An efficient liquid chromatography-high resolution mass spectrometry approach for the optimization of the metabolic stability of therapeutic peptides.

In drug discovery, there is increasing interest in peptides as therapeutic agents due to several appealing characteristics that are typical of this class of compounds, including high target affinity, excellent selectivity, and low toxicity. However, peptides usually present also some challenging ADME (absorption, distribution, metabolism, and excretion) issues such as limited metabolic stability, poor oral bioavailability, and short half-lives. In this context, early preclinical in vitro studies such as plasma metabolic stability assays are crucial to improve developability of a peptidic drug. In order to speed up the optimization of peptide metabolic stability, a strategy was developed for the integrated semi-quantitative determination of metabolic stability of peptides and qualitative identification/structural elucidation of their metabolites in preclinical plasma metabolic stability studies using liquid chromatography-high-resolution Orbitrap™ mass spectrometry (LC-HRMS). Sample preparation was based on protein precipitation: experimental conditions were optimized after evaluating and comparing different organic solvents in order to obtain an adequate extraction of the parent peptides and their metabolites and to minimize matrix effect. Peptides and their metabolites were analyzed by reverse-phase liquid chromatography: a template gradient (total run time, 6 min) was created to allow retention and good peak shape for peptides of different polarity and isoelectric points. Three LC columns were selected to be systematically evaluated for each series of peptides. Targeted and untargeted HRMS data were simultaneously acquired in positive full scan + data-dependent MS/MS acquisition mode, and then processed to calculate plasma half-life and to identify the major cleavage sites, this latter by using the software Biopharma Finder™. Finally, as an example of the application of this workflow, a study that shows the plasma stability improvement of a series of antimicrobial peptides is described. This approach was developed for the evaluation of in vitro plasma metabolic stability studies of peptides, but it could also be applied to other in vitro metabolic stability models (e.g., whole blood, hepatocytes). Graphical Abstract Left: trend plot for omiganan and major metabolites. Right: stability plot for five antimicrobial peptidesafter incubation with mouse plasma.

Addition of a cholesterol group to an HIV-1 peptide fusion inhibitor dramatically increases its antiviral potency.

Peptides derived from the heptad repeat 2 (HR2) region of the HIV fusogenic protein gp41 are potent inhibitors of viral infection, and one of them, enfuvirtide, is used for the treatment of therapy-experienced AIDS patients. The mechanism of action of these peptides is binding to a critical intermediate along the virus-cell fusion pathway, and accordingly, increasing the affinity for the intermediate yields more potent inhibitors. We took a different approach, namely to increase the potency of the HR2 peptide inhibitor C34 by targeting it to the cell compartment where fusion occurs, and we show here that a simple, yet powerful way to accomplish this is attachment of a cholesterol group. C34 derivatized with cholesterol (C34-Chol) shows dramatically increased antiviral potency on a panel of primary isolates, with IC(90) values 15- to 300-fold lower than enfuvirtide and the second-generation inhibitor T1249, making C34-Chol the most potent HIV fusion inhibitor to date. Consistent with its anticipated mechanism of action, the antiviral activity of C34-Chol is unusually persistent: washing target cells after incubation with C34-Chol, but before triggering fusion, increases IC(50) only 7-fold, relative to a 400-fold increase observed for C34. Moreover, derivatization with cholesterol extends the half-life of the peptide in vivo. In the mouse, s.c. administration of 3.5 mg/kg C34-Chol yields a plasma concentration 24 h after injection >300-fold higher than the measured IC(90) values. Because the fusion machinery targeted by C34-Chol is similar in several other enveloped viruses, we believe that these findings may be of general utility.

Oligomerization, albumin binding and catabolism of therapeutic peptides in the subcutaneous compartment: An investigation on lipidated GLP-1 analogs.

Lipidation, a common strategy to improve half-life of therapeutic peptides, affects their tendency to oligomerize, their interaction with plasmatic proteins, and their catabolism. In this work, we have leveraged the use of NMR and SPR spectroscopy to elucidate oligomerization propensity and albumin interaction of different analogs of the two marketed lipidated GLP-1 agonists liraglutide and semaglutide. As most lipidated therapeutic peptides are administered by subcutaneous injection, we have also assessed in vitro their catabolism in the SC tissue using the LC-HRMS-based SCiMetPep assay. We observed that oligomerization had a shielding effect against catabolism. At the same time, binding to albumin may provide only limited protection from proteolysis due to the higher unbound peptide fraction present in the subcutaneous compartment with respect to the plasma. Finally, identification of catabolites in rat plasma after SC dosing of semaglutide showed a good correlation with the in vitro data, with Tyr19-Leu20 being the major cleavage site. Early characterization of the complex interplay between oligomerization, albumin binding, and catabolism at the injection site is essential for the synthesis of lipidated peptides with good pharmacokinetic profiles.

