Discovery of novel polyheterocyclic neuraminidase inhibitors with 1,3,4-oxadiazole thioetheramide as core backbone

Inspired by our earlier findings regarding neuraminidase (NA) inhibitors interacting with 150-cavity or 430-cavity of NA, sixteen novel polyheterocyclic NA inhibitors with 1,3,4-oxadiazole thioetheramide as core backbone were designed and synthesized based on the lead compound ZINC13401480. Of the synthesized compounds, compound N5 targeting 150-cavity exerts the best inhibitory activity against the wild-type H5N1 NA, with IC50 value of 0.14 μM, which is superior to oseltamivir carboxylate (OSC) (IC50 = 0.31 μM). Compound N10 targeting 430-cavity exhibits the best activity against the H5N1-H274Y mutant NA. Although the activity of N10 is comparable to that of OSC for wild-type H5N1 inhibition, it is approximately 60-fold more potent than OSC against the H274Y mutant, suggesting that it is not easy for the virus to develop drug resistance and is attractive for drug development. N10 (EC50 = 0.11 μM) also exhibits excellent antiviral activity against H5N1, which is superior to the positive control OSC (EC50 = 1.47 μM). Molecular docking study shows that the occupation of aromatic fused rings and oxadiazole moiety at the active site and the extension of the substituted phenyl to the 150-cavity or 430-cavity make great contributions to the good potency of this series of polyheterocyclic NA inhibitors. Some advancements in the discovery of effective target-specific NA inhibitors in this study may offer some assistance in the development of more potent anti-influenza drugs.

Oseltamivir phosphate interaction with model membranes

Oseltamivir belongs to the neuraminidase inhibitors, developed against the influenza virus, and registered under the trademark Tamiflu. Despite its long-term acquaintance, there is limited information in the literature about its physicochemical and structural properties in a lipid-water system. We present an experimentally determined partition coefficient with structural information on the interaction of oseltamivir with the model membrane, its possible location, and its effect on the membrane thermodynamics. The hydrophobic part of the lipid bilayer is affected to a moderate extent, which was proved by slight changes in thermal and structural properties. Hereby, interaction of oseltamivir with the phospholipid bilayer induces concentration dependent decrease of lateral pressure in the bilayer acyl chain region. Oseltamivir charges the bilayer surface positively, which results in the zeta potential increase and changes in anisotropic properties studied by the polarised light microscopy. At the highest oseltamivir concentrations studied, the multilamellar structure is extensively disturbed, likely due to electrostatic repulsion between the adjacent bilayers.

Microsecond dynamics of H10N7 influenza neuraminidase reveals the plasticity of loop regions and drug resistance due to the R292K mutation

At the beginning of the last century, multiple pandemics caused by influenza (flu) viruses severely impacted public health. Despite the development of vaccinations and antiviral medications to prevent and control impending flu outbreaks, unforeseen novel strains and continuously evolving old strains continue to represent a serious threat to human life. Therefore, the recently identified H10N7, for which not much data is available for rational structure-based drug design, needs to be further explored. Here, we investigated the structural dynamics of neuraminidase N7 upon binding of inhibitors, and the drug resistance mechanisms against the oseltamivir (OTV) and laninamivir (LNV) antivirals due to the crucial R292K mutation on the N7 using the computational microscope, molecular dynamics (MD) simulations. In this study, each system underwent long 2 × 1 μs MD simulations to answer the conformational changes and drug resistance mechanisms. These long time-scale dynamics simulations and free energy landscapes demonstrated that the mutant systems showed a high degree of conformational variation compared to their wildtype (WT) counterparts, and the LNV-bound mutant exhibited an extended 150-loop conformation. Further, the molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) calculation and MM/GBSA free energy decomposition were used to characterize the binding of OTV and LNV with WT, and R292K mutated N7, revealing the R292K mutation as drug-resistant, facilitated by a decline in binding interaction and a reduction in the dehydration penalty. Due to the broader binding pocket cavity of the smaller K292 mutant residue relative to the wildtype, the drug carboxylate to K292 hydrogen bonding was lost, and the area surrounding the K292 residue was more accessible to water molecules. This implies that drug resistance could be reduced by strengthening the hydrogen bond contacts between N7 inhibitors and altered N7, creating inhibitors that can form a hydrogen bond to the mutant K292, or preserving the closed cavity conformations.

Design of new chemical entities targeting both native and H275Y mutant influenza a virus by deep reinforcement learning

Influenza virus remains a major public health challenge due to its high morbidity and mortality and seasonal surge. Although antiviral drugs against the influenza virus are widely used as a first-line defense, the virus undergoes rapid genetic changes, resulting in the emergence of drug-resistant strains. Thus, new antiviral drugs that can outwit resistant strains are of significant importance. Herein, we used deep reinforcement learning (RL) algorithm to design new chemical entities (NCEs) that are able to bind to the native and H275Y mutant (oseltamivir-resistant) neuraminidases (NAs) of influenza A virus with better binding energy than oseltamivir. We generated more than 66211 NCEs, which were prioritized based on the filtering rules, structural alerts, and synthetic accessibility. Then, 18 NCEs with better MM/PBSA scores than oseltamivir were further analyzed in molecular dynamics (MD) simulations conducted for 100 ns. The MD experiments showed that 8 NCEs formed very stable complexes with the binding pocket of both native and H275Y mutant NAs of H1N1. Furthermore, most NCEs demonstrated much better binding affinity to group 2 (N2, N3, and N9) and influenza B virus NAs than oseltamivir. Although all 8 NCEs have non-sialic acid-like structures, they showed a similar binding mode as oseltamivir, indicating that it is possible to find new scaffolds with better binding and antiviral properties than sialic acid-like inhibitors. In conclusion, we have designed potential compounds as antiviral candidates for further synthesis and testing against wild and mutant influenza virus.Communicated by Ramaswamy H. Sarma.

A novel N-heterocycles substituted oseltamivir derivatives as potent inhibitors of influenza virus neuraminidase: discovery, synthesis and biological evaluation

Our previous studies have shown that the introduction of structurally diverse benzyl side chains at the C5-NH2 position of oseltamivir to occupy 150-cavity contributes to the binding affinity with neuraminidase and anti-influenza activity. To obtain broad-spectrum neuraminidase inhibitors, we designed and synthesised a series of novel oseltamivir derivatives bearing different N-heterocycles substituents that have been proved to induce opening of the 150-loop of group-2 neuraminidases. Among them, compound 6k bearing 4-((r)-2-methylpyrrolidin-1-yl) benzyl group exhibited antiviral activities similar to or weaker than those of oseltamivir carboxylate against H1N1, H3N2, H5N1, H5N6 and H5N1-H274Y mutant neuraminidases. More encouragingly, 6k displayed nearly 3-fold activity enhancement against H3N2 virus over oseltamivir carboxylate and 2-fold activity enhancement over zanamivir. Molecular docking studies provided insights into the explanation of its broad-spectrum potency against wild-type neuraminidases. Overall, as a promising lead compound, 6k deserves further optimisation by fully considering the ligand induced flexibility of the 150-loop.

