Drug interaction of efavirenz and midazolam: efavirenz activates the CYP3A-mediated midazolam 1'-hydroxylation in vitro

Heterotropic Activation of Cytochrome P450 3A4 by Perillyl Alcohol

Background/Objectives: Perillyl alcohol (POH), a monoterpene natural product derived from the essential oils of plants such as perilla (Perilla frutescens), is currently in phase I and II clinical trials as a chemotherapeutic agent. In this study, we investigated the effect of POH on cytochrome P450 (CYP) activity for evaluating POH-drug interaction potential. Methods: The investigation was conducted using pooled human liver microsomes (HLMs), recombinant CYP3A4 (rCYP3A4) enzymes, and human pluripotent stem cell-derived hepatic organoids (hHOs) employing liquid chromatography-tandem mass spectrometry. Results: POH inhibited the activities of CYP2A6 and CYP2B6 with Ki of 6.35 and 3.78 μM, respectively, whereas it stimulated CYP3A4 activity in pooled HLMs incubated with midazolam (MDZ). In a direct CYP inhibition assay using HLMs, activities of CYP2C9, CYP2C19, and CYP2E1 were also inhibited by POH, with IC50 values greater than 50 μM, but those of CYP1A2, CYP2C8, CYP2D6, and CYP3A4 (testosterone) were not significantly inhibited. In pooled HLMs, the Vmax/Km value of 1'-hydroxy MDZ, but not that of 4-hydroxy MDZ, was increased 2.7-fold by 100 μM POH compared with that in the absence of POH. Moreover, stimulation of MDZ 1'-hydroxylation by CYP3A4 was observed in hHOs and rCYP3A4 with cytochrome b5 but not rCYP3A4 without cytochrome b5. Furthermore, activation of CYP3A4-mediated metabolism by POH was observed in HLMs incubated with fimasartan but not atorvastatin, buspirone, donepezil, nifedipine, or tadalafil, suggesting a substrate-dependent activation of CYP3A4 by POH. Conclusions: POH inhibits CYP2A6 and CYP2B6, but it activates CYP3A4. These findings underscore the need for further evaluation of the interactions of clinical drugs with POH.

Exploring the Impact of Efavirenz on Aflatoxin B1 Metabolism: Insights from a Physiologically Based Pharmacokinetic Model and a Human Liver Microsome Study

Physiologically based pharmacokinetic (PBPK) models were utilized to investigate potential interactions between aflatoxin B1 (AFB1) and efavirenz (EFV), a non-nucleoside reverse transcriptase inhibitor drug and inducer of several CYP enzymes, including CYP3A4. PBPK simulations were conducted in a North European Caucasian and Black South African population, considering different dosing scenarios. The simulations predicted the impact of EFV on AFB1 metabolism via CYP3A4 and CYP1A2. In vitro experiments using human liver microsomes (HLM) were performed to verify the PBPK predictions for both single- and multiple-dose exposures to EFV. Results showed no significant difference in the formation of AFB1 metabolites when combined with EFV (0.15 µM) compared to AFB1 alone. However, exposure to 5 µM of EFV, mimicking chronic exposure, resulted in increased CYP3A4 activity, affecting metabolite formation. While co-incubation with EFV reduced the formation of certain AFB1 metabolites, other outcomes varied and could not be fully attributed to CYP3A4 induction. Overall, this study provides evidence that EFV, and potentially other CYP1A2/CYP3A4 perpetrators, can impact AFB1 metabolism, leading to altered exposure to toxic metabolites. The results emphasize the importance of considering drug interactions when assessing the risks associated with mycotoxin exposure in individuals undergoing HIV therapy in a European and African context.