Determination of asymmetric dimethyl arginine in human serum by liquid chromatography-tandem mass spectrometry: clinical application in hypertensive subjects.

BACKGROUND: Asymmetric dimethylarginine (ADMA), an endogenous competitive inhibitor of nitric oxide synthase plays an important role in endothelial dysfunction processes. Recent studies have linked high ADMA levels with several pathological conditions. The interest as a marker of endothelial dysfunction has increased in the last few years. In this paper, a method for serum ADMA quantification by liquid chromatography tandem mass spectrometry has been described. To test the utility in a pathological condition ADMA levels in hypertensive subjects have been measured. METHODS: HPLC separation was performed by hydrophilic interaction chromatography using acetonitrile/water containing 0.1% formic acid and 20 mmol/L ammonium formate. Selected reaction monitoring was performed following the transitions m/z 203.1→46.4 for ADMA and 210.1→46.3 for the internal standard [2H7]ADMA. RESULTS: The method was linear up to 10 µmol/L, limit of detection and limit of quantification were 0.005 µmol/L and 0.01 µmol/L, respectively. Recovery was higher than 96%. Intra- and inter-assay imprecision were lower than 6%. The accuracy, expressed as bias %, was <2.5. ADMA in "healthy" subjects ranged from 0.343 to 0.608 µmol/L and resulted significantly lower than that measured in hypertensive subjects (p<0.001). CONCLUSIONS: The method developed is selective and sensitive, thus suitable not only for research purposes, but also for routinely work.

DPP-IV-resistant, long-acting oxyntomodulin derivatives.

Obesity is one of the major risk factors for type 2 diabetes, and the development of agents, that can simultaneously achieve glucose control and weight loss, is being actively pursued. Therapies based on peptide mimetics of the gut hormone glucagon-like peptide 1 (GLP-1) are rapidly gaining favor, due to their ability to increase insulin secretion in a strictly glucose-dependent manner, with little or no risk of hypoglycemia, and to their additional benefit of causing a modest, but durable weight loss. Oxyntomodulin (OXM), a 37-amino acid peptide hormone of the glucagon (GCG) family with dual agonistic activity on both the GLP-1 (GLP1R) and the GCG (GCGR) receptors, has been shown to reduce food intake and body weight in humans, with a lower incidence of treatment-associated nausea than GLP-1 mimetics. As for other peptide hormones, its clinical application is limited by the short circulatory half-life, a major component of which is cleavage by the enzyme dipeptidyl peptidase IV (DPP-IV). SAR studies on OXM, described herein, led to the identification of molecules resistant to DPP-IV degradation, with increased potency as compared to the natural hormone. Analogs derivatized with a cholesterol moiety display increased duration of action in vivo. Moreover, we identified a single substitution which can change the OXM pharmacological profile from a dual GLP1R/GCGR agonist to a selective GLP1R agonist. The latter finding enabled studies, described in detail in a separate study (Pocai A, Carrington PE, Adams JR, Wright M, Eiermann G, Zhu L, Du X, Petrov A, Lassman ME, Jiang G, Liu F, Miller C, Tota LM, Zhou G, Zhang X, Sountis MM, Santoprete A, Capitò E, Chicchi GG, Thornberry N, Bianchi E, Pessi A, Marsh DJ, SinhaRoy R. Glucagon-like peptide 1/glucagon receptor dual agonism reverses obesity in mice. Diabetes 2009; 58: 2258-2266), which highlight the potential of GLP1R/GCGR dual agonists as a potentially superior class of therapeutics over the pure GLP1R agonists currently in clinical use.

Turnover rate of coenzyme A in mouse brain and liver.

