and Zika viruses, represent a growing risk for global health. There are vaccines only for few flaviviruses while no effective treatments are available. Flaviviruses share epidemiological, structural, and ecologic features and often different viruses can co-infect the same host. Therefore, the identification of broad-spectrum inhibitors is highly desirable either for known flaviviruses or for viruses that likely will emerge in the future. Strategies targeting both virus and host factors have been pursued to identify broad-spectrum antiflaviviral agents. In this review, we describe the most promising and best characterized targets and their relative broad-spectrum inhibitors, identified by drug repurposing/libraries screenings and by focused medicinal chemistry campaigns. Finally, we discuss about future strategies to identify new broad-spectrum antiflavivirus agents.

Methylene blue is a potent and broad-spectrum inhibitor against Zika virus in vitro and in vivo

Many flaviviruses including the Dengue virus (DENV), Zika virus (ZIKV), West Nile virus, Yellow Fever virus, and Japanese encephalitis virus are significant human pathogens, unfortunately without any specific therapy. Here, we demonstrate that methylene blue, an FDA-approved drug, is a broad-spectrum and potent antiviral against Zika virus and Dengue virus both in vitro and in vivo. We found that methylene blue can considerably inhibit the interactions between viral protease NS3 and its NS2B co-factor, inhibit viral protease activity, inhibit viral growth, protect 3D mini-brain organoids from ZIKV infection, and reduce viremia in a mouse model. Mechanistic studies confirmed that methylene blue works in both entry and post entry steps, reduces virus production in replicon cells and inhibited production of processed NS3 protein. Overall, we have shown that methylene blue is a potent antiviral for management of flavivirus infections, particularly for Zika virus. As an FDA-approved drug, methylene blue is well-tolerated for human use. Therefore, methylene blue represents a promising and easily developed therapy for management of infections by ZIKV and other flaviviruses.

JMX0207, a Niclosamide Derivative with Improved Pharmacokinetics, Suppresses Zika Virus Infection Both In Vitro and In Vivo

Flaviviruses causes significant human disease. Recent outbreaks of the Zika virus highlight the need to develop effective therapies for this class of viruses. Previously we identified niclosamide as a broad-spectrum inhibitor for flaviviruses by targeting the interface between viral protease NS3 and its cofactor NS2B. Here, we screened a small library of niclosamide derivatives and identified a new analogue with improved pharmacokinetic properties. Compound JMX0207 showed improved efficacy in inhibition of the molecular interaction between NS3 and NS2B, better inhibition of viral protease function, and enhanced antiviral efficacy in the cell-based antiviral assay. The derivative also significantly reduced Zika virus infection on 3D mini-brain organoids derived from pluripotent neural stem cells. Intriguingly, the compound significantly reduced viremia in a Zika virus (ZIKV) animal model. In summary, a niclosamide derivative, JMX0207, was identified, which shows improved pharmacokinetics and efficacy against Zika virus both in vitro and in vivo.

Drugs, host proteins and viral proteins: how their promiscuities shape antiviral design

The reciprocal nature of drug specificity and target specificity implies that the same is true for their respective promiscuities. Protein promiscuity has two broadly different types of footprint in drug design. The first is relaxed specificity of binding sites for substrates, inhibitors, effectors or cofactors. The second involves protein-protein interactions of regulatory processes such as signal transduction and transcription, and here protein intrinsic disorder plays an important role. Both viruses and host cells exploit intrinsic disorder for their survival, as do the design and discovery programs for antivirals. Drug action, strictly speaking, always relies upon promiscuous activity, with drug promiscuity enlarging its scope. Drug repurposing searches for additional promiscuity on the part of both the drug and the target in the host. Understanding the subtle nuances of these promiscuities is critical in the design of novel and more effective antivirals.