High-throughput assay to simultaneously evaluate activation of CYP3A and the direct and time-dependent inhibition of CYP3A, CYP2C9, and CYP2D6 using liquid chromatography-tandem mass spectrometry

In the early stages of drug discovery, adequate evaluation of the potential drug-drug interactions (DDIs) of drug candidates is important. Several CYP3A activators are known to lead to underestimation of DDIs. These compounds affect midazolam 1'-hydroxylation but not midazolam 4-hydroxylation.We used both metabolic reactions of midazolam to evaluate the activation and inhibition of CYP3A activators simultaneously. For our CYP inhibition assay using cocktail probe substrates, simultaneous liquid chromatography-tandem mass spectrometry monitoring of 1'-hydroxymidazolam and 4-hydroxymidazolam for CYP3A was established in addition to monitoring of 4-hydroxydiclofenac and 1'-hydroxybufuralol for CYP2C9 and CYP2D6.The results of our cocktail inhibition assay were well correlated with those of a single inhibition assay, as were the estimated inhibition parameters for typical CYP3A inhibitors. In our assay, a proprietary compound that activated midazolam 1'-hydroxylation and tended to inhibit 4-hydroxylation was evaluated along with known CYP3A activators. All compounds were well characterised by comparison of the results of midazolam 1'- and 4-hydroxylation.In conclusion, our CYP cocktail inhibition assay can detect CYP3A activation and assess the direct and time-dependent inhibition potentials for CYP3A, CYP2C9, and CYP2D6. This method is expected to be very efficient in the early stages of drug discovery.

Effects of rifampicin, CYP2B6 and ABCB1 polymorphisms on efavirenz plasma concentration in Chinese patients living with HIV and tuberculosis

BACKGROUND

Tuberculosis (TB) is the leading opportunistic infection of people living with human immunodeficiency virus (HIV; PLWH). Cytochrome P450 (CYP) 2B6 and ATP-binding cassette sub-family B member 1 (ABCB1) are involved in the metabolism and transportation of efavirenz. The study was aimed to investigate the effects of rifampicin, CYP2B6 and ABCB1 polymorphisms on efavirenz exposure in Chinese PLWH co-infected with TB.

METHOD

PLWH were screened according to inclusion and exclusion criteria and divided into HIV group and HIV/TB group. Efavirenz plasma concentration (C₀) was determined, dose-adjusted concentration (C₀/D) was calculated, and genotypes of CYP2B6 516G>T, 785A>G, and ABCB1 2677G>T, 3435C>T were analyzed.

RESULTS

252 PLWH were enrolled, including 75 co-infected with TB and concomitant with rifampicin. Efavirenz C₀ and C₀/D were both higher in HIV group (1.94 μg/mL, 0.2007 (μg/ml)/(mg/kg/d)) compared with HIV/TB group (1.52 μg/mL, 0.1557 (μg/ml)/(mg/kg/d)) (p = .001). Efavirenz C₀/D was significantly higher in patients with variant genotypes of CYP2B6 516G>T and 785A>G (p<.001), and was significantly lower in HIV/TB group compared with HIV group among patients with CYP2B6 516 GG, TT, and 785 AA, AG genotypes (p < .05).

CONCLUSION

Efavirenz exposure is reduced by co-administration with rifampicin, and related to genetic polymorphisms of CYP2B6.

Molecular Insights into the Heterotropic Allosteric Mechanism in Cytochrome P450 3A4-Mediated Midazolam Metabolism

Cytochrome P450 3A4 (CYP3A4) is the main P450 enzyme for drug metabolism and drug-drug interactions (DDIs), as it is involved in the metabolic process of approximately 50% of drugs. A detailed mechanistic elucidation of DDIs mediated by CYP3A4 is commonly believed to be critical for drug optimization and rational use. Here, two typical probes, midazolam (MDZ, substrate) and testosterone (TST, allosteric effector), are used to investigate the molecular mechanism of CYP3A4-mediated heterotropic allosteric interactions, through conventional molecular dynamics (cMD) and well-tempered metadynamics (WT-MTD) simulations. Distance monitoring shows that TST can stably bind in two potential peripheral sites (Site 1 and Site 2) of CYP3A4. The binding of TST at these two sites can induce conformational changes in CYP3A4 flexible loops on the basis of conformational analysis, thereby promoting the transition of the MDZ binding mode and affecting the ratio of MDZ metabolites. According to the results of the residue interaction network, multiple allosteric communication pathways are identified that can provide vivid and applicable insights into the heterotropic allostery of TST on MDZ metabolism. Comparing the regulatory effects and the communication pathways, the allosteric effect caused by TST binding in Site 2 seems to be more pronounced than in Site 1. Our findings could provide a deeper understanding of CYP3A4-mediated heterotropic allostery at the atomic level and would be helpful for rational drug use as well as the design of new allosteric modulators.

