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.

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.

Targeting glycosphingolipid metabolism as a potential therapeutic approach for treating disease in female MRL/lpr lupus mice

Glycosphingolipids (GSLs) hexosylceramides and lactosylceramides are elevated in lupus mice and human patients with nephritis. Whereas other renal diseases characterized by increased GSL levels are thought to be a result of upregulated GSL synthesis, our results suggest elevated hexosylceramides and lactosylceramides in lupus nephritis is a result of increased catabolism of ganglioside GM3 due to significantly increased neuraminidase (NEU) activity. Thus, we hypothesized GM3 would be decreased in lupus nephritis kidneys and blocking NEU activity would reduce GSLs and improve disease in lupus mice. Female MRL/lpr lupus mice were treated with water or the NEU inhibitor oseltamivir phosphate at the onset of proteinuria to block GSL catabolism. Age-matched (non-nephritic) female MRL/MpJ lupus mice served as controls. Renal GM3 levels were significantly higher in the nephritic MRL/lpr water-treated mice compared to non-nephritic MRL/MpJ mice, despite significantly increased renal NEU activity. Blocking GSL catabolism increased, rather than decreased, renal and urine GSL levels and disease was not significantly impacted. A pilot study treating MRL/lpr females with GlcCer synthase inhibitor Genz-667161 to block GSL synthesis resulted in a strong significant negative correlation between Genz-667161 dose and renal GSL hexosylceramide and GM3 levels. Splenomegaly was negatively correlated and serum IgG levels were marginally correlated with increasing Genz-667161 dose. These results suggest accumulation of renal GM3 may be due to dysregulation of one or more of the GSL ganglioside pathways and inhibiting GSL synthesis, but not catabolism, may be a therapeutic approach for treating lupus nephritis.

Design, synthesis and biological evaluation of "Multi-Site"-binding influenza virus neuraminidase inhibitors

Encouraged by our earlier discovery of neuraminidase inhibitors targeting 150-cavity or 430-cavity, herein, to yield more potent inhibitors, we designed, synthesized, and biologically evaluated a series of novel oseltamivir derivatives via modification of C-1 and C5-NH2 of oseltamivir by exploiting 150-cavity and/or 430-cavity. Among the synthesized compounds, compound 15e, the most potent N1-selective inhibitor targeting 150-cavity, showed 1.5 and 1.8 times greater activity than oseltamivir carboxylate (OSC) against N1 (H5N1) and N1 (H5N1-H274Y). In cellular assays, 15e also exhibited greater potency than OSC against H5N1 with EC50 of 0.66 μM. In addition, 15e demonstrated low cytotoxicity in vitro and low acute toxicity in mice. Molecular docking studies provided insights into the high potency of 15e against N1 and N1-H274Y mutant NA. Overall, we envisioned that the significant breakthrough in the discovery of potent group-1-specific neuraminidase inhibitors may lead to further investigation of more potent anti-influenza agents.

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.

The novel carboxylesterase 1 variant c.662A>G may decrease the bioactivation of oseltamivir in humans

Background

Human carboxylesterase 1 (CES1) is a serine esterase that hydrolyses various exogenous and endogenous compounds including oseltamivir, a prodrug used to treat influenza. A novel CES1 c.662A>G single nucleotide polymorphism (SNP) was predicted to decrease CES1 enzymatic activity in an in silico analysis. This study evaluated the effect of the c.662A>G SNP on the pharmacokinetics (PK) of oseltamivir in humans.

Methods

A single oral dose of oseltamivir at 75 mg was administered to 20 healthy subjects, 8 heterozygous c.662A>G carriers (c.662AG) and 12 non-carriers (c.662AA). The concentrations of oseltamivir and its active metabolite, oseltamivir carboxylate, were measured in plasma and urine using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The PK parameters were calculated using a noncompartmental method. The geometric mean ratios (GMR, c.662AG to c.662AA) of the PK parameters and their 90% confidence intervals (CI) were calculated.

Results

The systemic exposure to oseltamivir, as assessed by the AUC_0-48h of oseltamivir, was increased by 10% in c.662AG subjects, whereas the AUC_0-48h of oseltamivir carboxylate was 5% lower in c.662AG subjects. The GMR and 90% CI of the metabolic ratio (AUC_{0-48h, Oseltamivir carboxylate}/AUC_{0-48h, Oseltamivir}) was 0.87 (0.66–1.14). The amount of unchanged oseltamivir excreted in the urine was increased by 15% in subjects with the c.662AG genotype.

