Reliable High-throughput Method for Inhibition Assay of 8 Cytochrome P450 Isoforms Using Cocktail of Probe Substrates and Stable Isotope-labeled Internal Standards

Inhibitory effect of Selaginella doederleinii hieron on human cytochrome P450

Introduction: Selaginella doederleinii Hieron is a traditional Chinese herbal medicine, the ethyl acetate extract from Selaginella doederleinii (SDEA) showed favorable anticancer potentials. However, the effect of SDEA on human cytochrome P450 enzymes (CYP450) remains unclear. To predict the herb-drug interaction (HDI) and lay the groundwork for further clinical trials, the inhibitory effect of SDEA and its four constituents (Amentoflavone, Palmatine, Apigenin, Delicaflavone) on seven CYP450 isoforms were investigated by using the established CYP450 cocktail assay based on LC-MS/MS. Methods: Appropriate substrates for seven tested CYP450 isoforms were selected to establish a reliable cocktail CYP450 assay based on LC-MS/MS. The contents of four constituents (Amentoflavone, Palmatine, Apigenin, Delicaflavone) in SDEA were determined as well. Then, the validated CYP450 cocktail assay was applied to test the inhibitory potential of SDEA and four constituents on CYP450 isoforms. Results: SDEA showed strong inhibitory effect on CYP2C9 and CYP2C8 (IC₅₀ ≈ 1 μg/ml), moderate inhibitory effect against CYP2C19, CYP2E1 and CYP3A (IC₅₀ < 10 μg/ml). Among the four constituents, Amentoflavone had the highest content in the extract (13.65%) and strongest inhibitory effect (IC₅₀ < 5 μM), especially for CYP2C9, CYP2C8 and CYP3A. Amentoflavone also showed time-dependent inhibition on CYP2C19 and CYP2D6. Apigenin and Palmatine both showed concentration-dependent inhibition. Apigenin inhibited CYP1A2, CYP2C8, CYP2C9, CYP2E1 and CYP3A. Palmatine inhibited CYP3A and had a weak inhibitory effect on CYP2E1. As for Delicaflavone, which has the potential to develop as an anti-cancer agent, showed no obvious inhibitory effect on CYP450 enzymes. Conclusion: Amentoflavone may be one of the main reasons for the inhibition of SDEA on CYP450 enzymes, the potential HDI should be considered when SDEA or Amentoflavone were used with other clinical drugs. On the contrast, Delicaflavone is more suitable to develop as a drug for clinical use, considering the low level of CYP450 metabolic inhibition.

Interaction study of Salvianolic acids for injection on pharmacokinetics of clopidogrel in rats by LC-MS/MS

Salvianolic acids for injection (SAI) is developed from traditional Chinese medicine and approved for the treatment of cardiovascular and cerebrovascular diseases. Clopidogrel is an inhibitor of platelet aggregation, which is often prescribed to patients in combination with SAI. This present study is aiming to assess the influences of SAI on the pharmacogenomics, pharmacokinetics and pharmacodynamics of clopidogrel, thereby ensuring the safety and efficacy of the co-administration. In vitro Cytochrome P450 isoenzymes assays were performed in human liver microsomes by LC-MS/MS method to assess the metabolites of CYPs substrates. The influences of SAI on the pharmacokinetics and pharmacodynamics behavior of clopidogrel were investigated in rats. The main pharmacokinetic parameters were analyzed by LC-MS/MS. Prothrombin time, activated partial thromboplastin time, bleeding time and inhibition of platelet aggregation were measured to evaluate the effects of pharmacodynamics. In our study, SAI at the clinical dose has no significant inhibitory effect on clopidogrel-related liver microsomes metabolic CYP450 isoenzymes. Moreover, SAI didn't affect the pharmacokinetics of clopidogrel both single dose and multiple dose in rats. In pharmacodynamics study, SAI has no effect on the platelet aggregation rate, PT and APTT time of clopidogrel, but could significantly prevent the risk of bleeding caused by clopidogrel.

Evaluation of the effect of Bovis Calculus Artifactus on eight rat liver cytochrome P450 isozymes using LC-MS/MS and cocktail approach

Bovis Calculus Artifactus (BCA) is the main substitute for natural Calculus bovis, a traditional drug in China used to treat high fever, convulsion, and sore throat. The effect of BCA on cytochrome P450 (CYP) activities is unknown. This study was to investigate the effect of BCA on eight rat hepatic microsomal CYPisozymes to evaluate the potential drug interactions using the cocktail approach.Metabolites of the eight isoform probe substrates of CYP isozymes were quantified by LC-MS/MS. The method was validated by incubating known CYP inhibitors α-naphthoflavone (CYP1A2), thiotepa (CYP2B1), quercetin (CYP2C7), sulfaphenazole (CYP2C6), ticlopidine (CYP2C11), quinidine (CYP2D1), ketoconazole (CYP3A1),4-methylpyrazole (CYP2E1) with individual probe substrate and rat liver microsomes. The formation rates of the corresponding metabolites of the eight probe substrates were determined to evaluate the activity of each isozyme.The results showed that BCA has different degrees of inhibitory effect on four CYP450 isoforms (CYP2C6, CYP2C11, CYP2D1, CYP3A1) (p < 0.05), but no significant influence on CYP1A2, 2B1, 2C7 or 2E1 (p > 0.05). Attention should be paid to the BCA-drug interactions by careful monitoring and appropriate dosage adjustments in the concurrent use of the drugs which are metabolized by CYP1A2, CYP2C19, and CYP3A4. Abbreviations: BCA, bovis calculus artifactus; CYP, cytochrome P450; DDIs, drug-drug interactions; ESI, electrospray ionization; MRM, multiple reaction monitoring; NBC, Natural Bovis Calculus; QC, quality control; T CM, traditional Chinese medicine.