Sensitive UHPLC-MS/MS quantification method for 4β- and 4α-hydroxycholesterol in human plasma for accurate CYP3A phenotyping

4β-Hydroxycholesterol (4β-OHC) is formed by CYP3A4 and CYP3A5 and has drawn attention as an endogenous phenotyping probe for CYP3A activity. However, 4β-OHC is also increased by cholesterol autooxidation occurring in vitro due to dysregulated storage and in vivo by oxidative stress or inflammation, independent of CYP3A activity. 4α-hydroxycholesterol (4α-OHC), a stereoisomer of 4β-OHC, is also formed via autooxidation of cholesterol, not by CYP3A, and thus may have clinical potential in reflecting the state of cholesterol autooxidation. In this study, we establish a sensitive method for simultaneous quantification of 4β-OHC and 4α-OHC in human plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Plasma samples were prepared by saponification, two-step liquid-liquid extraction, and derivatization using picolinic acid. Intense [M+H]+ signals for 4β-OHC and 4α-OHC di-picolinyl esters were monitored using electrospray ionization. The assay fulfilled the requirements of the US Food and Drug Administration guidance for bioanalytical method validation, with a lower limit of quantification of 0.5 ng/mL for both 4β-OHC and 4α-OHC. Apparent recovery rates from human plasma ranged from 88.2% to 101.5% for 4β-OHC, and 91.8% to 114.9% for 4α-OHC. Additionally, matrix effects varied between 86.2% and 117.6% for 4β-OHC, and between 89.5% and 116.9% for 4α-OHC. Plasma 4β-OHC and 4α-OHC concentrations in healthy volunteers, stage 3-5 chronic kidney disease (CKD) patients, and stage 5D CKD patients as measured by the validated assay were within the calibration ranges in all samples. We propose this novel quantification method may contribute to accurate evaluation of in vivo CYP3A activity.

Quantification of the Time Course of CYP3A Inhibition, Activation, and Induction Using a Population Pharmacokinetic Model of Microdosed Midazolam Continuous Infusion

BACKGROUND

Cytochrome P450 (CYP) 3A contributes to the metabolism of many approved drugs. CYP3A perpetrator drugs can profoundly alter the exposure of CYP3A substrates. However, effects of such drug-drug interactions are usually reported as maximum effects rather than studied as time-dependent processes. Identification of the time course of CYP3A modulation can provide insight into when significant changes to CYP3A activity occurs, help better design drug-drug interaction studies, and manage drug-drug interactions in clinical practice.

OBJECTIVE

We aimed to quantify the time course and extent of the in vivo modulation of different CYP3A perpetrator drugs on hepatic CYP3A activity and distinguish different modulatory mechanisms by their time of onset, using pharmacologically inactive intravenous microgram doses of the CYP3A-specific substrate midazolam, as a marker of CYP3A activity.

METHODS

Twenty-four healthy individuals received an intravenous midazolam bolus followed by a continuous infusion for 10 or 36 h. Individuals were randomized into four arms: within each arm, two individuals served as a placebo control and, 2 h after start of the midazolam infusion, four individuals received the CYP3A perpetrator drug: voriconazole (inhibitor, orally or intravenously), rifampicin (inducer, orally), or efavirenz (activator, orally). After midazolam bolus administration, blood samples were taken every hour (rifampicin arm) or every 15 min (remaining study arms) until the end of midazolam infusion. A total of 1858 concentrations were equally divided between midazolam and its metabolite, 1'-hydroxymidazolam. A nonlinear mixed-effects population pharmacokinetic model of both compounds was developed using NONMEM^®. CYP3A activity modulation was quantified over time, as the relative change of midazolam clearance encountered by the perpetrator drug, compared to the corresponding clearance value in the placebo arm.

