Computer-aided identification, design and synthesis of a novel series of compounds with selective antiviral activity against chikungunya virus

Inhibitors of the Structural and Nonstructural Proteins of Alphaviruses

The Alphavirus genus includes viruses that cause encephalitis due to neuroinvasion and viruses that cause arthritis due to acute and chronic inflammation. There is no approved therapeutic for alphavirus infections, but significant efforts are ongoing, more so in recent years, to develop vaccines and therapeutics for alphavirus infections. This review article highlights some of the major advances made so far to identify small molecules that can selectively target the structural and the nonstructural proteins in alphaviruses with the expectation that persistent investigation of an increasingly expanding chemical space through a variety of structure-based design and high-throughput screening strategies will yield candidate drugs for clinical studies. While most of the works discussed are still in the early discovery to lead optimization stages, promising avenues remain for drug development against this family of viruses.

In Silico Drug Repurposing Uncovered the Antiviral Potential of the Antiparasitic Drug Oxibendazole Against the Chikungunya Virus

Chikungunya virus (CHIKV) has been reported in over 120 countries and is the causative agent of Chikungunya fever. The debilitating nature of this disease, which can persist months to years after acute infection, drastically impacts the quality of life of patients. Yet, specific antivirals are lacking for the treatment of this disease, which makes the search for new drugs necessary. In this context, the nsP2 protease emerges as an attractive therapeutic target, and drug repurposing strategies have proven to be valuable. Therefore, we combined in silico and in vitro methods to identify known drugs as potential CHIKV nsP2 protease inhibitors with antiviral properties within DrugBank. Herein, we developed a hybrid virtual screening pipeline comprising pharmacophore- and target-based screening, drug-like, and pharmaceutical filtering steps. Six virtual hits were obtained, and two of them, capecitabine (CPB) and oxibendazole (OBZ), were evaluated against CHIKV replication in Vero cells. CPB did not present antiviral activity, whereas OBZ inhibited the replication of two different strains of CHIKV, namely, 181-25 (Asian genotype) and BRA/RJ/18 (clinical isolate from ECSA genotype). OBZ showed potent antiviral activity against the CHIKV BRA/RJ/18 (EC50 = 11.4 μM) with a high selectivity index (>44). Analogs of OBZ (albendazole, fenbendazole, and mebendazole) were also evaluated, but none exhibited anti-CHIKV activity, and further, their stereoelectronic features were analyzed. Additionally, we observed that OBZ acts mainly at post-entry steps. Hence, our results support further in vivo studies to investigate the antiviral potential of OBZ, which offers a new alternative to fight CHIKV infections.

Polymeric membrane potentiometric antibiotic sensors using computer-aided screening of supramolecular macrocyclic carriers

Carrier-based polymeric membrane potentiometric sensors are an ideal tool for detecting ionic species. However, in the fabrication of these sensors, the screening of carriers still relies on empirical trial- and error-based optimization, which requires tedious and time-consuming experimental verification. In this work, computer-aided screening of carriers is applied in the preparation of polymeric membrane potentiometric sensors. Molecular docking is used to study the host-guest interactions between receptors and targets. Binding energies are employed as the standard to screen the appropriate carrier. As a proof-of-concept experiment, the antibiotic ciprofloxacin is selected as the target model. A series of supramolecular macrocyclic receptors including cyclodextrins, cucurbiturils and calixarenes are chosen as potential receptors. The proposed sensor based on the receptor calix[4]arene screened by molecular docking shows a lower detection limit of 0.5 μmol L-1 for ciprofloxacin. It can be expected that the proposed computer-aided screening technique of carriers can provide a simple but highly efficient method for the fabrication of carrier-based electrochemical and optical sensors.

Preclinical data on morpholine (3,5-di-tertbutyl-4-hydroxyphenyl) methanone induced anxiolysis

Trimetozine is used to be indicated for the treatment of mental illnesses, particularly anxiety. The present study provides data on the pharmacological profile of trimetozine derivative morpholine (3,5-di-tert-butyl-4-hydroxyphenyl) methanone (LQFM289) which was designed from molecular hybridization of trimetozine lead compound and 2,6-di-tert-butyl-hydroxytoluene to develop new anxiolytic drugs. Here, we conduct molecular dynamics simulations, docking studies, receptor binding assays, and in silico ADMET profiling of LQFM289 before its behavioral and biochemical assessment in mice within the dose range of 5-20 mg/kg. The docking of LQFM289 showed strong interactions with the benzodiazepine binding sites and matched well with receptor binding data. With the ADMET profile of this trimetozine derivative that predicts a high intestinal absorption and permeability to blood-brain barrier without being inhibited by the permeability glycoprotein, the oral administration of LQFM289 10 mg/kg consistently induced anxiolytic-like behavior of the mice exposed to the open field and light-dark box apparatus without eliciting motor incoordination in the wire, rotarod, and chimney tests. A decrease in the wire and rotarod´s fall latency coupled with an increase in the chimney test´s climbing time and a decrease in the number of crossings in the open field apparatus at the dose of 20 mg/kg of this trimetozine derivative suggest sedative or motor coordination impairment at this highest dose. The attenuation of the anxiolytic-like effects of LQFM289 (10 mg/kg) by flumazenil pretreatment implicates the participation of benzodiazepine binding sites. The lowering of corticosterone and tumor necrosis factor alpha (cytokine) in LQFM289-treated mice at a single oral (acute) dose of 10 mg/kg suggests that the anxiolytic-like effect of this compound also involves the recruitment of non-benzodiazepine binding sites/GABAergic molecular machinery.

