Recent advances in neuraminidase inhibitor development as anti-influenza drugs

Inhaled Dry Powder of Antiviral Agents: A Promising Approach to Treating Respiratory Viral Pathogens

Inhaled dry powder formulations of antiviral agents represent a novel and potentially transformative approach to managing respiratory viral infections. Traditional antiviral therapies in the form of tablets or capsules often face limitations in terms of therapeutic activity, systemic side effects, and delayed onset of action. Dry powder inhalers (DPIs) provide a targeted delivery system, ensuring the direct administration of antivirals to the infection site, the respiratory tract, which potentially enhance therapeutic efficacy and minimize systemic exposure. This review explores the current state of inhaled dry powder antiviral agents, their advantages over traditional routes, and specific formulations under development. We discuss the benefits of targeted delivery, such as improved drug deposition in the lungs and reduced side effects, alongside considerations related to the formulation preparation. In addition, we summarize the developed (published and marketed) inhaled dry powders of antiviral agents.

Hazards of antiviral contamination in water: Dissemination, fate, risk and their impact on fish

Antiviral drugs are a cornerstone in the first line of antiviral therapy and their demand rises consistently with increments in viral infections and successive outbreaks. The drugs enter the waters due to improper disposal methods or via human excreta following their consumption; consequently, many of them are now classified as emerging pollutants. Hereby, we review the global dissemination of these medications throughout different water bodies and thoroughly investigate the associated risk they pose to the aquatic fauna, particularly our vertebrate relative fish, which has great economic and dietary importance and subsequently serves as a major doorway to the human exposome. Our risk assessment identifies eleven such drugs that presently pose high to moderate levels of risk to the fish. The antiviral drugs are likely to induce oxidative stress, alter the behaviour, affect different physiological processes and provoke various toxicological mechanisms. Many of the compounds exhibit elevated bioaccumulation potential, while, some have an increased tendency to leach through soil and contaminate the groundwater. Eight antiviral medications show a highly recalcitrant nature and would impact the aquatic life consistently in the long run and continue to influence the human exposome. Thereby, we call for urgent ecopharmacovigilance measures and modification of current water treatment methods.

A Systematic Review of Clinical Pharmacokinetics of Inhaled Antiviral

Background and Objectives: The study of clinical pharmacokinetics of inhaled antivirals is particularly important as it helps one to understand the therapeutic efficacy of these drugs and how best to use them in the treatment of respiratory viral infections such as influenza and the current COVID-19 pandemic. The article presents a systematic review of the available pharmacokinetic data of inhaled antivirals in humans, which could be beneficial for clinicians in adjusting doses for diseased populations. Materials and Methods: This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. A comprehensive literature search was conducted using multiple databases, and studies were screened by two independent reviewers to assess their eligibility. Data were extracted from the eligible studies and assessed for quality using appropriate tools. Results: This systematic review evaluated the pharmacokinetic parameters of inhaled antiviral drugs. The review analyzed 17 studies, which included Zanamivir, Laninamivir, and Ribavirin with 901 participants, and found that the non-compartmental approach was used in most studies for the pharmacokinetic analysis. The outcomes of most studies were to assess clinical pharmacokinetic parameters such as the Cmax, AUC, and t1/2 of inhaled antivirals. Conclusions: Overall, the studies found that the inhaled antiviral drugs were well tolerated and exhibited favorable pharmacokinetic profiles. The review provides valuable information on the use of these drugs for the treatment of influenza and other viral respiratory infections.

Glycyrrhizic Acid-Based Carbonized Dots Boost Antiviral Activity against Influenza A Virus via Multisite Inhibition Mechanisms

Influenza A virus (IVA) has been continuously causing pandemics in several animal hosts and has become a worldwide public health threat. Currently, antiviral drugs have become associated with a lot of side effects and limited activity against emerging drug-resistant influenza viruses. Therefore, the development of novel antiviral drugs is of great importance. In this study, we synthesized a kind of carbon dots (CDs) with high dispersibility from glycyrrhizic acid (GA) using a simple dry heating method. Compared with glycyrrhizic acid alone, GA-CDs exhibit superior solubility and significantly improve the antiviral property against IVA. Investigation of the mechanism revealed that GA-CDs act against IVA mainly by inhibiting viral internalization, replication of the viral genome, neuraminidase activity, and host inflammatory responses. More importantly, in a mouse model, GA-CDs can significantly alleviate the clinical symptoms and decrease mortality and lung viral titers. In vitro and in vivo experiments demonstrate that GA-CDs possess extraordinary therapeutic effects; therefore, we propose that GA-CDs may be a promising alternative therapy for IVA infection.

