Transporter-mediated Drug-drug Interactions Research Articles

Quantification of adefovir and pitavastatin in human plasma and urine by LC-MS/MS: A useful tool for drug-drug interaction studies

As a tool to be used in transporter-mediated drug-drug interaction studies, a sensitive LC-MS/MS method for the simultaneous quantification of adefovir and pitavastatin in human plasma and adefovir in urine was developed and successfully validated. Plasma samples were processed by protein precipitation using methanol with a subsequent concentrating step. Urine samples were diluted using 0.1% formic acid. Separation was achieved on a Synergy Polar-RP reversed phase column (50 × 4.6 mm, 2.5 μm) in gradient elution using a mobile phase composed of water and 0.1% formic acid and a mixture of methanol and acetonitrile (50:50, v/v) containing 0.1% formic acid at a flow rate of 1.0 mL/min. The linear range covered concentrations from 0.273 to 52.6 ng/mL for adefovir and from 0.539 to 104.2 ng/mL for pitavastatin in human plasma, respectively. The calibration curve for adefovir in urine ranged from 0.104 to 10.0 μg/mL. The weighted linear regression (1/conc2) implied excellent linearity with correlation coefficients ≥0.999.

Organic Anion Transporter Polypeptide 1B1 Polymorphism Modulates the Extent of Drug-Drug Interaction and Associated Biomarker Levels in Healthy Volunteers.

Understanding transporter‐mediated drug–drug interactions is an integral part of risk assessment in drug development. Recent studies support the use of hexadecanedioate (HDA), tetradecanedioate (TDA), coproporphyrin (CP)‐I, and CP‐III as clinical biomarkers for evaluating organic anion‐transporting polypeptide (OATP)1B1 (SLCO1B1) inhibition. The current study investigated the effect of OATP1B1 genotype c.521T>C (OATP1B1‐Val174Ala) on the extent of interaction between cyclosporin A (CsA) and pravastatin, and associated endogenous biomarkers of the transporter (HDA, TDA, CP‐I, and CP‐III), in 20 healthy volunteers. The results show that the levels of each clinical biomarker and pravastatin were significantly increased in plasma samples of the volunteers following administration of pravastatin plus CsA compared with pravastatin plus placebo. The overall fold change in the area under the concentration–time curve (AUC) and maximum plasma concentration (Cmax) was similar among the four biomarkers (1.8–2.5‐fold, paired t‐test P value < 0.05) in individuals who were homozygotes or heterozygotes of the major allele, c.521T. However, the fold change in AUC and Cmax for HDA and TDA was significantly abolished in the subjects who were c.521‐CC, whereas the respective fold change in AUC and Cmax for pravastatin and CP‐I and CP‐III were slightly weaker in individuals who were c.521‐CC compared with c.521‐TT/TC genotypes. In addition, this study provides the first evidence that SLCO1B1 c.521T>C genotype is significantly associated with CP‐I but not CP‐III levels. Overall, these results suggest that OATP1B1 genotype can modulate the effects of CsA on biomarker levels; the extent of modulation differs among the biomarkers.

Clinical Aspects of Transporter-Mediated Drug-Drug Interactions.

Drug transporters play an essential role in disposition and effects of multiple drugs. Plasma concentrations of the victim drug can be modified by drug-drug interactions occurring in enterocytes (e.g., P-glycoprotein), hepatocytes (e.g., organic anion-transporting polypeptide 1B1 (OATP1B1)), and/or renal proximal tubular cells (e.g., organic cation transporter 2 (OCT2)/multidrug and toxin extrusion 1 and 2-K (MATE1/MATE2-K)). In addition, transporter-mediated drug-drug interactions can cause altered local tissue concentrations and possibly altered effects/toxicity (e.g., in liver and kidneys). During drug development, there is now an intensive in vitro screening of new molecular entities as transporter substrates and inhibitors, followed if necessary by drug-drug interaction studies in healthy volunteers. Nevertheless, there are still unresolved issues, which will also be discussed in this review article (e.g., the clinical significance of transporter-mediated drug-drug interactions of particular relevance to the elderly who are prescribed multiple drugs, with additional impaired liver or kidney function, and the extent to which medication safety in real life could be improved by a reduction of those interactions).

