Effects of Quinidine or Rifampin Co-administration on the Single-Dose Pharmacokinetics and Safety of Rilzabrutinib (PRN1008) in Healthy Participants.

This open-label, phase 1 study was conducted with healthy adult participants to evaluate the potential drug-drug interaction between rilzabrutinib and quinidine (an inhibitor of P-glycoprotein [P-gp] and CYP2D6) or rifampin (an inducer of CYP3A and P-gp). Plasma concentrations of rilzabrutinib were measured after a single oral dose of rilzabrutinib 400 mg administered on day 1 and again, following a wash-out period, after co-administration of rilzabrutinib and quinidine or rifampin. Specifically, quinidine was given at a dose of 300 mg every 8 hours for 5 days from day 7 to day 11 (N = 16) while rifampin was given as 600 mg once daily for 11 days from day 7 to day 17 (N = 16) with rilzabrutinib given in the morning of day 10 (during quinidine dosing) or day 16 (during rifampin dosing). Quinidine had no significant effect on rilzabrutinib pharmacokinetics. Rifampin decreased rilzabrutinib exposure (the geometric mean of Cmax and AUC0-∞ decreased by 80.5% and 79.5%, respectively). Single oral doses of rilzabrutinib, with or without quinidine or rifampin, appeared to be well tolerated. These findings indicate that rilzabrutinib is a substrate for CYP3A but not a substrate for P-gp.

Physiologically-based pharmacokinetic modeling to evaluate in vitro-to-in vivo extrapolation for intestinal P-glycoprotein inhibition.

As one of the key components in model-informed drug discovery and development, physiologically-based pharmacokinetic (PBPK) modeling linked with in vitro-to-in vivo extrapolation (IVIVE) is widely applied to quantitatively predict drug-drug interactions (DDIs) on drug-metabolizing enzymes and transporters. This study aimed to investigate an IVIVE for intestinal P-glycoprotein (Pgp, ABCB1)-mediated DDIs among three Pgp substrates, digoxin, dabigatran etexilate, and quinidine, and two Pgp inhibitors, itraconazole and verapamil, via PBPK modeling. For Pgp substrates, assuming unbound Michaelis-Menten constant (Km ) to be intrinsic, in vitro-to-in vivo scaling factors for maximal Pgp-mediated efflux rate (Jmax ) were optimized based on the clinically observed results without co-administration of Pgp inhibitors. For Pgp inhibitors, PBPK models utilized the reported in vitro values of Pgp inhibition constants (Ki ), 1.0 µM for itraconazole and 2.0 µM for verapamil. Overall, the PBPK modeling sufficiently described Pgp-mediated DDIs between these substrates and inhibitors with the prediction errors of less than or equal to ±25% in most cases, suggesting a reasonable IVIVE for Pgp kinetics in the clinical DDI results. The modeling results also suggest that Pgp kinetic parameters of both the substrates (Km and Jmax ) and the inhibitors (Ki ) are sensitive to Pgp-mediated DDIs, thus being key for successful DDI prediction. It would also be critical to incorporate appropriate unbound inhibitor concentrations at the site of action into PBPK models. The present results support a quantitative prediction of Pgp-mediated DDIs using in vitro parameters, which will significantly increase the value of in vitro studies to design and run clinical DDI studies safely and effectively.

Intracellular uptake of agents that block the hERG channel can confound the assessment of QT interval prolongation and arrhythmic risk.