Discovery of M5049: A Novel Selective Toll-Like Receptor 7/8 Inhibitor for Treatment of Autoimmunity

Toll-like receptor (TLR) 7 and TLR8 are transmembrane receptors that recognize single-stranded RNA. Activation of these receptors results in immune cell stimulation and inflammatory cytokine production, which is normally a protective host response. However, aberrant activation of TLR7/8 is potentially pathogenic and linked to progression of certain autoimmune diseases such as lupus. Thus, we hypothesize that an inhibitor that blocks TLR7/8 would be an effective therapeutic treatment. Prior efforts to develop inhibitors of TLR7/8 have been largely unsuccessful as a result of the challenge of producing a small-molecule inhibitor for these difficult targets. Here, we report the characterization of M5049 and compound 2, molecules which were discovered in a medicinal chemistry campaign to produce dual TLR7/8 inhibitors with drug-like properties. Both compounds showed potent and selective activity in a range of cellular assays for inhibition of TLR7/8 and block synthetic ligands and natural endogenous RNA ligands such as microRNA and Alu RNA. M5049 was found to be potent in vivo as TLR7/8 inhibition efficaciously treated disease in several murine lupus models and, interestingly, was efficacious in a disease context in which TLR7/8 activity has not previously been considered a primary disease driver. Furthermore, M5049 had greater potency in disease models than expected based on its in vitro potency and pharmacokinetic/pharmacodynamic properties. Because of its preferential accumulation in tissues, and ability to block multiple TLR7/8 RNA ligands, M5049 may be efficacious in treating autoimmunity and has the potential to provide benefit to a variety of patients with varying disease pathogenesis. SIGNIFICANCE STATEMENT: This study reports discovery of a novel toll-like receptor (TLR) 7 and TLR8 inhibitor (M5049); characterizes its binding mode, potency/selectivity, and pharmacokinetic and pharmacodynamic properties; and demonstrates its potential for treating autoimmune diseases in two mouse lupus models. TLR7/8 inhibition is unique in that it may block both innate and adaptive autoimmunity; thus, this study suggests that M5049 has the potential to benefit patients with autoimmune diseases.

Pharmaceutical Excipients and Drug Metabolism: A Mini-Review

Conclusions from previously reported articles have revealed that many commonly used pharmaceutical excipients, known to be pharmacologically inert, show effects on drug transporters and/or metabolic enzymes. Thus, the pharmacokinetics (absorption, distribution, metabolism and elimination) of active pharmaceutical ingredients are possibly altered because of their transport and metabolism modulation from the incorporated excipients. The aim of this review is to present studies on the interaction of various commonly-used excipients on pre-systemic metabolism by CYP450 enzymes. Excipients such as surfactants, polymers, fatty acids and solvents are discussed. Based on all the reported outcomes, the most potent inhibitors were found to be surfactants and the least effective were organic solvents. However, there are many factors that can influence the inhibition of CYP450, for instance type of excipient, concentration of excipient, type of CYP450 isoenzyme, incubation condition, etc. Such evidence will be very useful in dosage form design, so that the right formulation can be designed to maximize drug bioavailability, especially for poorly bioavailable drugs.

Herb-drug interaction between Styrax and warfarin: Molecular basis and mechanism

BACKGROUND

Styrax, one of the most famous folk medicines, has been frequently used for the treatment of cardiovascular diseases and skin problems in Asia and Africa. It is unclear whether Styrax or Styrax-related herbal medicines may trigger clinically relevant herb-drug interactions.

PURPOSE

This study was carried out to investigate the inhibitory effects of Styrax on human cytochrome P450 enzymes (CYPs) and to clarify whether this herb may modulate the pharmacokinetic behavior of the CYP-substrate drug warfarin when co-administered.

STUDY DESIGN

The inhibitory effects of Styrax on CYPs were assayed in human liver microsomes (HLM), while the pharmacokinetic interactions between Styrax and warfarin were investigated in rats. The bioactive constituents in Styrax with strong CYP3A inhibitory activity were identified and their inhibitory mechanisms were carefully investigated.

METHODS

The inhibitory effects of Styrax on human CYPs were assayed in vitro, while the pharmacokinetic interactions between Styrax and warfarin were studied in rats. Fingerprinting analysis of Styrax coupled with LC-TOF-MS/MS profiling and CYP inhibition assays were used to identify the constituents with strong CYP3A inhibitory activity. The inhibitory mechanism of oleanonic acid (the most potent CYP3A inhibitor occurring in Styrax) against CYP3A4 was investigated by a panel of inhibition kinetics analyses and in silico analysis.

RESULTS

In vitro assays demonstrated that Styrax extract strongly inhibited human CYP3A and moderately inhibited six other tested human CYPs, as well as potently inhibited warfarin 10-hydroxylation in liver microsomes from both humans and rats. In vivo assays demonstrated that compared with warfarin given individually in rats, Styrax (100 mg/kg) significantly prolonged the plasma half-life of warfarin by 2.3-fold and increased the AUC_(0-inf) of warfarin by 2.7-fold when this herb was co-administrated with warfarin (2 mg/kg) in rats. Two LC fractions were found with strong CYP3A inhibitory activity and the major constituents in these fractions were characterized by LC-TOF-MS/MS. Five pentacyclic triterpenoid acids (including epibetulinic acid, betulinic acid, betulonic acid, oleanonic acid and maslinic acid) present in Styrax were potent CYP3A inhibitors, and oleanonic acid was a competitive inhibitor against CYP3A-mediated testosterone 6β-hydroxylation.

CONCLUSION

Styrax and the pentacyclic triterpenoid acids occurring in this herb strongly modulate the pharmacokinetic behavior of warfarin via inhibition of CYP3A.

