Emergence and transmission of influenza A viruses resistant to amantadine and rimantadine

Amantadine interactions with phase separated lipid membranes

Amantadine, a small amphilphic organic compound that consists of an adamantane backbone and an amino group, was first recognized as an antiviral in 1963 and received approval for prophylaxis against the type A influenza virus in 1976. Since then, it has also been used to treat Parkinson's disease-related dyskinesia and is being considered as a treatment for corona viruses. Since amantadine usually targets membrane-bound proteins, its interactions with the membrane are also thought to be important. Biological membranes are now widely understood to be laterally heterogeneous and certain proteins are known to preferentially co-localize within specific lipid domains. Does amantadine, therefore, preferentially localize in certain lipid composition domains? To address this question, we studied amantadine's interactions with phase separating membranes composed of cholesterol, DSPC (1,2-distearoyl-sn-glycero-3-phosphocholine), POPC (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine), and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine), as well as single-phase DPhPC (1,2-diphytanoyl-sn-glycero-3-phos-phocholine) membranes. From Langmuir trough and differential scanning calorimetry (DSC) measurements, we determined, respectively, that amantadine preferentially binds to disordered lipids, such as POPC, and lowers the phase transition temperature of POPC/DSPC/cholesterol mixtures, implying that amantadine increases membrane disorder. Further, using droplet interface bilayers (DIBs), we observed that amantadine disrupts DPhPC membranes, consistent with its disordering properties. Finally, we carried out molecular dynamics (MD) simulations on POPC/DSPC/cholesterol membranes with varying amounts of amantadine. Consistent with experiment, MD simulations showed that amantadine prefers to associate with disordered POPC-rich domains, domain boundaries, and lipid glycerol backbones. Since different proteins co-localize with different lipid domains, our results have possible implications as to which classes of proteins may be better targets for amantadine.

A systemic review on medicinal plants and their bioactive constituents against avian influenza and further confirmation through in-silico analysis

Background

Avian influenza or more commonly known as bird flu is a widespread infectious disease in poultry. This review aims to accumulate information of different natural plant sources that can aid in combating this disease. Influenza virus (IV) is known for its ability to mutate and infect different species (including humans) and cause fatal consequences.

Methods

Total 33 plants and 4 natural compounds were identified and documented. Molecular docking was performed against the target viral protein neuraminidase (NA), with some plant based natural compounds and compared their results with standard drugs Oseltamivir and Zanamivir to obtain novel drug targets for influenza in chickens.

Results

It was seen that most extracts exhibit their action by interacting with viral hemagglutinin or neuraminidase and inhibit viral entry or release from the host cell. Some plants also interacted with the viral RNA replication or by reducing proinflammatory cytokines. Ethanol was mostly used for extraction. Among all the plants Theobroma cacao, Capparis Sinaica Veil, Androgarphis paniculate, Thallasodendron cillatum, Sinularia candidula, Larcifomes officinalis, Lenzites betulina, Datronia molis, Trametes gibbose exhibited their activity with least concentration (below 10 μg/ml). The dockings results showed that some natural compounds (5,7- dimethoxyflavone, Aloe emodin, Anthocyanins, Quercetin, Hemanthamine, Lyocrine, Terpenoid EA showed satisfactory binding affinity and binding specificity with viral neuraminidase compared to the synthetic drugs.

Conclusion

This review clusters up to date information of effective herbal plants to bolster future influenza treatment research in chickens. The in-silico analysis also suggests some potential targets for future drug development but these require more clinical analysis.

Analysis of Components and Properties of Extractives from Alnus cremastogyne Pods from Different Provenances

Chemical components with anti-oxidant, anti-inflammatory, and anti-cancer properties extracted from Alnus bark and leaves have been extensively studied. However, less attention has been paid to extractives from Alnus pods, which are mostly treated as waste. Here, extractives of Alnus cremastogyne pods from 12 provenances in Sichuan Province were studied for high value-added utilization of Alnus waste. The extractives were analyzed by Gas Chromatography-Mass Spectrometer (GC-MS), Ultraviolet-visible spectroscopy (UV-Vis spectra), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity. A total of 58, 49, and 51 chemical components were found when the organic solvents of ethanol, petroleum ether, and ethyl acetate were used to collect extractives, respectively. These chemical components including Phytol, CIS-5,8,11,14,17-eicosapentaenoic acid, Germacrene D, Lupeol, and β-sitosterol, etc., have wide applications in the fields of pharmacy and cosmetics. Moreover, it was also found that extractives in ethanol and ethyl acetate had impressive UV resistance, especially for UV-C and UV-B blocking. The results showed that the maximum block ratio towards UV-C and UV-B could reach 99%. In addition, the ethanol extract showed good anti-oxidant activity with a maximum free radical scavenging rate of 96.19%. This comprehensive and systematic study on extractives from Alnus cremastogyne pods promotes the development of high-value utilization of Alnus components.

A Review on the Potential Species of the Zingiberaceae Family with Anti-viral Efficacy Towards Enveloped Viruses

Natural products are a great wellspring of biodiversity for finding novel antivirals, exposing new interactions between structure and operation and creating successful defensive or remedial methodologies against viral diseases. The members of Zingiberaceae traditional plant and herbal products have robust anti-viral action, and their findings will further lead to the production of derivatives and therapeutic. Additionally, it highlights the insight of utilizing these phytoextracts or their constituent compounds as an emergency prophylactic medicine during the pandemic or endemic situations for novel viruses. In this connection, this review investigates the potential candidates of the Zingiberaceae family, consisting of bioactive phytocompounds with proven antiviral efficacy against enveloped viruses. The present study was based on published antiviral efficacy of Curcuma longa, Zingiber officinale, Kaempferia parviflora, Aframomum melegueta Elettaria cardamomum, Alpina Sps (belongs to the Zingiberaceae family) towards the enveloped viruses. The relevant data was searched in Scopus”, “Scifinder”, “Springer”, “Pubmed”, “Google scholar” “Wiley”, “Web of Science”, “Cochrane “Library”, “Embase”, Dissertations, theses, books, and technical reports. Meticulously articles were screened with the subject relevancy and categorized for their ethnopharmacological significance with in-depth analysis. We have comprehensively elucidated the antiviral potency of phytoextracts, major composition, key compounds, mode of action, molecular evidence, immunological relevance, and potential bioactive phytocompounds of these five species belonging to the Zingiberaceae family. Conveniently, these phytoextracts exhibited multimode activity in combating the dreadful enveloped viruses.

Identification of Influenza PAN Endonuclease Inhibitors via 3D-QSAR Modeling and Docking-Based Virtual Screening

Structural and biochemical studies elucidate that PA_N may contribute to the host protein shutdown observed during influenza A infection. Thus, inhibition of the endonuclease activity of viral RdRP is an attractive approach for novel antiviral therapy. In order to envisage structurally diverse novel compounds with better efficacy as PA_N endonuclease inhibitors, a ligand-based-pharmacophore model was developed using 3D-QSAR pharmacophore generation (HypoGen algorithm) methodology in Discovery Studio. As the training set, 25 compounds were taken to generate a significant pharmacophore model. The selected pharmacophore Hypo1 was further validated by 12 compounds in the test set and was used as a query model for further screening of 1916 compounds containing 71 HIV-1 integrase inhibitors, 37 antibacterial inhibitors, 131 antiviral inhibitors and other 1677 approved drugs by the FDA. Then, six compounds (Hit01–Hit06) with estimated activity values less than 10 μM were subjected to ADMET study and toxicity assessment. Only one potential inhibitory ‘hit’ molecule (Hit01, raltegravir’s derivative) was further scrutinized by molecular docking analysis on the active site of PA_N endonuclease (PDB ID: 6E6W). Hit01 was utilized for designing novel potential PA_N endonuclease inhibitors through lead optimization, and then compounds were screened by pharmacophore Hypo1 and docking studies. Six raltegravir’s derivatives with significant estimated activity values and docking scores were obtained. Further, these results certainly do not confirm or indicate the seven compounds (Hit01, Hit07, Hit08, Hit09, Hit10, Hit11 and Hit12) have antiviral activity, and extensive wet-laboratory experimentation is needed to transmute these compounds into clinical drugs.