BACKGROUND: Oliceridine is a biased ligand at the µ-opioid receptor recently approved for the treatment of acute pain. In a thorough QT study, corrected QT (QTc) prolongation displayed peaks at 2.5 and 60 minutes after a supratherapeutic dose. The mean plasma concentration peaked at 5 minutes, declining rapidly thereafter. OBJECTIVE: The purpose of this study was to examine the basis for the delayed effect of oliceridine to prolong the QTc interval. METHODS: Repolarization parameters and tissue accumulation of oliceridine were evaluated in rabbit left ventricular wedge preparations over a period of 5 hours. The effects of oliceridine on ion channel currents were evaluated in human embryonic kidney and Chinese hamster ovary cells. Quinidine was used as a control. RESULTS: Oliceridine and quinidine produced a progressive prolongation of the QTc interval and action potential duration over a period of 5 hours, paralleling slow progressive tissue uptake of the drugs. Oliceridine caused modest prolongation of these parameters, whereas quinidine produced a prominent prolongation of action potential duration and QTc interval as well as development of early afterdepolarization (after 2 hours), resulting in a high torsades de pointes score. The 50% inhibitory concentration values for the oliceridine inhibition of the rapidly activating delayed rectifier current (human ether a-go-go current) and late sodium channel current were 2.2 and 3.45 µM when assessed after traditional acute exposure but much lower after 3 hours of drug exposure. CONCLUSION: Our findings suggest that a gradual increase of intracellular access of drugs to the hERG channels as a result of their intracellular uptake and accumulation can significantly delay effects on repolarization, thus confounding the assessment of QT interval prolongation and arrhythmic risk when studied acutely. The multi-ion channel effects of oliceridine, late sodium channel current inhibition in particular, point to a low risk of devloping torsades de pointes.

Characterization and Validation of Canine P-Glycoprotein-Deficient MDCK II Cell Lines for Efflux Substrate Screening.

PURPOSE: We characterized three canine P-gp (cP-gp) deficient MDCKII cell lines. Their relevance for identifying efflux transporter substrates and predicting limitation of brain penetration were evaluated. In addition, we discuss how compound selection can be done in drug discovery by using these cell systems. METHOD: hMDR1, hBCRP-transfected, and non-transfected MDCKII ZFN cells (all with knock-down of endogenous cP-gp) were used for measuring permeability and efflux ratios for substrates. The compounds were also tested in MDR1_Caco-2 and BCRP_Caco-2, each with a double knock-out of BCRP/MRP2 or MDR1/MRP2 transporters respectively. Efflux results were compared between the MDCK and Caco-2 models. Furthermore, in vitro MDR1_ZFN efflux data were correlated with in vivo unbound drug brain-to-plasma partition coefficient (Kp,uu). RESULTS: MDR1 and BCRP substrates are correctly classified and robust transporter affinities with control substrates are shown. Cell passage mildly influenced mRNA levels of transfected transporters, but the transporter activity was proven stable for several years. The MDCK and Caco-2 models were in high consensus classifying same efflux substrates. Approx. 80% of enlisted substances were correctly predicted with the MDR1_ZFN model for brain penetration. CONCLUSION: cP-gp deficient MDCKII ZFN models are reliable tools to identify MDR1 and BCRP substrates and useful for predicting efflux liability for brain penetration.

Predicted values for human total clearance of a variety of typical compounds with differently humanized-liver mouse plasma data.

Prediction of human pharmacokinetics is important in the preclinical stage. Values for total clearance of compounds from plasma should be one of the most important pharmacokinetic parameters for predictions. Although several physiological and empirical methods including single-species allometry for prediction of values for human clearance of compounds using humanized-liver mice have been reported, further improvement of prediction accuracies would be still expected. To optimize these approaches, we proposed methods for unbound intrinsic clearance in virtually 100% humanized-liver mouse by incorporating unbound plasma fractions of compounds in differently humanized-liver mice. Comparisons of prediction accuracies of values for human clearance of 15 model compounds were performed among our current physiological and previously reported models and single-species allometry using humanized-liver mice. Incorporation of the actual unbound plasma fractions of compounds and correction of residual mice hepatocyte in humanized-liver mice showed comparable prediction accuracy to that by single-species allometry. After exclusion of 3 compounds with large species differences in values of clearance and unbound plasma fractions between mice and humans out of 15 compounds, prediction accuracies were improved in the methods investigated. The previously and present reported physiological methods could show the good prediction accuracy of values for clearance of drugs from plasma.

