Method for predicting the risk of drug–drug interactions involving inhibition of intestinal CYP3A4 and P-glycoprotein

Findings on In Vitro Transporter-Mediated Drug Interactions and Their Follow-Up Actions for Labeling: Analysis of Drugs Approved by US FDA between 2017 and 2021

Understanding possible follow-up actions on in vitro findings helps determine the necessity of labeling for drug interactions. We analyzed information for in vitro findings on transporter-mediated interactions of drugs approved by the U.S. Food and Drug Administration’s Center for Drug Evaluation and Research for the last five years (i.e., 2017–2021) and their follow-up actions for labeling. Higher R values than the pre-defined cut-off were observed with 3.7–39.1% inhibitor drugs in a simple prediction. Among these drugs, 16–41.7% were labeled with their potential drug interactions, while results of supporting studies or scientific rationales were submitted for the other drugs leading to no interaction labeling. In vitro transporter substrates were reported with 1.7–67.6% of drugs. The interaction labels for these substrate drugs were observed in up to 40% of drugs, while the other drugs were not labeled on the drug interactions with claims for their low interaction potential, evidenced by clinical studies or scientific rationales. The systematic and comprehensive analysis in this study will provide insight into the management of in vitro findings for transporter substrate or inhibitor drugs.

In vitro evaluation suggests fenfluramine and norfenfluramine are unlikely to act as perpetrators of drug interactions

Studies support the safety and efficacy of fenfluramine (FFA) as an antiseizure medication (ASM) in Dravet syndrome, Lennox-Gastaut syndrome, or CDKL5 deficiency disorder, all pharmacoresistant developmental and epileptic encephalopathies. However, drug-drug interactions with FFA in multi-ASM regimens have not been fully investigated. We characterized the perpetrator potential of FFA and its active metabolite, norfenfluramine (nFFA), in vitro by assessing cytochrome P450 (CYP450) inhibition in human liver microsomes, CYP450 induction in cultured human hepatocytes, and drug transporter inhibition potential in permeability or cellular uptake assays. Mean plasma unbound fraction was ~50% for both FFA and nFFA, with no apparent concentration dependence. FFA and nFFA were direct in vitro inhibitors of CYP2D6 (IC₅₀ , 4.7 and 16 µM, respectively) but did not substantially inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, or CYP3A4/5. No time- or metabolism-dependent CYP450 inhibition occurred. FFA and nFFA did not induce CYP1A2; both induced CYP2B6 (up to 2.8-fold and up to 2.0-fold, respectively) and CYP3A4 (1.9- to 3.0-fold and 3.6- to 4.8-fold, respectively). Mechanistic static pharmacokinetic models predicted that neither CYP450 inhibition nor induction was likely to be clinically relevant at doses typically used for seizure reduction (ratio of area under curve [AUCR] for inhibition <1.25; AUCR for induction >0.8). Transporters OCT2 and MATE1 were inhibited by FFA (IC₅₀ , 19.8 and 9.0 μM) and nFFA (IC₅₀ , 5.2 and 4.6 μM) at concentrations higher than clinically achievable; remaining transporters were not inhibited. Results suggest that FFA and nFFA are unlikely drug-drug interaction perpetrators at clinically relevant doses of FFA (0.2-0.7 mg/kg/day).

Quantitative prediction of pharmacokinetic properties of drugs in humans: Recent advance in in vitro models to predict the impact of efflux transporters in the small intestine and blood-brain barrier

Efflux transport systems are essential to suppress the absorption of xenobiotics from the intestinal lumen and protect the critical tissues at the blood-tissue barriers, such as the blood-brain barrier. The function of drug efflux transport is dominated by various transporters. Accumulated clinical evidences have revealed that genetic variations of the transporters, together with coadministered drugs, affect the expression and/or function of transporters and subsequently the pharmacokinetics of substrate drugs. Thus, in the preclinical stage of drug development, quantitative prediction of the impact of efflux transporters as well as that of uptake transporters and metabolic enzymes on the pharmacokinetics of drugs in humans has been performed using various in vitro experimental tools. Various kinds of human-derived cell systems can be applied to the precise prediction of drug transport in humans. Mathematical modeling consisting of each intrinsic metabolic or transport process enables us to understand the disposition of drugs both at the organ level and at the level of the whole body by integrating a variety of experimental results into model parameters. This review focuses on the role of efflux transporters in the intestinal absorption and brain distribution of drugs, in addition to recent advances in predictive tools and methodologies.

