Nucleoside Analogs with Selective Antiviral Activity against Dengue Fever and Japanese Encephalitis Viruses

Advances in antiviral strategies targeting mosquito-borne viruses: cellular, viral, and immune-related approaches

Mosquito-borne viruses (MBVs) are a major global health threat, causing significant morbidity and mortality. MBVs belong to several distinct viral families, each with unique characteristics. The primary families include Flaviviridae (e.g., Dengue, Zika, West Nile, Yellow Fever, Japanese Encephalitis), transmitted predominantly by Aedes and Culex mosquitoes; Togaviridae, which consists of the genus Alphavirus (e.g., Chikungunya, Eastern and Western Equine Encephalitis viruses), also transmitted by Aedes and Culex; Bunyaviridae (recently reorganized), containing viruses like Rift Valley Fever and Oropouche virus, transmitted by mosquitoes and sometimes sandflies; and Reoviridae, which includes the genus Orbivirus (e.g., West Nile and Bluetongue viruses), primarily affecting animals and transmitted by mosquitoes and sandflies. Despite extensive research, effective antiviral treatments for MBVs remain scarce, and current therapies mainly provide symptomatic relief and supportive care. This review examines the viral components and cellular and immune factors involved in the life cycle of MBVs. It also highlights recent advances in antiviral strategies targeting host factors such as lipid metabolism, ion channels, and proteasomes, as well as viral targets like NS2B-NS3 proteases and nonstructural proteins. Additionally, it explores immunomodulatory therapies to enhance antiviral responses and emphasizes the potential of drug repurposing, bioinformatics, artificial intelligence, and deep learning in identifying novel antiviral candidates. Continued research is crucial in mitigating MBVs' impact and preventing future outbreaks.

The Flavivirus Non-Structural Protein 5 (NS5): Structure, Functions, and Targeting for Development of Vaccines and Therapeutics

Flaviviruses, including dengue (DENV), Zika (ZIKV), West Nile (WNV), Japanese encephalitis (JEV), yellow fever (YFV), and tick-borne encephalitis (TBEV) viruses, pose a significant global emerging threat. With their potential to cause widespread outbreaks and severe health complications, the development of effective vaccines and antiviral therapeutics is imperative. The flaviviral non-structural protein 5 (NS5) is a highly conserved and multifunctional protein that is crucial for viral replication, and the NS5 protein of many flaviviruses has been shown to be a potent inhibitor of interferon (IFN) signalling. In this review, we discuss the functions of NS5, diverse NS5-mediated strategies adopted by flaviviruses to evade the host antiviral response, and how NS5 can be a target for the development of vaccines and antiviral therapeutics.

Evaluation of Four Humanized NOD-Derived Mouse Models for Dengue Virus-2 Infection

Dengue is a significant public health problem with no specific viral treatment. One of the main challenges in studying dengue is the lack of adequate animal models recapitulating human immune responses. Most studies on humanized mice use NOD-scid IL2R gamma null (NSG) mice, which exhibit poor hematopoiesis for some cell populations. This study compares three humanized (hu) NOD-derived mouse models for dengue virus-2 (DENV-2) infection in the context of human cytokine expression. Three mouse strains (hu-NSG, hu-EXL, and hu-SGM3) received xenotransplants of human CD34+ fetal cord blood cells from a single donor, and one mouse strain received human peripheral blood mononuclear cells (hu-SGM3-PBMCs). All models exhibited infectious viruses in blood confirmed by plaque assay, but mice expressing human cytokines showed higher viremia compared to conventional NSG mice. The hu-SGM3-PBMCs model developed lethal infections, showing a significant increase in viremia and clinical signs. A detectable human cytokine response was observed in all the DENV-2-infected humanized mouse models. In conclusion, humanized NOD-derived mouse models expressing human cytokines offer a relevant platform for the study of dengue pathogenesis and antiviral therapies.