Characterization of two excipient interaction degradation products in oseltamivir phosphate powder for oral suspension by MS and NMR

Oseltamivir phosphate is widely used to treat and prevent influenza, and is available in the form of capsules, powder for oral suspension, pediatric solutions, and granules. Because of the amino group, oseltamivir is easy to react with the excipients of the formulation to generate drug-excipient interaction impurities. In this research, two degradation products in a commercial oseltamivir phosphate powder for oral suspension due to interaction between API and citrate were investigated. They were characterized to be 3-((-6-acetamido-3-(ethoxycarbonyl)-5-(pentan-3-yloxy)cyclohex-3-en-1-yl)carbamoyl)-3-hydroxypentanedioic acid and 2-(2-((-6-acetamido-3-(ethoxycarbonyl)-5-(pentan-3-yloxy)cyclohex-3-en-1-yl)amino)-2-oxoethyl)-2-hydroxysuccinic acid by MS and NMR, respectively. Furthermore, the formation mechanisms of these impurities were verified, and the method of analysis of covariance was used to assess the rate of impurities' degradation. HIGHLIGHTS: Two excipient interaction degradation products in commercial oseltamivir phosphate powder for oral suspension were studied and elucidated in detail via LC-MS/MS and NMR. The incompatibility risk of pH conditioners such as citrate and citric acid with formulations that contain an amino group was disclosed in this article. Analysis of covariance was demonstrated to assess the impact of various formulations and preparation techniques on the rate of impurity degradation.

Discovery of Novel Boron-Containing N-Substituted Oseltamivir Derivatives as Anti-Influenza A Virus Agents for Overcoming N1-H274Y Oseltamivir-Resistant

To address drug resistance to influenza virus neuraminidase inhibitors (NAIs), a series of novel boron-containing N-substituted oseltamivir derivatives were designed and synthesized to target the 150-cavity of neuraminidase (NA). In NA inhibitory assays, it was found that most of the new compounds exhibited moderate inhibitory potency against the wild-type NAs. Among them, compound 2c bearing 4-(3-boronic acid benzyloxy)benzyl group displayed weaker or slightly improved activities against group-1 NAs (H1N1, H5N1, H5N8 and H5N1-H274Y) compared to that of oseltamivir carboxylate (OSC). Encouragingly, 2c showed 4.6 times greater activity than OSC toward H5N1-H274Y NA. Moreover, 2c exerted equivalent or more potent antiviral activities than OSC against H1N1, H5N1 and H5N8. Additionally, 2c demonstrated low cytotoxicity in vitro and no acute toxicity at the dose of 1000 mg/kg in mice. Molecular docking of 2c was employed to provide a possible explanation for the improved anti-H274Y NA activity, which may be due to the formation of key additional hydrogen bonds with surrounding amino acid residues, such as Arg152, Gln136 and Val149. Taken together, 2c appeared to be a promising lead compound for further optimization.

Structural Investigations and Binding Mechanisms of Oseltamivir Drug Resistance Conferred by the E119V Mutation in Influenza H7N9 Virus

The use of vaccinations and antiviral medications have gained popularity in the therapeutic management of avian influenza H7N9 virus lately. Antiviral medicines are more popular due to being readily available. The presence of the neuraminidase protein in the avian influenza H7N9 virus and its critical role in the cleavage of sialic acid have made it a target drug in the development of influenza virus drugs. Generally, the neuraminidase proteins have common conserved amino acid residues and any mutation that occurs around or within these conserved residues affects the susceptibility and replicability of the influenza H7N9 virus. Herein, we investigated the interatomic and intermolecular dynamic impacts of the experimentally reported E119V mutation on the oseltamivir resistance of the influenza H7N9 virus. We extensively employed molecular dynamic (MD) simulations and subsequent post-MD analyses to investigate the binding mechanisms of oseltamivir-neuraminidase wildtype and E119V mutant complexes. The results revealed that the oseltamivir-wildtype complex was more thermodynamically stable than the oseltamivir-E119V mutant complex. Oseltamivir exhibited a greater binding affinity for wildtype (−15.46 ± 0.23 kcal/mol) relative to the E119V mutant (−11.72 ± 0.21 kcal/mol). The decrease in binding affinity (−3.74 kcal/mol) was consistent with RMSD, RMSF, SASA, PCA, and hydrogen bonding profiles, confirming that the E119V mutation conferred lower conformational stability and weaker protein–ligand interactions. The findings of this oseltamivir-E119V mutation may further assist in the design of compounds to overcome E119V mutation in the treatment of influenza H7N9 virus patients.

A nanotechnological approach in the current therapy of COVID-19: model drug oseltamivir-phosphate loaded PLGA nanoparticles targeted with spike protein binder peptide of SARS-CoV-2

Coronavirus disease 2019 (COVID-19) is today's most serious epidemic disease threatening the human race. The initial therapeutic approach of SARS-CoV-2 disease is based upon the binding the receptor-binding site of the spike protein to the host cell's ACE-2 receptor on the plasma membrane. In this study, it is aimed to develop a biocompatible and biodegradable polymeric drug delivery system that is targeted to the relevant receptor binding site and provides controlled drug release. Oseltamivir phosphate (OP) is an orally administered antiviral prodrug for primary therapy of the disease in biochemically activated carboxylate form (oseltamivir carboxylate OC). In the presented study, model drug OP loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) targeted with spike-binding peptide 1 (SBP1) of SARS-CoV-2 were designed to be used as an efficient and prolonged released antiviral drug delivery system. RY, EE, and DL values of the OP-loaded NPs produced by the solvent evaporation method were calculated to be 59.3%, 61.4%, and 26.9%, respectively. The particle size of OP-loaded NPs and OP-loaded NPs targeted with SBP1 peptide were 162.0 ± 11.0 and 226.9 ± 21.4 nm, respectively. While the zeta potential of the produced OP-loaded NPs was achieved negatively -23.9 ± 1.21 mV), the result of the modification with SBP1 peptide this value approached zero as -4.59 ± 0.728 mV. Morphological features of the OP-loaded NPs were evaluated using FEG-SEM. The further characterization and surface modification of the NPs were analyzed by FT-IR.In-vitrorelease studies of NPs showed that sustained release of OP occurred for two months that fitting the Higuchi kinetic model. By evaluating these outputs, it was reported that surface modification of OP-loaded NPs was significantly effective on characteristics such as size, zeta potential values, surface functionality, and release behavior. The therapeutic model drug-loaded polymeric formulation targeted with a specific peptide may serve as an alternative to more effective and controlled release pharmaceuticals in the treatment of COVID-19 upon an extensive investigation.

Deciphering molecular mechanics in the taste masking ability of Maltodextrin: Developing pediatric formulation of Oseltamivir for viral pandemia

Present research work was aimed at masking the bitter taste of anti- viral drug Oseltamivir phosphate (Ost) by complexing it with pea starch maltodextrin- Kleptose Linecaps® (Mld). The Ost groups involved in triggering the bitter sensation were identified by computationally assessing its interaction with human bitter taste receptor hTAS2R 38. A series of exhaustive molecular dynamics (MD) simulation was run using Schrodinger® suite to understand the type of interaction of Ost with Mld. Experimentally, complexes of Ost with Mld were realized by solution method. The complexes were characterized using differential scanning colorimetry (DSC), fourier transform-infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), hot stage microscopy (HSM), scanning electron microscopy (SEM), proton NMR (¹H-NMR) and Carbon-13 nuclear magnetic resonance (¹³C-NMR). Ost-oral dispersible mini tablets (ODMT) were prepared by direct compression and optimised using mixture designs. Finally, bitter taste perception of Ost-ODMT was evaluated in healthy human volunteers of either sex. Computational assessment, involving interaction of Ost with bitter receptor, predicted the involvement of free amino group of Ost in triggering the bitter response whereas, MD simulation predicted the formation of stable complex between Ost and double helical confirmation of Mld. Different characterization techniques confirmed the findings of MD simulation. Results from the taste assessment in human volunteers revealed a significant reduction in bitter taste of prepared Ost-ODMT.