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method development for screening of potential tamoxifen-drug/herb interaction via in vitro cytochrome P450 inhibition assay

Screening for potential drug-drug interaction (DDI) or herb-drug interaction (HDI) using in vitro cytochrome P450 inhibition (IVCI) assays requires robust analytical methods with high sensitivity and reproducibility. Utilization of liquid chromatography-mass spectrometry (LC-MS) for analyte quantification is often hampered by the presence of non-volatile IVCI sample buffer constituents that often results in ion suppression. In this study, to enable screening of drug interactions involving tamoxifen (TAM) metabolism using IVCI-LC-MS/MS, a liquid-liquid extraction (LLE) method was developed and optimized for sample clean-up. Utilization of chloroform as extraction solvent and adjustment of sample pH to 11 was found to result in satisfactory recovery (>70%) and low ion suppression (<19%). A LC-MS/MS method was subsequently developed and validated for simultaneous quantification of major TAM metabolites, such as N-desmethyltamoxifen (NDT), endoxifen (EDF) and 4-hydroxytamoxifen (HTF) to enable IVCI sample analysis. Satisfactory separation of E-/Z-isomers of endoxifen with peak resolution (Rs) of 1.9 was achieved. Accuracy and precision of the method was verified within the linear range of 0-50 ng/mL for NDT, 0-25 ng/mL for HTF and 0-25 ng/mL for EDF (E/Z isomers). Inhibitory potency (IC50, Ki and mode of inhibition) of known CYP inhibitors and Strobilanthes crispus extract was then evaluated using the validated method. In summary, the results demonstrated applicability of the developed LLE and validated LC-MS/MS method for in vitro screening of DDI and HDI involving TAM metabolism.

Pharmacokinetic interaction between a Chinese herbal formula Huosu Yangwei oral liquid and apatinib in vitro and in vivo

Objectives

This study aimed to evaluate the inhibitory effects of Huosu Yangwei oral liquid (HSYW) on cytochrome P450 enzymes (CYPs) and to investigate whether this herbal medicine could modulate the pharmacokinetic behaviour of the co-administered CYP-substrate drug apatinib.

Methods

Cytochrome P450 enzymes inhibition assays were conducted in human liver microsomes (HLM) by a LC-MS/MS method for simultaneous determination of the oxidative metabolites of eight probe substrates for hepatic CYPs. The modulatory effects of HSYW on the oxidative metabolism of apatinib were investigated in both HLM and rat liver microsomes (RLM). The influences of HSYW on the pharmacokinetic behaviour of apatinib were investigated in rats.

Key findings

Huosu Yangwei oral liquid inhibited all tested CYPs in human liver preparations, with the IC50 values ranged from 0.3148 to 2.642 mg/ml. HSYW could also inhibit the formation of two major oxidative metabolites of apatinib in liver microsomes from both human and rat. In-vivo assays demonstrated that HSYW could significantly prolong the plasma half-life of apatinib by 7.4-fold and increase the AUC0–inf (nm·h) of apatinib by 43%, when HSYW (10 ml/kg) was co-administered with apatinib (10 mg/kg) in rats.

Conclusions

Huosu Yangwei oral liquid could inhibit mammalian CYPs and modulated the metabolic half-life of apatinib both in vitro and in vivo.

Generation of human hepatic progenitor cells with regenerative and metabolic capacities from primary hepatocytes

Hepatocytes are regarded as the only effective cell source for cell transplantation to treat liver diseases; however, their availability is limited due to a donor shortage. Thus, a novel cell source must be developed. We recently reported that mature rodent hepatocytes can be reprogrammed into progenitor-like cells with a repopulative capacity using small molecule inhibitors. Here, we demonstrate that hepatic progenitor cells can be obtained from human infant hepatocytes using the same strategy. These cells, named human chemically induced liver progenitors (hCLiPs), had a significant repopulative capacity in injured mouse livers following transplantation. hCLiPs redifferentiated into mature hepatocytes in vitro upon treatment with hepatic maturation-inducing factors. These redifferentiated cells exhibited cytochrome P450 (CYP) enzymatic activities in response to CYP-inducing molecules and these activities were comparable with those in primary human hepatocytes. These findings will facilitate liver cell transplantation therapy and drug discovery studies.

One of the most successful treatments for liver disease is transplanting a donor liver into a patient. But demands for donor livers far outstrips supply. A promising alternative could be, rather than replacing the whole organ, to transplant patients with individual liver cells called hepatocytes. These cells can then move into the liver, replace damaged cells, and help support the organ. However, hepatocytes are also in short supply, as despite the liver’s amazing regenerative abilities, these cells struggle to divide outside of the body. Improving how these cells multiply, could therefore help more people receive hepatocyte transplants.

In 2017, researchers found a way to convert mouse and rat hepatocytes into cells that could divide more rapidly using a cocktail of three small molecules. These 'chemically induced liver progenitors', or CLiPs for short, were able to mature into working hepatocytes and support injured mouse livers. But, discoveries made in rats and mice are not always applicable to humans. Now, Katsuda et al. – including some of the researchers involved in the 2017 work – have set out to investigate whether CLiPs can also be made from human cells, and if so, whether these cells can be used for hepatocyte transplantations.

Using a similar cocktail of molecules, Katsuda et al. managed to convert infant human hepatocytes into CLiPs. As with the rodent cells, these human CLiPs were able to turn back into mature, working liver cells. When transplanted into mice with genetic liver diseases, the human CLiPs moved into the liver and became part of the organ. These transplanted cells were able to reconstruct the liver tissue of diseased mice, and in some cases, replaced more than 90% of the liver’s damaged cells.