Antimalarial drugs inhibit the replication of SARS-CoV-2: An in vitro evaluation

In December 2019, a new severe acute respiratory syndrome coronavirus (SARS-CoV-2) causing coronavirus diseases 2019 (COVID-19) emerged in Wuhan, China. African countries see slower dynamic of COVID-19 cases and deaths. One of the assumptions that may explain this later emergence in Africa, and more particularly in malaria endemic areas, would be the use of antimalarial drugs. We investigated the in vitro antiviral activity against SARS-CoV-2 of several antimalarial drugs. Chloroquine (EC50 = 2.1 μM and EC90 = 3.8 μM), hydroxychloroquine (EC50 = 1.5 μM and EC90 = 3.0 μM), ferroquine (EC50 = 1.5 μM and EC90 = 2.4 μM), desethylamodiaquine (EC50 = 0.52 μM and EC90 = 1.9 μM), mefloquine (EC50 = 1.8 μM and EC90 = 8.1 μM), pyronaridine (EC50 = 0.72 μM and EC90 = 0.75 μM) and quinine (EC50 = 10.7 μM and EC90 = 38.8 μM) showed in vitro antiviral effective activity with IC50 and IC90 compatible with drug oral uptake at doses commonly administered in malaria treatment. The ratio Clung/EC90 ranged from 5 to 59. Lumefantrine, piperaquine and dihydroartemisinin had IC50 and IC90 too high to be compatible with expected plasma concentrations (ratio Cmax/EC90 < 0.05). Based on our results, we would expect that countries which commonly use artesunate-amodiaquine or artesunate-mefloquine report fewer cases and deaths than those using artemether-lumefantrine or dihydroartemisinin-piperaquine. It could be necessary now to compare the antimalarial use and the dynamics of COVID-19 country by country to confirm this hypothesis.

A pharmacological perspective of chloroquine in SARS-CoV-2 infection: An old drug for the fight against a new coronavirus?

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is having serious consequences on health and the economy worldwide. All evidence-based treatment strategies need to be considered to combat this new virus. Drugs need to be considered on scientific grounds of efficacy, safety and cost. Chloroquine (CQ) and hydroxychloroquine (HCQ) are old drugs used in the treatment of malaria. Moreover, their antiviral properties have been previously studied, including against coronaviruses, where evidence of efficacy has been found. In the current race against time triggered by the COVID-19 pandemic, the search for new antivirals is very important. However, consideration should be given to old drugs with known anti-coronavirus activity, such as CQ and HCQ. These could be integrated into current treatment strategies while novel treatments are awaited, also in light of the fact that they display an anticoagulant effect that facilitates the activity of low-molecular-weight heparin, aimed at preventing acute respiratory distress syndrome (ARDS)-associated thrombotic events. The safety of CQ and HCQ has been studied for over 50 years, however recently published data raise concerns for cardiac toxicity of CQ/HCQ in patients with COVID-19. This review also re-examines the real information provided by some of the published alarming reports, although concluding that cardiac toxicity should in any case be stringently monitored in patients receiving CQ/HCQ.

Recent advances in antiviral drug development towards dengue virus

Despite the high disease burden of dengue virus, there is no approved antiviral treatment or broadly applicable vaccine to treat or prevent dengue virus infection. In the last decade, many antiviral compounds have been identified but only few have been further evaluated in pre-clinical or clinical trials. This review will give an overview of the direct-acting and host-directed antivirals identified to date. Furthermore, important parameters for further development that is, drug properties including efficacy, specificity and stability, pre-clinical animal testing, and combinational drug therapy will be discussed.

A systematic review on use of aminoquinolines for the therapeutic management of COVID-19: Efficacy, safety and clinical trials

Recent global outbreak of the pandemic caused by coronavirus (COVID-19) emphasizes the urgent need for novel antiviral therapeutics. It can be supplemented by utilization of efficient and validated drug discovery approaches such as drug repurposing/repositioning. The well reported and clinically used anti-malarial aminoquinoline drugs (chloroquine and hydroxychloroquine) have shown potential to be repurposed to control the present pandemic by inhibition of COVID-19. The review elaborates the mechanism of action, safety (side effects, adverse effects, toxicity) and details of clinical trials for chloroquine and hydroxychloroquine to benefit the clinicians, medicinal chemist, pharmacologist actively involved in controlling the pandemic and to provide therapeutics for the treatment of COVID-19 infection.