Hepatocyte Concentrations of Imaging Compounds Associated with Transporter Inhibition: Evidence in Perfused Rat Livers

In the liver, several approaches are used to investigate and predict the complex issue of drug-induced transporter inhibition. These approaches include in vitro assays and pharmacokinetic models that predict how inhibitors modify the systemic and liver concentrations of the victim drugs. Imaging is another approach that shows how inhibitors might alter liver concentrations stronger than systemic concentrations. In perfused rat livers associated with a gamma counter that measures liver concentrations continuously, we previously showed how fluxes across transporters generate the hepatocyte concentrations of two clinical imaging compounds, one with a low extraction ratio [gadobenate dimeglumine (BOPTA)] and one with a high extraction ratio [mebrofenin (MEB)]. BOPTA and MEB are transported by rat organic anion transporting polypeptide and multiple resistance-associated protein 2, which are both inhibited by rifampicin. The aim of the study is to measure how rifampicin modifies the hepatocyte concentrations and membrane clearances of BOPTA and MEB and to determine whether these compounds might be used to investigate transporter-mediated drug-drug interactions in clinical studies. We show that rifampicin coperfusion greatly decreases BOPTA hepatocyte concentrations, but increases those of MEB. Rifampicin strongly decreases BOPTA hepatic clearance. In contrast, rifampicin decreases moderately MEB hepatic clearance and blocks the biliary intrinsic clearance, increasing MEB hepatocyte concentrations. In conclusion, low concentrations prevent the quantification of BOPTA biliary intrinsic clearance, while MEB is a promising imaging probe substrate to evidence transporter-mediated drug-drug interactions when inhibitors act on influx and efflux transporters.

Transporter-Mediated Drug-Drug Interactions and Their Significance.

Drug transporters are considered to be determinants of drug disposition and effects/toxicities by affecting the absorption, distribution, and excretion of drugs. Drug transporters are generally divided into solute carrier (SLC) family and ATP binding cassette (ABC) family. Widely studied ABC family transporters include P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), and multidrug resistance proteins (MRPs). SLC family transporters related to drug transport mainly include organic anion-transporting polypeptides (OATPs), organic anion transporters (OATs), organic cation transporters (OCTs), organic cation/carnitine transporters (OCTNs), peptide transporters (PEPTs), and multidrug/toxin extrusions (MATEs). These transporters are often expressed in tissues related to drug disposition, such as the small intestine, liver, and kidney, implicating intestinal absorption of drugs, uptake of drugs into hepatocytes, and renal/bile excretion of drugs. Most of therapeutic drugs are their substrates or inhibitors. When they are comedicated, serious drug-drug interactions (DDIs) may occur due to alterations in intestinal absorption, hepatic uptake, or renal/bile secretion of drugs, leading to enhancement of their activities or toxicities or therapeutic failure. This chapter will illustrate transporter-mediated DDIs (including food drug interaction) in human and their clinical significances.

Clinical Probes and Endogenous Biomarkers as Substrates for Transporter Drug-Drug Interaction Evaluation: Perspectives From the International Transporter Consortium.

Drug transporters can govern the absorption, distribution, metabolism, and excretion of substrate drugs and endogenous substances. Investigations to examine their potential impact to pharmacokinetic (PK) drug-drug interactions (DDIs) are an integral part of the risk assessment in drug development. To evaluate a new molecular entity as a potential perpetrator of transporters, use of well characterized and/or clinically relevant probe substrates with good selectivity and sensitivity are critical for robust clinical DDI assessment that could inform DDI management strategy in the product labeling. The availability of endogenous biomarkers to monitor transporter-mediated DDIs in early phases of clinical investigations would greatly benefit downstream clinical plans. This article reviews the state-of-the-art in transporter clinical probe drugs and emerging biomarkers, including current challenges and limitations, delineates methods and workflows to identify and validate novel endogenous biomarkers to support clinical DDI evaluations, and proposes how these probe drugs or biomarkers could be used in drug development.

