Diansong Zhou

In Vitro Evaluation of Potential Drug-Drug Interactions with Ticagrelor: Cytochrome P450 Reaction Phenotyping, Inhibition, Induction, and Differential Kinetics

Ticagrelor is an orally administered, antiplatelet agent that inhibits the prothrombotic effects of ADP on the platelet by antagonizing the P2Y12 receptor. Ticagrelor is a reversibly binding direct-acting P2Y12 antagonist and does not require metabolic activation to achieve its antiplatelet effect. CYP3A4 and CYP3A5 appear to be the enzymes predominantly responsible for the formation of the ticagrelor active and inactive metabolites, AR-C124910XX and AR-C133913XX. The apparent Km values in human liver microsomes are 27.0 and 38.8 μM, with Vmax values of 730 and 417 pmol/min/mg for AR-C124910XX and AR-C133913XX, respectively. Ticagrelor moderately inhibited CYP2C9 activity in human liver microsomes with an IC50 of 10.5 μM, while exhibiting little or no inhibition of CYP1A2, CYP2B6, CYP2C8, CYP2C19, CYP2D6, and CYP2E1. In human liver microsomes, ticagrelor inhibited midazolam 4-hydroxylation with an IC50 of 8.2 μM, while activating 1′-hydroxylation of midazolam. Studies with recombinant enzymes suggested that cytochrome b5 and CYP3A4 interactions play a significant role in this differential kinetic behavior. Evaluated in fresh human hepatocytes at concentration up to 20 μM, ticagrelor was not an inducer of CYP1A2 or CYP3A4. Although ticagrelor exhibited a tendency for CYP2B6 and CYP2C9 induction, its potential to cause drug interactions via the induction of these enzymes is low when its exposure at a therapeutic dose is considered.

COMPARISON OF METHODS FOR THE PREDICTION OF THE METABOLIC SITES FOR CYP3A4-MEDIATED METABOLIC REACTIONS

Predictions of the metabolic sites for new chemical entities, synthesized or only virtual, are important in the early phase of drug discovery to guide chemistry efforts in the synthesis of new compounds with reduced metabolic liability. This information can now be obtained from in silico predictions, and therefore, a thorough and unbiased evaluation of the computational techniques available is needed. Several computational methods to predict the metabolic hot spots are emerging. In this study, metabolite identification using MetaSite and a docking methodology, GLUE, were compared. Moreover, the published CYP3A4 crystal structure and computed CYP3A4 homology models were compared for their usefulness in predicting metabolic sites. A total of 227 known CYP3A4 substrates reported to have one or more metabolites adding up to 325 metabolic pathways were analyzed. Distance-based fingerprints and four-point pharmacophore derived from GRID molecular interaction fields were used to characterize the substrate and protein in MetaSite and the docking methodology, respectively. The CYP3A4 crystal structure and homology model with the reactivity factor enabled achieved a similar prediction success (78%) using the MetaSite method. The docking method had a relatively lower prediction success (∼57% for the homology model), although it still may provide useful insights for interactions between ligand and protein, especially for uncommon reactions. The MetaSite methodology is automated, rapid, and has relatively accurate predictions compared with the docking methodology used in this study.

Role of Human UGT2B10 in N-Glucuronidation of Tricyclic Antidepressants, Amitriptyline, Imipramine, Clomipramine, and Trimipramine

The role of human UDP glucuronosyltransferase (UGT) 2B10 in the N-glucuronidation of a number of tricyclic antidepressants was investigated and compared with that of UGT1A4 in both the Sf9 expressed system and human liver microsomes. The apparent Km (S50) values for the formation of quaternary N-glucuronides of amitriptyline, imipramine, clomipramine, and trimipramine were 2.60, 16.8, 14.4, and 11.2 μM in UGT2B10 and 448, 262, 112, and 258 μM in UGT1A4, respectively. The kinetics of amitriptyline and imipramine glucuronidation in human liver microsomes exhibited a biphasic character, where the high- and low-affinity components were in good agreement with our results in expressed UGT2B10 and UGT1A4, respectively. The kinetics of clomipramine and trimipramine glucuronidation in human liver microsomes were sigmoidal in nature, and the S50 values were similar to those found for expressed UGT1A4. The in vitro clearances (CLint or CLmax) were comparable between UGT2B10 and UGT1A4 for glucuronidation of imipramine, clomipramine, and trimipramine, whereas CLint of amitriptyline glucuronidation by UGT2B10 was more than 10-fold higher than that by UGT1A4. Nicotine was found to selectively inhibit UGT2B10 but not UGT1A4 activity. At a low tricyclic antidepressant concentration, nicotine inhibited their glucuronidation by 33 to 50% in human liver microsomes. Our results suggest that human UGT2B10 is a high-affinity enzyme for tricyclic antidepressant glucuronidation and is likely to be a major UGT isoform responsible for the glucuronidation of these drugs at therapeutic concentrations in vivo.

