Current and novel antiviral strategies for influenza infection

Occurrence and environmental fate of anti-influenza drugs in a subcatchment of the Yodo River Basin, Japan

Understanding the current situation and risk of environmental contamination by anti-influenza drugs in aquatic environments is key to prevent the unexpected emergence and spread of drug-resistant viruses. However, few reports have been focused on newer drugs that have recently been introduced in clinical settings. In this study, the behaviour of the prodrug baloxavir marboxil (BALM)-the active ingredient of Xofluza, an increasingly popular anti-influenza drug-and its pharmacologically active metabolite baloxavir (BAL) in the aquatic environment was evaluated. Additionally, their presence in urban rivers and a wastewater treatment plant (WWTP) in the Yodo River basin was investigated and compared with those of the major anti-influenza drugs used to date (favipiravir (FAV), peramivir (PER), laninamivir (LAN), and its active metabolite, laninamivir octanoate (LANO), oseltamivir (OSE), and its active metabolite, oseltamivir carboxylate (OSEC), and zanamivir (ZAN)) to comprehensively assess their environmental fate in the aquatic environment. The results clearly showed that BALM, FAV, and BAL were rapidly degraded through photolysis (2-h, 0.6-h, and 0.4-h half-lives, respectively), followed by LAN, which was gradually biodegraded (7-h half-life). In addition, BALM and BAL decreased by up to 47 % after 4 days and 34 % after 2 days of biodegradation in river water. However, the remaining conventional drugs, except for LANO (<1 % after 10 days), were persistent, being transported from the upstream to downstream sites. The LogKd values for the rates of sorption of BALM (0.5-1.6) and BAL (1.8-3.1) on river sediment were higher than those of conventional drugs (-0.5 to 1.7). Notably, all anti-influenza drugs were effectively removed by ozonation (>90-99.9 % removal) after biological treatment at a WWTP. Thus, these findings suggest the importance of introducing ozonation to reduce pollution loads in rivers and the environmental risks associated with drug-resistant viruses in aquatic environments, thereby promoting safe river environments.

Unveiling the Antiviral Potential of Minocycline: Modulation of Nuclear Export of Viral Ribonuclear Proteins during Influenza Virus Infection

Influenza A virus (IAV) poses a global threat worldwide causing pandemics, epidemics, and seasonal outbreaks. Annual modification of vaccines is costly due to continual shifts in circulating genotypes, leading to inadequate coverage in low- and middle-income countries like India. Additionally, IAVs are evolving resistance to approved antivirals, necessitating a search for alternative treatments. In this study, the antiviral role of the FDA-approved antibiotic minocycline against IAV strains was evaluated in vitro and in vivo by quantifying viral gene expression by qRT-PCR, viral protein levels by Western blotting, and viral titers. Our findings demonstrate that minocycline at a non-toxic dose effectively inhibits IAV replication, regardless of viral strain or cell line. Its antiviral mechanism operates independently of interferon signaling by targeting the MEK/ERK signaling pathway, which is crucial for the export of viral ribonucleoproteins (vRNPs). Minocycline prevents the assembly and release of infectious viral particles by causing the accumulation of vRNPs within the nucleus. Moreover, minocycline also inhibits IAV-induced late-stage apoptosis, further suppressing viral propagation. The antiviral activity of minocycline against IAVs could offer a promising solution amidst the challenges posed by influenza and the limitations of current treatments.

Neuraminidase-1 (NEU1): Biological Roles and Therapeutic Relevance in Human Disease

Neuraminidases catalyze the desialylation of cell-surface glycoconjugates and play crucial roles in the development and function of tissues and organs. In both physiological and pathophysiological contexts, neuraminidases mediate diverse biological activities via the catalytic hydrolysis of terminal neuraminic, or sialic acid residues in glycolipid and glycoprotein substrates. The selective modulation of neuraminidase activity constitutes a promising strategy for treating a broad spectrum of human pathologies, including sialidosis and galactosialidosis, neurodegenerative disorders, cancer, cardiovascular diseases, diabetes, and pulmonary disorders. Structurally distinct as a large family of mammalian proteins, neuraminidases (NEU1 through NEU4) possess dissimilar yet overlapping profiles of tissue expression, cellular/subcellular localization, and substrate specificity. NEU1 is well characterized for its lysosomal catabolic functions, with ubiquitous and abundant expression across such tissues as the kidney, pancreas, skeletal muscle, liver, lungs, placenta, and brain. NEU1 also exhibits a broad substrate range on the cell surface, where it plays hitherto underappreciated roles in modulating the structure and function of cellular receptors, providing a basis for it to be a potential drug target in various human diseases. This review seeks to summarize the recent progress in the research on NEU1-associated diseases and highlight the mechanistic implications of NEU1 in disease pathogenesis. An improved understanding of NEU1-associated diseases should help accelerate translational initiatives to develop novel or better therapeutics.

Differential detection of H1N1 virus spiker proteins by two hexaphenylbutadiene isomers based on size-matching principle

As one of the high pathogenic influenza viruses, H1N1 virus easily induces to serious diseases, even leading to death. To date, all detection methods for H1N1 virus had shortcomings, including high equipment cost, time consumption, and etc. Therefore, a novel detection method should be established to achieve more convenient, rapid, and low-cost detection. In this work, an isomer of HPBmN-I with aggregation-induced emission characteristic was firstly synthesized on the basis of our previous reported HPBpN-I. The results showed that HPBmN-I only selectively binds to N1 in the presence of H1, while HPBpN-I can exhibit total fluorescence response to H1 and N1 in H1/N1 mixture. The limited of detection (LOD) of HPBmN-I to N1 was estimated to be 20.82 ng/mL in normal saline (NS) according to the IUPAC-based approach. The simulation calculations based on molecular docking revealed that four HPBmN-I molecules combine well with the hydrophobic cavity of N1 and achieve the fluorescence enhancement due to size matching with each other. The combination of HPBpN-I and HPBmN-I as probes was successfully used to quantitatively detect H1 and N1 in real H1N1 virus. Compared to enzyme-linked immunosorbent assay (ELISA) method, the established method not only showed the same detection accuracy but also had the advantages of real-time, ease of preparation, and low-cost, demonstrating potential market prospects.

