CYP2B6 Substrates Research Articles

Crystal Structure of CYP2B6 in Complex with an Efavirenz Analog.

The over two dozen CYP2B structures of human, rabbit, and woodrat enzymes solved in the last decade have significantly enhanced our understanding of the structure-function relationships of drug metabolizing enzymes. More recently, an important role has emerged for halogen-π interactions in the CYP2B6 active site in substrate selectivity, explaining in part the preference for halogenated ligands as substrates. The mechanism by which such ligands interact with CYP2B enzymes involves conserved phenylalanine side chains, in particular F108, F115, or F297, in the active site, which form π bonds with halogens. To illustrate such halogen-π interactions using drugs that are major substrates of CYP2B6, we present here a crystal structure of CYP2B6 in complex with an analog of the widely used anti-HIV drug efavirenz, which contains a methyl group in place of the carbonyl oxygen. The chlorine of the efavirenz analog forms a π bond with the aromatic ring of F108, whereas the putative metabolism site on the distal end of the molecule is oriented towards the heme iron. The crystal structure showcases how CYP2B6 accommodates this important drug analog of considerable size in the active site by movement of various side chains without substantially increasing the active site volume. Furthermore, the CYP2B6-efavirenz analog complex provides a useful platform to investigate computationally as well as biophysically the effect of genetic polymorphisms on binding of the widely studied efavirenz.

The use of bovine serum albumin in phenotyping experiments by substrate depletion approach to determine fm, cyp: Application to CYP2B6 substrates with emphasis on bupropion

The use of bovine serum albumin in phenotyping experiments by substrate depletion approach to determine fm, cyp: Application to CYP2B6 substrates with emphasis on bupropion

Quantitative in vitro phenotyping and prediction of drug interaction potential of CYP2B6 substrates as victims

1. Determination of fm, CYP for a compound is critical to assess the potential risk of a drug candidate as a victim of DDI. Several compounds are identified as CYP2B6 substrates, but the fm, CYP2B6 values are not determined quantitatively.2. Two methods of reaction phenotyping, the chemical inhibition method and metabolism in rCYP enzymes, were used to determine the relative contributions of the enzymes. Chemical inhibition method was also conducted in the presence of BSA (0.5% w/v).3. The results confirm with the earlier studies concerning the identity of the CYP2B6 enzyme. The fm, CYP2B6 values for artemisinin, bupropion, clopidogrel, ketamine, selegiline, sertraline and ticlopidine were 0.24, 0.28, 0.15, 0.45, 0.46, 0.42 and 0.54, respectively, in HLM determined by chemical inhibition method. The fm, CYP2B6 values for artemisinin, bupropion, clopidogrel, ketamine, selegiline, sertraline and ticlopidine were 0.46, 0.17, 0.15, 0.60, 0.51, 0.66 and 0.77, respectively, in HLM determined by chemical inhibition method in the presence of BSA (0.5% w/v).4. Bupropion metabolism is majorly mediated by CYP2C19 (0.41) with a minor contribution from CYP2B6 (0.16) in the presence of BSA. Ticlopidine is a time-dependent inhibitor of both CYP2B6 and CYP2C19 that can inhibit the bupropion metabolism by 50–60%.

In vitro evaluation of the inhibition and induction potential of olaparib, a potent poly(ADP-ribose) polymerase inhibitor, on cytochrome P450

1. In vitro studies were conducted to evaluate potential inhibitory and inductive effects of the poly(ADP-ribose) polymerase (PARP) inhibitor, olaparib, on cytochrome P450 (CYP) enzymes. Inhibitory effects were determined in human liver microsomes (HLM); inductive effects were evaluated in cultured human hepatocytes.2. Olaparib did not inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2D6 or CYP2E1 and caused slight inhibition of CYP2C9, CYP2C19 and CYP3A4/5 in HLM up to a concentration of 100 μM. However, olaparib (17–500 μM) inhibited CYP3A4/5 with an IC50 of 119 μM. In time-dependent CYP inhibition assays, olaparib (10 μM) had no effect against CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP2E1 and a minor effect against CYP3A4/5. In a further study, olaparib (2–200 μM) functioned as a time-dependent inhibitor of CYP3A4/5 (KI, 72.2 μM and Kinact, 0.0675 min−1). Assessment of the CYP induction potential of olaparib (0.061–44 μM) showed minor concentration-related increases in CYP1A2 and more marked increases in CYP2B6 and CYP3A4 mRNA, compared with positive control activity; however, no significant change in CYP3A4/5 enzyme activity was observed.3. Clinically significant drug–drug interactions due to olaparib inhibition or induction of hepatic or intestinal CYP3A4/5 cannot be excluded. It is recommended that olaparib is given with caution with narrow therapeutic range or sensitive CYP3A substrates, and that prescribers are aware that olaparib may reduce exposure to substrates of CYP2B6.

