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

Inhibiting influenza virus transmission using a broadly acting neuraminidase that targets host sialic acids in the upper respiratory tract

The ongoing transmission of influenza A viruses (IAV) for the past century continues to be a burden to humans. IAV binds terminal sialic acids (SA) of sugar molecules present within the upper respiratory tract (URT) in order to successfully infect hosts. The two most common SA structures that are important for IAV infection are those with α2,3- and α2,6-linkages. While mice were once considered to be an unsuitable system for studying IAV transmission due to their lack of α2,6-SA in the trachea, we have successfully demonstrated that IAV transmission in infant mice is remarkably efficient. This finding led us to re-evaluate the SA composition of the URT of mice using in situ immunofluorescence and examine its in vivo contribution to transmission for the first time. We demonstrate that mice express both α2,3- and α2,6-SA in the URT and that the difference in expression between infants and adults contributes to the variable transmission efficiencies observed. Furthermore, selectively blocking α2,3-SA or α2,6-SA within the URT of infant mice using lectins was necessary but insufficient at inhibiting transmission, and simultaneous blockade of both receptors was crucial in achieving the desired inhibitory effect. By employing a broadly acting neuraminidase to indiscriminately remove both SA moieties in vivo, we effectively suppressed viral shedding and halted the transmission of different strains of influenza viruses. These results emphasize the utility of the infant mouse model for studying IAV transmission and strongly indicate that broadly targeting host SA is an effective approach that inhibits IAV contagion.IMPORTANCEInfluenza virus transmission studies have historically focused on viral mutations that alter hemagglutinin binding to sialic acid (SA) receptors in vitro. However, SA binding preference does not fully account for the complexities of influenza A virus transmission in humans. Our previous findings reveal that viruses that are known to bind α2,6-SA in vitro have different transmission kinetics in vivo, suggesting that diverse SA interactions may occur during their life cycle. In this study, we examine the role of host SA on viral replication, shedding, and transmission in vivo. We highlight the critical role of SA presence during virus shedding, such that attachment to SA during virion egress is equally important as detachment from SA during virion release. These insights support the potential of broadly acting neuraminidases as therapeutic agents capable of restraining viral transmission in vivo. Our study unveils intricate virus-host interactions during shedding, highlighting the necessity to develop innovative strategies to effectively target transmission.

Influenza virus cell entry and targeted antiviral development

Influenza virus infection is currently one of the most prevalent and transmissible diseases in the world causing local outbreaks every year. It has the potential to cause devastating global pandemics as well. The development of anti-influenza drugs possessing novel mechanisms of action is urgently needed to control the spread of influenza infections; thus, drugs that inhibit influenza virus entry into target cells are emerging as a hot research topic. In addition to discussing the biological significance of hemagglutinin in viral replication, this article provides recent updates on the natural products, small molecules, proteins, peptides, and neutralizing antibody-like proteins that have anti-influenza potency.

Influenza antivirals and animal models

Influenza A and B viruses are among the most prominent human respiratory pathogens. About 3-5 million severe cases of influenza are associated with 300 000-650 000 deaths per year globally. Antivirals effective at reducing morbidity and mortality are part of the first line of defense against influenza. FDA-approved antiviral drugs currently include adamantanes (rimantadine and amantadine), neuraminidase inhibitors (NAI; peramivir, zanamivir, and oseltamivir), and the PA endonuclease inhibitor (baloxavir). Mutations associated with antiviral resistance are common and highlight the need for further improvement and development of novel anti-influenza drugs. A summary is provided for the current knowledge of the approved influenza antivirals and antivirals strategies under evaluation in clinical trials. Preclinical evaluations of novel compounds effective against influenza in different animal models are also discussed.

The role of influenza A virus-induced hypercytokinemia

Influenza viruses are one of the leading causes of respiratory tract infections in humans and their newly emerging and re-emerging virus strains are responsible for seasonal epidemics and occasional pandemics, leading to a serious threat to global public health systems. The poor clinical outcome and pathogenesis during influenza virus infection in humans and animal models are often associated with elevated proinflammatory cytokines and chemokines production, which is also known as hypercytokinemia or "cytokine storm", that precedes acute respiratory distress syndrome (ARDS) and often leads to death. Although we still do not fully understand the complex nature of cytokine storms, the use of immunomodulatory drugs is a promising approach for treating hypercytokinemia induced by an acute viral infection, including highly pathogenic avian influenza virus infection and Coronavirus Disease 2019 (COVID-19). This review aims to discuss the immune responses and cytokine storm pathology induced by influenza virus infection and also summarize alternative experimental strategies for treating hypercytokinemia caused by influenza virus.

A Perfect Storm? Health Anxiety, Contamination Fears, and COVID-19: Lessons Learned from Past Pandemics and Current Challenges

The novel coronavirus disease 2019 (COVID-19) rapidly spread, becoming a global pandemic with significant health, economic, and social impacts. COVID-19 has caused widespread anxiety, which at healthy levels leads to adaptive, protective behavioral changes. For some individuals, a pandemic outbreak can lead to excessive, maladaptive levels of anxiety, particularly among those with obsessive-compulsive disorder (OCD) and health anxiety. In the present paper, we review past research studies that examined anxiety in response to other disease outbreaks (including Swine Flu, Zika, and Ebola) to serve as a guide for expectable responses to COVID-19. Our review focused on the role of belief-based cognitive variables (obsessive beliefs, contamination cognitions), transdiagnostic processes (disgust sensitivity, anxiety sensitivity, an intolerance of uncertainty), social factors, and environmental/situational variables as contributing factors to excessive concerns about past pandemics. These factors in combination with unique characteristics of the virus (disease, behavioral, social and economic factors) and media consumption might enhance vulnerability to excessive anxiety about COVID-19, in line with a diathesis-stress model. COVID-19 is also unique from past pandemics due to its severity, easy transmissibility, and the nature of prescribed behavioral responses (i.e., hand washing and social distancing). We therefore discuss the ways in which COVID-19 may disproportionately affect individuals with OCD and health anxiety. We conclude with important topics for clinical and research attention to help mental health professionals respond in this time of crisis.