Cytochrome P450 and P-gp Mediated Herb-Drug Interactions and Molecular Docking Studies of Garcinol

Garcinol is an active constituent of Garcinia indica and Garcinia cambogia. Recent studies have proven that garcinol has anti-inflammatory, anti-cancer, and anti-oxidant activities. The objective of this study was to evaluate the inhibitory effects of garcinol on the activities of the drug metabolizing cytochrome P450 (CYP) isozymes to predict potential herb-drug interactions with co-administered drugs. Garcinol was incubated with a mixture of rat liver microsomes and eight CYP probe substrate cocktail under optimized incubation conditions and the samples were analyzed using a validated method on LC-MS/MS. Garcinol showed strong inhibition with IC₅₀ values of CYP1A2 (7.6 µM), CYP2C9 (8.0 µM), CYP2B6 (2.1 µM), CYP2D6 (9.5 µM), and CYP3A4 (5.1 µM), respectively, and moderate inhibition towards CYP2C19 (16.4 µM) and CYP2E1 (19.0 µM). Molecular docking studies were performed on garcinol against the active sites of CYP2B6 and CYP3A4 proteins. These results further confirmed that the inhibitory activity of garcinol occurred by occupying the active sites of these human CYPs and by making favorable interactions with its key residues. In-vivo CYP inhibition studies were carried out in Sprague-Dawley rats. These results suggest garcinol may cause herb-drug interactions, mediated by inhibition of CYPs involved in drug metabolism in-vivo by altering the pharmacokinetic parameters like AUC and C_max in a clinically significant manner. Garcinol was found to upregulate the expression and activity of P-gp in western blotting study and P-gp inhibition study in-vivo. These findings give a clear understanding to predict potential herb-drug/drug-drug interactions of garcinol for safe clinical use in future.

2020 FDA Drug-drug Interaction Guidance: A Comparison Analysis and Action Plan by Pharmaceutical Industrial Scientists

Background:

In January 2020, the US FDA published two final guidelines, one entitled “In vitro Drug Interaction Studies - Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions Guidance for Industry” and the other entitled “Clinical Drug Interaction Studies - Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions Guidance for Industry”. These were updated from the 2017 draft in vitro and clinical DDI guidance.

Methods:

This study is aimed to provide an analysis of the updates along with a comparison of the DDI guidelines published by the European Medicines Agency (EMA) and Japanese Pharmaceuticals and Medical Devices Agency (PMDA) along with the current literature.

Results:

The updates were provided in the final FDA DDI guidelines and explained the rationale of those changes based on the understanding from research and literature. Furthermore, a comparison among the FDA, EMA, and PMDA DDI guidelines are presented in Tables 1, 2 and 3.

Conclusion:

The new 2020 clinical DDI guidance from the FDA now has even higher harmonization with the guidance (or guidelines) from the EMA and PMDA. A comparison of DDI guidance from the FDA 2017, 2020, EMA, and PMDA on CYP and transporter based DDI, mathematical models, PBPK, and clinical evaluation of DDI is presented in this review.

Effects of Apatinib on the Pharmacokinetics of Nifedipine and Warfarin in Patients with Advanced Solid Tumors

Background and Purpose

Apatinib is a small-molecule tyrosine kinase inhibitor for the treatment of recurrent or progressive advanced-stage gastric adenocarcinoma or gastroesophageal junction cancer. The in vitro inhibition studies suggested that apatinib exerted potent inhibition on CYP3A4 and CYP2C9. To evaluate the potential of apatinib as a perpetrator in CYP450-based drug–drug interactions in vivo, nifedipine and warfarin were, respectively, selected in the present study as the probe substrates of CYP3A4 and CYP2C9 for clinical drug–drug interaction studies. Since hypertension and thrombus are common adverse effects of vascular targeting anticancer agents, nifedipine and warfarin are usually coadministered with apatinib in clinical practice.

Methods

A single-center, open-label, single-arm, and self-controlled trial was conducted in patients with advanced solid tumors. The patients received a single dose of 30 mg nifedipine on Day 1/14 and a single dose of 3 mg warfarin on Day 3/16. On Day 9–21, the subjects received a daily dose of 750 mg apatinib, respectively. The pharmacokinetics of nifedipine and warfarin in the absence or presence of apatinib was, respectively, investigated.

Results

Compared with the single oral administration, coadministration with apatinib contributed to the significant increases of AUC_0–48h and C_max of nifedipine by 83% (90% confidence interval [CI] 1.46–2.31) and 64% (90% CI 1.34–2.01), respectively. Similarly, coadministration with apatinib contributed to the significant increases of AUC_0-t and C_max of S-warfarin by 92% (90% CI 1.68–2.18) and 24% (90% CI 1.10–1.39), respectively.

