In vitro model for the prediction of clinical CYP3A4 induction using HepaRG cells

1. It is important to predict CYP3A enzyme induction in the drug-discovery process to avoid adverse effects in clinical. In the present study, we constructed a method to correct the variability of in vitro CYP3A induction assays and thereby a method for the prediction of CYP3A induction in the clinical setting.

2. Induction assays were performed in vitro using HepaRG cells and seven typical inducers. An index value was determined for enzyme induction, termed the relative factor (RF), from the ratio of the concentration of the inducers to the reference standards.

3. Using RF as an index, variation among the assays was reduced.

4. A good relationship was obtained between the ratio of the free plasma concentration at steady-state (C_ss,u) to RF (expressed as C_ss,u/RF) and the in vivo induction response. Using rifampicin as a reference standard, compounds with a C_ss,u/RF value greater than 7.31 nmol l^?1 may induce CYP3A in vivo in humans.

     

CYP450s体外重组技术及在药物代谢和安全性评价中的应用

药物代谢是在代谢酶催化下完成的 ,它决定着药物的药理学和毒理学特性。根据动物实验来预测人体的药物代谢时 ,代谢酶的种属差异性会使这项研究工作变得非常困难。本文对含有人体代谢酶系的重组技术模型的应用进行了介绍和评价。从而有助于预测新药在人体中的代谢机制     

Cultivation of RPMI 2650 cells as an in‐vitro model for human transmucosal nasal drug absorption studies: optimization of selected culture conditions

Objectives The kinetics of drug absorption for nasally administered drugs are often studied using excised mucosal tissue. To avoid the disadvantages of animal experiments, cellular in‐vitro models have been established. This study describes the optimization of culture conditions for a model based on the RPMI 2650 cell line, and an evaluation of this model's value for drug absorption studies. Methods The cells were cultured in two serum‐free media, serum‐reduced variants or minimum essential medium (MEM) containing 5–20% serum. Cell seeding efficiency and proliferation behavior were evaluated in addition to viability and attachment following cryopreservation and thawing. Cells were cultured on different filter inserts for varying cultivation times. The epithelial barrier properties were determined by measuring transepithelial electrical resistance (TEER). Permeability was assessed using marker substances. Key findings Serum supplementation of medium was necessary for cultivation, whereas the serum concentration showed little impact on proliferation and attachment following cryopreservation. A pronounced dependence of TEER on medium and filter material was observed. An optimized model cultured with MEM containing 10% serum on polyethylene terephthalate exhibited permeability that was similar to excised nasal mucosa. Conclusions These data indicate that this model could be an appropriate alternative to excised mucosa for the in‐vitro evaluation of nasal drug absorption.     

体外释放拟合模板编程及应用实例

目的:探索药物体外释放数据的处理方法及规范相应模板的编程.方法:以VBA语言自编体外释放模型拟合软件模块,加载于EXCEL平台,并予以剖析及实例应用.结果:获得中华人民共和国药典2000年版规范要求的3种释放模型的拟合结果,并经拟合优度检验,可优选优度最高的释放模型并予以输出.结论:本法运用方便,可正确使用公认准则进行数据处理.     

Prediction of in vivo drug-drug interactions from in vitro data: impact of incorporating parallel pathways of drug elimination and inhibitor absorption rate constant

AIMS: Success of the quantitative prediction of drug-drug interactions via inhibition of CYP-mediated metabolism from the inhibitor concentration at the enzyme active site ([I]) and the in vitro inhibition constant (K(i)) is variable. The aim of this study was to examine the impact of the fraction of victim drug metabolized by a particular CYP (f(mCYP)) and the inhibitor absorption rate constant (k(a)) on prediction accuracy. METHODS: Drug-drug interaction studies involving inhibition of CYP2C9, CYP2D6 and CYP3A4 (n = 115) were investigated. Data on f(mCYP) for the probe substrates of each enzyme and k(a) values for the inhibitors were incorporated into in vivo predictions, alone or in combination, using either the maximum hepatic input or the average systemic plasma concentration as a surrogate for [I]. The success of prediction (AUC ratio predicted within twofold of in vivo value) was compared using nominal values of f(mCYP) = 1 and k(a) = 0.1 min(-1). RESULTS: The incorporation of f(mCYP) values into in vivo predictions using the hepatic input plasma concentration resulted in 84% of studies within twofold of in vivo value. The effect of k(a) values alone significantly reduced the number of over-predictions for CYP2D6 and CYP3A4; however, less precision was observed compared with the f(mCYP). The incorporation of both f(mCYP) and k(a) values resulted in 81% of studies within twofold of in vivo value. CONCLUSIONS: The incorporation of substrate and inhibitor-related information, namely f(mCYP) and k(a), markedly improved prediction of 115 interaction studies with CYP2C9, CYP2D6 and CYP3A4 in comparison with [I]/K(i) ratio alone.     

