Mechanisms and Predictions of Drug-Drug Interactions of the Hepatitis C Virus Three Direct-Acting Antiviral Regimen: Paritaprevir/Ritonavir, Ombitasvir, and Dasabuvir.

To assess drug-drug interaction (DDI) potential for the three direct-acting antiviral (3D) regimen of ombitasvir, dasabuvir, and paritaprevir, in vitro studies profiled drug-metabolizing enzyme and transporter interactions. Using mechanistic static and dynamic models, DDI potential was predicted for CYP3A, CYP2C8, UDP-glucuronosyltransferase (UGT) 1A1, organic anion-transporting polypeptide (OATP) 1B1/1B3, breast cancer resistance protein (BCRP), and P-glycoprotein (P-gp). Perpetrator static model DDI predictions for metabolizing enzymes were within 2-fold of the clinical observations, but additional physiologically based pharmacokinetic modeling was necessary to achieve the same for drug transporters. When perpetrator interactions were assessed, ritonavir was responsible for the strong increase in exposure of sensitive CYP3A substrates, whereas paritaprevir (an OATP1B1/1B3 inhibitor) greatly increased the exposure of sensitive OATP1B1/1B3 substrates. The 3D regimen drugs are UGT1A1 inhibitors and are predicted to moderately increase plasma exposure of sensitive UGT1A1 substrates. Paritaprevir, ritonavir, and dasabuvir are BCRP inhibitors. Victim DDI predictions were qualitatively in line with the clinical observations. Plasma exposures of the 3D regimen were reduced by strong CYP3A inducers (paritaprevir and ritonavir; major CYP3A substrates) but were not affected by strong CYP3A4 inhibitors, since ritonavir (a CYP3A inhibitor) is already present in the regimen. Strong CYP2C8 inhibitors increased plasma exposure of dasabuvir (a major CYP2C8 substrate), OATP1B1/1B3 inhibitors increased plasma exposure of paritaprevir (an OATP1B1/1B3 substrate), and P-gp or BCRP inhibitors (all compounds are substrates of P-gp and/or BCRP) increased plasma exposure of the 3D regimen. Overall, the comprehensive mechanistic assessment of compound disposition along with mechanistic and PBPK approaches to predict victim and perpetrator DDI liability may enable better clinical management of nonstudied drug combinations with the 3D regimen.

Metabolism and Disposition of the Hepatitis C Protease Inhibitor Paritaprevir in Humans.

Paritaprevir (also known as ABT-450), a potent NS3-4A serine protease inhibitor [identified by AbbVie (North Chicago, IL) and Enanta Pharmaceuticals (Watertown, MA)] of the hepatitis C virus (HCV), has been developed in combination with ombitasvir and dasabuvir in a three-direct-acting antiviral agent (DAA) oral regimen for the treatment of patients infected with HCV genotype 1. This article describes the mass balance, metabolism, and disposition of paritaprevir in humans. After the administration of a single 200-mg oral dose of [(14)C]paritaprevir coadministered with 100 mg of ritonavir to four male healthy volunteers, the mean total percentage of the administered radioactive dose recovered was 96.5%, with recovery in individual subjects ranging from 96.0% to 96.9%. Radioactivity derived from [(14)C]paritaprevir was primarily eliminated in feces (87.8% of the dose). Radioactivity recovered in urine accounted for 8.8% of the dose. The biotransformation of paritaprevir in humans involves: 1) P450-mediated oxidation on the olefinic linker, the phenanthridine group, the methylpyrazinyl group, or combinations thereof; and 2) amide hydrolysis at the acyl cyclopropane-sulfonamide moiety and the pyrazine-2-carboxamide moiety. Paritaprevir was the major component in plasma [90.1% of total radioactivity in plasma, AUC from time 0 to 12 hours (AUC0-12hours) pool]. Five minor metabolites were identified in plasma, including the metabolites M2, M29, M3, M13, and M6; none of the metabolites accounted for greater than 10% of the total radioactivity. Paritaprevir was primarily eliminated through the biliary-fecal route followed by microflora-mediated sulfonamide hydrolysis to M29 as a major component in feces (approximately 60% of dose). In summary, the biotransformation and clearance pathways of paritaprevir were characterized, and the structures of metabolites in circulation and excreta were elucidated.

Metabolism and Disposition of Hepatitis C Polymerase Inhibitor Dasabuvir in Humans.