Simulation and Prediction of the Drug-Drug Interaction Potential of Naloxegol by Physiologically Based Pharmacokinetic Modeling

Naloxegol, a peripherally acting μ‐opioid receptor antagonist for the treatment of opioid‐induced constipation, is a substrate for cytochrome P450 (CYP) 3A4/3A5 and the P‐glycoprotein (P‐gp) transporter. By integrating in silico, preclinical, and clinical pharmacokinetic (PK) findings, minimal and full physiologically based pharmacokinetic (PBPK) models were developed to predict the drug‐drug interaction (DDI) potential for naloxegol. The models reasonably predicted the observed changes in naloxegol exposure with ketoconazole (increase of 13.1‐fold predicted vs. 12.9‐fold observed), diltiazem (increase of 2.8‐fold predicted vs. 3.4‐fold observed), rifampin (reduction of 76% predicted vs. 89% observed), and quinidine (increase of 1.2‐fold predicted vs. 1.4‐fold observed). The moderate CYP3A4 inducer efavirenz was predicted to reduce naloxegol exposure by ∼50%, whereas weak CYP3A inhibitors were predicted to minimally affect exposure. In summary, the PBPK models reasonably estimated interactions with various CYP3A modulators and can be used to guide dosing in clinical practice when naloxegol is coadministered with such agents.

The effect of quinidine, a strong P‐glycoprotein inhibitor, on the pharmacokinetics and central nervous system distribution of naloxegol

Naloxegol is a PEGylated, oral, peripherally acting μ‐opioid receptor antagonist approved in the United States for treatment of opioid‐induced constipation in patients with noncancer pain. Naloxegol is metabolized by CYP3A, and its properties as a substrate for the P‐glycoprotein (PGP) transporter limit its central nervous system (CNS) permeability. This double‐blind, randomized, 2‐part, crossover study in healthy volunteers evaluated the effect of quinidine (600 mg PO), a CYP3A/PGP transporter inhibitor, on the pharmacokinetics and CNS distribution of naloxegol (25 mg PO). In addition, the effects of quinidine on morphine (5 mg/70 kg IV)‐induced miosis and exposure to naloxegol were assessed. Coadministration of quinidine and naloxegol increased naloxegols AUC 1.4‐fold and Cmax 2.5‐fold but did not antagonize morphine‐induced miosis, suggesting that PGP inhibition does not increase the CNS penetration of naloxegol. Naloxegol pharmacokinetics was unaltered by coadministration of morphine and either quinidine or placebo; conversely, pharmacokinetics of morphine and its metabolites (in the presence of quinidine) were unaltered by coadministration of naloxegol. Naloxegol was safe and well tolerated, alone or in combination with quinidine, morphine, or both. The observed increase in exposure to naloxegol in the presence of quinidine is primarily attributed to quinidines properties as a weak CYP3A inhibitor.

Expression and Characterization of Dog Cytochrome P450 2A13 and 2A25 in Baculovirus-Infected Insect Cells

Dog CYP2A13 and CYP2A25 were coexpressed with dog NADPH-cytochrome P450 reductase (OR) in baculovirus-infected Sf9 insect cells. CYP2A13 effectively catalyzed 7-ethoxycoumarin (7EC) deethylation and coumarin hydroxylation with apparent Km values of 4.8 and 2.1 μM, respectively, similar to those observed using dog liver microsomes (7.5 and 0.75 μM, respectively). CYP2A25 exhibited much lower affinity toward 7EC, with an apparent Km value of 150 μM, which indicates that CYP2A13 plays a more significant role in the metabolism of these CYP2A substrates. Similar to the dog CYP1A2 enzyme, CYP2A13 efficiently catalyzed phenacetin deethylation with a Km value of 3.9 μM, which suggests that phenacetin is not a selective probe for dog CYP1A2 activity. Both dog CYP2A13 and CYP2A25 exhibited little or no catalytic activity toward other common cytochrome P450 probe substrates, including bupropion, amodiaquine, diclofenac, S-mephenytoin, bufuralol, dextromethorphan, midazolam, and testosterone. These results provided additional information about the selectivity of these commonly used probe substrates.

Liquid chromatography–tandem mass spectrometry method for measurement of nicotine N-glucuronide: A marker for human UGT2B10 inhibition