A synergistic therapy against influenza virus A/H1N1/PR8 by a HA1 specific neutralizing single-domain VL and an RNA hydrolyzing scFv

The emergence of anti-influenza drug-resistant strains poses a challenge for influenza therapy due to mutations in the virus's surface protein. Recently, there has been increasing interest in combination therapy consisting of two or more drugs as a potential alternative approach, aiming to enhance therapeutic efficacy. In this study, we investigated a novel synergistic therapy with a vertical effect using a single-domain VL-HA1-specific antibody against H1N1/PR8 and a horizontal effect using an RNA catalytic antibody with broad-spectrum influenza antiviral drug. We isolated a single-domain VL-HA1-specific (NVLH8) antibody binding to the virus particles showing a neutralizing activity against influenza virus A, specifically H1N1/PR8, as determined by the reduction in plaque number and lower viral HA protein expression in vitro. The neutralizing antibody likely prevented the viral entry, specifically at the viral genome-releasing step. Additionally, the 3D8 scFv hydrolyzed viral RNAs in the cytoplasm, including mRNA, vRNA, and cRNA in MDCK cells. The combined treatment of neutralizing antibodies for a vertical effect and 3D8 scFv for a horizontal effect produced a synergistic effect providing a novel approach against viral diseases when compared with a single treatment. Our results indicated that combining treatment, in particular two proteins exhibiting different mechanisms of action increased the antiviral activity against the influenza virus.

Expanded profiling of Remdesivir as a broad-spectrum antiviral and low potential for interaction with other medications in vitro

Remdesivir (GS-5734; VEKLURY) is a single diastereomer monophosphoramidate prodrug of an adenosine analog (GS-441524). Remdesivir is taken up by target cells and metabolized in multiple steps to form the active nucleoside triphosphate (GS-443902), which acts as a potent inhibitor of viral RNA-dependent RNA polymerases. Remdesivir and GS-441524 have antiviral activity against multiple RNA viruses. Here, we expand the evaluation of remdesivir's antiviral activity to members of the families Flaviviridae, Picornaviridae, Filoviridae, Orthomyxoviridae, and Hepadnaviridae. Using cell-based assays, we show that remdesivir can inhibit infection of flaviviruses (such as dengue 1-4, West Nile, yellow fever, Zika viruses), picornaviruses (such as enterovirus and rhinovirus), and filoviruses (such as various Ebola, Marburg, and Sudan virus isolates, including novel geographic isolates), but is ineffective or is significantly less effective against orthomyxoviruses (influenza A and B viruses), or hepadnaviruses B, D, and E. In addition, remdesivir shows no antagonistic effect when combined with favipiravir, another broadly acting antiviral nucleoside analog, and has minimal interaction with a panel of concomitant medications. Our data further support remdesivir as a broad-spectrum antiviral agent that has the potential to address multiple unmet medical needs, including those related to antiviral pandemic preparedness.

Antiviral effects of Atractyloside A on the influenza B virus (Victoria strain) infection

Influenza viruses pose a serious threat to human health, infecting hundreds of millions of people worldwide each year, resulting in a significant increase in global morbidity and mortality. Influenza activity has declined at the onset of the COVID-19 pandemic, but the genetic diversity of B/Victoria lineage viruses has increased significantly during this period. Therefore, the prevention and treatment of the influenza B Victoria strain virus should continue to attract research attention. In this study, we found that Atractyloside A (AA), one of the effective components in Atractylodes lancea (Thunb.) DC shows potential antiviral properties. This study shows that AA not only possesses anti-influenza B virus infection effects in vivo and in vitro but also can regulate macrophage polarization to the M2 type, which can effectively attenuate the damage caused by influenza B virus infection. Therefore, Atractyloside A may be an effective natural drug against B/Victoria influenza infection.

Exploration of Computational Aids for Effective Drug Designing and Management of Viral Diseases: A Comprehensive Review

BACKGROUND

Microbial diseases, specifically originating from viruses are the major cause of human mortality all over the world. The current COVID-19 pandemic is a case in point, where the dynamics of the viral-human interactions are still not completely understood, making its treatment a case of trial and error. Scientists are struggling to devise a strategy to contain the pandemic for over a year and this brings to light the lack of understanding of how the virus grows and multiplies in the human body.

METHODS

This paper presents the perspective of the authors on the applicability of computational tools for deep learning and understanding of host-microbe interaction, disease progression and management, drug resistance and immune modulation through in silico methodologies which can aid in effective and selective drug development. The paper has summarized advances in the last five years. The studies published and indexed in leading databases have been included in the review.

RESULTS

Computational systems biology works on an interface of biology and mathematics and intends to unravel the complex mechanisms between the biological systems and the inter and intra species dynamics using computational tools, and high-throughput technologies developed on algorithms, networks and complex connections to simulate cellular biological processes.

CONCLUSION

Computational strategies and modelling integrate and prioritize microbial-host interactions and may predict the conditions in which the fine-tuning attenuates. These microbial-host interactions and working mechanisms are important from the aspect of effective drug designing and fine- tuning the therapeutic interventions.

Integrated network pharmacology and intestinal flora analysis to determine the protective effect of Xuanbai-Chengqi decoction on lung and gut injuries in influenza virus-infected mice

ETHNOPHARMACOLOGICAL RELEVANCE

Xuanbai-Chengqi decoction (XBCQ) is a traditional Chinese medicine (TCM) compound used in the treatment of pulmonary infection in China. Despite the popular usage of XBCQ, its underlying protective roles and the associated molecular mechanisms with the gut-lung axis in influenza remain unclear.

AIM OF THE STUDY

We aimed to explore the protective effects and the underlying mechanism of XBCQ efficacy on lung and intestine injuries induced by influenza A virus as well as to identify the main active components through integrated network pharmacology, intestinal flora analysis and pathway validation.

MATERIALS AND METHODS

The potential active components and therapeutic targets of XBCQ in the treatment of influenza were hypothesized through a series of network pharmacological strategies, including components screening, targets prediction and bioinformatics analysis. Inflammatory cytokines and pathway proteins were assayed to validate the results of network pharmacology. Then the mechanism of XBCQ alleviating lung and intestine injuries was further explored via intestinal flora analysis. The important role of Rhubarb in the formula was verified by removing Rhubarb.

RESULTS

XBCQ could significantly improve the survival rate in IAV-infected mice. The network pharmacology results demonstrated that JUN, mitogen-activated protein kinase (MAPK), and tumor necrosis factor (TNF) are the key targets of XBCQ that can be useful in influenza treatment as it contains the core components luteolin, emodin, and aloe-emodin, which are related to the pathways of TNF, T-cell receptor (TCR), and NF-κB. Verification experiments demonstrated that XBCQ could significantly alleviate the immune injury of the lungs and the gut of the mice, which is attributable to the inhibition of the release of inflammatory cytokines (such as TNF-α, IL-6, and IL-1β), the downregulation of the protein expression levels of Toll-like receptors-7 (TLR7), MyD88, and p-NF-κB65, and the reduction in the relative abundance of Enterobacteriaceae and Proteus, while an increase in that of Firmicutes and Lachnospiraceae. The overall protective role of XBCQ contributing to the treatment of the lungs and the gut was impaired when Rhubarb was removed from XBCQ.

CONCLUSIONS

Our results suggest that the efficacy of XBCQ is related to the inhibition of the immune injury and remodeling of the intestinal flora, wherein Rhubarb plays an important role, which cumulatively provide the evidence applicable for the treatment of viral pneumonia induced by a different respiratory virus with XBCQ.