Recent Advances in Antivirals for Japanese Encephalitis Virus

Culex mosquitoes are the primary vectors of the Japanese encephalitis virus (JEV). Since its discovery in 1935, Japanese encephalitis (JE), caused by JEV, has posed a significant threat to human health. Despite the widespread implementation of several JEV vaccines, the transmission chain of JEV in the natural ecosystem has not changed, and the vector of transmission cannot be eradicated. Therefore, JEV is still the focus of attention for flaviviruses. At present, there is no clinically specific drug for JE treatment. JEV infection is a complex interaction between the virus and the host cell, which is the focus of drug design and development. An overview of antivirals that target JEV elements and host factors is presented in this review. In addition, drugs that balance antiviral effects and host protection by regulating innate immunity, inflammation, apoptosis, or necrosis are reviewed to treat JE effectively.

Synthesis and biological evaluation of new β-D-N4-hydroxycytidine analogs against SARS-CoV-2, influenza viruses and DENV-2

Drug repurposing approach was applied to find a potent antiviral agent against RNA viruses such as SARS-CoV-2, influenza viruses and dengue virus with a concise strategy of small change in parent molecular structure. For this purpose, β-D-N4-hydroxycytidine (NHC, 1) with a broad spectrum of antiviral activity was chosen as the parent molecule. Among the prepared NHC analogs (8a-g, and 9) from uridine, β-D-N4-O-isobutyrylcytidine (8a) showed potent activity against SARS-CoV-2 (EC50 3.50 μM), Flu A (H1N1) (EC50 5.80 μM), Flu A (H3N2) (EC50 7.30 μM), Flu B (EC50 3.40 μM) and DENV-2 (EC50 3.95 μM) in vitro. Furthermore, its potency against SARS-CoV-2 was >5-fold, 3.4-fold, and 3-fold compared to that of NHC (1), MK-4482 (2), and remdesivir (RDV) in vitro, respectively. Ultimately, compound 8a was expected to be a potent inhibitor toward RNA viruses as a viral mutagenic agent like MK-4482.

Small-Molecule Inhibitor of Flaviviral NS3-NS5 Interaction with Broad-Spectrum Activity and Efficacy In Vivo

Every year, dengue virus (DENV) causes one hundred million infections worldwide that can result in dengue disease and severe dengue. Two other mosquito-borne flaviviruses, i.e., Zika virus (ZIKV) and West Nile virus (WNV), are responsible of prolonged outbreaks and are associated with severe neurological diseases, congenital defects, and eventually death. These three viruses, despite their importance for global public health, still lack specific drug treatments. Here, we describe the structure-guided discovery of small molecules with pan-flavivirus antiviral potential by a virtual screening of ~1 million structures targeting the NS3-NS5 interaction surface of different flaviviruses. Two molecules inhibited the interaction between DENV NS3 and NS5 in vitro and the replication of all DENV serotypes as well as ZIKV and WNV and exhibited low propensity to select resistant viruses. Remarkably, one molecule demonstrated efficacy in a mouse model of dengue by reducing peak viremia, viral load in target organs, and associated tissue pathology. This study provides the proof of concept that targeting the flaviviral NS3-NS5 interaction is an effective therapeutic strategy able to reduce virus replication in vivo and discloses new chemical scaffolds that could be further developed, thus providing a significant milestone in the development of much awaited broad-spectrum antiflaviviral drugs. IMPORTANCE More than one-third of the human population is at risk of infection by different mosquito-borne flaviviruses. Despite this, no specific antiviral drug is currently available. In this work, using a computational approach based on molecular dynamics simulation and virtual screening of ~1 million small-molecule structures, we identified a compound that targets the interaction between the two sole flaviviral enzymes, i.e., NS3 and NS5. This compound demonstrated pan-serotype anti-DENV activity and pan-flavivirus potential in infected cells, low propensity to select viral resistant mutant viruses, and efficacy in a mouse model of dengue. Broad-spectrum antivirals are much awaited, and this work represents a significant advance toward the development of therapeutic molecules with extended antiflavivirus potential that act by an innovative mechanism and could be used alone or in combination with other antivirals.