Conclusion

Concomitant apatinib administration resulted in significant increases in systemic exposure to nifedipine and S-warfarin. Owing to the risk of pharmacokinetic drug–drug interactions based on CYP3A4/CYP2C9 inhibition by apatinib, caution is advised in the concurrent use of apatinib with either CYP2C9 or CYP3A4 substrates.

Quercetin Is a Flavonoid Breast Cancer Resistance Protein Inhibitor with an Impact on the Oral Pharmacokinetics of Sulfasalazine in Rats

The potential inhibitory effect of quercetin, a major plant flavonol, on breast cancer resistance protein (BCRP) activity was investigated in this study. The presence of quercetin significantly increased the cellular accumulation and associated cytotoxicity of the BCRP substrate mitoxantrone in human cervical cancer cells (HeLa cells) in a concentration-dependent manner. The transcellular efflux of prazosin, a stereotypical BCRP substrate, was also significantly reduced in the presence of quercetin in a bidirectional transport assay using human BCRP-overexpressing cells; further kinetic analysis revealed IC₅₀ and Ki values of 4.22 and 3.91 μM, respectively. Moreover, pretreatment with 10 mg/kg quercetin in rats led to a 1.8-fold and 1.5-fold increase in the AUC_8h (i.e., 44.5 ± 11.8 min∙μg/mL vs. 25.7 ± 9.98 min∙μg/mL, p < 0.05) and C_max (i.e., 179 ± 23.0 ng/mL vs. 122 ± 23.2 ng/mL, p < 0.05) of orally administered sulfasalazine, respectively. Collectively, these results provide evidence that quercetin acts as an in vivo as well as in vitro inhibitor of BCRP. Considering the high dietary intake of quercetin as well as its consumption as a dietary supplement, issuing a caution regarding its food-drug interactions should be considered.

Assessment of CYP-Mediated Drug Interactions for Evocalcet, a New Calcimimetic Agent, Based on In Vitro Investigations and a Cocktail Study in Humans

Evocalcet is a novel calcimimetic agent for the treatment of secondary hyperparathyroidism (SHPT). This study evaluated the effects of evocalcet on inhibition and induction of cytochrome P450 (CYP) isozymes. Although drug interactions arising from reversible inhibition of CYP isozymes by evocalcet were considered unlikely based on the results of in vitro studies and static model analyses, the potential for evocalcet to cause time‐dependent inhibition of CYP3A or induction of several CYP isozymes could not be ruled out. Therefore, a clinical drug‐drug interaction (DDI) study to evaluate the effects of evocalcet on the pharmacokinetics (PKs) of probe substrates for CYP isozymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, and CYP3A) was conducted in healthy male volunteers using a novel cocktail combination. Evocalcet did not significantly affect the PKs of the probe substrates, confirming that CYP‐mediated interactions were unlikely.

Quantitative Analysis of Complex Drug-Drug Interactions between Cerivastatin and Metabolism/Transport Inhibitors Using Physiologically Based Pharmacokinetic Modeling

Cerivastatin (CER) was withdrawn from the world market because of lethal rhabdomyolysis. Coadministrations of CER and cyclosporine A (CsA) or gemfibrozil (GEM) have been reported to increase the CER blood concentration. CsA is an inhibitor of organic anion transporting polypeptide (OATP)1B1 and CYP3A4, and GEM and its glucuronide (GEM-glu) inhibit OATP1B1 and CYP2C8. The purpose of this study was to describe the transporter-/enzyme-mediated drug-drug interactions (DDIs) of CER with CsA or GEM based on unified physiologically based pharmacokinetic (PBPK) models and to investigate whether the DDIs can be quantitatively analyzed by a bottom-up approach. Initially, the PBPK models for CER and GEM/GEM-glu were constructed based on the previously reported standard protocols. Next, the drug-dependent parameters were optimized by Cluster Newton Method. Thus, described concentration-time profiles for CER and GEM/GEM-glu agreed well with the clinically observed data. The DDIs were then simulated using the established PBPK models with previously obtained in vitro inhibition constants of CsA or GEM/GEM-glu against the OATP1B1 and cytochrome P450s. DDIs with the inhibitors were underestimated compared with observed data using the geometric means of reported values. To search for better described parameters within the range of in vitro values, sensitivity analyses were performed for DDIs of CER. Using the in vitro parameter sets selected by sensitivity analyses, these DDIs were well reproduced, indicating that the present PBPK models were able to describe adequately the clinical DDIs based on a bottom-up approach. The approaches in this study would be applicable to the prediction of other DDIs involving both transporters and metabolic enzymes.

