The Adenosine Analogue NITD008 has Potent Antiviral Activity against Human and Animal Caliciviruses

Identification of novel inhibitors of dengue viral NS5 RNA-dependent RNA polymerase through molecular docking, biological activity evaluation and molecular dynamics simulations

The DENV-NS5 RNA-dependent RNA polymerase (RdRp) is essential for viral replication, and one of the targets of anti-virus. In this study, the Uni-VSW module was used to virtual screen 1.6 million compounds in the ChemDiv and TargetMol (USA) database, 27 candidates were obtained. Thereby 23 candidates were selected based on their binding free energies by 50 ns MD simulations. The biological activity of the candidates and the reference compounds (BCX4430 and Compound 27) were evaluated on their IC50 values against DENV-NGC, CC50 values, and selectivity index. Among these, the IC50 values of D1 and D8 were 13.06 ± 1.17 μM and 14.79 ± 7.76 μM, respectively, which were better than that of Compound 27 (IC50 =19.67 ± 1.12 μM). The comprehensive MD simulations were performed on the candidates to assess the stability behaviour and binding mechanisms. The density functional theory (DFT) analysis was also conducted to explore the structural and electronic properties.

Discovery of novel inhibitors of dengue viral RNA-dependent RNA polymerase by molecular docking, in vitro assay, DFT, and MD simulations

Dengue virus (DENV) is a significant significant mosquito-borne pathogen. Its RNA-dependent RNA polymerase (RdRp) plays a crucial role in viral replication, making it a critical target for antiviral drug development. The goal of this study was to identify potential inhibitors of the DENV RdRp through virtual screening and experimental assays. In this study, based on Topscience and TargetMol database. 47 compounds were stand out from 1.1 million compounds with high binding energies between -77.24 kcal/mol and-44.08 kcal/mol by initial virtual screening. Their inhibition activity against dengue virus was evaluated by cell-based antiviral and RdRp enzyme assays, and 4 compounds (R2, R29, R37, and R39) identified in our study demonstrated promising in vitro activity, with IC₅₀ values of less than 10 μM, indicating their strong potential as antiviral agents against DENV. The RdRp enzyme inhibition assay revealed that R37 demonstrated significant activity against the DENV RdRp enzyme, with an IC₅₀ of 10.86 ± 2.06 μM, which was lower than that of 3'-dATP (IC₅₀ = 30.09 ± 8.26 μM). These 4 compounds were further subjected to DFT calculations and MD simulation, which not only provided valuable structural insights but also enhanced the reliability of our findings by offering a detailed understanding of the stability and binding interactions of the top compounds with the DENV RdRp enzyme. These results suggest that the identified compounds are promising candidates for novel DENV RdRp inhibitors and provide both theoretical and experimental groundwork for further optimization and validation.

Viral-host molecular interactions and metabolic modulation: Strategies to inhibit flaviviruses pathogenesis

Flaviviruses, which include globally impactful pathogens, such as West Nile virus, yellow fever virus, Zika virus, Japanese encephalitis virus, and dengue virus, contribute significantly to human infections. Despite the ongoing emergence and resurgence of flavivirus-mediated pathogenesis, the absence of specific therapeutic options remains a challenge in the prevention and treatment of flaviviral infections. Through the intricate processes of fusion, transcription, replication, and maturation, the complex interplay of viral and host metabolic interactions affects pathophysiology. Crucial interactions involve metabolic molecules, such as amino acids, glucose, fatty acids, and nucleotides, each playing a pivotal role in the replication and maturation of flaviviruses. These viral-host metabolic molecular interactions hijack and modulate the molecular mechanisms of host metabolism. A comprehensive understanding of these intricate metabolic pathways offers valuable insights, potentially unveiling novel targets for therapeutic interventions against flaviviral pathogenesis. This review emphasizes promising avenues for the development of therapeutic agents that target specific metabolic molecules, such as amino acids, glucose, fatty acids, and nucleotides, which interact with flavivirus replication and are closely linked to the modulation of host metabolism. The clinical limitations of current drugs have prompted the development of new inhibitory strategies for flaviviruses based on an understanding of the molecular interactions between the virus and the host.