Conclusions

This result suggests that CES1 enzymatic activity may be decreased in these heterozygous allele carriers, although further studies are warranted to investigate the clinical implications of this genetic variation on CES1 substrate drugs.

Trial registration

ClinicalTtrials.gov NCT01902342

Investigating clinically adequate concentrations of oseltamivir carboxylate in end-stage renal disease patients undergoing hemodialysis using a population pharmacokinetic approach

End-stage renal disease (ESRD) patients receiving hemodialysis (HD) are at heightened risk for influenza, but the optimal oseltamivir dosage regimen for treating or preventing influenza in this high-risk population is still uncertain. Pharmacokinetic data for 24 adults with ESRD were pooled from a single-dose and a multiple-dose study to develop a population pharmacokinetic model using nonlinear mixed-effects modeling. The final model comprised five compartments, two each to describe the systemic pharmacokinetics of oseltamivir phosphate and its metabolite, oseltamivir carboxylate (OC), and a delay compartment to describe oseltamivir metabolism. Estimated OC clearance in the model was markedly faster during HD sessions (7.43 liters/min) than at other times (0.19 liter/min). Model simulations showed that 30 mg oseltamivir given after every HD session is the most suitable regimen for influenza treatment, producing trough OC concentrations above the median value achieved with the 75-mg twice-daily regimen in patients with normal renal function and peak concentrations below the highest oseltamivir exposures known to be well tolerated (median exposures after twice-daily dosing of 450 mg). Administration of the first dose following diagnosis of influenza need not wait until after the next HD session: addition of a single 30-mg dose during the 12 h before the next HD session raises OC exposures quickly without posing any safety risk. Further simulation showed that 30 mg oseltamivir given after every other HD session is the most suitable regimen for influenza prophylaxis.

Oseltamivir Population Pharmacokinetics in the Ferret: Model Application for Pharmacokinetic/Pharmacodynamic Study Design

The ferret is a suitable small animal model for preclinical evaluation of efficacy of antiviral drugs against various influenza strains, including highly pathogenic H5N1 viruses. Rigorous pharmacokinetics/pharmacodynamics (PK/PD) assessment of ferret data has not been conducted, perhaps due to insufficient information on oseltamivir PK. Here, based on PK data from several studies on both uninfected and influenza-infected groups (i.e., with influenza A viruses of H5N1 and H3N2 subtypes and an influenza B virus) and several types of anesthesia we developed a population PK model for the active compound oseltamivir carboxylate (OC) in the ferret. The ferret OC population PK model incorporated delayed first-order input, two-compartment distribution, and first-order elimination to successfully describe OC PK. Influenza infection did not affect model parameters, but anesthesia did. The conclusion that OC PK was not influenced by influenza infection must be viewed with caution because the influenza infections in the studies included here resulted in mild clinical symptoms in terms of temperature, body weight, and activity scores. Monte Carlo simulations were used to determine that administration of a 5.08 mg/kg dose of oseltamivir phosphate to ferret every 12 h for 5 days results in the same median OC area under the plasma concentration-time curve 0–12 h (i.e., 3220 mg h/mL) as that observed in humans during steady state at the approved dose of 75 mg twice daily for 5 days. Modeling indicated that PK variability for OC in the ferret model is high, and can be affected by anesthesia. Therefore, for proper interpretation of PK/PD data, sparse PK sampling to allow the OC PK determination in individual animals is important. Another consideration in appropriate design of PK/PD studies is achieving an influenza infection with pronounced clinical symptoms and efficient virus replication, which will allow adequate evaluation of drug effects.

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.

Detection of peramivir and laninamivir, new anti-influenza drugs, in sewage effluent and river waters in Japan

This is the first report of the detection of two new anti-influenza drugs, peramivir (PER) and laninamivir (LAN), in Japanese sewage effluent and river waters. Over about 1 year from October 2013 to July 2014, including the influenza prevalence season in January and February 2014, we monitored for five anti-influenza drugs—oseltamivir (OS), oseltamivir carboxylate (OC), zanamivir (ZAN), PER, and LAN—in river waters and in sewage effluent flowing into urban rivers of the Yodo River system in Japan. The dynamic profiles of these anti-influenza drugs were synchronized well with that of the numbers of influenza patients treated with the drugs. The highest levels in sewage effluents and river waters were, respectively, 82 and 41 ng/L (OS), 347 and 125 ng/L (OC), 110 and 35 ng/L (ZAN), 64 and 11 ng/L (PER), and 21 and 9 ng/L (LAN). However, application of ozone treatment before discharge from sewage treatment plants was effective in reducing the levels of these anti-influenza drugs in effluent. The effectiveness of the ozone treatment and the drug dependent difference in susceptibility against ozone were further evidenced by ozonation of a STP effluent in a batch reactor. These findings should help to promote further environmental risk assessment of the generation of drug-resistant influenza viruses in aquatic environments.