Advances in Development and Application of Influenza Vaccines

Influenza A virus is one of the most important zoonotic pathogens that can cause severe symptoms and has the potential to cause high number of deaths and great economic loss. Vaccination is still the best option to prevent influenza virus infection. Different types of influenza vaccines, including live attenuated virus vaccines, inactivated whole virus vaccines, virosome vaccines, split-virion vaccines and subunit vaccines have been developed. However, they have several limitations, such as the relatively high manufacturing cost and long production time, moderate efficacy of some of the vaccines in certain populations, and lack of cross-reactivity. These are some of the problems that need to be solved. Here, we summarized recent advances in the development and application of different types of influenza vaccines, including the recent development of viral vectored influenza vaccines. We also described the construction of other vaccines that are based on recombinant influenza viruses as viral vectors. Information provided in this review article might lead to the development of safe and highly effective novel influenza vaccines.

Locally Acquired Human Infection with Swine-Origin Influenza A(H3N2) Variant Virus, Australia, 2018

In 2018, a 15-year-old female adolescent in Australia was infected with swine influenza A(H3N2) variant virus. The virus contained hemagglutinin and neuraminidase genes derived from 1990s-like human seasonal viruses and internal protein genes from influenza A(H1N1)pdm09 virus, highlighting the potential risk that swine influenza A virus poses to human health in Australia.

Aryl and Arylalkyl Substituted 3-Hydroxypyridin-2(1H)-ones: Synthesis and Evaluation as Inhibitors of Influenza A Endonuclease

Seasonal influenza infections are associated with an estimated 250-500 000 deaths annually. Resistance to the antiviral M2 ion-channel inhibitors has largely invalidated their clinical utility. Resistance to neuraminidase inhibitors has also been observed in several influenza A virus (IAV) strains. These data have prompted research on inhibitors that target the cap-snatching endonuclease activity of the polymerase acidic protein (PA). Baloxavir marboxil (Xofluza®), recently approved for clinical use, inhibits cap-snatching endonuclease. Resistance to Xofluza® has been reported in both in vitro systems and in the clinic. An X-ray crystallographic screening campaign of a fragment library targeting IAV endonuclease identified 5-chloro-3-hydroxypyridin-2(1H)-one as a bimetal chelating agent at the active site. We have reported the structure-activity relationships for 3-hydroxypyridin-2(1H)-ones and 3-hydroxyquinolin-2(1H)-ones as endonuclease inhibitors. These studies identified two distinct binding modes associated with inhibition of this enzyme that are influenced by the presence of substituents at the 5- and 6-positions of 3-hydroxypyridin-2(1H)-ones. Herein we report the structure-activity relationships associated with various para-substituted 5-phenyl derivatives of 6-(p-fluorophenyl)-3-hydroxypyridin-2(1H)-ones and the effect of using naphthyl, benzyl, and naphthylmethyl groups as alternatives to the p-fluorophenyl substituent on their activity as endonuclease inhibitors.

Lack of selective resistance of influenza A virus in presence of host-targeted antiviral, UV-4B

Development of antiviral drug resistance is a continuous concern for viruses with high mutation rates such as influenza. The use of antiviral drugs targeting host proteins required for viral replication is less likely to result in the selection of resistant viruses than treating with direct-acting antivirals. The iminosugar UV-4B is a host-targeted glucomimetic that inhibits endoplasmic reticulum α-glucosidase I and II enzymes resulting in improper glycosylation and misfolding of viral glycoproteins. UV-4B has broad-spectrum antiviral activity against diverse viruses including dengue and influenza. To examine the ability of influenza virus to develop resistance against UV-4B, mouse-adapted influenza virus was passaged in mice in the presence or absence of UV-4B and virus isolated from lungs was used to infect the next cohort of mice, for five successive passages. Deep sequencing was performed to identify changes in the viral genome during passaging in the presence or absence of UV-4B. Relatively few minor variants were identified within each virus and the ratio of nonsynonymous to synonymous (dN/dS) substitutions of minor variants confirmed no apparent positive selection following sustained exposure to UV-4B. Three substitutions (one synonymous in PB2, one nonsynonymous in M and PA each) were specifically enriched (>3%) in UV-4B-treated groups at passage five. Recombinant viruses containing each individual or combinations of these nonsynonymous mutations remained sensitive to UV-4B treatment in mice. Overall, these data provide evidence that there is a high genetic barrier to the generation and selection of escape mutants following exposure to host-targeted iminosugar antivirals.

Antiviral Therapy for the Next Influenza Pandemic

Influenza antivirals will play a critical role in the treatment of outpatients and hospitalised patients in the next pandemic. In the past decade, a number of new influenza antivirals have been licensed for seasonal influenza, which can now be considered for inclusion into antiviral stockpiles held by the World Health Organization (WHO) and individual countries. However, data gaps remain regarding the effectiveness of new and existing antivirals in severely ill patients, and regarding which monotherapy or combinations of antivirals may yield the greatest improvement in outcomes. Regardless of the drug being used, influenza antivirals are most effective when treatment is initiated early in the course of infection, and therefore in a pandemic, effective strategies which enable rapid diagnosis and prompt delivery will yield the greatest benefits.

Repurposing host-based therapeutics to control coronavirus and influenza virus

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Drug repositioning is a cost- and time-efficient approach for new indications.

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Targeting host machineries, used by viruses, could develop broad-spectrum antivirals.

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Repurposing existing drugs could efficiently identify antiviral agents.

The development of highly effective antiviral agents has been a major objective in virology and pharmaceutics. Drug repositioning has emerged as a cost-effective and time-efficient alternative approach to traditional drug discovery and development. This new shift focuses on the repurposing of clinically approved drugs and promising preclinical drug candidates for the therapeutic development of host-based antiviral agents to control diseases caused by coronavirus and influenza virus. Host-based antiviral agents target host cellular machineries essential for viral infections or innate immune responses to interfere with viral pathogenesis. This review discusses current knowledge, prospective applications and challenges in the repurposing of clinically approved and preclinically studied drugs for newly indicated antiviral therapeutics.

Global Interactomics Connect Nuclear Mitotic Apparatus Protein NUMA1 to Influenza Virus Maturation

Influenza A virus (IAV) infections remain a major human health threat. IAV has enormous genetic plasticity and can rapidly escape virus-targeted anti-viral strategies. Thus, there is increasing interest to identify host proteins and processes the virus requires for replication and maturation. The IAV non-structural protein 1 (NS1) is a critical multifunctional protein that is expressed to high levels in infected cells. Host proteins that interact with NS1 may serve as ideal targets for attenuating IAV replication. We previously developed and characterized broadly cross-reactive anti-NS1 monoclonal antibodies. For the current study, we used these mAbs to co-immunoprecipitate native IAV NS1 and interacting host proteins; 183 proteins were consistently identified in this NS1 interactome study, 124 of which have not been previously reported. RNAi screens identified 11 NS1-interacting host factors as vital for IAV replication. Knocking down one of these, nuclear mitotic apparatus protein 1 (NUMA1), dramatically reduced IAV replication. IAV genomic transcription and translation were not inhibited but transport of viral structural proteins to the cell membrane was hindered during maturation steps in NUMA1 knockdown (KD) cells.