Design, synthesis, antiviral evaluation, and In silico studies of acrylamides targeting nsP2 from Chikungunya virus

The Togaviridae family comprises several New- and Old-World Alphaviruses that have been responsible for thousands of human illnesses, including the RNA arbovirus Chikungunya virus (CHIKV). Firstly, it was reported in Tanzania in 1952 but rapidly it spread to several countries from Europe, Asia, and the Americas. Since then, CHIKV has been circulating in diverse countries around the world, leading to increased morbidity rates. Currently, there are no FDA-approved drugs or licensed vaccines to specifically treat CHIKV infections. Thus, there is a lack of alternatives to fight against this viral disease, making it an unmet need. Structurally, CHIKV is composed of five structural proteins (E3, E2, E1, C, and 6k) and four non-structural proteins (nsP1-4), in which nsP2 represents an attractive antiviral target for designing novel inhibitors since it has an essential role in the virus replication and transcription. Herein, we used a rational drug design strategy to select some acrylamide derivatives to be synthesized and evaluated against CHIKV nsP2 and also screened on CHIKV-infected cells. Thus, two regions of modifications were considered for these types of inhibitors, based on a previous study of our group, generating 1560 possible inhibitors. Then, the 24 most promising ones were synthesized and screened by using a FRET-based enzymatic assay protocol targeting CHIKV nsP2, identifying LQM330, 333, 336, and 338 as the most potent inhibitors, with Ki values of 48.6 ± 2.8, 92.3 ± 1.4, 2.3 ± 1.5, and 181.8 ± 2.5 μM, respectively. Still, their Km and Vmax kinetic parameters were also determined, along with their competitive binding modes of CHIKV nsP2 inhibition. Then, ITC analyses revealed KD values of 127, 159, 198, and 218 μM for LQM330, 333, 336, and 338, respectively. Also, their ΔH, ΔS, and ΔG physicochemical parameters were determined. MD simulations demonstrated that these inhibitors present a stable binding mode with nsP2, interacting with important residues of this protease, according to docking analyzes. Moreover, MM/PBSA calculations displayed that van der Waals interactions are mainly responsible for stabilizing the inhibitor-nsP2 complex, and their binding energies corroborated with their Ki values, having -198.7 ± 15.68, -124.8 ± 17.27, -247.4 ± 23.78, and -100.6 ± 19.21 kcal/mol for LQM330, 333, 336, and 338, respectively. Since Sindbis (SINV) nsP2 is similar to CHIKV nsP2, these best inhibitors were screened against SINV-infected cells, and it was verified that LQM330 presented the best result, with an EC50 value of 0.95 ± 0.09 μM. Even at 50 μM concentration, LQM338 was found to be cytotoxic on Vero cells after 48 h. Then, LQM330, 333, and 336 were evaluated against CHIKV-infected cells in antiviral assays, in which LQM330 was found to be the most promising antiviral candidate in this study, exhibiting an EC50 value of 5.2 ± 0.52 μM and SI of 31.78. The intracellular flow cytometry demonstrated that LQM330 is able to reduce the CHIKV cytopathogenic effect on cells, and also reduce the percentage of CHIKV-positive cells from 66.1% ± 7.05 to 35.8% ± 5.78 at 50 μM concentration. Finally, qPCR studies demonstrated that LQM330 was capable of reducing the number of viral RNA copies/μL, suggesting that CHIKV nsP2 is targeted by this inhibitor as its mechanism of action.

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.

Targeting the alphavirus virus replication process for antiviral development

Many alphaviruses, including chikungunya virus (CHIKV) are known human pathogens that lack specific and effective antivirals or vaccines available. The upstream portion of the positive-sense single-stranded RNA genome of alphaviruses encodes four nonstructural proteins: nsP1 to nsP4. They are expressed and autoprocessed to nonstructural proteins which assemble into a replication complex (RC) playing multiple essential roles on viral RNA replication and communication with the host components. The assembly of alphavirus RC and its RNA genome initiates the membrane-derived ultrastructure known as spherule which facilitates viral RNA synthesis protected from host immune responses. Recent advances in the molecular understanding of the high-resolution CHIKV RC heteromeric ultrastructure have provided new insights into the viral replication process. Hence, alphavirus RC presents as an ideal multi-enzyme target for the development of structure-based antiviral drugs. Moreover, the alphavirus RC has therapeutic potential in the form of self-amplifying RNA technology against both infectious and non-infectious diseases.

Identification of a novel P2X7 antagonist using structure-based virtual screening