Physiologically based pharmacokinetic modeling of impaired carboxylesterase-1 activity: effects on oseltamivir disposition

BACKGROUND AND OBJECTIVE

Human carboxylesterase-1 (CES1) is an enzyme that is primarily expressed in the liver, where it plays an important role in the metabolism of many commonly used medications. Ethanol (alcohol)-mediated inhibition of CES1 and loss-of-function polymorphisms in the CES1 gene can markedly reduce this enzyme's function. Such alterations in CES1 activity may have important effects on the disposition of substrate drugs. The aim of this study is to develop a physiologically based pharmacokinetic (PBPK) model to predict changes in CES1 substrate drug exposure in humans with CES1 activity impaired by ethanol or loss-of-function CES1 genetic polymorphisms.

METHODS

The antiviral drug oseltamivir, an ethyl ester prodrug that is rapidly converted in vivo to the active metabolite oseltamivir carboxylate (OSC) by CES1 was used as a probe drug for CES1 activity. Oseltamivir PBPK models integrating in vitro and in vivo data were developed and refined. Then the changes in oseltamivir and OSC exposure in humans with CES1 impaired by ethanol or polymorphisms were simulated using a PBPK model incorporating in vitro inhibition and enzyme kinetic data. Model assumptions were verified by comparison of simulations with observed and published data. A sensitivity analysis was performed to gain a mechanistic understanding of the exposure changes of oseltamivir and OSC.

RESULTS

The simulated changes in oseltamivir and OSC exposures in humans with CES1 impaired by ethanol or polymorphism were similar to the observed data. The observed exposures to oseltamivir were increased by 46 and 37 % for the area under the plasma concentration-time curve from time zero to 6 h (AUC6) and from time zero to 24 h (AUC24), respectively, with co-administration of ethanol 0.6 g/kg. In contrast, only a slight change was observed in OSC exposure. The simulated data show the same trend as evidenced by greater change in exposures to oseltamivir (27 and 26 % for AUC(6) and AUC(24), [corrected] respectively) than OSC (≤6 %).

CONCLUSIONS

The PBPK model of impaired CES1 activity correctly predicts observed human data. This model can be extended to predict the effects of drug interactions and other factors affecting the pharmacokinetics of other CES1 substrate drugs.

In vitro anti-influenza A activity of interferon (IFN)-λ1 combined with IFN-β or oseltamivir carboxylate

Influenza viruses, which can cross species barriers and adapt to new hosts, pose a constant potential threat to human health. The influenza pandemic of 2009 highlighted the rapidity with which an influenza virus can spread worldwide. Currently available antivirals have a number of limitations against influenza, and novel antiviral strategies, including novel drugs and drug combinations, are urgently needed. Here, we evaluated the in vitro effects of interferon (IFN)-β, IFN-λ1, oseltamivir carboxylate (a neuraminidase (NA) inhibitor), and combinations of these agents against two seasonal (i.e., H1N1 and H3N2) influenza A viruses. We observed that A/California/04/09 (H1N1) and A/Panama/2007/99 (H3N2) isolates were equally sensitive to the antiviral activity of IFN-β and oseltamivir carboxylate in A549 and Calu-3 cells. In contrast, IFN-λ1 exhibited substantially lower protective potential against the H1N1 strain (64-1030-fold ↓, P<0.05), and was ineffective against H3N2 virus in both cell lines. Three dimensional analysis of drug-drug interactions revealed that IFN-λ1 interacted with IFN-β and oseltamivir carboxylate in an additive or synergistic manner, respectively, to inhibit influenza A virus replication in human airway epithelial cells. Overall, the present study demonstrated that anti-influenza agents with different mechanisms of action (e.g., a NA inhibitor combined with IFN-λ1) exerted a significantly greater (P<0.05) synergistic effect compared to co-treatment with drugs that target the same signaling pathway (i.e., IFN-β plus IFN-λ1) in vitro. Our findings provide support for the combined use of interferon plus oseltamivir as a potential means for treating influenza infections.