RESULTS

Time course of CYP3A modulation and magnitude of maximum effect were identified for each perpetrator drug. While efavirenz CYP3A activation was relatively fast and short, reaching a maximum after approximately 2-3 h, the induction effect of rifampicin could only be observed after 22 h, with a maximum after approximately 28-30 h followed by a steep drop to almost baseline within 1-2 h. In contrast, the inhibitory impact of both oral and intravenous voriconazole was prolonged with a steady inhibition of CYP3A activity followed by a gradual increase in the inhibitory effect until the end of sampling at 8 h. Relative maximum clearance changes were +59.1%, +46.7%, -70.6%, and -61.1% for efavirenz, rifampicin, oral voriconazole, and intravenous voriconazole, respectively.

CONCLUSIONS

We could distinguish between different mechanisms of CYP3A modulation by the time of onset. Identification of the time at which clearance significantly changes, per perpetrator drug, can guide the design of an optimal sampling schedule for future drug-drug interaction studies. The impact of a short-term combination of different perpetrator drugs on the paradigm CYP3A substrate midazolam was characterized and can define combination intervals in which no relevant interaction is to be expected.

CLINICAL TRIAL REGISTRATION

The trial was registered at the European Union Drug Regulating Authorities for Clinical Trials (EudraCT-No. 2013-004869-14).

Effect of gastric pH and of a moderate CYP3A4 inducer on the pharmacokinetics of daridorexant, a dual orexin receptor antagonist

AIM

Daridorexant is a dual orexin receptor antagonist developed for the treatment of insomnia. The solubility of daridorexant is pH dependent and daridorexant has been shown to be a sensitive CYP3A4 substrate when co-administered with moderate CYP3A4 inhibitors. The purpose of this study was to assess the effect of an increased gastric pH on daridorexant pharmacokinetics (PK) and the extent of interaction when daridorexant is co-administered with a moderate CYP3A4 inducer.

METHODS

In this prospective, single-centre, randomized, open-label study, 24 male subjects consecutively received four treatments, i.e., daridorexant 50 mg single dose; famotidine 40 mg single dose + daridorexant 50 mg single dose; efavirenz 600 mg once a day (o.d.) during 10 days; and daridorexant 50 mg single dose + efavirenz 600 mg o.d. for 2 days. Plasma PK parameters of daridorexant were derived by noncompartmental analysis. Standard safety and tolerability evaluations were analysed descriptively.

RESULTS

When daridorexant administration was preceded by administration of famotidine, daridorexant C_max decreased by 39%, geometric means ratio (GMR) (90% confidence interval (90% CI)): 0.61 (0.50, 0.73). AUC_0-∞ remained unchanged. In the presence of steady-state efavirenz, daridorexant C_max , AUC_0-∞ , and t_½ decreased by approximately 35% (GMR (90% CI)): 0.65 (0.54, 0.78), 61% (0.39 (0.348, 0.44), and 35% (0.65 (0.58, 0.73), respectively. T_max remained unaffected. All treatments containing daridorexant were well tolerated.

CONCLUSION

Daridorexant 50 mg can be administered concomitantly with gastric pH modifiers or with moderate CYP3A4 inducers without dose adaptation based on efficacy observed at lower doses in Phase 3 studies.

Midazolam as a Probe for Drug-Drug Interactions Mediated by CYP3A4: Homotropic Allosteric Mechanism of Site-Specific Hydroxylation