P2X4 and P2X7 receptors are ATP-gated ion channels, which play important roles in neuropathic and inflammatory pain, and as such they are important drug targets in diseases of inflammatory origin. While several compounds targeting P2X4 and P2X7 receptors have been developed using traditional high-throughput screening approaches, relatively few compounds have been developed using structure-based design. We initially set out to develop compounds targeting human P2X4, by performing virtual screening on the orthosteric (ATP-binding) pocket of a molecular model of human P2X4 based on the crystal structure of the Danio rerio receptor. The screening of a library of approximately 300,000 commercially available drug-like compounds led to the initial selection of 17 compounds; however, none of these compounds displayed a significant antagonist effect at P2X4 in a Fluo-4 ATP-induced calcium influx assay. When the same set of compounds was tested against human P2X7 in an ATP-stimulated Yo-Pro1 dye uptake assay, one compound (an indeno(1,2-b)pyridine derivative; GP-25) reduced the response by greater than 50% when applied at a concentration of 30 µM. GP-25 displayed an IC₅₀ value of 8.7 μM at human P2X7 and 24.4 μM at rat P2X7, and was confirmed to be active using whole-cell patch clamp electrophysiology and not cytotoxic. Schild analysis suggested that mode of action of GP-25 was orthosteric. Screening of a further 16 commercially available analogues of GP-25 led to the discovery of five additional compounds with antagonist activity at human P2X7, enabling us to investigate the structure-activity relationship. Finally, docking of the R- and S-enantiomers of GP-25 into the orthosteric pocket of molecular models of human P2X4 and human P2X7 revealed that, while both enantiomers were able to make multiple interactions between their carboxyl moieties and conserved positively charged amino-acids in human P2X7, only the S-enantiomer of GP-25 was able to do this in human P2X4, potentially explaining the lack of activity of GP-25 at this receptor.

Synthesis and antiviral activity of diverse heterocyclic scaffolds

Heterocyclic moieties form a major part of organic chemistry as they are widely distributed in nature and have wide scale practical applications ranging from extensive clinical use to diverse fields such as medicine, agriculture, photochemistry, biocidal formulations, and polymer science. By virtue of their therapeutic properties, they could be employed in combating many infectious diseases. Among the common infectious diseases, viral infections are of great public health importance worldwide. Thus, there is an urgent need for the discovery and development of antiviral drugs and clinical methods to prevent various viral infections so as to increase the life expectancy. This review presents the comprehensive overview of the synthesis and antiviral activity of different heterocyclic compounds 2015 onwards, which aids in present knowledge and helps the researchers and other stakeholders to explore their field.

Structural insights into the inhibition of the nsP2 protease from Chikungunya virus by molecular modeling approaches

Chikungunya virus (CHIKV) is the etiological agent of the Chikungunya fever which has spread worldwide. Clinically, this disease may lead to prolonged incapacitating joint pain that can compromise remarkably the patients' quality of life. However, there are no licensed vaccines or specific drugs to fight this infection yet, making the search for novel therapies an imperative need. In this scenario, the CHIKV nsP2 protease emerged as an attractive therapeutic target once this protein plays a pivotal role in viral replication and pathogenesis. Hence, we investigated the structural basis for the inhibition of this enzyme by using molecular docking and dynamics simulations. Compounds with inhibitory activities against CHIKV nsP2 protease determined experimentally were selected from the literature. Docking studies with a set of stereoisomers showed that trans isomers, but not cis ones, bound close to the catalytic dyad which may explain isomerism requirements to the enzyme's inhibition. Further, binding mode analyses of other known inhibitors revealed highly conserved contacts between inhibitors and enzyme residues like N1011, C1013, A1046, Y1079, N1082, W1084, L1205, and M1242. Molecular dynamics simulations reinforced the importance of some of these interactions and pointed to nonpolar interactions as the main forces for inhibitors' binding. Finally, we observed that true inhibitors exhibited lower structural fluctuation, higher ligand efficiency and did not induce significant changes in protein correlated motions. Collectively, our findings might allow discerning true inhibitors from false ones and can guide drug development efforts targeting the nsP2 protease to fight CHIKV infections in the future.

MBZM-N-IBT, a Novel Small Molecule, Restricts Chikungunya Virus Infection by Targeting nsP2 Protease Activity In Vitro, In Vivo, and Ex Vivo

The increase in disease incidences and persistent Chikungunya virus (CHIKV)-induced arthritis have been a huge burden on public health globally. In the absence of specific antivirals or vaccines, it is essential to continue efforts to develop effective anti-CHIKV strategies. Our previous study showing the in vitro anti-CHIKV potential of a novel molecule 1-[(2-methylbenzimidazol-1-yl) methyl]-2-oxo-indolin-3-ylidene] amino] thiourea (MBZM-N-IBT) encouraged us to further validate its efficacy. Here, the effect of MBZM-N-IBT was evaluated in vitro in RAW 264.7 cells, in vivo in C57BL/6 mice, and ex vivo in human peripheral blood mononuclear cells (hPBMCs). The study demonstrated that CHIKV infection was efficiently abrogated in RAW 264.7 cells (IC₅₀ = 22.34 μM) with significant inhibition in viral proteins. The inhibition was effective in the postentry step, and MBZM-N-IBT predominately interfered in the early stages of CHIKV life cycle. It was further supported when the protease activity of CHIKV-nsP2 was hindered by the compound. Moreover, it diminished the CHIKV-induced inflammatory responses in vitro through significant downregulation of all the major mitogen-activated protein kinases (MAPKs), NF-κB, cyclooxygenase (COX)-2, and cytokines. Furthermore, MBZM-N-IBT restricted CHIKV infection and inflammation in vivo, leading to reduced clinical scores and complete survival of C57BL/6 mice. Additionally, it has been noticed that the CHIKV infection was reduced remarkably in hPBMC-derived monocyte-macrophage populations ex vivo by the compound. In conclusion, it can be suggested that this novel compound MBZM-N-IBT has been demonstrated to be a potential anti-CHIKV molecule in vitro, in vivo, and ex vivo and fulfilled all the criteria to investigate further for successful treatment of CHIKV infection.