Evaluation of Supermix as an in vitro model of human liver microsomal drug metabolism

SUPERMIX is a commercially available formulation of insect cell-expressed human drug-metabolizing cytochrome P450 (CYP) isoforms, mixed in proportions that are optimized to parallel their relative activities in human liver microsomes. We have evaluated the apparent functional affinity and capacity of individual CYP isoforms in SUPERMIX in comparison with microsomes from a panel of 12 human livers, using enzyme kinetic studies of isoform-selective index reactions. In addition, we have measured the concentration of NADPH cytochrome P450 oxidoreductase (OR) in SUPERMIX and compared it with the concentrations of this accessory electron transfer protein in human liver microsomes. No important differences were evident in the catalytic activities of CYPs 1A2, 2C8, 2C9, 2C19, 2D6 and 3A4 between SUPERMIX and human liver microsomes. However, SUPERMIX lacks CYP2B6 activity and did not hydroxylate the antidepressant bupropion, a clinically relevant substrate of this enzyme. In addition, the concentration of OR in SUPERMIX (1198 pmol mg protein(-1)) is 17-fold higher than the mean value in human liver microsomes (70 pmol mg protein(-1)). In conclusion, SUPERMIX lacks CYP2B6 activity and contains supraphysiological concentrations of the accessory electron transfer protein OR. These factors should be considered when this formulation is used as an in vitro model in human liver microsomal drug metabolism studies.     

Evaluation of the metabolic capability of primary human hepatocytes in three‐dimensional cultures on microstructural plates

The NanoCulture Plate (NCP) is a novel microstructural plate designed as a base for the three‐dimensional culture of cells/tissues. This study examined whether or not the metabolic capability of human primary hepatocytes is well maintained during culture on NCPs. The hepatocytes formed aggregates after seeding and their ATP content was well maintained during culture for 21 days. Expression of CYP1A2, 2B6, 2C9, 2C19, 2D6, 2E1 and 3A4 mRNAs was detected throughout the 21‐day culture period. Addition of CYP substrate drugs (midazolam, diclofenac, lamotrigine and acetaminophen) resulted in the formation of multiple metabolites with a corresponding decrease in the amounts of the unchanged compounds. The inducers omeprazole, phenobarbital and rifampicin increased the levels of CYP1A2, 2B6 and 3A4 mRNAs by 110‐fold, 12.5‐fold and 5.4‐fold, respectively, at day 2, compared with control human hepatocytes. CYP activities were also increased at 2 days after inducer treatment (CYP1A2, 2.2‐fold; CYP2B6, 20.6‐fold; CYP3A4, 3.3‐fold). The results indicate that the hepatocyte spheroids on NCP have detectable and inducible metabolic abilities during the 7‐day culture period.     

Screening of drug metabolizing enzymes for fusidic acid and its interactions with isoform-selective substrates in vitro

1.?Fusidic acid (FA) is widely used for the treatment of infections of sensitive osteomyelitis or skin and soft tissue caused by bacteria. However, the role of cytochrome P450s (CYPs) in the metabolism of FA is unclear. In the present study, we screened the main CYPs for the metabolism of FA and studied its interactions with isoform-selective substrates in vitro.

2.?The main CYP450s were screened according to the inhibitory effect of specific inhibitors on the metabolism of FA in human liver microsomes (HLMs) or recombinant CYP isoforms. Enzyme kinetic parameters including K_i, K_i′, V_max, and IC₅₀ were calculated to determine the potential of FA to affect CYP-mediated metabolism of isoform-selective substrates.

3.?FA metabolism rate was inhibited by 49.8% and 83.1% under CYP2D6, CYP3A4 selective inhibitors in HLMs. In recombinant experiment, the inhibitory effects on FA metabolism were 83.3% for CYP2D6 and 58.9% for CYP3A4, respectively. FA showed inhibition on CYP2D6 and CYP3A4 with K_is of 13.9 and 38.6?μM, respectively. Other CYP isoforms including CYP1A2, CYP2A6, CYP2C9, CYP2E1, and CYP2C19 showed minimal or no effect on the metabolism of FA.