The Cranberry Extract Oximacro® Exerts in vitro Virucidal Activity Against Influenza Virus by Interfering With Hemagglutinin

The defense against influenza virus (IV) infections still poses a series of challenges. The current antiviral arsenal against influenza viruses is in fact limited; therefore, the development of new anti-influenza strategies effective against antigenically different viruses is an urgent priority. Bioactive compounds derived from medicinal plants and fruits may provide a natural source of candidates for such broad-spectrum antivirals. In this regard, cranberry (Vaccinium macrocarpon Aiton) extracts on the basis of their recognized anti-adhesive activities against bacteria, may provide potential compounds able to prevent viral attachment to target cells. Nevertheless, only few studies have so far investigated the possible use of cranberry extracts as an antiviral tool. This study focuses on the suitability of a cranberry extract as a direct-acting anti-influenza compound. We show that the novel cranberry extract Oximacro® inhibits influenza A and B viruses (IAV, IBV) replication in vitro because of its high content of A-type proanthocyanidins (PAC-A) dimers and trimers. Mechanistic studies revealed that Oximacro® prevents attachment and entry of IAV and IBV into target cells and exerts a virucidal activity. Oximacro® was observed to interact with the ectodomain of viral hemagglutinin (HA) glycoprotein, thus suggesting the interference with HA functions and a consequent loss of infectivity of IV particles. Fluorescence spectroscopy revealed a reduction in the intrinsic fluorescence of HA protein after incubation with purified dimeric PAC-A (PAC-A2), thus confirming a direct interaction between HA and Oximacro® PAC-A2. In silico docking simulations further supported the in vitro results and indicated that among the different components of the Oximacro® chemical profile, PAC-A2 exhibited the best binding propensity with an affinity below 10 nM. The role of PAC-A2 in the anti-IV activity of Oximacro® was eventually confirmed by the observation that it prevented IAV and IVB replication and caused the loss of infectivity of IV particles, thus indicating PAC-A2 as the major active component of Oximacro®. As a whole, these results suggest Oximacro® as a potential candidate to create novel antiviral agents of natural origin for the prevention of IV infections.

Detection of adamantane-sensitive influenza A(H3N2) viruses in Australia, 2017: a cause for hope?

For over a decade virtually all A(H3N2) influenza viruses have been resistant to the adamantane class of antivirals. However, during the 2017 influenza season in Australia, 15/461 (3.3%) adamantane-sensitive A(H3N2) viruses encoding serine at residue 31 of the M2 protein were detected, more than the total number identified globally during the last 6 years. A return to wide circulation of adamantane-sensitive A(H3N2) viruses would revive the option of using these drugs for treatment and prophylaxis.

Regulation of influenza virus replication by Wnt/β-catenin signaling

Wnt/β-catenin signaling is an essential pathway in cell cycle control. Dysregulation of the Wnt/β-catenin signaling pathway during viral infection has been reported. In this study, we examined the effect of modulating Wnt/β-catenin signaling during influenza virus infection. The activation of the Wnt/β-catenin pathway by Wnt3a increased influenza virus mRNA and virus production in in vitro in mouse lung epithelial E10 cells and mRNA expresson of influenza virus genes in vivo in the lungs of mice infected with influenza virus A/Puerto Rico/8/34. However, the inhibition of Wnt/β-catenin signaling by iCRT14 reduced virus titer and viral gene expression in human lung epithelial A549 cells and viral replication in primary mouse alveolar epithelial cells infected with different influenza virus strains. Knockdown of β-catenin also reduced viral protein expression and virus production. iCRT14 acts at the early stage of virus replication. Treatment with iCRT14 inhibited the expression of the viral genes (vRNA, cRNA and mRNA) evaluated in this study. The intraperitoneal administration of iCRT14 reduced viral load, improved clinical signs, and partially protected mice from influenza virus infection.

Cell Cycle-independent Role of Cyclin D3 in Host Restriction of Influenza Virus Infection

To identify new host factors that modulate the replication of influenza A virus, we performed a yeast two-hybrid screen using the cytoplasmic tail of matrix protein 2 from the highly pathogenic H5N1 strain. The screen revealed a high-score interaction with cyclin D3, a key regulator of cell cycle early G₁ phase. M2-cyclin D3 interaction was validated through GST pull-down and recapitulated in influenza A/WSN/33-infected cells. Knockdown of Ccnd3 by small interfering RNA significantly enhanced virus progeny titers in cell culture supernatants. Interestingly, the increase in virus production was due to cyclin D3 deficiency per se and not merely a consequence of cell cycle deregulation. A combined knockdown of Ccnd3 and Rb1, which rescued cell cycle progression into S phase, failed to normalize virus production. Infection by influenza A virus triggered redistribution of cyclin D3 from the nucleus to the cytoplasm, followed by its proteasomal degradation. When overexpressed in HEK 293T cells, cyclin D3 impaired binding of M2 with M1, which is essential for proper assembly of progeny virions, lending further support to its role as a putative restriction factor. Our study describes the identification and characterization of cyclin D3 as a novel interactor of influenza A virus M2 protein. We hypothesize that competitive inhibition of M1-M2 interaction by cyclin D3 impairs infectious virion formation and results in attenuated virus production. In addition, we provide mechanistic insights into the dynamic interplay of influenza virus with the host cell cycle machinery during infection.

An M2-V27A channel blocker demonstrates potent in vitro and in vivo antiviral activities against amantadine-sensitive and -resistant influenza A viruses

Adamantanes such as amantadine (1) and rimantadine (2) are FDA-approved anti-influenza drugs that act by inhibiting the wild-type M2 proton channel from influenza A viruses, thereby inhibiting the uncoating of the virus. Although adamantanes have been successfully used for more than four decades, their efficacy was curtailed by emerging drug resistance. Among the limited number of M2 mutants that confer amantadine resistance, the M2-V27A mutant was found to be the predominant mutant under drug selection pressure, thereby representing a high profile antiviral drug target. Guided by molecular dynamics simulations, we previously designed first-in-class M2-V27A inhibitors. One of the potent lead compounds, spiroadamantane amine (3), inhibits both the M2-WT and M2-V27A mutant with IC₅₀ values of 18.7 and 0.3 μM, respectively, in in vitro electrophysiological assays. Encouraged by these findings, in this study we further examine the in vitro and in vivo antiviral activity of compound 3 in inhibiting both amantadine-sensitive and -resistant influenza A viruses. Compound 3 not only had single to sub-micromolar EC₅₀ values against M2-WT- and M2-V27A-containing influenza A viruses in antiviral assays, but also rescued mice from lethal viral infection by either M2-WT- or M2-V27A-containing influenza A viruses. In addition, we report the design of two analogs of compound 3, and one was found to have improved in vitro antiviral activity over compound 3. Collectively, this study represents the first report demonstrating the in vivo antiviral efficacy of inhibitors targeting M2 mutants. The results suggest that inhibitors targeting drug-resistant M2 mutants are promising antiviral drug candidates worthy of further development.

Identification and Characterization of Influenza Virus Entry Inhibitors through Dual Myxovirus High-Throughput Screening

Influenza A virus (IAV) infections cause major morbidity and mortality, generating an urgent need for novel antiviral therapeutics. We recently established a dual myxovirus high-throughput screening protocol that combines a fully replication-competent IAV-WSN strain and a respiratory syncytial virus reporter strain for the simultaneous identification of IAV-specific, paramyxovirus-specific, and broad-spectrum inhibitors. In the present study, this protocol was applied to a screening campaign to assess a diverse chemical library with over 142,000 entries. Focusing on IAV-specific hits, we obtained a hit rate of 0.03% after cytotoxicity testing and counterscreening. Three chemically distinct hit classes with nanomolar potency and favorable cytotoxicity profiles were selected. Time-of-addition, minigenome, and viral entry studies demonstrated that these classes block hemagglutinin (HA)-mediated membrane fusion. Antiviral activity extends to an isolate from the 2009 pandemic and, in one case, another group 1 subtype. Target identification through biolayer interferometry confirmed binding of all hit compounds to HA. Resistance profiling revealed two distinct escape mechanisms: primary resistance, associated with reduced compound binding, and secondary resistance, associated with unaltered binding. Secondary resistance was mediated, unusually, through two different pairs of cooperative mutations, each combining a mutation eliminating the membrane-proximal stalk N-glycan with a membrane-distal change in HA1 or HA2. Chemical synthesis of an analog library combined with in silico docking extracted a docking pose for the hit classes. Chemical interrogation spotlights IAV HA as a major druggable target for small-molecule inhibition. Our study identifies novel chemical scaffolds with high developmental potential, outlines diverse routes of IAV escape from entry inhibition, and establishes a path toward structure-aided lead development.

