A Phase I, Open-Label, Fixed Sequence Study to Investigate the Effect of Cytochrome P450 2D6 Inhibition on the Pharmacokinetics of Ulotaront in Healthy Subjects.

BACKGROUND: Ulotaront is a novel psychotropic agent with agonist activity at trace amine-associated receptor 1 (TAAR1) and 5-hydroxytryptamine type 1A (5-HT1A) receptors in phase III clinical development for the treatment of schizophrenia. OBJECTIVE: This study aimed to investigate the effect of paroxetine, a strong cytochrome P450 (CYP) 2D6 inhibitor, on ulotaront pharmacokinetics (PK) in healthy volunteers. METHODS: Subjects received a single oral dose of 25 mg ulotaront on Day 1 and an oral dose of 20 mg paroxetine once daily from Days 5 to 10 to achieve steady-state plasma paroxetine levels. On Day 11, subjects received another single oral dose of 25 mg ulotaront, with continued daily oral dosing of 20 mg paroxetine from Days 11 to 14. All 24 subjects were CYP2D6 normal metabolizers. RESULTS: Coadministration of paroxetine increased ulotaront maximum observed plasma concentration (Cmax) and area under the plasma concentration-time curve from time zero to infinity (AUC∞) by 31% and 72%, respectively, and decreased ulotaront apparent clearance (CL/F) by approximately 42%. While coadministration of paroxetine increased AUC∞ of active but minor metabolite SEP-363854 by 32%, it had no effect on SEP-363854 Cmax, or on SEP-363854 to the ulotaront AUC from time zero to the last quantifiable concentration (AUClast) ratio. Based on the acceptable adverse event profile of ulotaront across previous phase II studies, the increase in ulotaront exposure is unlikely to be clinically meaningful. CONCLUSIONS: Weak drug-drug interactions were observed between ulotaront and the strong CYP2D6 inhibitor paroxetine; however, dose adjustment as a precondition when ulotaront is coadministered with strong CYP2D6 inhibitors or administered to CYP2D6 poor metabolizers should not be necessary.

Physiologically-Based Pharmacokinetic Models of CYP2D6 Substrate and Inhibitors Nebivolol, Cinacalcet and Mirabegron to Simulate Drug-Drug Interactions.

BACKGROUND AND OBJECTIVES: Index substrates and inhibitors to investigate the role of the polymorphic enzyme, cytochrome P450 (CYP) 2D6, in the metabolism of new compounds have been proposed by regulatory agencies. This work describes the development and verification of physiologically-based pharmacokinetic (PBPK) models for the CYP2D6-sensitive substrate, nebivolol and the index CYP2D6 inhibitors, mirabegron and cinacalcet. METHODS: PBPK models for nebivolol, mirabegron and cinacalcet were developed using in vitro and clinical data. The performance of the PBPK models was verified by comparing the simulated results against reported human systemic exposure and clinical drug-drug interactions (DDIs) studies. RESULTS: The exposure of nebivolol, cinacalcet and mirabegron predicted by the PBPK models was verified against pharmacokinetic data from 13, 3 and 9 clinical studies, respectively. For nebivolol, the predicted mean maximum plasma concentration (Cmax) and area under the plasma concentration-time (AUC) values in CYP2D6 extensive metaboliser subjects were within 0.9- to 1.49-fold of the observed values. In poor metaboliser CYP2D6 subjects, the predicted Cmax and AUC values were within 0.41- to 0.81-fold of observed values. For cinacalcet, the predicted Cmax and AUC values were within 0.97- to 1.32-fold of the observed data. For mirabegron, the predicted AUC values across all the studies investigated were within 0.71- to 1.88-fold of observed values. The PBPK model-predicted DDIs were in good agreement (within 2-fold) with observed DDIs in all verification studies (n = 8) assessed. The overall precision was 1.26 and 1.21 for Cmax and the AUC ratio, respectively. CONCLUSIONS: The developed PBPK models can be used to assess the DDI potential liability of new chemical entities that are substrates or inhibitors of CYP2D6.

