M2 Inhibitors Research Articles

Chimiothérapies anti-influenza

L’actuelle épizootie de grippe A (H5N1) souligne la nécessité de traitements antiviraux pour faire face à une éventuelle pandémie grippale. Les traitements anti-influenza ont aussi pour objectif de réduire les symptômes et complications survenant lors des épidémies saisonnières. Deux classes d’antiviraux, les inhibiteurs du canal à protons M2 (amantadine, rimantadine), et les inhibiteurs de neuraminidase (zanamivir, oseltamivir), ont une efficacité prophylactique et thérapeutique. L’émergence de virus résistants est particulièrement fréquente lors du traitement avec les inhibiteurs de M2, et limite leur utilisation. Le développement d’une résistance à l’oseltamivir a été décrit chez plusieurs patients infectés avec le virus H5N1. Une surveillance étroite de la résistance aux anti-viraux s’impose, ainsi que le développement de nouveaux composés, pouvant cibler éventuellement d’autres protéines virales telles que l’hémagglutinine ou la polymérase, et pouvant être utilisés en polychimiothérapies.

Influenza Viruses: Basic Biology and Potential Drug Targets

Influenza A and influenza B viruses are continuing causes of morbidity and mortality on an annual basis. Influenza A viruses have historically caused periodic pandemics in the human population, sometimes with devastating consequences, such as in 1918. Fears of a new pandemic have increased in recent years because of continuing outbreaks of highly pathogenic H5N1 avian influenza viruses in birds with occasional, but often lethal infection of humans. Despite their importance as human pathogens, the antiviral drugs approved to treat influenza virus infections are currently limited to two targets, the viral neuraminidase and the viral ion channel, M2. The use of the M2 inhibitors amantadine and rimantadine is further limited by the propensity of these drugs to select for drug resistant variants. However, the replication cycle of influenza viruses has been intensively studied and is receiving increased attention. New opportunities exist to develop novel antiviral strategies targeting these viruses.

M2 Protein-A Proton Channel of Influenza A Virus

Recent outbreaks of highly pathogenic avian influenza A virus infections (H5 and H7 subtypes) in poultry and humans have raised concerns that a new influenza pandemic will occur in near future. Currently, four antivirals have proven efficacy in the treatment and prophylaxis of influenza A infections: two M2 inhibitors (amantadine and rimantadine) and two neuraminidase inhibitors (zanamivir and oseltamivir). Early treatment with antivirals reduces the duration of symptoms and the time to recovery by one to two days. However, when antivirals are used for the treatment the antiviral resistance develops rapidly, limiting their use. There is an urgent need for research on newer antiviral agents and "universal" vaccine against influenza virus. The M2 protein from the influenza A virus forms a proton channel in the virion and is essential for infection. As a relatively conserved protein, the M2 protein seems to be a suitable candidate for development of a new generation of vaccine or antiviral agents. This review describes the role of the M2 ion channel in virus replication and the structure-function relationship of the channel.

First Gallamine−Tacrine Hybrid: Design and Characterization at Cholinesterases and the M2 Muscarinic Receptor

Gallamine and tacrine are allosteric antagonists at muscarinic M2 acetylcholine receptors and inhibitors of acetylcholinesterase. At both acetylcholine-binding proteins, gallamine and tacrine are known to occupy two different binding sites: in M2 receptors within the allosteric binding area and in acetylcholinesterase at its catalytic and its peripheral site. To find new ligands of both targets, we designed a gallamine-tacrine dimer and several derived hybrid compounds to address the two binding sites. Their M2 receptor allosteric and acetylcholinesterase inhibitory potential was determined. The hybrid compounds revealed an allosteric potency in the low nanomolar range exceeding the allosteric potency of gallamine and tacrine by factors of 100 and 4800, respectively. Cholinesterase inhibition was augmented by hybrid formation, and all compounds exhibited IC50 values in the lower nanomolar range. Thus, gallamine-tacrine hybrid formation is a valuable approach toward high affinity ligands concurrently targeting these acetylcholine-binding proteins.