Inhibition and stimulation of the human breast cancer resistance protein as in vitro predictor of drug-drug interactions of drugs of abuse.

Transporter-mediated drug-drug interactions (DDI) may induce adverse clinical events. As drugs of abuse (DOA) are marketed without preclinical safety studies, only very limited information about interplay with membrane transporters are available. Therefore, 13 DOA of various classes were tested for their in vitro affinity to the human breast cancer resistance protein (hBCRP), an important efflux transporter. As adenosine 5'-triphosphate (ATP) hydrolysis is crucial for hBCRP activity, adenosine 5'-diphosphate (ADP) formation was measured and used as in vitro marker for hBCRP ATPase activity. ADP quantification was performed by hydrophilic interaction liquid chromatography coupled to high-resolution tandem mass spectrometry and its amount in test compound incubations was compared to that in reference incubations using the hBCRP substrate sulfasalazine or the hBCRP inhibitor orthovanadate. If DOA caused stimulation or inhibition, further investigations such as Michaelis-Menten kinetic modeling or IC50 value determination were conducted. Among the tested DOA, seven compounds showed statistically significant hBCRP ATPase stimulation. The entactogen 3,4-BDB and the plant alkaloid mitragynine were identified as strongest stimulators. Their affinity to the hBCRP ATPase was lower than that of sulfasalazine but comparable to that of rosuvastatin, another hBCRP model substrate. Five DOA showed statistically significant hBCRP ATPase inhibition. Determination of IC50 values identified the synthetic cannabinoid receptor agonists JWH-200 and WIN 55,212-2 as the strongest inhibitors comparable to orthovanadate. The present study clearly demonstrated that tested DOA show in part high affinities to the hBCRP within the range of model substrates or inhibitors. Thus, there is a risk of hBCRP-mediated DDI, which needs to be considered in clinical settings.

Importance of OCT2 and MATE1 for the Cimetidine–Metformin Interaction: Insights from Investigations of Polarized Transport in Single- And Double-Transfected MDCK Cells with a Focus on Perpetrator Disposition

Cimetidine decreases the renal clearance of metformin by inhibition of renal tubular cation transport, and the underlying molecular mechanisms are still not fully understood. We investigated polarized metformin transport without and with the addition of cimetidine as well as polarized cimetidine transport in double-transfected MDCK-OCT2-MATE1 cells that mimic organic cation transport processes in proximal renal tubule cells and in MDCK vector control and single-transfected MDCK-OCT2 and MDCK-MATE1 cells. At all tested concentrations (1, 10, 100 μM), the intracellular accumulation of cimetidine after administration to the basal compartment was considerably higher in MDCK-OCT2 cells compared to that in all other cells ( p < 0.001). Whereas cimetidine transcellular, basal-to-apical transport was only slightly higher in MDCK-OCT2 cells, the presence of MATE1 in the apical membrane caused a pronounced translocation of cimetidine in both single- and double-transfected cells ( p < 0.001). Transcellular, basal-to-apical metformin net transport was reduced by 89.1, 74.5, and 91.0% in MDCK-OCT2-MATE1 cells after the addition of cimetidine (100 μM) to the basal, the apical, or both compartments ( p < 0.001). In MDCK-MATE1 and MDCK-OCT2-MATE1 cells, transcellular net transport of metformin was inhibited by cimetidine with IC50 values of 8.0 and 6.6 μM, respectively. Our data confirm the relevance of MATE1 and suggest the relevance of OCT2 for the cimetidine-metformin interaction, primarily because OCT2 mediates uptake of the perpetrator cimetidine into renal proximal tubular cells and thereby to the site of the metformin exporter MATE1. This work supports the notion that a thorough understanding of transporter-mediated drug-drug interactions may require investigations on the impact of transporters on cellular uptake and transcellular transport of victim as well as perpetrator drugs.

Simultaneous Assessment of Transporter-Mediated Drug-Drug Interactions Using a Probe Drug Cocktail in Cynomolgus Monkey.

