Zanamivir: an update of its use in influenza

Natural Product-Derived Phytochemicals for Influenza A Virus (H1N1) Prevention and Treatment

Influenza A (H1N1) viruses are prone to antigenic mutations and are more variable than other influenza viruses. Therefore, they have caused continuous harm to human public health since the pandemic in 2009 and in recent times. Influenza A (H1N1) can be prevented and treated in various ways, such as direct inhibition of the virus and regulation of human immunity. Among antiviral drugs, the use of natural products in treating influenza has a long history, and natural medicine has been widely considered the focus of development programs for new, safe anti-influenza drugs. In this paper, we focus on influenza A (H1N1) and summarize the natural product-derived phytochemicals for influenza A virus (H1N1) prevention and treatment, including marine natural products, flavonoids, alkaloids, terpenoids and their derivatives, phenols and their derivatives, polysaccharides, and derivatives of natural products for prevention and treatment of influenza A (H1N1) virus. We further discuss the toxicity and antiviral mechanism against influenza A (H1N1) as well as the druggability of natural products. We hope that this review will facilitate the study of the role of natural products against influenza A (H1N1) activity and provide a promising alternative for further anti-influenza A drug development.

Synthetic pentatrideca-valent triazolylsialoside inhibits influenza virus hemagglutinin/neuraminidase and aggregates virion particles

A synthetic multivalent hemagglutinin and neuraminidase inhibitor was developed by the conjugation of a septa-valent triazolylsialoside to bovine serum albumin using di-(N-succinimidyl) adipate. Matrixassisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) confirmed the attachment of five septa-valent sialyl lactosides to the protein backbone, resulting in a pentatrideca-valent sialyl conjugate. This pseudo-glycoprotein demonstrated a high affinity for hemagglutinin/neuraminidase as well as for the drug-resistant NA mutation on the influenza virus surface due to the cluster effect. The conjugate also exhibited potent antiviral activity against a wide range of virus strains without cytotoxicity at high concentrations. Mechanistic studies revealed that the pentatrideca-valent sialyl conjugate bound strongly to the influenza virion particles through interactions with HA/NA on the virion surfaces. The KD of the interaction was approximately 1 μM, as determined by isothermal calorimetric titration, allowing the capture and trapping of the influenza virions and preventing their further infection of host cells. These findings provide insight into the development of new antiviral agents using multivalent sialic acid clusters.

Preparation of eicosavalent triazolylsialoside-conjugated human serum albumin as a dual hemagglutinin/neuraminidase inhibitor and virion adsorbent for the prevention of influenza infection

A triazolylsialoside-human serum albumin conjugate was prepared as a multivalent hemagglutinin and neuraminidase inhibitor using a di-(N-succinimidyl) adipate strategy. Matrix-Assisted Laser Desorption/Ionization-Time of Flight-Mass Spectrometry (MALDI-TOF-MS) indicated that five tetravalent sialyl galactosides were grafted onto the protein backbone resulting in an eicosavalent triazolylsialoside-protein complex. Compared with monomeric sialic acid, molecular interaction studies showed that the synthetic pseudo-glycoprotein bound tightly not only to hemagglutinin (HA)/neuraminidase (NA) but also to mutated drug-resistant NA on the surface of the influenza virus with a dissociation constant (KD) in the 1 μM range, attributed to the cluster effect. Moreover, this glycoconjugate exhibited potent antiviral activity against a broad spectrum of virus strains and showed no cytotoxicity towards Human Umbilical Vein Endothelial Cells (HUVECs) and Madin-Darby canine kidney (MDCK) cells at high concentrations. Further mechanistic studies demonstrated this multivalent sialyl conjugate showed strong capture and trapping of influenza virions, thus disrupting the ability of the influenza virus to infect host cells. This research lays the experimental foundation for the development of new antiviral agents based on multivalent sialic acid-protein conjugates.

Emerging antiviral therapies and drugs for the treatment of influenza

INTRODUCTION

Both vaccines and antiviral drugs represent the mainstay for preventing and treating influenza. However, approved M2 ion channel inhibitors, neuraminidase inhibitors, polymerase inhibitors, and various vaccines cannot meet therapeutic needs because of viral resistance. Thus, the discovery of new targets for the virus or host and the development of more effective inhibitors are essential to protect humans from the influenza virus.