Hydroxychloroquine in rheumatic autoimmune disorders and beyond

Initially used as antimalarial drugs, hydroxychloroquine (HCQ) and, to a lesser extent, chloroquine (CQ) are currently being used to treat several diseases. Due to its cost‐effectiveness, safety and efficacy, HCQ is especially used in rheumatic autoimmune disorders (RADs), such as systemic lupus erythematosus, primary Sjögren's syndrome and rheumatoid arthritis. Despite this widespread use in the clinic, HCQ molecular modes of action are still not completely understood. By influencing several cellular pathways through different mechanisms, CQ and HCQ inhibit multiple endolysosomal functions, including autophagy, as well as endosomal Toll‐like receptor activation and calcium signalling. These effects alter several aspects of the immune system with the synergistic consequence of reducing pro‐inflammatory cytokine production and release, one of the most marked symptoms of RADs. Here, we review the current knowledge on the molecular modes of action of these drugs and the circumstances under which they trigger side effects. This is of particular importance as the therapeutic use of HCQ is expanding beyond the treatment of malaria and RADs.

Potential Antiviral Options against SARS-CoV-2 Infection

As of June 2020, the number of people infected with severe acute respiratory coronavirus 2 (SARS-CoV-2) continues to skyrocket, with more than 6.7 million cases worldwide. Both the World Health Organization (WHO) and United Nations (UN) has highlighted the need for better control of SARS-CoV-2 infections. However, developing novel virus-specific vaccines, monoclonal antibodies and antiviral drugs against SARS-CoV-2 can be time-consuming and costly. Convalescent sera and safe-in-man broad-spectrum antivirals (BSAAs) are readily available treatment options. Here, we developed a neutralization assay using SARS-CoV-2 strain and Vero-E6 cells. We identified the most potent sera from recovered patients for the treatment of SARS-CoV-2-infected patients. We also screened 136 safe-in-man broad-spectrum antivirals against the SARS-CoV-2 infection in Vero-E6 cells and identified nelfinavir, salinomycin, amodiaquine, obatoclax, emetine and homoharringtonine. We found that a combination of orally available virus-directed nelfinavir and host-directed amodiaquine exhibited the highest synergy. Finally, we developed a website to disseminate the knowledge on available and emerging treatments of COVID-19.

Reporter Replicons for Antiviral Drug Discovery against Positive Single-Stranded RNA Viruses

Single-stranded positive RNA ((+) ssRNA) viruses include several important human pathogens. Some members are responsible for large outbreaks, such as Zika virus, West Nile virus, SARS-CoV, and SARS-CoV-2, while others are endemic, causing an enormous global health burden. Since vaccines or specific treatments are not available for most viral infections, the discovery of direct-acting antivirals (DAA) is an urgent need. Still, the low-throughput nature of and biosafety concerns related to traditional antiviral assays hinders the discovery of new inhibitors. With the advances of reverse genetics, reporter replicon systems have become an alternative tool for the screening of DAAs. Herein, we review decades of the use of (+) ssRNA viruses replicon systems for the discovery of antiviral agents. We summarize different strategies used to develop those systems, as well as highlight some of the most promising inhibitors identified by the method. Despite the genetic alterations introduced, reporter replicons have been shown to be reliable systems for screening and identification of viral replication inhibitors and, therefore, an important tool for the discovery of new DAAs.

A review on possible modes of action of chloroquine/hydroxychloroquine: repurposing against SAR-CoV-2 (COVID-19) pandemic

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Chloroquine (CQ) has diverse modes of action against viral infections.

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CQ may interfere with SARS-CoV-2 attachment to the host ACE2 receptor.

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CQ may hamper the STING pathway to attenuate the pro-inflammatory response.

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Hydroxychloroquine (HCQ) might be a logical approach in the treatment of SARS-CoV-2 infection.

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Large clinical trials are needed before clinical recommendations of HCQ against COVID-19.