Computer-Aided Design and Synthesis of (Functionalized quinazoline)–(α-substituted coumarin)–arylsulfonate Conjugates against Chikungunya Virus

Chikungunya virus (CHIKV) has repeatedly spread via the bite of an infected mosquito and affected more than 100 countries. The disease poses threats to public health and the economy in the infected locations. Many efforts have been devoted to identifying compounds that could inhibit CHIKV. Unfortunately, successful clinical candidates have not been found yet. Computations through the simulating recognition process were performed on complexation of the nsP3 protein of CHIKV with the structures of triply conjugated drug lead candidates. The outcomes provided the aid on rational design of functionalized quinazoline-(α-substituted coumarin)-arylsulfonate compounds to inhibit CHIKV in Vero cells. The molecular docking studies showed a void space around the β carbon atom of coumarin when a substituent was attached at the α position. The formed vacancy offered a good chance for a Michael addition to take place owing to steric and electronic effects. The best conjugate containing a quinazolinone moiety exhibited potency with EC₅₀ = 6.46 μM, low toxicity with CC₅₀ = 59.7 μM, and the selective index (SI) = 9.24. Furthermore, the corresponding 4-anilinoquinazoline derivative improved the anti-CHIKV potency to EC₅₀ = 3.84 μM, CC₅₀ = 72.3 μM, and SI = 18.8. The conjugate with 4-anilinoquinazoline exhibited stronger binding affinity towards the macro domain than that with quinazolinone via hydrophobic and hydrogen bond interactions.

A review on structural genomics approach applied for drug discovery against three vector-borne viral diseases: Dengue, Chikungunya and Zika

Structural genomics involves the advent of three-dimensional structures of the genome encoded proteins through various techniques available. Numerous structural genomics research groups have been developed across the globe and they contribute enormously to the identification of three-dimensional structures of various proteins. In this review, we have discussed the applications of the structural genomics approach towards the discovery of potential lead-like molecules against the genomic drug targets of three vector-borne diseases, namely, Dengue, Chikungunya and Zika. Currently, all these three diseases are associated with the most important global public health problems and significant economic burden in tropical countries. Structural genomics has accelerated the identification of novel drug targets and inhibitors for the treatment of these diseases. We start with the current development status of the drug targets and antiviral drugs against these three diseases and conclude by describing challenges that need to be addressed to overcome the shortcomings in the process of drug discovery.

The global emergence of Chikungunya infection: An integrated view

Chikungunya virus (CHIKV) is one of the emerging viruses around the globe. It belongs to the family Togaviridae and genus Alphavirus and is an arthropod borne virus that transmits by the bite of an infected mosquito, mainly through Aedes aegypti and Aedes albopcitus. It is a spherical, enveloped virus with positive single stranded RNA genome. It was first discovered during 1952-53 in Tanganyika, after which outbreaks were documented in many regions of the world. CHIKV has two transmission cycles; an enzootic sylvatic cycle and an urban cycle. CHIKV genome contains 11,900 nucleotides and two open reading frames and shows great sequence variability. Molecular mechanisms of virus host-cell interactions and the pathogenesis of disease are not fully understood. The disease involves three phases; acute, post-acute and chronic with symptoms including high-grade fever, arthralgia, macupapular rashes and headache. There is no licensed vaccine or specific treatment for CHIKV infection. This lack of specific interventions combined with difficulties in making a precise diagnosis together make the disease difficult to manage. In this review we aim to present the current knowledge of global epidemiology, transmission, structure, various aspects of diagnosis as well as highlight potential antiviral drugs and vaccines against CHIKV.

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.

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.

Novel Analogues of the Chikungunya Virus Protease Inhibitor: Molecular Design, Synthesis, and Biological Evaluation

The Chikungunya virus (CHIKV) is an arbovirus belonging to the genus Alphavirus of the Togaviridae family. CHIKV is transmitted by the mosquitoes and causes Chikungunya fever. CHIKV outbreaks have occurred in Africa, Asia, Europe, and the countries of Indian and Pacific Oceans. In 2013, CHIKV cases were registered for the first time in the Americas on the Caribbean islands. There is currently no vaccine to prevent or medicines to treat CHIKV infection. The CHIKV nonstructural protease (nsP2) is a promising potential target for the development of drugs against CHIKV infection because this protein is one of the key components of the viral replication complex and is involved in multiple steps of virus infection. In this work, novel analogues of the potential CHIKV nsP2 protease inhibitor, first reported by Das et al. in 2016, were identified using molecular modeling methods, synthesized, and evaluated in vitro. The optimization of the structure of the inhibitor allowed to increase the antiviral activity of the compound 2-10 times. The possible mechanism of action of the identified potential inhibitors of the CHIKV nsP2 protease was studied in detail using molecular dynamics (MD) simulations. According to the MD results, the most probable mechanism of action is the blocking of conformational changes in the nsP2 protease required for substrate recognition and binding.

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.

Repurposing of approved drug molecules for viral infectious diseases: a molecular modelling approach

The identification of new viral drugs has become a task of paramount significance due to the frequent occurrence of viral infections and especially during the current pandemic. Despite the recent advancements, the development of antiviral drugs has not made parallel progress. Reduction of time frame and cost of the drug development process is the major advantage of drug repurposing. Therefore, in this study, a drug repurposing strategy using molecular modelling techniques, i.e. biological activity prediction, virtual screening, and molecular dynamics simulation was employed to find promising repurposing candidates for viral infectious diseases. The biological activities of non-redundant (4171) drug molecules were predicted using PASS analysis, and 1401 drug molecules were selected which showed antiviral activities in the analysis. These drug molecules were subjected to virtual screening against the selected non-structural viral proteins. A series of filters, i.e. top 10 drug molecules based on binding affinity, mean value of binding affinity, visual inspection of protein-drug complexes, and number of H-bond between protein and drug molecules were used to narrow down the drug molecules. Molecular dynamics simulation analysis was carried out to validate the intrinsic atomic interactions and binding conformations of protein-drug complexes. The binding free energies of drug molecules were assessed by employing MMPBSA analysis. Finally, nine drug molecules were prioritized, as promising repurposing candidates with the potential to inhibit the selected non-structural viral proteins.Communicated by Ramaswamy H. Sarma.