Discovery of a 2'-Fluoro,2'-Bromouridine Phosphoramidate Prodrug Exhibiting Anti-Yellow Fever Virus Activity in Culture and in Mice

Yellow fever virus (YFV) is a potentially lethal, zoonotic, blood-borne flavivirus transmitted to humans and non-human primates by mosquitoes. Owing to multiple deadly epidemics, the WHO classifies YFV as a "high impact, high threat disease" with resurgent epidemic potential. At present, there are no approved antiviral therapies to combat YFV infection. Herein we report on 2'-halogen-modified nucleoside analogs as potential anti-YFV agents. Of 11 compounds evaluated, three showed great promise with low toxicity, high intracellular metabolism into the active nucleoside triphosphate form, and sub-micromolar anti-YFV activity. Notably, we investigated a 2'-fluoro,2'-bromouridine phosphate prodrug (C9), a known anti-HCV agent with good stability in human blood and favorable metabolism. Predictive modeling revealed that C9 could readily bind the active site of the YFV RdRp, conferring its anti-YFV activity. C9 displayed potent anti-YFV activity in primary human macrophages, 3D hepatocyte spheroids, and in mice. In an A129 murine model, shortly after infection, C9 significantly reduced YFV replication and protected against YFV-induced liver inflammation and pathology with no adverse effects. Collectively, this work identifies a potent new anti-YFV agent with strong therapeutic promise.

Targeting the Annexin A1-FPR2/ALX pathway for host-directed therapy in dengue disease

Host immune responses contribute to dengue's pathogenesis and severity, yet the possibility that failure in endogenous inflammation resolution pathways could characterise the disease has not been contemplated. The pro-resolving protein Annexin A1 (AnxA1) is known to counterbalance overexuberant inflammation and mast cell (MC) activation. We hypothesised that inadequate AnxA1 engagement underlies the cytokine storm and vascular pathologies associated with dengue disease. Levels of AnxA1 were examined in the plasma of dengue patients and infected mice. Immunocompetent, interferon (alpha and beta) receptor one knockout (KO), AnxA1 KO, and formyl peptide receptor 2 (FPR2) KO mice were infected with dengue virus (DENV) and treated with the AnxA1 mimetic peptide Ac_2-26 for analysis. In addition, the effect of Ac_2-26 on DENV-induced MC degranulation was assessed in vitro and in vivo. We observed that circulating levels of AnxA1 were reduced in dengue patients and DENV-infected mice. Whilst the absence of AnxA1 or its receptor FPR2 aggravated illness in infected mice, treatment with AnxA1 agonistic peptide attenuated disease manifestationsatteanuated the symptoms of the disease. Both clinical outcomes were attributed to modulation of DENV-mediated viral load-independent MC degranulation. We have thereby identified that altered levels of the pro-resolving mediator AnxA1 are of pathological relevance in DENV infection, suggesting FPR2/ALX agonists as a therapeutic target for dengue disease.

Carbohydrate Ligands for COVID-19 Spike Proteins

An outbreak of SARS-CoV-2 coronavirus (COVID-19) first detected in Wuhan, China, has created a public health emergency all over the world. The pandemic has caused more than 340 million confirmed cases and 5.57 million deaths as of 23 January 2022. Although carbohydrates have been found to play a role in coronavirus binding and infection, the role of cell surface glycans in SARS-CoV-2 infection and pathogenesis is still not understood. Herein, we report that the SARS-CoV-2 spike protein S1 subunit binds specifically to blood group A and B antigens, and that the spike protein S2 subunit has a binding preference for Le^a antigens. Further examination of the binding preference for different types of red blood cells (RBCs) indicated that the spike protein S1 subunit preferentially binds with blood group A RBCs, whereas the spike protein S2 subunit prefers to interact with blood group Le^a RBCs. Angiotensin converting enzyme 2 (ACE2), a known target of SARS-CoV-2 spike proteins, was identified to be a blood group A antigen-containing glycoprotein. Additionally, 6-sulfo N-acetyllactosamine was found to inhibit the binding of the spike protein S1 subunit with blood group A RBCs and reduce the interaction between the spike protein S1 subunit and ACE2.

Murine models of dengue virus infection for novel drug discovery

INTRODUCTION

Dengue virus (DENV) is the causative agent of the most prevalent human disease transmitted by mosquitoes in tropical and subtropical regions worldwide. At present, no antiviral drug is available and the difficulties to develop highly protective vaccines against the four DENV serotypes maintain the requirement of effective options for dengue chemotherapy.