A Therapeutically Active Minibody Exhibits an Antiviral Activity in Oseltamivir-Resistant Influenza-Infected Mice via Direct Hydrolysis of Viral RNAs

Emerging Oseltamivir-resistant influenza strains pose a critical public health threat due to antigenic shifts and drifts. We report an innovative strategy for controlling influenza A infections by use of a novel minibody of the 3D8 single chain variable fragment (scFv) showing intrinsic viral RNA hydrolyzing activity, cell penetration activity, and epidermal cell penetration ability. In this study, we examined 3D8 scFv’s antiviral activity in vitro on three different H1N1 influenza strains, one Oseltamivir-resistant (A/Korea/2785/2009pdm) strain, and two Oseltamivir-sensitive (A/PuertoRico/8/1934 and A/X-31) strains. Interestingly, the 3D8 scFv directly digested viral RNAs in the ribonucleoprotein complex. scFv’s reduction of influenza viral RNA including viral genomic RNA, complementary RNA, and messenger RNA during influenza A infection cycles indicated that this minibody targets all types of viral RNAs during the early, intermediate, and late stages of the virus’s life cycle. Moreover, we further addressed the antiviral effects of 3D8 scFv to investigate in vivo clinical outcomes of influenza-infected mice. Using both prophylactic and therapeutic treatments of intranasal administered 3D8 scFv, we found that Oseltamivir-resistant H1N1-infected mice showed 90% (prophylactic effects) and 40% (therapeutic effects) increased survival rates, respectively, compared to the control group. The pathological signs of influenza A in the lung tissues, and quantitative analyses of the virus proliferations supported the antiviral activity of the 3D8 single chain variable fragment. Taken together, these results demonstrate that 3D8 scFv has antiviral therapeutic potentials against a wide range of influenza A viruses via the direct viral RNA hydrolyzing activity.

Antiviral activity of Epimedium koreanum Nakai water extract against influenza viruses

Epimedium koreanum Nakai (EKN) is a popular plant in Korean and Chinese medicine for treating a variety of ailments. The aqueous extract of EKN has a significant inhibitory impact on influenza A virus (IAV) infection by directly blocking viral attachment and having a virucidal effect, according to this study. Using fluorescent microscopy and fluorescence-activated cell sorting (FACS) with a green fluorescent protein (GFP)-tagged Influenza A/PR/8/34 virus, we examined the effect of EKN on viral infection. By viral infection, EKN strongly suppresses GFP expression, and at a dosage of 100 µg/mL, EKN decreased GFP expression by up to 90% of the untreated infected control. Immunofluorescence and Western blot analyses against influenza viral proteins revealed that EKN decreased influenza viral protein expression in a dose-dependent manner. EKN inhibited the H1N1 influenza virus's hemagglutinin (HA) and neuraminidase (NA), preventing viral attachment to cells. Furthermore, EKN had a virucidal impact and inhibited the cytopathic effects of H1N1, H3N2 and influenza B virus infection. Finally, our findings show that EKN has the potential to be developed as a natural viral inhibitor against influenza virus infection.

Influenza virus and SARS-CoV-2: pathogenesis and host responses in the respiratory tract

Influenza viruses cause annual epidemics and occasional pandemics of respiratory tract infections that produce a wide spectrum of clinical disease severity in humans. The novel betacoronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019 and has since caused a pandemic. Both viral and host factors determine the extent and severity of virus-induced lung damage. The host's response to viral infection is necessary for viral clearance but may be deleterious and contribute to severe disease phenotypes. Similarly, tissue repair mechanisms are required for recovery from infection across the spectrum of disease severity; however, dysregulated repair responses may lead to chronic lung dysfunction. Understanding of the mechanisms of immunopathology and tissue repair following viral lower respiratory tract infection may broaden treatment options. In this Review, we discuss the pathogenesis, the contribution of the host response to severe clinical phenotypes and highlight early and late epithelial repair mechanisms following influenza virus infection, each of which has been well characterized. Although we are still learning about SARS-CoV-2 and its disease manifestations in humans, throughout the Review we discuss what is known about SARS-CoV-2 in the context of this broad knowledge of influenza virus, highlighting the similarities and differences between the respiratory viruses.

Development and Effects of Influenza Antiviral Drugs

Influenza virus is a highly contagious zoonotic respiratory disease that causes seasonal outbreaks each year and unpredictable pandemics occasionally with high morbidity and mortality rates, posing a great threat to public health worldwide. Besides the limited effect of vaccines, the problem is exacerbated by the lack of drugs with strong antiviral activity against all flu strains. Currently, there are two classes of antiviral drugs available that are chemosynthetic and approved against influenza A virus for prophylactic and therapeutic treatment, but the appearance of drug-resistant virus strains is a serious issue that strikes at the core of influenza control. There is therefore an urgent need to develop new antiviral drugs. Many reports have shown that the development of novel bioactive plant extracts and microbial extracts has significant advantages in influenza treatment. This paper comprehensively reviews the development and effects of chemosynthetic drugs, plant extracts, and microbial extracts with influenza antiviral activity, hoping to provide some references for novel antiviral drug design and promising alternative candidates for further anti-influenza drug development.

Direct inhibitory effect on viral entry of influenza A and SARS-CoV-2 viruses by azithromycin

Objectives

Using strategy of drug repurposing, antiviral agents against influenza A virus (IAV) and newly emerging SARS‐coronavirus 2 (SARS‐CoV‐2, also as 2019‐nCoV) could be quickly screened out.

Materials and Methods

A previously reported engineered replication‐competent PR8 strain carrying luciferase reporter gene (IAV‐luc) and multiple pseudotyped IAV and SARS‐CoV‐2 virus was used. To specifically evaluate the pH change of vesicles containing IAV, we constructed an A549 cell line with endosomal and lysosomal expression of pHluorin2.

Results

Here, we identified azithromycin (AZ) as an effective inhibitor against multiple IAV and SARS‐CoV‐2 strains. We found that AZ treatment could potently inhibit IAV infection in vitro. Moreover, using pseudotyped virus model, AZ could also markedly block the entry of SARS‐CoV‐2 in HEK293T‐ACE2 and Caco2 cells. Mechanistic studies further revealed that such effect was independent of interferon signalling. AZ treatment neither impaired the binding and internalization of IAV virions, nor the viral replication, but rather inhibited the fusion between viral and vacuolar membranes. Using a NPC1‐pHluorin2 reporter cell line, we confirmed that AZ treatment could alkalize the vesicles containing IAV virions, thereby preventing pH‐dependent membrane fusion.

Conclusions

Overall, our findings demonstrate that AZ can exert broad‐spectrum antiviral effects against IAV and SARS‐CoV‐2, and could be served as a potential clinical anti‐SARS‐CoV‐2 drug in emergency as well as a promising lead compound for the development of next‐generation anti‐IAV drugs.