Halogen−π Interactions in the Cytochrome P450 Active Site: Structural Insights into Human CYP2B6 Substrate Selectivity

Numerous cytochrome P450 (CYP) 2B6 substrates including drugs and environmental chemicals are halogenated. To assess the role of halogen-π bonds in substrate selectivity and orientation in the active site, structures of four CYP2B6 monoterpenoid complexes were solved by X-ray crystallography. Bornyl bromide exhibited dual orientations in the active site with the predominant orientation revealing a bromine-π bond with the Phe108 side chain. Bornane demonstrated two orientations with equal occupancy; in both, the C2 atom that bears the bromine in bornyl bromide was displaced by more than 2.5 Å compared with the latter complex. The bromine in myrtenyl bromide π-bonded with Phe297 in CYP2B6, whereas the two major orientations in the active site mutant I114V exhibited bromine-π interactions with two additional residues, Phe108 and Phe115. Analysis of existing structures suggests that halogen-π interactions may be unique to the CYP2B enzymes within CYP family 2 but are also important for CYP3A enzymes.

Halogen‐π Interactions in the Cytochrome P450 Active Site: Structural Insights into Human P450 2B6 Substrate Selectivity.

Numerous CYP2B6 substrates including drugs and environmental chemicals are halogenated. To assess the role of halogen‐π bonds in substrate selectivity and orientation in the active site, structures of four CYP2B6 monoterpenoid complexes were solved by X‐ray crystallography. Bornyl bromide exhibited dual orientations in the active site with the predominant orientation revealing a bromine‐π bond with the Phe‐108 side chain. Bornane demonstrated two orientations with equal occupancy; in both the C2‐atom that bears the bromine in bornyl bromide was displaced by more than 2.5 Å compared with the latter complex. The bromine in myrtenyl bromide π‐bonded with Phe‐297 in CYP2B6, whereas the two major orientations in the active site mutant I114V exhibited bromine‐π interactions with two additional residues, Phe‐108 and Phe‐115. Analysis of existing structures suggests that halogen‐π interactions may be unique to the CYP2B enzymes within CYP family 2 but are also important for CYP3A enzymes.Support or Funding InformationES003619 to Dr. James R. Halpert

Inhibitory Effects of Garcinia cambogia Extract on CYP2B6 Enzyme Activity.

This study assessed the inhibitory effects of Garcinia cambogia extract on the cytochrome P450 enzymes in vitro. G. cambogia extract was incubated with cytochrome P450 isozyme-specific substrates in human liver microsomes and recombinant CYP2B6 isozyme, and the formation of the marker metabolites was measured to investigate the inhibitory potential on cytochrome P450 enzyme activities. The results showed that G. cambogia extract has significant inhibitory effects on CYP2B6 activity in a concentration-dependent manner. Furthermore, the inhibition was potentiated following preincubation with NADPH, indicating that G. cambogia extract is a time-dependent inhibitor of CYP2B6. Meanwhile, hydroxycitric acid, the major bioactive ingredient of G. cambogia extract, did not exhibit significant inhibition effects on cytochrome P450 enzyme activities. G. cambogia extract could modulate the pharmacokinetics of CYP2B6 substrate drugs and lead to interactions with those drugs. Therefore, caution may be required with respect to concomitant intake of dietary supplements containing G. cambogia extract with CYP2B6 substrates.