We developed an efficient and sensitive probe for drug-drug interactions mediated by human CYP3A4 by using midazolam (MDZ) as a probe substrate. Using global analysis of four parameters over several experimental data sets, we demonstrate that the first MDZ molecule (MDZ1) binds with high affinity at the productive site near the heme iron and gives only hydroxylation at the 1 position (1OH). The second midazolam molecule (MDZ2) binds at an allosteric site at the membrane surface and perturbs the position and mobility of MDZ1 such that the minor hydroxylation product at the 4 position (4OH) is formed in a 1:2 ratio (35%). No increase in catalytic rate is observed after the second MDZ binding. Hence, the site of the 1OH:4OH metabolism ratio is a sensitive probe for drugs, such as progesterone, that bind with high affinity to the allosteric site and serve as effectors. We observe similar changes in the MDZ 1OH:4OH ratio in the presence of progesterone (PGS), suggesting a direct communication between the active and allosteric sites. Mutations introduced into the F-F' loop indicate that residues F213 and D214 are directly involved in allosteric interactions leading to MDZ homotropic cooperativity, and these same residues, together with L211, are involved in heterotropic allosteric interactions in which PGS is the effector and MDZ the substrate. Molecular dynamics simulations provide a mechanistic picture of the origin of this cooperativity. These results show that the midazolam can be used as a sensitive probe for drug-drug interactions in human P450 CYP3A4.

In vitro biotransformation of pharmaceuticals and pesticides by trout liver S9 in the presence and absence of carbamazepine

The aim of the present study was to develop (i) a technique for identifying metabolites of organic contaminants by using an in vitro system of trout S9 and liquid chromatography-high-resolution mass spectrometry-based identification method and (ii) to apply this technique to identify the interactive potential of carbamazepine on the formation rate of other metabolites. The pharmaceuticals carbamazepine and propranolol and the pesticides azoxystrobin, diazinon, and fipronil were selected as test contaminants. As a result, a total of ten metabolites were identified for the five parent substances, six of which were confirmed using reference standards. Metabolic reactions included hydroxylation, epoxidation, S-oxidation, and dealkylation. The metabolic transformation rate ranged from 0.2 to 3.5 pmol/mg protein/min/μmol substrate. In the binary exposure experiment with increasing carbamazepine concentration, the formation rates of diazinon and fipronil metabolites (MDI2 and MFP2, respectively) increased, while formation of metabolites of propranolol and azoxystrobin (MPR1, MPR2, MPR3, and MAZ1) slowed down. Meanwhile, S9 pre-exposed to carbamazepine produced diazoxon, a toxic metabolite of diazinon, and pyrimidinol, a less toxic metabolite, more rapidly. These results suggest that carbamazepine, a perennial environmental pollutant, might modulate the toxicity of other substances such as diazinon but further in vivo studies are needed.

Drug-drug interactions in the treatment for alcohol use disorders: A comprehensive review

Drug interactions are one of the most common causes of side effects in polypharmacy. Alcoholics are a category of patients at high risk of pharmacological interactions, due to the presence of comorbidities, the concomitant intake of several medications and the pharmacokinetic and pharmacodynamic interferences of ethanol. However, the data available on this issue are limited. These reasons often frighten clinicians when prescribing appropriate pharmacological therapies for alcohol use disorder (AUD), where less than 15% of patients receive an appropriate treatment in the most severe forms. The data available in literature regarding the relevant drug-drug interactions of the medications currently approved in United States and in some European countries for the treatment of AUD (benzodiazepines, acamprosate, baclofen, disulfiram, nalmefene, naltrexone and sodium oxybate) are reviewed here. The class of benzodiazepines and disulfiram are involved in numerous pharmacological interactions, while they are not conspicuous for acamprosate. The other drugs are relatively safe for pharmacological interactions, excluding the opioid withdrawal syndrome caused by the combination of nalmefene or naltrexone with an opiate medication. The information obtained is designed to help clinicians in understanding and managing the pharmacological interactions in AUDs, especially in patients under multi-drug treatment, in order to reduce the risk of a negative interaction and to improve the treatment outcomes.