Molecular Docking of Azithromycin, Ritonavir, Lopinavir, Oseltamivir, Ivermectin and Heparin Interacting with Coronavirus Disease 2019 Main and Severe Acute Respiratory Syndrome Coronavirus-2 3C-Like Proteases

In the current pandemic situation raised due to COVID-19, drug reuse is emerging as the first line of treatment. The viral agent that causes this highly contagious disease and the acute respiratory syndrome coronavirus (SARS-CoV) share high nucleotide similarity. Therefore, it is structurally expected that many existing viral targets are similar to the first SARS-CoV, probably being inhibited by the same compounds. Here, we selected two viral proteins based on their vital role in the viral life cycle: Structure of the main protease SARS-CoV-2 and the structural base of the SARS-CoV-2 protease 3CL, both supporting the entry of the virus into the human host. The approved drugs used were azithromycin, ritonavir, lopinavir, oseltamivir, ivermectin and heparin, which are emerging as promising agents in the fight against COVID-19. Our hypothesis behind molecular coupling studies is to determine the binding affinities of these drugs and to identify the main amino acid residues that play a fundamental role in their mechanism of action. Additional studies on a wide range of FDA-approved drugs, including a few more protein targets, molecular dynamics studies, in vitro and biological in vivo evaluation are needed to identify combination therapy targeted at various stages of the viral life cycle. In our experiment in silico, based mainly on the molecular coupling approach, we investigated six different types of pharmacologically active drugs, aiming at their potential application alone or in combination with the reuse of drugs. The ligands showed stable conformations when analyzing the affinity energy in both proteases: ivermectin forming a stable complex with the two proteases with values -8.727 kcal/mol for Main Protease and -9.784 kcal/mol for protease 3CL, Heparin with values of -7.647 kcal/mol for the Main protease and -7.737 kcal/mol for the 3CL protease. Both conform to the catalytic site of the proteases. Our studies can provide an insight into the possible interactions between ligands and receptors, through better conformation. The ligands ivermectin, heparin and ritonavir showed stable conformations. Our in-silica docking data shows that the drugs we have identified can bind to the binding compartment of both proteases, this strongly supports our hypothesis that the development of a single antiviral agent targeting Main protease, or 3CL protease, or an agent used in combination with other potential therapies, it could provide an effective line of defense against diseases associated with coronaviruses.

Is oseltamivir suitable for fighting against COVID-19: In silico assessment, in vitro and retrospective study

BACKGROUND

Oseltamivir is a first-line antiviral drug, especially in primary hospitals. During the ongoing outbreak of coronavirus disease 2019 (COVID-19), most patients with COVID-19 who are symptomatic have used oseltamivir. Considering its popular and important role as an antiviral drug, it is necessary to evaluate oseltamivir in the treatment of COVID-19.

OBJECTIVE

To evaluate the effect of oseltamivir against COVID-19.

METHODS

Swiss-model was used to construct the structure of the N-terminal RNA-binding domain (NRBD) of the nucleoprotein (NC), papain-like protease (PLpro), and RNA-directed RNA polymerase (RdRp) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). TM-align program was performed to compare the structure of the viral proteins with the structure of the neuraminidase of influenza A. Molecular docking was used to analyze the theoretical possibility of effective binding of oseltamivir with the active centers of the viral proteins. In vitro study was used to evaluate the antiviral efficiency of oseltamivir against SARS-CoV-2. By clinical case analysis, we statistically evaluated whether the history of oseltamivir use influenced the progression of the disease.

RESULTS

The structures of NRBD, PLpro, and RdRp were built successfully. The results from TM-align suggested that the S protein, NRBD, 3C-like protease (3CLpro), PLPrO, and RdRp were structurally similar to the influenza A neuraminidase, with TM-scores of 0.30077, 0.19254, 0.28766, 0.30666, and 0.34047, respectively. Interestingly, the active center of 3CL pro was found to be similar to the active center from the neuraminidase of influenza A. Through an analysis of molecular docking, we discovered that oseltamivir carboxylic acid was more favorable to bind to the active site of 3CLpro effectively, but its inhibitory effect was not strong compared with the positive group. Finally, we used in vitro study and retrospective case analysis to verify our speculations. We found that oseltamivir is ineffective against SARS-CoV-2 in vitro study and the clinical use of oseltamivir did not improve the patients' symptoms and signs and did not slow the disease progression.

CONCLUSIONS

We consider that oseltamivir isn't suitable for the treatment of COVID-19. During the outbreak of novel coronavirus, when oseltamivir is not effective for the patients after they take it, health workers should be highly vigilant about the possibility of COVID-19.

Compatibility of Baclofen, Carvedilol, Hydrochlorothiazide, Mercaptopurine, Methadone Hydrochloride, Oseltamivir Phosphate, Phenobarbital, Propranolol Hydrochloride, Pyrazinamide, Sotalol Hydrochloride, Spironolactone, Tacrolimus Monohydrate, Ursodeoxycholic Acid, and Vancomycin Hydrochloride Oral Suspensions Compounded with SyrSpend SF pH4

Compounded liquid medication is frequently required in children to allow easy dose adjustment and overcome swallowing difficulties. The objective of this study was to evaluate the stability of oral suspensions compounded with SyrSpend SF PH4 and the commonly used active pharmaceutical ingredients baclofen 2.0 mg/mL, carvedilol 5.0 mg/mL, hydrochlorothiazide 2.0 mg/mL, mercaptopurine 10.0 mg/mL, methadone hydrochloride 10.0 mg/mL, oseltamivir phosphate 6.0 mg/mL, phenobarbital 9.0 mg/mL and 15.0 mg/mL, propranolol hydrochloride 0.5 mg/mL and 5.0 mg/mL, pyrazinamide 100.0 mg/mL, spironolactone 2.0 mg/mL and 2.5 mg/mL, sotalol hydrochloride 5.0 mg/mL, tacrolimus monohydrate 0.5 mg/mL, ursodeoxycholic acid 20.0 mg/mL, and vancomycin hydrochloride 25.0 mg/mL. Suspensions were compounded with raw powders, except for mercaptopurine, pyrazinamide, and sotalol hydrochloride, which were made from commercial tablets. Stability was assessed by measuring the percentage recovery at 0 (baseline), 60 days, and 90 days after compounding for suspensions made with raw powders, which were stored at 2ÅãC to 8ÅãC. The stability of tablets, which were stored at 2ÅãC to 8ÅãC and 20ÅãC to 25ÅãC, was assessed by measuring the percentage recovery at 0 (baseline), 7 days, 14 days, 30 days, 60 days, and 90 days. Active pharmaceutical ingredients quantification was performed by ultraviolet high-performance liquid chromatography via a stability-indicating method. Given the percentage of recovery of the active pharmaceutical ingredients within the suspensions, the beyond-use date of the final products (active pharmaceutical ingredients + vehicle) was at least 90 days for all suspensions in the conditions tested. This suggests that SyrSpend SF PH4 is suitable for compounding active pharmaceutical ingredients from different pharmacological classes.