A review targeting the infection by CHIKV using computational and experimental approaches

The rise of normal body temperature of 98.6 °F beyond 100.4 °F in humans indicates fever due to some illness or infection. Viral infections caused by different viruses are one of the major causes of fever. One of such viruses is, Chikungunya virus (CHIKV) is known to cause Chikungunya fever (CHIKF) which is transmitted to humans through the mosquitoes, which actually become the primary source of transmission of the virus. The genomic structure of the CHIKV consists of the two open reading frames (ORFs). The first one is a 5' end ORF and it encodes the nonstructural protein (nsP1-nsP4). The second is a 3' end ORF and it encodes the structural proteins, which is consisted of capsid, envelope (E), accessory peptides, E3 and 6 K. Till date, there is no effective vaccine or medicine available for early detection of the CHIKV infection and appropriate diagnosis to cure the patients from the infection. NSP3 of CHIKV is the prime target of the researchers as it is responsible for the catalytic activity. This review has updates of literature on CHIKV; pathogenesis of CHIKV; inhibition of CHIKV using theoretical and experimental approaches.Communicated by Ramaswamy H. Sarma.

1,3-Thiazolbenzamide Derivatives as Chikungunya Virus nsP2 Protease Inhibitors

Chikungunya fever results from an infection with Chikungunya virus (CHIKV, genus Alphavirus) that is prevalent in tropical regions and is spreading fast to temperate climates with documented outbreaks in Europe and the Americas. Currently, there are no available vaccines or antiviral drugs for prevention or treatment of Chikungunya fever. The nonstructural proteins (nsPs) of CHIKV responsible for virus replication are promising targets for the development of new antivirals. This study was attempted to find out new potential inhibitors of CHIKV nsP2 protease using the ligand-based drug design. Two compounds 10 and 10c, identified by molecular docking, showed antiviral activity against CHIKV with IC₅₀ of 13.1 and 8.3 μM, respectively. Both compounds demonstrated the ability to inhibit the activity of nsP2 in a cell-free assay, and the impact of compound 10 on virus replication was confirmed by western blot. The molecular dynamics study of the interactions of compounds 10 and 10c with CHIKV nsP2 showed that a possible mechanism of action of these compounds is the blocking of the active site and the catalytic dyad of nsP2.

Prophylactic strategies to control chikungunya virus infection

Chikungunya virus (CHIKV) is a (re)emerging arbovirus and the causative agent of chikungunya fever. In recent years, CHIKV was responsible for a series of outbreaks, some of which had serious economic and public health impacts in the affected regions. So far, no CHIKV-specific antiviral therapy or vaccine has been approved. This review gives a brief summary on CHIKV epidemiology, spread, infection and diagnosis. It furthermore deals with the strategies against emerging diseases, drug development and the possibilities of testing antivirals against CHIKV in vitro and in vivo. With our review, we hope to provide the latest information on CHIKV, disease manifestation, as well as on the current state of CHIKV vaccine development and post-exposure therapy.

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.

Hybrids of Coumarin Derivatives as Potent and Multifunctional Bioactive Agents: A Review

BACKGROUND

Coumarins exhibit a plethora of biological activities, e.g. antiinflammatory and anti-tumor. Molecular hybridization technique has been implemented in the design of novel coumarin hybrids with several bioactive groups in order to obtain molecules with better pharmacological activity and improved pharmacokinetic profile.

OBJECTIVE

Therefore, we tried to gather as many as possible biologically active coumarin hybrids referred in the literature till now, to delineate the structural characteristics in relation to the activities and to have a survey that might help the medicinal chemists to design new coumarin hybrids with drug-likeness and varied bioactivities.

RESULTS

The biological activities of the hybrids in most of the cases were found to be different from the biological activities presented by the parent coumarins. The results showed that the hybrid molecules are more potent compared to the standard drugs used in the evaluation experiments.

CONCLUSION

Conjugation of coumarin with varied pharmacophore groups/druglike molecules responsible for different biological activities led to many novel hybrid molecules, with a multitarget behavior and improved pharmacokinetic properties.

Small-Molecule Inhibitors of Chikungunya Virus: Mechanisms of Action and Antiviral Drug Resistance

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that has spread to more than 60 countries worldwide. CHIKV infection leads to a febrile illness known as chikungunya fever (CHIKF), which is characterized by long-lasting and debilitating joint and muscle pain. CHIKV can cause large-scale epidemics with high attack rates, which substantiates the need for development of effective therapeutics suitable for outbreak containment. In this review, we highlight the different strategies used for developing CHIKV small-molecule inhibitors, ranging from high-throughput cell-based screening to in silico screens and enzymatic assays with purified viral proteins.