AREAS COVERED

The availability of animal models that reproduce human disease is a very valuable tool for the preclinical evaluation of potential antivirals. Here, the main murine models of dengue infection are described, including immunocompetent wild-type mice, immunocompromised mice deficient in diverse components of the interferon (IFN) pathway and humanized mice. The main findings in antiviral testing of DENV inhibitory compounds in murine models are also presented.

EXPERT OPINION

At present, there is no murine model that fully recapitulates human disease. However, immunocompromised mice deficient in IFN-α/β and -γ receptors, with their limitations, have shown to be the most suitable system for antiviral preclinical testing. In fact, the AG129 mouse model allowed the identification of celgosivir, an inhibitor of cellular glucosidases, as a promising option for DENV therapy. However, clinical trials still were not successful, emphasizing the difficulties in the transition from preclinical testing to human treatment.

Synthesis and anti-dengue virus activity of 5-ethynylimidazole-4-carboxamide (EICA) nucleotide prodrugs

We previously showed that 5-ethynyl-(1-β-D-ribofuranosyl)imidazole-4-carboxamide (1; EICAR) is a potent anti-dengue virus (DENV) compound but is cytotoxic to some cell lines, while its 4-thio derivative, 5-ethynyl-(4-thio-1-β-D-ribofuranosyl)imidazole-4-carboxamide (2; 4'-thioEICAR), has less cytotoxicity but also less anti-DENV activity. Based on the hypothesis that the lower anti-DENV activity of 2 is due to reduced susceptibility to phosphorylation by cellular kinase(s), we investigated whether a monophosphate prodrug of 2 can improve its activity. Here, we first prepared two types of prodrug of 1, which revealed that the S-acyl-2-thioethyl (SATE) prodrug had stronger anti-DENV activity than the aryloxyphosphoramidate (so-called ProTide) prodrug. Based on these findings, we next prepared the SATE prodrug of 4'-thioEICAR 18. As expected, the resulting 18 showed potent anti-DENV activity, which was comparable to that of 1; however, its cytotoxicity was also increased relative to 2. Our findings suggest that prodrugs of 4'-thioribonucleoside derivatives such as EICAR (1) represent an effective approach to developing potent biologically active compounds; however, the balance between antiviral activity and cytotoxicity remains to be addressed.

Antiviral activity of silymarin and baicalein against dengue virus

Dengue is an arthropod-borne viral disease that has become endemic and a global threat in many countries with no effective antiviral drug available currently. This study showed that flavonoids: silymarin and baicalein could inhibit the dengue virus in vitro and were well tolerated in Vero cells with a half-maximum cytotoxic concentration (CC₅₀) of 749.70 µg/mL and 271.03 µg/mL, respectively. Silymarin and baicalein exerted virucidal effects against DENV-3, with a selective index (SI) of 10.87 and 21.34, respectively. Baicalein showed a better inhibition of intracellular DENV-3 progeny with a SI of 7.82 compared to silymarin. Baicalein effectively blocked DENV-3 attachment (95.59%) to the Vero cells, while silymarin prevented the viral entry (72.46%) into the cells, thus reducing viral infectivity. Both flavonoids showed promising antiviral activity against all four dengue serotypes. The in silico molecular docking showed that silymarin could bind to the viral envelope (E) protein with a binding affinity of - 8.5 kcal/mol and form hydrogen bonds with the amino acids GLN120, TRP229, ASN89, and THR223 of the E protein. Overall, this study showed that silymarin and baicalein exhibited potential anti-DENV activity and could serve as promising antiviral agents for further development against dengue infection.

Dengue mouse models for evaluating pathogenesis and countermeasures

Dengue virus (DENV) causes the most prevalent arbovirus illness worldwide and is responsible for many debilitating epidemics. The four circulating DENV serotypes infect humans and can cause asymptomatic, mild, moderate, or severe Dengue. Because of the global morbidity and mortality due to Dengue, deployment of a safe and effective tetravalent vaccine has been a high priority, and to date, a partially realized goal. The study of pathogenesis and development of DENV therapeutics and vaccines has been limited by few animal models that recapitulate key features of human disease. Over the past two decades, mouse models of DENV infection have evolved with increasing success. Here, we review the utilization and limitations of mice for studying DENV pathogenesis and evaluating countermeasures.