Sialidase Inhibitors with Different Mechanisms

Sialidases, or neuraminidases, are enzymes that catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly removal of the terminal Sia (desialylation). By desialylation, sialidase can modulate the functionality of the target compound and is thus often involved in biological pathways. Inhibition of sialidases with inhibitors is an important approach for understanding sialidase function and the underlying mechanisms and could serve as a therapeutic approach as well. Transition-state analogues, such as anti-influenza drugs oseltamivir and zanamivir, are major sialidase inhibitors. In addition, difluoro-sialic acids were developed as mechanism-based sialidase inhibitors. Further, fluorinated quinone methide-based suicide substrates were reported. Sialidase product analogue inhibitors were also explored. Finally, natural products have shown competitive inhibiton against viral, bacterial, and human sialidases. This Perspective describes sialidase inhibitors with different mechanisms and their activities and future potential, which include transition-state analogue inhibitors, mechanism-based inhibitors, suicide substrate inhibitors, product analogue inhibitors, and natural product inhibitors.

Iterative Optimization and Structure-Activity Relationship Studies of Oseltamivir Amino Derivatives as Potent and Selective Neuraminidase Inhibitors via Targeting 150-Cavity

With our continuous endeavors in seeking neuraminidase (NA) inhibitors, we reported herein three series of novel oseltamivir amino derivatives with the goal of exploring the druggable chemical space inside the 150-cavity of influenza virus NAs. Among them, around half of the compounds in series C were demonstrated to be better inhibitors against both wild-type and oseltamivir-resistant group-1 NAs than oseltamivir carboxylate (OSC). Notably, compounds 12d, 12e, 15e, and 15i showed more potent or equipotent antiviral activity against H1N1, H5N1, and H5N8 viruses compared to OSC in cellular assays. Furthermore, compounds 12e and 15e exhibited high metabolic stability in human liver microsomes (HLMs) and low inhibitory effect on main cytochrome P450 (CYP) enzymes, as well as low acute/subacute toxicity and certain antiviral efficacy in vivo. Also, pharmacokinetic (PK) and molecular docking studies were performed. Overall, 12e and 15e possess great potential to serve as anti-influenza candidates and are worthy of further investigation.

Partial carbonization of quercetin boosts the antiviral activity against H1N1 influenza A virus

Inflenza A viruses (IAVs) are highly transmissible and pathogenic Orthomyxoviruses, which have led to worldwide outbreaks and seasonal pandemics of acute respiratory diseases, causing serious threats to public health. Currently used anti-influenza drugs may cause neurological side effects, and they are increasingly less effective against mutant strains. To help prevent the spread of IAVs, in this work, we have developed quercetin-derived carbonized nanogels (CNGs_Qur) that display potent viral inhibitory, antioxidative, and anti-inflammatory activities. The antiviral CNGs_Qur were synthesized by mild carbonization of quercetin (Qur), which successfully preserved their antioxidative and anti-inflammatory properties while also contributed enhanced properties, such as water solubility, viral binding, and biocompatibility. Antiviral assays of co-treatment, pre-treatment, and post-treatment indicate that CNGs_Qur interacts with the virion, revealing that the major antiviral mechanism resulting in the inhibition of the virus is by their attachment on the cell surface. Among them, the selectivity index (SI) of CNGs_Qur270 (>857.1) clearly indicated its great potential for clinical application in IAVs inhibition, which was much higher than that of pristine quercetin (63.7) and other clinical drugs (4-81). Compared with quercetin at the same dose, the combined effects of viral inhibition, antioxidative and anti-inflammatory activities impart the superior therapeutic effects of CNGs_Qur270 aerosol inhalation in the treatment of IAVs infection, as evidenced by a mouse model. These CNGs_Qur effectively prevent the spread of IAVs and suppress virus-induced inflammation while also exhibiting good in vivo biocompatibility. CNGs_Qur shows much promise as a clinical therapeutic agent against infection by IVAs.

Discovery of New Ginsenol-Like Compounds with High Antiviral Activity

A number of framework amides with a ginsenol backbone have been synthesized using the Ritter reaction. We named the acetamide as Ginsamide. A method was developed for the synthesis of the corresponding amine and thioacetamide. The new compounds revealed a high activity against H1N1 influenza, which was confirmed using an animal model. Biological experiments were performed to determine the mechanism of action of the new agents, a ginsamide-resistant strain of influenza virus was obtained, and the pathogenicity of the resistant strain and the control strain was studied. It was shown that the emergence of resistance to Ginsamide was accompanied by a reduction in the pathogenicity of the influenza virus.