Effects of Unprocessed Versus Vinegar-Processed Schisandra chinensis on the Activity of CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19 and CYP2D6 Enzymes in Rats

Schisandra chinensis (SC) is a well-known traditional Chinese herbal medicine that has been used in clinical practices for thousands of years. However, the differences between the effects of unprocessed and vinegarprocessed Schisandra chinensis (VSC) on cytochrome P450 (CYP450) activities are poorly understood. To evaluate the differences between processed and unprocessed SC on the metabolism of CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19 and CYP2D6 substrates in rats using a cocktail method based on a developed and validated high performance liquid chromatography-mass spectrometry (HPLC-MS) method. Six probe substrates (coumarin (CYP2A6), bupropion (CYP2B6), paclitaxel (CYP2C8), tolbutamide (CY2C9), omeprazole (CYP2C19) and metoprolol (CYP2D6)) were delivered simultaneously into rats treated with single or multiple doses of processed or crude SC extract. The plasma concentrations of the six probes were profiled by HPLC-MS, and their corresponding pharmacokinetic parameters were calculated. Treatment with single or multiple doses of either extract of SC or VSC induced CYP2A6, CYP2B6 and CYP2C9 enzyme activity and inhibited CYP2D6, CYP2C19 and CYP2C8 enzyme activity in rats. Furthermore, the inhibitory or induced effect of multiple doses of SC was more potent after vinegar processing than without vinegar processing. CYP2A6, 2B6 and 2C9 enzyme activity were induced significantly after treatment with multiple doses but not after a single dose. CYP2C19 enzyme activity were inhibited significantly after treatment with multiple doses but not after a single dose. These results provide useful scientific data for the safe clinical application of either extract of SC in combination with other drugs, which should lack the side effects induced by other herb-drug interactions.

In Vitro Regio- and Stereoselective Oxidation of β-Ionone by Human Liver Microsomes.

The metabolism of the norisoprenoid β-ionone was investigated in vitro using human liver microsomes and 11 different recombinant cytochrome P450 enzymes expressed in Trichoplusia ni cells. β-Ionone was found to be oxidized via 4S-hydroxylation by CYP2B6 in human liver microsomes. CYP1A2 also regioselectively catalyzed the hydroxylation of β-ionone to yield 4-hydroxylation; this conversion was not stereoselective. Further kinetic analysis revealed that CYP2B6 exhibited the highest activity for β-ionone 4-hydroxylation. Kinetic analysis showed that Km and Vmax for oxidation of β-ionone by CYP1A2 and CYP2B6 was 107.9 ± 36.0 µM and 3200.3 ± 323.0 nmol/min/nmol P450 and 5.6 ± 1.2 µM and 572.8 ± 29.8 nmol/min/nmol P450, respectively. The reaction rates observed using human liver microsomes and recombinant CYP2B6 were very high compared with those of other CYP2B6 substrates reported thus far. These results suggest that β-ionone, a norisoprenoid present in nature, is one of the effective substrates for CYP2B enzymes in human liver microsomes. To the best of our knowledge, this is the first time that 4-hydroxy β-ionone has been described as a human metabolite of β-ionone.

Towards a Best Practice Approach in PBPK Modeling: Case Example of Developing a Unified Efavirenz Model Accounting for Induction of CYPs 3A4 and 2B6.

In this study, we present efavirenz physiologically based pharmacokinetic (PBPK) model development as an example of our best practice approach that uses a stepwise approach to verify the different components of the model. First, a PBPK model for efavirenz incorporating in vitro and clinical pharmacokinetic (PK) data was developed to predict exposure following multiple dosing (600 mg q.d.). Alfentanil i.v. and p.o. drug‐drug interaction (DDI) studies were utilized to evaluate and refine the CYP3A4 induction component in the liver and gut. Next, independent DDI studies with substrates of CYP3A4 (maraviroc, atazanavir, and clarithromycin) and CYP2B6 (bupropion) verified the induction components of the model (area under the curve [AUC] ratios within 1.0–1.7‐fold of observed). Finally, the model was refined to incorporate the fractional contribution of enzymes, including CYP2B6, propagating autoinduction into the model (Racc 1.7 vs. 1.7 observed). This validated mechanistic model can now be applied in clinical pharmacology studies to prospectively assess both the victim and perpetrator DDI potential of efavirenz.

Effects of the selected cytochrome P450 oxidoreductase genetic polymorphisms on cytochrome P450 2B6 activity as measured by bupropion hydroxylation.

