Influenza Viral Hemagglutinin Peptide Inhibits Influenza Viral Entry by Shielding the Host Receptor

Inhibition of H1N1 by Picochlorum sp. 122 via AKT and p53 signaling pathways

Influenza viruses cause a severe threat to global health, which can lead to annual epidemics and cause pandemics occasionally. However, the number of anti-influenza therapeutic agents is very limited. Polysaccharides, extracted from Picochlorum sp. (PPE), seaweed Polysaccharides, have exhibited antiviral activity and were expected to be used for influenza treatment. In our research, the capability of PPE to inhibit H1N1 infection was proved in MDCK cells. PPE could make MDCK cells avoid being infected with H1N1 and inhibited nuclear fragmentation and condensation of chromatin. PPE evidently inhibited the generation of reactive oxygen species in MDCK cells. Mechanism study revealed that PPE prevented MDCK cells from H1N1 infection through induction of apoptosis by stimulating AKT signaling pathway and suppressing p-p53 signaling pathway. In conclusion, PPE turns out to act as a prospective antiviral drug for H1N1 influenza.

Nardosinone and aurantio-obtusin, two medicine food homology natural compounds, are anti-influenza agents as indicated by transcriptome signature reversion

BACKGROUND

Medicine food homology (MFH) refers to food that can be used as medicine, and compounds isolated from MFH materials are valuable in novel drug discovery due to their good safety. Transcriptome signature reversion (TSR) is an attractive method for discovering drugs through transcriptional reverse matching; namely, the changes in transcriptional signatures induced by compounds are matched to a certain disease. This strategy can be used to discover anti-influenza agents among MFH natural compounds.

PURPOSE

MFH natural compounds with anti-influenza activities were identified through analyses of the reversal in the expression of multiple informative genes followed by in vitro evaluation of the cytopathic effect (CPE) caused by influenza infection and relative quantification of the nucleoprotein (NP) gene in viral RNA (vRNA). The combined effect of active compounds was determined through network-based separation score prediction followed by quantification of the viral hemagglutinin (HA) level.

METHODS

The transcriptome profiles of 4 lung or airway cell lines infected with 7 influenza virus strains were analyzed by robust rank aggregation (RRA) to identify informative genes in the signature of influenza virus infection. The identified informative genes were then matched to a transcriptomic profile library of MFH natural compounds. The anti-influenza activities of MFH natural compounds with negative enrichment scores (ESs) were evaluated in vitro using a CPE assay and relative quantification of the NP gene in the vRNA in the supernatant and cytoplasm to identify anti-influenza agents. The effects of combinations of active compounds were analyzed using network-based calculations followed by confirmation through bioassays for quantifying the viral HA levels.

RESULTS

Among the 159 MFH natural compounds, 54 compounds had negative ESs, as determined through TSR, and the anti-influenza activities of nardosinone and aurantio-obtusin were confirmed by bioassays. The half-maximal effective concentrations (EC₅₀) of nardosinone and aurantio-obtusin were 4.3-84.4 μM and 31.9-113.6 μM, respectively. The separation score between the informative genes with expression that was negatively regulated by nardosinone and aurantio-obtusin in the human protein-protein interaction (PPI) network was calculated to be 0.10, which indicated that the two compounds potentially exert a synergistic effect, and this effect was confirmed by the finding that the combination indexes (CIs) were calculated to equal 0.86 at inhibition level of 50% and 0.44 at inhibition level of 90%.

CONCLUSION

The TSR analysis and in vitro evaluation identified nardosinone and aurantio-obtusin as anti-influenza agents. Their antiviral activities were exerted by reversing the expression of multiple informative genes of the host cells. The separation analysis between the informative genes that were reversely regulated by nardosinone and aurantio-obtusin indicated that their combination may exert a synergistic effect, which was confirmed in vitro.

Antiviral Peptides as Anti-Influenza Agents

Influenza viruses represent a leading cause of high morbidity and mortality worldwide. Approaches for fighting flu are seasonal vaccines and some antiviral drugs. The development of the seasonal flu vaccine requires a great deal of effort, as careful studies are needed to select the strains to be included in each year's vaccine. Antiviral drugs available against Influenza virus infections have certain limitations due to the increased resistance rate and negative side effects. The highly mutative nature of these viruses leads to the emergence of new antigenic variants, against which the urgent development of new approaches for antiviral therapy is needed. Among these approaches, one of the emerging new fields of "peptide-based therapies" against Influenza viruses is being explored and looks promising. This review describes the recent findings on the antiviral activity, mechanism of action and therapeutic capability of antiviral peptides that bind HA, NA, PB1, and M2 as a means of countering Influenza virus infection.