Chloroquine (CQ) and its analogue hydroxychloroquine (HCQ) have long been used worldwide as frontline drugs for the treatment and prophylaxis of human malaria. Since the first reported cases in Wuhan, China, in late December 2019, humans have been under threat from coronavirus disease 2019 (COVID-19) caused by the novel coronavirus SARS-CoV-2 (previously known as 2019-nCoV), subsequently declared a pandemic. While the world is searching for expedited approval for a vaccine, which may be only preventative and not a cure, physicians and country leaders are considering several concerted clinical trials suggesting that the age-old antimalarial drugs CQ/HCQ could be a potent therapeutic against COVID-19. Based on accumulating scientific reports, here we highlight the possible modes of action of CQ/HCQ that could justify its use against viral infections. Considering the global health crisis of the COVID-19 pandemic, the option of repurposing old drugs, e.g. CQ/HCQ, particularly HCQ, for the treatment of SARS-CoV-2 infection could be a good choice. CQ/HCQ has diverse modes of action, including alteration of the acidic environment inside lysosomes and late endosomes, preventing endocytosis, exosome release and phagolysosomal fusion, and inhibition of the host cytokine storm. One or more diverse mechanisms might work against viral infections and reduce mortality. As there is no cure for COVID-19, clinical testing of HCQ is urgently required to determine its potency against SARS-CoV-2, as this is the currently available treatment option. There remains a need to find other innovative drug candidates as possible candidates to enter clinical evaluation and testing.

Target Identification Using Homopharma and Network-Based Methods for Predicting Compounds Against Dengue Virus-Infected Cells

Drug target prediction is an important method for drug discovery and design, can disclose the potential inhibitory effect of active compounds, and is particularly relevant to many diseases that have the potential to kill, such as dengue, but lack any healing agent. An antiviral drug is urgently required for dengue treatment. Some potential antiviral agents are still in the process of drug discovery, but the development of more effective active molecules is in critical demand. Herein, we aimed to provide an efficient technique for target prediction using homopharma and network-based methods, which is reliable and expeditious to hunt for the possible human targets of three phenolic lipids (anarcardic acid, cardol, and cardanol) related to dengue viral (DENV) infection as a case study. Using several databases, the similarity search and network-based analyses were applied on the three phenolic lipids resulting in the identification of seven possible targets as follows. Based on protein annotation, three phenolic lipids may interrupt or disturb the human proteins, namely KAT5, GAPDH, ACTB, and HSP90AA1, whose biological functions have been previously reported to be involved with viruses in the family Flaviviridae. In addition, these phenolic lipids might inhibit the mechanism of the viral proteins: NS3, NS5, and E proteins. The DENV and human proteins obtained from this study could be potential targets for further molecular optimization on compounds with a phenolic lipid core structure in anti-dengue drug discovery. As such, this pipeline could be a valuable tool to identify possible targets of active compounds.

Repurposing approved drugs on the pathway to novel therapies

The time and cost of developing new drugs have led many groups to limit their search for therapeutics to compounds that have previously been approved for human use. Many "repurposed" drugs, such as derivatives of thalidomide, antibiotics, and antivirals have had clinical success in treatment areas well beyond their original approved use. These include applications in treating antibiotic-resistant organisms, viruses, cancers and to prevent burn scarring. The major theoretical justification for reusing approved drugs is that they have known modes of action and controllable side effects. Coadministering antibiotics with inhibitors of bacterial toxins or enzymes that mediate multidrug resistance can greatly enhance their activity. Drugs that control host cell pathways, including inflammation, tumor necrosis factor, interferons, and autophagy, can reduce the "cytokine storm" response to injury, control infection, and aid in cancer therapy. An active compound, even if previously approved for human use, will be a poor clinical candidate if it lacks specificity for the new target, has poor solubility or can cause serious side effects. Synergistic combinations can reduce the dosages of the individual components to lower reactivity. Preclinical analysis should take into account that severely ill patients with comorbidities will be more sensitive to side effects than healthy trial subjects. Once an active, approved drug has been identified, collaboration with medicinal chemists can aid in finding derivatives with better physicochemical properties, specificity, and efficacy, to provide novel therapies for cancers, emerging and rare diseases.

Discovery and development of safe-in-man broad-spectrum antiviral agents

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We reviewed the discovery and development process of broad-spectrum antiviral agents.

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We summarized the information on 120 safe-in-man agents in a freely accessible database.

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Further studies will increase the number of broad-spectrum antivirals, expand the spectrum of their indications, and identify drug combinations for treatment of emerging and re-emerging viral infections.