We aim to establish an in vivo preclinical model to enable simultaneous assessment of inhibition potential of an investigational drug on clinically relevant drug transporters, organic anion-transporting polypeptide (OATP)1B, breast cancer resistance protein (BCRP), P-glycoprotein (P-gp), and organic anion transporter (OAT)3. Pharmacokinetics of substrate cocktail consisting of pitavastatin (OATP1B substrate), rosuvastatin (OATP1B/BCRP/OAT3), sulfasalazine (BCRP), and talinolol (P-gp) were obtained in cynomolgus monkey-alone or in combination with transporter inhibitors. Single-dose rifampicin (30 mg/kg) significantly (P < 0.01) increased the plasma exposure of all four drugs, with a marked effect on pitavastatin and rosuvastatin [area under the plasma concentration-time curve (AUC) ratio ∼21-39]. Elacridar, BCRP/P-gp inhibitor, increased the AUC of sulfasalazine, talinolol, as well as rosuvastatin and pitavastatin. An OAT1/3 inhibitor (probenecid) significantly (P < 0.05) impacted the renal clearance of rosuvastatin (∼8-fold). In vitro, rifampicin (10 µM) inhibited uptake of pitavastatin, rosuvastatin, and sulfasalazine by monkey and human primary hepatocytes. Transport studies using membrane vesicles suggested that all probe substrates, except talinolol, are transported by cynoBCRP, whereas talinolol is a cynoP-gp substrate. Elacridar and rifampicin inhibited both cynoBCRP and cynoP-gp in vitro, indicating potential for in vivo intestinal efflux inhibition. In conclusion, a probe substrate cocktail was validated to simultaneously evaluate perpetrator impact on multiple clinically relevant transporters using the cynomolgus monkey. The results support the use of the cynomolgus monkey as a model that could enable drug-drug interaction risk assessment, before advancing a new molecular entity into clinical development, as well as providing mechanistic insights on transporter-mediated interactions.

Biomarkers for In Vivo Assessment of Transporter Function.

Drug-drug interactions are a major concern not only during clinical practice, but also in drug development. Due to limitations of in vitro-in vivo predictions of transporter-mediated drug-drug interactions, multiple clinical Phase I drug-drug interaction studies may become necessary for a new molecular entity to assess potential drug interaction liabilities. This is a resource-intensive process and exposes study participants, who frequently are healthy volunteers without benefit from study treatment, to the potential risks of a new drug in development. Therefore, there is currently a major interest in new approaches for better prediction of transporter-mediated drug-drug interactions. In particular, researchers in the field attempt to identify endogenous compounds as biomarkers for transporter function, such as hexadecanedioate, tetradecanedioate, coproporphyrins I and III, or glycochenodeoxycholate sulfate for hepatic uptake via organic anion transporting polypeptide 1B or N1-methylnicotinamide for multidrug and toxin extrusion protein-mediated renal secretion. We summarize in this review the currently proposed biomarkers and potential limitations of the substances identified to date. Moreover, we suggest criteria based on current experiences, which may be used to assess the suitability of a biomarker for transporter function. Finally, further alternatives and supplemental approaches to classic drug-drug interaction studies are discussed.

Development of an LC–MS method to quantify coproporphyrin I and III as endogenous biomarkers for drug transporter-mediated drug-drug interactions