Antiviral activity of novel oseltamivir derivatives against some influenza virus strains

The aim of this study was to investigate the in vitro cytotoxicity of oseltamivir derivatives and determine their activity against A/H1N1/PR/8/34 and A/H3N2/HongKong/8/68 - strains of influenza virus. Antiviral activity of these compounds was determined by using two methods. MTT staining was used to assess the viability of MDCK cells infected with influenza viruses and treated with various concentrations of drugs. In parallel, the effect of drugs on viral replication was assessed using the hemagglutination test. The most toxic compounds were: OS-64, OS-35, OS-29, OS-27 and OS-25, whereas OS-11, OS-20 and OS-23 were the least toxic ones. Statistically significant antiviral effect at a higher virus dose was shown by compounds: OS-11, OS-20, OS-27, OS-35, and OS-64. H3N2 virus was sensitive to 10-times lower concentrations of OS-11 and OS-35 than H1N1. At a lower infection dose, the antiviral activity was observed for OS-11, OS 27, OS-35 and OS-20. OS-64 turned out to be effective only at a high concentration. OS-23 showed no antiviral effect.

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.

Pharmacokinetics of orally administered oseltamivir in healthy obese and nonobese Thai subjects

Oseltamivir is the most widely used anti-influenza drug. In the 2009 H1N1 pandemic, in which the influenza viruses were oseltamivir sensitive, obesity was identified as a risk factor for severe disease and unfavorable outcomes. The aim of this study was to investigate the pharmacokinetic properties of oseltamivir and its active metabolite, oseltamivir carboxylate, in obese and nonobese healthy subjects. A single-dose, randomized, two-sequence crossover study was conducted in 12 obese and 12 nonobese healthy Thai volunteers. Each volunteer was given 75 mg and 150 mg oseltamivir orally with an intervening washout period of more than 3 days. The pharmacokinetic properties of oseltamivir and oseltamivir carboxylate were evaluated using a noncompartmental approach. The median (range) body mass indexes (BMIs) for obese subjects were 33.8 kg/m(2) (30.8 to 43.2) and 22.2 (18.8 to 24.2) for nonobese subjects. The pharmacokinetic parameters of oseltamivir carboxylate, the active metabolite of oseltamivir, were not significantly different between obese and nonobese subjects for both 75-mg and 150-mg doses. Both doses were well tolerated. Despite the lower dose per kilogram body weight in obese subjects, there was no significant difference in the exposure of oseltamivir carboxylate between the obese and nonobese groups. Standard dosing is appropriate for obese subjects. (The study was registered at ClinicalTrials.gov under registration no. NCT 01049763.).

Mass balance of anti-influenza drugs discharged into the Yodo River system, Japan, under an influenza outbreak

In February 2011, at the peak of an influenza outbreak, we performed a comprehensive analysis of the mass balances of four anti-influenza drugs-oseltamivir (OS), oseltamivir carboxylate (OC), amantadine (AMN), and zanamivir (ZAN)-in the urban area of the Yodo River system. This area includes three main river catchments (the Katsura, Uji, and Kidzu Rivers) and is home to 12 million people, about 10% of Japan's population. Water was sampled at six main rivers and 13 tributary sites and eight sewage treatment plants (STPs). We concluded that the STP effluents were the major sources of the anti-influenza drug load in the Yodo River system (68-94% of total mass fluxes). Extended measurement throughout the Yodo River system further showed only small fluctuations of the ratio of OS to OC from 0.2 to 0.3, suggesting that OS and its metabolite are environmentally stable. The results also clearly showed the importance of reducing the levels of anti-influenza drugs in the water environment by reducing their emission at STPs.

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.

