2-thiouridine is a broad-spectrum antiviral nucleoside analogue against positive-strand RNA viruses

β-d-N4-hydroxycytidine, a metabolite of molnupiravir, exhibits in vitro antiviral activity against rabies virus

Rabies is a fatal neurological disorder caused by rabies virus (RABV) infection. Approximately 60,000 patients die from rabies annually, and there are no effective treatments for this disease. Nucleoside analogs are employed as antiviral drugs based on their broad antiviral spectrum, and certain nucleoside analogs have been reported to exhibit anti-RABV activity. The nucleoside analog β-d-N4-hydroxycytidine (NHC) has antiviral effects against a range of RNA viruses. Molnupiravir (MPV), a prodrug of NHC, is clinically used as an oral antiviral drug for coronavirus infections. Despite its broad-spectrum activity, the antiviral activity of NHC against RABV remains unclear. In this study, we reveal that NHC exhibits comparable in vitro anti-RABV activity as ribavirin and favipiravir (also known as T-705) with a 90% effective concentration of 6 μM in mouse neuroblastoma cells. NHC reduced viral loads in neuronal and nonneuronal cells in a dose-dependent manner. Both laboratory and field RABVs (fixed and street strains, respectively) were susceptible to NHC. However, no increase in survival or reduction in viral titers in the brain was observed in RABV-infected mice treated prophylactically with MPV. These findings highlight the potential and challenges of NHC in the treatment of RABV infection.

Prophylactic effect of ensitrelvir in mice infected with SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiological cause of coronavirus disease 2019 (COVID-19) and continues to be a major health concern worldwide. Strategies to protect individuals at high risk of COVID-19 are critical but are currently a largely unmet need. We evaluated the oral antiviral drug ensitrelvir, which specifically targets the SARS-CoV-2 3CL protease, for its efficacy as a pre-exposure prophylactic treatment. Aged BALB/c mice were subcutaneously treated with various doses of ensitrelvir 24 h prior to a lethal SARS-CoV-2 challenge infection. Mouse body weight changes, survival rates, and viral titers in the lungs were evaluated, and plasma concentrations of ensitrelvir were determined. A single subcutaneous administration of ensitrelvir at 64 mg/kg or greater 24 h prior to SARS-CoV-2 challenge infection significantly protected aged mice against lethality and inhibited body weight loss. Pharmacokinetic analysis of ensitrelvir in the aged mice suggested that plasma concentrations ≥2.99 μg/mL resulted in a significant prophylactic effect against SARS-CoV-2 infection. In the aged mouse prophylaxis model, SARS-CoV-2 titers were suppressed in the lungs of mice treated with ensitrelvir 24 h prior to challenge infection, suggesting that the prophylactic administration of ensitrelvir exerted its prophylactic effect by suppressing viral proliferation. These findings suggest that ensitrelvir is a candidate drug for pre-exposure prophylactic treatment of individuals at high risk of COVID-19.

Shaping the future of antiviral Treatment: Spotlight on Nucleobase-Containing drugs and their revolutionary impact

Nucleobases serve as essential molecular frameworks present in both natural and synthetic compounds that exhibit notable antiviral activity. Through molecular modifications, novel nucleobase-containing drugs (NCDs) have been developed, exhibiting enhanced antiviral activity against a wide range of viruses, including the recently emerged SARS‑CoV‑2. This article provides a detailed examination of the significant advancements in NCDs from 2015 till current, encompassing various aspects concerning their mechanisms of action, pharmacology and antiviral properties. Additionally, the article discusses antiviral prodrugs relevant to the scope of this review. It fills in the knowledge gap by examining the structure-activity relationship and trend of NCDs as therapeutics against a diverse range of viral diseases, either as approved drugs, clinical candidates or as early-stage development prospects. Moreover, the article highlights on the status of this field of study and addresses the prevailing limitations encountered.