Cytochrome P450 oxidoreductase (POR) is required for drug metabolism by all microsomal cytochrome P450 (CYP) enzymes. The aim of this study was to investigate whether single-nucleotide polymorphisms in the POR gene were correlated with interindividual variations in CYP2B6 activity, as measured by bupropion hydroxylation. Thirty-five healthy individuals with selected CYP2B6 and POR polymorphisms were involved in the clinical study. The activity of CYP2B6 was evaluated on the basis of the area under the time-concentration curve (AUC) ratio of hydroxybupropion versus bupropion (AUC_hyd/AUC_bup). Individuals carrying CYP2B6*1/*1 showed a significantly higher mean AUC_hyd/AUC_bup than individuals carrying the CYP2B6*1/*6 and CYP2B6*6/*6 variants (17.1 ± 6.23 vs. 10.3 ± 4.53, P = 0.003 and 17.1 ± 6.23 vs. 9.41 ± 2.84, P = 0.002, respectively). POR g.6593A>G (rs2868177) AA homozygotes showed a significantly lower mean AUC_hyd/AUC_bup than POR g.6593A>G AG heterozygotes or GG homozygotes (8.54 ± 2.65 vs. 14.9 ± 6.06, P = 0.005 and 8.54 ± 2.65 vs. 16.8 ± 6.45, P = 0.002, respectively). Moreover, POR g.6593A>G AA homozygotes had a significantly lower mean AUC_hyd/AUC_bup than the POR g.6593A>G AG/GG genotypes in the CYP2B6*1/*1, CYP2B6*1/*6 and CYP2B6*6/*6 groups (10.9 ± 1.82 vs. 19.7 ± 5.53, P < 0.001; 6.18 ± 0.284 vs. 12.1 ± 4.31, P = 0.011; and 6.94 ± 1.48 vs. 10.9 ± 2.39, P = 0.043, respectively). There was no significant difference in the mean AUC_hyd/AUC_bup among different POR c.1508C>T (*28 or rs1057868) genotypes, even after the effect of CYP2B6*6 was excluded. These results indicate, for the first time, that the POR g.6593A>G polymorphism significantly influences CYP2B6 activity, as measured by bupropion hydroxylation, in humans, and the CYP2B6*6 and POR g.6593A>G polymorphisms might be considered simultaneously for the individualized therapy with CYP2B6 substrate drugs such as bupropion.

Abstract C62: Effects of rolapitant on the pharmacokinetics of dextromethorphan (CYP2D6), tolbutamide (CYP2C9), omeprazole (CYP2C19), efavirenz (CYP2B6), and repaglinide (CYP2C8) in healthy subjects