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that has spread to more than 60 countries worldwide. CHIKV infection leads to a febrile illness known as chikungunya fever (CHIKF), which is characterized by long-lasting and debilitating joint and muscle pain. CHIKV can cause large-scale epidemics with high attack rates, which substantiates the need for development of effective therapeutics suitable for outbreak containment. In this review, we highlight the different strategies used for developing CHIKV small-molecule inhibitors, ranging from high-throughput cell-based screening to in silico screens and enzymatic assays with purified viral proteins. We further discuss the current status of the most promising molecules, including in vitro and in vivo findings. In particular, we focus on describing host and/or viral targets, mode of action, and mechanisms of antiviral drug resistance and associated mutations. Knowledge of the key molecular determinants of drug resistance will aid selection of the most promising antiviral agent(s) for clinical use. For these reasons, we also summarize the available information about drug-resistant phenotypes in Aedes mosquito vectors. From this review, it is evident that more of the active molecules need to be evaluated in preclinical and clinical models to address the current lack of antiviral treatment for CHIKF.

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.

Computer-Aided Design, Synthesis, and Antiviral Evaluation of Novel Acrylamides as Potential Inhibitors of E3-E2-E1 Glycoproteins Complex from Chikungunya Virus

Chikungunya virus (CHIKV) causes an infectious disease characterized by inflammation and pain of the musculoskeletal tissues accompanied by swelling in the joints and cartilage damage. Currently, there are no licensed vaccines or chemotherapeutic agents to prevent or treat CHIKV infections. In this context, our research aimed to explore the potential in vitro anti-CHIKV activity of acrylamide derivatives. In silico methods were applied to 132 Michael's acceptors toward the six most important biological targets from CHIKV. Subsequently, the ten most promising acrylamides were selected and synthesized. From the cytotoxicity MTT assay, we verified that LQM330, 334, and 336 demonstrate high cell viability at 40 µM. Moreover, these derivatives exhibited anti-CHIKV activities, highlighting the compound LQM334 which exhibited an inhibition value of 81%. Thus, docking simulations were performed to suggest a potential CHIKV-target for LQM334. It was observed that the LQM334 has a high affinity towards the E3-E2-E1 glycoproteins complex. Moreover, LQM334 reduced the percentage of CHIKV-positive cells from 74.07 to 0.88%, 48h post-treatment on intracellular flow cytometry staining. In conclusion, all virtual simulations corroborated with experimental results, and LQM334 could be used as a promising anti-CHIKV scaffold for designing new drugs in the future.

Evaluation of novobiocin and telmisartan for anti-CHIKV activity

Chikungunya has re-emerged as an epidemic with global distribution and high morbidity, necessitating the need for effective therapeutics. We utilized already approved drugs with a good safety profile used in other diseases for their new property of anti-chikungunya activity. It provides a base for a fast and efficient approach to bring a novel therapy from bench to bedside by the process of drug-repositioning. We utilized an in-silico drug screening with FDA approved molecule library to identify inhibitors of the chikungunya nsP2 protease, a multifunctional and essential non-structural protein required for virus replication. Telmisartan, an anti-hypertension drug, and the antibiotic novobiocin emerged among top hits on the screen. Further, SPR experiments revealed strong in-vitro binding of telmisartan and novobiocin to nsP2 protein. Additionally, small angle x-ray scattering suggested binding of molecules to nsP2 and post-binding compaction and retention of monomeric state in the protein-inhibitor complex. Protease activity measurement revealed that both compounds inhibited nsP2 protease activity with IC₅₀ values in the low micromolar range. More importantly, plaque formation assays could show the effectiveness of these drugs in suppressing virus propagation in host cells. We propose novobiocin and telmisartan as potential inhibitors of chikungunya replication. Further research is required to establish the molecules as antivirals of clinical relevance against chikungunya.

Antivirals in medical biodefense

The viruses historically implicated or currently considered as candidates for misuse in bioterrorist events are poxviruses, filoviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and a number of arboviruses causing encephalitis, including alpha- and flaviviruses. All these viruses are of concern for public health services when they occur in natural outbreaks or emerge in unvaccinated populations. Recent events and intelligence reports point to a growing risk of dangerous biological agents being used for nefarious purposes. Public health responses effective in natural outbreaks of infectious disease may not be sufficient to deal with the severe consequences of a deliberate release of such agents. One important aspect of countermeasures against viral biothreat agents are the antiviral treatment options available for use in post-exposure prophylaxis. These issues were adressed by the organizers of the 16th Medical Biodefense Conference, held in Munich in 2018, in a special session on the development of drugs to treat infections with viruses currently perceived as a threat to societies or associated with a potential for misuse as biothreat agents. This review will outline the state-of-the-art methods in antivirals research discussed and provide an overview of antiviral compounds in the pipeline that are already approved for use or still under development.

Structural and mechanistic insight from antiviral and antiparasitic enzyme drug targets for tropical infectious diseases

With almost half of the world population living at risk, tropical infectious diseases cause millions of deaths every year in developing countries. Considering the lack of economic prospects for investment in this field, approaches aiming the rational design of compounds, such as structure-based drug discovery (SBDD), fragment screening, target-based drug discovery, and drug repurposing are of special interest. Herein, we focused in the advances on the field of SBDD targeting arboviruses such as dengue, yellow fever, zika and chikungunya enzymes of the RNA replication complex (RC) and enzymes involved in a variety of pathways essential to ensure parasitic survival in the host, for malaria, Chagas e leishmaniasis diseases. We also highlighted successful examples such as promising new inhibitors and molecules already in preclinical/clinical phase tests, major gaps in the field and perspectives for the future of drug design for tropical diseases.