Synchronous dynamics of observed and predicted values of anti-influenza drugs in environmental waters during a seasonal influenza outbreak

Time-dependent dynamics in the concentrations of four anti-influenza drugs (oseltamivir, oseltamivir carboxylate, zanamivir, and amantadine) in environmental waters collected from the Yodo River basin, Japan, were monitored for the first time over a 1 year period (July 2010 to June 2011). The clear, convex dynamic profiles of oseltamivir, oseltamivir carboxylate, and zanamivir during a 3 month seasonal influenza outbreak (January to March 2011) were synchronized well with that of the numbers of influenza patients treated with the drugs. The highest levels in sewage treatment plants (STPs) and river waters were, respectively, 177 and 60 ng/L (oseltamivir), 827 and 288 ng/L (oseltamivir carboxylate), and 30 and 15 ng/L (zanamivir). Fixed levels of amantadine were detectable year-round (100-200 ng/L in the STPs and 10-30 ng/L in river waters). The predicted convex profiles of oseltamivir, oseltamivir carboxylate, and zanamivir in both STPs and river waters were significantly correlated (0.714 < R < 0.932) with the observed values. The profiles were predicted successfully by simple mathematical principles, taking the number of influenza patients, quantities of Tamiflu and Relenza used, dilution by drainwaters passing through STPs, removal rates at STPs, dilution rates in river effluents, and attenuation rates in rivers into consideration.

Oseltamivir analog with boron cluster modulator

Synthesis of novel neuraminidase inhibitor -- carborane ester of oseltamivir carboxylic acid is described, and its physicochemical and spectral characteristics is provided. Surprisingly, carborane analog of oseltamivir is of an order of magnitude less active than its precursor, the corresponding ethyl ester, which is the active principle of pharmaceutical preparations used in influenza prophylactics and therapy.

Transplacental transfer of oseltamivir and its metabolite using the human perfused placental cotyledon model

OBJECTIVE

Given the lack of data regarding the use of oseltamivir (Tamiflu) during pregnancy, we aimed to evaluate the placental transfer of oseltamivir phosphate and its active metabolite oseltamivir carboxylate, using the perfused placental cotyledon model.

STUDY DESIGN

Cotyledons were coperfused with oseltamivir phosphate and oseltamivir carboxylate using the maximal concentrations described with a 75 mg, twice-daily oral dose. Main transfer parameters such as fetal transfer rate (FTR) and clearance index (CI) were assessed.

RESULTS

Five placentas were coperfused with oseltamivir phosphate and oseltamivir carboxylate. The median FTR of oseltamivir phosphate was 8.5% (range, 5.0-11.6%) and the median CI was 0.3 (range, 0.2-0.6). Regarding oseltamivir carboxylate transplacental transfer, the median FTR was 6.6% (range, 3.9-9.7%), whereas the median CI was 0.2 (range, 0.2-0.5).

CONCLUSION

A transplacental transfer of oseltamivir phosphate and its metabolite oseltamivir carboxylate was detected and might have clinical relevance. Clinicians should be encouraged to report oseltamivir treatment outcomes during pregnancy.

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.

Pharmacokinetics of oseltamivir according to trimester of pregnancy

The purpose of this study was to determine pharmacokinetic parameters for oseltamivir in all trimesters of pregnancy. Thirty pregnant women, 10 per trimester, who were receiving oseltamivir phosphate (75 mg) were recruited to study first-dose pharmacokinetics. Plasma samples were obtained at 0, 0.5, 1, 2, 4, 8, and 12 hours after the first dose. Samples were analyzed for oseltamivir and oseltamivir carboxylate levels. With the use of a noncompartmental model, we estimated the area-under-the-curve, maximum concentration, time-to-maximum concentration, and half-life. There were no significant differences in the pharmacokinetics of oseltamivir by trimester, except for an increased half-life in the first trimester for oseltamivir phosphate and an increased maximum concentration in the third trimester for oseltamivir carboxylate. The levels of oseltamivir carboxylate that were observed were within the range that was needed to achieve inhibitory concentrations at 50% for pandemic H1N1. The pharmacokinetics of oseltamivir does not change significantly according to trimester of pregnancy.

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.

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.

Plasma concentrations of oseltamivir and oseltamivir carboxylate in critically ill children on extracorporeal membrane oxygenation support

INTRODUCTION

To evaluate the effect of extracorporeal membrane oxygenation (ECMO) support on pharmacokinetics of oseltamivir and oseltamivir carboxylate (OC) in children.

METHODOLOGY

Steady state 0-12 hour pharmacokinetic sampling was performed in new influenza A (H1N1) infected children treated with oseltamivir while on ECMO support. Cmax, Cmin and AUC(0-12 h) were calculated. The age-specific oseltamivir dosage was doubled to counter expected decreased plasma drug concentrations due to increased volume of distribution on ECMO support.