Physiologically Based Pharmacokinetic Modeling to Assess the Impact of CYP2D6-Mediated Drug-Drug Interactions on Tramadol and O-Desmethyltramadol Exposures via Allosteric and Competitive Inhibition.

Tramadol is an opioid medication used to treat moderately severe pain. Cytochrome P450 (CYP) 2D6 inhibition could be important for tramadol, as it decreases the formation of its pharmacologically active metabolite, O-desmethyltramadol, potentially resulting in increased opioid use and misuse. The objective of this study was to evaluate the impact of allosteric and competitive CYP2D6 inhibition on tramadol and O-desmethyltramadol pharmacokinetics using quinidine and metoprolol as prototypical perpetrator drugs. A physiologically based pharmacokinetic model for tramadol and O-desmethyltramadol was developed and verified in PK-Sim version 8 and linked to respective models of quinidine and metoprolol to evaluate the impact of allosteric and competitive CYP2D6 inhibition on tramadol and O-desmethyltramadol exposure. Our results show that there is a differentiated impact of CYP2D6 inhibitors on tramadol and O-desmethyltramadol based on their mechanisms of inhibition. Following allosteric inhibition by a single dose of quinidine, the exposure of both tramadol (51% increase) and O-desmethyltramadol (52% decrease) was predicted to be significantly altered after concomitant administration of a single dose of tramadol. Following multiple-dose administration of tramadol and a single-dose or multiple-dose administration of quinidine, the inhibitory effect of quinidine was predicted to be long (≈42 hours) and to alter exposure of tramadol and O-desmethyltramadol by up to 60%, suggesting that coadministration of quinidine and tramadol should be avoided clinically. In comparison, there is no predicted significant impact of metoprolol on tramadol and O-desmethyltramadol exposure. In fact, tramadol is predicted to act as a CYP2D6 perpetrator and increase metoprolol exposure, which may necessitate the need for dose separation.

Characterization of the Effect of Upadacitinib on the Pharmacokinetics of Bupropion, a Sensitive Cytochrome P450 2B6 Probe Substrate.

This phase 1 study characterized the effect of multiple doses of upadacitinib, an oral Janus kinase 1 selective inhibitor, on the pharmacokinetics of the cytochrome P450 (CYP) 2B6 substrate bupropion. Healthy subjects (n = 22) received a single oral dose of bupropion 150 mg alone (study period 1) and on day 12 of a 16-day regimen of upadacitinib 30 mg once daily (study period 2). Serial blood samples for measurement of bupropion and hydroxybupropion plasma concentrations were collected in each study period. The central values (90% confidence intervals) for the ratios of change were 0.87 (0.79-0.96) for bupropion maximum plasma concentration (Cmax ), 0.92 (0.87-0.98) for bupropion area under the plasma-concentration time curve from time 0 to infinity (AUCinf ), 0.78 (0.72-0.85) for hydroxybupropion Cmax , and 0.72 (0.67-0.78) for hydroxybupropion AUCinf when administered with, relative to when administered without, upadacitinib. After multiple-dose administration of upadacitinib 30 mg once daily, upadacitinib mean ± SD AUC0-24 was 641 ± 177 ng·h/mL, and Cmax was 83.3 ± 30.7 ng/mL. These results confirm that upadacitinib has no relevant effect on pharmacokinetics of substrates metabolized by CYP2B6.

Drug interactions with Bruton's tyrosine kinase inhibitors: clinical implications and management.

Bruton's tyrosine kinase (BTK) plays an essential role in B-cell development, differentiation and B-cell receptor (BCR) signaling. The use of Bruton's tyrosine kinase inhibitors (BTKi) in the treatment of lymphoid malignancies has dramatically increased, owing to both impressive efficacy and ease of administration. However, BTKi have a range of drug-drug and drug-food interactions, which may alter drug efficacy and/or increase toxicity. Healthcare professionals should be aware of the probability of drug interactions with BTKi and make recommendations accordingly. In this article, we discuss the relevant drug-drug and drug-food interactions associated with ibrutinib, acalabrutinib, and zanubrutinib, and provide clinical practice recommendations for managing these interactions based on the available literature.