Developing human CLiP technology could provide a new way to support people on the waiting list for liver transplantation. But there are some obstacles still to overcome. At present the technique only works with hepatocytes from infant donors. The next step is to improve the method so that it works with liver cells donated by adults.

Screening of ten cytochrome P450 enzyme activities with 12 probe substrates in human liver microsomes using cocktail incubation and liquid chromatography-tandem mass spectrometry

Testing for potential drug interactions of new chemical entities is essential when developing a novel drug. In this study, an assay was designed to evaluate drug interactions with 10 major human cytochrome P450 (P450) enzymes incubated in liver microsomes, involving 12 probe substrates with two cocktail incubation sets used in a single liquid chromatography-tandem mass spectrometry (LC-MS/MS) run. The P450 substrate composition in each cocktail set was optimized to minimize solvent effects and mutual drug interactions among substrates as follows: cocktail A was composed of phenacetin for CYP1A2, bupropion for CYP2B6, amodiaquine for CYP2C8, diclofenac for CYP2C9, S-mephenytoin for CYP2C19, and dextromethorphan for CYP2D6; cocktail B was composed of coumarin for CYP2A6, chlorzoxazone for CYP2E1, astemizole for CYP2J2, and midazolam, nifedipine, and testosterone for CYP3A. Multiple probe substrates were used for CYP3A owing to the multiple substrate-binding sites and substrate-dependent inhibition. After incubation in human liver microsomes, each incubation mixture was pooled and all probe metabolites were simultaneously analysed in a single LC-MS/MS run. Polarity switching was used to acquire the negative-ion mode for hydroxychlorzoxazone and positive-ion mode for the remaining analytes. The method was validated by comparing the inhibition data obtained from incubation of each individual probe substrate alone and with the substrate cocktails. The half-maximal inhibitory concentration values obtained from the cocktail and individual incubations were well correlated and in agreement with previously reported values. This new method will be useful in assessing the drug interaction potential of new chemical entities during new drug development.

Effects of Oridonin on Hepatic Cytochrome P450 Expression and Activities in PXR-Humanized Mice

Oridonin, the major terpene found in Rabdosia rubescens, is widely used as dietary supplement or therapeutic drug, while the effects of oridonin on CYP450 were still unclear. The pregnane X receptor (PXR) is an important regulatory factor for major drug metabolism enzyme CYPs, and it has been reported to have species-specific differences. Therefore, this study has employed more reliable models PXR-humanized mouse to investigate the influence of oridonin on PXR and downstream metabolism enzyme. Eight-week-old male PXR-humanized mice were treated with oridonin by orally (0, 25, 50, 100, 200 mg/kg) for 15 d. The effects of oridonin on major downstream CYPs of PXR were examined at both the mRNA and enzyme activity levels by RT-PCR and HPLC-MS/MS. In general, there was no significant toxic reaction in liver of PXR-humanized mice. The mRNA expression of CYPs and cytochrome P450 oxidoreductase (POR) were increased with oridonin treatment in a dose-dependent manner. CYP2c and CYP3a family catalytic activity were increased significantly in two higher doses groups. These results indicate that oridonin induced the expression and activation of CYP2c and CYP3a family, which might contribute to potential drug-drug interactions and appear to be a risk when co-administered with other clinical drugs.

Design and optimization of the cocktail assay for rapid assessment of the activity of UGT enzymes in human and rat liver microsomes

Along with the prevalence of drug combination therapies, an increasing number of cases about drug-drug interactions (DDI) have been reported, which has drawn a lot of attention due to the potential toxicity and/or therapeutic failure. Pharmacokinetic interactions based on drug metabolic enzymes should be responsible for a great many of DDI. UDP-glucuronosyltransferases (UGT) as the main phase II metabolic enzymes are involved in the metabolism of many endogenous and exogenous substrates. Herein, we designed and optimized a validated cocktail method for the simultaneous evaluation of drug-mediated inhibition of the main five UGT isoforms using respective specific probe substrates (estradiol for UGT1A1, chenodeoxycholic acid for UGT1A3, serotonin for UGT1A6, propofol for UGT1A9/PROG and zidovudine for UGT2B7/AZTG) in human and rat liver microsomes by liquid chromatography-tandem mass spectrometry (LCMS/MS). Moreover, we investigated the risk of interactions among UGT probe substrates, and validated the cocktail method by known positive inhibitors of UGT isoforms. To minimize the substrates interaction, we developed two cocktail subgroups which were further optimized via exploring the experimental conditions. In particular, the cocktail inhibition assay for rapid assessment of in vitro rat UGTs was firstly reported and the values of K_m in the liver microsomes from humans and rats were close to each other in the specific UGT subtype. In conclusion, this study has successfully established the cocktail approach to explore UGT activity, especially for UGT inhibition in a fast and efficient way.

Effect of Oridonin on Cytochrome P450 Expression and Activities in HepaRG Cell

Oridonin, the major terpene found in Rabdosia rubescens, is widely used as a dietary supplement or therapeutic drug. However, the effects of oridonin on major CYP450s are still unclear. As oridonin can enhance the effect of other clinical drugs, in this study, we investigated the influence of oridonin on CYP450s mRNA expression and its impact on activities in human HepaRG cell to evaluate the safety by studying its potential drug interaction. HepaRG cells were cultured with series concentrations of oridonin (1, 5, 10, and 20 μmol/L), and the major CYP450s mRNA and protein expression, as well as enzyme activities were analyzed by real-time polymerase chain reaction, Western blot analysis and UPLC-MS/MS-based metabolite assay. In general, ordonin has induced effects on the major member of CYP450s mRNA and protein expression, as well as on the enzyme activity in human HepaRG cells, especially on CYP3A4 and CYP2C9. To our knowledge, this is the first systematic research about the inductive effects of oridonin on the major member of CYP450s in human cell line. These results may provide at least partly of the basis for potential drug-drug interactions and oridonin should be used with caution to avoid potential risk.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