Hepatic transporter drug-drug interactions: an evaluation of approaches and methodologies

INTRODUCTION

Drug-drug interactions (DDIs) continue to account for 5% of hospital admissions and therefore remain a major regulatory concern. Effective, quantitative prediction of DDIs will reduce unexpected clinical findings and encourage projects to frontload DDI investigations rather than concentrating on risk management ('manage the baggage') later in drug development. A key challenge in DDI prediction is the discrepancies between reported models. Areas covered: The current synopsis focuses on four recent influential publications on hepatic drug transporter DDIs using static models that tackle interactions with individual transporters and in combination with other drug transporters and metabolising enzymes. These models vary in their assumptions (including input parameters), transparency, reproducibility and complexity. In this review, these facets are compared and contrasted with recommendations made as to their application. Expert opinion: Over the past decade, static models have evolved from simple [I]/k_i models to incorporate victim and perpetrator disposition mechanisms including the absorption rate constant, the fraction of the drug metabolised/eliminated and/or clearance concepts. Nonetheless, models that comprise additional parameters and complexity do not necessarily out-perform simpler models with fewer inputs. Further, consideration of the property space to exploit some drug target classes has also highlighted the fine balance required between frontloading and back-loading studies to design out or 'manage the baggage'.

Clinical Pharmacokinetics and Pharmacodynamics of Afatinib

Afatinib is an oral, irreversible ErbB family blocker that covalently binds to the kinase domains of epidermal growth factor receptor (EGFR), human EGFRs (HER) 2, and HER4, resulting in irreversible inhibition of tyrosine kinase autophosphorylation. Studies in healthy volunteers and patients with advanced solid tumours have shown that once-daily afatinib has time-independent pharmacokinetic characteristics. Maximum plasma concentrations of afatinib are reached approximately 2–5 h after oral administration and thereafter decline, at least bi-exponentially. Food reduces total exposure to afatinib. Over the clinical dose range of 20–50 mg, afatinib exposure increases slightly more than dose proportional. Afatinib metabolism is minimal, with unchanged drug predominantly excreted in the faeces and approximately 5 % in urine. Apart from the parent drug afatinib, the major circulation species in human plasma are the covalently bound adducts to plasma protein. The effective elimination half-life is approximately 37 h, consistent with an accumulation of drug exposure by 2.5- to 3.4-fold based on area under the plasma concentration–time curve (AUC) after multiple dosing. The pharmacokinetic profile of afatinib is consistent across a range of patient populations. Age, ethnicity, smoking status and hepatic function had no influence on afatinib pharmacokinetics, while females and patients with low body weight had increased exposure to afatinib. Renal function is correlated with afatinib exposure, but, as for sex and body weight, the effect size for patients with severe renal impairment (approximately 50 % increase in AUC) is only mildly relative to the extent of unexplained interpatient variability in afatinib exposure. Afatinib has a low potential as a victim or perpetrator of drug–drug interactions, especially with cytochrome P450-modulating agents. However, concomitant treatment with potent inhibitors or inducers of the P-glycoprotein transporter can affect the pharmacokinetics of afatinib. At a dose of 50 mg, afatinib does not have proarrhythmic potential.

Appropriate risk criteria for OATP inhibition at the drug discovery stage based on the clinical relevancy between OATP inhibitors and drug-induced adverse effect

DDI could be caused by the inhibition of OATP-mediated hepatic uptakes. The aim of this study is to set the risk criteria for the compounds that would cause DDI via OATP inhibition at the drug discovery stage. The IC₅₀ values of OATP inhibitors for human OATP-mediated atorvastatin uptake were evaluated in the expression system. In order to set the risk criteria for OATP inhibition, the relationship was clarified between OATP inhibitory effect and severe adverse effects of OATP substrates, rhabdomyolysis, hyperbilirubinemia and jaundice. Rhabdomyolysis would be caused in the atorvastatin AUC more than 9-fold of that at a minimum therapeutic dose. The atorvastatin AUC was 6- to 9-fold increased with the OATP inhibitors of which IC₅₀ values were ≤1 μmol/L. Hyperbilirubinemia and jaundice would be caused with the OATP inhibitors of which IC₅₀ values were ≤6 μmol/L. This investigation showed that the compounds with IC₅₀ of ≤1 μmol/L would have high risk for OATP-mediated DDI that would cause severe side effects. Before the detailed analysis based on the dosage, unbound fraction in blood and effective concentration to evaluate the clinical DDI potency, this criteria enable high throughput screening and optimize lead compounds at the drug discovery stage.