Dasabuvir [also known as ABT-333 or N-(6-(3-(tert-butyl)-5-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-2-methoxyphenyl)naphthalen-2-yl)methanesulfonamide] is a potent non-nucleoside NS protein 5B polymerase inhibitor of the hepatitis C virus (HCV) and is being developed in combination with paritaprevir/ritonavir and ombitasvir in an oral regimen with three direct-acting antivirals for the treatment of patients infected with HCV genotype 1. This article describes the mass balance, metabolism, and disposition of dasabuvir in humans. After administration of a single oral dose of 400-mg [(14)C]dasabuvir (without coadministration of paritaprevir/ritonavir and ombitasvir) to four healthy male volunteers, the mean total percentage of the administered radioactive dose recovered was 96.6%. The recovery from the individual subjects ranged from 90.8% to 103%. Dasabuvir and corresponding metabolites were predominantly eliminated in feces (94.4% of the dose) and minimally through renal excretion (2.2% of the dose). The biotransformation of dasabuvir primarily involves hydroxylation of the tert-butyl group to form active metabolite M1 [N-(6-(5-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-3-(1-hydroxy-2-methylpropan-2-yl)-2-methoxyphenyl)naphthalen-2-yl)methanesulfonamide], followed by glucuronidation and sulfation of M1 and subsequent secondary oxidation. Dasabuvir was the major circulating component (58% of total radioactivity) in plasma, followed by metabolite M1 (21%). Other minor metabolites represented < 10% each of total circulating radioactivity. Dasabuvir was cleared mainly through cytochrome P450-mediated oxidation metabolism to M1. M1 and its glucuronide and sulfate conjugates were primarily eliminated in feces. Subsequent oxidation of M1 to the tert-butyl acid, followed by formation of the corresponding glucuronide conjugate, plays a secondary role in elimination. Cytochrome P450 profiling indicated that dasabuvir was mainly metabolized by CYP2C8, followed by CYP3A4. In summary, the biotransformation pathway and clearance routes of dasabuvir were characterized, and the structures of metabolites in circulation and excreta were elucidated.

Metabolism and Disposition of Pan-Genotypic Inhibitor of Hepatitis C Virus NS5A Ombitasvir in Humans.

Ombitasvir (also known as ABT-267) is a potent inhibitor of hepatitis C virus (HCV) nonstructural protein 5A (NS5A), which has been developed in combination with paritaprevir/ritonavir and dasabuvir in a three direct-acting antiviral oral regimens for the treatment of patients infected with HCV genotype 1. This article describes the mass balance, metabolism, and disposition of ombitasvir in humans without coadministration of paritaprevir/ritonavir and dasabuvir. Following the administration of a single 25-mg oral dose of [(14)C]ombitasvir to four healthy male volunteers, the mean total percentage of the administered radioactive dose recovered was 92.1% over the 192-hour sample collection in the study. The recovery from the individual subjects ranged from 91.4 to 93.1%. Ombitasvir and corresponding metabolites were primarily eliminated in feces (90.2% of dose), mainly as unchanged parent drug (87.8% of dose), but minimally through renal excretion (1.9% of dose). Biotransformation of ombitasvir in human involves enzymatic amide hydrolysis to form M23 (dianiline), which is further metabolized through cytochrome P450-mediated oxidative metabolism (primarily by CYP2C8) at the tert-butyl group to generate oxidative and/or C-desmethyl metabolites. [(14)C]Ombitasvir, M23, M29, M36, and M37 are the main components in plasma, representing about 93% of total plasma radioactivity. The steady-state concentration measurement of ombitasvir metabolites by liquid chromatography-mass spectrometry analysis in human plasma following multiple doses of ombitasvir, in combination with paritaprevir/ritonavir and dasabuvir, confirmed that ombitasvir is the main component (51.9% of all measured drug-related components), whereas M29 (19.9%) and M36 (13.1%) are the major circulating metabolites. In summary, the study characterized ombitasvir metabolites in circulation, the metabolic pathways, and the elimination routes of the drug.

Challenges in the indirect quantitation of acyl-glucuronide metabolites of a cardiovascular drug from complex biological mixtures in the absence of reference standards.

This paper describes the quantitation of acyl-glucuronide metabolites (M26 and M5) of a cardiovascular-drug (torcetrapib) from monkey urine, in the absence of their reference standards. LC/MS/MS assays for M1 and M4 (aglycones of M26 and M5, respectively) were characterized from normal and base-treated urine, as their respective reference standards were available. The in vivo study samples containing M26 and M5 were treated with 1 n sodium hydroxide to hydrolyze them to their respective aglycones. The study samples were assayed for M1 and M4 before and after alkaline hydrolysis and the difference in the concentrations provided an estimate of the urinary levels of M26 and M5. Prior to the main sample analysis, conditions for alkaline hydrolysis of the glucuronides were optimized by incubating pooled study samples. During incubations, a prolonged increase in M4 levels over time was observed, which is inconsistent with the base-hydrolysis of an acyl-glucuronide (expected to hydrolyze rapidly). Possible interference of the metabolite M9 (an ether-glucuronide metabolite isobaric to M4) was investigated to explain this observation using chromatographic and wet-chemistry approaches. The strategies adopted herein established that the LC/MS/MS assay and our approach were reliable. The metabolite exposure was then correlated to toxicological observations to gain initial insights into the physiological role of these metabolites.