Nanofractionation Platform with Parallel Mass Spectrometry for Identification of CYP1A2 Inhibitors in Metabolic Mixtures

With early assessment of inhibitory properties of drug candidates and their circulating metabolites toward cytochrome P450 enzymes, drug attrition, especially later in the drug development process, can be decreased. Here we describe the development and validation of an at-line nanofractionation platform, which was applied for screening of CYP1A2 inhibitors in Phase I metabolic mixtures. With this platform, a metabolic mixture is separated by liquid chromatography (LC), followed by parallel nanofractionation on a microtiter well plate and mass spectrometry (MS) analysis. After solvent evaporation, all metabolites present in the nanofractionated mixture are assayed utilizing a fluorescence CYP1A2 inhibition bioassay performed on the plate. Next, a bioactivity chromatogram is constructed from the bioassay results. By peak shape and retention time correlation of the bioactivity peaks with the obtained MS data, CYP1A2-bioactive inhibiting metabolites can be identified. The method correctly evaluated the potency of five CYP1A2 inhibitors. Mixtures comprising potent inhibitors of CYP1A2 or in vitro-generated metabolites of ellipticine were evaluated for their inhibitory bioactivities. In both cases, good LC separation of all compounds was achieved and bioactivity data could be accurately correlated with the parallel recorded MS data. Generation and evaluation of Phase II metabolites of hydroxylated ellipticine was also pursued.

Development of GC-MS based cytochrome P450 assay for the investigation of multi-herb interaction

As drug interactions with cytochrome P450 enzymes become increasingly important in the field of drug discovery, a high-throughput screening method for analysing the effects of a drug is needed. We have developed a simple and rapid simultaneous analytical method using a cocktail approach for measuring the activities of seven cytochrome P450 enzymes (CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4). Human liver microsomes were used as a source for the seven cytochrome P450 enzymes, and a gas chromatography-mass spectrometry (GC-MS) was used for analysing their activities. Kinetic studies and inhibition assays of CYP enzymes were performed using known substrates and inhibitors for validating and comparing the reaction rates and time-dependent activities between methods using each substrate versus a method using a cocktail solution. The optimized cocktail method was successfully applied to evaluate the effects of the decoction of Socheongryong-tang (SCRT) on cytochrome P450 enzymes. Our cocktail method provides a simultaneous high-throughput activity assay using GC-MS for the first time. This method is applicable for analysing the drug interactions of various plant-derived mixtures.

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

During the last 10-15 years, cytochrome P450 (CYP) 2C8 has emerged as an important drug-metabolizing enzyme. CYP2C8 is highly expressed in human liver and is known to metabolize more than 100 drugs. CYP2C8 substrate drugs include amodiaquine, cerivastatin, dasabuvir, enzalutamide, imatinib, loperamide, montelukast, paclitaxel, pioglitazone, repaglinide, and rosiglitazone, and the number is increasing. Similarly, many drugs have been identified as CYP2C8 inhibitors or inducers. In vivo, already a small dose of gemfibrozil, i.e., 10% of its therapeutic dose, is a strong, irreversible inhibitor of CYP2C8. Interestingly, recent findings indicate that the acyl-β-glucuronides of gemfibrozil and clopidogrel cause metabolism-dependent inactivation of CYP2C8, leading to a strong potential for drug interactions. Also several other glucuronide metabolites interact with CYP2C8 as substrates or inhibitors, suggesting that an interplay between CYP2C8 and glucuronides is common. Lack of fully selective and safe probe substrates, inhibitors, and inducers challenges execution and interpretation of drug-drug interaction studies in humans. Apart from drug-drug interactions, some CYP2C8 genetic variants are associated with altered CYP2C8 activity and exhibit significant interethnic frequency differences. Herein, we review the current knowledge on substrates, inhibitors, inducers, and pharmacogenetics of CYP2C8, as well as its role in clinically relevant drug interactions. In addition, implications for selection of CYP2C8 marker and perpetrator drugs to investigate CYP2C8-mediated drug metabolism and interactions in preclinical and clinical studies are discussed.

An improved substrate cocktail for assessing direct inhibition and time-dependent inhibition of multiple cytochrome P450s

AIM

The substrate cocktail is frequently used to evaluate cytochrome P450 (CYP) enzyme-mediated drug interactions and potential interactions among the probe substrates. Here, we re-optimized the substrate cocktail method to increase the reliability and accuracy of screening for candidate compounds and expanded the method from a direct CYP inhibition assay to a time-dependent inhibition (TDI) assay.

METHODS

In the reaction mixtures containing human liver microsome (0.1 mg/mL), both the concentrations of a substrate cocktail (phenacetin for 1A2, coumarin for 2A6, bupropion for 2B6, diclofenac for 2C9, dextromethorphan for 2D6, and testosterone for 3A4) and the incubation time were optimized. Metabolites of the substrate probes were simultaneously analyzed by multiple-reaction monitoring (MRM) using a routine LC/MS/MS. Direct CYP inhibition was validated using 7 inhibitors (α-naphthoflavone, tranylcypromine, ticlopidine, fluconazole, quinidine, ketoconazole and 1-ABT). The time-dependent inhibition was partially validated with 5 inhibitors (ketoconazole, verapamil, quinidine, paroxetine and 1-ABT).

RESULTS

The inhibition curve profiles and IC50 values of 7 CYP inhibitors were approximate when a single substrate and the substrate cocktail were tested, and were consistent with the previously reported values. Similar results were obtained in the IC50 shifts of 5 inhibitors when a single substrate and the substrate cocktail were tested in the TDI assay.