Kinetics and Mechanisms of Virus Inactivation by Chlorine Dioxide in Water Treatment: A Review

Chlorine dioxide (ClO₂), an alternative disinfectant to chlorine, has been widely applied in water and wastewater disinfection. This paper aims at presenting an overview of the inactivation kinetics and mechanisms of ClO₂ with viruses. The inactivation efficiencies vary greatly among different virus species. The inactivation rates for different serotypes within a family of viruses can differ by over 284%. Generally, to achieve a 4-log removal, the exposure doses, also being referred to as Ct values (mutiplying the concentration of ClO₂ and contact time) vary in the range of 0.06-10 mg L^-1 min. Inactivation kinetics of viruses show two phases: an initial rapid inactivation phase followed by a tailing phase. Inactivation rates of viruses increase as pH or temperature increases, but show different trends with increasing concentrations of dissolved organic matter (DOM). Both damages in viral proteins and in the 5' noncoding region within the genome contribute to virus inactivation upon ClO₂ disinfection.

Peptide-Based Antiviral Drugs

Three types of chemical entities, namely, small organic molecules (organics), peptides, and biologics, are mainly used as drug candidates for the treatment of various diseases. Even though the peptide drugs are known since 1920 in association with the clinical use of insulin, only a limited number of peptides are currently used for therapeutics due to various disadvantages associated with them such as limited serum and blood stability, oral bioavailability, and permeability. Since, through chemical modifications and structure tuning, many of these limitations can be overcome, peptide-based drugs are gaining attention in pharmaceutical research. As of today, there are more than 60 peptide-based drugs approved by FDA, and over 150 peptides are in the advanced clinical studies. In this book chapter, the peptide-based lead compounds and drugs available for treating various viral diseases and their advantages and disadvantages when compared to small molecules drugs are discussed.

Emerging and state of the art hemagglutinin-targeted influenza virus inhibitors

Introduction: Seasonal influenza vaccination, together with FDA-approved neuraminidase (NA) and polymerase acidic (PA) inhibitors, is the most effective way for prophylaxis and treatment of influenza infections. However, the low efficacy of prevailing vaccines to newly emerging influenza strains and increasing resistance to available drugs drives intense research to explore more effective inhibitors. Hemagglutinin (HA), one of the major surface proteins of influenza strains, represents an attractive therapeutic target to develop such new inhibitors.Areas covered: This review summarizes the current progress of HA-based influenza virus inhibitors and their mechanisms of action, which may facilitate further research in developing novel antiviral inhibitors for controlling influenza infections.Expert opinion: HA-mediated entry of influenza virus is an essential step for successful infection of the host, which makes HA a promising target for the development of antiviral drugs. Recent progress in delineating the crystal structures of HA, especially HA-inhibitors complexes, has revealed a number of key residues and conserved binding pockets within HA. This has opened up important insights for developing HA-based antiviral inhibitors that have a high resistance barrier and broad-spectrum activities.

Development of Novel Anti-influenza Thiazolides with Relatively Broad-Spectrum Antiviral Potentials

Seasonal and pandemic influenza causes 650,000 deaths annually in the world. The emergence of drug resistance to specific anti-influenza virus drugs such as oseltamivir and baloxavir marboxil highlights the urgency of novel anti-influenza chemical entity discovery. In this study, we report a series of novel thiazolides derived from an FDA-approved drug, nitazoxanide, with antiviral activity against influenza and a broad range of viruses. The preferred candidates 4a and 4d showed significantly enhanced anti-influenza virus potentials, with 10-fold improvement compared to results with nitazoxanide, and were effective against a variety of influenza virus subtypes including oseltamivir-resistant strains. Notably, the combination using compounds 4a/4d and oseltamivir carboxylate or zanamivir displayed synergistic antiviral effects against oseltamivir-resistant strains. Mode-of-action analysis demonstrated that compounds 4a/4d acted at the late phase of the viral infection cycle through inhibiting viral RNA transcription and replication. Further experiments showed that treatment with compounds 4a/4d significantly inhibited influenza virus infection in human lung organoids, suggesting the druggability of the novel thiazolides. In-depth transcriptome analysis revealed a series of upregulated cellular genes that may contribute to the antiviral activities of 4a/4d. Together, the results of our study indicated the direction to optimize nitazoxanide as an anti-influenza drug and discovered two candidates with novel structures, compounds 4a/4d, that have relatively broad-spectrum antiviral potentials.