Targeted cell‐ablation in Xenopus embryos using the conditional, toxic viral protein M2(H37A)

Harnessing toxic proteins to destroy selective cells in an embryo is an attractive method for exploring details of cell fate and cell-cell interdependency. However, no existing "suicide gene" system has proved suitable for aquatic vertebrates. We use the M2(H37A) toxic ion channel of the influenza-A virus to induce cell-ablations in Xenopus laevis. M2(H37A) RNA injected into blastomeres of early stage embryos causes death of their progeny by late-blastula stages. Moreover, M2(H37A) toxicity can be controlled using the M2 inhibitor rimantadine. We have tested the ablation system using transgenesis to target M2(H37A) expression to selected cells in the embryo. Using the myocardial MLC2 promoter, M2(H37A)-mediated cell death causes dramatic loss of cardiac structure and function by stage 39. With the LURP1 promoter, we induce cell-ablations of macrophages. These experiments demonstrate the effectiveness of M2(H37A)-ablation in Xenopus and its utility in monitoring the progression of developmental abnormalities during targeted cell death experiments.

MUSCARINIC RECEPTOR-INDEPENDENT ACTIVATION OF CYCLIC ADENOSINE MONOPHOSPHATE-DEPENDENT PROTEIN KINASE IN ROSTRAL VENTROLATERAL MEDULLA UNDERLIES THE SYMPATHOEXCITATORY PHASE OF CARDIOVASCULAR RESPONSES DURING MEVINPHOS INTOXICATION IN THE RAT

As inhibitors of acetylcholinesterase, clinical presentations of poisoning from organophosphate compounds are generally believed to entail overstimulation by the accumulated acetylcholine on muscarinic receptors at peripheral and central synapses. That some patients still yielded to acute organophosphate poisoning despite repeated dosing of atropine suggests that cellular mechanisms that are independent of muscarinic receptor activation may also be engaged in organophosphate poisoning. The present study was undertaken to test the hypothesis that muscarinic receptor-independent activation of cyclic adenosine monophosphate-dependent protein kinase A (PKA) in rostral ventrolateral medulla (RVLM), a medullary site where sympathetic vasomotor tone originates and where the organophosphate poison mevinphos (Mev) acts, is involved in the cardiovascular responses exhibited during organophosphate intoxication. In Sprague-Dawley rats, microinjection bilaterally of Mev (10 nmol) into the RVLM significantly augmented PKA activity in ventrolateral medulla that was not antagonized by coadministration of an equimolar concentration (1 nmol) of atropine or selective muscarinic receptor type M1 (pirenzepine), M2 (methoctramine), M3 (4-diphenyl-acetoxy-N-dimethylpiperidinium), or M4 (tropicamide) inhibitor. Comicroinjection of two selective PKA antagonists (100 pmol), N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide and (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolol[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-1][1,6]benzodiazocine-10-carboxylic acid, significantly blunted the initial sympathoexcitatory cardiovascular response and the accompanying augmentation of nitric oxide synthase (NOS I) expression in the ventrolateral medulla exhibited during Mev intoxication; the secondary sympathoinhibitory phase and associated elevation in NOS II expression were unaffected. We conclude that whereas a muscarinic receptor-independent augmentation of PKA activity in the ventrolateral medulla was manifested throughout acute Mev intoxication, this activation was preferentially involved in the sympathoexcitatory phase by an upregulation of NOS I expression.

The Clinical Need for New Antiviral Drugs Directed against Influenza Virus

In this issue of the Journal of Infectious Diseases, Ison et al. present data on the emergence of resistance to the neuraminidase (NA) inhibitor class of influenza antiviral drugs in immunocompromised hosts [1, 2]. Some patients with severe immunosuppression, such as those undergoing bone marrow or solid-organ transplantation, may have prolonged viral replication or severe lower respiratory tract disease. When administered early in the course of disease, antiviral treatment can be effective at preventing progression to pneumonia and reducing mortality in these patients [3]. Antiviral agents targeting the M2 ion channel (amantadine and rimantadine) or the NA enzyme (oseltamivir and zanamivir) can both be used for influenza A virus infections, whereas only the NA inhibitors are useful against influenza B viruses. NA inhibitors have advantages in pharmacokinetics, frequency of adverse effects, and rates of resistance, compared with M2 inhibitors, but are more costly [4]. Prolonged therapy may be necessary to control