CONCLUSION

The 6-in-1 substrate cocktail (for 1A2, 2A6, 2B6, 2C9, 2D6 and 3A) is reliable for assessing CYP inhibition and time-dependent inhibition of drug candidates.

Application of a cocktail approach to screen cytochrome P450 BM3 libraries for metabolic activity and diversity

In the present study, the validity of using a cocktail screening method in combination with a chemometrical data mining approach to evaluate metabolic activity and diversity of drug-metabolizing bacterial Cytochrome P450 (CYP) BM3 mutants was investigated. In addition, the concept of utilizing an in-house-developed library of CYP BM3 mutants as a unique biocatalytic synthetic tool to support medicinal chemistry was evaluated. Metabolic efficiency of the mutant library towards a selection of CYP model substrates, being amitriptyline (AMI), buspirone (BUS), coumarine (COU), dextromethorphan (DEX), diclofenac (DIC) and norethisterone (NET), was investigated. First, metabolic activity of a selection of CYP BM3 mutants was screened against AMI and BUS. Subsequently, for a single CYP BM3 mutant, the effect of co-administration of multiple drugs on the metabolic activity and diversity towards AMI and BUS was investigated. Finally, a cocktail of AMI, BUS, COU, DEX, DIC and NET was screened against the whole in-house CYP BM3 library. Different validated quantitative and qualitative (U)HPLC-MS/MS-based analytical methods were applied to screen for substrate depletion and targeted product formation, followed by a more in-depth screen for metabolic diversity. A chemometrical approach was used to mine all data to search for unique metabolic properties of the mutants and allow classification of the mutants. The latter would open the possibility of obtaining a more in-depth mechanistic understanding of the metabolites. The presented method is the first MS-based method to screen CYP BM3 mutant libraries for diversity in combination with a chemometrical approach to interpret results and visualize differences between the tested mutants.

Development and validation of an in vitro, seven-in-one human cytochrome P450 assay for evaluation of both direct and time-dependent inhibition

INTRODUCTION

Direct and time-dependent inhibition (TDI) of cytochrome P450 enzymes (CYP) raises drug safety concerns and has major implications in drug development. This study describes the development of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) based screening tool to simultaneously assess both the direct and the time-dependent inhibitory potential of xenobiotics on the seven major CYPs using a two-step approach.

METHODS

The in vitro cocktail of FDA recognized model substrates was incubated with human liver microsomes (HLM) and consisted of caffeine (CYP1A2), bupropion (CYP2B6), rosiglitazone (CYP2C8), tolbutamide (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6) and midazolam (CYP3A4). Direct and time-dependent inhibitory profiles of direct and time-dependent reference inhibitors for each CYP were studied. For validation, the results were compared to those obtained with the traditional single substrate approach. Statistical uncertainty was quantified using the bootstrap method.

RESULTS

The direct inhibition assay showed an acceptable fold bias of 1.35 (geometric mean fold absolute deviation, range 1.01-2.61) in the IC50 values for the cocktail assay compared to the single substrate results with no trend for under- or overestimation. Using a single point inactivation assay to assess TDI, we were able to identify all seven tested time-dependent reference inhibitors, without any false negatives.

DISCUSSION

The presented design enhances throughput by assessing the seven major CYPs simultaneously and allows for detection of and discrimination between direct and time-dependent CYP inhibition via IC50 and single point inactivation experiments. For the latter, a threshold of 10% TDI is proposed for carrying out more detailed inactivation kinetic experiments.

Comprehensive assessment of Cytochrome P450 reactions: A multiplex approach using real-time ESI-MS

BACKGROUND

The detailed analysis of Cytochrome P450 (CYP) catalyzed reactions is of great interest, since those are of importance for biotechnical applications, drug interaction studies and environmental research. Often cocktail approaches are carried out in order to monitor several CYP activities in a single experiment. Commonly in these approaches product formation is detected and IC50 values are determined.

METHODS

In the present work, the reactions of two different CYP isoforms were monitored using real-time electrospray ionization mass spectrometry. Multiplex experiments using the highly specific CYP2A6 with its corresponding substrate coumarin as well as the highly promiscuous CYP3A4 with testosterone were conducted. Product formation and substrate depletion were simultaneously monitored and compared to the single CYP experiments. The diffusion-controlled rate of reaction and conversion rates that are used as parameters to assess the enzymatic activity were calculated for all measurements conducted.

RESULTS

Differences in conversion rates and the theoretical rate of reaction that were observed for single CYP and multiplex experiments, respectively, reveal the complexity of the underlying mechanisms. Findings of this study imply that there might be distinct deviations between product formation and substrate degradation when mixtures are used.

CONCLUSIONS

Detailed results indicate that for a comprehensive assessment of these enzymatic reactions both product and substrate should be considered.

GENERAL SIGNIFICANCE

The direct hyphenation of enzymatic reactions to mass spectrometry allows for a comprehensive assessment of enzymatic behavior. Due to the benefits of this technique, the entire system which includes substrate, product and intermediates can be investigated. Thus, besides IC50 values further information regarding the enzymatic behavior offers the opportunity for a more detailed insight.

High-Throughput Cytochrome P450 Cocktail Inhibition Assay for Assessing Drug-Drug and Drug-Botanical Interactions

Detection of drug-drug interactions is essential during the early stages of drug discovery and development, and the understanding of drug-botanical interactions is important for the safe use of botanical dietary supplements. Among the different forms of drug interactions that are known, inhibition of cytochrome P450 (P450) enzymes is the most common cause of drug-drug or drug-botanical interactions. Therefore, a rapid and comprehensive mass spectrometry-based in vitro high-throughput P450 cocktail inhibition assay was developed that uses 10 substrates simultaneously against nine CYP isoforms. Including probe substrates for CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and two probes targeting different binding sites of CYP3A4/5, this cocktail simultaneously assesses at least as many P450 enzymes as previous assays while remaining among the fastest due to short incubation times and rapid analysis using ultrahigh pressure liquid chromatography-tandem mass spectrometry. The method was validated using known inhibitors of each P450 enzyme and then shown to be useful not only for single-compound testing but also for the evaluation of potential drug-botanical interactions using the botanical dietary supplement licorice (Glycyrrhiza glabra) as an example.