AREAS COVERED

This review summarizes the latest progress in vaccines and antiviral drug research to prevent and treat influenza, providing the foothold for developing novel antiviral inhibitors.

EXPERT OPINION

Vaccines embody the most effective approach to preventing influenza virus infection, and recombinant protein vaccines show promising prospects in developing next-generation vaccines. Compounds targeting the viral components of RNA polymerase, hemagglutinin and nucleoprotein, and the modification of trusted neuraminidase inhibitors are future research directions for anti-influenza virus drugs. In addition, some host factors affect the replication of virus in vivo, which can be used to develop antiviral drugs.

Recent Advances in Application of Computer-Aided Drug Design in Anti-Influenza A Virus Drug Discovery

Influenza A is an acute respiratory infectious disease caused by the influenza A virus, which seriously threatens global human health and causes substantial economic losses every year. With the emergence of new viral strains, anti-influenza drugs remain the most effective treatment for influenza A. Research on traditional, innovative small-molecule drugs faces many challenges, while computer-aided drug design (CADD) offers opportunities for the rapid and effective development of innovative drugs. This literature review describes the general process of CADD, the viral proteins that play an essential role in the life cycle of the influenza A virus and can be used as therapeutic targets for anti-influenza drugs, and examples of drug screening of viral target proteins by applying the CADD approach. Finally, the main limitations of current CADD strategies in anti-influenza drug discovery and the field's future directions are discussed.

A roadmap to pulmonary delivery strategies for the treatment of infectious lung diseases

Pulmonary drug delivery is a highly attractive topic for the treatment of infectious lung diseases. Drug delivery via the pulmonary route offers unique advantages of no first-pass effect and high bioavailability, which provides an important means to deliver therapeutics directly to lung lesions. Starting from the structural characteristics of the lungs and the biological barriers for achieving efficient delivery, we aim to review literatures in the past decade regarding the pulmonary delivery strategies used to treat infectious lung diseases. Hopefully, this review article offers new insights into the future development of therapeutic strategies against pulmonary infectious diseases from a delivery point of view.

Airway Delivery of Anti-influenza Monoclonal Antibodies Results in Enhanced Antiviral Activities and Enables Broad-Coverage Combination Therapies

Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

Effective and reliable anti-influenza treatments are acutely needed and passive immunizations using broadly neutralizing anti-influenza monoclonal antibodies (bNAbs) are a promising emerging approach. Because influenza infections are initiated in and localized to the pulmonary tract, and newly formed viral particles egress from the apical side of the lung epithelium, we compared the effectiveness of hemagglutinin (HA) stalk-binding bNAbs administered through the airway (intranasal or via nebulization) versus the systemic route (intraperitoneal or intravenous). Airway deliveries of various bNAbs were 10- to 50-fold more effective than systemic deliveries of the same bNAbs in treating H1N1, H3N2, B/Victoria-, and B/Yamagata-lineage influenza viral infections in mouse models. The potency of airway-delivered anti-HA bNAbs was highly dependent on antiviral neutralization activity, with little dependence on the effector function of the antibody. In contrast, the effectiveness of systemically delivered anti-HA bNAbs was not dependent on antiviral neutralization, but critically dependent on antibody effector functions. Concurrent administration of a neutralizing/effector function-positive bNAb via the airway and systemic routes showed increased effectiveness. The small amount of airway-delivered bNAbs needed for effective influenza treatment creates the opportunity to combine potent bNAbs with different anti-influenza specificities to generate a cost-effective antiviral therapy that provides broad coverage against all circulating influenza strains infecting humans. A 3 mg/kg dose of the novel triple antibody combination CF-404 (i.e., 1 mg/kg of each component bNAb) delivered to the airway was shown to effectively prevent weight loss and death in mice challenged with ten 50% lethal dose (LD₅₀) inoculums of either H1N1, H3N2, B/Victoria-lineage, or B/Yamagata-lineage influenza viruses.