The Respective Roles of CYP3A4 and CYP2D6 in the Metabolism of Pimozide to Established and Novel Metabolites.

Pimozide is a dopamine receptor antagonist indicated for the treatment of Tourette syndrome. Prior in vitro studies characterized N-dealkylation of pimozide to 1,3-dihydro-1-(4-piperidinyl)-2H-benzimidazol-2-one (DHPBI) via CYP3A4 and, to a lesser extent, CYP1A2 as the only notable routes of pimozide biotransformation. However, drug-drug interactions between pimozide and CYP2D6 inhibitors and CYP2D6 genotype-dependent effects have since been observed. To reconcile these incongruities between the prior in vitro and in vivo studies, we characterized two novel pimozide metabolites: 5-hydroxypimozide and 6-hydroxypimozide. Notably, 5-hydroxypimozide was the major metabolite produced by recombinant CYP2D6 (Km ∼82 nM, V max ∼0.78 pmol/min per picomoles), and DHPBI was the major metabolite produced by recombinant CYP3A4 (apparent Km ∼1300 nM, V max ∼2.6 pmol/min per picomoles). Kinetics in pooled human liver microsomes (HLMs) for the 5-hydroxylation (Km ∼2200 nM, V max ∼59 pmol/min per milligram) and N-dealkylation (Km ∼3900 nM, V max ∼600 pmol/min per milligram) reactions were also determined. Collectively, formation of DHPBI, 5-hydroxypimozide, and 6-hydroxypimozide accounted for 90% of pimozide depleted in incubations of NADPH-supplemented pooled HLMs. Studies conducted in HLMs isolated from individual donors with specific cytochrome P450 isoform protein abundances determined via mass spectrometry revealed that 5-hydroxypimozide (r 2 = 0.94) and 6-hydroxypimozide (r 2 = 0.86) formation rates were correlated with CYP2D6 abundance, whereas the DHPBI formation rate (r 2 = 0.98) was correlated with CYP3A4 abundance. Furthermore, the HLMs differed with respect to their capacity to form 5-hydroxypimozide relative to DHPBI. Collectively, these data confirm a role for CYP2D6 in pimozide clearance via 5-hydroxylation and provide an explanation for a lack of involvement when only DHPBI formation was monitored in prior in vitro studies. SIGNIFICANCE STATEMENT: Current CYP2D6 genotype-guided dosing information in the pimozide label is discordant with available knowledge regarding the primary biotransformation pathways. Herein, we characterize the CYP2D6-dependent biotransformation of pimozide to previously unidentified metabolites. In human liver microsomes, formation rates for the novel metabolites and a previously identified metabolite were determined to be a function of CYP2D6 and CYP3A4 content, respectively. These findings provide a mechanistic basis for observations of CYP2D6 genotype-dependent pimozide clearance in vivo.

Influence of Zuojin Pill on the Metabolism of Venlafaxine in Vitro and in Rats and Associated Herb-Drug Interaction.