Recovery of Drug‐Resistant Influenza Virus from Immunocompromised Patients: A Case Series

Influenza virus with resistance to antiviral drugs emerges with increased frequency in immunocompromised patients and can limit the benefit of M2 and neuraminidase (NA) inhibitors. We document 3 cases of influenza in severely immunocompromised patients from whom virus variants with molecular markers of resistance to anti-influenza drugs were recovered. Virus variants recovered from 2 patients had mutations in the M2, NA (with a previously recognized Glu119Val NA substitution), and hemagglutinin genes. We describe a novel Asp198Asn NA mutation in an influenza B virus and its decreased susceptibility to both oseltamivir and zanamivir.

Influenza M2 envelope protein augments avian influenza hemagglutinin pseudotyping of lentiviral vectors

Lentivirus-based gene transfer has the potential to efficiently deliver DNA-based therapies into non-dividing epithelial cells of the airway for the treatment of lung diseases such as cystic fibrosis. However, significant barriers both to lung-specific gene transfer and to production of lentivirus vectors must be overcome before these vectors can be routinely used for applications to the lung. In this study, we investigated whether the ability to produce lentiviral vectors pseudotyped with fowl plague virus hemagglutinin (HA) could be improved by co-expression of influenza virus M2 in vector-producing cells. We found that M2 expression led to a 10-30-fold increase in production of HA-pseudotyped lentivirus vectors based upon equine infectious anemia virus (EIAV) or human immunodeficiency virus type 1 (HIV-1). Experiments using the M2 inhibitor amantadine and a drug-resistant mutant of M2 established that the ion channel activity of M2 was important for M2-dependent augmentation of vector production. Furthermore, the neuraminidase activity necessary for particle release from producer cells could also be incorporated into producer cells by co-expression of influenza NA cDNA. Lentiviral vectors pseudotyped with influenza envelope proteins were able to efficiently transduce via the apical membrane of polarized mouse tracheal cultures in vitro as well as mouse tracheal epithelia in vivo.

Developing Infectious Disease Strategies for the Developing World

Publisher SummaryThis chapter discusses various drugs for human influenza A (H5N1) and multidrug-resistant mycobacterium tuberculosis (MDR-TB). The H5N1 avian influenza does not presently meet the criteria of an antigenically shifted strain. It is presently an avian strain that has not undergone reassortment with a human strain and is not well adapted to humans. H5N1 isolates are resistant to the M2 inhibitors amantadine and rimantadine; these antivirals do not have a role for the treatment or prophylaxis against the strain. The neuraminidase inhibitors, oseltamivir and zanamivir, have in vitro activities against the human H5N1 isolates; however, recent data suggest that higher doses for longer periods may be required to be effective. Oseltamivir is an oral agent approved for prophylaxis and the treatment of influenza infections. Zanamivir is delivered topically to the respiratory tract with similar indications. The drugs discussed in the chapter for MDR-TB fall into three categories—quinolones, nitroimidazoles, and pyrroles. Drugs such as moxifloxacin are methoxyfluoroquinolones, which are already available and approved for the treatment of acute respiratory infections, such as community-acquired pneumonia, intra-abdominal infections, acute sinusitis, and skin infections. Gatifloxacin 5, is another methoxyfluoroquinolone that is in clinical development for tuberculosis treatment.

Preparing for Flu Outbreaks: Antiviral Drugs Alone Will Not Suffice

How effective would anti-influenza drugs — the M2 inhibitors amantadine and rimantadine, and the newer neuraminidase inhibitors zanamivir and oseltamivir — be in a pandemic? Should they be used widely in nonpandemic seasonal influenza outbreaks? These investigators reviewed 53 randomized controlled trials of these agents in otherwise healthy adults. Amantadine, compared with placebo, prevented 61% of cases of influenza …

Oseltamivir-Resistant Influenza A

The neuraminidase inhibitors, oseltamivir and zanamivir, and the M2 inhibitors, amantadine and rimantadine, have been approved for treatment of

Antiviral chemotherapeutic agents against respiratory viruses: where are we now and what's in the pipeline?