A network-based pharmacology study of active compounds and targets of Fritillaria thunbergii against influenza

Seasonal and pandemic influenza infections are serious threats to public health and the global economy. Since antigenic drift reduces the effectiveness of conventional therapies against the virus, herbal medicine has been proposed as an alternative. Fritillaria thunbergii (FT) have been traditionally used to treat airway inflammatory diseases such as coughs, bronchitis, pneumonia, and fever-based illnesses. Herein, we used a network pharmacology-based strategy to predict potential compounds from Fritillaria thunbergii (FT), target genes, and cellular pathways to better combat influenza and influenza-associated diseases. We identified five compounds, and 47 target genes using a compound-target network (C-T). Two compounds (beta-sitosterol and pelargonidin) and nine target genes (BCL2, CASP3, HSP90AA1, ICAM1, JUN, NOS2, PPARG, PTGS1, PTGS2) were identified using a compound-influenza disease target network (C-D). Protein-protein interaction (PPI) network was constructed and we identified eight proteins from nine target genes formed a network. The compound-disease-pathway network (C-D-P) revealed three classes of pathways linked to influenza: cancer, viral diseases, and inflammation. Taken together, our systems biology data from C-T, C-D, PPI and C-D-P networks predicted potent compounds from FT and new therapeutic targets and pathways involved in influenza.

Protease Inhibitor Use in COVID-19

The outbreak of a large plaque, novel coronavirus pneumonia (NCP), which also named Coronavirus Disease 2019 (COVID-19) by the WHO, has detrimentally affected the livelihood and health of people in China. During the spread of COVID-19, colleagues who have been working at the frontline have had to face many new challenges in the treatment and prevention of NCP. Therefore, we have provided suggestions for the diagnosis, treatment, and prevention of the novel coronavirus pneumonia in the current epidemic situation based on the latest reports and the experience of doctors treating COVID-19 in our hospital. We recommend lopinavir/ritonavir as the effective drugs for antiviral treatment according to our experience in administering lopinavir/ritonavir to COVID-19 patients and the successful cases of these drugs in treating MERS and SARS, but need more clinical data to prove their efficacy in treating COVID-19.

Structure of avian influenza hemagglutinin in complex with a small molecule entry inhibitor

The binding properties of fusion inhibitor CBS1117 to hemagglutinin by x-ray crystallography, NMR, and mutagenesis give insights into mechanism and guidance for chemical optimization.

HA plays a critical role in influenza infection and, thus HA is a potential target for antivirals. Recently, our laboratories have described a novel fusion inhibitor, termed CBS1117, with EC₅₀ ∼3 μM against group 1 HA. In this work, we characterize the binding properties of CBS1117 to avian H5 HA by x-ray crystallography, NMR, and mutagenesis. The x-ray structure of the complex shows that the compound binds near the HA fusion peptide, a region that plays a critical role in HA-mediated fusion. NMR studies demonstrate binding of CBS1117 to H5 HA in solution and show extensive hydrophobic contacts between the compound and HA surface. Mutagenesis studies further support the location of the compound binding site proximal to the HA fusion peptide and identify additional amino acids that are important to compound binding. Together, this work gives new insights into the CBS1117 mechanism of action and can be exploited to further optimize this compound and better understand the group specific activity of small-molecule inhibitors of HA-mediated entry.

Effectiveness of favipiravir (T-705) against wild-type and oseltamivir-resistant influenza B virus in mice

The emergence of resistant mutants to the wildly used neuraminidase inhibitors (NAIs) makes the development of novel drugs necessary. Favipiravir (T-705) is one of the RNA-dependent RNA polymerase (RdRp) inhibitors developed in recent years. To examine the efficacy of T-705 against influenza B virus infections in vivo, C57BL/6 mice infected with wild-type or oseltamivir-resistant influenza B/Memphis/20/96 viruses were treated with T-705. Starting 2 h post inoculation (hpi), T-705 was orally administered to mice BID at dosages of 50, 150, or 300 mg/kg/day for 5 days. Oseltamivir was used as control. Here, we showed that T-705 protected mice from lethal infection in a dose-dependent manner. T-705 administration also significantly reduced viral loads and suppressed pulmonary pathology. In addition, phenotypic assays demonstrated that no T-705-resistant viruses emerged after T-705 treatment. In conclusion, T-705 can be effective to protect mice from lethal infection with both wild-type and oseltamivir-resistant influenza B viruses.

The Central Role of Non-Structural Protein 1 (NS1) in Influenza Biology and Infection

Influenza (flu) is a contagious viral disease, which targets the human respiratory tract and spreads throughout the world each year. Every year, influenza infects around 10% of the world population and between 290,000 and 650,000 people die from it according to the World Health Organization (WHO). Influenza viruses belong to the Orthomyxoviridae family and have a negative sense eight-segment single-stranded RNA genome that encodes 11 different proteins. The only control over influenza seasonal epidemic outbreaks around the world are vaccines, annually updated according to viral strains in circulation, but, because of high rates of mutation and recurrent genetic assortment, new viral strains of influenza are constantly emerging, increasing the likelihood of pandemics. Vaccination effectiveness is limited, calling for new preventive and therapeutic approaches and a better understanding of the virus-host interactions. In particular, grasping the role of influenza non-structural protein 1 (NS1) and related known interactions in the host cell is pivotal to better understand the mechanisms of virus infection and replication, and thus propose more effective antiviral approaches. In this review, we assess the structure of NS1, its dynamics, and multiple functions and interactions, to highlight the central role of this protein in viral biology and its potential use as an effective therapeutic target to tackle seasonal and pandemic influenza.

A Novel Sulfonated Derivative of β-Cyclodextrin Effectively Inhibits Influenza A Virus Infection in vitro and in vivo

The development of novel drugs against the influenza virus with high efficiency and low toxicity is an urgent and important task. Previous reports have demonstrated that compounds based on sulfo derivatives of oligo- and polysaccharides possess high antiviral activity. In this study, we have examined the ability of a novel sulfonated derivative of β-cyclodextrin (KS-6469) to inhibit the influenza virus A/WSN/33 (H1N1) infection in vitro and in vivo. The antiviral potential of KS-6469 against the influenza virus was evaluated in Madin-Darby Canine Kidney epithelial cells treated with serially diluted KS-6469. We found out that KS-6469 completely inhibited viral reproduction after treatment of the infected cells with the compound for 48 h. Our data show that double intranasal treatment of mice with KS-6469 fully protected the animals from a lethal infection and significantly decreased the viral titers in the lungs of the infected animals. Thus, the novel sulfonated β-cyclodextrin derivative KS-6469 is a promising candidate for the development of antiviral drugs for preventing and treating the influenza infection.