4.?FA was primarily metabolized by CYP2D6 and CYP3A4 and showed a noncompetitive inhibition on CYP2D6 and a mixed competitive inhibition on CYP3A4. Drug–drug interactions between FA and other chemicals, especially with substrates of CYP2D6 and CYP3A4, are phenomena that clinicians need to be aware of and cautious about.     

Diazepam–omeprazole inhibition interaction: an in vitro investigation using human liver microsomes

1 The metabolism of diazepam to its primary metabolites 3-hydroxydiazepam (3HDZ) and nordiazepam (NDZ) was evaluated in human liver microsomes. The 3HDZ pathway was the major route of metabolism representing 90% of total metabolism with a V _max /K _m ratio of 0.50–7.26  μl  min⁻¹  mg ⁻¹ protein.
2 Inhibition of the two metabolic pathways of diazepam by omeprazole was investigated. The NDZ pathway was not affected by omeprazole whilst a K _i of 201±89  μm was obtained for the 3HDZ pathway ( K _m /K _i ratio of 3.0±0.9).
3 Inhibitory effects of omeprazole sulphone on the 3HDZ and NDZ pathways were also investigated. Omeprazole sulphone inhibited both pathways with similar K_is of 121±45 and 188±73  μm respectively ( K _m /K _i ratios of 5.2±2.3 and 3.3±1.5 respectively).
4 These in vitro data provide direct evidence for cytochrome P450 inhibition as the mechanism for the well documented diazepam-omeprazole clinical interaction and indicate that omeprazole sulphone, as well as the parent drug, contribute to the inhibition effect.     

Different in vitro and in vivo tools for elucidating the human metabolism of alpha‐cathinone‐derived drugs of abuse

In vitro and in vivo experiments are widely used for studying the metabolism of new psychoactive substances (NPS). The availability of such data is required for toxicological risk assessments and development of urine screening approaches. This study investigated the in vitro metabolism of the 5 pyrrolidinophenone‐derived NPS alpha‐pyrrolidinobutyrophenone (alpha‐PBP), alpha‐pyrrolidinopentiothiophenone (alpha‐PVT), alpha‐pyrrolidinohexanophenone (alpha‐PHP), alpha‐pyrrolidinoenanthophenone (alpha‐PEP, PV8), and alpha‐pyrrolidinooctanophenone (alpha‐POP, PV9). First, they were incubated with pooled human liver microsomes (pHLM) or pooled human liver S9 fraction (pS9) for identification of the main phase I and II metabolites. All substances formed hydroxy metabolites and lactams. Longer alkyl chains resulted in keto group and carboxylic acid formation. Comparing these results with published data obtained using pHLM, primary human hepatocytes (PHH), and authentic human urine samples, PHH provided the most extensive metabolism. Second, enzyme kinetic studies showed that the initial metabolic steps were formed by cytochrome P450 isoforms (CYP) CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 resulting in pyrrolidine, thiophene or alkyl hydroxy metabolites depending on the length of the alkyl chain. The kinetic parameters indicated an increasing affinity of the CYP enzymes with increase of the length of the alkyl chain. These parameters were then used to calculate the contribution of a single CYP enzyme to the in vivo hepatic clearance. CYP2C19 and CYP2D6 were mainly involved in the case of alpha‐PBP and CYP1A2, CYP2C9 and CYP2C19 in the case of alpha‐PVT, alpha‐PHP, alpha‐PEP, and alpha‐POP.     

Metabolic interactions between mibefradil and HMG-CoA reductase inhibitors: an in vitro investigation with human liver preparations