Chikungunya virus inhibition by synthetic coumarin-guanosine conjugates

Since its discovery in Tanganyika, Africa in 1952, chikungunya virus (CHIKV) outbreaks have occurred in Africa, Asia, Europe, and America. Till now chikungunya fever has spread in nearly 40 countries. Because of lack of effective vaccines and antiviral drugs to intervene this disease, 21 new conjugated compounds were designed and synthesized by coupling of 6,8-dithioguanosine at its C-6 position with 3-(chloromethyl)coumarins bearing an F, Cl, Br, Me, or -OMe substituent through the -SCH₂- joint. Meanwhile, an organic "dummy" ligand (e.g., methyl, benzyl, and naphthylmethyl) or a coumarinyl moiety was attached at the C-8 position. By high through-put screening, three of these new conjugates were found to inhibit CHIKV in Vero cells with significant potency (EC₅₀ = 9.9-13.9 μM) and showed low toxicity (CC₅₀ = 96.5-212 μM). The selectivity index values were 9.37-21.7. Their structure-activity relationship was deduced, which indicates that the coumarin moiety is essential and the presence of a -OMe group enhances the antiviral activity.

A compendium of small molecule direct-acting and host-targeting inhibitors as therapies against alphaviruses

Alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally widespread, infecting a large variety of terrestrial animals, birds, insects and even fish. Moreover, they are capable of surviving and circulating in both sylvatic and urban environments, causing considerable human morbidity and mortality. The re-emergence of Chikungunya virus (CHIKV) in almost every part of the world has caused alarm to many health agencies throughout the world. The mosquito vector for this virus, Aedes, is globally distributed in tropical and temperate regions and capable of thriving in both rural and urban landscapes, giving the opportunity for CHIKV to continue expanding into new geographical regions. Despite the importance of alphaviruses as human pathogens, there is currently no targeted antiviral treatment available for alphavirus infection. This mini-review discusses some of the major features in the replication cycle of alphaviruses, highlighting the key viral targets and host components that participate in alphavirus replication and the molecular functions that were used in drug design. Together with describing the importance of these targets, we review the various direct-acting and host-targeting inhibitors, specifically small molecules that have been discovered and developed as potential therapeutics as well as their reported in vitro and in vivo efficacies.

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.

In silico screening for human norovirus antivirals reveals a novel non-nucleoside inhibitor of the viral polymerase

Human norovirus causes approximately 219,000 deaths annually, yet there are currently no antivirals available. A virtual screening of commercially available drug-like compounds (~300,000) was performed on the suramin and PPNDS binding-sites of the norovirus RNA-dependent RNA polymerase (RdRp). Selected compounds (n = 62) were examined for inhibition of norovirus RdRp activity using an in vitro transcription assay. Eight candidates demonstrated RdRp inhibition (>25% inhibition at 10 µM), which was confirmed using a gel-shift RdRp assay for two of them. The two molecules were identified as initial hits and selected for structure-activity relationship studies, which resulted in the synthesis of novel compounds that were examined for inhibitory activity. Five compounds inhibited human norovirus RdRp activity (>50% at 10 µM), with the best candidate, 54, demonstrating an IC₅₀ of 5.6 µM against the RdRp and a CC₅₀ of 62.8 µM. Combinational treatment of 54 and the known RdRp site-B inhibitor PPNDS revealed antagonism, indicating that 54 binds in the same binding pocket. Two RdRps with mutations (Q414A and R419A) previously shown to be critical for the binding of site-B compounds had no effect on inhibition, suggesting 54 interacts with distinct site-B residues. This study revealed the novel scaffold 54 for further development as a norovirus antiviral.

Rational modifications on a benzylidene-acrylohydrazide antiviral scaffold, synthesis and evaluation of bioactivity against Chikungunya virus

Chikungunya virus is a re-emerging arbovirus transmitted to humans by Aedes mosquitoes, responsible for an acute febrile illness associated with painful and debilitating arthralgia, which can persist for several months or become chronic. Over the past few years, infection with this virus has spread worldwide with a previously unknown virulence. No specific antiviral treatments nor vaccines are currently available against this important pathogen. Starting from the structure of a class of selective anti-CHIKV agents previously identified in our research group, different modifications to this scaffold were rationally designed, and 69 novel small-molecule derivatives were synthesised and evaluated for their inhibition of Chikungunya virus replication in Vero cells. Further structure-activity relationships associated with this class of antiviral agents were elucidated for the original scaffolds, and novel antiviral compounds with EC₅₀ values in the low micromolar range were identified. This work provides the foundation for further investigation of these new structures as antivirals against Chikungunya virus.

Nonstructural Proteins of Alphavirus-Potential Targets for Drug Development

Alphaviruses are enveloped, positive single-stranded RNA viruses, typically transmitted by arthropods. They often cause arthralgia or encephalitic diseases in infected humans and there is currently no targeted antiviral treatment available. The re-emergence of alphaviruses in Asia, Europe, and the Americas over the last decade, including chikungunya and o'nyong'nyong viruses, have intensified the search for selective inhibitors. In this review, we highlight key molecular determinants within the alphavirus replication complex that have been identified as viral targets, focusing on their structure and functionality in viral dissemination. We also summarize recent structural data of these viral targets and discuss how these could serve as templates to facilitate structure-based drug design and development of small molecule inhibitors.