Antiviral efficacy of nanoparticulate vacuolar ATPase inhibitors against influenza virus infection

Background

Influenza virus infections are a major public health concern worldwide. Conventional treatments against the disease are designed to target viral proteins. However, the emergence of viral variants carrying drug-resistant mutations can outpace the development of pathogen-targeting antivirals. Diphyllin and bafilomycin are potent vacuolar ATPase (V-ATPase) inhibitors previously shown to have broad-spectrum antiviral activity. However, their poor water solubility and potential off-target effect limit their clinical application.

Methods

In this study, we report that nanoparticle encapsulation of diphyllin and bafilomycin improves the drugs’ anti-influenza applicability.

Results

Using PEG-PLGA diblock copolymers, sub-200 nm diphyllin and bafilomycin nanoparticles were prepared, with encapsulation efficiency of 42% and 100%, respectively. The drug-loaded nanoparticles have sustained drug release kinetics beyond 72 hours and facilitate intracellular drug delivery to two different influenza virus-permissive cell lines. As compared to free drugs, the nanoparticulate V-ATPase inhibitors exhibited lower cytotoxicity and greater in vitro antiviral activity, improving the therapeutic index of diphyllin and bafilomycin by approximately 3 and 5-fold, respectively. In a mouse model of sublethal influenza challenge, treatment with diphyllin nanoparticles resulted in reduced body weight loss and viral titer in the lungs. In addition, following a lethal influenza viral challenge, diphyllin nanoparticle treatment conferred a survival advantage of 33%.

Conclusions

These results demonstrate the potential of the nanoparticulate V-ATPase inhibitors for host-targeted treatment against influenza.

De Novo Design of α-Helical Lipopeptides Targeting Viral Fusion Proteins: A Promising Strategy for Relatively Broad-Spectrum Antiviral Drug Discovery

Class I enveloped viruses share similarities in their apparent use of a hexameric coiled-coil assembly to drive the merging of virus and host cell membranes. Inhibition of coiled coil-mediated interactions using bioactive peptides that replicate an α-helical chain from the viral fusion machinery has significant antiviral potential. Here, we present the construction of a series of lipopeptides composed of a de novo heptad repeat sequence-based α-helical peptide plus a hydrocarbon tail. Promisingly, the constructs adopted stable α-helical conformations and exhibited relatively broad-spectrum antiviral activities against Middle East respiratory syndrome coronavirus (MERS-CoV) and influenza A viruses (IAVs). Together, these findings reveal a new strategy for relatively broad-spectrum antiviral drug discovery by relying on the tunability of the α-helical coiled-coil domains present in all class I fusion proteins and the amphiphilic nature of the individual helices from this multihelix motif.

Substituted 3-benzylcoumarins 13 and 14 suppress enterovirus A71 replication by impairing viral 2Apro dependent IRES-driven translation

Activation of the ERK signaling cascade in host cells has been demonstrated to be essential for enterovirus A71 (EV-A71) replication. Our previous study showed that MEK kinase, which specially activated downstream ERK kinase, is an important and potential target against EV-A71. Furthermore, we reported that a series of substituted 3-benzylcoumarins designed and synthesized as well as verified for inhibiting the MEK-ERK cascade were found to be effective on anti-EV-A71. In this study, we further demonstrated that two substituted 3-benzylcoumarins designated as 13 and 14 were more effective anti-MEK/ERK activity, less cytotoxicity and stronger antiviral effect represented by inhibition of viral-induced CPE, the expression of viral proteins and the replication of the viral genome, as well as the production of progeny virions, compared to those of U0126, an available MEK inhibitor, and sorafenib, a multiple-targeted kinase inhibitor in clinical use. Moreover, we explored that the likely mechanism of action of these two test compounds were to block EV-A71 2A dependent IRES-driven activity essential for successful viral replication. Hence, our results suggest that two substituted 3-benzylcoumarins 13 and 14 could be candidates as potential anti-EV-A71 agents.

Computational screening of known broad-spectrum antiviral small organic molecules for potential influenza HA stem inhibitors

Background

With the emergence of new influenza virus strains that are resistant to current inhibitors such as oseltamivir (anti-neuraminidase (NA)) and amantadine (anti-M2 proton channel), influenza A viruses continue to be a serious threat to the public health worldwide. With this in view, there is a persistent need for the development of broader and more effective vaccines and therapeutics. Identification of broadly neutralizing antibodies (bNAbs) that recognize relatively invariant structures ‎on influenza haemagglutinin (HA) stem has invigorated efforts to develop universal influenza vaccines.

Aim

The current computational study is designed to identify potential flavonoid inhibitors that bind to the contact epitopes of HA stem that are targeted by broadly neutralizing antibodies (bNAb).

Method

In this study, we utilized the three-dimensional crystallographic structure of different HA subtypes (H1, H2, H5, H3, and H7) in complex with bNAb to screen for potential broadly reactive influenza inhibitors. We performed Quantitative Structure-Activity and Relationship (QSAR) for 100 natural compounds known for their antiviral activity and performed molecular docking using AutoDock 4.2 suite. Furthermore, we conducted virtual screening of 1413 bioassay hit compounds by using virtual lab bench CLC Drug Discovery.

Results

The results showed 18 lead flavonoids with strong binding abilities to bNAb epitopes of various HA subtypes. These 18 broadly reactive compounds exhibited significant interactions with an average of seven Hbonds, docking energy of -22.43 kcal·mol⁻¹, and minimum interaction ‎ energy of -4.65 kcal·mol⁻¹, with functional contact residues. Procyanidin depicted strong interactions with group 1 HAs, whereas both sorbitol and procyanidin exhibited significant interactions with group 2 HAs.

Conclusion

Using in silico docking analysis, we identified 18 bioactive flavonoids with potential strong binding cababilities to influenza HA-stems of various subtypes, which are the target for bNAb. The virtual screened bioassay hit compounds depicted a high number of Hbonds but low interaction and docking values compared to antiviral flavonoids. Using structure-based design and nanotechnology-based approaches, identified molecules could be modified to generate next generation anti-influenza drugs.

Hydrogen sulfide in physiology and pathogenesis of bacteria and viruses

An increasing number of studies have established hydrogen sulfide (H₂S) gas as a major cytoprotectant and redox modulator. Following its discovery, H₂S has been found to have pleiotropic effects on physiology and human health. H₂S acts as a gasotransmitter and exerts its influence on gastrointestinal, neuronal, cardiovascular, respiratory, renal, and hepatic systems. Recent discoveries have clearly indicated the importance of H₂S in regulating vasorelaxation, angiogenesis, apoptosis, ageing, and metabolism. Contrary to studies in higher organisms, the role of H₂S in the pathophysiology of infectious agents such as bacteria and viruses has been less studied. Bacterial and viral infections are often accompanied by changes in the redox physiology of both the host and the pathogen. Emerging studies indicate that bacterial-derived H₂S constitutes a defense system against antibiotics and oxidative stress. The H₂S signaling pathway also seems to interfere with redox-based events affected on infection with viruses. This review aims to summarize recent advances on the emerging role of H₂S gas in the bacterial physiology and viral infections. Such studies have opened up new research avenues exploiting H₂S as a potential therapeutic intervention.