Viral diseases are one of the leading causes of morbidity and mortality in the world. Virus-specific vaccines and antiviral drugs are the most powerful tools to combat viral diseases. However, broad-spectrum antiviral agents (BSAAs, i.e. compounds targeting viruses belonging to two or more viral families) could provide additional protection of the general population from emerging and re-emerging viral diseases, reinforcing the arsenal of available antiviral options. Here, we review discovery and development of BSAAs and summarize the information on 120 safe-in-man agents in a freely accessible database (https://drugvirus.info/). Future and ongoing pre-clinical and clinical studies will increase the number of BSAAs, expand the spectrum of their indications, and identify drug combinations for treatment of emerging and re-emerging viral infections as well as co-infections.

Antiviral Drugs Against Severe Fever With Thrombocytopenia Syndrome Virus Infection

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by SFTS virus (SFTSV), which is a novel bunyavirus. SFTSV was first isolated from patients who presented with fever, thrombocytopenia, leukocytopenia, and multiorgan dysfunction in China. Subsequently, it was found to be widely distributed in Southeast Asia (Korea, Japan, and Vietnam). SFTSV can be transmitted not only from ticks but also from domestic animals, companion animals, and humans. Because the case fatality rate of SFTS is high (6–30%), development of specific and effective treatment for SFTS is required. Studies of potential antiviral drugs for SFTS-specific therapy have been conducted on existing or newly discovered agents in vitro and in vivo, with ribavirin and favipiravir being the most promising candidates. While animal experiments and retrospective studies have demonstrated the limited efficacy of ribavirin, it was also speculated that ribavirin would be effective in patients with a viral load <1 × 10⁶ copies/mL. Favipiravir showed higher efficacy than ribavirin against SFTSV in in vitro assays and greater efficacy in animal models, even administrated 3 days after the virus inoculation. Although clinical trials evaluating the efficacy of favipiravir in SFTS patients in Japan are underway, this has yet to be confirmed. Other drugs, including hexachlorophene, calcium channel blockers, 2′-fluoro-2′-deoxycytidine, caffeic acid, amodiaquine, and interferons, have also been evaluated for their inhibitory efficacy against SFTSV. Among them, calcium channel blockers are promising because in addition to their efficacy in vitro and in vivo, retrospective clinical data have indicated that nifedipine, one of the calcium channel blockers, reduced the case fatality rate by >5-fold. Although further research is necessary to develop SFTS-specific therapy, considerable progress has been achieved in this area. Here we summarize and discuss recent advances in antiviral drugs against SFTSV.

The Use of Antimalarial Drugs against Viral Infection

In recent decades, drugs used to treat malaria infection have been shown to be beneficial for many other diseases, including viral infections. In particular, they have received special attention due to the lack of effective antiviral drugs against new emerging viruses (i.e., HIV, dengue virus, chikungunya virus, Ebola virus, etc.) or against classic infections due to drug-resistant viral strains (i.e., human cytomegalovirus). Here, we reviewed the in vitro/in vivo and clinical studies conducted to evaluate the antiviral activities of four classes of antimalarial drugs: Artemisinin derivatives, aryl-aminoalcohols, aminoquinolines, and antimicrobial drugs.

In Vivo Activity of Amodiaquine against Ebola Virus Infection

During the Ebola virus disease (EVD) epidemic in Western Africa (2013‒2016), antimalarial treatment was administered to EVD patients due to the high coexisting malaria burden in accordance with World Health Organization guidelines. In an Ebola treatment center in Liberia, EVD patients receiving the combination antimalarial artesunate-amodiaquine had a lower risk of death compared to those treated with artemether-lumefantrine. As artemether and artesunate are derivatives of artemisinin, the beneficial anti-Ebola virus (EBOV) effect observed could possibly be attributed to the change from lumefantrine to amodiaquine. Amodiaquine is a widely used antimalarial in the countries that experience outbreaks of EVD and, therefore, holds promise as an approved drug that could be repurposed for treating EBOV infections. We investigated the potential anti-EBOV effect of amodiaquine in a well-characterized nonhuman primate model of EVD. Using a similar 3-day antimalarial dosing strategy as for human patients, plasma concentrations of amodiaquine in healthy animals were similar to those found in humans. However, the treatment regimen did not result in a survival benefit or decrease of disease signs in EBOV-infected animals. While amodiaquine on its own failed to demonstrate efficacy, we cannot exclude potential therapeutic value of amodiaquine when used in combination with artesunate or another antiviral.