Pharmacokinetic drug interactions of afatinib with rifampicin and ritonavir

BACKGROUND AND OBJECTIVE

Afatinib is a potent, irreversible, ErbB family blocker in clinical development for the treatment of advanced non-small cell lung cancer, metastatic head and neck cancer, and other solid tumours. As afatinib is a substrate for the P-glycoprotein (P-gp) pump transporter the three studies presented here investigated the pharmacokinetics of afatinib in the presence of a potent inhibitor (ritonavir) or inducer [rifampicin (rifampin)] of P-gp.

METHODS

We conducted phase I, open-label, single-centre studies in healthy male volunteers who received a single once-daily oral dose of afatinib (20 or 40 mg) together with either ritonavir or rifampicin; two studies had a randomised, two- and three-way crossover design and the third was a non-randomised, two-period sequential study.

RESULTS

When afatinib 20 mg was administered 1 h after ritonavir, afatinib geometric mean (gMean) maximum plasma concentration (C max) and area under the plasma concentration-time curve from time zero to infinity (AUC∞) increased by 38.5 and 47.6 %, respectively. Coadministration of ritonavir either simultaneously or 6 h later than afatinib 40 mg resulted in minimal increase in the afatinib gMean C max and AUC∞ (4.1 and 18.6 % for simultaneous administration with AUC∞ not completely within the bioequivalence limits; 5.1 and 10.8 % for timed administration within the bioequivalence limits). Administration of afatinib 40 mg in the presence of rifampicin led to reduction in C max and AUC∞ by 21.6 and 33.8 %, respectively. In all studies, P-gp modulation mainly affected the extent of absorption of afatinib; there was no change in the terminal elimination half-life. The overall safety profile of afatinib was acceptable.

CONCLUSION

Coadministration of potent P-gp modulators had no clinically relevant effect on afatinib exposure. Effects of potent P-gp inhibitors were minimal at higher afatinib doses and can be readily managed by the timing of concomitant therapy. As afatinib is not a relevant modulator or substrate of cytochrome P450 enzymes, the drug-drug interaction potential is considered to be low.

Effect of epigallocatechin gallate on drug transport mediated by the proton-coupled folate transporter

Folic acid (FA) is a water-soluble vitamin, and orally ingested FA is absorbed from the small intestine by the proton-coupled folate transporter (PCFT). In the present study, we investigated whether epigallocatechin gallate (EGCG), one of the tea catechins, affects the transport of FA by PCFT. EGCG inhibited the uptake of FA into Caco-2 cells and human PCFT-expressing HEK293 cells (PCFT-HEK293 cells). The initial rate of uptake of FA into PCFT-HEK293 cells followed Michaelis-Menten kinetics (K(m) = 1.9 µM). Dixon plots revealed that PCFT-mediated FA uptake was competitively inhibited by EGCG (K(i) ≒ 9 µM). The uptake of the PCFT substrate methotrexate (MTX) was competitively inhibited by EGCG as well (K(i) ≒ 15 µM). In conclusion, it is suggested that when FA or MTX is ingested with tea, it is likely that the intestinal absorption of these compounds by PCFT is inhibited, which could result in insufficient efficacy.

Interaction of novel platelet-increasing agent eltrombopag with rosuvastatin via breast cancer resistance protein in humans

Eltrombopag (ELT), an orally available thrombopoietin receptor agonist, is a substrate of organic anion transporting polypeptide 1B1 (OATP1B1), and coadministration of ELT increases the plasma concentration of rosuvastatin in humans. Since the pharmacokinetic mechanism(s) of the interaction is unknown, the present study aimed to clarify the drug interaction potential of ELT at transporters. The OATP1B1-mediated uptake of ELT was inhibited by several therapeutic agents used to treat lifestyle diseases. Among them, rosuvastatin was a potent inhibitor with an IC(50) of 0.05 µM, which corresponds to one-seventh of the calculated maximum unbound rosuvastatin concentration at the inlet to the liver. Nevertheless, a simulation study using a physiologically based pharmacokinetic model predicted that the effect of rosuvastatin on the pharmacokinetic profile of ELT in vivo would be minimal. On the other hand, ELT potently inhibited uptake of rosuvastatin by OATP1B1 and human hepatocytes, with an IC(50) of 0.1 µM. However, the results of the simulation study indicated that inhibition of OATP1B1 by ELT can only partially explain the clinically observed interaction with rosuvastatin. ELT also inhibited transcellular transport of rosuvastatin in MDCKII cells stably expressing breast cancer resistance protein (BCRP), and was found to be a substrate of BCRP. The interaction of ELT with rosuvastatin can be almost quantitatively explained on the assumption that intestinal secretion of rosuvastatin is essentially completely inhibited by ELT. These results suggest that BCRP in small intestine may be the major target for interaction between ELT and rosuvastatin in humans.