Immunogenicity and protective efficacy of a co-formulated two-in-one inactivated whole virus particle COVID-19/influenza vaccine

Due to the synchronous circulation of seasonal influenza viruses and severe acute respiratory coronavirus 2 (SARS-CoV-2) which causes coronavirus disease 2019 (COVID-19), there is need for routine vaccination for both COVID-19 and influenza to reduce disease severity. Here, we prepared individual WPVs composed of formalin-inactivated SARS-CoV-2 WK 521 (Ancestral strain; Co WPV) or influenza virus [A/California/07/2009 (X-179A) (H1N1) pdm; Flu WPV] to produce a two-in-one Co/Flu WPV. Serum analysis from vaccinated mice revealed that a single dose of Co/Flu WPV induced antigen-specific neutralizing antibodies against both viruses, similar to those induced by either type of WPV alone. Following infection with either virus, mice vaccinated with Co/Flu WPV showed no weight loss, reduced pneumonia and viral titers in the lung, and lower gene expression of proinflammatory cytokines, as observed with individual WPV-vaccinated. Furthermore, a pentavalent vaccine (Co/qFlu WPV) comprising of Co WPV and quadrivalent influenza vaccine (qFlu WPV) was immunogenic and protected animals from severe COVID-19. These results suggest that a single dose of the two-in-one WPV provides efficient protection against SARS-CoV-2 and influenza virus infections with no evidence of vaccine interference in mice. We propose that concomitant vaccination with the two-in-one WPV can be useful for controlling both diseases.

Unusual Base Pair between Two 2-Thiouridines and Its Implication for Nonenzymatic RNA Copying

2-Thiouridine (s2U) is a nucleobase modification that confers enhanced efficiency and fidelity both on modern tRNA codon translation and on nonenzymatic and ribozyme-catalyzed RNA copying. We have discovered an unusual base pair between two 2-thiouridines that stabilizes an RNA duplex to a degree that is comparable to that of a native A:U base pair. High-resolution crystal structures indicate similar base-pairing geometry and stacking interactions in duplexes containing s2U:s2U compared to those with U:U pairs. Notably, the C═O···H-N hydrogen bond in the U:U pair is replaced with a C═S···H-N hydrogen bond in the s2U:s2U base pair. The thermodynamic stability of the s2U:s2U base pair suggested that this self-pairing might lead to an increased error frequency during nonenzymatic RNA copying. However, competition experiments show that s2U:s2U base-pairing induces only a low level of misincorporation during nonenzymatic RNA template copying because the correct A:s2U base pair outcompetes the slightly weaker s2U:s2U base pair. In addition, even if an s2U is incorrectly incorporated, the addition of the next base is greatly hindered. This strong stalling effect would further increase the effective fidelity of nonenzymatic RNA copying with s2U. Our findings suggest that s2U may enhance the rate and extent of nonenzymatic copying with only a minimal cost in fidelity.

Viral uptake and pathophysiology of the lung endothelial cells in age-associated severe SARS-CoV-2 infection models

Thrombosis is the major cause of death in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and the pathology of vascular endothelial cells (ECs) has received much attention. Although there is evidence of the infection of ECs in human autopsy tissues, their detailed pathophysiology remains unclear due to the lack of animal model to study it. We used a mouse-adapted SARS-CoV-2 virus strain in young and mid-aged mice. Only mid-aged mice developed fatal pneumonia with thrombosis. Pulmonary ECs were isolated from these infected mice and RNA-Seq was performed. The pulmonary EC transcriptome revealed that significantly higher levels of viral genes were detected in ECs from mid-aged mice with upregulation of viral response genes such as DDX58 and IRF7. In addition, the thrombogenesis-related genes encoding PLAT, PF4, F3 PAI-1, and P-selectin were upregulated. In addition, the inflammation-related molecules such as CXCL2 and CXCL10 were upregulated in the mid-aged ECs upon viral infection. Our mouse model demonstrated that SARS-CoV-2 virus entry into aged vascular ECs upregulated thrombogenesis and inflammation-related genes and led to fatal pneumonia with thrombosis. Current results of EC transcriptome showed that EC uptake virus and become thrombogenic by activating neutrophils and platelets in the aged mice, suggesting age-associated EC response as a novel finding in human severe COVID-19.