Drug-Drug Interactions Of Amiodarone And Quinidine On The Pharmacokinetics Of Eliglustat In Rats.

BACKGROUND: Eliglustat, a new oral substrate-reduction therapy, was recently approved as a first-line therapy for Gaucher's disease type 1 (GD1) patients. PURPOSE: The purpose of the present study was to develop and validate a simple UPLC-MS/MS method for the measurement of plasma-eliglustat concentration and to investigate the effects of amiodarone and quinidine on eliglustat metabolism in rats. METHODS: Eighteen rats were randomly divided into three groups (n=6): control (0.5% CMC-Na, group A), amiodarone (60 mg/kg, group B), and quinidine (100 mg/kg, group C). Thirty minutes later, 10 mg/kg eliglustat was orally administered to each rat and concentrations of eliglustat in the rats determined by our UPLC-MS/MS method. RESULTS: Amiodarone and quinidine increased the main pharmacokinetic parameters (AUC0→ t , AUC0→∞, and Cmax) of eliglustat significantly and decreased clearance obviously. CONCLUSION: Amiodarone and quinidine can elevate eliglustat exposure and have an inhibitory effect on eliglustat metabolism. Clearly, appropriate pharmacological studies of eliglustat in patients treated with amiodarone or quinidine should be done in future.

Correction of the QRS duration for heart rate.

OBJECTIVE: To determine the clinical value of correcting the QRS duration for heart rate. BACKGROUND: We recently observed [1] that the QRS duration shortens during spontaneous increases in heart rate. In the current study, we analyzed ECG and pharmacokinetic data of 21 subjects who received quinidine in a recent study [2]. They experienced the expected post-quinidine increase in heart rate, allowing us to determine if quinidine's well-known QRS prolongation might be attenuated due to the concomitant rate increase. METHODS: In a crossover-designed study, after baseline ECG recording, the subjects received quinidine 400 mg orally or placebo, and ECGs and quinidine plasma concentrations were then obtained at 15 prespecified timepoints over 24 h. The previously determined QRS-RR regression slope (0.0125) [1] was used to rate-correct QRS. Change in QRS from baseline (dQRS) and rate-corrected change in QRS from baseline (dQRSc) over time were plotted with the mean quinidine concentration and the correlation of plasma concentration with dQRS and dQRSc was assessed by pairwise correlation and linear regression. RESULTS: There was a statistically significantly greater increase in heart rate at all timepoints combined in the quinidine arm compared with the placebo arm (9.9 ±â€¯6.80 vs. 5.2 ±â€¯7.42, respectively, p < 0.0001). dQRSc was significantly greater at all timepoints combined compared with dQRS (1.99 ±â€¯4.824 vs -0.68 ±â€¯4.640 msec, respectively, p < 0.0001). dQRS correlated poorly with quinidine plasma concentration (p = 0.127), with no clear change in QRS observed. On the other hand, dQRSc correlated well with quinidine concentration (p = 0.010), with a clear rise and fall in dQRSc that mirrored the rise and fall of quinidine concentration. CONCLUSION: Rate correction of the QRS duration improves detection of QRS prolongation in the presence of heart rate change. CONDENSED ABSTRACT: Using the mean QRS - RR slope determined previously in normal volunteers [1], we corrected the QRS duration for its known dependency on heart rate in 21 subjects who received quinidine and experienced the expected post-quinidine increase in heart rate in a recent clinical trial [2]. We found that uncorrected QRS did not correlate with quinidine concentration (p = 0.127), while rate-corrected QRS correlated well (p = 0.010) and mirrored the rise and fall of quinidine concentration. Rate correction of the QRS duration improves detection of QRS prolongation in the presence of heart rate change.

Changes in tramadol enantioselective pharmacokinetics and metabolism in rats with experimental diabetes treated or not with insulin.