Protein disulfide isomerases as potential therapeutic targets for influenza A and B viruses

Seasonal flu as well as potential pandemic flu outbreaks continuously underscores the importance of the preventive and therapeutic measures against influenza viruses. During screening of natural and synthetic small molecules against influenza A and B virus, we identified juniferdin as a highly effective inhibitor against both viruses in cells. Since juniferdin is known to inhibit protein disulfide isomerases (PDIs), multiple PDI inhibitors were tested against these viruses. Among PDI inhibitors, 16F16, PACMA31, isoquercetin, epigallocatechin-3-gallate or nitazoxanide significantly reduced the replication of influenza A and B viruses in MDCK and A549 cells. Furthermore, siRNAs specific to three PDI family members (PDI1, PDIA3 or PDIA4) also significantly reduced the replication of influenza A and B viruses in cells. These results suggest that PDIs may serve as excellent targets for the development of new anti-influenza drugs.

Successful treatment of Marburg virus with orally administrated T-705 (Favipiravir) in a mouse model

Filoviruses, such as Marburg and Ebola viruses, cause severe disease in humans with high case fatality rates and are therefore considered biological threat agents. To date, no licensed vaccine or therapeutic exists for their treatment. T-705 (favipiravir) is a pyrazinecarboxamide derivative that has shown broad antiviral activity against a number of viruses and is clinically licenced in Japan to treat influenza. Here we report the efficacy of T-705 against Marburg virus infection in vitro and in vivo. Notably, oral administration of T-705 beginning one or two days post-infection and continuing for eight days resulted in complete survival of mice that had been intraperitoneally infected with mouse-adapted Marburg virus (variant Angola). Moreover, lower doses of T-705 and higher doses administered later during infection (day 3 or 4 post-infection) showed partial efficacy, with at least half the infected mice surviving. Accordingly, we observed reductions in infectious virus particles and virus RNA levels following drug treatment that appeared to correlate with survival. Our findings suggest that T-705 may be an effective therapeutic against Marburg virus and might be especially promising for use in the event of an outbreak, where it could be orally administered quickly and safely even after exposure.

Glycans with Antiviral Activity from Marine Organisms

There remains today a critical need for new antiviral agents, particularly in view of the alarming increase in drug resistance and associated issues. The marine environment has been a prolific contributor towards the identification of novel therapeutic agents in the recent few decades. Added to this, glycans (or carbohydrate- or sugar-based compounds) have in very recent decades made outstanding contributions to the development of novel therapeutics. This review brings together these significant facets of modern drug discovery by presenting the reported literature on glycans derived from marine organisms that possess antiviral activity.The glycans have been grouped together based on the marine organism they were isolated from, namely, (1) bacteria, (2) chromists, (3) plants and (4) animals. For chromists, glycans are further subsectioned into Ochrophyta (brown algae), Miozoa (according to www.algaebase.org ; also called Myzozoa according to WoRMS, www.marinespecies.org ) (dinoflagellates) and Bacillariophyta (diatoms). For plants, glycans are further subsectioned into Chlorophyta, Rhodophyta and Tracheophyta. Glycans isolated to date are reported as alginates, chitosan, extracellular polysaccharides, fucans (e.g. fucoidans), galactans (e.g. carrageenans), glycolipids, glycosaminoglycans, glycosides, glycosylated haemocyanin, laminarans, mannans, polysaccharides (not defined), rhamnans and xylomannans. Interestingly, many of the glycans displaying antiviral properties are sulfated.Reports indicate that marine-sourced glycans have exhibited antiviral activity against African swine fever virus, cytomegalovirus, dengue virus, Epstein-Barr virus, encephalomyocarditis virus, human immunodeficiency virus, hepatitis C virus, herpes simplex virus, human cytomegalovirus, human papilloma virus, human rhino virus, influenza virus, Japanese encephalitis virus, murine leukaemia virus, murine sarcoma virus, Newcastle disease virus, parainfluenza virus, respiratory syncytial virus, Semliki Forest virus, tobacco mosaic virus, vaccinia virus, varicella zoster virus, viral haemorrhagic septicaemia virus and vesicular stomatitis virus. Selected representative glycan structures are presented in Fig. 20.1.

Protein-Structure Assisted Optimization of 4,5-Dihydroxypyrimidine-6-Carboxamide Inhibitors of Influenza Virus Endonuclease

Influenza is a serious hazard to human health that causes hundreds of thousands of deaths annually. Though vaccines and current therapeutics can blunt some of the perilous impact of this viral infection, new treatments are needed due to the constantly evolving nature of this virus. Recently, our growing understanding of an essential influenza viral protein, PA, has led to the development of focused libraries of new small molecules that specifically target the active site of the PA influenza endonuclease, which we report here. Our overarching approach has been to proactively develop lead inhibitors that are less likely to rapidly develop clinical resistance by optimizing inhibitors that retain activity against induced resistant mutants. Here, we report details behind the discovery of new potent inhibitors of wild type and resistant mutant endonucleases along with their high-resolution co-crystal structure-activity relationships. These results add to our understanding of nuclease protein targets and potentially serve as starting points for a new therapeutic approach to the treatment of influenza.

Protective Effect of Panax notoginseng Root Water Extract against Influenza A Virus Infection by Enhancing Antiviral Interferon-Mediated Immune Responses and Natural Killer Cell Activity

Influenza is an acute respiratory illness caused by the influenza A virus, which causes economic losses and social disruption mainly by increasing hospitalization and mortality rates among the elderly and people with chronic diseases. Influenza vaccines are the most effective means of preventing seasonal influenza, but can be completely ineffective if there is an antigenic mismatch between the seasonal vaccine virus and the virus circulating in the community. In addition, influenza viruses resistant to antiviral drugs are emerging worldwide. Thus, there is an urgent need to develop new vaccines and antiviral drugs against these viruses. In this study, we conducted in vitro and in vivo analyses of the antiviral effect of Panax notoginseng root (PNR), which is used as an herbal medicine and nutritional supplement in Korea and China. We confirmed that PNR significantly prevented influenza virus infection in a concentration-dependent manner in mouse macrophages. In addition, PNR pretreatment inhibited viral protein (PB1, PB2, HA, NA, M1, PA, M2, and NP) and viral mRNA (NS1, HA, PB2, PA, NP, M1, and M2) expression. PNR pretreatment also increased the secretion of pro-inflammatory cytokines [tumor necrosis factor alpha and interleukin 6] and interferon (IFN)-beta and the phosphorylation of type-I IFN-related proteins (TANK-binding kinase 1, STAT1, and IRF3) in vitro. In mice exposed to the influenza A H1N1 virus, PNR treatment decreased mortality by 90% and prevented weight loss (by approximately 10%) compared with the findings in untreated animals. In addition, splenocytes from PNR-administered mice displayed significantly enhanced natural killer (NK) cell activity against YAC-1 cells. Taking these findings together, PNR stimulates an antiviral response in murine macrophages and mice that protects against viral infection, which may be attributable to its ability to stimulate NK cell activity. Further investigations are needed to reveal the molecular mechanisms underlying the protective effects of PNR and its components against influenza virus A infection.