Reductive amination assistance for quantification of oseltamivir phosphate and oseltamivir carboxylate by HPLC-MS/MS

Oseltamivir phosphate (OP) is the first line therapy for influenza, and its primary metabolite oseltamivir carboxylate (OC) is the active agent via inhibition of neuraminidase of influenza virus. Dosages of OP and OC might affect human causing nausea and vomiting and it is therefore necessary to evaluate their toxicity and safety. The separation system: liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful technique to monitor OP and OC. However, quantification of OP and OC needs isotopic analogs as internal standards to monitor the stability of the sample pretreatment procedures and instruments. In this study, we demonstrated a modified method (i.e., reductive amination) to synthesize OP and OC deuterated and hydrogenated analogs as internal standards (ISs) and for illustration of calibration curves, respectively. This modification allowed to overcome ISs selection and to enhance the signal intensities via high yield reductive amination in MS detection. We utilized the multiple reaction monitoring (MRM) mode to target m/z values of precursor and product ions. N-dimethylated OP and N-dimethylated OC showed linearity ranging from 1 to 1000 ng/mL with coefficient of determination (R²) values of 0.9995 and 0.9999, respectively. Additionally, the relative standard deviations (RSD) of intra-day ranged from 0.3% to 5.2%, and the RSD of inter-day ranged from 2.0% to 18.8%, respectively. This quantitative method utilized spiked OP and OC at low (20 ng/mL), intermediate (100 ng/mL), and high (500 ng/mL) concentrations in human serum samples. The average recoveries for OP and OC were 84.6%-107.7% and 94.9%-98.5%, respectively.

Design, in silico studies, synthesis and in vitro evaluation of oseltamivir derivatives as inhibitors of neuraminidase from influenza A virus H1N1

Since the neuraminidase (NA) enzyme of the influenza A virus plays a key role in the process of release of new viral particles from a host cell, it is often a target for new drug design. The emergence of NA mutations, such as H275Y, has led to great resistance against neuraminidase inhibitors, including oseltamivir and zanamivir. Hence, we herein designed a set of derivatives by modifying the amine and/or carboxylic groups of oseltamivir. After being screened for their physicochemical (Lipinski's rule) and toxicological properties, the remaining compounds were submitted to molecular and theoretical studies. The docking simulations provided insights into NA recognition patterns, demonstrating that oseltamivir modified at the carboxylic moiety and coupled with anilines had higher affinity and a better binding pose for NA than the derivatives modified at the amine group. Based on these theoretical studies, the new oseltamivir derivatives may have higher affinity to mutant variants and possibly to other viral subtypes. Accordingly, two compounds were selected for synthesis, which together with their respective intermediates were evaluated for their cytotoxicity and antiviral activities. Their biological activity was then tested in cells infected with the A/Puerto Rico/916/34 (H1N1) influenza virus, and virus yield reduction assays were performed. Additionally, by measuring neuraminidase activity with the neuraminidase assay kit it was found that the compounds produced inhibitory activity on this enzyme. Finally, the infected cells were analysed with atomic force microscopy (AFM), observing morphological changes strongly suggesting that these compounds interfered with cellular release of viral particles.

Role of R292K mutation in influenza H7N9 neuraminidase toward oseltamivir susceptibility: MD and MM/PB(GB)SA study

The H7N9 avian influenza virus is a novel re-assortment from at least four different strains of virus. Neuraminidase, which is a glycoprotein on the surface membrane, has been the target for drug treatment. However, some H7N9 strains that have been isolated from patient after drug treatment have a R292K mutation in neuraminidase. This substitution was found to facilitate drug resistance using protein- and virus- assays, in particular it gave a high resistance to the most commonly used drug, oseltamivir. The aim of this research is to understand the source of oseltamivir resistance using MD simulations and the MM/PB(GB)SA binding free energy approaches. Both methods can predict the reduced susceptibility of oseltamivir in good agreement to the IC ₅₀ binding energy, although MM/GBSA underestimates this prediction compared to the MM/PBSA calculation. Electrostatic interaction is the main contribution for oseltamivir binding in terms of both interaction and solvation. We found that the source of the drug resistance is a decrease in the binding interaction combined with the reduction of the dehydration penalty. The smaller K292 mutated residue has a larger binding pocket cavity compared to the wild-type resulting in the loss of drug carboxylate-K292 hydrogen bonding and an increased accessibility for water molecules around the K292 mutated residue. In addition, oseltamivir does not bind well to the R292K mutant complex as shown by the high degree of fluctuation in ligand RMSD during the simulation and the change in angular distribution of bulky side chain groups.

systemsDock: a web server for network pharmacology-based prediction and analysis

We present systemsDock, a web server for network pharmacology-based prediction and analysis, which permits docking simulation and molecular pathway map for comprehensive characterization of ligand selectivity and interpretation of ligand action on a complex molecular network. It incorporates an elaborately designed scoring function for molecular docking to assess protein-ligand binding potential. For large-scale screening and ease of investigation, systemsDock has a user-friendly GUI interface for molecule preparation, parameter specification and result inspection. Ligand binding potentials against individual proteins can be directly displayed on an uploaded molecular interaction map, allowing users to systemically investigate network-dependent effects of a drug or drug candidate. A case study is given to demonstrate how systemsDock can be used to discover a test compound's multi-target activity. systemsDock is freely accessible at http://systemsdock.unit.oist.jp/.

Drug Repurposing Identifies Inhibitors of Oseltamivir-Resistant Influenza Viruses

The neuraminidase (NA) inhibitor, oseltamivir, is a widely used anti-influenza drug. However, oseltamivir-resistant H1N1 influenza viruses carrying the H275Y NA mutation spontaneously emerged as a result of natural genetic drift and drug treatment. Because H275Y and other potential mutations may generate a future pandemic influenza strain that is oseltamivir-resistant, alternative therapy options are needed. Herein, we show that a structure-based computational method can be used to identify existing drugs that inhibit resistant viruses, thereby providing a first line of pharmaceutical defense against this possible scenario. We identified two drugs, nalidixic acid and dorzolamide, that potently inhibit the NA activity of oseltamivir-resistant H1N1 viruses with the H275Y NA mutation at very low concentrations, but have no effect on wild-type H1N1 NA even at a much higher concentration, suggesting that the oseltamivir-resistance mutation itself caused susceptibility to these drugs.

Adsorption removal of antiviral drug oseltamivir and its metabolite oseltamivir carboxylate by carbon nanotubes: Effects of carbon nanotube properties and media

This investigation evaluated the adsorption behavior of the antiviral drugs of oseltamivir (OE) and its metabolites (i.e., oseltamivir carboxylate (OC)) on three types of carbon nanotubes (CNTs) including single-walled CNT (SWCNT), multi-walled CNT (MWCNT), and carboxylated SWCNT (SWCNT-COOH). CNTs can efficiently remove more than 90% of the OE and OC from aqueous solution when the initial concentration was lower than 10(-4) mmol/L. The Polanyi-Manes model depicted the adsorption isotherms of OE and OC on CNTs better than the Langmuir and Freundlich models. The properties of OE/OC and the characteristics of CNTs, particularly the oxygen functional groups (e.g., SWCNT-COOH) played important roles during the adsorption processes. OE showed a higher adsorption affinity than OC. By comparing the different adsorbates adsorption on each CNT and each adsorbate adsorption on different CNTs, the adsorption mechanisms of hydrophobic interaction, electrostatic interaction, van der Waals force, and H-bonding were proposed as the contributing factors for OE and OC adsorption on CNTs. Particularly, for verifying the contribution of electrostatic interaction, the changes of adsorption partition efficiency (Kd) of OE and OC on CNTs were evaluated by varying pH from 2 to 11 and the importance of isoelectric point (pHIEP) of CNTs on OE and OC adsorption was addressed.