Coenzyme A (CoA) is a fundamental cofactor involved in a number of important biochemical reactions in the cell. Altered CoA metabolism results in severe conditions such as pantothenate kinase-associated neurodegeneration (PKAN) in which a reduction of the activity of pantothenate kinase isoform 2 (PANK2) present in CoA biosynthesis in the brain consequently lowers the level of CoA in this organ. In order to develop a new drug aimed at restoring the sufficient amount of CoA in the brain of PKAN patients, we looked at its turnover. We report here the results of two experiments that enabled us to measure the half-life of pantothenic acid, free CoA (CoASH) and acetylCoA in the brains and livers of male and female C57BL/6N mice, and total CoA in the brains of male mice. We administered (intrastriatally or orally) a single dose of a [13C3-15N-18O]-labelled coenzyme A precursor (fosmetpantotenate or [13C3-15N]-pantothenic acid) to the mice and measured, by liquid chromatography-mass spectrometry, unlabelled- and labelled-coenzyme A species appearance and disappearance over time. We found that the turnover of all metabolites was faster in the liver than in the brain in both genders with no evident gender difference observed. In the oral study, the CoASH half-life was: 69 ± 5 h (male) and 82 ± 6 h (female) in the liver; 136 ± 14 h (male) and 144 ± 12 h (female) in the brain. AcetylCoA half-life was 74 ± 9 h (male) and 71 ± 7 h (female) in the liver; 117 ± 13 h (male) and 158 ± 23 (female) in the brain. These results were in accordance with the corresponding values obtained after intrastriatal infusion of labelled-fosmetpantotenate (CoASH 124 ± 13 h, acetylCoA 117 ± 11 and total CoA 144 ± 17 in male brain).

ApoA-I mimetic peptides promote pre-ß HDL formation in vivo causing remodeling of HDL and triglyceride accumulation at higher dose.

Reverse cholesterol transport promoted by HDL-apoA-I is an important mechanism of protection against atherosclerosis. We have previously identified apoA-I mimetic peptides by synthesizing analogs of the 22 amino acid apoA-I consensus sequence (apoA-I(cons)) containing non-natural aliphatic amino acids. Here we examined the effect of different aliphatic non-natural amino acids on the structure-activity relationship (SAR) of apoA-I mimetic peptides. These novel apoA-I mimetics, with long hydrocarbon chain (C(5-8)) amino acids incorporated in the amphipathic α helix of the apoA-I(cons), have the following properties: (i) they stimulate in vitro cholesterol efflux from macrophages via ABCA1; (ii) they associate with HDL and cause formation of pre-ß HDL particles when incubated with human and mouse plasma; (iii) they associate with HDL and induce pre-ß HDL formation in vivo, with a corresponding increase in ABCA1-dependent cholesterol efflux capacity ex vivo; (iv) at high dose they associate with VLDL and induce hypertriglyceridemia in mice. These results suggest our peptide design confers activities that are potentially anti-atherogenic. However a dosing regimen which maximizes their therapeutic properties while minimizing adverse effects needs to be established.

Quantitative prediction of human clearance guiding the development of Raltegravir (MK-0518, isentress) and related HIV integrase inhibitors.

Human HIV integrase inhibitors are a novel class of antiretroviral drugs that act by blocking incorporation of the proviral DNA into the host cell genome, a crucial step in the life cycle of HIV. In the present work, quantitative methods for prediction of human pharmacokinetics were used to guide the selection of development candidates from a series of dihydroxypyrimidine and N-methylpyrimidinone carboxamide inhibitors of HIV integrase, which are cleared mainly by O-glucuronidation. The pharmacokinetics of 10 drugs from this series was determined in several preclinical species, including rats, dogs, rhesus monkeys, and rabbits, and the in vitro turnover, plasma protein binding, and blood/plasma partition ratio were studied using preparations from both preclinical species and humans. Two clearance prediction methods, based on physiologically based scaling or allometric scaling normalized for differences in microsomal turnover, were used to extrapolate human clearance. For three clinical candidates, including the novel AIDS drug raltegravir (MK-0518, Isentress), oral drug exposure was predicted and compared with that observed in healthy human volunteers. Both scaling methods gave a reasonable correspondence between predicted and observed oral exposure. Prediction errors for the physiologically based method were less than 1.7-fold for two drugs, including raltegravir, and less than 3.5-fold for one drug. The exposures predicted using normalized allometric scaling were within 1.1- to 1.5-fold of observed values for all three compounds. The accuracy of prediction by normalized allometric scaling was similar when using data from either four preclinical species or from rats and dogs only. The prediction methods used may be applicable to other drugs cleared predominantly by glucuronidation.

HILIC LC-MS for the determination of 2'-C-methyl-cytidine-triphosphate in rat liver.