Rapid determination of the applicability of hydrophilic interaction chromatography utilizing ACD labs log D suite: a bioanalytical application.

Hydrophilic interaction chromatography (HILIC) is an effective technique for retaining and separating polar compounds. This approach offers several advantages for bioanalytical liquid chromatography/mass spectrometry, considering that a majority of active pharmaceutical ingredients are polar amines. HILIC employs high concentrations of relatively polar organic mobile phase components (i.e. acetonitrile), providing enhanced desolvation and electrospray ionization efficiency, as well as allowing direct injection of many protein precipitation, liquid/liquid, and solid phase extracts. A set of 30 probe compounds was evaluated to demonstrate a relationship between a compound's HILIC capacity factor (k'), and pH dependent distribution coefficient (D), using three sets of generic isocratic conditions. Plots of logk' versus logD(pH3.0) produced correlation coefficients of 0.751, 0.696, and 0.689 at acetonitrile mobile phase concentrations of 85%, 90%, and 95% (v/v), respectively. For bioanalytical applications a k'>2 is typically targeted to ensure adequate retention of a given analyte relative to extracted matrix components. Using k'> or =2 as a measure of HILIC applicability, the linear relationships for each of the three acetonitrile levels predicted whether or not HILIC was able to meet this criterion for at least 90% of the compounds tested. Overall, the relationship between k' and logD can serve as a valuable tool for identifying the applicability of HILIC and a starting point for the chromatographic conditions, prior to the initiation of any laboratory activities. Additionally, this relationship can assist with the selection of appropriate chemical analog internal standards.

Development and application of a new on-line SPE system combined with LC-MS/MS detection for high throughput direct analysis of pharmaceutical compounds in plasma.

A technique using a fully automated on-line solid phase extraction (SPE) system (Symbiosis, Spark Holland) combined with liquid chromatography (LC)-mass spectrometry (MS/MS) has been investigated for fast bioanalytical method development, method validation and sample analysis using both conventional C18 and monolithic columns. Online SPE LC-MS/MS methods were developed in the automated mode for the quantification of model compounds (propranolol and diclofenac) directly in rat plasma. Accuracy and precision using online SPE LC-MS/MS with conventional C18 and monolithic columns were in the range of 88-111% and 0.5-14%, respectively. Total analysis cycle time of 4 min per sample was demonstrated using the C18 column. Monolithic column allowed for 2 min total cycle time without compromising the quality and validation criteria of the method. Direct plasma sample injection without on-line SPE resulted in poor accuracy and precision in the range of 41-108% and 3-81%. Furthermore, the increase in back pressure resulted in column damage after the injection of only 60 samples.

Toxicokinetic evaluation of atrasentan in mice utilizing serial microsampling: validation and sample analysis in GLP study.

BACKGROUND: A semi-automated 96-well protein precipitation followed by HPLC-MS/MS method for the determination of atrasentan (2R-[4-methoxyphenyl]-4S-[1,3-benzodioxol-5-yl]-1-[N,N-di-(N-butyl)-aminocarbonyl-methyl]-pyrrolidine-3R-carboxylic acid) in mouse whole blood was developed, validated and utilized in GLP toxicokinetic evaluations. Six 40-µl whole blood samples were collected from a single mouse over the course of a 12 h blood collection window. To avoid sample volume losses, whole blood was selected as the matrix in place of the more typically used plasma. A 10-µl assay volume was used to ensure sufficient volumes are available for dilutions, repeats and incurred sample reanalysis. The samples (10-µl aliquot) were fortified with stable-labeled internal standard (d18-atrasentan) and lysed thoroughly prior to protein precipitation. The chromatographic separation was performed on a Zorbax(®) SB-C18 (50 x 2.1 mm; 5 µm) HPLC column with a mobile phase consisting of 25 mM ammonium acetate and 0.25% (v/v) acetic acid in 50/50 (v/v) acetonitrile/water. The MS measurement was conducted under positive ion mode using multiple-reaction monitoring of m/z 511→354 for analyte and 529→354 for stable-labeled internal standard. The peak area ratio (analyte:stable-labeled internal standard) was used to quantitate atrasentan. RESULTS: A dynamic range of 5-1400 ng/ml was established after validation. The challenges associated with a small-volume whole-blood assay involved anticoagulant overloading with commercial blood collection tubes, managing phospholipids to ensure a robust assay and automation. In-depth discussions are provided in this article. The validated method was then used for GLP toxicokinetic evaluations. To demonstrate the method reproducibility, approximately 10% of the incurred samples from the study were repeated in singlet. Excellent assay reproducibility was demonstrated where 100% of samples met incurred sample reanalysis acceptance criteria. CONCLUSION: Good quality exposure data were obtained from every serial sampled mouse in the study.