Host-directed Therapy: A New Arsenal to Come

The emergence of drug-resistant strains among the variety of pathogens worsens the situation in today's scenario. In such a situation, a very heavy demand for developing the new antibiotics has arisen, but unfortunately, very limited success has been achieved in this arena till now. Infectious diseases usually make their impression in the form of severe pathology. Intracellular pathogens use the host's cell machinery for their survival. They alter the gene expression of several host's pathways and endorse to shut down the cell's innate defense pathway like apoptosis and autophagy. Intracellular pathogens are co-evolved with hosts and have a striking ability to manipulate the host's factors. They also mimic the host molecules and secrete them to prevent the host's proper immune response against them for their survival. Intracellular pathogens in chronic diseases create excessive inflammation. This excessive inflammation manifests in pathology. Host directed therapy could be alternative medicine in this situation; it targets the host factors, and abrogates the replication and persistence of pathogens inside the cell. It also provokes the anti-microbial immune response against the pathogen and reduces the exacerbation by enhancing the healing process to the site of pathology. HDT targets the host's factor involved in a certain pathway that ultimately targets the pathogen life cycle and helps in eradication of the pathogen. In such a scenario, HDT could also play a significant role in the treatment of drugsensitive as well with drug resistance strains because it targets the host's factors, which favors the pathogen survival inside the cell.

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.

Respiratory Barrier as a Safeguard and Regulator of Defense Against Influenza A Virus and Streptococcus pneumoniae

The primary function of the respiratory system of gas exchange renders it vulnerable to environmental pathogens that circulate in the air. Physical and cellular barriers of the respiratory tract mucosal surface utilize a variety of strategies to obstruct microbe entry. Physical barrier defenses including the surface fluid replete with antimicrobials, neutralizing immunoglobulins, mucus, and the epithelial cell layer with rapidly beating cilia form a near impenetrable wall that separates the external environment from the internal soft tissue of the host. Resident leukocytes, primarily of the innate immune branch, also maintain airway integrity by constant surveillance and the maintenance of homeostasis through the release of cytokines and growth factors. Unfortunately, pathogens such as influenza virus and Streptococcus pneumoniae require hosts for their replication and dissemination, and prey on the respiratory tract as an ideal environment causing severe damage to the host during their invasion. In this review, we outline the host-pathogen interactions during influenza and post-influenza bacterial pneumonia with a focus on inter- and intra-cellular crosstalk important in pulmonary immune responses.

Effect of aloin on viral neuraminidase and hemagglutinin-specific T cell immunity in acute influenza

BACKGROUND

Millions of people are infected by the influenza virus worldwide every year. Current selections of anti-influenza agents are limited and their effectiveness and drug resistance are still of concern.

PURPOSE

Investigation on in vitro and in vivo effect of aloin from Aloe vera leaves against influenza virus infection.

METHODS

In vitro antiviral property of aloin was measured by plaque reduction assay in which MDCK cells were infected with oseltamivir-sensitive A(H1N1)pdm09, oseltamivir-resistant A(H1N1)pdm09, H1N1 or H3N2 influenza A or with influenza B viruses in the presence of aloin. In vivo activity was tested in H1N1 influenza virus infected mice. Aloin-mediated inhibition of influenza neuraminidase activity was tested by MUNANA assay. Aloin treatment-mediated modulation of anti-influenza immunity was tested by the study of hemagglutinin-specific T cells in vivo.

RESULTS

Aloin significantly reduced in vitro infection by all the tested strains of influenza viruses, including oseltamivir-resistant A(H1N1)pdm09 influenza viruses, with an average IC₅₀ value 91.83 ± 18.97 μM. In H1N1 influenza virus infected mice, aloin treatment (intraperitoneal, once daily for 5 days) reduced virus load in the lungs and attenuated body weight loss and mortality. Adjuvant aloin treatment also improved the outcome with delayed oseltamivir treatment. Aloin inhibited viral neuraminidase and impeded neuraminidase-mediated TGF-β activation. Viral neuraminidase mediated immune suppression with TGF-β was constrained and influenza hemagglutinin-specific T cell immunity was increased. There was more infiltration of hemagglutinin-specific CD4+ and CD8+ T cells in the lungs and their production of effector cytokines IFN-γ and TNF-α was boosted.

CONCLUSION

Aloin from Aloe vera leaves is a potent anti-influenza compound that inhibits viral neuraminidase activity, even of the oseltamivir-resistant influenza virus. With suppression of this virus machinery, aloin boosts host immunity with augmented hemagglutinin-specific T cell response to the infection. In addition, in the context of compromised benefit with delayed oseltamivir treatment, adjuvant aloin treatment ameliorates the disease and improves survival. Taken together, aloin has the potential to be further evaluated for clinical applications in human influenza.

Overview of Current Therapeutics and Novel Candidates Against Influenza, Respiratory Syncytial Virus, and Middle East Respiratory Syndrome Coronavirus Infections

Emergence and re-emergence of respiratory virus infections represent a significant threat to global public health, as they occur seasonally and less frequently (such as in the case of influenza virus) as pandemic infections. Some of these viruses have been in the human population for centuries and others had recently emerged as a public health problem. Influenza viruses have been affecting the human population for a long time now; however, their ability to rapidly evolve through antigenic drift and antigenic shift causes the emergence of new strains. A recent example of these events is the avian-origin H7N9 influenza virus outbreak currently undergoing in China. Human H7N9 influenza viruses are resistant to amantadines and some strains are also resistant to neuraminidase inhibitors greatly limiting the options for treatment. Respiratory syncytial virus (RSV) may cause a lower respiratory tract infection characterized by bronchiolitis and pneumonia mainly in children and the elderly. Infection with RSV can cause severe disease and even death, imposing a severe burden for pediatric and geriatric health systems worldwide. Treatment for RSV is mainly supportive since the only approved therapy, a monoclonal antibody, is recommended for prophylactic use in high-risk patients. The Middle East respiratory syndrome coronavirus (MERS-CoV) is a newly emerging respiratory virus. The virus was first recognized in 2012 and it is associated with a lower respiratory tract disease that is more severe in patients with comorbidities. No licensed vaccines or antivirals have been yet approved for the treatment of MERS-CoV in humans. It is clear that the discovery and development of novel antivirals that can be used alone or in combination with existing therapies to treat these important respiratory viral infections are critical. In this review, we will describe some of the novel therapeutics currently under development for the treatment of these infections.

Sowing the Seeds of a Pandemic? Mammalian Pathogenicity and Transmissibility of H1 Variant Influenza Viruses from the Swine Reservoir

Emergence of genetically and antigenically diverse strains of influenza to which the human population has no or limited immunity necessitates continuous risk assessments to determine the likelihood of these viruses acquiring adaptations that facilitate sustained human-to-human transmission. As the North American swine H1 virus population has diversified over the last century by means of both antigenic drift and shift, in vivo assessments to study multifactorial traits like mammalian pathogenicity and transmissibility of these emerging influenza viruses are critical. In this review, we examine genetic, molecular, and pathogenicity and transmissibility data from a panel of contemporary North American H1 subtype swine-origin viruses isolated from humans, as compared to H1N1 seasonal and pandemic viruses, including the reconstructed 1918 virus. We present side-by-side analyses of experiments performed in the mouse and ferret models using consistent experimental protocols to facilitate enhanced interpretation of in vivo data. Contextualizing these analyses in a broader context permits a greater appreciation of the role that in vivo risk assessment experiments play in pandemic preparedness. Collectively, we find that despite strain-specific heterogeneity among swine-origin H1 viruses, contemporary swine viruses isolated from humans possess many attributes shared by prior pandemic strains, warranting heightened surveillance and evaluation of these zoonotic viruses.