Venlafaxine (VEN), a first-line antidepressant, and Zuojin Pill (ZJP), a common Chinese herbal medicine consisting of Rhizoma Coptidis and Fructus Evodiae, have a high likelihood of combination usage in patients with depression with gastrointestinal complications. ZJP exhibits inhibitory effects on recombinant human cytochrome P450 isoenzymes (rhP450s), especially on CYP2D6, whereas VEN undergoes extensive metabolism by CYP2D6. From this perspective, we investigated the influence of ZJP on the metabolism of VEN in vitro and in rats for the first time. In this study, ZJP significantly inhibited the metabolism of VEN in both rat liver microsomes (RLM) and human liver microsomes (HLM); meanwhile, it inhibited the O-demethylation catalytic activity of RLM, HLM, rhCYP2D6*1/*1, and rhCYP2D6*10/*10, primarily through CYP2D6, with IC50 values of 129.9, 30.5, 15.4, and 2.3 µg/ml, respectively. Furthermore, the inhibitory effects of ZJP on hepatic metabolism and pharmacokinetics of VEN could also be observed in the pharmacokinetic study of rats. The area under drug concentration-time curve0-24 hour of VEN and its major metabolite O-desmethylvenlafaxine (ODV) increased by 39.6% and 22.8%, respectively. The hepatic exposure of ODV decreased by 57.2% 2 hours after administration (P = 0.014). In conclusion, ZJP displayed inhibitory effects on hepatic metabolism and pharmacokinetics of VEN in vitro and in rats mainly through inhibition of CYP2D6 activity. The human pharmacokinetic interaction between ZJP and VEN and its associated clinical significance needed to be seriously considered. SIGNIFICANCE STATEMENT: Zuojin Pill, a commonly used Chinese herbal medicine, demonstrates significant inhibitory effects on hepatic metabolism and pharmacokinetics of venlafaxine in vitro and in rats mainly through suppression of CYP2D6 activity. The human pharmacokinetic interaction between Zuojin Pill and venlafaxine and its associated clinical significance needs to be seriously considered.

A Scoping Review of the Evidence Behind Cytochrome P450 2D6 Isoenzyme Inhibitor Classifications.

The US Food and Drug Administration (FDA) lists 22 medications as clinical inhibitors of cytochrome P450 2D6 isoenzyme, with classifications of strong, moderate, and weak. It is accepted that strong inhibitors result in nearly null enzymatic activity, but reduction caused by moderate and weak inhibitors is less well characterized. The objective was to identify if the classification of currently listed FDA moderate and weak inhibitors is supported by publicly available primary literature. We conducted a literature search and reviewed product labels for area under the plasma concentration-time curve (AUC) fold-changes caused by inhibitors in humans and identified 89 inhibitor-substrate pairs. Observed AUC fold-change of the substrate was used to create an observed inhibitor classification per FDA-defined AUC fold-change thresholds. We then compared the observed inhibitor classification with the classification listed in the FDA Table of Inhibitors. We found 62% of the inhibitors within the pairs matched the listed FDA classification. We explored reasons for discordance and suggest modifications to the FDA table of clinical inhibitors for cimetidine, desvenlafaxine, and fluvoxamine.

Numerical Analysis of Time-Dependent Inhibition by MDMA.

Methylenedioxymethamphetamine (MDMA) is a known drug of abuse and schedule 1 narcotic under the Controlled Substances Act. Previous pharmacokinetic work on MDMA used classic linearization techniques to conclude irreversible mechanism-based inhibition of CYP2D6. The current work challenges this outcome by assessing the possibility of two alternative reversible kinetic inhibition mechanisms known as the quasi-irreversible (QI) model and equilibrium model (EM). In addition, progress curve experiments were used to investigate the residual metabolism of MDMA by liver microsomes and CYP2D6 baculosomes over incubation periods up to 30 minutes. These experiments revealed activity in a terminal linear phase at the fractional rates with respect to initial turnover of 0.0354 ± 0.0089 in human liver microsomes and 0.0114 ± 0.0025 in baculosomes. Numerical model fits to percentage of remaining activity (PRA) data were consistent with progress curve modeling results, wherein an irreversible inhibition pathway was found unnecessary for good fit scoring. Both QI and EM kinetic mechanisms fit the PRA data well, although in CYP2D6 baculosomes the inclusion of an irreversible inactivation pathway did not allow for convergence to a reasonable fit. The kinetic complexity accessible to numerical modeling has been used to determine that MDMA is not an irreversible inactivator of CYP2D6, and instead follows what can be generally referred to as slowly reversible inhibition. SIGNIFICANCE STATEMENT: The work herein describes the usage of computational models to delineate between irreversible and slowly reversible time-dependent inhibition. Such models are used in the paper to analyze MDMA and classify it as a reversible time-dependent inhibitor.

Physiologically Based Pharmacokinetic Modeling Suggests Limited Drug-Drug Interaction for Fesoterodine When Coadministered With Mirabegron.