Identification of Potential Inhibitors for Targets Involved in Dengue Fever

Lethality due to dengue infection is a global threat. Nearly 400 million people are affected every year, which approximately costs 500 million dollars for surveillance and vector control itself. Many investigations on the structure-function relationship of proteins expressed by the dengue virus are being made for more than a decade and had come up with many reports on small molecule drug discovery. In this review, we present a detailed note on viral proteins and their functions as well as the inhibitors discovered/designed so far using experimental and computational methods. Further, the phytoconstituents from medicinal plants, specifically the extract of the papaya leaves, neem and bael, which combat dengue infection via dengue protease, helicase, methyl transferase and polymerase are summarized.

The burden of Japanese encephalitis, the catch-up vaccination campaign, and health service providers' perceptions in Myanmar: 2012-2017

Background

Myanmar is endemic for Japanese encephalitis (JE) and has experienced several outbreaks in recent years. The vector-borne disease control (VBDC) program has collected hospital-based surveillance data since 1974. There is an urgent need to collate, analyze, and interpret the most recent information. The study aimed to describe (i) hospital-based JE cases and deaths between 2012 and 2017, (ii) a catch-up vaccination campaign in children in 2017, and (iii) health service provider perceptions about JE in one township in 2018.

Methods

This was a cross-sectional study of cases, deaths, and catch-up childhood vaccinations using secondary data from program records and a survey database of health service provider perceptions.

Results

Between 2012 and 2017, there were 872 JE cases and 79 deaths with a case fatality rate of 91 per 1000; 2016 was the year with most cases and deaths. Most cases (n = 324) and deaths (n = 37) occurred in children aged 5–9 years. Large case numbers were reported in delta and lowland regions (n = 550) and during the wet season (n = 580). The highest case fatality rates were observed in the hills and coastal regions (120 and 112 per 1000, respectively). Nationwide coverage of the catch-up JE vaccination campaign among 13.7 million eligible children was 92%, with coverage lower in the hills and coastal regions (84%) compared with delta and lowland regions and plains (94%). More vaccinations (65%) occurred through school-based campaigns with the remainder (35%) vaccinated through community-based campaigns. Structured interviews in one township showed that service providers (n = 47) had good perceptions about various aspects of JE, although perceived benefits of specific vector control measures were poor: spraying/fumigation (38%), garbage removal (36%), larvicide use (36%), and drainage of standing/stagnant water (32%).

Conclusion

The catch-up vaccination campaign was a successful response to high JE case numbers and deaths in children. However, ongoing surveillance for JE needs to continue and be strengthened to ensure comprehensive reporting of all cases, more knowledge is needed on disability in JE survivors, and all attempts must be made to ensure high percentage coverage of vaccination through routine and catch-up campaigns.

Childhood Infectious Encephalitis: An Overview of Clinical Features, Investigations, Treatment, and Recent Patents

BACKGROUND

Infectious encephalitis is a serious and challenging condition to manage. This overview summarizes the current literature regarding the etiology, clinical manifestations, diagnosis, management, and recent patents of acute childhood infectious encephalitis.

METHODS

We used PubMed Clinical Queries as a search engine and used keywords of "encephalitis" AND "childhood" Patents were searched using the key term "encephalitis" in google.patents.- com and patentsonline.com.

RESULTS

Viral encephalitis is the most common cause of acute infectious encephalitis in children. In young children, the clinical manifestations can be non-specific. Provision of empiric antimicrobial therapy until a specific infectious organism has been identified, which in most cases includes acyclovir, is the cornerstone of therapy. Advanced investigation tools, including nucleic acid-based test panel and metagenomic next-generation sequencing, improve the diagnostic yield of identifying an infectious organism. Supportive therapy includes adequate airway and oxygenation, fluid and electrolyte balance, cerebral perfusion pressure support, and seizure control. Recent patents are related to the diagnosis, treatment, and prevention of acute infectious encephalitis.

CONCLUSION

Viral encephalitis is the most common cause of acute infectious encephalitis in children and is associated with significant morbidity. Recent advances in understanding the genetic basis and immunological correlation of infectious encephalitis may improve treatment. Third-tier diagnostic tests may be incorporated into clinical practice. Treatment is targeted at the infectious process but remains mostly supportive. However, specific antimicrobial agents and vaccines development is ongoing.