A very accurate and selective LC-MS/MS method was developed and validated for the quantification of 2'-C-modified nucleoside triphosphate in liver tissue samples. An efficient pretreatment procedure of liver tissue samples was developed, using a fully automated SPE procedure with 96-well SPE plate (weak anion exchange sorbent, 30 mg). Nucleotide hydrophilic interaction chromatography has been performed on an aminopropyl column (100 mm x 2.0 mm, 3 microm) using a gradient mixture of ACN and ACN/water (5:95 v/v) with 20 mM ammonium acetate at pH 9.45 as mobile phase at 300 microL/min flow rate. The 2'-C-modified nucleoside triphosphate was detected in the negative ESI mode in multiple reaction monitoring (MRM) mode. Calibration curve was linear over the 0.05-50 microM concentration range. Satisfying results, confirming the high reliability of the established LC-MS/MS method, were obtained for intraday precision (CV = 2.5-9.1%) and accuracy (92.6-94.8%) and interday precision (CV = 9.6-11.5%) and accuracy (94.4-102.4%) as well as for recovery (82.0-112.6%) and selectivity. The method has been successfully applied for pharmacokinetic studies of 2'-C-methyl-cytidine-triphosphate in liver tissue samples.

Development of 2-t butyl-N-methyl pyrimidones as potent inhibitors of HIV integrase.

A series of novel 2-(t)butyl-N-methyl pyrimidone HIV-1 integrase inhibitors have been identified. Optimization of the initial lead resulted in compounds such as 9d and 14a, which showed high levels of activity in cell culture inhibiting viral replication with CIC(95) of 10nM in the presence of 50% normal human serum.

Determination of acetyl coenzyme A in human whole blood by ultra-performance liquid chromatography-mass spectrometry.

Acetyl coenzyme A is involved in several key metabolic pathways. Its concentration can vary considerably in response to physiological or pathological conditions making it a potentially valuable biomarker. However, little information about the measurement and concentration of acetyl CoA in human whole blood is found in the literature. The aim of this study was the development of an accurate method for the determination of acetyl CoA in human whole blood by LC-MS/MS. The method, involving extraction from whole blood by a rapid protein precipitation procedure was thoroughly validated: limit of quantitation was 3.91 ng mL-1. Accuracy and precision were calculated at five concentrations and were within ±15%. The average endogenous level of acetyl CoA in human whole blood was determined in 17 healthy individuals to be 220.9 ng mL-1 (ranging from 124.0 to 308.0 ng mL-1). This represents, to our knowledge, the first report of acetyl CoA levels in human whole blood, and the first practical and reliable method for its determination.

Dihydroxypyrimidine-4-carboxamides as novel potent and selective HIV integrase inhibitors.

Human immunodeficiency virus type-1 (HIV-1) integrase, one of the three constitutive viral enzymes required for replication, is a rational target for chemotherapeutic intervention in the treatment of AIDS that has also recently been confirmed in the clinical setting. We report here on the design and synthesis of N-benzyl-5,6-dihydroxypyrimidine-4-carboxamides as a class of agents which exhibits potent inhibition of the HIV-integrase-catalyzed strand transfer process. In the current study, structural modifications on these molecules were made in order to examine effects on HIV-integrase inhibitory potencies. One of the most interesting compounds for this series is 2-[1-(dimethylamino)-1-methylethyl]-N-(4-fluorobenzyl)-5,6-dihydroxypyrimidine-4-carboxamide 38, with a CIC95 of 78 nM in the cell-based assay in the presence of serum proteins. The compound has favorable pharmacokinetic properties in preclinical species (rats, dogs, and monkeys) and shows no liabilities in several counterscreening assays, highlighting its potential as a clinically useful antiviral agent.

Discovery and synthesis of HIV integrase inhibitors: development of potent and orally bioavailable N-methyl pyrimidones.

The human immunodeficiency virus type-1 (HIV-1) encodes three enzymes essential for viral replication: a reverse transcriptase, a protease, and an integrase. The latter is responsible for the integration of the viral genome into the human genome and, therefore, represents an attractive target for chemotherapeutic intervention against AIDS. A drug based on this mechanism has not yet been approved. Benzyl-dihydroxypyrimidine-carboxamides were discovered in our laboratories as a novel and metabolically stable class of agents that exhibits potent inhibition of the HIV integrase strand transfer step. Further efforts led to very potent compounds based on the structurally related N-Me pyrimidone scaffold. One of the more interesting compounds in this series is the 2-N-Me-morpholino derivative 27a, which shows a CIC95 of 65 nM in the cell in the presence of serum. The compound has favorable pharmacokinetic properties in three preclinical species and shows no liabilities in several counterscreening assays.