An Infant Mouse Model of Influenza Virus Transmission Demonstrates the Role of Virus-Specific Shedding, Humoral Immunity, and Sialidase Expression by Colonizing Streptococcus pneumoniae

The pandemic potential of influenza A viruses (IAV) depends on the infectivity of the host, transmissibility of the virus, and susceptibility of the recipient. While virus traits supporting IAV transmission have been studied in detail using ferret and guinea pig models, there is limited understanding of host traits determining transmissibility and susceptibility because current animal models of transmission are not sufficiently tractable. Although mice remain the primary model to study IAV immunity and pathogenesis, the efficiency of IAV transmission in adult mice has been inconsistent. Here we describe an infant mouse model that supports efficient transmission of IAV. We demonstrate that transmission in this model requires young age, close contact, shedding of virus particles from the upper respiratory tract (URT) of infected pups, the use of a transmissible virus strain, and a susceptible recipient. We characterize shedding as a marker of infectiousness that predicts the efficiency of transmission among different influenza virus strains. We also demonstrate that transmissibility and susceptibility to IAV can be inhibited by humoral immunity via maternal-infant transfer of IAV-specific immunoglobulins and modifications to the URT milieu, via sialidase activity of colonizing Streptococcus pneumoniae Due to its simplicity and efficiency, this model can be used to dissect the host's contribution to IAV transmission and explore new methods to limit contagion.IMPORTANCE This study provides insight into the role of the virus strain, age, immunity, and URT flora on IAV shedding and transmission efficiency. Using the infant mouse model, we found that (i) differences in viral shedding of various IAV strains are dependent on specific hemagglutinin (HA) and/or neuraminidase (NA) proteins, (ii) host age plays a key role in the efficiency of IAV transmission, (iii) levels of IAV-specific immunoglobulins are necessary to limit infectiousness, transmission, and susceptibility to IAV, and (iv) expression of sialidases by colonizing S. pneumoniae antagonizes transmission by limiting the acquisition of IAV in recipient hosts. Our findings highlight the need for strategies that limit IAV shedding and the importance of understanding the function of the URT bacterial composition in IAV transmission. This work reinforces the significance of a tractable animal model to study both viral and host traits affecting IAV contagion and its potential for optimizing vaccines and therapeutics that target disease spread.

Respiratory Viral Infections in Patients With Cancer or Undergoing Hematopoietic Cell Transplant

Survival rates for pediatric cancer have steadily improved over time but it remains a significant cause of morbidity and mortality among children. Infections are a major complication of cancer and its treatment. Community acquired respiratory viral infections (CRV) in these patients increase morbidity, mortality and can lead to delay in chemotherapy. These are the result of infections with a heterogeneous group of viruses including RNA viruses, such as respiratory syncytial virus (RSV), influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (HMPV), rhinovirus (RhV), and coronavirus (CoV). These infections maintain a similar seasonal pattern to those of immunocompetent patients. Clinical manifestations vary significantly depending on the type of virus and the type and degree of immunosuppression, ranging from asymptomatic or mild disease to rapidly progressive fatal pneumonia Infections in this population are characterized by a high rate of progression from upper to lower respiratory tract infection and prolonged viral shedding. Use of corticosteroids and immunosuppressive therapy are risk factors for severe disease. The clinical course is often difficult to predict, and clinical signs are unreliable. Accurate prognostic viral and immune markers, which have become part of the standard of care for systemic viral infections, are currently lacking; and management of CRV infections remains controversial. Defining effective prophylactic and therapeutic strategies is challenging, especially considering, the spectrum of immunocompromised patients, the variety of respiratory viruses, and the presence of other opportunistic infections and medical problems. Prevention remains one of the most important strategies against these viruses. Early diagnosis, supportive care and antivirals at an early stage, when available and indicated, have proven beneficial. However, with the exception of neuraminidase inhibitors for influenza infection, there are no accepted treatments. In high-risk patients, pre-emptive treatment with antivirals for upper respiratory tract infection (URTI) to decrease progression to LRTI is a common strategy. In the future, viral load and immune markers may prove beneficial in predicting severe disease, supporting decision making and monitor treatment in this population.

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.

Treating Influenza Infection, From Now and Into the Future

Influenza viruses (IVs) are a continual threat to global health. The high mutation rate of the IV genome makes this virus incredibly successful, genetic drift allows for annual epidemics which result in thousands of deaths and millions of hospitalizations. Moreover, the emergence of new strains through genetic shift (e.g., swine-origin influenza A) can cause devastating global outbreaks of infection. Neuraminidase inhibitors (NAIs) are currently used to treat IV infection and act directly on viral proteins to halt IV spread. However, effectivity is limited late in infection and drug resistance can develop. New therapies which target highly conserved features of IV such as antibodies to the stem region of hemagglutinin or the IV RNA polymerase inhibitor: Favipiravir are currently in clinical trials. Compared to NAIs, these treatments have a higher tolerance for resistance and a longer therapeutic window and therefore, may prove more effective. However, clinical and experimental evidence has demonstrated that it is not just viral spread, but also the host inflammatory response and damage to the lung epithelium which dictate the outcome of IV infection. Therapeutic regimens for IV infection should therefore also regulate the host inflammatory response and protect epithelial cells from unnecessary cell death. Anti-inflammatory drugs such as etanercept, statins or cyclooxygenase enzyme 2 inhibitors may temper IV induced inflammation, demonstrating the possibility of repurposing these drugs as single or adjunct therapies for IV infection. IV binds to sialic acid receptors on the host cell surface to initiate infection and productive IV replication is primarily restricted to airway epithelial cells. Accordingly, targeting therapies to the epithelium will directly inhibit IV spread while minimizing off target consequences, such as over activation of immune cells. The neuraminidase mimic Fludase cleaves sialic acid receptors from the epithelium to inhibit IV entry to cells. While type III interferons activate an antiviral gene program in epithelial cells with minimal perturbation to the IV specific immune response. This review discusses the above-mentioned candidate anti-IV therapeutics and others at the preclinical and clinical trial stage.