Hydroxycarbonylation of alkenes with formic acid using a rhodium iodide complex and alkyl ammonium iodide

Hydroxycarbonylation of alkenes using formic acid (HCOOH) is ideal for the synthesis of various carboxylic acids as a means to develop a sustainable reaction system with lower environmental impact. In this study, we developed a new catalytic system for hydroxycarbonylation of alkenes with HCOOH using a Vaska-type Rh complex with an iodide ligand, RhI(CO)(PPh3)2 (1), as the catalyst, and a quaternary ammonium iodide salt as the promoter for the catalyst. In comparison with similar reaction systems using Rh catalysts, our reaction system is safer and more environmentally friendly since it does not require high-pressure conditions, explosive gases, or environmentally unfriendly CH3I and extra PPh3 promoters. In addition, we also experimentally clarified that the catalytic reaction proceeds via RhHI2(CO)(PPh3)2 (2), which is formed by the reaction of 1 with a quaternary ammonium iodide salt and p-TsOH. Furthermore, the Rh(iii) complex 2 can catalyze hydroxycarbonylation of alkenes with HCOOH without any promoters.

Filamentous anti-influenza agents wrapping around viruses

Owing to the emerging resistance to current anti-influenza therapies, strategies for blocking virus-cell interaction with agents that mimic interactions with host cell receptors are garnering interest. In this context, a multivalent presentation of sialyl groups on various types of scaffold materials such as dendrimers, liposomes, nanoparticles, and natural/synthetic polymers has been investigated for the inhibition of influenza A virus infection. However, the development of versatile antiviral agents based on monodisperse scaffolds capable of precise molecular design remains challenging. Whether an anisotropically extended filamentous nanostructure can serve as an effective scaffold for maximum inhibition of viral cell attachment has not been investigated. In this study, the preparation of a series of sialyllactose-conjugated filamentous bacteriophages (SLPhages), with controlled loading levels, ligand valencies, and two types of sialyllactose (α2,3' and α2,6'), is demonstrated. With optimal ligand loading and valency, SLPhages showed inhibitory activity (in vitro) against influenza A viruses at concentrations of tens of picomolar. This remarkable inhibition is due to the strong interaction between the SLPhage and the virus; this interaction is adequately potent to compensate for the cost of the bending and wrapping of the SLPhage around the influenza virus. Our study may open new avenues for the development of filamentous anti-viral agents, in which virus-wrapping or aggregation is the primary feature responsible for the blocking of cell entry.

Inhibition of Influenza A virus propagation by benzoselenoxanthenes stabilizing TMPRSS2 Gene G-quadruplex and hence down-regulating TMPRSS2 expression

Proteolytic cleavage of influenza A virus (IAV) hemagglutinin by host proteases is crucial for virus infectivity and spread. The transmembrane serine protease TMPRSS2 was previously identified as the essential protease that can cleave hemagglutinin of many subtypes of influenza virus and spike protein of coronavirus. Herein, we found that a guanine rich tract, capable of forming intramolecular G-quadruplex in the presence of potassium ions, in the promoter region of human TMPRSS2 gene was quite important for gene transcriptional activity, hence affecting its function. Furthermore, 7 new synthesized benzoselenoxanthene analogues were found to enable stabilizing such G-quadruplex. More importantly, compounds can down-regulate TMPRSS2 gene expression, especially endogenous TMPRSS2 protein levels, and consequently suppress influenza A virus propagation in vitro. Our results provide a new strategy for anti-influenza A virus infection by small molecules targeting the TMPRSS2 gene G-quadruplex and thus inhibiting TMPRSS2 expression, which is valuable for developing small molecule drugs against influenza A virus and also may be a potential candidate as anti- SARS-CoV-2 (Severe Acute Respiratory Syndrome CoV 2) lead molecules.

Peramivir binding affinity with influenza A neuraminidase and research on its mutations using an induced-fit docking approach

Influenza A virus (IAV) has caused epidemic infections worldwide, with many strains resistant to inhibitors of a surface protein, neuraminidase (NA), due to point mutations on its structure. A novel NA inhibitor named peramivir was recently approved, but no exhaustive computational research regarding its binding affinity with wild-type and mutant NA has been conducted. In this study, a thorough investigation of IAV-NA PDB entries of 9 subtypes is described, providing a list of residues constituting the protein-ligand binding sites. The results of induced-fit docking approach point out key residues of wild-type NA participating in hydrogen bonds and/or ionic interactions with peramivir, among which Arg 368 is responsible for a peramivir-NA ionic interaction. Mutations on this residue greatly reduced the binding affinity of peramivir with NA, with 3 mutations R378Q, R378K and R378L (NA6) capable of deteriorating the docking performance of peramivir by over 50%. 200 compounds from 6-scaffolds were docked into these 3 mutant versions, revealing 18 compounds giving the most promising results. Among them, CMC-2012-7-1527-56 (benzoic acid scaffold, IC50 = 32 nM in inhibitory assays with IAV) is deemed the most potential inhibitor of mutant NA resisting both peramivir and zanamivir, and should be further investigated.