Discovery and characterization of a novel peptide inhibitor against influenza neuraminidase

Neuraminidase, an abundant glycoprotein on the influenza virus surface, plays crucial roles in virus replication. Targeting neuraminidase could be a splendid way for the prevention of the spread of influenza infections. Herein, we have identified an octapeptide (errKPAQP) from a synthesized peptide library, originating from mimicking the binding pocket of oseltamivir in neuraminidase, as a potent peptide neuraminidase inhibitor. The docking-based virtual studies showed that errKPAQP exhibited a strong binding affinity (a docking score of -20.03) and nanomolar affinity (11 nM) to influenza neuraminidase, and can inhibit neuraminidase activity at a concentration as low as 4.25 μM, leading to effective protection of MDCK cells from influenza virus-induced death and replication. Furthermore, errKPAQP presented low hemolytic activity, minimal cytotoxicity, and good pharmacokinetic characteristics, which are imperative for an anti-influenza drug. Importantly, errKPAQP was capable of reducing influenza virus-induced inflammation, the serious damage to the lung tissues, and mortality rates in infected mice, indicating that it could protect against the lethal challenge of influenza viruses in vivo. Therefore, we have developed a novel neuraminidase peptide inhibitor with advantageous biological properties and high inhibitory activity towards neuraminidase, and it can serve as a promising anti-influenza drug.

Hemagglutinin Inhibitors are Potential Future Anti-Influenza Drugs for Mono- and Combination Therapies

Infections by H1-H16 influenza A viruses require sufficient binding of viral hemagglutinins (HAs) to specific target receptors, glycoconjugates bearing sialyl sugar chains, on the host cell surface. Synthesized sialyl sugar chains targeting sialyl sugar-binding sites in HAs that are immutable as long as the virus does not switch to a different host species might therefore be highly effective candidate drugs for inhibition of the initial required step of virus entry. In this chapter, we describe the following aspects of updated sialyl sugar chains as influenza A virus HA inhibitors (HAIs): (1) mode of terminal sialyl-galactose linkage, (2) molecular length and structure of sialyl glycan receptors, (3) multivalent sialyl sugar chain dimension, (4) clustering of sialyl sugar chains on macromolecular scaffolds, and (5) enhancement of the stability of sialyl sugar chain HA inhibitors. We also discuss about the use of HAI-based combinations that should be considered for future influenza therapy.

Competition for Membrane Receptors: Norovirus Detachment via Lectin Attachment

Virus internalization into the host cells occurs via multivalent interactions, in which a single virus binds to multiple receptors in parallel. Because of analytical and experimental limitations this complex type of interaction is still poorly understood and quantified. Herein, the multivalent interaction of norovirus-like particles (noroVLPs) with H or B type 1 glycosphingolipids (GSLs), embedded in a supported phospholipid bilayer, is investigated by following the competition between noroVLPs and a lectin (from Ralstonia solanacearum) upon binding to these GSLs. Changes in noroVLP and lectin coverage, caused by competition, were monitored for both GSLs and at different GSL concentrations using quartz crystal microbalance with dissipation monitoring. The study yields information about the minimum GSL concentration needed for (i) noroVLPs to achieve firm attachment to the bilayer prior to competition and to (ii) remain firmly attached to the bilayer during competition. We show that these two concentrations are almost identical for the H type 1-noroVLP interaction but differ for B type 1, indicating an accumulation of B type 1 GSLs in the noroVLP-bilayer interaction area. Furthermore, the GSL concentration required for firm attachment is significantly larger for H type 1 than for B type 1, indicating a higher affinity of noroVLP toward B type 1. This finding is supported by extracting the energy of single noroVLP-H type 1 and noroVLP-B type 1 bonds from the competition kinetics, which were estimated to be 5 and 6 kcal/mol, respectively. This demonstrates the potential of utilizing competitive binding kinetics to analyze multivalent interactions, which has remained difficult to quantify using conventional approaches.