Drug screening identified that handelin inhibits feline calicivirus infection by inhibiting HSP70 expression in vitro

Feline calicivirus (FCV) is considered one of the major pathogens of cats worldwide and causes upper respiratory tract disease in all cats. In some cats, infection is by a highly virulent strain of FCV (vs.-FCV), which can cause severe and fatal systemic disease symptoms. At present, few antiviral drugs are approved for clinical treatment against FCV. Therefore, there is an imminent need for effective FCV antiviral agents. Here, we used observed a cytopathic effect (CPE) assay to screen 1746 traditional Chinese medicine monomer compounds and found one that can effectively inhibit FCV replication, namely, handelin, with an effective concentration (EC50) value of approximately 2.5 µM. Further study showed that handelin inhibits FCV replication via interference with heat shock protein 70 (HSP70), which is a crucial host factor and plays a positive role in regulating viral replication. Moreover, handelin and HSP70 inhibitors have broad-spectrum antiviral activity. These findings indicate that handelin is a potential candidate for the treatment of FCV infection and that HSP70 may be an important drug target.

Calicivirus Infection in Cats

Feline calicivirus (FCV) is a common pathogen in domestic cats that is highly contagious, resistant to many disinfectants and demonstrates a high genetic variability. FCV infection can lead to serious or even fatal diseases. In this review, the European Advisory Board on Cat Diseases (ABCD), a scientifically independent board of experts in feline medicine from 11 European countries, presents the current knowledge of FCV infection and fills gaps with expert opinions. FCV infections are particularly problematic in multicat environments. FCV-infected cats often show painful erosions in the mouth and mild upper respiratory disease and, particularly in kittens, even fatal pneumonia. However, infection can be associated with chronic gingivostomatitis. Rarely, highly virulent FCV variants can induce severe systemic disease with epizootic spread and high mortality. FCV can best be detected by reverse-transcriptase PCR. However, a negative result does not rule out FCV infection and healthy cats can test positive. All cats should be vaccinated against FCV (core vaccine); however, vaccination protects cats from disease but not from infection. Considering the high variability of FCV, changing to different vaccine strain(s) may be of benefit if disease occurs in fully vaccinated cats. Infection-induced immunity is not life-long and does not protect against all strains; therefore, vaccination of cats that have recovered from caliciviral disease is recommended.

Design, synthesis and evaluation of 2'-acetylene-7-deaza-adenosine phosphoamidate derivatives as anti-EV71 and anti-EV-D68 agents

A series of phosphoamidate derivatives of nucleoside 2'-acetylene-7-deaza-adenosine (NITD008) were synthesized and evaluated for their in vitro antiviral activities against the enteroviruses EV71 and EV-D68. The phosphoamidate (15f) containing a hexyl ester of l-alanine exhibited the most promising activity against EV71 (IC₅₀ = 0.13 ± 0.08 μM) and was 4-times more potent than NITD008. Meanwhile, the derivative containing a cyclohexyl ester of l-alanine (15l) exhibited the most potent activity with high selectivity index against both EV71 (IC₅₀ = 0.19 ± 0.27 μM, SI = 117.00) and EV-D68 (IC₅₀ = 0.17 ± 0.16 μM, SI = 130.76), which were both higher than that of NITD008. The results indicated that the phosphoamidate 15l was the most promising candidate for further development as antiviral agents for the treatment of both EV71 and EV-D68 infection.