Coproporphyrins are proposed as endogenous biomarkers of hepatic Organic Anion Transporting Polypeptide (OATP)1B functional activity. In this study, a new sample extraction method based on a mixed-mode anion exchange sorbent (SPE clean-up using Oasis 30mg Max 96 well plates) was developed for absolute quantification of coproporphyrin I and III (CP-I and CP-III) in human plasma. Chromatographic separation was performed with an Ace Excel 2 C18 PFP, 3μm, 2.1×150mm, maintained at 60°C. A 10mM ammonium formate containing 0.1% HCOOH and acetonitrile (100%) was used as mobile phase A and B, respectively. Mass transition, m/z 655.3→596.3 was selected to monitor CP-I and CP-III, while m/z 659.3→600.3 transition was used for the stable isotope labelled internal standard. Optimization of the liquid chromatography tandem mass spectrometry method ensured a lower limit of quantification (LLOQ) of 20pg/mL. Both CP-I and CP-III had extraction recoveries of 70%. The calibration range was 0.02–100ng/mL for both CP-I and CP-III, yielding calibration curves with correlation coefficients greater than 0.988. Inter day precision (CV<9%) and accuracy (84.3–103.9%) complied with the recommendation of the European Bioanalytical Forum.The optimized method was used to analyse plasma samples originating from three independent clinical studies. Obtained CP-I and CP-III plasma baseline levels in healthy volunteers were in good agreement with previously published data. Moreover, CP-I and CP-III plasma levels in human subjects dosed with a clinically confirmed OATP inhibitor were significantly increased compared to their baseline levels. These data demonstrate the potential of CP-I and CP-III as endogenous biomarkers to predict the drug-drug interaction (DDI) related to hepatic OATP1B inhibition. Stability of CP-I and CP-III in plasma and solvents under different processing and storage conditions was also evaluated.

Prediction of drug-drug interaction potential using physiologically based pharmacokinetic modeling.

The occurrence of drug-drug interactions (DDIs) can significantly affect the safety of a patient, and thus assessing DDI risk is important. Recently, physiologically based pharmacokinetic (PBPK) modeling has been increasingly used to predict DDI potential. Here, we present a PBPK modeling concept and strategy. We also surveyed PBPK-related articles about the prediction of DDI potential in humans published up to October 10, 2017. We identified 107 articles, including 105 drugs that fit our criteria, with a gradual increase in the number of articles per year. Studies on antineoplastic and immunomodulatory drugs (26.7%) contributed the most to published PBPK models, followed by cardiovascular (20.0%) and anti-infective (17.1%) drugs. Models for specific products such as herbal products, therapeutic protein drugs, and antibody-drug conjugates were also described. Most PBPK models were used to simulate cytochrome P450 (CYP)-mediated DDIs (74 drugs, of which 85.1% were CYP3A4-mediated), whereas some focused on transporter-mediated DDIs (15 drugs) or a combination of CYP and transporter-mediated DDIs (16 drugs). Full PBPK, first-order absorption modules and Simcyp® software were predominantly used for modeling. Recently, DDI predictions associated with genetic polymorphisms, special populations, or both have increased. The 107 published articles reasonably predicted the DDI potentials, but further studies of physiological properties and harmonization of in vitro experimental designs are required to extend the application scope, and improvement of DDI predictions using PBPK modeling will be possible in the future.

MDR1 and BCRP Transporter-Mediated Drug-Drug Interaction between Rilpivirine and Abacavir and Effect on Intestinal Absorption.

Rilpivirine (TMC278) is a highly potent nonnucleoside reverse transcriptase inhibitor (NNRTI) representing an effective component of combination antiretroviral therapy (cART) in the treatment of HIV-positive patients. Many antiretroviral drugs commonly used in cART are substrates of ATP-binding cassette (ABC) and/or solute carrier (SLC) drug transporters and, therefore, are prone to pharmacokinetic drug-drug interactions (DDIs). The aim of our study was to evaluate rilpivirine interactions with abacavir and lamivudine on selected ABC and SLC transporters in vitro and assess its importance for pharmacokinetics in vivo Using accumulation assays in MDCK cells overexpressing selected ABC or SLC drug transporters, we revealed rilpivirine as a potent inhibitor of MDR1 and BCRP, but not MRP2, OCT1, OCT2, or MATE1. Subsequent transport experiments across monolayers of MDCKII-MDR1, MDCKII-BCRP, and Caco-2 cells demonstrated that rilpivirine inhibits MDR1- and BCRP-mediated efflux of abacavir and increases its transmembrane transport. In vivo experiments in male Wistar rats confirmed inhibition of MDR1/BCRP in the small intestine, leading to a significant increase in oral bioavailability of abacavir. In conclusion, rilpivirine inhibits MDR1 and BCRP transporters and may affect pharmacokinetic behavior of concomitantly administered substrates of these transporters, such as abacavir.