Bioassay of ferulic acid derivatives as influenza neuraminidase inhibitors

Four series of ferulic acid derivatives were designed, synthesized, and evaluated for their neuraminidase (NA) inhibitory activities against influenza virus H1N1 in vitro. The pharmacological results showed that the majority of the target compounds exhibited moderate influenza NA inhibitory activity, which was also better than that of ferulic acid. The two most potent compounds were 1m and 4a with IC₅₀ values of 12.77 ± 0.47 and 12.96 ± 1.34 μg/ml, respectively. On the basis of the biological results, a preliminary structure-activity relationship (SAR) was derived and discussed. Besides, molecular docking was performed to study the possible interactions of compounds 1p, 2d, 3b, and 4a with the active site of NA. It was found that the 4-OH-3-OMe group and the amide group (CON) of ferulic acid amide derivatives were two key pharmacophores for NA inhibitory activity. It is meaningful to further modify the natural product ferulic acid to improve its influenza NA inhibitory activity.

Herbal Medicines with Antiviral Activity Against the Influenza Virus, a Systematic Review

The rapidly changing influenza virus has remained a consistent threat to the well-being of a variety of species on the planet. Influenza virus' high mutation rate has allowed the virus to rapidly and continuously evolve, as well as generate new strains that are resistant to the current commercially available antivirals. Thus, the increased resistance has compelled the scientific community to explore alternative compounds that have antiviral effects against influenza virus. In this paper, the authors systematically review numerous herbal extracts that were shown to have antiviral effects against the virus. Specifically, the herbal antiviral targets mainly include hemagglutinin, neuraminidase and matrix 2 proteins. In some instances, herbal extracts inhibited the replication of oseltamivir-resistant strains and certain pentacyclic triterpenes exhibited higher antiviral activity than oseltamivir. This paper also explores the possibility of targeting various host-cell signaling pathways that are utilized by the virus during its replication process. Infected cell pathways are hijacked by intracellular signaling cascades such as NF-kB signaling, PI3K/Akt pathway, MAPK pathway and PKC/PKR signaling cascades. Herbal antivirals have been shown to target these pathways by suppressing nuclear export of influenza vRNP and thus inhibiting the phosphorylation signaling cascade. In conclusion, copious amounts of herbal antivirals have been shown to inhibit influenza virus, however further studies are needed for these new compounds to be up to modern pharmacological standards.

Implications of protein conformations to modifying novel inhibitor Oseltamivir for 2009 H1N1 influenza A virus by simulation and docking studies

Recently three FDA approved existing drugs, namely-Oseltamivir, Peramivir and Zanamivir, used against Neuraminidase (NA) for the inhibitory effect on the process of viral progeny release to inhibit infection. All NA subtypes has been divided into two groups (Group 1 and Group 2) based on phylogenetic study. Oseltamivir and Zanamivir drugs are designed for Group 2 NA but are also used against 2009 H1N1 NA that lies in Group 1. There is no specific drug available for H1N1 and, consequently, there is an urgent requirement for the same. The structure-based drug design and fragment-based drug design methods are used for building more effective and economic drug molecules. In this work, the fragment-based drug development followed by fragment evolution on the basis of protein conformations after every 10 ns of 100 ns simulation. There are two analogs of Oseltamivir acid drug discovered in this study. Only analog 1, along with Oseltamivir acid, were then docked with the native protein. The analog 1 (benzoic acid inhibitor 11) exhibited higher binding affinity value of - 10.70 kcal/mol in comparison to its predecessor. The concept of conformations and protein-ligand interactions can be useful in designing new drugs for H1N1 with high specific binding.

Antiviral effects and mechanisms of Yinhuapinggan granule against H1N1 influenza virus infection in RAW264.7 cells

Yinhuapinggan granule (YHPG), a modified prescription based on Ma-Huang-Tang (MHT), is used in traditional Chinese medicine (TCM) to treat influenza, cough, and viral pneumonia. In this study, we investigated the antiviral effects of YHPG by means of pre-, post-, and co-treatment, and its underlying mechanisms on regulating the levels of inflammatory-related cytokines, modulating the mRNA expressions of interferon-stimulated genes in influenza virus-infected murine macrophage cells (RAW264.7), and evaluating the protein expressions of key effectors in the Type I IFN and pattern recognition receptor (PRRs) signaling pathways. The results showed that YHPG markedly inhibited influenza virus (IFV) replication in pre-, post- and co-treatment assay, especially in post-treatment assay. Antiviral mechanisms studies revealed that YHPG (500 and 250 μg/mL) significantly up-regulated levels of IFN-β, IFN-stimulated genes (Mx-1, ISG-15 and ISG-56) compared with the IFV control group, while the levels of IL-6 and TNF-α were significantly down-regulated. Furthermore, western blot analysis results revealed that the protein expressions of the phosphorylated forms of TBK1, IRF3, ERK1/2, P38 MAPK and NF-κB p65 were significantly down-regulated in RAW264.7 cells with the YHPG (500 and 250 μg/mL) treatment, while the expression of the phosphorylated form of STAT1 was significantly enhanced. Based on these results, YHPG had antiviral effects in IFV-infected RAW264.7 cells, which might be associated with regulation of the inflammatory cytokines production, evaluation of the levels of IFN-stimulated genes, and modulation of the protein expressions of key effectors in the Type I IFN and PRRs signaling pathways.