Abstract Introduction: Rolapitant is a selective and long acting NK-1 receptor antagonist for the prevention of chemotherapy-induced nausea and vomiting (CINV). In vitro results indicated rolapitant mildly inhibited cytochrome P450 (CYP450) enzymes (2D6/2C9/2C19/2B6/2C8) at high concentrations (IC50s &amp;gt; 7 μM). The major metabolite SCH720881 did not inhibit these CYP enzymes. This study aimed to 1) evaluate the effects of rolapitant on the pharmacokinetics (PK) of CYP probe substrates (dextromethorphan [DET] for CYP2D6, tolbutamide [TOL] for CYP2C9, omeprazole [OMP] for CYP2C19, efavirenz [EFA] for CYP2B6 and repaglinide [REP] for CYP2C8), and 2) evaluate the safety and tolerability of rolapitant co-administered with these substrates in healthy subjects. Methods: This was an open-label, multi-part drug-drug interaction study in cohorts of 20 to 26 healthy subjects of orally-administered CYP probe substrates (Part-A: 30 mg DET; Part-B: 500 mg TOL plus 40 mg OMP; Part-C: 600 mg EFA; Part-D: 0.25 mg REP) in the absence and presence of single oral dose 180 mg rolapitant. Blood samples for determination of plasma concentration of CYP substrates and relevant metabolites were collected during 3 dosing periods in each part: 1) Period-1: CYP probe substrate alone as baseline; 2) Period-2: CYP probe substrate plus rolapitant concomitantly after a washout of probe given in Period 1 to evaluate the potential impact of rolapitant on probe substrate; and 3) Period-3: CYP probe substrate alone 7 days after the concomitant dose in Period-2 (approximating the peak time of metabolite SCH720881) to evaluate the impact of metabolite/rolapitant on probe substrate. Results: Rolapitant inhibited CYP2D6 following concomitant dose (Period-2) and 7 days after concomitant dose (Period-3), resulting in 2.2- to 3.3-fold higher exposure (Cmax and AUC) of DET. Rolapitant did not inhibit CYP2C9 following exposure to TOL. The exposure (Cmax &amp; AUC) of CYP2C19 substrate OMP was minimally increased by rolapitant (1.1- to1.4-fold) and is unlikely to be clinically relevant. Rolapitant did not inhibit CYP2B6 or result in clinically relevant changes in exposure of EFA. Rolapitant did not inhibit CYP2C8 or result in clinically relevant changes in exposure of REP. There were no noteworthy adverse events or laboratory findings in any part of the study. Conclusions: Rolapitant was well-tolerated when co-administered with CYP probe substrates. Co-administration of rolapitant increased the exposure of DET. The inhibition of CYP2D6 can last at least 7 days following single dose of rolapitant. No clinically significant interaction was observed between rolapitant and substrates of CYP2C9, CYP2C19, CYP2B6 or CYP2C8; therefore no dosing adjustment is necessary for drugs which are metabolized by these CYPs. Citation Format: Xiaodong Wang, Zhi-Yi Zhang, Jing Wang, Sharon Lu, Sujata Arora, Lorraine Hughes, Jennifer Christensen, Vikram Kansra. Effects of rolapitant on the pharmacokinetics of dextromethorphan (CYP2D6), tolbutamide (CYP2C9), omeprazole (CYP2C19), efavirenz (CYP2B6), and repaglinide (CYP2C8) in healthy subjects. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C62.

Evaluation of metabolism dependent inhibition of CYP2B6 mediated bupropion hydroxylation in human liver microsomes by monoamine oxidase inhibitors and prediction of potential as perpetrators of drug interaction

The objective of the study was to evaluate the metabolism dependent inhibition of CYP2B6 catalyzed bupropion hydroxylation in human liver microsomes by monoamine oxidase (MAO) inhibitors and to predict the drug–drug interaction potential of monoamine oxidase inhibitors as perpetrators of drug interaction. Human liver microsomal CYP2B6 activities were investigated using bupropion hydroxylation as probe substrate marker. The results from single point time dependent inhibition and shift assays suggest that clorgyline, pargyline, phenelzine, and selegiline were metabolism based inhibitors of CYP2B6. In IC50 shift assays, clorgyline, pargyline, phenelzine and selegiline are metabolism based inhibitors of CYP2B6 with fold shit of 3.0-, 3.7-, 2.9-, and 11.4-fold respectively. The inactivation of clorgyline was characterized by KI value of 2.5±0.3 and kinact value of 0.045±0.001min−1. Phenelzine inactivated CYP2B6 with KI and kinact values of 44.9±6.9μM and 0.085±0.003min−1 respectively. Inactivation of selegiline was characterized with KI and kinact values of 22.0±3.3 and 0.074±0.002min−1 respectively. The inactivation caused by these inhibitors was not reversed by dialysis indicating irreversible inhibition. Based on the mechanistic static model, selegiline showed an increase in the area under the curve (AUC) of efavirenz and bupropion by 1.01-fold. Phenelzine predicted to cause an increase in the AUC of efavirenz and bupropion by 9.4- and 2.4-fold respectively considering unbound hepatic inlet concentrations of phenelzine. In conclusion, the results from this study demonstrated that MAO inhibitors can inactivate human liver microsomal CYP2B6. The likelihood of drug interaction when selegiline co-administered with CYP2B6 substrates is remote. Caution is required while co-administering phenelzine with substrates that are exclusively metabolized by CYP2B6 enzyme and substrates that have narrow therapeutic index.

Effect of honokiol on the induction of drug-metabolizing enzymes in human hepatocytes.