Addressing Antiretroviral Therapy-Associated Drug-Drug Interactions in Patients Requiring Treatment for Opportunistic Infections in Low-Income and Resource-Limited Settings

An increasing number of human immunodeficiency virus (HIV)-infected patients are achieving virologic suppression on antiretroviral therapy (ART) limiting the use of primary and secondary antimicrobial prophylaxis. However, in low-income and resource-limited settings, half of those infected with HIV are unaware of their diagnosis, and fewer than 50% of patients on ART achieve virologic suppression. Management of comorbidities and opportunistic infections among patients on ART may lead to inevitable drug-drug interactions (DDIs) and even toxicities. Elderly patients, individuals with multiple comorbidities, those receiving complex ART, and patients living in low-income settings experience higher rates of DDIs. Management of these cytochrome P450-mediated, nonmediated, and drug transport system DDIs is critical in HIV-infected patients, particularly those in resource-limited settings with few options for ART. This article critically analyzes and provides recommendations to manage significant DDIs and drug toxicities in HIV-infected patients receiving ART.

Perspective: 4β-hydroxycholesterol as an emerging endogenous biomarker of hepatic CYP3A

A key goal in the clinical development of a new molecular entity is to quickly identify whether it has the potential for drug-drug interactions. In particular, confirmation of in vitro data in the early stage of clinical development would facilitate the decision making and inform future clinical pharmacology study designs. Plasma 4β-hydroxycholesterol (4β-HC) is considered as an emerging endogenous biomarker for cytochrome P450 3A (CYP3A), one of the major drug metabolizing enzymes. Although there are increasing reports of the use of 4β-HC in academic- and industry-sponsored clinical studies, a thorough review, summary and consideration of the advantages and challenges of using 4β-HC to evaluate changes in CYP3A activity has not been attempted. Herein, we review the biology of 4β-HC, its response to treatment with CYP3A inducers, inhibitors and mixed inducer/inhibitors in healthy volunteers and patients, the association of 4β-HC with other probes of CYP3A activity (e.g. midazolam, urinary cortisol ratios), and present predictive pharmacokinetic models. We provide recommendations for studying hepatic CYP3A activity in clinical pharmacology studies utilizing 4β-HC at different stages of drug development.

CYP3A activity: towards dose adaptation to the individual

INTRODUCTION

Co-medication, gene polymorphisms and co-morbidity are main causes for high variability in expression and function of the CYP3A isoenzymes. Pharmacokinetic variability is a major source of interindividual variability of drug effect and response of CYP3A substrates. While CYP3A genotyping is of limited use, direct testing of enzyme function ('phenotyping') may be more promising to achieve individualized dosing of CYP3A substrates.

AREAS COVERED

We will discuss available phenotyping strategies for CYP3A isoenzymes and causes of intra- and interindividual variability of CYP3A. The impact of phenotyping on the dose selection and pharmacokinetics of CYP3A substrates (docetaxel, irinotecan, tyrosine kinase inhibitors, ciclosporin, tacrolimus) are reviewed. Pubmed searches were conducted during March-November 2015 to retrieve articles related to CYP3A enzyme, phenotyping, drug interactions with CYP3A probe substrates, and phenotyping-guided dosing algorithms.

EXPERT OPINION

While ample data is available on the choice appropriate phenotyping drugs (midazolam, alfentanil, aplrazolam, buspirone, triazolam), less clinical trial data is available concerning strategies to usefully guide dosing in the clinical practice. Implementation into the clinical routine necessitates further research to identify (1) an easy-to-use and cheap test for CYP3A activity that (2) adequately predicts drug exposure to (3) allow a sound decision on dose adaptation and hence (4) improve clinical outcome and/or reduce the intensity or frequency of adverse drug effects.

A Screen of Approved Drugs Identifies the Androgen Receptor Antagonist Flutamide and Its Pharmacologically Active Metabolite 2-Hydroxy-Flutamide as Heterotropic Activators of Cytochrome P450 3A In Vitro and In Vivo