Hydrogen-deuterium exchange of aromatic amines and amides using deuterated trifluoroacetic acid

The H-D exchange of aromatic amines and amides, including pharmaceutically relevant compounds such as acetaminophen and diclofenac, was investigated using CF3COOD as both the sole reaction solvent and source of deuterium label. The described method is amenable to efficient deuterium incorporation for a wide variety of substrates possessing both electron-donating and electron-withdrawing substituents. Best results were seen with less basic anilines and highly activated acetanilides, reflecting the likelihood of different mechanistic pathways.

Simultaneous determination of bupropion, metroprolol, midazolam, phenacetin, omeprazole and tolbutamide in rat plasma by UPLC-MS/MS and its application to cytochrome P450 activity study in rats

A specific ultra-performance liquid chromatography tandem mass spectrometry method is described for the simultaneous determination of bupropion, metroprolol, midazolam, phenacetin, omeprazole and tolbutamide in rat plasma with diazepam as internal standard, which are the six probe drugs of the six cytochrome P450 isoforms CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19 and CYP2C9. Plasma samples were protein precipitated with acetonitrile. The chromatographic separation was achieved using a UPLC® BEH C18 column (2.1 × 100 mm, 1.7 µm). The mobile phase consisted of acetonitrile and water (containing 0.1% formic acid) with gradient elution. The triple quadrupole mass spectrometric detection was operated by multiple reaction monitoring in positive electrospray ionization. The precisions were <13%, and the accuracy ranged from 93.3 to 110.4%. The extraction efficiency was >90.5%, and the matrix effects ranged from 84.3 to 114.2%. The calibration curves in plasma were linear in the range of 2-2000 ng/mL, with correlation coefficient (r(2) ) >0.995. The method was successfully applied to pharmacokinetic studies of the six probe drugs of the six CYP450 isoforms and used to evaluate the effects of erlotinib on the activities of CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19 and CYP2C9 in rats. Erlotinib may inhibit the activity of CYP2B6 and CYP3A4, and may induce CYP2C9 of rats.

Dose-response of oridonin on hepatic cytochromes P450 mRNA expression and activities in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Oridonin, the major terpene found in Rabdosia rubescens, is widely used as a dietary supplement or therapeutic drug. The effects of oridonin on drug processing genes, such as cytochrome P450 and nuclear receptors, were still unclear. Therefore, the present study investigated the influence of oridonin on the hepatic drug metabolizing system to evaluate the safety through its drug interaction potential.

MATERIALS AND METHODS

In this study, eight-week-old male C57BL/6 mice were treated oridonin orally (0, 25, 50, 100, 200 mg/kg, i.g.) for 15 days. The effects of oridonin on major Cyps in mice livers were examined at both the mRNA and enzyme activity levels.

RESULTS

In general, there are no significant influence of various dose of oridonin on mice liver function. However, oridonin significantly increased Cyps (1a, 2a, 2d, 2e, 2c and 3a family) mRNA expression. In addition, it could induce Cyps activity in microsome incubation at maximum dosage. To our knowledge, it is the first time to identify oridonin as a Cyps inducer in vivo. It also promotes the expression of CAR, PXR and POR.

CONCLUSION

These results indicate that, if studies in mice extrapolate to humans by orthologous genes, oridonin appears to be a risk to herb-drug interactions due to its induction effects on drug processing genes expression and activation.

The effects of acute hydrogen sulfide poisoning on cytochrome P450 isoforms activity in rats

Hydrogen sulfide (H2S) is the second leading cause of toxin related death (after carbon monoxide) in the workplace. H2S is absorbed by the upper respiratory tract mucosa, and it causes histotoxic hypoxemia and respiratory depression. Cocktail method was used to evaluate the influences of acute H2S poisoning on the activities of cytochrome P450 isoforms CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19, and CYP2C9, which were reflected by the changes of pharmacokinetic parameters of six specific probe drugs, bupropion, metoprolol, midazolam, phenacetin, omeprazole, and tolbutamide, respectively. The experimental rats were randomly divided into two groups, control group and acute H2S poisoning group (inhaling 300 ppm for 2 h). The mixture of six probes was given to rats by oral administration and the blood samples were obtained at a series of time points through the caudal vein. The concentrations of probe drugs in rat plasma were measured by LC-MS. The results for acute H2S poisoning and control groups were as follows: there was a statistically significant difference in the AUC and C max for bupropion, metoprolol, phenacetin, and tolbutamide, while there was no statistical pharmacokinetic difference for midazolam and omeprazole. Acute H2S poisoning could inhibit the activity of CYP2B6, CYP2D6, CYP1A2, and CYP2C9 in rats.