Signal suppression/enhancement in HPLC-ESI-MS/MS from concomitant medications.

This paper presents a study of the signal suppression and enhancement effects in assays based on HPLC-ESI-MS/MS detection. The major focus was to investigate the effect of signal suppression/enhancement of typical co-administered (concomitant) medications, i.e. naproxen and ibuprofen. The results demonstrate that the analyte and internal standard can experience signal enhancement up to a factor of ca 2.9 if the test analyte or internal standard co-elute with concomitant. Experimental results also demonstrate that the analyte and internal standard signal increased by a factor of ca 2.0 in the negative ion mode at physiological relevant levels of naproxen (100 microg/mL) and by a factor of ca 1.6 in the negative ion mode at physiological relevant level of ibuprofen (10 microg/mL) in both neat and plasma samples. Signal enhancement significantly increased when concomitant medications ionized in the same ion mode as the analyte and internal standard. To overcome signal enhancement or potential suppression from concomitant medications, a comprehensive HPLC method needs to be developed with sufficient separation of concomitant medication from the analyte and internal standard. Other means to reduce signal enhancement or potential suppression include switching ionization polarity and performing comprehensive sample clean-up to remove concomitant medications before analysis.

Strategies for bioanalysis of an oligonucleotide class macromolecule from rat plasma using liquid chromatography-tandem mass spectrometry.

Electrospray ionization (ESI) liquid chromatography-tandem mass spectrometry (LC/MS/MS) assays provide high-throughput and selective methods for quantitation of small molecules. Use of LC/MS/MS assays for macromolecules, like oligonucleotides, is challenging due to lack of sensitivity and low analyte recovery from biomatrixes. Due to this fact, the method of choice for oligonucleotides quantitation remains hybridization-based ligand-binding assays. These biological assays usually possess high sensitivity but low selectivity and narrow dynamic range. They also require optimizing suitable "capture and detection" probes, which can be prohibitively time-consuming and expensive in a drug discovery lead-optimization scenario. In this paper, we present a unique LC/MS/MS assay for a model phosphorothioate backbone oligodeoxynucleotide (ODN) drug (7692 amu) from rat plasma. Multiple analytical challenges were encountered. The strategies used to solve these challenges should prove useful to scientists pursuing mass spectrometry (MS) to quantitate oligonucleotides. The challenges include analyte multiple charging and cation adduction (reduced sensitivity), oxidation of analyte on drying and high protein binding (low recovery), ODN affinity to exposed silica (low chromatographic reproducibility and high carryover), nonspecific binding of analyte to containers (low storage stability), and optimization/synthesis of an appropriate internal standard (interference and cross-talk). A buffer (7 mM triethylamine and 3 mM ammonium formate)/methanol, 50:50 (v/v), was used as an ESI-MS infusion solvent and produced a sharp multiple charge-state distribution. The sample extraction method combined a phenol/chloroform liquid-liquid extraction and solid-phase extraction steps, which improved the absolute recovery to >70%. The method was validated in the range of 5-2000 ng/mL and had precision (percent relative standard deviation)<10.1% and accuracy (percent relative error)<11.4%.

Method for internal standard introduction for quantitative analysis using on-line solid-phase extraction LC-MS/MS.

A novel approach for on-line introduction of internal standard (IS) for quantitative analysis using LC-MS/MS has been developed. In this approach, analyte and IS are introduced into the sample injection loop in different steps. Analyte is introduced into the injection loop using a conventional autosampler (injector) needle pickup from a sample vial. IS is introduced into the sample injection loop on-line from a microreservoir containing the IS solution using the autosampler. As a result, both analyte and IS are contained in the sample loop prior to the injection into the column. Methodology allowed to reliably introduce IS and demonstrated injection accuracy and precision comparable to those obtained using off-line IS introduction (i.e., IS and analyte are premixed before injection) while maintaining chromatographic parameters (i.e., analyte and IS elution time and peak width). This new technique was applied for direct analysis of model compounds in rat plasma using on-line solid-phase extraction (SPE) LC-MS/MS quantification. In combination with on-line SPE, IS serves as a surrogate IS and compensates for signal variations attributed to sample preparation and instrumentation factors including signal suppression. The assays yielded accuracy (85-119%), precision (2-16%), and analyte recovery comparable to those obtained using off-line IS introduction. Furthermore, on-line IS introduction allows for nonvolumetric sample (plasma) collection and direct analysis without the need of measuring and aliquoting a fixed sample volume prior to the on-line SPE LC-MS/MS analysis. Therefore, this methodology enables direct sample (plasma) analysis without any sample manipulation and preparation.