IMPORTANCE

This study is one of the first to apply a fully replication-competent third-generation IAV reporter strain to a large-scale high-throughput screen (HTS) drug discovery campaign, allowing multicycle infection and screening in physiologically relevant human respiratory cells. A large number of potential druggable targets was thus chemically interrogated, but mechanistic characterization, positive target identification, and resistance profiling demonstrated that three chemically promising and structurally distinct hit classes selected for further analysis all block HA-mediated membrane fusion. Viral escape from inhibition could be achieved through primary and secondary resistance mechanisms. In silico docking predicted compound binding to a microdomain located at the membrane-distal site of the prefusion HA stalk that was also previously suggested as a target site for chemically unrelated HA inhibitors. This study identifies an unexpected chemodominance of the HA stalk microdomain for small-molecule inhibitors in IAV inhibitor screening campaigns and highlights a novel mechanism of cooperative resistance to IAV entry blockers.

Influenza A Virus in Backyard Pigs and Poultry in Rural Cambodia

Surveillance of influenza virus in humans and livestock is critical, given the worldwide public health threats and livestock production losses. Livestock farming involving close proximity between humans, pigs and poultry is often practised by smallholders in low-income countries and is considered an important driver of influenza virus evolution. This study determined the prevalence and genetic characteristics of influenza A virus (IAV) in backyard pigs and poultry in Cambodia. A total of 751 animals were tested by matrix gene-based rRT-PCR, and influenza virus was detected in 1.5% of sampled pigs, 1.4% of chickens and 1.0% of ducks, but not in pigeons. Full-length genome sequencing confirmed triple reassortant H3N2 in all IAV-positive pigs and various low pathogenic avian influenza subtypes in poultry. Phylogenetic analysis of the swine influenza viruses revealed that these had haemagglutinin and neuraminidase genes originating from human H3N2 viruses previously isolated in South-East Asia. Phylogenetic analysis also revealed that several of the avian influenza subtypes detected were closely related to internal viral genes from highly pathogenic H5N1 and H9N2 formerly sequenced in the region. High sequence homology was likewise found with influenza A viruses circulating in pigs, poultry and wild birds in China and Vietnam, suggesting transboundary introduction and cocirculation of the various influenza subtypes. In conclusion, highly pathogenic subtypes of influenza virus seem rare in backyard poultry, but virus reassortment, involving potentially zoonotic and pandemic subtypes, appears to occur frequently in smallholder pigs and poultry. Increased targeted surveillance and monitoring of influenza circulation on smallholdings would further improve understanding of the transmission dynamics and evolution of influenza viruses in humans, pigs and poultry in the Mekong subregion and could contribute to limit the influenza burden.

Coupling high-throughput genetics with phylogenetic information reveals an epistatic interaction on the influenza A virus M segment

Background

Epistasis is one of the central themes in viral evolution due to its importance in drug resistance, immune escape, and interspecies transmission. However, there is a lack of experimental approach to systematically probe for epistatic residues.

Results

By utilizing the information from natural occurring sequences and high-throughput genetics, this study established a novel strategy to identify epistatic residues. The rationale is that a substitution that is deleterious in one strain may be prevalent in nature due to the presence of a naturally occurring compensatory substitution. Here, high-throughput genetics was applied to influenza A virus M segment to systematically identify deleterious substitutions. Comparison with natural sequence variation showed that a deleterious substitution M1 Q214H was prevalent in circulating strains. A coevolution analysis was then performed and indicated that M1 residues 121, 207, 209, and 214 naturally coevolved as a group. Subsequently, we experimentally validated that M1 A209T was a compensatory substitution for M1 Q214H.

Conclusions

This work provided a proof-of-concept to identify epistatic residues by coupling high-throughput genetics with phylogenetic information. In particular, we were able to identify an epistatic interaction between M1 substitutions A209T and Q214H. This analytic strategy can potentially be adapted to study any protein of interest, provided that the information on natural sequence variants is available.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2358-7) contains supplementary material, which is available to authorized users.

Repurposing Kinase Inhibitors as Antiviral Agents to Control Influenza A Virus Replication

Influenza A virus (IAV) infection causes seasonal epidemics of contagious respiratory illness that causes substantial morbidity and some mortality. Regular vaccination is the principal strategy for controlling influenza virus, although vaccine efficacy is variable. IAV antiviral drugs are available; however, substantial drug resistance has developed to two of the four currently FDA-approved antiviral drugs. Thus, new therapeutic approaches are being sought to reduce the burden of influenza-related disease. A high-throughput screen using a human kinase inhibitor library was performed targeting an emerging IAV strain (H7N9) in A549 cells. The inhibitor library contained 273 structurally diverse, active cell permeable kinase inhibitors with known bioactivity and safety profiles, many of which are at advanced stages of clinical development. The current study shows that treatment of human A549 cells with kinase inhibitors dinaciclib, flavopiridol, or PIK-75 exhibits potent antiviral activity against H7N9 IAV as well as other IAV strains. Thus, targeting host kinases can provide a broad-spectrum therapeutic approach against IAV. These findings provide a path forward for repurposing existing kinase inhibitors safely as potential antivirals, particularly those that can be tested in vivo and ultimately for clinical use.

Favipiravir inhibits acetaminophen sulfate formation but minimally affects systemic pharmacokinetics of acetaminophen

Aims

The antiviral agent favipiravir is likely to be co-prescribed with acetaminophen (paracetamol). The present study evaluated the possiblility of a pharmacokinetic interaction between favipiravir and acetaminophen, in vitro and in vivo.

Methods

The effect of favipivir on the transformation of acetaminophen to its glucuronide and sulfate metabolites was studied using a pooled human hepatic S9 fraction in vitro. The effect of acute and extended adminstration of favipiravir on the pharmacokinetics of acetaminophen and metabolites was evaluated in human volunteers.

Results

Favipiravir inhibited the in vitro formation of acetaminophen sulfate, but not acetaminophen glucuronide. In human volunteers, both acute (1 day) and extended (6 days) administration of favipiravir slightly but significantly increased (by about 20 %) systemic exposure to acetaminophen (total AUC), whereas C_max was not significantly changed. AUC for acetaminophen glucuronide was increased by 23 to 35 % above control by favipiravir, while AUC for acetaminophen sulfate was reduced by about 20 % compared to control. Urinary excretion of acetaminophen sulfate was likewise reduced to 44 to 65 % of control values during favipiravir co-administration, while excretion of acetaminophen glucuronide increased to 17 to 32 % above control.

Conclusion

Favipiravir inhibits acetaminophen sulfate formation in vitro and in vivo. However the increase in systemic exposure to acetaminophen due to favipiravir co-administration, though statistically significant, is small in magnitude and unlikely to be of clinical importance.