5-Hydroxymethyl tolterodine (5-HMT; the active fesoterodine metabolite) is metabolized via the cytochrome P450 (CYP) 2D6 and CYP3A pathways. Mirabegron is a moderate CYP2D6 inhibitor and weak CYP3A inhibitor. Potential drug-drug interactions (DDIs) following coadministration of these 2 overactive bladder treatments were estimated using physiologically based pharmacokinetic models, developed and verified by comparing predicted and observed pharmacokinetic profiles from clinical studies. Models predicted and verified mirabegron and desipramine (CYP2D6 substrate) and 5-HMT and ketoconazole (strong CYP3A inhibitor) DDIs. Mirabegron model-predicted mean steady-state AUC and Cmax were within 11% of clinical observations. The predicted versus observed geometric mean ratio (GMR) of AUCinf for CYP2D6 substrates desipramine and metoprolol coadministered with mirabegron 100 or 160 mg once daily were 3.47 versus 3.41 and 2.97 versus 3.29, respectively, indicating that the mirabegron model can be used to predict clinical CYP2D6 inhibition. 5-HMT fractional clearance by CYP3A and CYP2D6 was verified from clinical DDI studies with a potent CYP3A4 inhibitor (ketoconazole) and inducer (rifampicin) in CYP2D6 extensive and poor metabolizers and with a moderate CYP3A inhibitor (fluconazole) in healthy volunteers. 5-HMT AUCinf and Cmax GMRs for fesoterodine DDIs were all predicted within 1.26-fold of clinical observation, providing verification for the fesoterodine substrate model. The predicted changes in 5-HMT AUCinf and Cmax ratios for 8 mg fesoterodine when coadministered with 50 mg mirabegron were 1.22-fold and 1.17-fold, respectively, relative to 8 mg fesoterodine given alone. This modest increase in 5-HMT exposures by approximately 20% is considered clinically insignificant and would not require fesoterodine dose adjustment when coadministered with mirabegron within approved daily-dose ranges.

Application of a physiologically based pharmacokinetic model for the prediction of mirabegron plasma concentrations in a population with severe renal impairment.

We previously verified a physiologically based pharmacokinetic (PBPK) model for mirabegron in healthy subjects using the Simcyp Simulator by incorporating data on the inhibitory effect on cytochrome P450 (CYP) 2D6 and a multi-elimination pathway mediated by CYP3A4, uridine 5'-diphosphate-glucuronosyltransferase (UGT) 2B7 and butyrylcholinesterase (BChE). The aim of this study was to use this PBPK model to assess the magnitude of drug-drug interactions (DDIs) in an elderly population with severe renal impairment (sRI), which has not been evaluated in clinical trials. We first determined the system parameters, and meta-analyses of literature data suggested that the abundance of UGT2B7 and the BChE activity in an elderly population with sRI was almost equivalent to and 20% lower than that in healthy young subjects, respectively. Other parameters, such as the CYP3A4 abundance, for an sRI population were used according to those built into the Simcyp Simulator. Second, we confirmed that the PBPK model reproduced the plasma concentration-time profile for mirabegron in an sRI population (simulated area under the plasma concentration-time curve (AUC) was within 1.5-times that of the observed value). Finally, we applied the PBPK model to simulate DDIs in an sRI population. The PBPK model predicted that the AUC for mirabegron with itraconazole (a CYP3A4 inhibitor) was 4.12-times that in healthy elderly subjects administered mirabegron alone, and predicted that the proportional change in AUC for desipramine (a CYP2D6 substrate) with mirabegron was greater than that in healthy subjects. In conclusion, the PBPK model was verified for the purpose of DDI assessment in an elderly population with sRI.

Genotype-sensitive reversible and time-dependent CYP2D6 inhibition in human liver microsomes.