The emergence of severe acute respiratory syndrome in late 2002 and the recent outbreaks of avian influenza in Asia are timely reminders of the ever present risks from respiratory viral diseases. Apart from influenza, there are no vaccines and very few antiviral chemotherapeutic agents available for the prevention and treatment of respiratory viral infections-the most common cause of human illness. If the current H5N1 avian influenza outbreak ever assumes the role of a pandemic, formidable technical difficulties relating to the properties of the agent, itself, will ensure that vaccines will only become available after a significant lead time and then only to a relatively small percentage of the population. The use of existing antivirals could be critical in limiting the initial spread of a pandemic, although their use in the control of epidemics caused by nonpandemic viruses has not been evaluated. It is against this background that a review of recent developments in respiratory antivirals has been undertaken. The late 1990s were a period of unprecedented activity in the development of new and much superior antivirals for the treatment of influenza infections. However, during the past 2 to 3 years and largely for commercial reasons, there has been a decline in interest in their further development by major drug companies. This situation may soon change with the possible advent of new pandemic viruses, and moves are afoot in several countries to consider the stockpiling of antivirals. The neuraminidase inhibitors zanamivir and oseltamivir, and the M2 inhibitors amantadine and rimantadine, remain the only options for controlling respiratory disease caused by influenza viruses, although the latter two could not be used against very recent H5N1 strains. There are several other neuraminidase inhibitors in development. Compounds with activity against other respiratory viruses, notably rhinoviruses, are also in development, many based on a newer knowledge of viral protein structure and function (rational drug design). The following is an overview of recent papers on the further development of neuraminidase inhibitors against influenza viruses and on recent development of newer antivirals against RSV and rhinoviruses. Where possible, comparisons are made with existing antivirals. For considerations of space, this review has been structured around stages in the replication cycle of significant respiratory viruses that have been traditionally used as targets for inhibition.

The role of antivirals in the control of influenza

Antivirals are effective in the prophylaxis and therapy of influenza and are likely to be active against a new pandemic variant. They can be divided into the M2 inhibitors, amantadine and rimantadine, and the neuraminidase inhibitors (NIs), zanamivir and oseltamivir. The former are limited in activity to type A viruses, while the latter are also active against type B viruses. Both classes of drugs are approximately 70–90% efficacious when used as prophylaxis. However, the use of M2 inhibitors in therapy is frequently limited by side effects, more common with amantadine, by the emergence of antiviral resistance and by the lack of demonstrated prevention of complications. In contrast, the NIs are better tolerated, antiviral resistance has not emerged as a significant problem and limited evidence suggests they may reduce the frequency of influenza complications. Antiviral agents have not been widely used for either prophylaxis or treatment of annual influenza epidemics. During the early months of the next pandemic they will be the only specific agents that could be used for prevention and treatment. Their availability will depend entirely on the creation of stockpiles of these agents well in advance of the arrival of the pandemic.

Treatment and prevention of influenza: Swedish recommendations.