Chinese herbal medicine compound Yi-Zhi-Hao pellet inhibits replication of influenza virus infection through activation of heme oxygenase-1

As a leading cause of respiratory disease, influenza A virus (IAV) presents a pandemic threat in annual seasonal outbreaks. Given the limitation of existing anti-influenza therapies, there remains to be a requirement for new drugs. Compound Yi-Zhi-Hao pellet (CYZH) is a famous traditional Chinese medicine (TCM) used in the clinic, whose formula has been recorded in Complication of National Standard for Traditional Chinese Medicine to treat common cold. In this study, we found that CYZH exhibited a broad-spectrum anti-influenza activity and inhibited the expression of viral RNA and proteins in vitro. Mechanistically, CYZH had no inhibitory activities against viral protein hemagglutinin and IAV RNA-dependent RNA polymerase. Instead, it induced activation of erythroid 2-related factor 2 (Nrf2) and nuclear factor kappa B (NF-κB), which subsequently upregulated heme oxygenase-1 (HO-1) expression. Also, CYZH protected cells from oxidative damage induced by reactive oxygen series. In conclusions, CYZH inhibits IAV replication in vitro, at least partly by activating expression of the Nrf2/HO-1 pathway.

ATP catabolism by tissue nonspecific alkaline phosphatase contributes to development of ARDS in influenza-infected mice

Influenza A viruses are highly contagious respiratory pathogens that are responsible for significant morbidity and mortality worldwide on an annual basis. We have shown previously that influenza infection of mice leads to increased ATP and adenosine accumulation in the airway lumen. Moreover, we demonstrated that A₁-adenosine receptor activation contributes significantly to influenza-induced acute respiratory distress syndrome (ARDS). However, we found that development of ARDS in influenza-infected mice does not require catabolism of ATP to adenosine by ecto-5'-nucleotidase (CD73). Hence, we hypothesized that increased adenosine generation in response to infection is mediated by tissue nonspecific alkaline phosphatase (TNAP), which is a low-affinity, high-capacity enzyme that catabolizes nucleotides in a nonspecific manner. In the current study, we found that whole lung and BALF TNAP expression and alkaline phosphatase enzymatic activity increased as early as 2 days postinfection (dpi) of C57BL/6 mice with 10,000 pfu/mouse of influenza A/WSN/33 (H1N1). Treatment at 2 and 4 dpi with a highly specific quinolinyl-benzenesulfonamide TNAP inhibitor (TNAPi) significantly reduced whole lung alkaline phosphatase activity at 6 dpi but did not alter TNAP gene or protein expression. TNAPi treatment attenuated hypoxemia, lung dysfunction, histopathology, and pulmonary edema at 6 dpi without impacting viral replication or BALF adenosine. Treatment also improved epithelial barrier function and attenuated cellular and humoral immune responses to influenza infection. These data indicate that TNAP inhibition can attenuate influenza-induced ARDS by reducing inflammation and fluid accumulation within the lung. They also further emphasize the importance of adenosine generation for development of ARDS in influenza-infected mice.

Influenza Virus Infection, Interferon Response, Viral Counter-Response, and Apoptosis

Human influenza A viruses (IAVs) cause global pandemics and epidemics, which remain serious threats to public health because of the shortage of effective means of control. To combat the surge of viral outbreaks, new treatments are urgently needed. Developing new virus control modalities requires better understanding of virus-host interactions. Here, we describe how IAV infection triggers cellular apoptosis and how this process can be exploited towards the development of new therapeutics, which might be more effective than the currently available anti-influenza drugs.

Combating mutations in genetic disease and drug resistance: understanding molecular mechanisms to guide drug design

INTRODUCTION

Mutations introduce diversity into genomes, leading to selective changes and driving evolution. These changes have contributed to the emergence of many of the current major health concerns of the 21st century, from the development of genetic diseases and cancers to the rise and spread of drug resistance. The experimental systematic testing of all mutations in a system of interest is impractical and not cost-effective, which has created interest in the development of computational tools to understand the molecular consequences of mutations to aid and guide rational experimentation. Areas covered: Here, the authors discuss the recent development of computational methods to understand the effects of coding mutations to protein function and interactions, particularly in the context of the 3D structure of the protein. Expert opinion: While significant progress has been made in terms of innovative tools to understand and quantify the different range of effects in which a mutation or a set of mutations can give rise to a phenotype, a great gap still exists when integrating these predictions and drawing causality conclusions linking variants. This often requires a detailed understanding of the system being perturbed. However, as part of the drug development process it can be used preemptively in a similar fashion to pharmacokinetics predictions, to guide development of therapeutics to help guide the design and analysis of clinical trials, patient treatment and public health policy strategies.

Anti-influenza A Virus Activity of Dendrobine and Its Mechanism of Action

Dendrobine, a major component of Dendrobium nobile, increasingly draws attention for its wide applications in health care. Here we explore potential effects of dendrobine against influenza A virus and elucidate the underlying mechanism. Our results indicated that dendrobine possessed antiviral activity against influenza A viruses, including A/FM-1/1/47 (H1N1), A/Puerto Rico/8/34 H274Y (H1N1), and A/Aichi/2/68 (H3N2) with IC₅₀ values of 3.39 ± 0.32, 2.16 ± 0.91, 5.32 ± 1.68 μg/mL, respectively. Mechanism studies revealed that dendrobine inhibited early steps in the viral replication cycle. Notably, dendrobine could bind to the highly conserved region of viral nucleoprotein (NP), subsequently restraining nuclear export of viral NP and its oligomerization. In conclusion, dendrobine shows potential to be developed as a promising agent to treat influenza virus infection. More importantly, the results provide invaluable information for the full application of the Traditional Chinese Medicine named "Shi Hu".