AIMS: To determine the effects of mibefradil on the nletabolism in human liver microsomal preparations of the HMG-CoA reductase inhibitors simvastatin, lovastatin, atorvastatin, cerivastatin and fluvastatin. METHODS: Metabolism of the above five statins (0.5, 5 or 10 microM), as well as of specific CYP3A4/5 and CYP2C8/9 marker substrates, was examined in human liver microsomal preparations in the presence and absence of mibefradil (0.1-50 microM). RESULTS: Mibefradil inhibited, in a concentration-dependent fashion, the metabolism of the four statins (simvastatin, lovastatin, atorvastatin and cerivastatin) known to be substrates for CYP3A. The potency of inhibition was such that the IC50 values (<1 microM) for inhibition of all of the CYP3A substrates fell within the therapeutic plasma concentrations of mibefradil, and was comparable with that of ketoconazole. However, the inhibition by mibefradil, unlike that of ketoconazole, was at least in part mechanism-based. Based on the kinetics of its inhibition of hepatic testosterone 6beta-hydroxylase activity, mibefradil was judged to be a powerful mechanism-based inhibitor of CYP3A4/5, with values for Kinactivation, Ki and partition ratio (moles of mibefradil metabolized per moles of enzyme inactivated) of 0.4 min(-1), 2.3 microM and 1.7, respectively. In contrast to the results with substrates of CYP3A, metabolism of fluvastatin, a substrate of CYP2C8/9, and the hydroxylation of tolbutamide, a functional probe for CYP2C8/9, were not inhibited by mibefradil. CONCLUSION: Mibefradil, at therapeutically relevant concentrations, strongly suppressed the metabolism in human liver microsomes of simvastatin, lovastatin, atorvastatin and cerivastatin through its inhibitory effects on CYP3A4/5, while the effects of mibefradil on fluvastatin, a substrate for CYP2C8/9, were minimal in this system. Since mibefradil is a potent mechanism-based inhibitor of CYP3A4/5, it is anticipated that clinically significant drug-drug interactions will likely ensue when mibefradil is coadministered with agents which are cleared primarily by CYP3A-mediated pathways.     

The cytokine-dependent MUTZ-3 cell line as an in vitro model for the screening of contact sensitizers

Langerhans cells (LC) are key mediators of contact allergenicity in the skin. However, no in vitro methods exist which are based on the activation process of LC to predict the sensitization potential of chemicals. In this study, we have evaluated the performances of MUTZ-3, a cytokine-dependent human monocytic cell line, in its response to sensitizers. First, we compared undifferentiated MUTZ-3 cells with several standard human cells such as THP-1, KG-1, HL-60, K-562, and U-937 in their response to the strong sensitizer DNCB and the irritant SDS by monitoring the expression levels of HLA-DR, CD54, and CD86 by flow cytometry. Only MUTZ-3 and THP-1 cells show a strong and specific response to sensitizer, while other cell lines showed very variable responses. Then, we tested MUTZ-3 cells against a wider panel of sensitizers and irritants on a broader spectrum of cell surface markers (HLA-DR, CD40, CD54, CD80, CD86, B7-H1, B7-H2, B7-DC). Of these markers, CD86 proved to be the most reliable since it detected all sensitizers, including benzocaine, a classical false negative in local lymph node assay (LLNA) but not irritants. We confirmed the MUTZ-3 response to DNCB by real-time PCR analysis. Taken together, our data suggest that undifferentiated MUTZ-3 cells may represent a valuable in vitro model for the screening of potential sensitizers.     

Assessment of CYP3A‐mediated drug–drug interaction potential for victim drugs using an in vivo rat model

The present study aims to determine if an in vivo rat model of drug–drug interaction (DDI) could be useful to discriminate a sensitive (buspirone) from a ‘non‐sensitive’ (verapamil) CYP3A substrate, using ketoconazole and ritonavir as perpetrator drugs. Prior to in vivo studies, ketoconazole and ritonavir were shown to inhibit midazolam hydroxylation with IC₅₀ values of 350 ± 60 nm and 11 ± 3 nm , respectively, in rat liver microsomes (RLM). Buspirone and verapamil were also shown to be substrates of recombinant rat CYP3A1/3A2. In the rat model, the mean plasma AUC_0‐inf of buspirone (10 mg/kg, p.o.) was increased by 7.4‐fold and 12.8‐fold after co‐administration with ketoconazole and ritonavir (20 mg/kg, p.o.), respectively. The mean plasma AUC_0‐inf of verapamil (10 mg/kg, p.o.) was increased by 3.0‐fold and 4.8‐fold after co‐administration with ketoconazole and ritonavir (20 mg/kg, p.o.), respectively. Thus, the rat DDI model correctly identified buspirone as a sensitive CYP3A substrate (>5‐fold AUC change) in contrast to verapamil. In addition, for both victim drugs, the extent of DDI when co‐administered was greater with ritonavir compared with ketoconazole, in line with their in vitro CYP3A inhibition potency in RLM. In conclusion, our study extended the rat DDI model applicability to two additional victim/perpetrator pairs. In addition, we suggest that use of this model would increase our confidence in estimation of the DDI potential for victim drugs in early discovery. Copyright © 2013 John Wiley & Sons, Ltd.     

Organ slice viability extended for pathway characterization: an in vitro model to investigate fibrosis.