Nicotine is considered to be a specific substrate for UGT2B10, an isoform of human uridine diphosphate glucuronosyltransferase (UGT). In the present study, a sensitive and selective liquid chromatography/tandem mass spectrometry (LC-MS-MS) method for quantification of nicotine N-glucuronide in pooled human liver microsomal incubates was developed and validated. Proteins in a 200μL aliquot of incubation solution were precipitated by adding 40μL 35% perchloric acid. The overall extraction efficiency was greater than 98%. Nicotine N-glucuronide and internal standard were recorded using selected reaction monitoring in positive ion electrospray with ion transitions of m/z 339-163 and m/z 342-166, respectively. The linear calibration curve was obtained over the concentration range of 10-1000nM, with a lower limit of quantification of 10nM. The intra-day and inter-day precision (% CV) and accuracy (% bias) of the method were within 15% at all quality control levels. Nicotine glucuronide in processed samples was stable for 24h at room temperature and 48h at 4°C based on the stability experiments performed in this study. This established method was employed to evaluate the inhibitory effects of five target compounds including amitriptyline, hecogenin, imipramine, lamotrigine, and trifluoperazine on enzymatic activity of UGT2B10. IC(50) values for inhibition of nicotine N-glucuronidation by amitriptyline, imipramine, lamotrigine, and trifluoperazine were calculated. Trifluoperazine was found to be a non-substrate inhibitor for human UGT2B10.

In vitro assessment of metabolic drug–drug interaction potential of AZD2624, neurokinin-3 receptor antagonist, through cytochrome P450 enzyme identification, inhibition, and induction studies

AZD2624 was pharmacologically characterized as a NK3 receptor antagonist intended for treatment of schizophrenia. The metabolic drug–drug interaction potential of AZD2624 was evaluated in in vitro studies. CYP3A4 and CYP3A5 appeared to be the primary enzymes mediating the formation of pharmacologically active ketone metabolite (M1), whereas CYP3A4, CYP3A5, and CYP2C9 appeared to be the enzymes responsible for the formation of the hydroxylated metabolite (M2). The apparent Km values were 1.5 and 6.3 µM for the formation of M1 and M2 in human liver microsomes, respectively. AZD2624 exhibited an inhibitory effect on microsomal CYP3A4/5 activities with apparent IC50 values of 7.1 and 19.8 µM for midazolam and testosterone assays, respectively. No time-dependent inactivation of CYP3A4/5 activity (midazolam 1′-hydroxylation) by AZD2624 was observed. AZD2624 demonstrated weak to no inhibition of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP2D6. AZD2624 was not an inducer of CYP1A2 or CYP2B6. Although AZD2624-induced CYP3A4 activity in hepatocytes, the potential of AZD2624 to cause inductive drug interactions of this enzyme was low at relevant exposure concentration. Together with targeted low efficacious concentration, the results of this study demonstrated AZD2624 has a relatively low metabolic drug–drug interaction potential towards co-administered drugs. However, metabolism of AZD2624 might be inhibited when co-administrated with potent CYP3A4/5 inhibitors.

Effects of CYP3A Modulators on the Pharmacokinetics of Naloxegol

Naloxegol, a peripherally acting μ‐opioid receptor antagonist, was recently approved in the United States for the treatment of opioid‐induced constipation. This study evaluated the effects of CYP3A inhibition and induction on the pharmacokinetics, safety, and tolerability of naloxegol. Separate open‐label, nonrandomized, fixed‐sequence, 3‐period, 3‐treatment, crossover studies of naloxegol (25 mg by mouth [PO]) in the absence or presence of the inhibitors ketoconazole (400 mg PO) and diltiazem extended release (240 mg PO), or the inducer rifampin (600 mg PO) were conducted in healthy volunteers. Area under the curve (AUC∞) for naloxegol was increased with coadministration of either ketoconazole (12.9‐fold) or diltiazem (3.4‐fold) and decreased by 89% with coadministration of rifampin compared with AUC∞ for naloxegol alone. Naloxegol was generally safe and well tolerated when given alone or coadministered with the respective CYP3A modulators; 1 subject discontinued because of elevations in liver enzymes attributed to rifampin. The exposure of naloxegol was affected substantially by ketoconazole, diltiazem, and rifampin, suggesting that it is a sensitive in vivo substrate of CYP3A4.

In vitro metabolism of α7 neuronal nicotinic receptor agonist AZD0328 and enzyme identification for its N-oxide metabolite

AZD0328 was pharmacologically characterized as a α7 neuronal nicotinic receptor agonist intended for treatment of Alzheimer′s disease. In vitro AZD0328 cross species metabolite profile and enzyme identification for its N-oxide metabolite were evaluated in this study. AZD0328 was very stable in the human hepatocyte incubation, whereas extensively metabolized in rat, dog and guinea pig hepatocyte incubations. The N-oxidation metabolite (M6) was the only metabolite detected in human hepatocyte incubations, and it also appeared to be the major in vitro metabolic pathway in a number of preclinical species. In addition, N-glucuronide metabolite of AZD0328 was observed in human liver microsomes. Other metabolic pathways in the preclinical species include hydroxylation in azabicyclo octane or furopyridine part of the molecule. Pyridine N-methylation of AZD0328 (M2) was identified as a dog specific metabolite, not observed in human or other preclinical species. Multiple enzymes including CYP2D6, CYP3A4/5, FMO1 and FMO3 catalyzed AZD0328 metabolism. The potential for AZD0328 to be inhibited clinically by co-administered drugs or genetic polymorphism is relative low.