Photocatalytic degradation of the antiviral drug Tamiflu by UV-A/TiO2: Kinetics and mechanisms

The photocatalytic degradation of the antiviral drug Tamiflu (oseltamivir phosphate, OP) by TiO2 - P25, ST-01 and ATO was investigated in aqueous solution under ultraviolet (UV-A) irradiation. The photocatalysis of OP is well described by pseudo-first-order kinetics with r2>98.0% for all cases. The kinetic constant of P25 with 80% anatase and 20% rutile (0.040 min(-1)) is 4 and 10 times higher than that of ATO and ST-01 with 100% purity of anatase, respectively. We examined the effects of the catalyst loading and initial OP concentration on the photodegradation of OP, and used potassium iodine, isopropanol, and calcium fluorine as radical quenchers to evaluate the contributions of the hydroxyl radical (OH) and photo hole (h+) in the photodegradation. Results confirmed that 80% of the contribution came from the OH species. Although more than 95% of the OP (21 μM) was removed after 80 min of UV-A irradiation with 20 and 100 mg L(-1) P25, the removal efficiencies of total organic carbon (TOC) were only 45.6% and 67.0%, respectively, after 360 min UV-A irradiation. Based on an intermediate analysis by HPLC coupled with a triple quadrupole spectrometer and an ion trap mass spectrometer, typical intermediate species such as hydration derivatives, hydroxyl substitutes and keto-derivatives were identified and possible degradation pathways of OP by P25 were proposed.

Insight into the oseltamivir resistance R292K mutation in H5N1 influenza virus: a molecular docking and molecular dynamics approach

H5N1 is a subtype of the influenza A virus that can cause disease in humans and many other animal species. Oseltamivir (Tamiflu) is a potent and selective antiviral drug employed to fight the flu virus in infected individuals by inhibiting neuraminidase (NA), a flu protein responsible for the release and spread of the progeny virions. However, oseltamivir resistance has become a critical problem. In particular, influenza strains with a R292K NA mutation are highly resistant to the oseltamivir. Though the biological functions of the mutations have previously been characterized, the structural basis behind the reduced catalytic activity and reduced protein level is not clear. In this study, molecular docking and molecular dynamics (MD) approach were employed to investigate the structural and dynamical effects throughout the protein structure and specifically, at the drug-binding pocket. Furthermore, potential of mean force was analyzed using explicit solvent MD simulations with the umbrella sampling method to explore the free energy of binding. It is believed that this study provides valuable guidance for the resistance management of oseltamivir and designing of more potent antiviral inhibitor.

Development of 3D-QSAR combination approach for discovering and analysing neuraminidase inhibitors in silico

Zanamivir and Oseltamivir are both sialic acid analog inhibitors of Neuraminidase (NA), which is an important target in influenza A virus treatment. Quantitative Structure-Activity Relationships (QSAR) is a common computational method for correlating the structural properties of compounds (or inhibitors) with their biological activities. The pharmcophore model easily and quickly recognises related inhibitors and also fits the binding site interaction features of a protein structure. The Comparative Molecular Similarity Index Analysis (CoMSIA) model easily optimises molecular structures and describes the limit range of molecule weights. This study proposes a combination approach that integrates these two models based on the same training set inhibitors in order to screen and optimize NA inhibitor candidates during drug design.

Synthesis and biological evaluation of oseltamivir analogues from shikimic acid

New oseltamivir analogues were designed and synthesized, starting from shikimic acid. Biological evaluation against three human cancer cell lines (KB, MCF7 and Lu-1) showed that many of them exhibited cytotoxic activity. Azides 5 are more active than the corresponding amines 6. Thus, the reduction of the azide group into amine led to the loss of cytotoxicity. The compounds with a cyclohexanemethyloxy group at C-3 were more active than the other investigated compounds belonging to the same series. This cyclohexanemethyloxy group seems to be critical for the cytotoxic activity of this class of compounds. The synthetic oseltamivir analogues 6a-e had no inhibition activity, even at the concentration of 50 microM when they were evaluated for their in vitro influenza A neuraminidase inhibitory activity by an enzymatic assay.

Noninvasive visualization of respiratory viral infection using bioorthogonal conjugated near-infrared-emitting quantum dots

Highly pathogenic avian influenza A viruses are emerging pandemic threats in human beings. Monitoring the in vivo dynamics of avian influenza viruses is extremely important for understanding viral pathogenesis and developing antiviral drugs. Although a number of technologies have been applied for tracking viral infection in vivo, most of them are laborious with unsatisfactory detection sensitivity. Herein we labeled avian influenza H5N1 pseudotype virus (H5N1p) with near-infrared (NIR)-emitting QDs by bioorthogonal chemistry. The conjugation of QDs onto H5N1p was highly efficient with superior stability both in vitro and in vivo. Furthermore, QD-labeled H5N1p (QD-H5N1p) demonstrated bright and sustained fluorescent signals in mouse lung tissues, allowing us to visualize respiratory viral infection in a noninvasive and real-time manner. The fluorescence signals of QD-H5N1p in lung were correlated with the severity of virus infection and significantly attenuated by antiviral agents, such as oseltamivir carboxylate and mouse antiserum against H5N1p. The biodistribution of QD-H5N1p in lungs and other organs could be easily quantified by measuring fluorescent signals and cadmium concentration of virus-conjugated QDs in tissues. Hence, virus labeling with NIR QDs provides a simple, reliable, and quantitative strategy for tracking respiratory viral infection and for antiviral drug screening.

A phospha-oseltamivir-biotin conjugate as a strong and selective adhesive for the influenza virus

We present the synthesis and application of a molecule containing both the powerful influenza neuraminidase (NA) inhibitor phospha-oseltamivir and d-biotin, connected via an undecaethylene glycol spacer. It inhibits influenza virus neuraminidase (from the H3N2 X31 virus) in the same range as oseltamivir, with a slow off-rate, and produces a stable NA-coated surface when loaded onto streptavidin-coated biosensors. Purified X31 virus binds to these loaded biosensors with an apparent dissociation constant in the low picomolar range and binding of antibodies to the immobilized virus could be readily detected. The compound is thus a potential candidate for the selective immobilization of influenza virus in influenza diagnosis, vaccine choice, development or testing.

A non-biological method for screening active components against influenza virus from traditional Chinese medicine by coupling a LC column with oseltamivir molecularly imprinted polymers

To develop a non-biological method for screening active components against influenza virus from traditional Chinese medicine (TCM) extraction, a liquid chromatography (LC) column prepared with oseltamivir molecularly imprinted polymer (OSMIP) was employed with LC-mass spectrometry (LC-MS). From chloroform extracts of compound TCM liquid preparation, we observed an affinitive component m/z 249, which was identified to be matrine following analysis of phytochemical literatures, OSMIP-LC column on-line of control compounds and MS/MS off-line. The results showed that matrine had similar bioactivities with OS against avian influenza virus H9N2 in vitro for both alleviating cytopathic effect and hemagglutination inhibition and that the stereostructures of these two compounds are similar while their two-dimensional structures were different. In addition, our results suggested that the bioactivities of those affinitive compounds were correlated with their chromatographic behaviors, in which less difference of the chromatographic behaviors might have more similar bioactivities. This indicates that matrine is a potential candidate drug to prevent or cure influenza for human or animal. In conclusion, the present study showed that molecularly imprinted polymers can be used as a non-biological method for screening active components against influenza virus from TCM.