The PA Endonuclease Inhibitor RO-7 Protects Mice from Lethal Challenge with Influenza A or B Viruses

Current influenza treatment relies on a single class of antiviral drugs, the neuraminidase inhibitors (NAIs), raising concern over the potential emergence of resistant variants and necessitating the development of novel drugs. In recent years, investigational inhibitors targeting the endonuclease activity of the influenza acidic polymerase (PA) protein have yielded encouraging results, although there are only limited data on their in vivo efficacy. Here, we examined the antiviral potential of the PA endonuclease inhibitor RO-7 in prophylactic and therapeutic regimens in BALB/c mice inoculated with influenza A/California/04/2009 (H1N1)pdm09 or B/Brisbane/60/2008 viruses, which represent currently circulating antigenic variants. RO-7 was administered to mice intraperitoneally twice daily at dosages of 6, 15, or 30 mg/kg/day for 5 days, starting 4 h before or 24 or 48 h after virus inoculation, and showed no adverse effects. Prophylactic administration completely protected mice from lethal infection by influenza A or B virus. The level of therapeutic protection conferred depended upon the time of treatment initiation and RO-7 dosage, resulting in 60 to 100% and 80 to 100% survival with influenza A and B viruses, respectively. RO-7 treatment significantly decreased virus titers in the lung and lessened the extent and severity of lung damage. No PA endonuclease-inhibitor resistance was observed in viruses isolated from lungs of RO-7-treated mice, and the viruses remained susceptible to the drug at nanomolar concentrations in phenotypic assays. These in vivo efficacy results further highlight the potential of RO-7 for development as antiviral therapy for influenza A and B virus infections.

Drug resistance in influenza A virus: the epidemiology and management

Influenza A virus (IAV) is the sole cause of the unpredictable influenza pandemics and deadly zoonotic outbreaks and constitutes at least half of the cause of regular annual influenza epidemics in humans. Two classes of anti-IAV drugs, adamantanes and neuraminidase (NA) inhibitors (NAIs) targeting the viral components M2 ion channel and NA, respectively, have been approved to treat IAV infections. However, IAV rapidly acquired resistance against both classes of drugs by mutating these viral components. The adamantane-resistant IAV has established itself in nature, and a majority of the IAV subtypes, especially the most common H1N1 and H3N2, circulating globally are resistant to adamantanes. Consequently, adamantanes have become practically obsolete as anti-IAV drugs. Similarly, up to 100% of the globally circulating IAV H1N1 subtypes were resistant to oseltamivir, the most commonly used NAI, until 2009. However, the 2009 pandemic IAV H1N1 subtype, which was sensitive to NAIs and has now become one of the dominant seasonal influenza virus strains, has replaced the pre-2009 oseltamivir-resistant H1N1 variants. This review traces the epidemiology of both adamantane- and NAI-resistant IAV subtypes since the approval of these drugs and highlights the susceptibility status of currently circulating IAV subtypes to NAIs. Further, it provides an overview of currently and soon to be available control measures to manage current and emerging drug-resistant IAV. Finally, this review outlines the research directions that should be undertaken to manage the circulation of IAV in intermediate hosts and develop effective and alternative anti-IAV therapies.

Ultrasensitive Fluorogenic Reagents for Neuraminidase Titration

Influenza viral neuraminidase plays a crucial role during infections. It is a major target for the development of anti-influenza drugs and is also attracting increasing attention as a vaccine target as evidence accumulates that neuraminidase-neutralizing antibodies contribute to protection. However, no method currently exists to accurately and efficiently measure concentrations of active neuraminidase in virus samples or other crude mixtures, which hampers development on both fronts. In this report, we describe the development of a selective and sensitive active-site titration reagent for neuraminidase that can quantify viral neuraminidases down to sub-nanomolar levels in crude samples, with no background from non-viral neuraminidases. By using this reagent, we determined accurate k_cat values for six influenza A and two influenza B neuraminidases for the first time. We also quantified the neuraminidase content in a commercial influenza vaccine, thus demonstrating that this titration reagent opens the possibility for better vaccine analysis.

Inhibitors of Influenza Virus Polymerase Acidic (PA) Endonuclease: Contemporary Developments and Perspectives

Influenza virus (IFV) causes periodic global influenza pandemics, resulting in substantial socioeconomic loss and burden on medical facilities. Yearly variation in the effectiveness of vaccines, slow responsiveness to vaccination in cases of pandemic IFV, and emerging resistance to available drugs highlight the need to develop additional small-molecular inhibitors that act on IFV proteins. One promising target is polymerase acidic (PA) endonuclease, which is a bridged dinuclear metalloenzyme that plays a crucial role in initiating IFV replication. During the past decade, intensive efforts have been made to develop small-molecular inhibitors of this endonuclease as candidate agents for treatment of IFV infection. Here, we review the current status of development of PA endonuclease inhibitors and we discuss the applicability of newer medicinal-chemistry strategies for the discovery more potent, selective, and safer inhibitors.

Immunization and treatment updates: 2016-2017 influenza season

Influenza-associated infections cause significant morbidity and mortality worldwide, particularly among immunocompromised patients. Immunization is the primary mode of prevention of disease; however, efficacy in immunocompromised patients may be limited. Antiviral medications are important for treatment and prophylaxis of affected individuals. This article reviews treatment and prevention recommendations for the 2016-2017 influenza season in the Northern Hemisphere and Southern Hemisphere.

Broad-Range Antiviral Activity of Hydrogen Sulfide Against Highly Pathogenic RNA Viruses

Hydrogen sulfide is an important endogenous mediator that has been the focus of intense investigation in the past few years, leading to the discovery of its role in vasoactive, cytoprotective and anti-inflammatory responses. Recently, we made a critical observation that H₂S also has a protective role in paramyxovirus infection by modulating inflammatory responses and viral replication. In this study we tested the antiviral and anti-inflammatory activity of the H₂S slow-releasing donor GYY4137 on enveloped RNA viruses from Ortho-, Filo-, Flavi- and Bunyavirus families, for which there is no FDA-approved vaccine or therapeutic available, with the exception of influenza. We found that GYY4137 significantly reduced replication of all tested viruses. In a model of influenza infection, GYY4137 treatment was associated with decreased expression of viral proteins and mRNA, suggesting inhibition of an early step of replication. The antiviral activity coincided with the decrease of viral-induced pro-inflammatory mediators and viral-induced nuclear translocation of transcription factors from Nuclear Factor (NF)-kB and Interferon Regulatory Factor families. In conclusion, increasing cellular H₂S is associated with significant antiviral activity against a broad range of emerging enveloped RNA viruses, and should be further explored as potential therapeutic approach in relevant preclinical models of viral infections.

Therapeutics Against Filovirus Infection

Therapies for filovirus infections are urgently needed. The paradoxical issue facing therapies is the need for rigorous safety and efficacy testing, adhering to the principle tenant of medicine to do no harm, while responding to the extreme for a treatment option during an outbreak. Supportive care remains a primary goal for infected patients. Years of research into filoviruses has provided possible medical interventions ranging from direct antivirals, host-factor supportive approaches, and passive immunity. As more basic research is directed toward understanding these pathogens and their impact on the host, effective approaches to treat patients during infection will be identified. The ability to manage outbreaks with medical interventions beyond supportive care will require clinical trial design that will balance the benefits of the patient and scientific community.