Liver slice viability is extended to 96 h for rat, expanding the use of this in vitro model for studying mechanisms of injury and repair, including pathways of fibrosis. The contributing factors to increased organ slice survival consist of the use of a preservation solution for liver perfusion and slice preparation, obtaining rats that are within the weight range of 250-325 g, placing a cellulose filter atop the titanium mesh roller-insert to support the slice, and maintaining the slices in an optimized culture medium which is replaced daily. The liver slices remain metabolically active, synthesizing adenosine triphosphate (ATP), glutathione, and glycogen, and exhibit preserved organelle integrity and slice morphology. Slice preparation results in 2-cut surfaces which likely triggers a repair and regenerative response. The fibrogenic pathways are evident by the activation of stellate cells, the proliferation of myofibroblast-like cells, and an increased collagen deposition by 48 h. Markers indicative of activated stellate cells, alpha-smooth muscle actin, collagen 1a1, desmin, and HSP47 are substantiated by real time-PCR. Increased staining of alpha-smooth muscle actin initially around the vessels and by 72-96 h in the tissue is accompanied by increased collagen staining. Microarray gene expression revealed extracellular matrix changes with the up-regulation of cytoskeleton, filaments, collagens, and actin genes; and the down-regulation of genes linked with lipid metabolism. The improvements in extending liver slice survival, in conjunction with its three-dimensional multi-cellular complexity, increases the application of this in vitro model for investigating pathways of injury and repair, and fibrosis.     

Primary human sinonasal epithelial cell culture model for topical drug delivery in patients with chronic rhinosinusitis with nasal polyposis

Objectives The primary human sinonasal epithelial cell culture (HSNEC) allows for in‐vitro modelling of mucosal responses to topical therapy. Cultures grown from healthy donors may underestimate changes in individuals with chronic sinonasal disease thereby yielding inaccurate results with respect to this large patient population. The purpose of this study was to analyse HSNECs derived from patients with chronic rhinosinusitis with nasal polyposis (CRSwNP) to determine whether expected disease dependent variables salient to topical drug delivery persist in culture. Methods Cultures were grown from patients with CRSwNP. Ciliary beat frequency (CBF) (basal and stimulated), permeability (trans and paracellular), inflammatory response, and glucocorticoid dose response were measured and compared with healthy controls. Key findings Methylcholine stimulated CBF was greater in CRSwNP versus controls (ΔCBF_60min 7.25 ± 1.02 vs 0.89 ± 1.04 Hz, respectively). Paracellular permeability was greater in CRSwNP versus controls (basolateral dextran_120min 18.97 ± 3.90 vs 11.31 ± 4.35 µg/ml, respectively). Lipopolysaccharide (0.1 mg/ml) stimulated interleukin‐6 (IL‐6) and IL‐8 secretion was increased in CRSwNP versus controls (IL‐6 Δbaseline 1738.72 ± 654.82 vs 1461.61 ± 533.51%, respectively; IL‐8 Δbaseline 137.11 ± 0.83 vs 111.27 ± 0.67%, respectively). CRSwNP cultures were more sensitive than controls to dexamethasone (1 µg/ml) dependent IL‐6 and IL‐8 suppression. Conclusions HSNECs derived from patients with CRSwNP retained their primary phenotype with respect to ciliary function, epithelial permeability, irritant induced inflammatory cytokine secretion, and glucocorticoid dose response.     

Characterization of preclinical in vitro and in vivo ADME properties and prediction of human PK using a physiologically based pharmacokinetic model for YQA‐14, a new dopamine D3 receptor antagonist candidate for treatment of drug addiction

YQA‐14 is a novel and selective dopamine D3 receptor antagonist, with potential for the treatment of drug addiction. However, earlier compounds in its structural class tend to have poor oral bioavailability. The objectives of this study were to characterize the preclinical absorption, distribution, metabolism and excretion (ADME) properties and pharmacokinetics (PK) of YQA‐14, then to simulate the clinical PK of YQA‐14 using a physiologically based pharmacokinetics (PBPK) model to assess the likelihood of developing YQA‐14 as a clinical candidate. For human PK prediction, PBPK models were first built in preclinical species, rats and dogs, for validation purposes. The model was then modified by input of human in vitro ADME data obtained from in vitro studies. The study data showed that YQA‐14 is a basic lipophilic compound, with rapid absorption (T_max ~ 1 h) in both rats and dogs. Liver microsomal clearances and in vivo clearances were moderate in rats and dogs consistent with the moderate bioavailability observed in both species. The PBPK models built for rats and dogs simulated the observed PK data well in both species. The PBPK model refined with human data predicted that YQA‐14 would have a clearance of 8.0 ml/min/kg, a volume distribution of 1.7 l/kg and a bioavailability of 16.9%. These acceptable PK properties make YQA‐14 an improved candidate for further research and development as a potential dopamine D3R antagonism for the treatment of drug addiction in the clinic. Copyright © 2014 John Wiley & Sons, Ltd.     