Resistance mutation R292K is induced in influenza A(H6N2) virus by exposure of infected mallards to low levels of oseltamivir

Resistance to neuraminidase inhibitors (NAIs) is problematic as these drugs constitute the major treatment option for severe influenza. Extensive use of the NAI oseltamivir (Tamiflu®) results in up to 865 ng/L of its active metabolite oseltamivir carboxylate (OC) in river water. There one of the natural reservoirs of influenza A, dabbling ducks, can be exposed. We previously demonstrated that an influenza A(H1N1) virus in mallards (Anas platyrhynchos) exposed to 1 µg/L of OC developed oseltamivir resistance through the mutation H274Y (N2-numbering). In this study, we assessed the resistance development in an A(H6N2) virus, which belongs to the phylogenetic N2 group of neuraminidases with distinct functional and resistance characteristics. Mallards were infected with A(H6N2) while exposed to 120 ng/L, 1.2 µg/L or 12 µg/L of OC in their sole water source. After 4 days with 12 µg/L of OC exposure, the resistance mutation R292K emerged and then persisted. Drug sensitivity was decreased ≈13,000-fold for OC and ≈7.8-fold for zanamivir. Viral shedding was similar when comparing R292K and wild-type virus indicating sustained replication and transmission. Reduced neuraminidase activity and decrease in recovered virus after propagation in embryonated hen eggs was observed in R292K viruses. The initial, but not the later R292K isolates reverted to wild-type during egg-propagation, suggesting a stabilization of the mutation, possibly through additional mutations in the neuraminidase (D113N or D141N) or hemagglutinin (E216K). Our results indicate a risk for OC resistance development also in a N2 group influenza virus and that exposure to one NAI can result in a decreased sensitivity to other NAIs as well. If established in influenza viruses circulating among wild birds, the resistance could spread to humans via re-assortment or direct transmission. This could potentially cause an oseltamivir-resistant pandemic; a serious health concern as preparedness plans rely heavily on oseltamivir before vaccines can be mass-produced.

Nonvolatile salt-free stabilizer for the quantification of polar imipenem and cilastatin in human plasma using hydrophilic interaction chromatography/quadrupole mass spectrometry with contamination sensitive off-axis electrospray

A hydrophilic interaction chromatography/mass spectrometry (HILIC-MS)-based assay for imipenem (IMP) and cilastatin (CIL) was recently reported. This orthogonal electrospray ion source-based (ORS) assay utilized nonvolatile salt (unremovable) to stabilize IMI in plasma. Unfortunately, this method was not applicable to conventional MS with off-axis spray (OAS-MS) because MS sensitivity was rapidly deteriorated by the nonvolatile salt. Therefore, we aimed to find a nonvolatile salt- and ion suppression-free approach to stabilize and measure the analytes in plasma using OAS-MS. Acetonitrile and methanol were tested to stabilize the analytes in the plasma samples. The recoveries, matrix effects and stabilities of the analytes in the stabilizer-treated samples were studied. The variations in MS signal intensities were used as the indicator of the assay ruggedness. The results show that a mixture of methanol and acetonitrile (1:1) is best for the storage and measurement of IMP and CIL in human plasma. Utilization of this precipitant not only blocked the hydrolysis of the analytes in plasma but also resulted in an ion suppression-free, fast (120 s per sample) and sensitive detection. The sensitivity obtained using the less sensitive OAS-MS (API3000, 4 pg on column) is much greater than that of the published ORS-MS-based assay (API4000, 77 pg on column). The ruggedness of the assay was demonstrated by its constant MS signal intensity. In conclusion, an improved HILIC/MS-based assay for IMP and CIL was established. The approach presented here provides a simple solution to the challenge of analyzing hydrolytically unstable β-lactam antibiotics in biological samples.

In silico analysis of drug-resistant mutant of neuraminidase (N294S) against oseltamivir

The recent H1N1 influenza pandemic has attracted worldwide attention due to the high infection rate. Oseltamivir is a new class of anti-viral agent approved for the treatment and prevention of influenza infections. The principal target for this drug is a virus surface glycoprotein, neuraminidase (NA), which facilitates the release of nascent virus and thus spreads infection. Until recently, only a low prevalence of neuraminidase inhibitor (NAI) resistance (<1 %) had been detected in circulating viruses. However, there have been reports of significant numbers of A (H1N1) influenza strains with a N294S neuraminidase mutation that was highly resistant to the NAI, oseltamivir. Hence, in the present study, we highlight the effect of point mutation-induced oseltamivir resistance in H1N1 subtype neuraminidases by molecular simulation approach. The docking analysis reveals that mutation (N294S) significantly affects the binding affinity of oseltamivir with mutant type NA. This is mainly due to the decrease in the flexibility of binding site residues and the difference in prevalence of hydrogen bonds in the wild and mutant structures. This study throws light on the possible effects of drug-resistant mutations on the large functionally important collective motions in biological systems.

Removal of the antiviral agent oseltamivir and its biological activity by oxidative processes

The antiviral agent oseltamivir acid (OA, the active metabolite of Tamiflu(®)) may occur at high concentrations in wastewater during pandemic influenza events. To eliminate OA and its antiviral activity from wastewater, ozonation and advanced oxidation processes were investigated. For circumneutral pH, kinetic measurements yielded second-order rate constants of 1.7 ± 0.1 × 10(5) and 4.7 ± 0.2 × 10(9) M(-1) s(-1) for the reaction of OA with ozone and hydroxyl radical, respectively. During the degradation of OA by both oxidants, the antiviral activity of the treated aqueous solutions was measured by inhibition of neuraminidase activity of two different viral strains. A transient, moderate (two-fold) increase in antiviral activity was observed in solutions treated up to a level of 50% OA transformation, while for higher degrees of transformation the activity corresponded to that caused exclusively by OA. OA was efficiently removed by ozonation in a wastewater treatment plant effluent, suggesting that ozonation can be applied to remove OA from wastewater.

Independent-Trajectory Thermodynamic Integration: a practical guide to protein-drug binding free energy calculations using distributed computing

The Independent-Trajectory Thermodynamic Integration (IT-TI) approach for free energy calculation with distributed computing is described. IT-TI utilizes diverse conformational sampling obtained from multiple, independent simulations to obtain more reliable free energy estimates compared to single TI predictions. The latter may significantly under- or over-estimate the binding free energy due to finite sampling. We exemplify the advantages of the IT-TI approach using two distinct cases of protein-ligand binding. In both cases, IT-TI yields distributions of absolute binding free energy estimates that are remarkably centered on the target experimental values. Alternative protocols for the practical and general application of IT-TI calculations are investigated. We highlight a protocol that maximizes predictive power and computational efficiency.

Environmental release of oseltamivir from a Norwegian sewage treatment plant during the 2009 influenza A (H1N1) pandemic

During the 2009 influenza type A(H1N1) pandemic, the antiviral drug oseltamivir (OP, Tamiflu®) was extensively used for treatment and prophylaxis after recommendation from World Health Organisation (WHO). Previous studies have indicated that the pharmaceutically active metabolite of OP, oseltamivir carboxylate (OC), is not readily degraded in sewage treatment plants (STPs) and therefore will be released into receiving waters in elevated concentrations during a pandemic outbreak of influenza. A method for analyzing OP and OC in wastewater by UPLC-TOF has been developed and validated. This analytical method has been used to study the release of OP and OC from a sewage treatment plant outside Oslo, Norway during the 2009 pandemic. Daily flow-proportional influent and effluent samples from 11 weeks covering the main wave of the influenza pandemic were analyzed, and the observed trend in OP and OC concentrations closely followed the trend in percentage of medical consultations caused by influenza-like illness. Concentrations in wastewater influent were in the range of 5-529 ng/L and 28-1213 ng/L for OP and OC, respectively. Concentration data from the 54 influent/effluent sample sets suggest STP removal in the range of -0.8% to 8% for OP and -14% to 0.6% for OC. Statistical analysis of the data sets was inconclusive in determining a removal rate different from 0.