Honokiol, 2-(4-hydroxy-3-prop-2-enyl-phenyl)-4-prop-2-enyl-phenol, an active component of Magnolia officinalis and Magnolia grandiflora, exerts various pharmacological activities such as antitumorigenic, antioxidative, anti-inflammatory, neurotrophic, and antithrombotic effects. To investigate whether honokiol acts as a perpetrator in drug interactions, messenger ribonucleic acid (mRNA) levels of phase I and II drug-metabolizing enzymes, including cytochrome P450 (CYP), UDP-glucuronosyltransferase (UGT), and sulfotransferase 2A1 (SULT2A1), were analyzed by real-time reverse transcription polymerase chain reaction following 48-hour honokiol exposure in three independent cryopreserved human hepatocyte cultures. Honokiol treatment at the highest concentration tested (50 μM) increased the CYP2B6 mRNA level and CYP2B6-catalyzed bupropion hydroxylase activity more than two-fold in three different hepatocyte cultures, indicating that honokiol induces CYP2B6 at higher concentrations. However, honokiol treatment (0.5–50 μM) did not significantly alter the mRNA levels of phase I enzymes (CYP1A2, CYP3A4, CYP2C8, CYP2C9, and CYP2C19) or phase II enzymes (UGT1A1, UGT1A4, UGT1A9, UGT2B7, and SULT2A1) in cryopreserved human hepatocyte cultures. CYP1A2-catalyzed phenacetin O-deethylase and CYP3A4-catalyzed midazolam 1′-hydroxylase activities were not affected by 48-hour honokiol treatment in cryopreserved human hepatocytes. These results indicate that honokiol is a weak CYP2B6 inducer and is unlikely to increase the metabolism of concomitant CYP2B6 substrates and cause pharmacokinetic-based drug interactions in humans.

Evaluation of 89 compounds for identification of substrates for cynomolgus monkey CYP2C76, a new bupropion/nifedipine oxidase.

Cynomolgus monkeys are widely used in preclinical studies during drug development because of their evolutionary closeness to humans, including their cytochrome P450s (P450s). Most cynomolgus monkey P450s are almost identical (≥90%) to human P450s; however, CYP2C76 has low sequence identity (approximately 80%) to any human CYP2Cs. Although CYP2C76 has no ortholog in humans and is partly responsible for species differences in drug metabolism between cynomolgus monkeys and humans, a broad evaluation of potential substrates for CYP2C76 has not yet been conducted. In this study, a screening of 89 marketed compounds, including human CYP2C and non-CYP2C substrates or inhibitors, was conducted to find potential CYP2C76 substrates. Among the compounds screened, 19 chemicals were identified as substrates for CYP2C76, including substrates for human CYP1A2 (7-ethoxyresorufin), CYP2B6 (bupropion), CYP2D6 (dextromethorphan), and CYP3A4/5 (dextromethorphan and nifedipine), and inhibitors for CYP2B6 (sertraline, clopidogrel, and ticlopidine), CYP2C8 (quercetin), CYP2C19 (ticlopidine and nootkatone), and CYP3A4/5 (troleandomycin). CYP2C76 metabolized a wide variety of the compounds with diverse structures. Among them, bupropion and nifedipine showed high selectivity to CYP2C76. As for nifedipine, CYP2C76 formed methylhydroxylated nifedipine, which was not produced by monkey CYP2C9, CYP2C19, or CYP3A4, as identified by mass spectrometry and estimated by a molecular docking simulation. This unique oxidative metabolite formation of nifedipine could be one of the selective marker reactions of CYP2C76 among the major CYP2Cs and CYP3As tested. These results suggest that monkey CYP2C76 contributes to bupropion hydroxylation and formation of different nifedipine oxidative metabolites as a result of its relatively large substrate cavity.

Metformin Represses Drug-Induced Expression of CYP2B6 by Modulating the Constitutive Androstane Receptor Signaling