The hydrophobic side chain of oseltamivir influences type A subtype selectivity of neuraminidase inhibitors

Neuraminidase, which plays a critical role in the influenza virus life cycle, is a target for new therapeutic agents. The study of structure-activity relationships revealed that the C-5 position amino group of oseltamivir was pointed to 150-cavity of the neuraminidase in group 1. This cavity is important for selectivity of inhibitors against N1 versus N2 NA. A serial of influenza neuraminidase inhibitors with the oseltamivir scaffold containing lipophilic side chains at the C-5 position have been synthesized and evaluated for their influenza neuraminidase inhibitory activity and selectivity. The results indicated that compound 13o (H5N1 IC₅₀  = 0.1 ± 0.04 μm, H3N2 IC₅₀  = 0.26 ± 0.18 μm) showed better inhibitory activity and selectivity against the group 1 neuraminidase. This study may provide a clue to design of better group 1 neuraminidase inhibitors.

Influenza Neuraminidase Inhibitors: Synthetic Approaches, Derivatives and Biological Activity

Despite being a common viral disease, influenza has very negative consequences, causing the death of around half a million people each year. A neuraminidase located on the surface of the virus plays an important role in viral reproduction by contributing to the release of viruses from infected host cells. The treatment of influenza is mainly based on the administration of neuraminidase inhibitors. The neuraminidase inhibitors zanamivir, laninamivir, oseltamivir and peramivir have been commercialized and have been demonstrated to be potent influenza viral neuraminidase inhibitors against most influenza strains. In order to create more potent neuraminidase inhibitors and fight against the surge in resistance resulting from naturally-occurring mutations, these anti-influenza drugs have been used as templates for the development of new neuraminidase inhibitors through structure-activity relationship studies. Here, we review the synthetic routes to these commercial drugs, the modifications which have been performed on these structures and the effects of these modifications on their inhibitory activity.

The Intersection of Structural and Chemical Biology - An Essential Synergy

The continual improvement in our ability to generate high resolution structural models of biological molecules has stimulated and supported innovative chemical biology projects that target increasingly challenging ligand interaction sites. In this review we outline some of the recent developments in chemical biology and rational ligand design and show selected examples that illustrate the synergy between these research areas.

Synthetic Mucus Nanobarriers for Identification of Glycan-Dependent Primary Influenza A Infection Inhibitors

Current drugs against the influenza A virus (IAV) act by inhibiting viral neuraminidase (NA) enzymes responsible for the release of budding virions from sialoglycans on infected cells. Here, we describe an approach focused on a search for inhibitors that reinforce the protective functions of mucosal barriers that trap viruses en route to the target cells. We have generated mimetics of sialo-glycoproteins that insert into the viral envelope to provide a well-defined mucus-like environment encapsulating the virus. By introducing this barrier, which the virus must breach using its NA enzymes to infect a host cell, into a screening platform, we have been able to identify compounds that provide significant protection against IAV infection. This approach may facilitate the discovery of potent new IAV prophylactics among compounds with NA activities too weak to emerge from traditional drug screens.

Applying high-performance computing in drug discovery and molecular simulation

In recent decades, high-performance computing (HPC) technologies and supercomputers in China have significantly advanced, resulting in remarkable achievements. Computational drug discovery and design, which is based on HPC and combines pharmaceutical chemistry and computational biology, has become a critical approach in drug research and development and is financially supported by the Chinese government. This approach has yielded a series of new algorithms in drug design, as well as new software and databases. This review mainly focuses on the application of HPC to the fields of drug discovery and molecular simulation at the Chinese Academy of Sciences, including virtual drug screening, molecular dynamics simulation, and protein folding. In addition, the potential future application of HPC in precision medicine is briefly discussed.

The chemistry and biology of guanidine natural products

The present review discusses the isolation, structure determination, synthesis, biosynthesis and biological activities of secondary metabolites bearing a guanidine group.

An easy access to carboxylic acids via Pd-catalyzed hydrocarboxylation of olefins with HCOOLi as a CO surrogate under mild conditions

This paper describes an easy access to carboxylic acids via Pd-catalyzed hydrocarboxylation of olefins with HCOOLi and Ac₂O under mild conditions without using external CO gas.