The effects of H2S on the activities of CYP2B6, CYP2D6, CYP3A4, CYP2C19 and CYP2C9 in vivo in rat

Hydrogen sulfide (H₂S) is a colorless, flammable, extremely hazardous gas with a “rotten egg” smell. The human body produces small amounts of H₂S and uses it as a signaling molecule. The cocktail method was used to evaluate the influence of H₂S on the activities of CYP450 in rats, which were reflected by the changes of pharmacokinetic parameters of five specific probe drugs: bupropion, metroprolol, midazolam, omeprazole and tolbutamide, respectively. The rats were randomly divided into two groups, control group and H₂S group. The H₂S group rats were given 5 mg/kg NaHS by oral administration once a day for seven days. The mixture of five probes was given to rats through oral administration and the blood samples were obtained at a series of time-points through the caudal vein. The concentrations of probe drugs in rat plasma were measured by LC-MS. In comparing the H₂S group with the control group, there was a statistically pharmacokinetics difference for midazolam and tolbutamide; the area under the plasma concentration-time curve (AUC) was decreased for midazolam (p < 0.05) and increased for tolbutamide (p < 0.05); while there was no statistical pharmacokinetics difference for bupropion, metroprolol and omeprazole. H₂S could not influence the activities of CYP2B6, CYP2D6 and CYP2C19 in rats, while H₂S could induce the activity of CYP3A4 and inhibit the activity of CYP2C9 in rats.

Cocktail-substrate approach-based high-throughput assay for evaluation of direct and time-dependent inhibition of multiple cytochrome P450 isoforms

Avoiding drug-drug interactions (DDIs) mediated through inhibition of cytochrome P450 (CYP) activity is highly desirable. Direct inhibition (DI) of CYP through new chemical entities (NCEs) or time-dependent inhibition (TDI) through reactive metabolites should be elucidated at an early stage of drug discovery research. In particular, TDI of CYP occurring through reactive metabolites may be irreversible and even sustained, causing far more serious DDIs for TDIs than for DIs. Furthermore, it is important to ascertain whether an NCE inhibits multiple CYP isoforms. Hence, using a cocktail-substrate approach that we previously established (in which the activity of 8 CYP isoforms is simultaneously evaluated in a single run), we evaluated the IC50 values of direct inhibitors and TDI parameters (kobs, shifted IC50, KI and kinact) of time-dependent inhibitors that affect multiple CYP isoforms. The IC50 values for 8 CYP isoforms obtained using the cocktail-substrate approach were nearly identical to values previously reported. The TDI parameters for CYP1A2, 2C9, 2C19, 2D6, and CYP3A4/5 obtained using the cocktail-substrate approach were also nearly identical to those obtained using a single-substrate approach. Thus, the cocktail-substrate approach is useful for evaluating DI and TDI in the early stages of drug discovery and development processes.

Sample reduction strategies in discovery bioanalysis

It is a constant challenge to provide timely bioanalytical support for the evaluation of drug-like properties and PK/PD profiles for the ever-increasing numbers of new chemical entities in a cost-effective manner. While technological advancement in various aspects of LC–MS/MS analysis has significantly improved bioanalytical efficiency, a number of simple sample reduction strategies can be employed to reduce the number of samples requiring analysis, and as a result increase the bioanalytical productivity without deploying additional instruments. In this review, advantages and precautions of common sample reduction strategies, such as sample pooling and cassette dosing, are discussed. In addition, other approaches such as reducing calibration standards and eliminating over-the-curve sample reanalysis will also be discussed. Taken together, these approaches can significantly increase the capacity and throughput of discovery bioanalysis without adding instruments, and are viable means to enhance the overall productivity of the bioanalytical laboratory.

In vitro approaches to investigate cytochrome P450 activities: update on current status and their applicability

INTRODUCTION

Cytochromes P450 (CYPs) play a central role in the Phase I metabolism of drugs and other xenobiotics. It is estimated that CYPs can metabolize up to two-thirds of drugs present in humans. Over the past two decades, there have been numerous advances in in vitro methodologies to characterize drug metabolism and interaction involving CYPs.

AREAS COVERED

This review focuses on the use of in vitro methodologies to examine CYPs' role in drug metabolism and interaction. There is an emphasis on their current development, applicability, advantages and limitations as well as the use of in silico approaches in complementing and supporting in vitro data. The article also highlights the challenges in extrapolating in vitro data to in vivo situations.

EXPERT OPINION

Advances in in vitro methodologies have been made such that data can be used for in vivo prediction with comfortable degree of confidence. Improved assay designs and analytical techniques have permitted development of miniaturized assay format and automated system with improved sensitivity and throughput capacity. High-quality experimental designs and scientifically rigorous assessment/validation protocols remain crucial in developing reliable and robust in vitro models. With continued progress made in the field, in vitro methodologies will continually be employed in evaluating CYP activities in pharmaceutical industries and laboratories.

A sensitive and specific CYP cocktail assay for the simultaneous assessment of human cytochrome P450 activities in primary cultures of human hepatocytes using LC-MS/MS

A sensitive and specific CYP cocktail assay for simultaneous measurement of the activities of major human cytochrome P450 enzymes (CYP1A2 (phenacetin), CYP3A4/5 (midazolam), CYP2C9 (diclofenac), CYP2C19 (S-mephenytoin) and CYP2D6 (dextromethorphan)) in primary cultures of human hepatocytes, was developed and validated using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Hepatocyte incubation medium was processed by a solid phase extraction (SPE) using Oasis SPE extraction cartridges prior to chromatography. The metabolites derived from each of the substrates were simultaneously quantitated using the corresponding stable isotope-labeled internal standards by a positive electrospray ionization mode using multiple reactions monitoring with a single eight minute run. The mean accuracy was in the range of 98-114%. The interday and intraday precision over the concentration ranges evaluated for all the analytes were lower than 15%, and 14%, respectively. All the generated metabolites were stable under the conditions used for sample analysis. Additionally, the interaction of a cocktail substrate on other CYP substrates was also analyzed. Due to substantial inter-substrate interaction, chlorzoxazone (CYP2E1) and bupropion (CYP2B6) were removed from the initial seven probes CYP cocktail assay. Therefore, the final CYP cocktail assay consisting of five probes provides a robust method to simultaneously measure activities of CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4/5 in primary cultures of human hepatocytes.