IMPORTANCE Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

Development of effective anti-influenza drugs: congeners and conjugates - a review

Influenza is a long-standing health problem. For treatment of seasonal flu and possible pandemic infections, there is a need to develop new anti-influenza drugs that have good bioavailability against a broad spectrum of influenza viruses, including the resistant strains. Relenza™ (zanamivir), Tamiflu™ (the phosphate salt of oseltamivir), Inavir™ (laninamivir octanoate) and Rapivab™ (peramivir) are four anti-influenza drugs targeting the viral neuraminidases (NAs). However, some problems of these drugs should be resolved, such as oral availability, drug resistance and the induced cytokine storm. Two possible strategies have been applied to tackle these problems by devising congeners and conjugates. In this review, congeners are the related compounds having comparable chemical structures and biological functions, whereas conjugate refers to a compound having two bioactive entities joined by a covalent bond. The rational design of NA inhibitors is based on the mechanism of the enzymatic hydrolysis of the sialic acid (Neu5Ac)-terminated glycoprotein. To improve binding affinity and lipophilicity of the existing NA inhibitors, several methods are utilized, including conversion of carboxylic acid to ester prodrug, conversion of guanidine to acylguanidine, substitution of carboxylic acid with bioisostere, and modification of glycerol side chain. Alternatively, conjugating NA inhibitors with other therapeutic entity provides a synergistic anti-influenza activity; for example, to kill the existing viruses and suppress the cytokines caused by cross-species infection.

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

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

Seasonal, avian, and novel H1N1 influenza: prevention and treatment modalities

OBJECTIVE

To review the pathophysiology, pandemics/epidemics, transmissibility, clinical presentation, treatment, prevention/immunization, and resistance associated with seasonal, avian, and swine influenza.

DATA SOURCES

Literature was obtained from MEDLINE (1966-October 2009) and International Pharmaceutical Abstracts (1971-October 2009) using the search terms influenza, seasonal influenza, avian influenza, swine influenza, H1N1, novel H1N1, H3N2, and H5N1.

STUDY SELECTION AND DATA EXTRACTION

Available English-language articles were reviewed, along with information obtained from the Centers for Disease Control and Prevention, the Food and Drug Administration, and the World Health Organization.

DATA SYNTHESIS

The influenza virus has caused disease in birds, swine, and humans for many centuries. Pandemics and epidemics have occurred throughout history and reports of new strains continue to emerge. Two major surface antigenic glycoproteins, hemagglutinin and neuraminidase, have various subtypes, resulting in numerous combinations of these proteins. For example, combinations occur when an influenza strain from a bird "mixes" with a strain from a human. This mixing occurs in a host, often in pigs, resulting in a new strain. This new strain can cause pandemics since people have no immunity to the new strain. An H1N1 subtype pandemic occurred in 1918, causing millions of deaths. Simultaneously, veterinary reports of "influenza" in pigs also emerged. It is postulated that humans infected pigs with this H1N1 virus. H1N1 reappeared in humans in 1976, and more recently in 2009. Other pandemics have occurred with H2N2 and H3N2 strains. In 1997, strain H5N1, which usually causes disease in fowl, was able to infect humans.

CONCLUSIONS

Influenza subtypes continue to change, causing disease in animals and humans. Utilization of immunization and antiviral treatment options are available to prevent, treat, and contain the spread of this infection.

Neuraminidase inhibitor resistance in influenza viruses

Zanamivir and oseltamivir, the currently marketed influenza virus neuraminidase inhibitors (NAIs), are prescribed for the treatment and prophylaxis of influenza and are being stockpiled for pandemic influenza. Oseltamivir resistance has been reported in up to 2% of patients in clinical trials of oseltamivir and in up to 18% of treated children. There are also reports in at least three patients treated with oseltamivir for influenza A (H5N1) infections. At this stage, there are no reports of resistance occurring to zanamivir in immunocompetent patients. Zanamivir and oseltamivir bind differently at the neuraminidase catalytic site and this contributes to different drug resistance profiles. The magnitude and duration of NAI concentrations at the site of infection are also expected to be important factors and are determined by route and timing of drug administration, dose, and pharmacokinetic differences between patients. In addition, the type, strain, and virulence of the influenza strain and the nature of the immune response all appear to play a role in determining the likelihood of drug resistance arising. The clinical significance of a particular NAI-resistant isolate from a patient is often not clear but virus viability and transmissibility are clearly important characteristics. Early initiation of NAI treatment in suspected cases of influenza is important for maximizing efficacy and minimizing the risk of drug resistance. Higher NAI doses and longer periods of treatment may be required for patients with influenza A (H5N1) infections but further work is needed in this area.