Verdinexor Targeting of CRM1 is a Promising Therapeutic Approach against RSV and Influenza Viruses

Two primary causes of respiratory tract infections are respiratory syncytial virus (RSV) and influenza viruses, both of which remain major public health concerns. There are a limited number of antiviral drugs available for the treatment of RSV and influenza, each having limited effectiveness and each driving selective pressure for the emergence of drug-resistant viruses. Novel broad-spectrum antivirals are needed to circumvent problems with current disease intervention strategies, while improving the cytokine-induced immunopathology associated with RSV and influenza infections. In this review, we examine the use of Verdinexor (KPT-335, a novel orally bioavailable drug that functions as a selective inhibitor of nuclear export, SINE), as an antiviral with multifaceted therapeutic potential. KPT-335 works to (1) block CRM1 (i.e., Chromosome Region Maintenance 1; exportin 1 or XPO1) mediated export of viral proteins critical for RSV and influenza pathogenesis; and (2) repress nuclear factor κB (NF-κB) activation, thus reducing cytokine production and eliminating virus-associated immunopathology. The repurposing of SINE compounds as antivirals shows promise not only against RSV and influenza virus but also against other viruses that exploit the nucleus as part of their viral life cycle.

Influenza Virus: Small Molecule Therapeutics and Mechanisms of Antiviral Resistance

BACKGROUND

Influenza viruses cause severe upper respiratory illness in children and the elderly during seasonal epidemics. Influenza viruses from zoonotic reservoirs can also cause pandemics with significant loss of life in all age groups. Although vaccination is one of the most effective methods to protect against seasonal epidemics, seasonal vaccines vary in efficacy, can be ineffective in the elderly population, and do not provide protection against novel strains. Small molecule therapeutics are a critical part of our antiviral strategies to control influenza virus epidemics and pandemics as well as to ameliorate disease in elderly and immunocompromised individuals.

OBJECTIVE

This review aims to summarize the existing antiviral strategies for combating influenza viruses, the mechanisms of antiviral resistance for available drugs, and novel therapeutics currently in development.

METHODS

We systematically evaluated and synthesized the published scientific literature for mechanistic detail into therapeutic strategies against influenza viruses.

RESULTS

Current IAV strains have developed resistance to neuraminidase inhibitors and nearly complete resistance to M2 ion channel inhibitors, exacerbated by sub-therapeutic dosing used for treatment and chemoprophylaxis. New tactics include novel therapeutics targeting host components and combination therapy, which show potential for fighting influenza virus disease while minimizing viral resistance.

CONCLUSION

Antiviral drugs are crucial for controlling influenza virus disease burden, but their efficacy is limited by human misuse and the capacity of influenza viruses to circumvent antiviral barriers. To relieve the public health hardship of influenza virus, emerging therapies must be selected for their capacity to impede not only influenza virus disease, but also the development of antiviral resistance.

Geniposide demonstrates anti-inflammatory and antiviral activity against pandemic A/Jiangsu/1/2009 (H1N1) influenza virus infection in vitro and in vivo

BACKGROUND

Influenza A viruses (IAVs) have been a great threat to human health for centuries, without effective control. Geniposide, a main iridoid glycoside compound extracted from Gardenia jasminoides Ellis fruit, possesses various biological activities including anti-inflammation and anti-virus.

METHODS

Madin-Darby canine kidney (MDCK) cells were infected with pandemic A/Jiangsu/1/2009 (H1N1) influenza virus in vitro. Cytotoxicity and antiviral activity of geniposide were estimated by MTT assay. The influenza respiratory tract infection murine model was established by intranasal instillation of pandemic A/Jiangsu/1/2009 (H1N1) influenza virus. One day after infection, the mice were administered with geniposide (5, 10 or 20 mg/kg/day) or the neuraminidase inhibitor (NAI) peramivir (30 mg/kg/day). Body weight, survival time, viral titre and lung index of the mice were measured. The sandwich enzyme-linked immunosorbent assay (ELISA) was used to examine levels of inflammatory cytokines.

RESULTS

The data showed that geniposide had little cytotoxicity on MDCK cells and protected them from pandemic A/Jiangsu/1/2009 (H1N1) influenza virus-induced cell injury. In the infected mice, geniposide treatment significantly restored the body weights, decreased the mortality, alleviated viral titres and virus-induced lung lesions. Geniposide substantially inhibited the virus-induced alveolar wall changes, alveolar haemorrhage and neutrophil-infiltration in lung tissues. Levels of inflammatory mediators, including tumour necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin (IL)-4, IL-6 and IL-10 were also markedly altered after treatment with geniposide.

CONCLUSIONS

Our investigation suggested that geniposide effectively inhibited cell damage mediated by pandemic A/Jiangsu/1/2009 (H1N1) influenza virus and mitigated virus-induced acute inflammation.

Influenza antivirals currently in late-phase clinical trial

Influenza antiviral drugs are important for the control of influenza, most specifically for the treatment of influenza patients with severe disease following infection with a seasonal influenza virus, a newly emerging influenza strain, or in the event of a pandemic. Many influenza antivirals that are currently under investigation in late‐stage clinical trials differ in their mechanism of action compared to drugs currently licensed for the treatment of influenza. Nitazoxanide and DAS181 target components of the host cell and alter the ability of the virus to replicate efficiently, while small molecule drugs such as T705, JNJ63623872 and S‐033188 bind to the viral polymerase complex and restrict viral replication. Monoclonal antibodies that are currently in clinical trial for the treatment of influenza most commonly are targeted to the stem region of the haemagglutinin molecule. Early findings from animal models and in vitro studies suggest that many of the new antiviral drugs when tested in combination with oseltamivir have improved effectiveness over monotherapy. Clinical trials assessing both monotherapy and combination therapy are currently under investigation. It is hoped that as new antivirals are licensed, they will improve the standard of care and outcomes for influenza patients with severe disease.

Progress of small molecular inhibitors in the development of anti-influenza virus agents

The influenza pandemic is a major threat to human health, and highly aggressive strains such as H1N1, H5N1 and H7N9 have emphasized the need for therapeutic strategies to combat these pathogens. Influenza anti-viral agents, especially active small molecular inhibitors play important roles in controlling pandemics while vaccines are developed. Currently, only a few drugs, which function as influenza neuraminidase (NA) inhibitors and M2 ion channel protein inhibitors, are approved in clinical. However, the acquired resistance against current anti-influenza drugs and the emerging mutations of influenza virus itself remain the major challenging unmet medical needs for influenza treatment. It is highly desirable to identify novel anti-influenza agents. This paper reviews the progress of small molecular inhibitors act as antiviral agents, which include hemagglutinin (HA) inhibitors, RNA-dependent RNA polymerase (RdRp) inhibitors, NA inhibitors and M2 ion channel protein inhibitors etc. Moreover, we also summarize new, recently reported potential targets and discuss strategies for the development of new anti-influenza virus drugs.