Accelerated molecular dynamics in computational drug design

The method of accelerated molecular dynamics (aMD) has been shown to increase the rate of phase-space sampling in biomolecular simulations. In this chapter, we discuss the theory behind aMD and describe the implementation of two versions: dual-boost and selective aMD. Each method has its practical advantages: dual-boost aMD is useful for increasing sampling of global conformational motions while selective aMD can improve the rate of convergence of free energy calculations. Special emphasis is placed on the use of these methods in computer-aided drug design, and the example of oseltamivir binding to neuraminidase is highlighted for both cases.

Structural and functional analysis of laninamivir and its octanoate prodrug reveals group specific mechanisms for influenza NA inhibition

The 2009 H1N1 influenza pandemic (pH1N1) led to record sales of neuraminidase (NA) inhibitors, which has contributed significantly to the recent increase in oseltamivir-resistant viruses. Therefore, development and careful evaluation of novel NA inhibitors is of great interest. Recently, a highly potent NA inhibitor, laninamivir, has been approved for use in Japan. Laninamivir is effective using a single inhaled dose via its octanoate prodrug (CS-8958) and has been demonstrated to be effective against oseltamivir-resistant NA in vitro. However, effectiveness of laninamivir octanoate prodrug against oseltamivir-resistant influenza infection in adults has not been demonstrated. NA is classified into 2 groups based upon phylogenetic analysis and it is becoming clear that each group has some distinct structural features. Recently, we found that pH1N1 N1 NA (p09N1) is an atypical group 1 NA with some group 2-like features in its active site (lack of a 150-cavity). Furthermore, it has been reported that certain oseltamivir-resistant substitutions in the NA active site are group 1 specific. In order to comprehensively evaluate the effectiveness of laninamivir, we utilized recombinant N5 (typical group 1), p09N1 (atypical group 1) and N2 from the 1957 pandemic H2N2 (p57N2) (typical group 2) to carry out in vitro inhibition assays. We found that laninamivir and its octanoate prodrug display group specific preferences to different influenza NAs and provide the structural basis of their specific action based upon their novel complex crystal structures. Our results indicate that laninamivir and zanamivir are more effective against group 1 NA with a 150-cavity than group 2 NA with no 150-cavity. Furthermore, we have found that the laninamivir octanoate prodrug has a unique binding mode in p09N1 that is different from that of group 2 p57N2, but with some similarities to NA-oseltamivir binding, which provides additional insight into group specific differences of oseltamivir binding and resistance.

The influenza neuraminidase (NA) enzyme is the most successful drug target against the seasonal and pandemic flu. The 2009 H1N1 flu pandemic led to record sales of the NA inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza). Recently, a new drug, laninamivir (Inavir), has been approved for use in Japan can also be administered effectively using a single dose via its octanoate prodrug (CS-8958), however its effectiveness against oseltamivir-resistant influenza infection has not been demonstrated in clinical studies. In this study we comprehensively evaluate the effectiveness of laninamivir and its prodrug using NA from different groups with different active site features. We expressed and purified a group 2 NA from the 1957 pandemic H2N2, an atypical group 1 NA from the 2009 H1N1 pandemic and a group 1 NA from avian H12N5. NA inhibition was assayed and NAs were further crystallized with each inhibitor to determine the structural basis of their action. We found that laninamivir inhibition is highly potent for each NA, however binding and inhibition of laninamivir and its prodrug showed group specific preferences. Our results provide the structural and functional basis of NA inhibition using classical and novel inhibitors, with NAs from multiple serotypes with different properties.

Photofate of oseltamivir (Tamiflu) and oseltamivir carboxylate under natural and simulated solar irradiation: kinetics, identification of the transformation products, and environmental occurrence

In this work the photodegradation pathways and rates of oseltamivir ester (OE) and oseltamivir carboxylate (OC) were studied under artificial and natural solar irradiation with the goal of assessing the potential of photolysis as a removal mechanism in aquatic environments. The structures of the photoproducts of OE, elucidated by ultra performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (UPLC-QToF-MS), were proposed to originate from hydration of the cyclohexene ring (TP330), ester hydrolysis (TP284), a combination thereof (TP302), intramolecular cyclization involving the ester (TP312), and cleavage of the ethylpropoxy side chain (TP226). The only photoproduct detected in case of OC was postulated to correspond to the hydration of the α,β-unsaturated acid (TP302). Under simulated solar irradiation the degradation rate of OC was approximately 10 times slower than that of OE, with half-lives ranging from 48 h in ultrapure water to 12 h in surface water from Sant Joan Despi, Llobregat river. The photodegradation under natural solar irradiation during the season of pandemic Influenza peak incidence was about 150 days for OC and 15 days for OE. In general, the photoproducts proved to be more resistant toward further photodegradation than the parent antivirals. In a monitoring survey of surface waters from the Ebro river (NE Spain), OC and OE were detected along with the photoproducts TP330 and 312.

Development of a concise synthesis of (-)-oseltamivir (Tamiflu)

We report a full account of our work towards the development of an eight-step synthesis of anti-influenza drug (-)-oseltamivir (Tamiflu) from commercially available starting materials. The final synthetic route proceeds with an overall yield of 30 %. Key transformations include a novel palladium-catalyzed asymmetric allylic alkylation reaction (Pd-AAA) as well as a rhodium-catalyzed chemo-, regio-, and stereoselective aziridination reaction.

Effect of the antiviral drug oseltamivir (Tamiflu) on the bacterial community structure of a surface water ecosystem analyzed using fluorescence in situ hybridization

The antiviral drug Tamiflu has received particular attention because of its recommended use against the influenza A H5N1 and H1N1 viruses. Given its resistance to degradation and its hydrophilicity the active metabolite, Oseltamivir Carboxylate (OC), is expected to enter the aquatic ecosystem from sewage treatment plants. In the present paper the bacterial community of surface water samples, treated with OC (1.5 mg L⁻¹), was characterized by Fluorescence In Situ Hybridization (FISH) in microcosm experiments. The α-, β- and γ-Proteobacteria increased in OC-treated versus non-treated water samples during the incubation period, suggesting these bacterial groups had an active role in OC degradation.

Molecular dynamics simulations suggest that electrostatic funnel directs binding of Tamiflu to influenza N1 neuraminidases

Oseltamivir (Tamiflu) is currently the frontline antiviral drug employed to fight the flu virus in infected individuals by inhibiting neuraminidase, a flu protein responsible for the release of newly synthesized virions. However, oseltamivir resistance has become a critical problem due to rapid mutation of the flu virus. Unfortunately, how mutations actually confer drug resistance is not well understood. In this study, we employ molecular dynamics (MD) and steered molecular dynamics (SMD) simulations, as well as graphics processing unit (GPU)-accelerated electrostatic mapping, to uncover the mechanism behind point mutation induced oseltamivir-resistance in both H5N1 “avian” and H1N1pdm “swine” flu N1-subtype neuraminidases. The simulations reveal an electrostatic binding funnel that plays a key role in directing oseltamivir into and out of its binding site on N1 neuraminidase. The binding pathway for oseltamivir suggests how mutations disrupt drug binding and how new drugs may circumvent the resistance mechanisms.