Neutralization of Acidic Intracellular Vesicles by Niclosamide Inhibits Multiple Steps of the Dengue Virus Life Cycle In Vitro

Dengue fever is one of the most important mosquito-borne viral infections in large parts of tropical and subtropical countries and is a significant public health concern and socioeconomic burden. There is an urgent need to develop antivirals that can effectively reduce dengue virus (DENV) replication and decrease viral load. Niclosamide, an antiparasitic drug approved for human use, has been recently identified as an effective antiviral agent against a number of pH-dependent viruses, including flaviviruses. Here, we reveal that neutralization of low-pH intracellular compartments by niclosamide affects multiple steps of the DENV infectious cycle. Specifically, niclosamide-induced endosomal neutralization not only prevents viral RNA replication but also affects the maturation of DENV particles, rendering them non-infectious. We found that niclosamide-induced endosomal neutralization prevented E glycoprotein conformational changes on the virion surface of flaviviruses, resulting in the release of non-infectious immature virus particles with uncleaved pr peptide from host cells. Collectively, our findings support the potential application of niclosamide as an antiviral agent against flavivirus infection and highlight a previously uncharacterized mechanism of action of the drug.

Recent update on anti-dengue drug discovery

Dengue is the most important arthropod-borne viral disease of humans, with more than half of the global population living in at-risk areas. Despite the negative impact on public health, there are no antiviral therapies available, and the only licensed vaccine, Dengvaxia^®, has been contraindicated in children below nine years of age. In an effort to combat dengue, several small molecules have entered into human clinical trials. Here, we review anti-DENV molecules and their drug targets that have been published within the past five years (2014-2018). Further, we discuss their probable mechanisms of action and describe a role for classes of clinically approved drugs and also an unclassified class of anti-DENV agents. This review aims to enhance our understanding of novel agents and their cognate targets in furthering innovations in the use of small molecules for dengue drug therapies.

Exploiting the unique features of Zika and Dengue proteases for inhibitor design

Zika and Dengue viruses have attracted substantial attention from researchers in light of recent outbreaks of Dengue fever and increases in cases of congenital microcephaly in areas with Zika incidence. This review summarizes the current state of knowledge about Zika and Dengue proteases. These enzymes have several interesting features: 1) NS3 serine protease requires the activating co-factor NS2B, which is anchored in the membrane of the endoplasmic reticulum; 2) NS2B displays extensive conformational dynamics; 3) NS3 is a multidomain protein with proteolytic, NTPase, RNA 5' triphosphatase and helicase activity and has many protein-protein interaction partners; 4) NS3 is autoproteolytically released from its precursor. Attempts to design tight-binding and specific active-site inhibitors are complicated by the facts that the substrate pocket of the NS2B-NS3 protease is flat and the active-site ligands are charged. The ionic character of potential active-site inhibitors negatively influences their cell permeability. Possibilities to block cis-autoprocessing of the protease precursor have recently been considered. Additionally, potential allosteric sites on NS2B-NS3 proteases have been identified and allosteric compounds have been designed to impair substrate binding and/or block the NS2B-NS3 interaction. Such compounds could be specific to viral proteases, without off-target effects on host serine proteases, and could have favorable pharmacokinetic profiles. This review discusses various groups of inhibitors of these proteases according to their mechanisms of action and chemical structures.

Drug repurposing for new, efficient, broad spectrum antivirals

Emerging viruses are a major threat to human health. Recent outbreaks have emphasized the urgent need for new antiviral treatments. For several pathogenic viruses, considerable efforts have focused on vaccine development. However, during epidemics infected individuals need to be treated urgently. High-throughput screening of clinically tested compounds provides a rapid means to identify undiscovered, antiviral functions for well-characterized therapeutics. Repurposed drugs can bypass part of the early cost and time needed for validation and authorization. In this review we describe recent efforts to find broad spectrum antivirals through drug repurposing. We have chosen several candidates and propose strategies to understand their mechanism of action and to determine how resistance to antivirals develops in infected cells.