How I treat respiratory viral infections in the setting of intensive chemotherapy or hematopoietic cell transplantation

The widespread use of multiplex molecular diagnostics has led to a significant increase in the detection of respiratory viruses in patients undergoing cytotoxic chemotherapy and hematopoietic cell transplantation (HCT). Respiratory viruses initially infect the upper respiratory tract and then progress to lower respiratory tract disease in a subset of patients. Lower respiratory tract disease can manifest itself as airflow obstruction or viral pneumonia, which can be fatal. Infection in HCT candidates may require delay of transplantation. The risk of progression differs between viruses and immunosuppressive regimens. Risk factors for progression and severity scores have been described, which may allow targeting treatment to high-risk patients. Ribavirin is the only antiviral treatment option for noninfluenza respiratory viruses; however, high-quality data demonstrating its efficacy and relative advantages of the aerosolized versus oral form are lacking. There are significant unmet needs, including data defining the virologic characteristics and clinical significance of human rhinoviruses, human coronaviruses, human metapneumovirus, and human bocavirus, as well as the need for new treatment and preventative options.

Using the Ferret as an Animal Model for Investigating Influenza Antiviral Effectiveness

The concern of the emergence of a pandemic influenza virus has sparked an increased effort toward the development and testing of novel influenza antivirals. Central to this is the animal model of influenza infection, which has played an important role in understanding treatment effectiveness and the effect of antivirals on host immune responses. Among the different animal models of influenza, ferrets can be considered the most suitable for antiviral studies as they display most of the human-like symptoms following influenza infections, they can be infected with human influenza virus without prior viral adaptation and have the ability to transmit influenza virus efficiently between one another. However, an accurate assessment of the effectiveness of an antiviral treatment in ferrets is dependent on three major experimental considerations encompassing firstly, the volume and titer of virus, and the route of viral inoculation. Secondly, the route and dose of drug administration, and lastly, the different methods used to assess clinical symptoms, viral shedding kinetics and host immune responses in the ferrets. A good understanding of these areas is necessary to achieve data that can accurately inform the human use of influenza antivirals. In this review, we discuss the current progress and the challenges faced in these three major areas when using the ferret model to measure influenza antiviral effectiveness.

Phase 1 clinical trials of DAS181, an inhaled sialidase, in healthy adults

DAS181, (study drug, Fludase®) was developed for treatment of influenza and parainfluenza infections. Delivered by inhalation, DAS181 cleaves sialic acid receptors from respiratory epithelial cells. Treatment of influenza for three days with DAS181 reduced viral shedding. To increase deposition in the upper airways and decrease systemic absorption, the particle size was increased to 10μm. We conducted two Phase I trials with three cohorts, randomized 2:1, active drug to placebo. The initial cohort got a single 20mg dose of DAS181, or placebo; the second, 20mg DAS181 or placebo for 10days, and the third got 20mg of DAS181 or placebo for 3days. Formulations differed slightly in their excipients. Subjects in the 1- and 3-day cohorts completed dosing without serious adverse events. Two subjects in the 10-day cohort stopped at Day 9 after developing respiratory and systemic symptoms, and a third experienced a decrease in FEV1 (Forced Expiratory Volume in 1s) after the 9th dose and a further decline after the 10th dose. Plasma DAS181, in the 10-day cohort, peaked and began falling before the last dose. Antibodies, predominately IgG with neutralizing activity, were detected in 15/18 subjects by Day 30. The highest IgG concentrations were in the 10-day cohort. The respiratory adverse events occurring after seven days and rapid drug clearance during continued dosing are consistent with the induction of DAS181 antibodies. This could preclude use of this medication for longer than seven days or for repeated courses. (These studies have been registered at ClinicalTrials.gov under registration Nos. NCT 00527865 and NCT 01651494.).

Influenza virus-host interactomes as a basis for antiviral drug development

Currently, antiviral drugs that target specific viral protein functions are available for the treatment of influenza; however, concern regarding the emergence of drug-resistant viruses is warranted, as is the urgent need for new antiviral targets, including non-viral targets, such as host cellular factors. Viruses rely on host cellular functions to replicate, and therefore a thorough understanding of the roles of virus-host interactions during influenza virus replication is essential to develop novel anti-influenza drugs that target the host factors involved in virus replication. Here, we review recent studies that used several approaches to identify host factors involved in influenza virus replication. These studies have permitted the construction of an interactome map of virus-host interactions in the influenza virus life cycle, clarifying the entire life cycle of this virus and accelerating the development of new antiviral drugs with a low propensity for the development of resistance.

Antiviral therapy in seasonal influenza and 2009 H1N1 pandemic influenza: Korean experiences and perspectives

Influenza is a major cause of substantial morbidity and mortality in humans every year. Vaccination is the main strategy to prevent influenza infection, but antiviral agents also play an important role in the control of both seasonal and pandemic influenza. During the influenza A/H1N1 pandemic in 2009, early prompt antiviral therapy may have reduced the severity of the influenza outcomes including pneumonia, hospitalization and mortality in the Republic of Korea. Since the 2009 H1N1 pandemic, there have been increasing usages of antiviral agents for the treatment of patients with seasonal influenza. Although currently rare, antiviral resistance among influenza viruses may emerge and increase with increased use of neuraminidase inhibitors. New agents with different modes of action are under investigation, including favipiravir, DAS181, nitazoxanide and broad-spectrum neutralizing monoclonal antibodies. Data are limited with respect to high-dose and combination antiviral therapies. So, clinical trials are warranted to evaluate diverse antiviral combinations that may be synergistic and less likely to induce breakthrough resistance.

Developments in the treatment of severe influenza: lessons from the pandemic of 2009 and new prospects for therapy

PURPOSE OF REVIEW

Cases of severe influenza may occur during seasonal epidemics, following sporadic zoonotic influenza A transmission from animal reservoirs or on a massive scale with the unpredictable emergence of a new pandemic influenza strain. Clinical experience identifies unmet medical need for additional therapies for influenza, in particular to treat severely unwell adults and children. During and following the pandemic of 2009, a wealth of data from hospitalized cases of influenza from many different countries accumulated and are now starting to emerge. Observational clinical data provide information about the efficacy of existing antiviral drugs in severely ill patients. The development pipeline for new therapies contains several promising agents which are focussed on a range of viral targets, and opens the possibility of combination antiviral therapy for the first time, which may be especially useful in clinically challenging cases. Advances in immunological methods and recombinant protein engineering support the potential for use of immunomodulating therapies as adjuncts in treatment of severe influenza.

RECENT FINDINGS

The main themes are the importance of treating severe influenza early, considering multiple therapy options and the relevance of observational clinical data to treatment of severely ill and risk groups.