Characterization of potent fusion inhibitors of influenza virus

New inhibitors of influenza viruses are needed to combat the potential emergence of novel human influenza viruses. We have identified a class of small molecules that inhibit replication of influenza virus at picomolar concentrations in plaque reduction assays. The compound also inhibits replication of vesicular stomatitis virus. Time of addition and dilution experiments with influenza virus indicated that an early time point of infection was blocked and that inhibitor 136 tightly bound to virions. Using fluorescently labeled influenza virus, inhibition of viral fusion to cellular membranes by blocked lipid mixing was established as the mechanism of action for this class of inhibitors. Stabilization of the neutral pH form of hemagglutinin (HA) was ruled out by trypsin digestion studies in vitro and with conformation specific HA antibodies within cells. Direct visualization of 136 treated influenza virions at pH 7.5 or acidified to pH 5.0 showed that virions remain intact and that glycoproteins become disorganized as expected when HA undergoes a conformational change. This suggests that exposure of the fusion peptide at low pH is not inhibited but lipid mixing is inhibited, a different mechanism than previously reported fusion inhibitors. We hypothesize that this new class of inhibitors intercalate into the virus envelope altering the structure of the viral envelope required for fusion to cellular membranes.

Adamantane-resistant influenza a viruses in the world (1902-2013): frequency and distribution of M2 gene mutations

Adamantanes (amantadine and rimantadine) have been used to prevent and treat influenza A virus infections for many years; however, resistance to these drugs has been widely reported in the world. To investigate the frequency and distribution of M2 gene mutations in adamantane-resistant influenza variants circulated in the world between 1902 and 2013, 31251 available M2 protein sequences from different HA-subtype influenza A viruses (H1–H17) were analyzed and adamantane resistance-associated mutations were compared (L26F, V27A, A30T, A30V, S31N, G34E, and L38F). We find that 45.2% (n = 14132) of influenza A (H1–H17) viruses circulating globally were resistant to adamantanes, and the vast majority of resistant viruses (95%) bear S31N mutations. Whereas, only about 1% have V27A mutations and other mutations (L26F, A30T, G34E, and L38F) were extremely rare (their prevalence appeared to be < 0.2%). Our results confirm that H1, H3, H5, H7, H9, and H17 subtype influenza A viruses exhibit high-level resistance to adamantanes. In contrast, the appearance of adamantane-resistant mutants in H2, H4, H6, H10, and H11 subtypes was rare. However, no adamantane resistance viruses were identified among other HA subtypes (H8, H12–H16). Our findings indicate that the frequency and distribution of adamantane-resistant influenza variants varied among different HA subtypes, host species, years of isolation, and geographical areas. This comprehensive study raises concerns about the increasing prevalence of adamantane-resistant influenza A viruses and highlights the importance of monitoring the emergence and worldwide spread of adamantane-resistant variants.

A monoclonal antibody binds to threonine 49 in the non-structural 1 protein of influenza A virus and interferes with its ability to modulate viral replication

The emergence of resistant influenza A viruses highlights the continuous requirement of new antiviral drugs that can treat the viral infection. Non-structural 1 (NS1) protein, an indispensable component for efficient virus replication, can be used as a potential target for generating new antiviral agents. Here, we study the interaction of 2H6 monoclonal antibody with NS1 protein and also determine whether influenza virus replication can be inhibited by blocking NS1. The 2H6-antigen binding fragment (Fab) forms a multimeric complex with the NS1 RNA-binding domain (RBD). T49, a residue which forms a direct hydrogen bond with double stranded RNA, in NS1 protein was found to be critical for its interaction with 2H6 antibody. NS1(RBD) has high affinity to 2H6 with KD of 43.5±4.24nM whereas NS1(RBD)-T49A has more than 250 times lower affinity towards 2H6. Interestingly, the intracellular expression of 2H6-single-chain variable fragment (scFv) in mammalian cells caused a reduction in viral growth and the M1 viral protein level was significantly reduced in 2H6-scFv transfected cells in comparison to vector transfected cells at 12h post infection. These results indicate that the tight binding of 2H6 to NS1 could lead to reduction in viral replication and release of progeny virus. In future, 2H6 antibody in combination with other neutralizing antibodies can be used to increase the potency of viral inhibition.

Phenyl substituted 4-hydroxypyridazin-3(2H)-ones and 5-hydroxypyrimidin-4(3H)-ones: inhibitors of influenza A endonuclease

Seasonal and pandemic influenza outbreaks remain a major human health problem. Inhibition of the endonuclease activity of influenza RNA-dependent RNA polymerase is attractive for the development of new agents for the treatment of influenza infection. Our earlier studies identified a series of 5- and 6-phenyl substituted 3-hydroxypyridin-2(1H)-ones that were effective inhibitors of influenza endonuclease. These agents identified as bimetal chelating ligands binding to the active site of the enzyme. In the present study, several aza analogues of these phenyl substituted 3-hydroxypyridin-2(1H)-one compounds were synthesized and evaluated for their ability to inhibit the endonuclease activity. In contrast to the 4-aza analogue of 6-(4-fluorophenyl)-3-hydroxypyridin-2(1H)-one, the 5-aza analogue (5-hydroxy-2-(4-fluorophenyl)pyrimidin-4(3H)-one) did exhibit significant activity as an endonuclease inhibitor. The 6-aza analogue of 5-(4-fluorophenyl)-3-hydroxypyridin-2(1H)-one (6-(4-fluorophenyl)-4-hydroxypyridazin-3(2H)-one) also retained modest activity as an inhibitor. Several varied 6-phenyl-4-hydroxypyridazin-3(2H)-ones and 2-phenyl-5-hydroxypyrimidin-4(3H)-ones were synthesized and evaluated as endonuclease inhibitors. The SAR observed for these aza analogues are consistent with those previously observed with various phenyl substituted 3-hydroxypyridin-2(1H)-ones.

Virus-vectored influenza virus vaccines

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.

Novel hemagglutinin-based influenza virus inhibitors

Influenza virus has caused seasonal epidemics and worldwide pandemics, which caused tremendous loss of human lives and socioeconomics. Nowadays, only two classes of anti-influenza drugs, M2 ion channel inhibitors and neuraminidase inhibitors respectively, are used for prophylaxis and treatment of influenza virus infection. Unfortunately, influenza virus strains resistant to one or all of those drugs emerge frequently. Hemagglutinin (HA), the glycoprotein in influenza virus envelope, plays a critical role in viral binding, fusion and entry processes. Therefore, HA is a promising target for developing anti-influenza drugs, which block the initial entry step of viral life cycle. Here we reviewed recent understanding of conformational changes of HA in protein folding and fusion processes, and the discovery of HA-based influenza entry inhibitors, which may provide more choices for preventing and controlling potential pandemics caused by multi-resistant influenza viruses.

Matriptase proteolytically activates influenza virus and promotes multicycle replication in the human airway epithelium

Influenza viruses do not encode any proteases and must rely on host proteases for the proteolytic activation of their surface hemagglutinin proteins in order to fuse with the infected host cells. Recent progress in the understanding of human proteases responsible for influenza virus hemagglutinin activation has led to the identification of members of the type II transmembrane serine proteases TMPRSS2 and TMPRSS4 and human airway trypsin-like protease; however, none has proved to be the sole enzyme responsible for hemagglutinin cleavage. In this study, we identify and characterize matriptase as an influenza virus-activating protease capable of supporting multicycle viral replication in the human respiratory epithelium. Using confocal microscopy, we found matriptase to colocalize with hemagglutinin at the apical surface of human epithelial cells and within endosomes, and we showed that the soluble form of the protease was able to specifically cleave hemagglutinins from H1 virus, but not from H2 and H3 viruses, in a broad pH range. We showed that small interfering RNA (siRNA) knockdown of matriptase in human bronchial epithelial cells significantly blocked influenza virus replication in these cells. Lastly, we provide a selective, slow, tight-binding inhibitor of matriptase that significantly reduces viral replication (by 1.5 log) of H1N1 influenza virus, including the 2009 pandemic virus. Our study establishes a three-pronged model for the action of matriptase: activation of incoming viruses in the extracellular space in its shed form, upon viral attachment or exit in its membrane-bound and/or shed forms at the apical surface of epithelial cells, and within endosomes by its membrane-bound form where viral fusion takes place.