The introduction of the 2 neuraminidase inhibitors (NAIs) zanamivir and oseltamivir has offered new options for the prevention and treatment of influenza. This article summarizes a Swedish consensus guidance document on the rational use of antiviral drugs in the management of influenza virus infections. Vaccination remains the cornerstone for influenza prophylaxis. Target groups for the annual vaccination programme are the 'at-risk' individuals, i.e. elderly patients ( > or = 65 y) and patients with chronic pulmonary disease or cardiovascular disease or other chronic diseases predisposing for a complicated course of influenza. Antiviral drugs are not a substitute for influenza vaccination, but could be used as adjuncts. Currently, 3 drugs have been approved for the treatment of influenza, including zanamivir and oseltamivir and the M2 inhibitor amantadin. Amantadin has come to very limited use, has recently been withdrawn from the Swedish market and is available only on a named patient basis. Compared with amantadin, the NAIs have clear advantages because of their broader anti-influenza activity against both type A and B, improved safety profiles and low potential for inducing drug resistance. The NAls are therefore recommended as first options in the treatment of influenza. Oseltamivir can be taken orally, whereas zanamivir is for oral inhalation. Limited in vitro and in vivo data suggest that oseltamivir is less potent against influenza B, whereas zanamivir seems equally effective against influenza A and B. In influenza-positive healthy adults and children, treated within 48 h after symptom onset, the NAIs shorten the duration of illness by about 1 d. No significant effect on the duration of symptoms has been documented in treated at-risk patients with influenza. Owing to their limited therapeutic benefit, general use of the NAIs in the treatment of influenza is not recommended, but they can be advocated on an individualized basis for patients with severe influenza who can start therapy within 48 h of the onset of symptoms. Zanamivir is the preferred choice in a confirmed influenza B epidemic. For prevention of influenza, 2 drugs are approved, oseltamivir in adults above 12 y old and amantadin in people above 10 y old. The 70-90% protective efficacy of oseltamivir for household postexposure prophylaxis and for seasonal prophylaxis is comparable to that reported for amantadin. Oseltamivir is the preferred drug for prophylactic use. Chemoprophylaxis is targeted at high-risk groups and should be considered on a case-by-case basis depending on the circumstances and the population requiring protection. A broader preventive use of oseltamivir can be advocated in at-risk groups during seasons when there is a poor antigenic match between the epidemic strains and the vaccine strains. Oseltamivir prophylaxis is otherwise recommended for patients unable to be vaccinated and for families exposed to influenza which include a member of the at-risk groups. In high-risk hospital units and in institutions caring for the elderly, oseltamivir prophylaxis, in combination with vaccination, can be recommended as measures to control an influenza outbreak.

Muscarinic M2 receptors inhibit Ca2+-activated K+ channels in rat bladder smooth muscle.

To clarify the functional relationship between M2 muscarinic receptor and Ca2+-activated K+ channel, we investigated the effect of carbachol (CCh) on the membrane current of rat bladder smooth muscle cells. Rat bladder single smooth muscle cells were patch clamped with whole-cell configuration. CCh (10 micro mol/L) transiently induced an outward current in the presence of K+ in the pipette solution. A high Ca2+ concentration in the pipette solution persistently induced an outward current, which was inhibited by CCh. In the presence of M2 inhibitor, AFDX-384, CCh induced the outward current persistently, indicating that M2 was involved in the current inhibition. In pertussis toxin pretreated cells, CCh did not apparently inhibit the outward current. The CCh-induced outward current was inhibited by iberiotoxin, a selective inhibitor of large-conductance Ca2+-activated K+ channels (BKCa). CCh induces BKCa, which is inhibited by M2- and Gi-mediated signal transduction pathway. This M2-mediated pathway may enhance contraction which is initiated by M3-stimulation in rat bladder smooth muscle.

Inflammation Inhibits Muscarinic Signaling in In Vivo Canine Colonic Circular Smooth Muscle Cells

We investigated the effects of experimental colitis on the muscarinic signaling properties and contractile behavior of canine colonic circular smooth muscle. The hypotheses that inflammation 1) inhibits in vivo muscarinic receptor mediated contractions, and 2) alters receptor density or receptor-binding affinities were tested. Muscarine was infused close-intra-arterially in seven conscious dogs during normal and experimental colitis states. Colonic circular muscle contractions were recorded via surgically attached strain gauge transducers. Muscarine stimulated phasic contractions in a dose-dependent manner, whereas colitis was inhibited. The inhibitory concentration 50% dose of M3 receptor inhibitor was several times lower than that of M1, M2, and M4 inhibitors during normal and colitis. However, inflammation induced a significant leftward shift in the circular muscle inhibitory dose-response curve of M2 inhibitor. Muscarinic receptor density and binding analyses in isolated circular muscle cells was done in normal and colitis states. Inflammation significantly decreased maximum binding from 4082 fmol/mg to 2708 fmol/mg, whereas affinity constant remained unaffected. The conclusions were that 1) spontaneous and muscarine-activated in vivo phasic contractile activity of colonic circular muscle cells is primarily mediated by M3 receptors; 2) inflammation was associated with a shift in M2 receptor potency, due chiefly to a decrease in receptor density; and 3) this inhibitory effect was seen in normal and inflamed states, suggesting the importance of M2 receptor. These findings suggest that changes in muscarinic response during colitis may contribute to the abnormal motility seen with inflammatory bowel disease.