Structure-aided optimization of 3-O-β-chacotriosyl ursolic acid as novel H5N1 entry inhibitors with high selective index

Currently, entry inhibitors contribute immensely in developing a new generation of anti-influenza virus drugs. Our earlier studies have identified that 3-O-β-chacotriosyl ursolic acid (1) could inhibit H5N1 pseudovirus by targeting hemagglutinin (HA). In the present study, a series of C-28 modified pentacyclic triterpene saponins via conjugation with a series of amide derivatives were synthesized and their antiviral activities against influenza A/Duck/Guangdong/99 virus (H5N1) in MDCK cells were evaluated. The SARs analysis of these compounds revealed that introduction of certain amide structures at the 17-COOH of ursolic acid could significantly enhance both their antiviral activity and selective index. This study indicated that the attachment of the methoxy group or Cl atom to the phenyl ring at the ortho- or para-position was crucial to improve inhibitory activity. Mechanism studies demonstrated that these title triterpenoids could bind tightly to the viral envelope HA to block the attachment of viruses to host cells, which was consistent with docking studies.

Effective in Vivo Targeting of Influenza Virus through a Cell-Penetrating/Fusion Inhibitor Tandem Peptide Anchored to the Plasma Membrane

The impact of influenza virus infection is felt each year on a global scale when approximately 5-10% of adults and 20-30% of children globally are infected. While vaccination is the primary strategy for influenza prevention, there are a number of likely scenarios for which vaccination is inadequate, making the development of effective antiviral agents of utmost importance. Anti-influenza treatments with innovative mechanisms of action are critical in the face of emerging viral resistance to the existing drugs. These new antiviral agents are urgently needed to address future epidemic (or pandemic) influenza and are critical for the immune-compromised cohort who cannot be vaccinated. We have previously shown that lipid tagged peptides derived from the C-terminal region of influenza hemagglutinin (HA) were effective influenza fusion inhibitors. In this study, we modified the influenza fusion inhibitors by adding a cell penetrating peptide sequence to promote intracellular targeting. These fusion-inhibiting peptides self-assemble into ∼15-30 nm nanoparticles (NPs), target relevant infectious tissues in vivo, and reduce viral infectivity upon interaction with the cell membrane. Overall, our data show that the CPP and the lipid moiety are both required for efficient biodistribution, fusion inhibition, and efficacy in vivo.

Influenza Virus: A Master Tactician in Innate Immune Evasion and Novel Therapeutic Interventions

Influenza is a contagion that has plagued mankind for many decades, and continues to pose concerns every year, with millions of infections globally. The frequent mutations and recombination of the influenza A virus (IAV) cast a looming threat that antigenically novel strains/subtypes will rise with unpredictable pathogenicity and fear of it evolving into a pandemic strain. There have been four major influenza pandemics, since the beginning of twentieth century, with the great 1918 pandemic being the most severe, killing more than 50 million people worldwide. The mechanisms of IAV infection, host immune responses, and how viruses evade from such defensive responses at the molecular and structural levels have been greatly investigated in the past 30 years. While this has advanced our understanding of virus–host interactions and human immunology, and has led to the development of several antiviral drugs, they have minimal impact on the clinical outcomes of infection. The heavy use of these drugs has also imposed selective pressure on IAV to evolve and develop resistance. Vaccination remains the cornerstone of public health efforts to protect against influenza; however, rapid mass-production of sufficient vaccines is unlikely to occur immediately after the beginning of a pandemic. This, therefore, requires novel therapeutic strategies against this continually emerging infectious virus with higher specificity and cross-reactivity against multiple strains/subtypes of IAVs. This review discusses essential virulence factors of IAVs that determine sustainable human-to-human transmission, the mechanisms of viral hijacking of host cells and subversion of host innate immune responses, and novel therapeutic interventions that demonstrate promising antiviral properties against IAV. This hopefully will promote discussions and investigations on novel avenues of prevention and treatment strategies of influenza, that are effective and cross-protective against multiple strains/subtypes of IAV, in preparation for the advent of future IAVs and pandemics.

Inhibition of H1N1 influenza virus-induced apoptosis by functionalized selenium nanoparticles with amantadine through ROS-mediated AKT signaling pathways

Introduction

As a therapeutic antiviral agent, the clinical application of amantadine (AM) is limited by the emergence of drug-resistant viruses. To overcome the drug-resistant viruses and meet the growing demand of clinical diagnosis, the use of biological nanoparticles (NPs) has increased in order to develop novel anti-influenza drugs. The antiviral activity of selenium NPs with low toxicity and excellent activities has attracted increasing attention for biomedical intervention in recent years.