Increasing oral absorption of polar neuraminidase inhibitors: a prodrug transporter approach applied to oseltamivir analogue

Poor oral absorption is one of the limiting factors in utilizing the full potential of polar antiviral agents. The neuraminidase target site requires a polar chemical structure for high affinity binding, thus limiting oral efficacy of many high affinity ligands. The aim of this study was to overcome this poor oral absorption barrier, utilizing prodrug to target the apical brush border peptide transporter 1 (PEPT1). Guanidine oseltamivir carboxylate (GOCarb) is a highly active polar antiviral agent with insufficient oral bioavailability (4%) to be an effective therapeutic agent. In this report we utilize a carrier-mediated targeted prodrug approach to improve the oral absorption of GOCarb. Acyloxy(alkyl) ester based amino acid linked prodrugs were synthesized and evaluated as potential substrates of mucosal transporters, e.g., PEPT1. Prodrugs were also evaluated for their chemical and enzymatic stability. PEPT1 transport studies included [(3)H]Gly-Sar uptake inhibition in Caco-2 cells and cellular uptake experiments using HeLa cells overexpressing PEPT1. The intestinal membrane permeabilities of the selected prodrugs and the parent drug were then evaluated for epithelial cell transport across Caco-2 monolayers, and in the in situ rat intestinal jejunal perfusion model. Prodrugs exhibited a pH dependent stability with higher stability at acidic pHs. Significant inhibition of uptake (IC(50) <1 mM) was observed for l-valyl and l-isoleucyl amino acid prodrugs in competition experiments with [(3)H]Gly-Sar, indicating a 3-6 times higher affinity for PEPT1 compared to valacyclovir, a well-known PEPT1 substrate and >30-fold increase in affinity compared to GOCarb. The l-valyl prodrug exhibited significant enhancement of uptake in PEPT1/HeLa cells and compared favorably with the well-absorbed valacyclovir. Transepithelial permeability across Caco-2 monolayers showed that these amino acid prodrugs have a 2-5-fold increase in permeability as compared to the parent drug and showed that the l-valyl prodrug (P(app) = 1.7 × 10(-6) cm/s) has the potential to be rapidly transported across the epithelial cell apical membrane. Significantly, only the parent drug (GOCarb) appeared in the basolateral compartment, indicating complete activation (hydrolysis) during transport. Intestinal rat jejunal permeability studies showed that l-valyl and l-isoleucyl prodrugs are highly permeable compared to the orally well absorbed metoprolol, while the parent drug had essentially zero permeability in the jejunum, consistent with its known poor low absorption. Prodrugs were rapidly converted to parent in cell homogenates, suggesting their ability to be activated endogenously in the epithelial cell, consistent with the transport studies. Additionally, l-valyl prodrug was found to be a substrate for valacyclovirase (K(m) = 2.37 mM), suggesting a potential cell activation mechanism. Finally we determined the oral bioavailability of our most promising candidate, GOC-l-Val, in mice to be 23% under fed conditions and 48% under fasted conditions. In conclusion, GOC-l-Val prodrug was found to be a very promising antiviral agent for oral delivery. These findings indicate that the carrier-mediated prodrug approach is an excellent strategy for improving oral absorption of polar neuraminidase inhibitors. These promising results demonstrate that the oral peptide transporter-mediated prodrug strategy has enormous promise for improving the oral mucosal cell membrane permeability of polar, poorly absorbed antiviral agents and treating influenza via the oral route of administration.

Small molecule inhibitors of influenza A and B viruses that act by disrupting subunit interactions of the viral polymerase

Influenza viruses are the cause of yearly epidemics and occasional pandemics that represent a significant challenge to public health. Current control strategies are imperfect and there is an unmet need for new antiviral therapies. Here, we report the identification of small molecule compounds able to effectively and specifically inhibit growth of influenza A and B viruses in cultured cells through targeting an assembly interface of the viral RNA-dependent RNA polymerase. Using an existing crystal structure of the primary protein-protein interface between the PB1 and PA subunits of the influenza A virus polymerase, we conducted an in silico screen to identify potential small molecule inhibitors. Selected compounds were then screened for their ability to inhibit the interaction between PB1 and PA in vitro using an ELISA-based assay and in cells, to inhibit nuclear import of a binary PB1-PA complex as well as transcription by the full viral ribonucleoprotein complex. Two compounds emerged as effective inhibitors with IC(50) values in the low micromolar range and negligible cytotoxicity. Of these, one compound also acted as a potent replication inhibitor of a variety of influenza A virus strains in Madin-Darby canine kidney (MDCK) cells, including H3N2 and H1N1 seasonal and 2009 pandemic strains. Importantly, this included an oseltamivir-resistant isolate. Furthermore, potent inhibition of influenza B viruses but not other RNA or DNA viruses was seen. Overall, these compounds provide a foundation for the development of a new generation of therapeutic agents exhibiting high specificity to influenza A and B viruses.

Clinical effectiveness of peramivir in comparison with other neuraminidase inhibitors in pediatric influenza patients

The currently used antivirals in the treatment of influenza in Japan include amantadine, oseltamivir, zanamivir, laninamivir, and peramivir. We compared the efficacy of intravenous peramivir with that of other neuraminidase inhibitors for treating pediatric influenza. The present study included 223 influenza patients (≤18 years) who presented at the Hikita Pediatric Clinic between February and April 2011. We compared fever duration after starting treatment with antiviral drugs. Because inhalation drugs are difficult to use in <5-year-old patients and because of the potential adverse effects of oseltamivir in teenagers, we created two different age groups (<10-year-old group and 5–18-year-old group) to evaluate treatment results. In influenza A patients between 5 and 18 years old, the median fever duration after treatment with zanamivir was 2 days, compared with 1 day for peramivir (P = 0.0242). In influenza B patients between 5 and 18 years old, the median fever duration after treatment with laninamivir was 3 days, compared with 1 day for peramivir (P = 0.0097). We found no significant difference for any of the other combinations of drug/disease type/age groups. No adverse effects were observed with the antiviral drugs used. The results suggest that peramivir is very useful in pediatric influenza patients.

In vitro anti-influenza virus activity of a cardiotonic glycoside from Adenium obesum (Forssk.)

Methanolic extracts of six Saudi plants were screened for their in vitro antiviral activity using influenza virus A/PR/8/34 (H1N1) and MDCK cells in an MTT assay. The results indicated that the extracts of Adeniumobesum and Tephorosianubica possessed antiviral activity (99.3 and 93.3% inhibition at the concentration of 10 μg/ml, respectively). Based on these results A. obesum was selected for further study by applying bioactivity-guided fractionation to isolate its antiviral principle. The antiviral principle was isolated from the chloroform fraction through solvent fractionation, combined open liquid chromatography and HPLC. The isolated active compound A was identified as oleandrigenin-β-D-glucosyl (1→4)-β-D-digitalose, on the basis of its spectral analysis (MS, 1D and 2D NMR). The isolated glycoside showed reduction of virus titre by 69.3% inhibition at concentration of 1 μg/ml (IC(50)=0.86 μg/ml).

Potent neutralization of influenza A virus by a single-domain antibody blocking M2 ion channel protein

Influenza A virus poses serious health threat to humans. Neutralizing antibodies against the highly conserved M2 ion channel is thought to offer broad protection against influenza A viruses. Here, we screened synthetic Camel single-domain antibody (VHH) libraries against native M2 ion channel protein. One of the isolated VHHs, M2-7A, specifically bound to M2-expressed cell membrane as well as influenza A virion, inhibited replication of both amantadine-sensitive and resistant influenza A viruses in vitro, and protected mice from a lethal influenza virus challenge. Moreover, M2-7A showed blocking activity for proton influx through M2 ion channel. These pieces of evidence collectively demonstrate for the first time that a neutralizing antibody against M2 with broad specificity is achievable, and M2-7A may have potential for cross protection against a number of variants and subtypes of influenza A viruses.