This study aimed to investigate the impact of diabetes treated or not with insulin in the enantioselective pharmacokinetics of tramadol (trans-T) and its phase 1 metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2). The CYP2D inhibitor quinidine was used to simulate the poor metabolizer phenotype. Male Wistar rats were divided into groups: control, quinidine (80-mg/kg quinidine intraperitoneally 4 h before trans-T), diabetic (45-mg/kg STZ i.v.), diabetes + insulin (2 IU/day insulin for 12 days), diabetes + quinidine and diabetes + insulin + quinidine. All animals (n = 6, per sampling time) received 20-mg/kg trans-T orally. The kinetic disposition of trans-T is enantioselective in control with higher AUC of (+)-trans-T than for its antipode. Quinidine reduced AUC ratios (+)-M1/(+)-trans-T and (-)-M1/(-)-trans-T compared to Control. Diabetes increased plasma concentrations of (+)-trans-T, (-)-trans-T, (+)-M1, (-)-M1 and (+)-M2 compared to control, but without changing AUC ratios M1/trans-T or M2/trans-T. Insulin reverted the effect of diabetes only for (-)-trans-T. The simulated diabetes in CYP2D poor metabolizers showed reduced metabolic ratios for M1 enantiomers. In conclusion, diabetes resulted in higher plasma concentrations of the active (+)-trans-T, (-)-trans-T and (+)-M1, suggesting down-regulation of CYP3A and OCT1. The glycemic control of diabetes by insulin reduces partially the impact of diabetes on trans-T pharmacokinetics.

Prediction of drug-drug interactions using physiologically-based pharmacokinetic models of CYP450 modulators included in Simcyp software.

In recent years, physiologically based PharmacoKinetic (PBPK) modeling has received growing interest as a useful tool for the assessment of drug pharmacokinetics. It has been demonstrated to be informative and helpful to quantify the modification in drug exposure due to specific physio-pathological conditions, age, genetic polymorphisms, ethnicity and particularly drug-drug interactions (DDIs). In this paper, the prediction success of DDIs involving various cytochrome P450 isoenzyme (CYP) modulators namely ketoconazole (a competitive inhibitor of CYP3A), itraconazole (a competitive inhibitor of CYP3A), clarithromycin (a mechanism-based inhibitor of CYP3A), quinidine (a competitive inhibitor of CYP2D6), paroxetine (a mechanism-based inhibitor of CYP2D6), ciprofloxacin (a competitive inhibitor of CYP1A2), fluconazole (a competitive inhibitor of CYP2C9/2C19) and rifampicin (an inducer of CYP3A) were assessed using Simcyp® software. The aim of this report was to establish confidence in each CYP-specific modulator file so they can be used in the future for the prediction of DDIs involving new victim compounds. Our evaluation of these PBPK models suggested that they can be successfully used to evaluate DDIs in untested scenarios. The only noticeable exception concerned a quinidine inhibitor model that requires further improvement. Additionally, other important aspects such as model validation criteria were discussed.

An ECV304 monoculture model for permeability assessment of blood-brain barrier.

OBJECTIVE: ECV304/C6 co-culture model is a widely used tool for BBB studies. However, cell source may influence the establishment of co-culture model and some C6 cells could damage the barrier integrity. Here, we established an ECV304 monoculture model and evaluated it in the respect of tightness, tight junction proteins and discriminative brain penetration. METHODS: The tightness of ECV304 cell layers was evaluated by the measurement of permeability to hydrophilic marker Lucifer yellow. Immunofluorescence method was explored to detect the expression of tight junction proteins occludin, claudin-5 and ZO-1 in ECV304 cells. The discriminative brain penetration of the model was assessed by a permeability testing of compounds with different penetration rates, including digoxin, quinidine, and propranolol. RESULTS: The ECV304 monolayers developed low permeability to Lucifer yellow (permeability coefficient: 0.31 ± 0.02 × 10-3 cm/min) and exhibited positive immunostaining of occludin, claudin-5 and ZO-1. The permeability coefficients of high permeable quinidine and propranolol across ECV304 cell layers were higher than that of low permeable digoxin by 3.6 and 2.8-fold, respectively. CONCLUSIONS: The ECV304 monoculture model developed tight paracellular barrier and discriminated between compounds with different permeability, indicating it as a potential in vitro model for BBB permeability assessment.