Antiviral effects of Yinhuapinggan granule against influenza virus infection in the ICR mice model

Yinhuapinggan granule (YHPG), a Chinese medicine granule based on Ma-Huang-Tang (Ephedra Decoction) and the clinical experience of Professor Wan Haitong, is used in traditional Chinese medicine (TCM) for the treatment of colds, influenza, fever, inflammation and cough. This study investigated the antiviral effects of YHPG on the production of inflammatory cytokines in influenza virus (IFV)-infected mice and evaluated the effect of YHPG on the expression of NF-κB p65 and the level of key signaling molecules in the TLR4 signaling pathway. ICR mice were orally administrated YHPG at doses of 7.5, 15 and 30 g kg(-1) day(-1) for 2 or 6 days after IFV infection. On days 3 and 7 after infection, YHPG (15 g/kg and 30 g/kg) significantly increased levels of interleukin (IL)-2 and interferon gamma and decreased levels of IL-4, IL-5 and tumor necrosis factor (TNF) in serum compared with the IFV control group. Furthermore, the expression of TLR4, MyD88, TRAF6 and NF-κB p65 at the mRNA and protein level was significantly lower in the YHPG (15 and 30 g/kg) treatment groups than in the IFV control group. These results suggest that YHPG has antiviral effects in IFV-infected mice, which is associated with the inhibition of the TLR4-MyD88-TRAF6 signaling pathway and the expression of NF-κB p65.

Neuraminidase of Influenza A Virus Binds Lysosome-Associated Membrane Proteins Directly and Induces Lysosome Rupture

As a recycling center, lysosomes are filled with numerous acid hydrolase enzymes that break down waste materials and invading pathogens. Recently, lysosomal cell death has been defined as "lysosomal membrane permeabilization and the consequent leakage of lysosome contents into cytosol." Here, we show that the neuraminidase (NA) of H5N1 influenza A virus markedly deglycosylates and degrades lysosome-associated membrane proteins (LAMPs; the most abundant membrane proteins of lysosome), which induces lysosomal rupture, and finally leads to cell death of alveolar epithelial carcinoma A549 cells and human tracheal epithelial cells. The NA inhibitors peramivir and zanamivir could effectively block the deglycosylation of LAMPs, inhibit the virus cell entry, and prevent cell death induced by the H5N1 influenza virus. The NA of seasonal H1N1 virus, however, does not share these characteristics. Our findings not only reveal a novel role of NA in the early stage of the H5N1 influenza virus life cycle but also elucidate the molecular mechanism of lysosomal rupture crucial for influenza virus induced cell death.

IMPORTANCE

The integrity of lysosomes is vital for maintaining cell homeostasis, cellular defense and clearance of invading pathogens. This study shows that the H5N1 influenza virus could induce lysosomal rupture through deglycosylating lysosome-associated membrane proteins (LAMPs) mediated by the neuraminidase activity of NA protein. NA inhibitors such as peramivir and zanamivir could inhibit the deglycosylation of LAMPs and protect lysosomes, which also further interferes with the H5N1 influenza virus infection at early stage of life cycle. This work is significant because it presents new concepts for NA's function, as well as for influenza inhibitors' mechanism of action, and could partially explain the high mortality and high viral load after H5N1 virus infection in human beings and why NA inhibitors have more potent therapeutic effects for lethal avian influenza virus infections at early stage.

New small-molecule drug design strategies for fighting resistant influenza A

Influenza A virus is the major cause of seasonal or pandemic flu worldwide. Two main treatment strategies-vaccination and small molecule anti-influenza drugs are currently available. As an effective vaccine usually takes at least 6 months to develop, anti-influenza small molecule drugs are more effective for the first line of protection against the virus during an epidemic outbreak, especially in the early stage. Two major classes of anti-influenza drugs currently available are admantane-based M2 protein blockers (amantadine and rimantadine) and neuraminidase (NA) inhibitors (oseltamivir, zanamivir, and peramivir). However, the continuous evolvement of influenza A virus and the rapid emergence of resistance to current drugs, particularly to amantadine, rimantadine, and oseltamivir, have raised an urgent need for developing new anti-influenza drugs against resistant forms of influenza A virus. In this review, we first give a brief introduction of the molecular mechanisms behind resistance, and then discuss new strategies in small-molecule drug development to overcome influenza A virus resistance targeting mutant M2 proteins and neuraminidases, and other viral proteins not associated with current drugs.

X-ray crystallography over the past decade for novel drug discovery - where are we heading next?

INTRODUCTION

Macromolecular X-ray crystallography has been the primary methodology for determining the three-dimensional structures of proteins, nucleic acids and viruses. Structural information has paved the way for structure-guided drug discovery and laid the foundations for structural bioinformatics. However, X-ray crystallography still has a few fundamental limitations, some of which may be overcome and complemented using emerging methods and technologies in other areas of structural biology.