Antiviral drugs for viruses other than human immunodeficiency virus

Most viral diseases, with the exception of those caused by human immunodeficiency virus, are self-limited illnesses that do not require specific antiviral therapy. The currently available antiviral drugs target 3 main groups of viruses: herpes, hepatitis, and influenza viruses. With the exception of the antisense molecule fomivirsen, all antiherpes drugs inhibit viral replication by serving as competitive substrates for viral DNA polymerase. Drugs for the treatment of influenza inhibit the ion channel M(2) protein or the enzyme neuraminidase. Combination therapy with Interferon-α and ribavirin remains the backbone treatment for chronic hepatitis C; the addition of serine protease inhibitors improves the treatment outcome of patients infected with hepatitis C virus genotype 1. Chronic hepatitis B can be treated with interferon or a combination of nucleos(t)ide analogues. Notably, almost all the nucleos(t) ide analogues for the treatment of chronic hepatitis B possess anti-human immunodeficiency virus properties, and they inhibit replication of hepatitis B virus by serving as competitive substrates for its DNA polymerase. Some antiviral drugs possess multiple potential clinical applications, such as ribavirin for the treatment of chronic hepatitis C and respiratory syncytial virus and cidofovir for the treatment of cytomegalovirus and other DNA viruses. Drug resistance is an emerging threat to the clinical utility of antiviral drugs. The major mechanisms for drug resistance are mutations in the viral DNA polymerase gene or in genes that encode for the viral kinases required for the activation of certain drugs such as acyclovir and ganciclovir. Widespread antiviral resistance has limited the clinical utility of M(2) inhibitors for the prevention and treatment of influenza infections. This article provides an overview of clinically available antiviral drugs for the primary care physician, with a special focus on pharmacology, clinical uses, and adverse effects.

Structure-based drug design of a new chemical class of small molecules active against influenza A nucleoprotein in vitro and in vivo

We report preliminary results and a summary of a bottom-up approach to identify new, active, nontoxic, small-molecule antivirals designed to have а novel mechanism of action. We employed the procedure to identify 3-mercapto-1,2,4-triazoles derivatives as potential NP inhibitors in silico and subsequently demonstrated the in vitro efficacy of the molecules against various strains of the influenza A virus. The most efficacious compounds were successfully tested in an in vivo influenza challenge experiment.

Antiviral activity of the effective monomers from Folium Isatidis against influenza virus in vivo

In order to evaluate the anti-influenza virus activity of the effective monomer from Folium Isatidis (FI) in vivo, we established mice model with viral pneumonia and divided them into 3 different dose groups, then observed their lung indexes, pulmonary pathological changes, pulmonary virus hemagglitination titers, living time and death rates. The results showed that the monomer could reduce the pulmonary index from 2.64 to 1.93, 1.63 and 1.40 (P<0.01) and decrease the hemagglitination titer from 1.15 to 0.84, 0.70 and 0.59 (P<0.01). In addition, different groups of FI could significantly lessen the mortality rate from 100% to 30%, 25% and 15%, and prolong the living time from 5.1d to 6.5d, 8.4d and 8.9 d respectively(P<0.01). The high dose (75 mg/kg/d) has the similar effect with 100 mg/kg/d dose of virazole(P>0.05), and more effective than 200 mg/kg/d dose of antiviral liquor (P<0.05).

Phenotypic and genotypic characterization of influenza virus mutants selected with the sialidase fusion protein DAS181

BACKGROUND

influenza viruses (IFVs) frequently achieve resistance to antiviral drugs, necessitating the development of compounds with novel mechanisms of action. DAS181 (Fludase), a sialidase fusion protein, may have a reduced potential for generating drug resistance due to its novel host-targeting mechanism of action.

METHODS

IFV strains B/Maryland/1/59 and A/Victoria/3/75 (H3N2) were subjected to >30 passages under increasing selective pressure with DAS181. The DAS181-selected IFV isolates were characterized in vitro and in mice.

RESULTS

despite extensive passaging, DAS181-selected viruses exhibited a very low level of resistance to DAS181, which ranged between 3- and 18-fold increase in EC(50). DAS181-selected viruses displayed an attenuated phenotype in vitro, as exhibited by slower growth, smaller plaque size and increased particle to pfu ratios relative to wild-type virus. Further, the DAS181 resistance phenotype was unstable and was substantially reversed over time upon DAS181 withdrawal. In mice, the DAS181-selected viruses exhibited no greater virulence than their wild-type counterparts. Genotypic and phenotypic analysis of DAS181-selected viruses revealed mutations in the haemagglutinin (HA) and neuraminidase (NA) molecules and also changes in HA and NA function.

CONCLUSIONS

results indicate that resistance to DAS181 is minimal and unstable. The DAS181-selected IFV isolates exhibit reduced fitness in vitro, likely due to altered HA and NA functions.

Inhibitory effects of baicalein on the influenza virus in vivo is determined by baicalin in the serum

Baicalein, an extract from Scutellaria baicalensis, was evaluated for its ability to inhibit the influenza virus in vivo. Oral administration of baicalein to BALB/c mice infected with the influenza A/FM1/1/47(H1N1) virus showed significant effects in preventing death, increasing the mean time to death, inhibiting lung consolidation, and reducing the lung virus titer in a dose-dependent manner. These effects are believed to be due to baicalin, the metabolite of baicalein in the serum. At a concentration of baicalin 2 microg/ml in overlay medium, it showed significant inhibition in the plaque assay, and the mean IC(50) value of baicalin was calculated as 1.2 microg/ml in the cytopathic effect assay. Our results showed that baicalein warrants further research as a potential antiinfluenza viral agent.

Antiviral properties, metabolism, and pharmacokinetics of a novel azolo-1,2,4-triazine-derived inhibitor of influenza A and B virus replication

Influenza viruses of types A and B cause periodic pandemics in the human population. The antiviral drugs approved to combat influenza virus infections are currently limited. We have investigated an effective novel inhibitor of human influenza A and B viruses, triazavirine [2-methylthio-6-nitro-1,2,4-triazolo[5,1-c]-1,2,4-triazine-7(4I)-one] (TZV). TZV suppressed the replication of influenza virus in cell culture and in chicken chorioallantoic membranes, and it protected mice from death caused by type A and B influenza viruses. TZV was also effective against a rimantadine-resistant influenza virus strain and against avian influenza A virus H5N1 strains. The pharmacokinetic parameters and bioavailability of TZV were calculated after the administration of TZV to rabbits. The TZV metabolite AMTZV [2-methylthio-6-amino-1,2,4-triazolo[5,1-s]-1,2,4-triazin(e)-7(4I)-one] was discovered in IAK 293T and Huh7 cell cultures, a liver homogenate, and rabbit blood after intragastric administration of TZV. AMTZV was nontoxic and inactive as an inhibitor of influenza virus in cell culture. Most likely, this metabolite is a product of TZV elimination.

Occurrence of mixed populations of influenza A viruses that can be maintained through transmission in a single host and potential for reassortment

Reassortment, which is the rearrangement of viral gene segments in a host cell infected with two different viruses, is an important mechanism for the evolution of influenza viruses. Mixed infections with multiple virus types could lead to reassortment. To better understand the occurrence of quasispecies in a single host, we investigated mixed infections in individual isolates of seasonal influenza A viruses using amantadine sensitivity as a marker. We cultured viruses with amantadine and performed sequencing, restriction fragment length polymorphism analysis, cloning, and quantitative PCR to detect mixed populations. Culturing with amantadine showed evidence of a high number of mixed populations, while the other assays could hardly detect mixed populations. The existence of quasispecies in each isolate was common. However, the proportion of these, which can be less than 1%, is too low to be detected by conventional methods. Such mixed populations in which reassortment occurs may have a significant role in the evolution of viruses.