A randomized, proof-of-concept clinical trial on repurposing chlorcyclizine for the treatment of chronic hepatitis C

BACKGROUND & AIMS

Chlorcyclizine HCl (CCZ) is a piperazine-class antihistamine with anti-hepatitis C virus (HCV) activity in vitro and in vivo. In a first-in-humans study for HCV, we evaluated the antiviral effects and safety of CCZ±ribavirin (RBV), characterized pharmacokinetic (PK) and viral kinetic (VK) patterns, and provide insights into CCZs mode of action against HCV.

METHODS

Chronic HCV patients were randomized to CCZ (75 mg twice daily) or CCZ+weight-based RBV (1000/1200 mg daily) for 28 days. Therapy started with a loading dose of CCZ 150 mg ± RBV. Serial assessments of safety, liver tests, PK and VK markers were obtained.

RESULTS

24 HCV patients were treated; 54% male, median age 56 years, median HCV RNA 6.30 log IU/ml, without baseline differences between groups. At the end of therapy, subjects treated with CCZ monotherapy did not show any significant or sustained reduction in viremia (p = 0.69), whereas 7/12 (58%) subjects treated with CCZ+RBV had a >3-fold decline in HCV RNA. Subjects who responded demonstrated monophasic (n = 2), biphasic (n = 2) and triphasic (n = 3) VK responses. Contrary to historical RBV monotherapy response, CCZ+RBV demonstrated a continued viral decline suggesting a possible synergistic effect of CCZ+RBV. Mathematical modeling predicts a median effectiveness of CCZ+RBV in blocking viral production (ε) of 59% (Interquartile range, IQR: 50%) and blocking infection (η) of 78% (IQR: 23%). Adverse events (AEs) were mild-moderate without treatment discontinuations for AEs.

CONCLUSIONS

In this human pilot study, CCZ demonstrated some anti-HCV effects, mostly in combination with RBV. More potent CCZ derivatives with optimal PK features may be more suitable for future therapeutic development. ClinicalTrials.gov number: NCT02118012.

Drug repositioning for dengue haemorrhagic fever by integrating multiple omics analyses

To detect drug candidates for dengue haemorrhagic fever (DHF), we employed a computational drug repositioning method to perform an integrated multiple omics analysis based on transcriptomic, proteomic, and interactomic data. We identified 3,892 significant genes, 389 proteins, and 221 human proteins by transcriptomic analysis, proteomic analysis, and human–dengue virus protein–protein interactions, respectively. The drug candidates were selected using gene expression profiles for inverse drug–disease relationships compared with DHF patients and healthy controls as well as interactomic relationships between the signature proteins and chemical compounds. Integrating the results of the multiple omics analysis, we identified eight candidates for drug repositioning to treat DHF that targeted five proteins (ACTG1, CALR, ERC1, HSPA5, SYNE2) involved in human–dengue virus protein–protein interactions, and the signature proteins in the proteomic analysis mapped to significant pathways. Interestingly, five of these drug candidates, valparoic acid, sirolimus, resveratrol, vorinostat, and Y-27632, have been reported previously as effective treatments for flavivirus-induced diseases. The computational approach using multiple omics data for drug repositioning described in this study can be used effectively to identify novel drug candidates.

Inhibition of dengue virus by curcuminoids

The dengue virus is considered to be a globally important human pathogen prevalent in tropical and subtropical regions of the world. According to a recent estimate, the disease burden due to DENV infections is ∼390 million infections per year globally in ∼100 countries including the southern US, Puerto Rico and Hawaii, resulting in nearly ∼25,000 deaths mostly among children. Despite the significant morbidity and mortality that results from DENV infections, there is currently no effective chemotherapeutic treatment for DENV infections. We identified curcumin as an inhibitor of DENV2 NS2B/NS3protease in a previous high-throughput screening (HTS) campaign. We synthesized four analogues of curcumin (curcuminoids) and tested the in vitro protease inhibition activity and inhibition of replication by cell-based assays. The results revealed that curcumin is a weak inhibitor of the viral protease. However, the analogues exhibited more potent inhibition of DENV infectivity in plaque assays suggesting that the cellular pathway(s) required for viral replication and/or assembly are targeted by these compounds. Further analysis shows that inhibition of genes involved in lipid biosynthesis, and of actin polymerization by curcuminoids, are likely to be involved as their mode of action in DENV2-infected cells. Three of the curcumin derivatives possess good selectivity indices (SI) (>10) when compared to the parent curcumin.