The Role of Quinidine in the Pharmacological Therapy of Ventricular Arrhythmias 'Quinidine'.

Historically, quinidine was the first medicine used in the therapy of heart arrhythmias. Studies in the early 20th century identified quinidine, a diastereomer of the antimalarial quinine, as the most potent of the antiarrhythmic substances extracted from the cinchona plant. Quinidine is used by the 1920s, as an antiarrhythmic agent to maintain sinus rhythm after the conversion from atrial flutter or atrial fibrillation and to prevent recurrence of ventricular tachycardia or ventricular fibrillation. Its value in chronic prophylaxis of relapse of ventricular arrhythmia was brought under suspicion after publishing of meta analysis that showed that the application of quinidine increases mortality. Due to numerous proofs of increased risk for the appearance of ventricular arrhythmia and sudden death, as well as a number of other adverse effects and drug interactions, quinidine was withdrawn from use and in the recent years has become unavailable in many countries. On the other hand, recent studies have demonstrated that quinidine is the only oral medication that has consistently shown efficacy in preventing arrhythmias and terminating storms due to recurrent ventricular fibrillation, in patients with Brugada syndrome, idiopathic ventricular fibrillation and early repolarization syndrome. Quinidine is also the only antiarrhythmic drug that normalized the QT interval in patients with the congenital short QT syndrome. The aim of this review is to provide good insight into pro and contra arguments for quinidine use in ventricular arrhythmias evidence based on recently published literature.

Pharmacokinetic interaction of green tea beverage containing cyclodextrins and high concentration catechins with P-glycoprotein substrates in LLC-GA5-COL150 cells in vitro and in the small intestine of rats in vivo.

OBJECTIVES: Possible interaction of green tea beverage (GT) containing cyclodextrins and high concentration catechins, a drinking water, with P-glycoprotein (P-gp) substrates was examined in vitro and in vivo. METHODS: Effects of GT on the uptake of rhodamine 123 by LLC-GA5-COL150 cells and intestinal efflux of rhodamine 123 from blood, intestinal absorption of quinidine from ileum loop and oral absorption of digoxin were examined in rats. Effects of GT and GT components on digoxin solubility were also examined. KEY FINDINGS: Green tea increased the uptake of rhodamine 123 by LLC-GA5-COL150 cells, suppressed the intestinal efflux of rhodamine 123 from blood and increased the absorption of quinidine in the ileum of rats. Also, GT increased the solubility of digoxin, and ingestion of GT significantly increased the oral absorption of digoxin given at a high dose in rats. CONCLUSIONS: Green tea suppressed the P-gp-mediated efflux transport of hydrophilic compounds and increased the solubility of lipophilic compounds. Thus, GT may cause interaction with various P-gp substrates, due to the combined effects of catechins and cyclodextrins. Especially, cyclodextrin alone can cause interaction with various low-solubility compounds in vivo. In taking low-solubility drugs including low-solubility P-gp substrates, cyclodextrin-containing foods and beverages such as GT should be avoided.

Quantification of Transporter and Receptor Proteins in Dog Brain Capillaries and Choroid Plexus: Relevance for the Distribution in Brain and CSF of Selected BCRP and P-gp Substrates.