Once thought to be an artifact of microsomal systems, atypical kinetics with cytochrome P450 (CYP) enzymes have been extensively investigated in vitro and found to be substrate and species dependent. Building upon increasing reports of heterotropic CYP activation and inhibition in clinical settings, we screened a compound library of clinically approved drugs and various probe compounds to identify the frequency of heterotropism observed with different drug classes and the associated CYP enzymes thereof (1A2, 2C9, 2D6, and 3A4/5). Results of this screen revealed that the prescribed androgen receptor antagonist flutamide activated the intrinsic midazolam hydroxylase activity of CYP3A in human hepatic microsomes (66%), rat and human hepatocytes (36 and 160%, respectively), and in vivo in male Sprague-Dawley rats (>2-fold, combined area under the curve of primary rat in vivo midazolam metabolites). In addition, a screen of the pharmacologically active metabolite 2-hydroxy-flutamide revealed that this principle metabolite increased CYP3A metabolism of midazolam in human microsomes (30%) and hepatocytes (110%). Importantly, both flutamide and 2-hydroxy-flutamide demonstrated a pronounced increase in the CYP3A-mediated metabolism of commonly paired medications, nifedipine (antihypertensive) and amiodarone (antiarrhythmic), in multispecies hepatocytes (100% over baseline). These data serve to highlight the importance of an appropriate substrate and in vitro system selection in the pharmacokinetic modeling of atypical enzyme kinetics. In addition, the results of our investigation have illuminated a previously undiscovered class of heterotropic CYP3A activators and have demonstrated the importance of selecting commonly paired therapeutics in the in vitro and in vivo modeling of projected clinical outcomes.

Regulation of multidrug resistance proteins by genistein in a hepatocarcinoma cell line: impact on sorafenib cytotoxicity

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide. Sorafenib is the only drug available that improves the overall survival of HCC patients. P-glycoprotein (P-gp), Multidrug resistance-associated proteins 2 and 3 (MRP2 and 3) and Breast cancer resistance protein (BCRP) are efflux pumps that play a key role in cancer chemoresistance. Their modulation by dietary compounds may affect the intracellular accumulation and therapeutic efficacy of drugs that are substrates of these transporters. Genistein (GNT) is a phytoestrogen abundant in soybean that exerts its genomic effects through Estrogen-Receptors and Pregnane-X-Receptor (PXR), which are involved in the regulation of the above-mentioned transporters. We evaluated the effect of GNT on the expression and activity of P-gp, MRP2, MRP3 and BCRP in HCC-derived HepG2 cells. GNT (at 1.0 and 10 μM) increased P-gp and MRP2 protein expression and activity, correlating well with an increased resistance to sorafenib cytotoxicity as detected by the methylthiazole tetrazolium (MTT) assay. GNT induced P-gp and MRP2 mRNA expression at 10 but not at 1.0 μM concentration suggesting a different pattern of regulation depending on the concentration. Induction of both transporters by 1.0 μM GNT was prevented by cycloheximide, suggesting translational regulation. Downregulation of expression of the miR-379 by GNT could be associated with translational regulation of MRP2. Silencing of PXR abolished P-gp induction by GNT (at 1.0 and 10 μM) and MRP2 induction by GNT (only at 10 μM), suggesting partial mediation of GNT effects by PXR. Taken together, the data suggest the possibility of nutrient-drug interactions leading to enhanced chemoresistance in HCC when GNT is ingested with soy rich diets or dietary supplements.

Pre-systemic elimination of tilidine: localization and consequences for the formation of the active metabolite nortilidine

The therapeutic activity of tilidine, an opioid analgesic, is mainly related to its active metabolite nortilidine. Nortilidine formation mainly occurs during the high intestinal first-pass metabolism of tilidine by N-demethylation. Elimination of the active nortilidine to the inactive bisnortilidine is also mediated by N-demethylation and is supposed to take place in the liver, probably at a smaller rate. The aim of this study was the investigation of the pre-systemic elimination of tilidine using grapefruit juice (GFJ) as an intestinal CYP3A4 inhibitor and efavirenz (EFV) as a CYP3A4 activator. A randomized, open, placebo-controlled, cross-over study was conducted in 12 healthy volunteers using 100 mg tilidine solution p.o., regular strength GFJ 250 mL (3 times at 12-hr intervals) and EFV 400 mg (12 hr before tilidine administration). Tilidine, nortilidine and bisnortilidine in plasma and urine were quantified by a validated LC/MS/MS analysis. GFJ did not change any pharmacokinetic parameter of tilidine and its metabolites, which suggests that intestinal CYP3A4 does not contribute to the first-pass metabolism of tilidine. No effect of EFV on the pharmacokinetics of the active nortilidine was observed except a significant reduction of the terminal elimination half-life by 15%. Overall elimination (renal and metabolic clearances) was unaffected by every treatment. CYP3A4 does not seem to play a major role in tilidine first-pass and overall metabolism. Other unknown metabolites and their enzymes responsible for their formation have to be investigated as they account for the majority of renally excreted metabolites.