Use of 'dilute-and-shoot' liquid chromatography-high resolution mass spectrometry in preclinical research: application to a DMPK study of perhexiline in mouse plasma.

This work describes a simple, sensitive and rapid liquid chromatography-high resolution mass spectrometry method for the quantitation of perhexiline and the simultaneous detection of perhexiline metabolites in C57bl/6 mice plasma. Only 5 µL of plasma was used for analysis. Pretreatment was limited to a 100-fold dilution ('dilute-and-shoot'). The analyte was detected by high resolution mass spectrometry (Orbitrap™ technology). Three scan events were performed over the entire chromatogram. Targeted single ion monitoring with data dependent acquisition was employed for perhexiline quantitation and confirmation, while full scan was used to perform untargeted detection of perhexiline phase I and phase II circulating metabolites. The calibration curve was linear (r(2)=0.990) ranging from 0.305 ng/mL (LLOQ) to 10000 ng/mL. Matrix effect was limited to 6.1%. The method was applied to a pharmacokinetic study of perhexiline in mouse plasma and the results obtained were compared to a standard sample preparation method based on protein precipitation and liquid chromatography-tandem mass spectrometry (MRM mode) detection. The new approach provided comparable results in terms of pharmacokinetics parameters estimate with a high sensitivity, additional information on perhexiline circulating metabolites and a low consumption of biological sample. The combination of the 'dilute-and-shoot' approach together with HRMS targeted and untargeted detection represents a suitable alternative to classic bioanalytical approaches in preclinical research.

Potent inhibitors of subgenomic hepatitis C virus RNA replication through optimization of indole-N-acetamide allosteric inhibitors of the viral NS5B polymerase.

Infections caused by hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. Compounds that block replication of subgenomic HCV RNA in liver cells are of interest because of their demonstrated antiviral effect in the clinic. In followup to our recent report that indole-N-acetamides (e.g., 1) are potent allosteric inhibitors of the HCV NS5B polymerase enzyme, we describe here their optimization as cell-based inhibitors. The crystal structure of 1 bound to NS5B was a guide in the design of a two-dimensional compound array that highlighted that formally zwitterionic inhibitors have strong intracellular potency and that pregnane X receptor (PXR) activation (an undesired off-target activity) is linked to a structural feature of the inhibitor. Optimized analogues devoid of PXR activation (e.g., 55, EC(50) = 127 nM) retain strong cell-based efficacy under high serum conditions and show acceptable pharmacokinetics parameters in rat and dog.

Inhibition of retinal and choroidal neovascularization by a novel KDR kinase inhibitor.

PURPOSE: Inhibition of vascular endothelial growth factor (VEGF) signaling has shown great promise for the treatment of ocular neovascular disease. Current anti-VEGF therapies in late-stage development, while efficacious, require dosing by frequent intravitreal injections that are inconvenient to patients. VEGF signaling inhibitors that demonstrate more convenient dosing regimens could lead to the improved treatment of neovascular diseases such as wet age related macular degeneration (AMD) and proliferative diabetic retinopathy (PDR). Here we describe the assessment of a KDR (VEGFR2) kinase inhibitor in two well-established models of ocular neovascularization following oral administration. METHODS: A novel KDR kinase inhibitor was dosed by oral gavage for 12 days at 0, 10, 30, or 100 mg/kg in an adult male Brown Norway rat laser induced choroidal neovascularization (CNV) model. The areas of CNV lesions were quantitated by fluorescence image analysis of FITC-dextran perfused animals. The kinase inhibitor was also assessed in a rat oxygen induced retinopathy (OIR) model in which neonatal rats were placed in an oxygen chamber that delivered alternating 24 h cycles of 50% and 10% oxygen for 14 days. After 14 days of oxygen treatment, the animals were returned to room air and dosed orally for 7 days with 0, 10, or 30 mg/kg kinase inhibitor. The extent of retinal neovascularization was assessed by counting pre-retinal neovascular nuclei on histological sections. RESULTS: At doses of 100 mg/kg, the KDR kinase inhibitor resulted in a 98% reduction in lesion size in the rat CNV model. 30 mg/kg doses of the inhibitor showed a 70% and 80% reduction in lesion size in the laser CNV and OIR models, respectively. CONCLUSIONS: Oral dosing of the described KDR kinase inhibitor effectively inhibits neovascularization in two well-established animal models of ocular neovascularization. These data suggest that compounds of this class may prove to be useful for the treatment of a variety of ocular neovascular diseases using a convenient oral dosing regimen.