SUMMARY

Clinicians, who may have only seen the media headlines following discussion of reviews which deal with randomized controlled trials of neuraminidase inhibitor drug use in mild uncomplicated influenza in the community, may be hesitant to prescribe these drugs. Observational data arising from treatment of severely ill individuals support use of these drugs early in illness and show improvement in outcomes associated with drug use.

Management of respiratory viral infections in hematopoietic cell transplant recipients and patients with hematologic malignancies

Despite preventive strategies and increased awareness, a high incidence of respiratory viral infections still occur in patients with hematologic malignancies (HMs) and in recipients of hematopoietic cell transplant (HCT). Progression of these viral infections to lower respiratory tract may prove fatal, especially in HCT recipients. Increasing evidence on the successful use of ribavirin (alone or in combination with immunomodulators) for the treatment of respiratory syncytial virus infections in HM patients and HCT recipients is available from retrospective studies; however, prospective clinical trials are necessary to establish its efficacy with confidence. The impact on progression to pneumonitis and/or mortality of treating parainfluenza virus infections with available (ribavirin) or investigational (DAS181) antiviral agents still needs to be determined. Influenza infections have been successfully treated with neuraminidase inhibitors (oseltamivir or zanamivir); however, the efficacy of these agents for influenza pneumonia has not been established, and immunocompromised patients are highly susceptible to emergence of antiviral drug resistance, most probably due to prolonged viral shedding. Infection control measures and an appreciation of the complications following respiratory viral infections in immunocompromised patients remain crucial for reducing transmission. Future studies should focus on strategies to identify patients at high risk for increased morbidity and mortality from these infections and to determine the efficacy of novel or available antiviral drugs.

Treatment of resistant influenza virus infection in a hospitalized patient with cystic fibrosis with DAS181, a host-directed antiviral

We report a cystic fibrosis patient infected with influenza 2009H1N1 who had persistent viral shedding and clinical deterioration despite prolonged treatment with oseltamivir and zanamivir. The patient was diagnosed with H275Y neuraminidase inhibitor resistant influenza during treatment, thus was treated for 10 days with DAS181, an investigational host-directed inhaled sialidase fusion protein. Viral clearance occurred after 5 days of therapy and the patient became eligible for lung transplantation. Although the patient succumbed prior to receiving a transplant, this case exemplifies the potential utility of a host-directed approach against influenza which has potential to become resistant to neuraminidase inhibitors.

Experimental antiviral drugs against pandemic influenza

ABSTRACT 

The aim of this review is to selectively identify some representative experimental antiviral drugs which are promising in preclinical and clinical studies, but yet to be fully licensed, and discuss how they have a potential role in complementing our existing arsenal of antiviral drugs to combat pandemic influenza. This review will focus on discussing their mechanisms of actions, current state of development, safety, efficacy from preclinical and/or clinical studies. These experimental drugs can be classified into virus or host specific, depending on the individual drug's targeting action. This article will highlight novel anti-inflammatory drugs which can be used to mitigate cytokine storm caused by pandemic influenza viruses as a treatment option or strategy.

Compounds with anti-influenza activity: present and future of strategies for the optimal treatment and management of influenza. Part II: Future compounds against influenza virus

In the first part of this overview, we described the life cycle of the influenza virus and the pharmacological action of the currently available drugs. This second part provides an overview of the molecular mechanisms and targets of still-experimental drugs for the treatment and management of influenza. Briefly, we can distinguish between compounds with anti-influenza activity that target influenza virus proteins or genes, and molecules that target host components that are essential for viral replication and propagation. These latter compounds have been developed quite recently. Among the first group, we will focus especially on hemagglutinin, M2 channel and neuraminidase inhibitors. The second group of compounds may pave the way for personalized treatment and influenza management. Combination therapies are also discussed. In recent decades, few antiviral molecules against influenza virus infections have been available; this has conditioned their use during human and animal outbreaks. Indeed, during seasonal and pandemic outbreaks, antiviral drugs have usually been administered in mono-therapy and, sometimes, in an uncontrolled manner to farm animals. This has led to the emergence of viral strains displaying resistance, especially to compounds of the amantadane family. For this reason, it is particularly important to develop new antiviral drugs against influenza viruses. Indeed, although vaccination is the most powerful means of mitigating the effects of influenza epidemics, antiviral drugs can be very useful, particularly in delaying the spread of new pandemic viruses, thereby enabling manufacturers to prepare large quantities of pandemic vaccine. In addition, antiviral drugs are particularly valuable in complicated cases of influenza, especially in hospitalized patients. To write this overview, we mined various databases, including Embase, PubChem, DrugBank and Chemical Abstracts Service, and patent repositories.

Antiviral combinations for severe influenza

Observational data suggest that the treatment of influenza infection with neuraminidase inhibitors decreases progression to more severe illness, especially when treatment is started soon after symptom onset. However, even early treatment might fail to prevent complications in some patients, particularly those infected with novel viruses such as the 2009 pandemic influenza A H1N1, avian influenza A H5N1 virus subtype, or the avian influenza A H7N9 virus subtype. Furthermore, treatment with one antiviral drug might promote the development of antiviral resistance, especially in immunocompromised hosts and critically ill patients. An obvious strategy to optimise antiviral therapy is to combine drugs with different modes of action. Because host immune responses to infection might also contribute to illness pathogenesis, improved outcomes might be gained from the combination of antiviral therapy with drugs that modulate the immune response in an infected individual. We review available data from preclinical and clinical studies of combination antiviral therapy and of combined antiviral-immunomodulator therapy for influenza. Early-stage data draw attention to several promising antiviral combinations with therapeutic potential in severe infections, but there remains a need to substantiate clinical benefit. Combination therapies with favourable experimental data need to be tested in carefully designed aclinical trials to assess their efficacy.

An investigational antiviral drug, DAS181, effectively inhibits replication of zoonotic influenza A virus subtype H7N9 and protects mice from lethality

Human infections caused by avian influenza A virus type subtype H7N9 have been associated with substantial morbidity and mortality. Emergence of virus variants carrying markers of decreased susceptibility to neuraminidase inhibitors was reported. Here we show that DAS181 (Fludase), an antiviral drug with sialidase activity, potently inhibited replication of wild-type influenza A(H7N9) and its oseltamivir-resistant R292K variants in mice. A once-daily administration initiated early after lethal infection hampered body weight loss and completely protected mice from lethality. We observed a time-dependent effect for 24-72-hour delayed DAS181 treatments on morbidity and mortality. The results warrant further investigation of DAS181 for influenza treatment.