Transporters at the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) play a pivotal role as gatekeepers for efflux or uptake of endogenous and exogenous molecules. The protein expression of a number of them has already been determined in the brains of rodents, nonhuman primates, and humans using quantitative targeted absolute proteomics (QTAP). The dog is an important animal model for drug discovery and development, especially for safety evaluations. The purpose of the present study was to clarify the relevance of the transporter protein expression for drug distribution in the dog brain and CSF. We used QTAP to examine the protein expression of 17 selected transporters and receptors at the dog BBB and BCSFB. For the first time, we directly linked the expression of two efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), to regional brain and CSF distribution using specific substrates. Two cocktails, each containing one P-gp substrate (quinidine or apafant) and one BCRP substrate (dantrolene or daidzein) were infused intravenously prior to collection of the brain. Transporter expression varied only slightly between the capillaries of different brain regions and did not result in region-specific distribution of the investigated substrates. There were, however, distinct differences between brain capillaries and choroid plexus. Largest differences were observed for BCRP and P-gp: both were highly expressed in brain capillaries, but no BCRP and only low amounts of P-gp were detected in the choroid plexus. Kp,uu,brain and Kp,uu,CSF of both P-gp substrates were indicative of drug efflux. Also, Kp,uu,brain for the BCRP substrates was low. In contrast, Kp,uu,CSF for both BCRP substrates was close to unity, resulting in Kp,uu,CSF/Kp,uu,brain ratios of 7 and 8, respectively. We conclude that the drug transporter expression profiles differ between the BBB and BCSFB in dogs, that there are species differences in the expression profiles, and that CSF is not a suitable surrogate for unbound brain concentrations of BCRP substrates in dogs.

AVP-786 for the treatment of agitation in dementia of the Alzheimer's type.

INTRODUCTION: Agitation is common and distressing in patients with Alzheimer-type dementia, but safe, effective treatments remain elusive. Psychological treatments are first-line options, but they have limited efficacy. Off-label psychotropic medications are frequently used, but they also have limited effectiveness, and their use may have harmful side effects, including death. Areas covered: This review discusses the history leading to the conception of AVP-786 (deuterated (d6)-dextromethorphan/quinidine), its pharmacokinetic and pharmacodynamic profiles and safety issues, together with an overview of recent clinical trials. Data were found in the medical literature, in US and EU clinical trial registries and in information provided by the manufacturer. Expert opinion: AVP-786 is one of six investigational compounds in recent phase III clinical development for agitation in Alzheimer disease (AD). Quinidine and deuteration appear to prolong dextromethorphan's plasma half-life and facilitate brain penetration. The FDA granted fast-track designation to AVP-786 and allowed use of data generated on dextromethorphan-quinidine (AVP-923, Nuedexta®) for regulatory filings. AVP-923 reduced agitation in AD and was well tolerated in a phase II RCT that included more than 200 patients. A phase III clinical development program of AVP-786 for AD agitation was recently initiated. This program is expected to start generating results in July 2018.

The consequence of regional gradients of P-gp and CYP3A4 for drug-drug interactions by P-gp inhibitors and the P-gp/CYP3A4 interplay in the human intestine ex vivo.

Intestinal P-gp and CYP3A4 work coordinately to reduce the intracellular concentration of drugs, and drug-drug interactions (DDIs) based on this interplay are of clinical importance and require pre-clinical investigation. Using precision-cut intestinal slices (PCIS) of human jejunum, ileum and colon, we investigated the P-gp/CYP3A4 interplay and related DDIs with P-gp inhibitors at the different regions of the human intestine with quinidine (Qi), dual substrate of P-gp and CYP3A4, as probe. All the P-gp inhibitors increased the intracellular concentrations of Qi by 2.1-2.6 fold in jejunum, 2.6-3.8 fold in ileum but only 1.2-1.3 fold in colon, in line with the different P-gp expression in these intestinal regions. The selective P-gp inhibitors (CP100356 and PSC833) enhanced 3-hydroxy-quinidine (3OH-Qi) in jejunum and ileum, while dual inhibitors of P-gp and CYP3A4 (verapamil and ketoconazole) decreased the 3OH-Qi production, despite of the increased intracellular Qi concentration, due to inhibition of CYP3A4. The outcome of DDIs based on P-gp/CYP3A4 interplay, shown as remarkable changes in the intracellular concentration of both the parent drug and the metabolite, varied among the intestinal regions, probably due to the different expression of P-gp and CYP3A4, and were different from those found in rat PCIS, which may have important implications for the disposition and toxicity of drugs and their metabolites.