PRINCIPAL FINDINGS

Three patients were enrolled aged 15, 6 and 14 years in this pharmacokinetic case series. For two children the OC plasma concentrations were higher than those found in children and adults not on ECMO. These increased plasma concentrations related to the increased oseltamivir dosage and decreased kidney function. In one patient suboptimal plasma concentrations coincided with a decreased gastric motility.

CONCLUSION

Oseltamivir pharmacokinetics do not appear to be significantly influenced by ECMO support. Caution is required in case of nasogastric administration and decreased gastric motility. Due to the limited number of (paediatric) patients available further multicenter studies are warranted.

Effect of neuraminidase inhibitor-resistant mutations on pathogenicity of clade 2.2 A/Turkey/15/06 (H5N1) influenza virus in ferrets

The acquisition of neuraminidase (NA) inhibitor resistance by H5N1 influenza viruses has serious clinical implications, as this class of drugs can be an essential component of pandemic control measures. The continuous evolution of the highly pathogenic H5N1 influenza viruses results in the emergence of natural NA gene variations whose impact on viral fitness and NA inhibitor susceptibility are poorly defined. We generated seven genetically stable recombinant clade 2.2 A/Turkey/15/06-like (H5N1) influenza viruses carrying NA mutations located either in the framework residues (E119A, H274Y, N294S) or in close proximity to the NA enzyme active site (V116A, I117V, K150N, Y252H). NA enzyme inhibition assays showed that NA mutations at positions 116, 117, 274, and 294 reduced susceptibility to oseltamivir carboxylate (IC(50)s increased 5- to 940-fold). Importantly, the E119A NA mutation (previously reported to confer resistance in the N2 NA subtype) was stable in the clade 2.2 H5N1 virus background and induced cross-resistance to oseltamivir carboxylate and zanamivir. We demonstrated that Y252H NA mutation contributed for decreased susceptibility of clade 2.2 H5N1 viruses to oseltamivir carboxylate as compared to clade 1 viruses. The enzyme kinetic parameters (V(max), K(m) and K(i)) of the avian-like N1 NA glycoproteins were highly consistent with their IC(50) values. None of the recombinant H5N1 viruses had attenuated virulence in ferrets inoculated with 10(6) EID(50) dose. Most infected ferrets showed mild clinical disease signs that differed in duration. However, H5N1 viruses carrying the E119A or the N294S NA mutation were lethal to 1 of 3 inoculated animals and were associated with significantly higher virus titers (P<0.01) and inflammation in the lungs compared to the wild-type virus. Our results suggest that highly pathogenic H5N1 variants carrying mutations within the NA active site that decrease susceptibility to NA inhibitors may possess increased virulence in mammalian hosts compared to drug-sensitive viruses. There is a need for novel anti-influenza drugs that target different virus/host factors and can limit the emergence of resistance.

[Establishment of a cell-based 2009 H1N1 influenza neuraminidase inhibitors evaluation system]

This study is to establish a cell-based model targeting to neuraminidase (NA) of the 2009 H1N1 influenza A virus. NA is an influenza virus structural protein with enzymatic activity of the cleavage of HA-sialic acid interaction to release new viral particles from cells. A model of HIV-1 (pNL4-3.Luc.R(-)E(-)) based pseudovirions packed with HA [hemagglutinin, A/VietNam/1203/2004 (H5N1)] and NA [A/California/04/2009 (H1N1)] was established to evaluate compounds activities on NA function. The viral release can be blocked by neuraminidase inhibitors, oseltamivir and oseltamivir carboxylate, with IC50 of (61 +/- 31) nmol L(-1) and (5.5 +/- 2.9) nmol L(-1) respectively. A point mutation of H275Y on NA leads oseltamivir-resistance. This corresponding mutation was introduced into the system which was also confirmed by oseltamivir and oseltamivir carboxylate.

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.

Oseltamivir carboxylate, the active metabolite of oseltamivir phosphate (Tamiflu), detected in sewage discharge and river water in Japan

BACKGROUND

Oseltamivir phosphate (OP; Tamiflu) is a prodrug of the anti-influenza neuraminidase inhibitor oseltamivir carboxylate (OC) and has been developed for the treatment and prevention of both A and B strains of influenza. The recent increase in OP resistance in influenza A virus (H1N1; commonly called "swine flu") has raised questions about the widespread use of Tamiflu in seasonal epidemics and the potential ecotoxicologic risk associated with its use in the event of a pandemic.