Methods and results

In the present study, surface decoration of selenium NPs by AM (Se@AM) was designed to reverse drug resistance caused by influenza virus infection. Se@ AM with less toxicity remarkably inhibited the ability of H1N1 influenza to infect host cells through suppression of the neuraminidase activity. Moreover, Se@AM could prevent H1N1 from infecting Madin Darby Canine Kidney cell line and causing cell apoptosis supported by DNA fragmentation and chromatin condensation. Furthermore, Se@AM obviously inhibited the generation of reactive oxygen species and activation of phosphorylation of AKT.

Conclusion

These results demonstrate that Se@AM is a potentially efficient antiviral pharmaceutical agent for H1N1 influenza virus.

Probing the metastable state of influenza hemagglutinin

Viral entry into host cells is mediated by membrane proteins in a metastable state that transition to a more stable state upon a stimulus. For example, in the influenza envelope protein hemagglutinin (HA), the low pH in the endosome triggers a transition from the metastable prefusion conformation to the stable fusion conformation. To identify probes that interfere with HA function, here we screened a library of H7 HA peptides for inhibition of H7 HA-mediated entry. We discovered a peptide, PEP87 (WSYNAELLVAMENQHTI), that inhibited H7 and H5 HA-mediated entry. PEP87 corresponds to a highly conserved helical region of the HA2 subunit of HA that self-interacts in the neutral pH conformation. Mutagenesis experiments indicated that PEP87 binds to its native region in the HA trimer. We also found that PEP87 is unstructured in isolation but tends to form a helix as evidenced by CD and NMR studies. Fluorescence, chemical cross-linking, and saturation transfer difference NMR data suggested that PEP87 binds to the neutral pH conformation of HA and disrupts the HA structure without affecting its oligomerization state. Together, this work provides support for a model in which PEP87 disrupts HA function by displacing native interactions of the neutral pH conformation. Moreover, our observations indicate that the HA prefusion structure (and perhaps the metastable states of other viral entry proteins) is more dynamic with transient motions being larger than generally appreciated. These findings also suggest that the ensemble of prefusion structures presents many potential sites for targeting in therapeutic interventions.

Establishment of pseudovirus infection mouse models for in vivo pharmacodynamics evaluation of filovirus entry inhibitors

Filoviruses cause severe and fatal viral hemorrhagic fever in humans. Filovirus research has been extensive since the 2014 Ebola outbreak. Due to their high pathogenicity and mortality, live filoviruses require Biosafety Level-4 (BSL-4) facilities, which have restricted the development of anti-filovirus vaccines and drugs. An HIV-based pseudovirus cell infection assay is widely used for viral entry studies in BSL-2 conditions. Here, we successfully constructed nine in vitro pseudo-filovirus models covering all filovirus genera and three in vivo pseudo-filovirus-infection mouse models using Ebola virus, Marburg virus, and Lloviu virus as representative viruses. The pseudo-filovirus-infected mice showed visualizing bioluminescence in a dose-dependent manner. A bioluminescence peak in mice was reached on day 5 post-infection for Ebola virus and Marburg virus and on day 4 post-infection for Lloviu virus. Two known filovirus entry inhibitors, clomiphene and toremiphene, were used to validate the model. Collectively, our study shows that all genera of filoviruses can be well-pseudotyped and are infectious in vitro. The pseudo-filovirus-infection mouse models can be used for in vivo activity evaluation of anti-filovirus drugs. This sequential in vitro and in vivo evaluation system of filovirus entry inhibitors provides a secure and efficient platform for screening and assessing anti-filovirus agents in BSL-2 facilities.

Detachment of Membrane Bound Virions by Competitive Ligand Binding Induced Receptor Depletion

Multivalent receptor-mediated interactions between virions and a lipid membrane can be weakened using competitive nonpathogenic ligand binding. In particular, the subsequent binding of such ligands can induce detachment of bound virions, a phenomenon of crucial relevance for the development of new antiviral drugs. Focusing on the simian virus 40 (SV40) and recombinant cholera toxin B subunit (rCTB), and using (monosialotetrahexosyl)ganglioside (GM1) as their common receptor in a supported lipid bilayer (SLB), we present the first detailed investigation of this phenomenon by employing the quartz crystal microbalance with dissipation (QCM-D) and total internal reflection fluorescence (TIRF) microscopy assisted 2D single particle tracking (SPT) techniques. Analysis of the QCM-D-measured release kinetics made it possible to determine the binding strength of a single SV40-GM1 pair. The release dynamics of SV40, monitored by SPT, revealed that a notable fraction of SV40 becomes mobile just before the release, allowing to estimate the distribution of SV40-bound GM1 receptors just prior to release.