Text Mining Driven Drug-Drug Interaction Detection

Identifying drug-drug interactions is an important and challenging problem in computational biology and healthcare research. There are accurate, structured but limited domain knowledge and noisy, unstructured but abundant textual information available for building predictive models. The difficulty lies in mining the true patterns embedded in text data and developing efficient and effective ways to combine heterogenous types of information. We demonstrate a novel approach of leveraging augmented text-mining features to build a logistic regression model with improved prediction performance (in terms of discrimination and calibration). Our model based on synthesized features significantly outperforms the model trained with only structured features (AUC: 96% vs. 91%, Sensitivity: 90% vs. 82% and Specificity: 88% vs. 81%). Along with the quantitative results, we also show learned "latent topics", an intermediary result of our text mining module, and discuss their implications.

Clinical significance of organic anion transporting polypeptides (OATPs) in drug disposition: their roles in hepatic clearance and intestinal absorption

Organic anion transporting polypeptide (OATP) family transporters accept a number of drugs and are increasingly being recognized as important factors in governing drug and metabolite pharmacokinetics. OATP1B1 and OATP1B3 play an important role in hepatic drug uptake while OATP2B1 and OATP1A2 might be key players in intestinal absorption and transport across blood-brain barrier of drugs, respectively. To understand the importance of OATPs in the hepatic clearance of drugs, the rate-determining process for elimination should be considered; for some drugs, hepatic uptake clearance rather than metabolic intrinsic clearance is the more important determinant of hepatic clearances. The importance of the unbound concentration ratio (liver/blood), K(p,uu) , of drugs, which is partly governed by OATPs, is exemplified in interpreting the difference in the IC(50) of statins between the hepatocyte and microsome systems for the inhibition of HMG-CoA reductase activity. The intrinsic activity and/or expression level of OATPs are affected by genetic polymorphisms and drug-drug interactions. Their effects on the elimination rate or intestinal absorption rate of drugs may sometimes depend on the substrate drug. This is partly because of the different contribution of OATP isoforms to clearance or intestinal absorption. When the contribution of the OATP-mediated pathway is substantial, the pharmacokinetics of substrate drugs should be greatly affected. This review describes the estimation of the contribution of OATP1B1 to the total hepatic uptake of drugs from the data of fold-increases in the plasma concentration of substrate drugs by the genetic polymorphism of this transporter. To understand the importance of the OATP family transporters, modeling and simulation with a physiologically based pharmacokinetic model are helpful.

ITC recommendations for transporter kinetic parameter estimation and translational modeling of transport-mediated PK and DDIs in humans

This white paper provides a critical analysis of methods for estimating transporter kinetics and recommendations on proper parameter calculation in various experimental systems. Rational interpretation of transporter-knockout animal findings and application of static and dynamic physiologically based modeling approaches for prediction of human transporter-mediated pharmacokinetics and drug-drug interactions (DDIs) are presented. The objective is to provide appropriate guidance for the use of in vitro, in vivo, and modeling tools in translational transporter science.

Effects of green tea catechins on cytochrome P450 2B6, 2C8, 2C19, 2D6 and 3A activities in human liver and intestinal microsomes

The effects of green tea catechins on the main drug-metabolizing enzymatic system, cytochrome P450 (CYP), have not been fully elucidated. The objective of the present study was to evaluate the effects of green tea extract (GTE, total catechins 86.5%, w/w) and (-)-epigallocatechin-3-gallate (EGCG) on the activities of CYP2B6, CYP2C8, CYP2C19, CYP2D6 and CYP3A in vitro, using pooled human liver and intestinal microsomes. Bupropion hydroxylation, amodiaquine N-deethylation, (S)-mephenytoin 4'-hydroxylation, dextromethorphan O-demethylation and midazolam 1'-hydroxylation were assessed in the presence or absence of various concentrations of GTE and EGCG to test their effects on CYP2B6, CYP2C8, CYP2C19, CYP2D6 and CYP3A activities, respectively. Each metabolite was quantified using UPLC/ESI-MS, and the inhibition kinetics of GTE and EGCG on CYP enzymes was analyzed. In human liver microsomes, IC50 values of GTE were 5.9, 4.5, 48.7, 25.1 and 13.8 µg/mL, for CYP2B6, CYP2C8, CYP2C19, CYP2D6 and CYP3A, respectively. ECGC also inhibited these CYP isoforms with properties similar to those of GTE, and produced competitive inhibitions against CYP2B6 and CYP2C8, and noncompetitive inhibition against CYP3A. In human intestinal microsomes, IC50 values of GTE and EGCG for CYP3A were 18.4 µg/mL and 31.1 µM, respectively. EGCG moderately inhibited CYP3A activity in a noncompetitive manner. These results suggest that green tea catechins cause clinically relevant interactions with substrates for CYP2B6 and CYP2C8 in addition to CYP3A.