The Role of the Kidney in Drug Elimination: Transport, Metabolism, and the Impact of Kidney Disease on Drug Clearance.

Recent advances in the identification and characterization of renal drug transporters and drug-metabolizing enzymes has led to greater understanding of their roles in drug and chemical elimination and in modulation of the intrarenal exposure and response to drugs, nephrotoxic compounds, and physiological mediators. Furthermore, there is increasing awareness of the potential importance of drug-drug interactions (DDIs) arising from inhibition of renal transporters, and regulatory agencies now provide recommendations for the evaluation of transporter-mediated DDIs. Apart from the well-recognized effects of kidney disease on renal drug clearance, there is a growing body of evidence demonstrating that the nonrenal clearances of drugs eliminated by certain transporters and drug-metabolizing enzymes are decreased in patients with chronic kidney disease (CKD). Based on these observations, renal impairment guidance documents of regulatory agencies recommend pharmacokinetic characterization of both renally cleared and nonrenally cleared drugs in CKD patients to inform possible dosage adjustment.

In vitro evaluation of potential transporter-mediated drug interactions of evogliptin.

To date, little is known about the transporter-mediated drug-drug interaction (DDI) potential of evogliptin, a novel DPP-4 inhibitor. The objective of this study was to evaluate the DDI potential of evogliptin using various in vitro assays in transporter-expressing cell lines. After incubating evogliptin with cells overexpressing OAT1, OAT3, OCT2, OATP1B1 and OATP1B3, there was no notable cellular accumulation of evogliptin (fold accumulation, 0.41-1.86). In bidirectional transport assays using a Caco-2 cell monolayer, a high efflux ratio (ER, 522) of evogliptin was observed, which was significantly decreased (97.96%) in the presence of a potent P-gp inhibitor. In assays using MDCKII-BCRP cell monolayers, by contrast, a low net ER (1.16-1.26) was found. In similar cellular uptake and bidirectional studies with probe substrates of P-gp, BCRP, OAT1, OAT3, OCT2, OATP1B1 and OATP1B3, the active transport of the substrates was not significantly suppressed by evogliptin. These results suggest that evogliptin may be a substrate of P-gp, but not a substrate of BCRP, OAT1B1, OAT1B3, OAT1, OAT3 or OCT2, and not an inhibitor of any of these transporters. Therefore, it could be concluded that evogliptin has some DDI potential involving P-gp, but it has low potential of DDI mediated by the other transporters.

Evaluation of transporters in drug development: Current status and contemporary issues.

Transporters govern the access of molecules to cells or their exit from cells, thereby controlling the overall distribution of drugs to their intracellular site of action. Clinically relevant drug-drug interactions mediated by transporters are of increasing interest in drug development. Drug transporters, acting alone or in concert with drug metabolizing enzymes, can play an important role in modulating drug absorption, distribution, metabolism and excretion, thus affecting the pharmacokinetics and/or pharmacodynamics of a drug. The drug interaction guidance documents from regulatory agencies include various decision criteria that may be used to predict the need for in vivo assessment of transporter-mediated drug-drug interactions. Regulatory science research continues to assess the prediction performances of various criteria as well as to examine the strength and limitations of each prediction criterion to foster discussions related to harmonized decision criteria that may be used to facilitate global drug development. This review discusses the role of transporters in drug development with a focus on methodologies in assessing transporter-mediated drug-drug interactions, challenges in both in vitro and in vivo assessments of transporters, and emerging transporter research areas including biomarkers, assessment of tissue concentrations, and effect of diseases on transporters.