Viral infections in immunocompromised patients: what's new with respiratory viruses?

The leading cause of death in solid organ and hematopoietic stem cell transplant recipients is infection. The respiratory viruses, particularly respiratory syncytial virus, influenza, parainfluenza, adenovirus, and picornaviruses, are increasingly recognized as significant pathogens in these populations. Respiratory syncytial virus has again been found to be the most common of the respiratory viruses causing severe infections in transplant recipients. Advances in prevention, particularly with regard to infection control practices, and to lesser extent treatment have had a substantial impact on the frequency and outcomes of this infection. New studies have clarified the impact of influenza in the hematopoietic stem cell transplant recipients and have provided evidence to support the use of M2 and neuraminidase inhibitors for early treatment. The epidemiology of parainfluenza and adenovirus in transplant recipients has been clarified, although therapeutic modalities are still limited and understudied. New antiviral medications may bring improved outcomes of picornavirus infections in this population. Finally, a new virus, the human metapneumovirus, has recently been described and may be a significant respiratory pathogen in immunocompromised transplant recipients. Studies published over the past year have documented a new respiratory pathogen. They have also resulted in improved understanding of the epidemiology of all of the respiratory virus pathogens, and have contributed to improve management of respiratory syncytial virus and influenza infection in hematopoietic stem cell transplant and solid organ transplant recipients.

Perspectives on antiviral use during pandemic influenza.

Antiviral agents could potentially play a major role in the initial response to pandemic influenza, particularly with the likelihood that an effective vaccine is unavailable, by reducing morbidity and mortality. The M2 inhibitors are partially effective for chemoprophylaxis of pandemic influenza and evidence from studies of interpandemic influenza indicate that the neuraminidase inhibitors would be effective in prevention. In addition to the symptom benefit observed with M2 inhibitor treatment, early therapeutic use of neuraminidase inhibitors has been shown to reduce the risk of lower respiratory complications. Clinical pharmacology and adverse drug effect profiles indicate that the neuraminidase inhibitors and rimantadine are preferable to amantadine with regard to the need for individual prescribing and tolerance monitoring. Transmission of drug-resistant virus could substantially limit the effectiveness of M2 inhibitors and the possibility exists for primary M2 inhibitor resistance in a pandemic strain. The frequency of resistance emergence is lower with neuraminidase inhibitors and mathematical modelling studies indicate that the reduced transmissibility of drug-resistant virus observed with neuraminidase inhibitor-resistant variants would lead to negligible community spread of such variants. Thus, there are antiviral drugs currently available that hold considerable promise for response to pandemic influenza before a vaccine is available, although considerable work remains in realizing this potential. Markedly increasing the quantity of available antiviral agents through mechanisms such as stockpiling, educating health care providers and the public and developing effective means of rapid distribution to those in need are essential in developing an effective response, but remain currently unresolved problems.

Therapeutic options for the management of influenza.

Over the past few years a novel class of antiviral agents, the neuraminidase inhibitors, has been found to be safe and effective in the prevention and treatment of influenza. Previously available agents, the M2 inhibitors amantadine and rimantadine, could only be used to treat influenza A infections and resistance develops rapidly. Zanamivir (Relenza) and oseltamivir (Tamiflu), the two clinically available neuraminidase inhibitors, are effective for treating both influenza A and B infections in adults and children and have also been shown to reduce the frequency of antibiotic-requiring complications of influenza infections. Inhaled zanamivir has shown benefit in treating acute influenza with mild to moderate underlying asthma or chronic obstructive pulmonary disease. Studies are needed to examine the use of these agents, alone or in combination with M2 inhibitors or ribavirin, in the management of severe infections in hospitalized patients and immunocompromised hosts. Studies are also needed to address other groups at increased risk for influenza complications, such as pregnant women and children below one year of age.