Cytochrome P450 (CYP) 2D6 metabolizes a wide range of xenobiotics and is characterized by a huge interindividual variability. A recent clinical study highlighted differential magnitude of CYP inhibition as a function of CYP2D6 genotype. The aim of this study was to investigate the effect of CYP2D6 genotype on the inhibition of dextromethorphan O-demethylation by duloxetine and paroxetine in human liver microsomes (HLMs). The study focused on genotypes defined by the combination of two fully functional alleles (activity score 2, AS 2, n = 6), of one fully functional and one reduced allele (activity score 1.5, AS 1.5, n = 4) and of one fully functional and one non-functional allele (activity score 1, AS 1, n = 6), which all predict extensive metabolizer phenotype. Kinetic experiments showed that maximal reaction velocity was affected by CYP2D6 genotype, with a decrease in 33% of Vmax in AS 1 HLMs compared to AS 2 (P = 0.06). No difference in inhibition parameters Ki , KI and kinact was observed neither with the competitive inhibitor duloxetine nor with the time-dependent inhibitor paroxetine. Among the genotypes tested, we found no difference in absolute CYP2D6 microsomal levels with ELISA immunoquantification. Therefore, our results suggest that genotype-sensitive magnitude of drug-drug interactions recently observed in vivo is likely to be due to differential amounts of functional enzymes at the microsomal level rather than to a difference in inhibition potencies across genotypes, which motivates for further quantitative proteomic investigations of functional and variant CYP2D6 alleles.

How to Treat Hypertension in Venlafaxine-Medicated Patients-Pharmacokinetic Considerations in Prescribing Amlodipine and Ramipril.

BACKGROUND: Amlodipine (AMLO) and ramipril (RAMI) belong to the most prescribed drugs in patients with hypertension, a condition also encountered in depression. Venlafaxine may worsen hypertension because of noradrenergic properties. Although of special clinical relevance, data on pharmacokinetic interactions between AMLO, RAMI, and venlafaxine (VEN) are lacking. METHODS: Two TDM databases consisting of plasma concentrations of VEN and its active metabolite O-desmethylvenlafaxine (ODVEN) were analyzed. We considered a group of patients comedicated with AMLO, VAMLO (n = 22); a group comedicated with RAMI, VRAMI (n = 20); and a 4:1 control group age matched to the VAMLO group receiving VEN without confounding medications, V0 (n = 88). Plasma concentrations of VEN, ODVEN, and active moiety, AM (VEN + ODVEN); metabolic ratio (ODVEN/VEN); and dose-adjusted plasma concentrations (C/D) were compared using nonparametric tests. RESULTS: Groups did not differ in daily VEN dose, age, or sex. The metabolic ratio (ODVEN/VEN) was lower in the AMLO group (P = 0.029), whereas the RAMI group showed lower values for ODVEN (P = 0.029). All other parameters showed no significant differences. CONCLUSIONS: Significantly lower values for the metabolic ratio in the AMLO group are unlikely to be explained by cytochrome P450 (CYP) 3A4 and weak CYP2D6 inhibition by AMLO. Other factors such as differences in CYP2D6 polymorphisms and metabolizer status may better explain the findings. Ramipril showed modest effects with changes in ODVEN concentrations that did not remain significant after dose-adjusted comparisons.

Discontinuation and dose adjustment of metoprolol after metoprolol-paroxetine/fluoxetine co-prescription in Dutch elderly.