Prediction of renal transporter-mediated drug-drug interactions for a drug which is an OAT substrate and inhibitor using PBPK modelling

A PBPK modelling approach was used to predict organic anion transporter (OAT) mediated drug-drug interactions involving S44121, a substrate and an inhibitor of OAT1 and OAT3. Model predictions were then compared to the results of a clinical DDI study which was carried out to investigate the interaction of S44121 with probenecid, tenofovir and ciprofloxacin. PBPK models were developed and qualified using existing clinical data, and inhibition constants were determined in vitro. The model predictions for S44121 as an OAT inhibitor were similar to the results obtained from the clinical DDI study, with no interaction observed for tenofovir or ciprofloxacin in the presence of S44121. An observed AUC ratio of 2.2 was obtained for S44121 in the presence of probenecid, which was slightly higher than the model predicted AUC ratio of 1.6. A DDI study in the monkey was also carried out for the interaction between S44121 and probenecid, since the monkey has previously been reported to be a good preclinical model for OAT-mediated DDI. However, this study highlighted a species difference in the major route of S44121 elimination between monkey (mainly hepatic metabolism) and human (mainly renal excretion of unchanged drug), rendering a comparison between the two DDI studies difficult. Overall, for S44121 the PBPK modelling approach gave a better prediction of the extent of DDI than the static predictions based on inhibitor Cmax and IC50, therefore this can be considered a potentially valuable tool within drug development.

Evaluation of New Chemical Entities as Substrates of Liver Transporters in the Pharmaceutical Industry: Response to Regulatory Requirements and Future Steps

This article discusses the evaluation of drug candidates as hepatic transporter substrates. Recently, research on the applications of hepatic transporters in the pharmaceutical industry has improved to meet the requirements of the regulatory guidelines for the evaluation of drug interactions. To identify the risk of transporter-mediated drug-drug interactions at an early stage of drug development, we used a strategy of reviewing the in vivo animal pharmacokinetics and tissue distribution data obtained in the discovery stage together with the in vitro data obtained for regulatory submission. In the context of nonclinical evaluation of new chemical entities as medicines, we believe that transporter studies are emerging as a key strategy to predict their pharmacological and toxicological effects. In combination with the recent progress in systems approaches, the estimation of effective concentrations in the target tissues, by using mathematical models to describe the transporter-mediated distribution and elimination, has enabled us to identify promising compounds for clinical development at the discovery stage.

Quantitative Analysis of the Transporter-Mediated Drug-Drug Interaction Between Atorvastatin and Rifampicin Using a Stable Isotope-IV Method

This study aims to investigate the drug-drug interactions (DDIs) between orally administered atorvastatin (ATV) and rifampicin (RIF) in rats. The isotope-IV method was used for the analysis of the increased systemic exposure (AUCpo) of ATV, in which a small amount of deuterium-labeled ATV (ATV-d5) was intravenously injected after oral administration of ATV. By assuming ATV-d5 showed same pharmacokinetic properties with ATV, this method enabled to calculate the systemic clearance (CLtot) and the oral bioavailability (Foral) of ATV for each individual rat in a single experiment. RIF was orally pretreated to rats to inhibit the organic anion transporting polypeptide 1B1 (OATP1B1). From the analysis using pharmacokinetic parameters in each rat, it was revealed that the AUCpo of ATV increased depending on the plasma level of RIF, showing that the interindividual difference in the absorption of RIF caused the large variability in the extent of DDI. Furthermore, it was indicated that not only the decrease in CLtot but also the increase in Foral caused the significant increase in the AUCpo of ATV. In conclusion, the isotope-IV method possesses various advantages over the conventional method for the analysis of DDIs which affects both absorption and elimination processes of oral drugs.

In Vitro–In Vivo Extrapolation of Metabolism- and Transporter-Mediated Drug–Drug Interactions—Overview of Basic Prediction Methods

Evaluation of drug–drug interaction (DDI) risk is vital to establish benefit–risk profiles of investigational new drugs during drug development. In vitro experiments are routinely conducted as an important first step to assess metabolism- and transporter-mediated DDI potential of investigational new drugs. Results from these experiments are interpreted, often with the aid of in vitro–in vivo extrapolation methods, to determine whether and how DDI should be evaluated clinically to provide the basis for proper DDI management strategies, including dosing recommendations, alternative therapies, or contraindications under various DDI scenarios and in different patient population. This article provides an overview of currently available in vitro experimental systems and basic in vitro–in vivo extrapolation methodologies for metabolism- and transporter-mediated DDIs.