Feline Calicivirus Virulent Systemic Disease: Clinical Epidemiology, Analysis of Viral Isolates and In Vitro Efficacy of Novel Antivirals in Australian Outbreaks

Feline calicivirus (FCV) causes upper respiratory tract disease (URTD) and sporadic outbreaks of virulent systemic disease (FCV-VSD). The basis for the increased pathogenicity of FCV-VSD viruses is incompletely understood, and antivirals for FCV-VSD have yet to be developed. We investigated the clinicoepidemiology and viral features of three FCV-VSD outbreaks in Australia and evaluated the in vitro efficacy of nitazoxanide (NTZ), 2′-C-methylcytidine (2CMC) and NITD-008 against FCV-VSD viruses. Overall mortality among 23 cases of FCV-VSD was 39%. Metagenomic sequencing identified five genetically distinct FCV lineages within the three outbreaks, all seemingly evolving in situ in Australia. Notably, no mutations that clearly distinguished FCV-URTD from FCV-VSD phenotypes were identified. One FCV-URTD strain likely originated from a recombination event. Analysis of seven amino-acid residues from the hypervariable E region of the capsid in the cultured viruses did not support the contention that properties of these residues can reliably differentiate between the two pathotypes. On plaque reduction assays, dose–response inhibition of FCV-VSD was obtained with all antivirals at low micromolar concentrations; NTZ EC₅₀, 0.4–0.6 µM, TI = 21; 2CMC EC₅₀, 2.7–5.3 µM, TI > 18; NITD-008, 0.5 to 0.9 µM, TI > 111. Investigation of these antivirals for the treatment of FCV-VSD is warranted.

Current and Future Antiviral Strategies to Tackle Gastrointestinal Viral Infections

Acute gastroenteritis caused by virus has a major impact on public health worldwide in terms of morbidity, mortality, and economic burden. The main culprits are rotaviruses, noroviruses, sapoviruses, astroviruses, and enteric adenoviruses. Currently, there are no antiviral drugs available for the prevention or treatment of viral gastroenteritis. Here, we describe the antivirals that were identified as having in vitro and/or in vivo activity against these viruses, originating from in silico design or library screening, natural sources or being repurposed drugs. We also highlight recent advances in model systems available for this (hard to cultivate) group of viruses, such as organoid technologies, and that will facilitate antiviral studies as well as fill some of current knowledge gaps that hamper the development of highly efficient therapies against gastroenteric viruses.

Broad spectrum antiviral nucleosides-Our best hope for the future

The current focus for many researchers has turned to the development of therapeutics that have the potential for serving as broad-spectrum inhibitors that can target numerous viruses, both within a particular family, as well as to span across multiple viral families. This will allow us to build an arsenal of therapeutics that could be used for the next outbreak. In that regard, nucleosides have served as the cornerstone for antiviral therapy for many decades. As detailed herein, many nucleosides have been shown to inhibit multiple viruses due to the conserved nature of many viral enzyme binding sites. Thus, it is somewhat surprising that up until very recently, many researchers focused more on "one bug one drug," rather than trying to target multiple viruses given those similarities. This attitude is now changing due to the realization that we need to be proactive rather than reactive when it comes to combating emerging and reemerging infectious diseases. A brief summary of prominent nucleoside analogues that previously exhibited broad-spectrum activity and are now under renewed interest, as well as new analogues, that are currently under investigation against SARS-CoV-2 and other viruses is discussed herein.

Nitazoxanide protects cats from feline calicivirus infection and acts synergistically with mizoribine in vitro

Feline calicivirus (FCV) is a highly contagious pathogen that causes acute upper respiratory infections and oral disease in cats, thus seriously endangering feline health. Recently, there have been outbreaks of particularly virulent variant strains of FCV, which can cause both acute symptoms and fatal systemic disease. The discovery of effective antiviral agents to treat FCV infection is, therefore, gradually assuming increased importance. In this study, we showed that both nitazoxanide and mizoribine had antiviral activity in F81 cells infected with different strains of FCV and also demonstrated a synergistic effect between the two drugs. Experiments in cats challenged with FCV showed that nitazoxanide significantly reduced the clinical symptoms of FCV infection, reduced viral load in the trachea and lungs, and reduced viral shedding. Our results showed that nitazoxanide and mizoribine could potentially be used as therapeutic agents to treat FCV infection.