PURPOSE: Co-prescription of paroxetine/fluoxetine (a strong CYP2D6 inhibitor) in metoprolol (a CYP2D6 substrate) users is common, but data on the clinical consequences of this drug-drug interaction are limited and inconclusive. Therefore, we assessed the effect of paroxetine/fluoxetine initiation on the existing treatment with metoprolol on the discontinuation and dose adjustment of metoprolol among elderly. METHODS: We performed a cohort study using the University of Groningen IADB.nl prescription database (www.IADB.nl). We selected all elderly (≥60 years) who had ever been prescribed metoprolol and had a first co-prescription of paroxetine/fluoxetine, citalopram (weak CYP2D6 inhibitor), or mirtazapine (negative control) from 1994 to 2015. The exposure group was metoprolol and paroxetine/fluoxetine co-prescription, and the other groups acted as controls. The outcomes were early discontinuation and dose adjustment of metoprolol. Logistic regression was applied to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI). RESULTS: Combinations of metoprolol-paroxetine/fluoxetine, metoprolol-citalopram, and metoprolol-mirtazapine were started in 528, 673, and 625 patients, respectively. Compared with metoprolol-citalopram, metoprolol-paroxetine/fluoxetine was not significantly associated with the early discontinuation and dose adjustment of metoprolol (OR = 1.07, 95% CI:0.77-1.48; OR = 0.87, 95% CI:0.57-1.33, respectively). In comparison with metoprolol-mirtazapine, metoprolol-paroxetine/fluoxetine was associated with a significant 43% relative increase in early discontinuation of metoprolol (OR = 1.43, 95% CI:1.01-2.02) but no difference in the risk of dose adjustment. Stratified analysis by gender showed that women have a significantly high risk of metoprolol early discontinuation (OR = 1.62, 95% CI:1.03-2.53). CONCLUSION: Paroxetine/fluoxetine initiation in metoprolol prescriptions, especially for female older patients, is associated with the risk of early discontinuation of metoprolol.

The oral bioavailability, excretion and cytochrome P450 inhibition properties of epiberberine: an in vivo and in vitro evaluation.

Epiberberine (EPI) is a novel and potentially effective therapeutic and preventive agent for diabetes and cardiovascular disease. To evaluate its potential value for drug development, a specific, sensitive and robust high-performance liquid chromatography-tandem mass spectrometry assay for the determination of EPI in rat biological samples was established. This assay was used to study the pharmacokinetics, bioavailability and excretion of EPI in rats after oral administration. In addition, a cocktail method was used to compare the inhibition characteristics of EPI on cytochrome P450 (CYP450) isoforms in human liver microsomes (HLMs) and rat liver microsomes (RLMs). The results demonstrated that EPI was rapidly absorbed and metabolized after oral administration (10, 54 or 81 mg/kg) in rats, with Tmax of 0.37-0.42 h and T1/2 of 0.49-2.73 h. The Cmax and area under the curve values for EPI increased proportionally with the dose, and the oral absolute bioavailability was 14.46%. EPI was excreted mainly in bile and feces, and after its oral administration to rats, EPI was eliminated predominantly by the kidneys. A comparison of the current half-maximal inhibitory concentration and Ki values revealed that EPI demonstrated an obvious inhibitory effect on CYP2C9 and CYP2D6. Furthermore, its effect was stronger in HLM than in RLM, more likely to be a result of noncompetitive inhibition.

Prediction of drug-drug interactions using physiologically-based pharmacokinetic models of CYP450 modulators included in Simcyp software.

In recent years, physiologically based PharmacoKinetic (PBPK) modeling has received growing interest as a useful tool for the assessment of drug pharmacokinetics. It has been demonstrated to be informative and helpful to quantify the modification in drug exposure due to specific physio-pathological conditions, age, genetic polymorphisms, ethnicity and particularly drug-drug interactions (DDIs). In this paper, the prediction success of DDIs involving various cytochrome P450 isoenzyme (CYP) modulators namely ketoconazole (a competitive inhibitor of CYP3A), itraconazole (a competitive inhibitor of CYP3A), clarithromycin (a mechanism-based inhibitor of CYP3A), quinidine (a competitive inhibitor of CYP2D6), paroxetine (a mechanism-based inhibitor of CYP2D6), ciprofloxacin (a competitive inhibitor of CYP1A2), fluconazole (a competitive inhibitor of CYP2C9/2C19) and rifampicin (an inducer of CYP3A) were assessed using Simcyp® software. The aim of this report was to establish confidence in each CYP-specific modulator file so they can be used in the future for the prediction of DDIs involving new victim compounds. Our evaluation of these PBPK models suggested that they can be successfully used to evaluate DDIs in untested scenarios. The only noticeable exception concerned a quinidine inhibitor model that requires further improvement. Additionally, other important aspects such as model validation criteria were discussed.