Clinical pharmacology of midazolam in neonates and children: effect of disease-a review

Midazolam is a benzodiazepine with rapid onset of action and short duration of effect. In healthy neonates the half-life (t_1/2) and the clearance (Cl) are 3.3-fold longer and 3.7-fold smaller, respectively, than in adults. The volume of distribution (Vd) is 1.1 L/kg both in neonates and adults. Midazolam is hydroxylated by CYP3A4 and CYP3A5; the activities of these enzymes surge in the liver in the first weeks of life and thus the metabolic rate of midazolam is lower in neonates than in adults. Midazolam acts as a sedative, as an antiepileptic, for those infants who are refractory to standard antiepileptic therapy, and as an anaesthetic. Information of midazolam as an anaesthetic in infants are very little. Midazolam is usually administered intravenously; when minimal sedation is required, intranasal administration of midazolam is employed. Disease affects the pharmacokinetics of midazolam in neonates; multiple organ failure reduces the Cl of midazolam and mechanical ventilation prolongs the t_1/2 of this drug. ECMO therapy increases t_1/2, Cl, and Vd of midazolam several times. The adverse effects of midazolam in neonates are scarce: pain, tenderness, and thrombophlebitis may occur. Respiratory depression and hypotension appear in a limited percentage of infants following intravenous infusion of midazolam. In conclusion, midazolam is a safe and effective drug which is employed as a sedative, as antiepileptic agent, for infants who are refractory to standard antiepileptic therapy, and as an anaesthetic.

Heterotropic activation of the midazolam hydroxylase activity of CYP3A by a positive allosteric modulator of mGlu5: in vitro to in vivo translation and potential impact on clinically relevant drug-drug interactions

Allosteric modulation of G protein-coupled receptors has gained considerable attention in the drug discovery arena because it opens avenues to achieve greater selectivity over orthosteric ligands. We recently identified a series of positive allosteric modulators (PAMs) of metabotropic glutamate receptor 5 (mGlu(5)) for the treatment of schizophrenia that exhibited robust heterotropic activation of CYP3A4 enzymatic activity. The prototypical compound from this series, 5-(4-fluorobenzyl)-2-((3-fluorophenoxy)methyl)-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine (VU0448187), was found to activate CYP3A4 to >100% of its baseline intrinsic midazolam (MDZ) hydroxylase activity in vitro; activation was CYP3A substrate specific and mGlu(5) PAM dependent. Additional studies revealed the concentration-dependence of CYP3A activation by VU0448187 in multispecies hepatic and intestinal microsomes and hepatocytes, as well as a diminished effect observed in the presence of ketoconazole. Kinetic analyses of the effect of VU0448187 on MDZ metabolism in recombinant P450 or human liver microsomes resulted in a significant increase in V(max) (minimal change in K(m)) and required the presence of cytochrome b5. The atypical kinetics translated in vivo, as rats receiving an intraperitoneal administration of VU0448187 prior to MDZ treatment demonstrated a significant increase in circulating 1- and 4-hydroxy- midazolam (1-OH-MDZ, 4-OH-MDZ) levels compared with rats administered MDZ alone. The discovery of a potent substrate-selective activator of rodent CYP3A with an in vitro to in vivo translation serves to illuminate the impact of increasing intrinsic enzymatic activity of hepatic and extrahepatic CYP3A in rodents, and presents the basis to build models capable of framing the clinical relevance of substrate-dependent heterotropic activation.