Pharmacokinetic interaction study of sulphasalazine in healthy subjects and the impact of curcumin as an in vivo inhibitor of BCRP

BACKGROUND AND PURPOSE An ATP-binding cassette (ABC) transporter, breast cancer resistance protein (BCRP)/ABCG2, limits oral bioavailability of sulphasalazine. Here we examined the effect of curcumin, the principal curcuminoid of turmeric, on oral bioavailability of microdoses and therapeutic doses of sulphasalazine in humans. EXPERIMENTAL APPROACH Effects of curcumin were measured on the ATP-dependent sulphasalazine uptake by hBCRP-expressing membrane vesicles and on oral bioavailability of sulphasalazine in wild-type and Bcrp(-/-) mice. Eight healthy Japanese subjects received an oral dose of sulphasalazine suspension (100 µg) or tablets (2 g) alone or after curcumin tablets (2 g). Uptake of sulphasalazine was studied in HEK293 cells transfected with the influx transporter (OATP)2B1. KEY RESULTS Curcumin was a potent hBCRP inhibitor in vitro (K(i) 0.70 ± 0.41 µM). Curcumin increased the area under the curve (AUC)(0-8) of plasma sulphasalazine eightfold in wild-type mice at 300 and 400 mg·kg(-1), but not in Bcrp(-/-) mice. Curcumin increased AUC(0-24) of plasma sulphasalazine 2.0-fold at microdoses and 3.2-fold at therapeutic doses in humans. Non-linearity of the dose-exposure relationship was observed between microdoses and therapeutic doses of sulphasalazine. Sulphasalazine was a substrate for OATP2B1 (K(m) 1.7 ± 0.3 µM). Its linear index (dose/K(m)) at the therapeutic dose was high and may saturate OATP2B1. CONCLUSIONS AND IMPLICATIONS Curcumin can be used to investigate effects of BCRP on oral bioavailability of drugs in humans. Besides the limited dissolution, OATP2B1 saturation is a possible mechanism underlying non-linearity in the dose-exposure relationship of sulphasalazine.

Transporter-mediated drug--drug interactions involving OATP substrates: predictions based on in vitro inhibition studies

Transporter-mediated drug–drug interactions (DDIs) are among the most important of the clinically relevant pharmacokinetic DDIs. We investigated the validity of a static prediction of area under the plasma concentration-time curve (AUC) ratios (AUCRs; AUC(with inhibitor)/AUC(control) using in vitro inhibition profiles, and selected the types of assumptions that improved the prediction accuracy with minimizing false-negative predictions. We used data from 58 DDI studies involving 12 substrates of hepatic organic anion–transporting polypeptides (OATPs). With original assumptions regarding the maximal increase in intestinal availability, maximum unbound concentration at the inlet to the liver, and inhibition of only the hepatic uptake process, the predicted AUCRs were comparable to those reported within a two/threefold error margin in 44/52 studies, whereas in 16 studies, the predictions were judged to be falsenegatives. When the inhibitory effects on both hepatic uptake and efflux/metabolisms were considered, the overall prediction accuracy became worse, although the false-negative prediction decreased to 11 studies. This illustrates that if appropriate assumptions are selected, unnecessary clinical DDI studies can be reasonably avoided.

Analysis of the pharmacokinetic boosting effects of ritonavir on oral bioavailability of drugs in mice

  Ritonavir dramatically increases the bioavailability of a variety of concurrently administered drugs by inhibition of metabolic enzymes and drug transporters. The purpose of this study was to investigate the extent to which ritonavir's inhibition of drug transporters and/or CYP3A contributes to the increased oral bioavailability in mice. The area under the plasma concentration-time curves (AUC) for orally administered saquinavir after coadministration with 50 mg/kg ritonavir dramatically increased (325-fold). As a result, the bioavailability, Fa·Fg and Fh increased 75-, 38- and twofold, respectively. In addition, the increase in the AUC predicted from the in vitro Ki value was ninefold, which was derived from the inhibition of metabolic enzymes by ritonavir in the liver. The remaining 36-fold increase in the AUC was considered to be derived from the inhibition in the small intestine. The AUCinf for probe substrate midazolam, fexofenadine, and pravastatin increased after the oral administration of ritonavir by only five-, 13-, and sevenfold, respectively. Moreover, the AUC0-12 for saquinavir was affected negligibly by itraconazole. These results indicate ritonavir mainly affects the first-pass effect of saquinavir in the small intestine, increasing the bioavailability of orally administered saquinavir. Furthermore, cyp isoforms other than CYP3A, which contribute to the metabolism of saquinavir in humans, are involved in the metabolism of saquinavir in mice.