A single-run liquid chromatography mass spectrometry method to quantify neuroactive kynurenine pathway metabolites in rat plasma.

Neuroactive metabolites in the kynurenine pathway of tryptophan catabolism are associated with neurodegenerative disorders. Tryptophan is transported across the blood-brain barrier and converted via the kynurenine pathway to N-formyl-L-kynurenine, which is further degraded to L-kynurenine. This metabolite can then generate a group of metabolites called kynurenines, most of which have neuroactive properties. The association of tryptophan catabolic pathway alterations with various central nervous system (CNS) pathologies has raised interest in analytical methods to accurately quantify kynurenines in body fluids. We here describe a rapid and sensitive reverse-phase HPLC-MS/MS method to quantify L-kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxy-L-kynurenine (3HK) and anthranilic acid (AA) in rat plasma. Our goal was to quantify these metabolites in a single run; given their different physico-chemical properties, major efforts were devoted to develop a chromatography suitable for all metabolites that involves plasma protein precipitation with acetonitrile followed by chromatographic separation by C18 RP chromatography, detected by electrospray mass spectrometry. Quantitation range was 0.098-100 ng/ml for 3HK, 9.8-20,000 ng/ml for KYN, 0.49-1000 ng/ml for KYNA and AA. The method was linear (r>0.9963) and validation parameters were within acceptance range (calibration standards and QC accuracy within ±30%).

Turbulent flow chromatography TFC-tandem mass spectrometry supporting in vitro/vivo studies of NCEs in high throughput fashion.

Turbulent Flow Chromatography (TFC) is a powerful approach for on-line extraction in bioanalytical studies. It improves sensitivity and reduces sample preparation time, two factors that are of primary importance in drug discovery. In this paper the application of the ARIA system to the analytical support of in vivo pharmacokinetics (PK) and in vitro drug metabolism studies is described, with an emphasis in high throughput optimization. For PK studies, a comparison between acetonitrile plasma protein precipitation (APPP) and TFC was carried out. Our optimized TFC methodology gave better S/N ratios and lower limit of quantification (LOQ) than conventional procedures. A robust and high throughput analytical method to support hepatocyte metabolic stability screening of new chemical entities was developed by hyphenation of TFC with mass spectrometry. An in-loop dilution injection procedure was implemented to overcome one of the main issues when using TFC, that is the early elution of hydrophilic compounds that renders low recoveries. A comparison between off-line solid phase extraction (SPE) and TFC was also carried out, and recovery, sensitivity (LOQ), matrix effect and robustness were evaluated. The use of two parallel columns in the configuration of the system provided a further increase of the throughput.

A novel strategy for reducing phospholipids-based matrix effect in LC-ESI-MS bioanalysis by means of HybridSPE.

A novel strategy to minimize phospholipids-based matrix effects in bioanalytical LC-MS/MS assays was evaluated. The phospholipids-based matrix effect was investigated with a commercially available electrospray ionization (ESI) source coupled with a triple quadrupole mass spectrometer. A systematic comparison approach of two sample preparation procedures was performed. In particular, the matrix effect on mass spectrometry response in rat and human plasma samples was studied by comparing sample extracts obtained by means of a conventional plasma protein precipitation with acetonitrile and the novel HybridSPE-Precipitation procedure. The HybridSPE dramatically reduced the levels of residual phospholipids in biological samples, leading to significant reduction in matrix effects. This new procedure which combines the simplicity of precipitation with the selectivity of SPE allows to obtain much cleaner extracts than with conventional procedures. The effective targeted removal of phospholipids and proteins in biological plasma samples achieved with the HybridSPE-Precipitation procedure provides significant improvement in bioanalysis and a practical and fast way to ensure the avoidance of phospholipids-based matrix effects.

Optimization of thienopyrrole-based finger-loop inhibitors of the hepatitis C virus NS5B polymerase.

Infections caused by the hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. The NS5B polymerase of HCV is responsible for the replication of viral RNA and has been a prime target in the search for novel treatment options. We had discovered allosteric finger-loop inhibitors based on a thieno[3,2-b]pyrrole scaffold as an alternative to the related indole inhibitors. Optimization of the thienopyrrole series led to several N-acetamides with submicromolar potency in the cell-based replicon assay, but they lacked oral bioavailability in rats. By linking the N4-position to the ortho-position of the C5-aryl group, we were able to identify the tetracyclic thienopyrrole 40, which displayed a favorable pharmacokinetic profile in rats and dogs and is equipotent with recently disclosed finger-loop inhibitors based on an indole scaffold.