Oseltamivir (Tamiflu) is the main antiviral drug used to fight viral influenza outbreaks such as the recent swine flu (H1N1pdm) global pandemic and avian (H5N1) outbreak in Asia. Oseltamivir inhibits a protein on the surface of flu viruses called neuraminidase, which is responsible for releasing newly formed viruses. The rapid emergence of drug resistance in H5N1 avian flu (and recently the H1N1pdm strain) has already motivated numerous studies to understand how mutations render oseltamivir ineffective, but no focused investigation has yet elucidated the specific mechanism behind mutation-induced drug resistance. Here, large scale computer simulations are employed to study both H5N1 and H1N1pdm neuraminidase to answer the questions: how does N1-subtype neuraminidase bind oseltamivir, and how would mutations alter this process? The key finding revealed in our simulations is the discovery of oseltamivir binding to neuraminidase by a charged pathway on the protein surface. We suggest that point mutations may disrupt drug binding by interfering with this pathway. Our results explain the fundamental mechanism behind oseltamivir resistance and pave the way for the design of drugs that circumvent viral drug resistance.

Occurrence and fate of oseltamivir carboxylate (Tamiflu) and amantadine in sewage treatment plants

We investigated the occurrence and fate of the two antiviral drugs oseltamivir carboxylate (OC)-the active metabolite of Tamiflu-and amantadine (AMT) at three sewage treatment plants (STPs) during the 2008-2009 and 2009-2010 influenza seasons in Japan. Both compounds were detected in all samples analyzed. The concentrations in raw influents at the STPs ranged from 140 to 460 ng L(-1) OC and from 184 to 538 ng L(-1) AMT. Primary treatment gave no substantial removal of the drugs (OC, 2-9%; AMT, 7-17%). Biological nutrient-removal-based secondary treatment (anoxic-oxic-anoxic-oxic and anaerobic-anoxic-oxic) removed 20-37% of OC, whereas extended-aeration-based conventional activated sludge treatment removed <20%. STPs using primary plus biological secondary treatment removed <50% of the drugs. The incorporation of tertiary treatment by ozonation removed >90%. Ozonation after secondary treatment in STPs will be necessary during an influenza pandemic to reduce the risks associated with the widespread use of antiviral drugs.

[Research progress of anti-influenza virus agents]

Influenza is a major threat to millions of people worldwide. Vaccines and antiviral agents are two main options available to reduce the impact of the influenza virus, while anti-influenza agents are the most effective means to prevent the transmission of the highly contagious virus and to treat the epidemics of disease. At present, four anti-influenza agents have been approved by the FDA for the treatment of influenza, including two M2 protein ion channel inhibitors-amantadine and rimantadine and two neuraminidase inhibitors-zanamivir and oseltamivir. Arbidol hydrochloride, launched in Russia, is a potent inhibitor of influenza virus, too. Neuraminidase inhibitors could be classified generally by structure into six different kinds: sialic acid derivatives, benzoic acid derivatives, cyclohexene derivatives, cyclopentane derivatives, pyrrolidine derivatives and natural products. In this paper, recent progress in the research of the action mechanisms and structure-activity relationships of these anti-influenza virus agents were reviewed.

Mixture toxicity of the antiviral drug Tamiflu((R)) (oseltamivir ethylester) and its active metabolite oseltamivir acid

Tamiflu (oseltamivir ethylester) is an antiviral agent for the treatment of influenza A and B. The pro-drug Tamiflu is converted in the human body to the pharmacologically active metabolite, oseltamivir acid, with a yield of 75%. Oseltamivir acid is indirectly photodegradable and slowly biodegradable in sewage works and sediment/water systems. A previous environmental risk assessment has concluded that there is no bioaccumulation potential of either of the compounds. However, little was known about the ecotoxicity of the metabolite. Ester hydrolysis typically reduces the hydrophobicity and thus the toxicity of a compound. In this case, a zwitterionic, but overall neutral species is formed from the charged parent compound. If the speciation and predicted partitioning into biological membranes is considered, the metabolite may have a relevant contribution to the overall toxicity. These theoretical considerations triggered a study to investigate the toxicity of oseltamivir acid (OA), alone and in binary mixtures with its parent compound oseltamivir ethylester (OE). OE and OA were found to be baseline toxicants in the bioluminescence inhibition test with Vibrio fischeri. Their mixture effect lay between predictions for concentration addition and independent action for the mixture ratio excreted in urine and nine additional mixture ratios of OE and OA. In contrast, OE was an order of magnitude more toxic than OA towards algae, with a more pronounced effect when the direct inhibition of photosystem II was used as toxicity endpoint opposed to the 24h growth rate endpoint. The binary mixtures in this assay yielded experimental mixture effects that agreed with predictions for independent action. This is consistent with the finding that OE exhibits slightly enhanced toxicity, while OA acts as baseline toxicant. Therefore, with respect to mixture classification, the two compounds can be considered as acting according to different modes of toxic action, although there are indications that the difference is a toxicokinetic effect, not a true difference of mechanism of toxicity. The general mixture results illustrate the need to consider the role of metabolites in the risk assessment of pharmaceuticals. However, in the concentration ratio of parent to metabolite excreted by humans, the experimental results confirm that the active metabolite does not significantly contribute to the risk quotient of the mixture.

Environmental fate of the antiviral drug Tamiflu in two aquatic ecosystems

The antiviral drug Tamiflu (Oseltamivir Phosphate, OP), has been indicated by the World Health Organization as a first-line defense in case of an avian influenza pandemic. Recent studies have demonstrated that Oseltamivir Carboxylate (OC), the active metabolite of the prodrug OP, has the potential to be released into water bodies. The present laboratory study focused on basic processes governing the environmental fate of OC in surface water from two contrasting aquatic ecosystems of northern Italy, the River Po and the Venice lagoon. Results of this study confirmed the potential of OC to persist in surface water. However, addition of 5% of sediments resulted in rapid OC degradation. Estimated half-life of OC in water/sediment of the River Po was 15 days. After three weeks of incubation at 20 degrees C, more than 8% of (14)C-OC evolved as (14)CO(2) from water/sediment samples of the River Po and Venice lagoon. At the end of the 21-day incubation period, more than 65% of the (14)C-residues were recovered from the liquid phase of both Po and Venice water/sediment samples. OC was moderately retained onto coarse sediments from the two sites. In water/sediment samples of the River Po and Venice lagoon treated with (14)C-OC, more than 30% of the (14)C-residues remained water-extractable after three weeks of incubation. The low affinity of OC to sediments suggests that presence of sediments would not reduce its bioavailability to microbial degradation.

The environmental fate of the antiviral drug oseltamivir carboxylate in different waters

Since the efficacy of oseltamivir carboxylate (OC) as the active metabolite of Tamiflu has been demonstrated against influenza viruses and even against the avian influenza virus (H5N1), millions of Tamiflu treatment courses are stockpiled worldwide. This was done not at least to follow the recommendations of the World Health Organization (WHO) to cope with a viral influenza pandemic. Concentrations up to 26-32 microg l(-1) OC in river catchment areas in the United States and in the United Kingdom had been predicted recently for a pandemic case, assuming an apparent persistence of the Tamiflu metabolite. Such concentrations may involve the risk of generation of antiviral resistance. But there is still a lack of data concerning the stability of OC in a surface water environment. Under this aspect these predictions have to be validated with concrete facts about the environmental fate of OC. In this article we summarized the results of three different daylight exposure experiments with OC in different waters under sterile and non-sterile conditions simulating shallow water processes at the latitude of approximately 52 degrees N. Using a river water solution containing 50 microg l(-1) OC under non-sterile conditions a half-life time of 17.8 days was observed. Direct photolysis plays no or only a negligible role for the decomposition of OC. Degradation of OC seems to occur as a combination of microbial metabolism and indirect photolysis.

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.