Inhibition of neuraminidase inhibitor-resistant influenza virus by DAS181, a novel sialidase fusion protein

Antiviral drug resistance for influenza therapies remains a concern due to the high prevalence of H1N1 2009 seasonal influenza isolates which display H274Y associated oseltamivir-resistance. Furthermore, the emergence of novel H1N1 raises the potential that additional reassortments can occur, resulting in drug resistant virus. Thus, additional antiviral approaches are urgently needed. DAS181 (Fludase®), a sialidase fusion protein, has been shown to have inhibitory activity against a large number of seasonal influenza strains and a highly pathogenic avian influenza (HPAI) strain (H5N1). Here, we examine the in vitro activity of DAS181 against a panel of 2009 oseltamivir-resistant seasonal H1N1 clinical isolates. The activity of DAS181 against nine 2009, two 2007, and two 2004 clinical isolates of seasonal IFV H1N1 was examined using plaque number reduction assay on MDCK cells. DAS181 strongly inhibited all tested isolates. EC50 values remained constant against isolates from 2004, 2007, and 2009, suggesting that there was no change in DAS181 sensitivity over time. As expected, all 2007 and 2009 isolates were resistant to oseltamivir, consistent with the identification of the H274Y mutation in the NA gene of all these isolates. Interestingly, several of the 2007 and 2009 isolates also exhibited reduced sensitivity to zanamivir, and accompanying HA mutations near the sialic acid binding site were observed. DAS181 inhibits IFV that is resistant to NAIs. Thus, DAS181 may offer an alternative therapeutic option for seasonal or pandemic IFVs that become resistant to currently available antiviral drugs.

Novel pandemic influenza A(H1N1) viruses are potently inhibited by DAS181, a sialidase fusion protein

BACKGROUND

The recent emergence of a novel pandemic influenza A(H1N1) strain in humans exemplifies the rapid and unpredictable nature of influenza virus evolution and the need for effective therapeutics and vaccines to control such outbreaks. However, resistance to antivirals can be a formidable problem as evidenced by the currently widespread oseltamivir- and adamantane-resistant seasonal influenza A viruses (IFV). Additional antiviral approaches with novel mechanisms of action are needed to combat novel and resistant influenza strains. DAS181 (Fludase) is a sialidase fusion protein in early clinical development with in vitro and in vivo preclinical activity against a variety of seasonal influenza strains and highly pathogenic avian influenza strains (A/H5N1). Here, we use in vitro, ex vivo, and in vivo models to evaluate the activity of DAS181 against several pandemic influenza A(H1N1) viruses.

METHODS AND FINDINGS

The activity of DAS181 against several pandemic influenza A(H1N1) virus isolates was examined in MDCK cells, differentiated primary human respiratory tract culture, ex-vivo human bronchi tissue and mice. DAS181 efficiently inhibited viral replication in each of these models and against all tested pandemic influenza A(H1N1) strains. DAS181 treatment also protected mice from pandemic influenza A(H1N1)-induced pathogenesis. Furthermore, DAS181 antiviral activity against pandemic influenza A(H1N1) strains was comparable to that observed against seasonal influenza virus including the H274Y oseltamivir-resistant influenza virus.

CONCLUSIONS

The sialidase fusion protein DAS181 exhibits potent inhibitory activity against pandemic influenza A(H1N1) viruses. As inhibition was also observed with oseltamivir-resistant IFV (H274Y), DAS181 may be active against the antigenically novel pandemic influenza A(H1N1) virus should it acquire the H274Y mutation. Based on these and previous results demonstrating DAS181 broad-spectrum anti-IFV activity, DAS181 represents a potential therapeutic agent for prevention and treatment of infections by both emerging and seasonal strains of IFV.

Large-scale sequence analysis of M gene of influenza A viruses from different species: mechanisms for emergence and spread of amantadine resistance

Influenza A virus infects many species, and amantadine is used as an antiviral agent. Recently, a substantial increase in amantadine-resistant strains has been reported, most of which have a substitution at amino acid position 31 in the M2 gene. Understanding the mechanism responsible for the emergence and spread of antiviral resistance is important for developing a treatment protocol for seasonal influenza and for deciding on a policy for antiviral stockpiling for pandemic influenza. The present study was conducted to identify the existence of drug pressure on the emergence and spread of amantadine-resistant influenza A viruses. We analyzed data on more than 5,000 virus sequences and constructed a phylogenetic tree to calculate selective pressures on sites in the M2 gene associated with amantadine resistance (positions 26, 27, 30, and 31) among different hosts. The phylogenetic tree revealed that the emergence and spread of the drug-resistant M gene in different hosts and subtypes were independent and not through reassortment. For human influenza virus, positive selection was detected only at position 27. Selective pressures on the sites were not always higher for human influenza virus than for viruses of other hosts. Additionally, selective pressure on position 31 did not increase after the introduction of amantadine. Although there is a possibility of drug pressure on human influenza virus, we could not find positive pressure on position 31. Because the recent rapid increase in drug-resistant virus is associated with the substitution at position 31, the resistance may not be related to drug use.

Triple combination of oseltamivir, amantadine, and ribavirin displays synergistic activity against multiple influenza virus strains in vitro

The recurring emergence of influenza virus strains that are resistant to available antiviral medications has become a global health concern, especially in light of the potential for a new influenza virus pandemic. Currently, virtually all circulating strains of influenza A virus in the United States are resistant to either of the two major classes of anti-influenza drugs (adamantanes and neuraminidase inhibitors). Thus, new therapeutic approaches that can be rapidly deployed and that will address the issue of recurring resistance should be developed. We have tested double and triple combinations of the approved anti-influenza drugs oseltamivir and amantadine together with ribavirin against three influenza virus strains using cytopathic effect inhibition assays in MDCK cells. We selected A/New Caledonia/20/99 (H1N1) and A/Sydney/05/97 (H3N2) as representatives of the wild-type versions of the predominant circulating seasonal influenza virus strains and A/Duck/MN/1525/81 (H5N1) as a representative of avian influenza virus strains. Dose-response curves were generated for all drug combinations, and the degree of drug interaction was quantified using a model that calculates the synergy (or antagonism) between the drugs in double and triple combinations. This report demonstrates that a triple combination of antivirals was highly synergistic against influenza A virus. Importantly, the synergy of the triple combination was 2- to 13-fold greater than the synergy of any double combination depending on the influenza virus subtype. These data support the investigation of a novel combination of oseltamivir, amantadine, and ribavirin as an effective treatment for both seasonal and pandemic influenza virus, allowing the efficient use of the existing drug supplies.

Influenza virus resistance to antiviral agents: a plea for rational use

Although influenza vaccine can prevent influenza virus infection, the only therapeutic options to treat influenza virus infection are antiviral agents. At the current time, nearly all influenza A/H3N2 viruses and a percentage of influenza A/H1N1 viruses are adamantane resistant, which leaves only neuraminidase inhibitors available for treatment of infection with these viruses. In December 2008, the Centers for Disease Control and Prevention released new data demonstrating that a high percentage of circulating influenza A/H1N1 viruses are now resistant to oseltamivir. In addition, oseltamivir-resistant influenza B and A/H5N1 viruses have been identified. Thus, use of monotherapy for influenza virus infection is irrational and may contribute to mutational pressure for further selection of antiviral-resistant strains. History has demonstrated that monotherapy for influenza virus infection leads to resistance, resulting in the use of a new monotherapy agent followed by resistance to that new agent and thus resulting in a background of viruses resistant to both drugs. We argue that combination antiviral therapy, new guidelines for indications for treatment, point-of-care diagnostic testing, and a universal influenza vaccination recommendation are critical to protecting the population against influenza virus and to preserving the benefits of antiviral agents.