OBJECTIVES

The objectives of this study were to develop an analytical method for quantitative determination of OC in sewage treatment plant (STP) effluent and receiving river water, and to investigate the occurrence of OC in STP effluent and river water in Japan during a seasonal flu outbreak.

METHODS

We developed an analytical method based on solid-phase extraction followed by liquid chromatography-tandem mass spectrometry. Using this method, we analyzed samples from three sampling campaigns conducted during the 2008-2009 flu season in Kyoto City, Japan.

RESULTS

The highest concentration of OC detected in STP discharge was 293.3 ng/L from a conventional activated-sludge-based STP; however, we detected only 37.9 ng/L from an advanced STP with ozonation as a tertiary treatment. In the receiving river water samples, we detected 6.6-190.2 ng/L OC, during the peak of the flu season.

CONCLUSION

OC is present in STP effluent and river water only during the flu season. Ozonation as tertiary treatment in STP will substantially reduce the OC load in STP effluent during an influenza epidemic or pandemic.

Oseltamivir oral suspension and capsules are bioequivalent for the active metabolite in healthy adult volunteers

AIMS

The objective of this study was to assess the relative bioavailability of oseltamivir carboxylate (active metabolite) following oral administration of the market suspension, the clinical trial suspension and the market capsule formulations of oseltamivir (prodrug) in healthy subjects.

METHODS

In this single-center, open-label, three-period crossover study, 24 healthy adult volunteers were randomized to receive one dose (150 mg oseltamivir) of each of the three formulations (market suspension, clinical trial suspension, market capsule formulation), with a 7-day washout period between each administration. Blood samples, collected for up to 48 h post-dosing, were analyzed for plasma oseltamivir and oseltamivir carboxylate. Adverse events were monitored.

RESULTS

Pharmacokinetic parameters for oseltamivir and oseltamivir carboxylate were similar for the three formulations. Bioequivalence for oseltamivir carboxylate was demonstrated between the market capsule and the two suspensions: 90% confidence intervals for the log-transformed Cmax, AUClast and AUCinf ratios fell within the 80 - 125% criteria. Similarly, the two suspensions were also demonstrated as bioequivalent for oseltamivir carboxylate. Oseltamivir was well tolerated. The majority of adverse events observed were mild in intensity, with the most common being nausea and headache.

CONCLUSIONS

This study demonstrates that the market suspension, the clinical trial suspension and the market capsule formulations of oseltamivir are bioequivalent for the active metabolite, oseltamivir carboxylate. Based on this finding, the market suspension may be used to achieve comparable exposure in patients unable to take capsules.

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.

On the structure-based design of novel inhibitors of H5N1 influenza A virus neuraminidase (NA)

The structure-based design of novel H5N1 neuraminidase inhibitors is currently a research topic of vital importance owing to both a recent pandemic threat by the worldwide spread of H5N1 avian influenza and the high resistance of H5N1 virus to the most widely used commercial drug, oseltamivir-OTV (Tamiflu). A specific criterion used in this work for determining fully acceptable conformations of potential inhibitors is a previous experimental proposal of exploiting potential benefits for drug design offered by the '150-cavity' adjacent to the NA active site. Using the crystal structure of H5N1 NA (PDB ID: 2hty) as the starting point, in a set of 54 inhibitors previously proposed by modifying the side chains of oseltamivir, 4 inhibitors were identified using two different computational strategies (ArgusLab4.0.1, FlexX-E3.0.1) both to lower the binding free energy (BFE) of oseltamivir and to have partially acceptable conformations. These 4 oseltamivr structure-based analogues were found to adopt the most promising conformations by identifying the guanidinium side chain of Arg156 as a prospective partner for making polar contacts, but none of the modified 4-amino groups of oseltamivir in the 4 favorable conformations was found to make polar contacts with the guanidinium side chain of Arg156. Hence, the structures of two additional inhibitors were designed and shown to further lower the binding free energy of OTV relative to the previous 54 inhibitors. These two novel structures clearly suggest that it may be possible for a new substituent to be developed by functional modifications at position of the 4-amino group of oseltamivir in order to make polar contacts with the guanidinium side chain of Arg156, and thereby enhance the binding of a more potent inhibitor. Several standpoints of vital importance for designing novel structures of potentially more effective H5N1 NA inhibitors are established.