Seasonal Human Influenza: Treatment Options

Seasonal influenza can be a self-limiting illness in healthy individuals but is associated with short-term morbidity and economic burden. Influenza can cause significant morbidity and mortality in young children, the elderly, pregnant and post-partum women, patients with co-morbidities and the immunocompromised. Neuraminidase inhibitors (NAIs) are the treatment of choice for influenza due to widespread resistance to the adamantanes. NAIs are efficacious for the treatment of influenza in ambulatory patients with mild illness, when initiated within 48 h of symptom onset. Early treatment with NAIs has been shown to reduce otitis media in children, and lower respiratory tract complications, resulting in antibiotic therapy, in adults. Evidence on the efficacy of NAIs for the prevention of influenza-related complications in at-risk populations, based on reviews of data from randomised trials is inconclusive. However, observational studies suggest that in hospitalised patients early treatment with NAIs has been associated with reduced mortality. NAIs should be initiated as soon as possible in patients at high-risk of influenza-related complications, with suspected or proven influenza, hospitalised patients and patients with severe or progressive disease. NAIs can be considered in previously healthy patients when therapy can be initiated within 48 h of symptom onset. In previously healthy patients, the therapeutic efficacy of oseltamivir is time-dependent, with maximal benefit observed when therapy is initiated within 48 h of symptom onset. However, several observational studies suggest therapeutic benefit beyond 48 h, in hospitalised patients, severe disease, and patients at high risk of complications, including pregnant women. NAIs should be considered in patients at high risk of influenza-related complications who present late. Further studies are needed to define the optimal timing of NAIs. Oseltamivir-resistant virus has been widely reported but is predominantly an issue in H1N1 seasonal influenza. Zanamivir-resistant influenza virus is rare, and inhaled or intravenous (IV) zanamivir is the treatment of choice in proven or suspected oseltamivir-resistant virus. Intubated patients with severe influenza can be treated with oseltamivir (suspension) administered via nasogastric tube. The commercial dry powder formulation of zanamivir should not be administered, via nebulisation, as it has been associated with ventilator malfunction and mortality. In intubated patients, when there are concerns about gastric absorption, IV zanamivir should be obtained under Emergency Investigational New Drug access schemes. Currently available evidence does not support the use of high-dose or extended-duration oseltamivir in patients with severe influenza, but does require further investigation. Extracorporeal membrane oxygenation has not been shown to be superior to conventional management in patients with influenza-associated acute respiratory distress syndrome and should be considered as salvage therapy. Corticosteriods should not be used in the treatment of severe influenza as this has been associated with increased risk of mortality and bacterial superinfection.

Designing anti-influenza aptamers: novel quantitative structure activity relationship approach gives insights into aptamer-virus interaction

This study describes the development of aptamers as a therapy against influenza virus infection. Aptamers are oligonucleotides (like ssDNA or RNA) that are capable of binding to a variety of molecular targets with high affinity and specificity. We have studied the ssDNA aptamer BV02, which was designed to inhibit influenza infection by targeting the hemagglutinin viral protein, a protein that facilitates the first stage of the virus' infection. While testing other aptamers and during lead optimization, we realized that the dominant characteristics that determine the aptamer's binding to the influenza virus may not necessarily be sequence-specific, as with other known aptamers, but rather depend on general 2D structural motifs. We adopted QSAR (quantitative structure activity relationship) tool and developed computational algorithm that correlate six calculated structural and physicochemical properties to the aptamers' binding affinity to the virus. The QSAR study provided us with a predictive tool of the binding potential of an aptamer to the influenza virus. The correlation between the calculated and actual binding was R2 = 0.702 for the training set, and R2 = 0.66 for the independent test set. Moreover, in the test set the model's sensitivity was 89%, and the specificity was 87%, in selecting aptamers with enhanced viral binding. The most important properties that positively correlated with the aptamer's binding were the aptamer length, 2D-loops and repeating sequences of C nucleotides. Based on the structure-activity study, we have managed to produce aptamers having viral affinity that was more than 20 times higher than that of the original BV02 aptamer. Further testing of influenza infection in cell culture and animal models yielded aptamers with 10 to 15 times greater anti-viral activity than the BV02 aptamer. Our insights concerning the mechanism of action and the structural and physicochemical properties that govern the interaction with the influenza virus are discussed.

Detection and management of antiviral resistance for influenza viruses

Neuraminidase inhibitors (NAIs) are first-line agents for the treatment and prevention of influenza virus infections. As for other antivirals, the development of resistance to NAIs has become an important concern particularly in the case of A(H1N1) viruses and oseltamivir. The most frequently reported change conferring oseltamivir resistance in that viral context is the H275Y neuraminidase mutation (N1 numbering). Recent studies have shown that, in the presence of the appropriate permissive mutations, the H275Y variant can retain virulence and transmissibility in some viral backgrounds. Most oseltamivir-resistant influenza A virus infections can be managed with the use of inhaled or intravenous zanamivir, another NAI. New NAI compounds and non-neuraminidase agents as well as combination therapies are currently in clinical evaluation for the treatment for severe influenza infections.

Advances in antivirals for non-influenza respiratory virus infections

Progress in the development of antivirals for non‐influenza respiratory viruses has been slow with the result that many unmet medical needs and few approved agents currently exist. This commentary selectively reviews examples of where specific agents have provided promising clinical benefits in selected target populations and also considers potential therapeutics for emerging threats like the SARS and Middle East respiratory syndrome coronaviruses. Recent studies have provided encouraging results in treating respiratory syncytial virus infections in lung transplant recipients, serious parainfluenza virus and adenovirus infections in immunocompromised hosts, and rhinovirus colds in outpatient asthmatics. While additional studies are needed to confirm the efficacy and safety of the specific agents tested, these observations offer the opportunity to expand therapeutic studies to other patient populations.

Prevention of influenza by targeting host receptors using engineered proteins

There is a need for new approaches for the control of influenza given the burden caused by annual seasonal outbreaks, the emergence of viruses with pandemic potential, and the development of resistance to current antiviral drugs. We show that multivalent biologics, engineered using carbohydrate-binding modules specific for sialic acid, mask the cell-surface receptor recognized by the influenza virus and protect mice from a lethal challenge with 2009 pandemic H1N1 influenza virus. The most promising biologic protects mice when given as a single 1-μg intranasal dose 7 d in advance of viral challenge. There also is sufficient virus replication to establish an immune response, potentially protecting the animal from future exposure to the virus. Furthermore, the biologics appear to stimulate inflammatory mediators, and this stimulation may contribute to their protective ability. Our results suggest that this host-targeted approach could provide a front-line prophylactic that has the potential to protect against any current and future influenza virus and possibly against other respiratory pathogens that use sialic acid as a receptor.