Current non-AIDS antiviral chemotherapy

The evolution of antiviral therapy began with developments in the management of influenza and herpes simplex keratitis in the 1960s and early 1970s. However, the field exploded with the successful treatment of herpes simplex encephalitis, herpes zoster and genital herpes simplex virus infections, all occurring in the late 1970s and early 1980s. These advances have contributed to the development of therapies for HIV that have transformed the lives of infected patients in recent years. The clinical fruit of all of these research advances has been an armamentarium of drugs that can be used to successfully treat a variety of viral illnesses. In addition to HIV/AIDS, current antiviral therapy focuses primarily on herpesviruses, hepatitis viruses and influenza. Notably, considerable progress remains to be made in these areas. Moreover, a variety of additional viral diseases currently require the development of specific therapies.

Zanamivir: an influenza virus neuraminidase inhibitor

Zanamivir is the first of two registered neuraminidase inhibitors for the treatment and prophylaxis of influenza. Relenza, an orally inhaled powder form of zanamivir, is currently approved in 19 countries for treatment, and in two for prophylaxis. Relenza reduces the time to alleviation of symptoms by 1 to 2 days in the influenza-positive population, if taken within 48 h of symptom onset, and in prophylaxis in family settings, it confers an 80% reduction in the odds of contracting influenza. The resistance profile of zanamivir is encouraging in the sense that there are still no reports of patients on acute therapy shedding drug-resistant virus. However, patient uptake of the inhaled drug has been insufficient to conclude that drug resistance will not be an issue in the future. All zanamivir-resistant variants selected in the laboratory so far have diminished viability.

Brote nosocomial de gripe en pacientes hematológicos de alto riesgo. Eficacia de las medidas de control y del uso de zanamivir

INTRODUCTION

This study describes a nosocomial outbreak of influenza in high-risk-hematological patients, and the usefulness of epidemiological measures and zanamivir administration for its control.

METHODS

Fifteen patients who had been in contact with a patient with influenza A were included in the study. Viral culture of nasopharyngeal exudate was performed and the epidemiological data, risk factors and clinical outcome were evaluated. The efficacy of early therapy and preventive use of zanamivir was also assessed.

RESULTS

Seven out of 15 patients (46.6%) developed symptoms and in 5 of these 7 cases (71.4%), influenza A virus was isolated. Eight patients did not develop symptoms and viral culture was sterile. All symptomatic patients were isolated, and treatment with inhaled zanamivir (10 mg/12 h, 5 days) was initiated as soon as possible; only one patient developed respiratory failure; the remaining cases had self-limited upper respiratory tract symptoms. There was no associated mortality. Zanamivir prophylaxis was used in three non-symptomatic patients considered to be at high risk. Tolerance to zanamivir was excellent. No new cases were observed after initiation of the preventive measures and use of zanamivir.

CONCLUSION

The attack rate in a nosocomial influenza outbreak can be very high in immunocompromised patients. Prompt initiation of preventive measures, early treatment and prophylaxis with zanamivir may help to limit the extension of these outbreaks.

Management of influenza virus infections with neuraminidase inhibitors: detection, incidence, and implications of drug resistance