Design, synthesis and evaluation against Chikungunya virus of novel small-molecule antiviral agents

Chikungunya virus is a re-emerging arbovirus transmitted to humans by mosquitoes, responsible for an acute flu-like illness associated with debilitating arthralgia, which can persist for several months or become chronic. In recent years, this viral infection has spread worldwide with a previously unknown virulence. To date, no specific antivirals treatments nor vaccines are available against this important pathogen. Starting from the structures of two antiviral hits previously identified in our research group with in silico techniques, this work describes the design and preparation of 31 novel structural analogues, with which different pharmacophoric features of the two hits have been explored and correlated with the inhibition of Chikungunya virus replication in cells. Structure-activity relationships were elucidated for the original scaffolds, and different novel antiviral compounds with EC₅₀ values in the low micromolar range were identified. This work provides the foundation for further investigation of these promising novel structures as antiviral agents against Chikungunya virus.

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.

Chikungunya: vaccines and therapeutics

Chikungunya virus (CHIKV) has come to prominence as a global, re-emerging pathogen over the last two decades, progressing from sporadic, remote outbreaks to worldwide explosive epidemics. From contained, though considerable, outbreaks in the southern Indian Ocean, parts of South America and the Caribbean, CHIKV continues to be a significant pathogen in Southeast Asia and India. CHIKV circulates during epidemics through an urban mosquito-to-human transmission cycle, and with no available treatments or licensed vaccines to specifically target CHIKV disease, limiting transmission relies on vector control, which poses significant challenges, especially in developing countries. This review summarizes the current findings and progress in the development of safe, effective and affordable therapeutics and vaccines for CHIKV disease.

Synthesis and biological evaluation of 6-substituted-5-fluorouridine ProTides

A new family of thirteen phosphoramidate prodrugs (ProTides) of different 6-substituted-5-fluorouridine nucleoside analogues were synthesized and evaluated as potential anticancer agents. In addition, antiviral activity against Chikungunya (CHIKV) virus was evaluated using a cytopathic effect inhibition assay. Although a carboxypeptidase Y assay supported a putative mechanism of activation of ProTides built on 5-fluorouridine with such C6-modifications, the Hint docking studies revealed a compromised substrate-activity for the Hint phosphoramidase-type enzyme that is likely responsible for phosphoramidate bioactivation through P-N bond cleavage and free nucleoside 5'-monophosphate delivery. Our observations may support and explain to some extent the poor in vitro biological activity generally demonstrated by the series of 6-substituted-5-fluorouridine phosphoramidates (ProTides) and will be of guidance for the design of novel phosphoramidate prodrugs.

Middle East Respiratory Syndrome and Severe Acute Respiratory Syndrome: Current Therapeutic Options and Potential Targets for Novel Therapies

No specific antivirals are currently available for two emerging infectious diseases, Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS). A literature search was performed covering pathogenesis, clinical features and therapeutics, clinically developed drugs for repurposing and novel drug targets. This review presents current knowledge on the epidemiology, pathogenesis and clinical features of the SARS and MERS coronaviruses. The rationale for and outcomes with treatments used for SARS and MERS is discussed. The main focus of the review is on drug development and the potential that drugs approved for other indications provide for repurposing. The drugs we discuss belong to a wide range of different drug classes, such as cancer therapeutics, antipsychotics, and antimalarials. In addition to their activity against MERS and SARS coronaviruses, many of these approved drugs have broad-spectrum potential and have already been in clinical use for treating other viral infections. A wealth of knowledge is available for these drugs. However, the information in this review is not meant to guide clinical decisions, and any therapeutic described here should only be used in context of a clinical trial. Potential targets for novel antivirals and antibodies are discussed as well as lessons learned from treatment development for other RNA viruses. The article concludes with a discussion of the gaps in our knowledge and areas for future research on emerging coronaviruses.

In silico analysis of natural compounds targeting structural and nonstructural proteins of chikungunya virus

Background: Chikungunya fever presents as a high-grade fever during its acute febrile phase and can be prolonged for months as chronic arthritis in affected individuals. Currently, there are no effective drugs or vaccines against this virus. The present study was undertaken to evaluate protein-ligand interactions of all chikungunya virus (CHIKV) proteins with natural compounds from a MolBase library in order to identify potential inhibitors of CHIKV. Methods: Virtual screening of the natural compound library against four non-structural and five structural proteins of CHIKV was performed. Homology models of the viral proteins with unknown structures were created and energy minimized by molecular dynamic simulations. Molecular docking was performed to identify the potential inhibitors for CHIKV. The absorption, distribution, metabolism and excretion (ADME) toxicity parameters for the potential inhibitors were predicted for further prioritization of the compounds. Results: Our analysis predicted three compounds, Catechin-5-O-gallate, Rosmarinic acid and Arjungenin, to interact with CHIKV proteins; two (Catechin-5-O-gallate and Rosmarinic acid) with capsid protein, and one (Arjungenin) with the E3. Conclusion: The compounds identified show promise as potential antivirals, but further in vitro studies are required to test their efficacy against CHIKV.

The medicinal chemistry of Chikungunya virus

Arthropod-borne viruses (arboviruses) are an important threat to human and animal health globally. Among these, zoonotic diseases account for billions of cases of human illness and millions of deaths every year, representing an increasing public health problem. Chikungunya virus belongs to the genus Alphavirus of the family Togariridae, and is transmitted mainly by the bite of female mosquitoes of the Aedes aegypti and/or A. albopictus species. The focus of this review will be on the medicinal chemistry of Chikungunya virus, including synthetic and natural products, as well as rationally designed compounds.