Antiviral susceptibility of variant influenza A(H3N2)v viruses isolated in the United States from 2011 to 2013

Since 2011, outbreaks caused by influenza A(H3N2) variant [A(H3N2)v] viruses have become a public health concern in the United States. The A(H3N2)v viruses share the A(H1N1)pdm09 M gene containing the marker of M2 blocker resistance, S31N, but do not contain any known molecular markers associated with resistance to neuraminidase (NA) inhibitors (NAIs). Using a fluorescent NA inhibition (NI) assay, the susceptibilities of recovered A(H3N2)v viruses (n=168) to FDA-approved (oseltamivir and zanamivir) and other (peramivir, laninamivir, and A-315675) NAIs were assessed. All A(H3N2)v viruses tested, with the exception of a single virus strain, A/Ohio/88/2012, isolated from an untreated patient, were susceptible to the NAIs tested. The A/Ohio/88/2012 virus contained two rare substitutions, S245N and S247P, in the NA and demonstrated reduced inhibition by oseltamivir (31-fold) and zanamivir (66-fold) in the NI assay. Using recombinant NA (recNA) proteins, S247P was shown to be responsible for the observed altered NAI susceptibility, in addition to an approximately 60% reduction in NA enzymatic activity. The S247P substitution has not been previously reported as a molecular marker of reduced susceptibility to the NAIs. Using cell culture assays, the investigational antiviral drugs nitazoxanide, favipiravir, and fludase were shown to inhibit the replication of A(H3N2)v viruses, including the virus with the S247P substitution in the NA. This report demonstrates the importance of continuous monitoring of susceptibility of zoonotic influenza viruses to available and investigational antiviral drugs.

Receptor binding properties of the influenza virus hemagglutinin as a determinant of host range

Host cell attachment by influenza A viruses is mediated by the hemagglutinin glycoprotein (HA), and the recognition of specific types of sialic acid -containing glycan receptors constitutes one of the major determinants of viral host range and transmission properties. Structural studies have elucidated some of the viral determinants involved in receptor recognition of avian-like and human-like receptors for various subtypes of influenza A viruses, and these provide clues relating to the mechanisms by which viruses evolve to adapt to human hosts. We discuss structural aspects of receptor binding by influenza HA, as well as the biological implications of functional interplay involving HA binding, NA sialidase functions, the effects of antigenic drift, and the inhibitory properties of natural glycans present on mucosal surfaces.

Bitter-sweet symphony: glycan-lectin interactions in virus biology

Glycans are carbohydrate modifications typically found on proteins or lipids, and can act as ligands for glycan-binding proteins called lectins. Glycans and lectins play crucial roles in the function of cells and organs, and in the immune system of animals and humans. Viral pathogens use glycans and lectins that are encoded by their own or the host genome for their replication and spread. Recent advances in glycobiological research indicate that glycans and lectins mediate key interactions at the virus-host interface, controlling viral spread and/or activation of the immune system. This review reflects on glycan–lectin interactions in the context of viral infection and antiviral immunity. A short introduction illustrates the nature of glycans and lectins, and conveys the basic principles of their interactions. Subsequently, examples are discussed highlighting specific glycan–lectin interactions and how they affect the progress of viral infections, either benefiting the host or the virus. Moreover, glycan and lectin variability and their potential biological consequences are discussed. Finally, the review outlines how recent advances in the glycan–lectin field might be transformed into promising new approaches to antiviral therapy.

Novel antiviral agents for respiratory viral infection in immunocompromised adults

Respiratory viruses cause significant morbidity and mortality in immunocompromised populations such as stem cell transplant and solid organ transplant patients. Few viruses causing respiratory tract infection have an approved therapy, and many of the viruses have no therapeutic options at all. In this article, we describe novel agents under development for treatment options against several respiratory viruses.

Jiawei-Yupingfeng-Tang, a Chinese herbal formula, inhibits respiratory viral infections in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Jiawei-Yupingfeng-Tang (JYT) is a Chinese herbal formula that is widely used to treat respiratory tract illness. However, the effect of JYT on respiratory viruses remains unknown. The influenza virus (IFV) and the human respiratory syncytial virus (HRSV) cause millions of cases of severe illness per year, and many of these illnesses develop into lethal pneumonia. The aim of this study is to evaluate whether JYT can be used to treat these infections.

MATERIALS AND METHODS

The effect of JYT against IFV and HRSV was tested using a plaque reduction assay in the lower respiratory tract cell line A549. The expression of ICAM-1 was determined by real-time RT-PCR and western blotting. A mouse model infected with lethal influenza developing into interstitial pneumonia was used to evaluate the effect of JYT in vivo.

RESULTS

JYT extract inhibited both IFV and HRSV in a dose-dependent manner when given before, during and after a viral infection. JYT was effective in blocking the entry of the virus. Furthermore, pre-treatment with JYT reduced the susceptibility of cells to the invasion of HRSV by inhibiting the expression of ICAM-1. Importantly, JYT extract increased the survival rate of lethal influenza-infected mice, prolonged the survival time and alleviated the virus-induced lung lesions, which is comparable with the effects of ribavirin treatment.

CONCLUSIONS

These data support JYT as an alternative modality to be used in the treatment of respiratory viral infection induced by HRSV and IFV.

A comprehensive map of the influenza A virus replication cycle

Background

Influenza is a common infectious disease caused by influenza viruses. Annual epidemics cause severe illnesses, deaths, and economic loss around the world. To better defend against influenza viral infection, it is essential to understand its mechanisms and associated host responses. Many studies have been conducted to elucidate these mechanisms, however, the overall picture remains incompletely understood. A systematic understanding of influenza viral infection in host cells is needed to facilitate the identification of influential host response mechanisms and potential drug targets.

Description

We constructed a comprehensive map of the influenza A virus (‘IAV’) life cycle (‘FluMap’) by undertaking a literature-based, manual curation approach. Based on information obtained from publicly available pathway databases, updated with literature-based information and input from expert virologists and immunologists, FluMap is currently composed of 960 factors (i.e., proteins, mRNAs etc.) and 456 reactions, and is annotated with ~500 papers and curation comments. In addition to detailing the type of molecular interactions, isolate/strain specific data are also available. The FluMap was built with the pathway editor CellDesigner in standard SBML (Systems Biology Markup Language) format and visualized as an SBGN (Systems Biology Graphical Notation) diagram. It is also available as a web service (online map) based on the iPathways+ system to enable community discussion by influenza researchers. We also demonstrate computational network analyses to identify targets using the FluMap.

Conclusion

The FluMap is a comprehensive pathway map that can serve as a graphically presented knowledge-base and as a platform to analyze functional interactions between IAV and host factors. Publicly available webtools will allow continuous updating to ensure the most reliable representation of the host-virus interaction network. The FluMap is available at http://www.influenza-x.org/flumap/.