Potential P-glycoprotein-mediated drug-drug interactions of antimalarial agents in Caco-2 cells

Antimalarials are widely used in African and Southeast Asian countries, where they are combined with other drugs for the treatment of concurrent ailments. The potential for P-glycoprotein (P-gp)-mediated drug-drug interactions (DDIs) between antimalarials and P-gp substrates was examined using a Caco-2 cell-based model. Selected antimalarials were initially screened for their interaction with P-gp based on the inhibition of rhodamine-123 (Rho-123) transport in Caco-2 cells. Verapamil (100 μM) and quinidine (1 μM) were used as positive inhibition controls. Lumefantrine, amodiaquin, and artesunate all showed blockade of Rho-123 transport. Subsequently, the inhibitory effect of these antimalarials on the bi-directional passage of digoxin (DIG) was examined. All of the drugs decreased basal-to-apical (B-A) P-gp-mediated DIG transport at concentrations of 100 μM and 1 mM. These concentrations may reflect therapeutic doses for amodiaquin and artesunate. Therefore, clinically relevant DDIs may occur between certain antimalarials and P-gp substrates in general.

Effects of aripiprazole and its active metabolite dehydroaripiprazole on the activities of drug efflux transporters expressed both in the intestine and at the blood-brain barrier

The inhibition potencies of aripiprazole and its active metabolite, dehydroaripiprazole, on the activities of human multidrug resistance protein 1 (MDR1/ABCB1; P-glycoprotein), breast cancer resistance protein (BCRP/ABCG2) and multidrug resistance-associated protein 4 (MRP4/ABCC4), that are drug efflux transporters expressed both in the intestine and at the blood-brain barrier (BBB), were investigated. Aripiprazole and dehydroapripiprazole showed relatively strong inhibitory effects on human MDR1 with IC(50) values of 1.2 and 1.3 µm in human MDR1-transfected Mardin-Darby canine kidney (MDCKII-MDR1) cells, respectively. The inhibition potencies of other atypical antipsychotics (risperidone, paliperidone, olanzapine and ziprasidone) for human MDR1 were also evaluated using the same in vitro experimental system and IC(50) values were more than 10-fold higher than those of the two compounds. Aripiprazole and dehydroaripiprazole also had inhibition potencies against human BCRP with IC(50) values of 3.5 and 0.52 µm, respectively. The ratios of steady-state unbound concentrations of aripiprazole and dehydroaripiprazole to their IC(50) values against human MDR1 and BCRP activities were less than 0.1, whereas the theoretically maximum gastrointestinal concentration of aripiprazole ([I](2) ) to its IC(50) values was much higher than the cut-off value of 10, proposed by the International Transporter Consortium (ITC) and the Food and Drug Administration (FDA). In contrast, aripiprazole and dehydroaripiprazole showed almost no inhibitory effect against the activity of human MRP4. These findings indicate that aripiprazole is unlikely to cause drug-drug interactions (DDIs) at the BBB when co-administered with substrate drugs of these drug transporters investigated. However, interactions at the intestinal absorption process may be of concern.

Novel strategies for microdose studies using non-radiolabeled compounds

Microdose studies using non-radiolabeled compounds enable assessment of the clinical pharmacokinetics of drug candidates in humans without the need to synthesize radiolabeled compounds. We have demonstrated that the quantification limits of many drugs measured by LC-MS/MS are low enough to allow estimation of their pharmacokinetic parameters following administration of a microdose. Our previous microdose studies with LC-MS/MS demonstrated the linear pharmacokinetics of fexofenadine between microdoses and therapeutic doses. We also obtained time profiles of plasma concentrations of nicardipine and its multiple metabolites following administration of a microdose. A significant advantage of using non-radiolabeled compounds is the ability to perform cassette microdose studies. By administering multiple drug candidates to the same subject, we can select compounds with appropriate pharmacokinetic properties simultaneously. We can also clarify major factors dominating the pharmacokinetics of drug candidates by cocktail microdosing of the test compounds and probe substrates with or without specific inhibitors for enzymes/transporters.