Scaffold Hopping and Optimization of Maleimide Based Porcupine Inhibitors.

Porcupine is an O-acyltransferase that regulates Wnt secretion. Inhibiting porcupine may block the Wnt pathway which is often dysregulated in various cancers. Consequently porcupine inhibitors are thought to be promising oncology therapeutics. A high throughput screen against porcupine revealed several potent hits that were confirmed to be Wnt pathway inhibitors in secondary assays. We developed a pharmacophore model and used the putative bioactive conformation of a xanthine inhibitor for scaffold hopping. The resulting maleimide scaffold was optimized to subnanomolar potency while retaining good physical druglike properties. A preclinical development candidate was selected for which extensive in vitro and in vivo profiling is reported.

Discovery of indazole aldosterone synthase (CYP11B2) inhibitors as potential treatments for hypertension.

We report the discovery and hit-to-lead optimization of a structurally novel indazole series of CYP11B2 inhibitors. Benchmark compound 34 from this series displays potent inhibition of CYP11B2, high selectivity versus related steroidal and hepatic CYP targets, and lead-like physical and pharmacokinetic properties. On the basis of these and other data, the indazole series was progressed to lead optimization for further refinement.

Discovery of SMP-304, a novel benzylpiperidine derivative with serotonin transporter inhibitory activity and 5-HT1A weak partial agonistic activity showing the antidepressant-like effect.

We report the discovery of a novel benzylpiperidine derivative with serotonin transporter (SERT) inhibitory activity and 5-HT1A receptor weak partial agonistic activity showing the antidepressant-like effect. The 3-methoxyphenyl group and the phenethyl group of compound 1, which has weak SERT binding activity, but potent 5-HT1A binding activity, were optimized, leading to compound 35 with potent and balanced dual SERT and 5-HT1A binding activity, but also potent CYP2D6 inhibitory activity. Replacement of the methoxy group in the left part of compound 35 with a larger alkoxy group, such as ethoxy, isopropoxy or methoxy-ethoxy group ameliorated CYP2D6 inhibition, giving SMP-304 as a candidate. SMP-304 with serotonin uptake inhibitory activity and 5-HT1A weak partial agonistic activity, which could work as a 5-HT1A antagonist, displayed faster onset of antidepressant-like effect than a representative SSRI paroxetine in an animal model.

Enhanced oral bioavailability of metoprolol with gallic acid and ellagic acid in male Wistar rats: involvement of CYP2D6 inhibition.

BACKGROUND: Cytochrome P450-2D6 (CYP2D6), a member of the CYP450 mixed function oxidase system, is an important CYP isoform with regard to herbal-drug interactions and is responsible for the metabolism of nearly 25% of drugs. Until now, studies on the effects of various phytochemicals on CYP2D6 activity in vivo have been very rare. Gallic acid and ellagic acid are natural polyphenols which are widely distributed in fruits and medicinal plants. In the present study, the effects of gallic acid and ellagic acid pretreatment on intestinal transport and oral bioavailability of metoprolol were investigated. METHODS: The intestinal transport of metoprolol was assessed by conducting an in situ single pass intestinal perfusion (SPIP) study. The bioavailability study was conducted to evaluate the pharmacokinetic parameters of orally administered metoprolol in rats. RESULTS: After pretreatment with gallic acid and ellagic acid, no significant change in effective permeability of metoprolol was observed at the ileum part of rat intestine. A significant improvement in the peak plasma concentration (Cmax) and area under the serum concentration-time profile (AUC) and decrease in clearance were observed in rats pretreated with gallic acid and ellagic acid. CONCLUSIONS: Gallic acid and ellagic acid significantly enhanced the oral bioavailability of metoprolol by inhibiting CYP2D6-mediated metabolism in the rat liver. Hence, adverse herbal-drug interactions may result with concomitant ingestion of gallic acid and ellagic acid supplements and drugs that are CYP2D6 substrates. The clinical assessment of these interactions should be further investigated in human volunteers.