Extrapolation of Elementary Rate Constants of P-glycoprotein-Mediated Transport from MDCKII-hMDR1-NKI to Caco-2 Cells.

The best parameters for incorporation into mechanistic physiologically based pharmacokinetic models for transporters are system-independent kinetic parameters and active (not total) transporter levels. Previously, we determined the elementary rate constants for P-glycoprotein (P-gp)-mediated transport (on- and off-rate constants from membrane to P-gp binding pocket and efflux rate constant into the apical chamber) using the structural mass action kinetic model in confluent MDCKII-hMDR1-NKI cell monolayers. In the present work, we extended the kinetic analysis to Caco-2 cells for the first time and showed that the elementary rate constants are very similar compared with MDCKII-hMDR1-NKI cells, suggesting they primarily depend on the interaction of the compound with P-gp and are therefore mostly independent of the in vitro system used. The level of efflux active (not total) P-gp is also fitted by our model. The estimated level of efflux active P-gp was 5.0 ± 1.4-fold lower in Caco-2 cells than in MDCKII-hMDR1-NKI cells. We also kinetically identified the involvement of a basolateral uptake transporter for both digoxin and loperamide in Caco-2 cells, as found previously in MDCKII-hMDR1-NKI cells, due to their low passive permeability. This demonstrates the value of our P-gp structural model as a diagnostic tool in detecting the importance of other transporters, which cannot be unambiguously done by the Michaelis-Menten approach. The system-independent elementary rate constants for P-gp obtained in vitro are more fundamental parameters than those obtained using Michaelis-Menten steady-state equations. This suggests they will be more robust mechanistic parameters for incorporation into physiologically based pharmacokinetic models for transporters.

Quantitative Targeted Absolute Proteomics of Transporters and Pharmacoproteomics-Based Reconstruction of P-Glycoprotein Function in Mouse Small Intestine.

The purpose of this study was to investigate whether a pharmacokinetic model integrating in vitro mdr1a efflux activity (which we previously reported) with in vitro/in vivo differences in protein expression level can reconstruct intestinal mdr1a function. In situ intestinal permeability-surface area product ratio between wild-type and mdr1a/1b (-/-) mice is one of the parameters used to describe intestinal mdr1a function. The reconstructed ratios of six mdr1a substrates (dexamethasone, digoxin, loperamide, quinidine, verapamil, vinblastine) and one nonsubstrate (diazepam) were consistent with the observed values reported by Adachi et al. within 2.1-fold difference. Thus, intestinal mdr1a function can be reconstructed by our pharmacoproteomic modeling approach. Furthermore, we evaluated regional differences in protein expression levels of mouse intestinal transporters. Sixteen (mdr1a, mrp4, bcrp, abcg5, abcg8, glut1, 4f2hc, sglt1, lat2, pept1, mct1, slc22a18, ostß, villin1, Na(+)/K(+)-ATPase, γ-gtp) out of 46 target molecules were detected by employing our established quantitative targeted absolute proteomics technique. The protein expression amounts of mdr1a and bcrp increased progressively from duodenum to ileum. Sglt1, lat2, and 4f2hc were highly expressed in jejunum and ileum. Mct1 and ostß were highly expressed in ileum. The quantitative expression profiles established here should be helpful to understand and predict intestinal transporter functions.

In vitro and in vivo evaluations of the P-glycoprotein-mediated efflux of dibenzoylhydrazines.