AREAS COVERED

This review describes how structural knowledge gained from X-ray crystallography has been used to advance other biophysical methods for structure determination (and vice versa). This article also covers current practices for integrating data generated by other biochemical and biophysical methods with those obtained from X-ray crystallography. Finally, the authors articulate their vision about how a combination of structural and biochemical/biophysical methods may improve our understanding of biological processes and interactions.

EXPERT OPINION

X-ray crystallography has been, and will continue to serve as, the central source of experimental structural biology data used in the discovery of new drugs. However, other structural biology techniques are useful not only to overcome the major limitation of X-ray crystallography, but also to provide complementary structural data that is useful in drug discovery. The use of recent advancements in biochemical, spectroscopy and bioinformatics methods may revolutionize drug discovery, albeit only when these data are combined and analyzed with effective data management systems. Accurate and complete data management is crucial for developing experimental procedures that are robust and reproducible.

A review of neuraminidase inhibitor susceptibility in influenza strains

Influenza human infections are considered as a persistent global public health issue. Whereas vaccination is important for prevention, given its limitations, antiviral therapy is at the forefront of treatment, while it also plays a significant role in prevention. Currently, two classes of drugs, adamantanes (M2 blockers) and neuraminidase inhibitors (NAIs), are available for treatment and chemoprophylaxis of influenza infections. Given the resistance patterns of circulating influenza strains, adamantanes are not currently recommended. The current review mainly focuses on the development of resistance to NAIs among A and B subtypes of influenza virus strains over the last 5 years. 'Permissive' drift mutations and reassortment of viral gene segments have resulted in NAI oseltamivir-resistant A/(H1N1) variants that rapidly became predominant worldwide in the period 2007-2009. However, the prevalence of antiviral resistance to NAI zanamivir remains relatively low. In addition, the recently developed NAIs, peramivir and laninamivir, while licensed in certain countries, are still under evaluation and only a few reports have described resistance to peramivir. Although in 2014, the majority of circulating human influenza viruses remains susceptible to all NAIs, the emergence of oseltamivir-resistant influenza variants that could retain viral transmissibility, highlights the necessity for enhanced epidemiological and microbiological surveillance and clinical assessment of antiviral resistance.

A virtual screening approach for identifying plants with anti H5N1 neuraminidase activity

Recent outbreaks of highly pathogenic and occasional drug-resistant influenza strains have highlighted the need to develop novel anti-influenza therapeutics. Here, we report computational and experimental efforts to identify influenza neuraminidase inhibitors from among the 3000 natural compounds in the Malaysian-Plants Natural-Product (NADI) database. These 3000 compounds were first docked into the neuraminidase active site. The five plants with the largest number of top predicted ligands were selected for experimental evaluation. Twelve specific compounds isolated from these five plants were shown to inhibit neuraminidase, including two compounds with IC50 values less than 92 μM. Furthermore, four of the 12 isolated compounds had also been identified in the top 100 compounds from the virtual screen. Together, these results suggest an effective new approach for identifying bioactive plant species that will further the identification of new pharmacologically active compounds from diverse natural-product resources.

From neuraminidase inhibitors to conjugates: a step towards better anti-influenza drugs?

For the treatment of seasonal flu and possible pandemic infections the development of new anti-influenza drugs that have good bioavailability against a broad spectrum of influenza viruses including the resistant strains is needed. In this review, we summarize previous methods for the structural modification of zanamivir, a potent neuraminidase inhibitor that has rare drug resistance, in order to develop effective anti-influenza drugs. We also report recent research into the design of multivalent zanamivir drugs and bifunctional zanamivir conjugates, some of which have shown better efficacy in animal experiments. As a step towards developing improved antivirals, conjugating anti-influenza drugs with anti-inflammatory agents can improve oral bioavailability and also exert synergistic effect in influenza therapy.

An atom-economic approach to carboxylic acids via Pd-catalyzed direct addition of formic acid to olefins with acetic anhydride as a co-catalyst

An effective Pd-catalyzed hydrocarboxylation of olefins using formic acid with acetic anhydride as a co-catalyst is described.

#Nitrosocarbonyls 1: antiviral activity of N-(4-hydroxycyclohex-2-en-1-yl)quinoline-2-carboxamide against the influenza A virus H1N1

Influenza virus flu A H1N1 still remains a target for its inhibition with small molecules. Fleeting nitrosocarbonyl intermediates are at work in a short-cut synthesis of carbocyclic nucleoside analogues. The strategy of the synthetic approaches is presented along with the in vitro antiviral tests. The nucleoside derivatives were tested for their inhibitory activity against a variety of viruses. Promising antiviral activities were found for specific compounds in the case of flu A H1N1.