Metformin is currently the most widely used drug for the treatment of type 2 diabetes. Mechanistically, metformin interacts with many protein kinases and transcription factors that alter the expression of numerous downstream target genes governing lipid metabolism, cell proliferation, and drug metabolism. The constitutive androstane receptor (CAR, NR1i3), a known xenobiotic sensor, has recently been recognized as a novel signaling molecule, in that its activation could be regulated by protein kinases in addition to the traditional ligand binding. We show that metformin could suppress drug-induced expression of CYP2B6 (a typical target gene of CAR) by modulating the phosphorylation status of CAR. In human hepatocytes, metformin robustly suppressed the expression of CYP2B6 induced by both indirect (phenobarbital) and direct CITCO [6-(4-chlorophenyl)imidazo[2,1-b]1,3thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime] activators of human CAR. Mechanistic investigation revealed that metformin specifically enhanced the phosphorylation of threonine-38 of CAR, which blocks CAR nuclear translocation and activation. Moreover, we showed that phosphorylation of CAR by metformin was primarily an AMP-activated protein kinase- and extracellular signal-regulated kinase 1/2-dependent event. Additional two-hybrid and coimmunoprecipitation assays demonstrated that metformin could also disrupt CITCO-mediated interaction between CAR and the steroid receptor coactivator 1 or the glucocorticoid receptor-interacting protein 1. Our results suggest that metformin is a potent repressor of drug-induced CYP2B6 expression through specific inhibition of human CAR activation. Thus, metformin may affect the metabolism and clearance of drugs that are CYP2B6 substrates.

Abstract C84: Nonclinical metabolism, disposition, pharmacokinetics, and in vitro drug-drug interaction assessment of ARQ 087, a pan-FGFR inhibitor.

Abstract Introduction: ARQ 087 is a potent multi-tyrosine kinase inhibitor with activity against the FGFR family currently in Phase I clinical studies for the treatment of advanced solid tumors. Here, we present preclinical metabolism, disposition, pharmacokinetic and in vitro drug-drug interaction studies with ARQ 087. Methods: ARQ 087 was assessed in vitro for cross-species metabolic stability; CYP450 (cytochrome P450) reaction phenotyping; CYP450 inhibition/induction; Caco-2 absorption and efflux; and P-gp (P-glycoprotein), BCRP (Breast Cancer Resistance Protein), and MRP2 (Multidrug Resistance-associated Protein 2)-mediated ATPase stimulation. Distribution of ARQ 087 to various tissues was measured after single and repeat dosing to mice as well as pharmacokinetics in mice, rats, and dogs. Results: Cross-species NADPH-dependent metabolism studies revealed that ARQ 087 undergoes little, if any, NADPH-dependent metabolism in human, rat, dog, mouse, and monkey microsomes. Half-lives generally exceeded 60 minutes, with little or no variation observed between gender and species tested. Reaction phenotyping with CYP450 and CYP450 inhibitors/antibodies indicated that ARQ 087 was generally stable against all CYP450 isoforms tested (1A2/3A4/2C9/2C19/2D6/2C8). Average half-lives against all isoforms were greater than 50 minutes. ARQ 087 showed no significant potential to inhibit CYP3A4, 2C19, 2C8, or 2C9, with average IC50s greater than 20 µM. Some inhibition of CYP1A2, and 2D6 was observed in HLM, with IC50 values of 12 and 19 µM respectively. ARQ 087 did not induce CYP3A4 or 1A2, however concentrations of 1 µM or greater did appear to induce CYP2B6 in cells from one of three individuals tested. Based on these in vitro results interactions with CYP2B6 substrates and/or inhibitors in the clinic are possible. Caco-2 and ATPase transporter studies showed that ARQ 087 was highly permeable with little efflux in Caco-2 monolayers but may be an inhibitor/substrate of P-gp and mutant BCRP. Oral bioavailability values were determined to be 32% - 46% in mice, rats, and dogs. The elimination half-lives following intravenous administration were 2.1, 5.9, and 9.0 hrs in mice, rats, and dogs, respectively. Flip-flop pharmacokinetic profiles following oral administrations in mice and rats were observed, but not in dogs. Moderate systemic clearance were observed in all 3 species with hepatic extraction ratio ranging from 40% - 70%. Conclusion: Collectively, these data indicate that ARQ 087 has sufficient oral bioavailability to advance into clinical testing. There appears to be a low likelihood, with the possible exception of CYP2B6 substrates, of drug-drug interactions based on Phase I metabolism. However, the high degree metabolic stability along with the potential to accumulate in tissues/organs observed in preclinical testing suggests that careful selection of dosing regimens for ARQ 087 will be crucial to maximize patient benefit. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C84. Citation Format: Terence G. Hall, Laurie P. Volak, Karen R. Bresciano, Yunxia Wang, Chang-Rung Chen, Syed Ali, David Mckearn, Inese Smukste, Ronald E. Savage. Nonclinical metabolism, disposition, pharmacokinetics, and in vitro drug-drug interaction assessment of ARQ 087, a pan-FGFR inhibitor. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C84.