Although influenza vaccination remains the primary method for the prevention of influenza, efficacy may be limited by a poor match between the vaccine and circulating strains and the poor response of elderly patients. Hence, there is an important role for antiviral therapy in the management of influenza. While amantadine and rimantadine have been available for the treatment of influenza in some countries for several years, they are only effective against influenza A viruses, they can have neurological and gastrointestinal adverse effects, and resistant virus is rapidly generated. Neuraminidase inhibitors, a new class of drug, are potent and specific inhibitors of all strains of influenza virus, and they have minimal adverse effects. The greatest benefit is seen in those patients presenting <30 hours after development of influenza symptoms, those with severe symptoms or those in high-risk groups. In addition to treatment of the infection, both drugs are effective prophylactically and have been shown to limit spread of infection in close communities, such as families and in nursing homes. No resistant virus strains have been isolated from normal individuals treated with zanamivir. Resistant virus can be isolated from approximately 1% of adults and 5% of paediatric patients with influenza treated with oseltamivir. However, infectivity of mutant viruses is generally compromised. Governments spend millions of dollars on influenza vaccination campaigns; however, once influenza virus is circulating in the community, vaccination cannot limit the spread of disease. A greater promotion of the use of neuraminidase inhibitors for the treatment and prevention of influenza could have a significant impact on limiting its spread. This could result in saving millions of dollars, not only in direct costs associated with medical and hospital care, but also significant savings in indirect costs associated with the loss of productivity at work, school and home environments. For the benefit of all communities, there needs to be a greater awareness of the symptoms of influenza and the efficacy of neuraminidase inhibitors in disease treatment.

Potent and long-acting dimeric inhibitors of influenza virus neuraminidase are effective at a once-weekly dosing regimen

Dimeric derivatives (compounds 7 to 9) of the influenza virus neuraminidase inhibitor zanamivir (compound 2), which have linking groups of 14 to 18 atoms in length, are approximately 100-fold more potent inhibitors of influenza virus replication in vitro and in vivo than zanamivir. The observed optimum linker length of 18 to 22 A, together with observations that the dimers cause aggregation of isolated neuraminidase tetramers and whole virus, indicate that the dimers benefit from multivalent binding via intertetramer and intervirion linkages. The outstanding long-lasting protective activities shown by compounds 8 and 9 in mouse influenza infectivity experiments and the extremely long residence times observed in the lungs of rats suggest that a single low dose of a dimer would provide effective treatment and prophylaxis for influenza virus infections.

[Bilateral influenza-triggered panuveitis and subsequent therapy with amantadine and hyperimmunoglobulins]

BACKGROUND

Influenza A is one type of influenza virus that commonly causes acute respiratory illness. Outbreaks of influenza occur every year. Major antigenic variations preclude permanent immunity in the population. Often signs of conjunctivitis or photophobia are common during acute infection. Posterior uveitis is very rare.

PATIENT

A young lady with a diagnosed anterior uveitis was sent for further evaluation to the eye department with a known history of flu.

RESULTS

This patient had a severe ocular manifestation of influenza A infection. There was bilateral panuveitis with keratic precipitates, cells and flare, and an impressive retinopathy in both eyes. Serology was positive for influenza A.

CONCLUSION

The course of an influenza A infection is usually uncomplicated. Severe affection of the choriocapillaris results in a complicated post-influenza retinal pigmentary degeneration. Treatment with amantadine and therapy with hyperimmunoglobulins seem to be useful.

Highly potent and long-acting trimeric and tetrameric inhibitors of influenza virus neuraminidase

A set of trimeric and tetrameric derivatives 6-11 of the influenza virus neuraminidase inhibitor zanamivir 1 have been synthesized by coupling a common monomeric zanamivir derivative 3 onto various multimeric carboxylic acid core groups. These discrete multimeric compounds are all significantly more antiviral than zanamivir and also show outstanding long-lasting protective activity when tested in mouse influenza infectivity experiments.

New millennium antivirals against pandemic and epidemic influenza: the neuraminidase inhibitors

The mushroom shaped outer spike protein of influenza, neuraminidase, was first discovered nearly 60 years ago. Its importance in viral replication was soon recognised both at the point of viral release from the cell and also enabling passage of virus through nasal fluid to reach the cell. The enzyme active site was identified by x-ray crystallography, allowing an atomic study of interaction of enzyme with the sialic acid substrate. Analogues could then be identified and synthesized and became a focused target for antivirals. With the current threat of bioterrorism and the potential for the emergence of a new pandemic strain in the near future, efforts are underway to develop more potent second-generation anti-neuraminidase inhibitors with enhanced protective and therapeutic effects. Here we review older and newer neuraminidase inhibitors and the role that they will play in the fight against influenza in its epidemic and pandemic face.