P-glycoprotein (P-gp) is a member of the ATP-binding cassette transporter family. It actively transports a wide variety of compounds out of cells to protect humans from xenobiotics. Thus, determining whether chemicals are substrates and/or inhibitors of P-gp is important in risk assessments of pharmacokinetic interactions among chemicals because P-gp-mediated transport processes play a significant role in their absorption and disposition. We previously reported that dibenzoylhydrazines (DBHs) such as tebufenozide and methoxyfenozide (agrochemicals) stimulated P-gp ATPase activity. However, it currently remains unclear whether these derivatives are transport substrates of P-gp and inhibit transport of other chemicals by P-gp. In the present study, in order to evaluate the interactions of DBHs with other chemicals in humans, we determined whether DBHs are P-gp transport substrates using both the in vitro bidirectional transport assay and the in vivo study of rats. In the in vivo study, we investigated the influence of P-gp inhibitors on the brain to plasma ratio of methoxyfenozide in rats. We also examined the inhibitory effects of DBHs on quinidine (a P-gp substrate) transport by P-gp in order to ascertain whether these derivatives are inhibitors of P-gp. Based on the results, DBHs were concluded to be weak P-gp transport substrates and moderate P-gp inhibitors. However, the risk of DBHs caused by interaction with other chemicals including drugs was considered to be low by considering the DBHs' potential as the substrates and inhibitors of P-gp as well as their plasma concentrations as long as DBHs are properly used.

Species differences in metabolism of EPZ015666, an oxetane-containing protein arginine methyltransferase-5 (PRMT5) inhibitor.

1. Metabolite profiling and identification studies were conducted to understand the cross-species differences in the metabolic clearance of EPZ015666, a first-in-class protein arginine methyltransferase-5 (PRMT5) inhibitor, with anti-proliferative effects in preclinical models of Mantle Cell Lymphoma. EPZ015666 exhibited low clearance in human, mouse and rat liver microsomes, in part by introduction of a 3-substituted oxetane ring on the molecule. In contrast, a higher clearance was observed in dog liver microsomes (DLM) that translated to a higher in vivo clearance in dog compared with rodent. 2. Structure elucidation via high resolution, accurate mass LC-MS(n) revealed that the prominent metabolites of EPZ015666 were present in hepatocytes from all species, with the highest turnover rate in dogs. M1 and M2 resulted from oxidative oxetane ring scission, whereas M3 resulted from loss of the oxetane ring via an N-dealkylation reaction. 3. The formation of M1 and M2 in DLM was significantly abrogated in the presence of the specific CYP2D inhibitor, quinidine, and to a lesser extent by the CYP3A inhibitor, ketoconazole, corroborating data from human recombinant isozymes. 4. Our data indicate a marked species difference in the metabolism of the PRMT5 inhibitor EPZ015666, with oxetane ring scission the predominant metabolic pathway in dog mediated largely by CYP2D.

Circadian modulation in the intestinal absorption of P-glycoprotein substrates in monkeys.

Recent studies in laboratory rodents have revealed that circadian oscillation in the physiologic functions affecting drug disposition underlies the dosing time-dependent change in pharmacokinetics. However, it is difficult to predict the circadian change in the drug pharmacokinetics in a diurnal human by using the data collected from nocturnal rodents. In this study, we used cynomolgus monkeys, diurnal active animals, to evaluate the relevance of intestinal expression of P-glycoprotein (P-gp) to the dosing time dependency of the pharmacokinetics of its substrates. The rhythmic phases of circadian gene expression in the suprachiasmatic nuclei (the mammalian circadian pacemaker) of cynomolgus monkeys were similar to those reported in nocturnal rodents. On the other hand, the expression of circadian clock genes in the intestinal epithelial cells of monkeys oscillated at opposite phases in rodents. The intestinal expression of P-gp in the small intestine of monkeys was also oscillated in a circadian time-dependent manner. Furthermore, the intestinal absorption of P-gp substrates (quinidine and etoposide) was substantially suppressed by administering the drugs at the times of day when P-gp levels were abundant. By contrast, there was no significant dosing time-dependent difference in the absorption of the non-P-gp substrate (acetaminophen). The oscillation in the intestinal expression of P-gp appears to affect the pharmacokinetics of its substrates. Identification of circadian factors affecting the drug disposition in laboratory monkeys may improve the predictive accuracy of pharmacokinetics in humans.