Pharmacokinetic Drug Interactions Involving Vortioxetine (Lu AA21004), a Multimodal Antidepressant

Background and ObjectiveThe identification and quantification of potential drug–drug interactions is important for avoiding or minimizing the interaction-induced adverse events associated with specific drug combinations. Clinical studies in healthy subjects were performed to evaluate potential pharmacokinetic interactions between vortioxetine (Lu AA21004) and co-administered agents, including fluconazole (cytochrome P450 [CYP] 2C9, CYP2C19 and CYP3A inhibitor), ketoconazole (CYP3A and P-glycoprotein inhibitor), rifampicin (CYP inducer), bupropion (CYP2D6 inhibitor and CYP2B6 substrate), ethinyl estradiol/levonorgestrel (CYP3A substrates) and omeprazole (CYP2C19 substrate and inhibitor).MethodsThe ratio of central values of the test treatment to the reference treatment for relevant parameters (e.g., area under the plasma concentration–time curve [AUC] and maximum plasma concentration [C max]) was used to assess pharmacokinetic interactions.ResultsCo-administration of vortioxetine had no effect on the AUC or C max of ethinyl estradiol/levonorgestrel or 5′-hydroxyomeprazole, or the AUC of bupropion; the 90 % confidence intervals for these ratios of central values were within 80–125 %. Steady-state AUC and C max of vortioxetine increased when co-administered with bupropion (128 and 114 %, respectively), fluconazole (46 and 15 %, respectively) and ketoconazole (30 and 26 %, respectively), and decreased by 72 and 51 %, respectively, when vortioxetine was co-administered with rifampicin. Concomitant therapy was generally well tolerated; most adverse events were mild or moderate in intensity.ConclusionDosage adjustment may be required when vortioxetine is co-administered with bupropion or rifampicin.Electronic supplementary materialThe online version of this article (doi:10.1007/s40261-013-0117-6) contains supplementary material, which is available to authorized users.

CYP2B6 Pharmacogenetics–Based In Vitro–In Vivo Extrapolation of Efavirenz Clearance by Physiologically Based Pharmacokinetic Modeling

Efavirenz is mainly cleared by CYP2B6. The CYP2B6*6 allele is associated with lower efavirenz clearance. Efavirenz clearance was predictable using in vitro data for carriers of the CYP2B6*1/*1 genotype, but the prediction in carriers of the CYP2B6*6 allele was poor. To test the hypothesis that incorporation of mechanism of reduced efavirenz metabolism by the CYP2B6*6 allele can predict the genetic effect on efavirenz pharmacokinetics, in vitro-in vivo extrapolation of efavirenz clearance was performed by physiologically based pharmacokinetic modeling (Simcyp Simulator; Simcyp Ltd., Sheffield, UK) using data obtained from expressed CYP2B6.1 and CYP2B6.6 as well as human liver microsomes (HLMs) with CYP2B6*1/*1, *1/*6, and *6/*6 genotypes. Simulated pharmacokinetics of a single 600-mg oral dose of efavirenz for individuals with each genotype was compared with data observed in healthy subjects genotyped for the CYP2B6*6 allele (n = 20). Efavirenz clearance for carriers of the CYP2B6*1/*1 genotype was predicted reasonably well using HLM data, but the clearance in carriers of the CYP2B6*6 allele was underpredicted using both expressed and HLM systems. Improved prediction of efavirenz clearance was obtained from expressed CYP2B6 after recalculating intersystem extrapolation factors for CYP2B6.1 and CYP2B6.6 based on in vitro intrinsic clearance of bupropion 4-hydroxylation. These findings suggest that genetic effect on both CYP2B6 protein expression and catalytic efficiency needs to be taken into account for the prediction of pharmacokinetics in individuals carrying the CYP2B6*6/*6 genotype. Expressed CYP2B6 proteins may be a reliable in vitro system to predict effect of the CYP2B6*6 allele on the metabolism of CYP2B6 substrates.

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.