Antiviral strategies against influenza virus: towards new therapeutic approaches

Influenza viruses are major human pathogens responsible for respiratory diseases affecting millions of people worldwide and characterized by high morbidity and significant mortality. Influenza infections can be controlled by vaccination and antiviral drugs. However, vaccines need annual updating and give limited protection. Only two classes of drugs are currently approved for the treatment of influenza: M2 ion channel blockers and neuraminidase inhibitors. However, they are often associated with limited efficacy and adverse side effects. In addition, the currently available drugs suffer from rapid and extensive emergence of drug resistance. All this highlights the urgent need for developing new antiviral strategies with novel mechanisms of action and with reduced drug resistance potential. Several new classes of antiviral agents targeting viral replication mechanisms or cellular proteins/processes are under development. This review gives an overview of novel strategies targeting the virus and/or the host cell for counteracting influenza virus infection.

The relationship between in vivo antiviral activity and pharmacokinetic parameters of peramivir in influenza virus infection model in mice

The purpose of this study was to investigate the relationship between pharmacokinetic (PK) parameters of intravenous (IV) peramivir and in vivo antiviral activity pharmacodynamic (PD) outcomes in a mouse model of influenza virus infection. Peramivir was administrated to mice in three dosing schedules; once, twice and four times after infection of A/WS/33 (H1N1). The survival rate at day 14 after virus infection was employed as the antiviral activity outcome for analysis. The relationship between day 14 survival and PK parameters, including area under the concentration-time curve (AUC), maximum concentration (Cmax) and time that drug concentration exceeds IC95 (T(>IC95)), was estimated using a logistic regression model, and model fitness was evaluated by calculation of the Akaike information criterion (AIC) index. The AIC indices of AUC, Cmax and T(>IC95) were about 114, 151 and 124, respectively. The AIC of AUC and T(>IC95) were smaller than that of Cmax. Therefore, both AUC and T(>IC95) were the PK parameters that correlated best with the antiviral activity of peramivir IV against influenza virus infection in mice.

The future of crystallography in drug discovery

INTRODUCTION

X-ray crystallography plays an important role in structure-based drug design (SBDD), and accurate analysis of crystal structures of target macromolecules and macromolecule-ligand complexes is critical at all stages. However, whereas there has been significant progress in improving methods of structural biology, particularly in X-ray crystallography, corresponding progress in the development of computational methods (such as in silico high-throughput screening) is still on the horizon. Crystal structures can be overinterpreted and thus bias hypotheses and follow-up experiments. As in any experimental science, the models of macromolecular structures derived from X-ray diffraction data have their limitations, which need to be critically evaluated and well understood for structure-based drug discovery.

AREAS COVERED

This review describes how the validity, accuracy and precision of a protein or nucleic acid structure determined by X-ray crystallography can be evaluated from three different perspectives: i) the nature of the diffraction experiment; ii) the interpretation of an electron density map; and iii) the interpretation of the structural model in terms of function and mechanism. The strategies to optimally exploit a macromolecular structure are also discussed in the context of 'Big Data' analysis, biochemical experimental design and structure-based drug discovery.

EXPERT OPINION

Although X-ray crystallography is one of the most detailed 'microscopes' available today for examining macromolecular structures, the authors would like to re-emphasize that such structures are only simplified models of the target macromolecules. The authors also wish to reinforce the idea that a structure should not be thought of as a set of precise coordinates but rather as a framework for generating hypotheses to be explored. Numerous biochemical and biophysical experiments, including new diffraction experiments, can and should be performed to verify or falsify these hypotheses. X-ray crystallography will find its future application in drug discovery by the development of specific tools that would allow realistic interpretation of the outcome coordinates and/or support testing of these hypotheses.

Influenza treatment and prophylaxis with neuraminidase inhibitors: a review

Influenza virus is a pathogen that causes morbidity and mortality worldwide. Whereas vaccination is important for prevention of disease, given its limitations, antiviral therapy is at the forefront of treatment and also plays a role in prevention. Currently, two classes of antiviral medications, the adamantanes and the neuraminidase inhibitors, are approved for treatment. Given the resistance patterns of circulating influenza, adamantanes are not recommended. Within the US, two neuraminidase inhibitors are currently approved for both treatment and prevention, while worldwide there are four available. In this review, we will briefly discuss the epidemiology and pathology of influenza and then discuss neuraminidase inhibitors: their mechanism of action, resistance, development, and future applications.

Synthesis of oseltamivir and tamiphosphor from N-acetyl-D-glucosamine

Using N-acetyl-D-glucosamine as a starting material, the anti-influenza drugs oseltamivir and tamiphosphor were synthesized via a pivotal intermediate of aldehyde 8. An intramolecular Horner-Wadsworth-Emmons reaction was utilized to construct the highly functionalized cyclohexene ring. The existing N-acetyl group was transformed into an azido group for the subsequent aziridination, followed by implantation of a 3-pentoxy group of the desired stereochemistry.