利用诱导多能干细胞构建流产毒性药物的体外筛查模型

妊娠期用药不可避免,如何帮助孕妇合理用药以减少自发流产、早产和低体重儿的发生,对于医务工作者至关重要.本研究建立了药物流产毒性的检测模型,可筛除疑似流产的药物,避免用药不当导致的孕妇流产.通过三维悬浮培养诱导多能干细胞(induced pluripotent stem cells,iPSCs)的方式,诱导其形成拟胚体(...     

Non-occlusive topical exposure of human skin in vitro as model for cytotoxicity testing of irritant compounds

Testing of irritant compounds has traditionally been performed on animals and human volunteers. Animal testing should always be restricted and for skin irritancy mice and rabbits hold poor predictive value for irritant potential in humans. Irritant testing on human volunteers is restricted by the duration subjects can be exposed, and by the subjectivity of interpreting the visual signs of skin irritation. We propose an irritant testing system using viable human full thickness skin with the loss of cell viability in the exposed skin area as end point measurement. Skin was exposed to sodium dodecyl sulfate (SDS) at 20% concentration by non-occluded topical exposure to establish a positive control response and subsequent test compounds were statistically compared with the 20% SDS response. Cell viability and metabolism were measured with 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The model presents correlation between increased concentration of SDS and decreased viability of cells in the exposed skin area (R²?=?0.76). We propose the model to be used for cytotoxicity testing of irritant compounds. With fully intact barrier function, the model comprises all cells present in the skin with quantifiable end point measurement.     

Characterization of cytochrome P450 enzymes and P‐glycoprotein involved in the metabolism and transport of a new anti‐angiogenic agent KR‐31831

The in vitro metabolism and the transport of a novel anti‐angiogenic agent KR‐31831, (2R,3R,4S)‐6‐amino‐4‐[N‐(4‐chlorophenyl)‐N‐(1H‐imidazol‐2‐ylmethyl)amino]‐3‐hydroxy‐2‐dimethyoxymethyl‐3,4‐dihydro‐2‐methyl‐2H‐1‐benzopyran were investigated. Liquid chromatography‐mass spectrometry and tandem mass spectrometry were used for qualitative and quantitative analysis. The bidirectional transport studies of KR‐31831 using Caco‐2 cell monolayers showed the efflux to be significantly higher than influx (29.1 × 10^?6 compared to 11.5 × 10^?6 cm/s). P‐glycoprotein inhibitors significantly increased the influx of KR‐31831 and decreased the efflux of KR‐31831. These data indicate that KR‐313831 is a substrate for an efflux pump, P‐glycoprotein. The incubations of KR‐31831 with human liver microsomes produced three metabolites, M1, M2, and M3. M1 and M2 were identified as N‐(4‐chlorophenyl)‐N‐(1H‐imidazol‐2‐ylmethyl)amine and (2R,3R,4S)‐6‐amino‐4‐[N‐(4‐chlorophenyl)‐N‐(1H‐imidazol‐2‐ylmethyl)amino]‐3‐hydroxy‐2‐hydroxymethyl‐3,4‐dihydro‐2‐methyl‐2H‐1‐benzopyran by comparison with the authentic standards. M3 was tentatively characterized as hydroxy‐KR‐31831. CYP3A4 was identified as the major enzyme responsible for KR‐31831 metabolism to a major metabolite M1 using the combination of correlation analysis, immuno‐inhibition, chemical inhibition in human liver microsomes, and metabolism by cDNA expressed CYP enzymes. There is the possibility of drug–drug interactions when prescribing KR‐31831 concomitantly with known inhibitors or inducers of CYP3A4 and P‐glycoprotein. KR‐31831 was found to inhibit potently the metabolism of CYP2D6 substrate, suggesting that coadministration of KR‐31831 with CYP2D6 substrates may have significant effects on the pharmacokinetics of CYP2D6 substrates. Drug Dev. Res. 66:40–49. 2006. © 2006 Wiley‐Liss, Inc.