Quantitative Prediction of Drug-Drug Interactions Caused by CYP3A Induction Using Endogenous Biomarker 4β-Hydroxycholesterol

Evaluation of the CYP3A induction risk is important in early drug development stages. This study focused on 4β-hydroxycholesterol (4β-HC) as an endogenous biomarker of drug-drug interactions (DDIs) caused by CYP3A induction. We investigated a new approach using 4β-HC for quantitative prediction of DDIs caused by CYP3A induction based on the mechanistic static pharmacokinetic (MSPK) model. The induction ratio, i.e., the ratio of plasma 4β-HC or 4β-HC/cholesterol (4β-HC/C) with and without a coadministered CYP3A inducer, and the ratio of the area under the plasma concentration-time curve (AUCR), i.e., the ratio of the AUC of plasma CYP3A substrate drugs with and without a coadministered CYP3A inducer, were collected. The scaling factor (d) in the MSPK model was calculated from the induction ratio of 4β-HC or 4β-HC/C based on the systemic term in the MSPK model. The AUCR of 18 CYP3A substrates with and without coadministration of seven CYP3A inducers were then predicted by substituting the calculated d value into the MSPK model. This approach showed that approximately 84% of the predicted AUCR values were within a twofold range of the observed values, showing that this approach can be a good tool to quantitatively predict DDIs caused by CYP3A induction. SIGNIFICANCE STATEMENT: A concise approach to predict drug interactions with adequate accuracy is preferable in the early drug development stage. In this study, a new approach using 4β-hydroxycholesterol for quantitative prediction of drug-drug interactions caused by CYP3A induction was investigated. The predictability was verified using seven CYP3A inducers and 18 substrates.

Effects of Berberis vulgaris, and its active constituent berberine on cytochrome P450: a review

The cytochrome P450 (CYP450) family is crucial for metabolizing drugs and natural substances. Numerous compounds, such as pharmaceuticals and dietary items, can influence CYP activity by either enhancing or inhibiting these enzymes, potentially leading to interactions between drugs or between drugs and food. This research explores the impact of barberry and its primary component "berberine" on key human CYP450 enzymes. The text discusses the effects of this plant on the 12 primary human CYP450 enzymes, with summarized data presented in tables. Berberine exerts an influence on the function of various CYP450 isoforms, including CYP3A4/5, CYP2D6, CYP2C9, CYP2E1, CYP1A1/2, and most isoforms within the CYP2B subfamily. Given the significant role of these CYP450 isoforms in metabolizing commonly used drugs and endogenous substances, as well as activating procarcinogens into carcinogenic metabolites, the influence of barberry and its active constituent on these enzymes may impact the pharmacokinetics and toxicity profiles of various compounds. More specifically, regarding the crucial role of CYP2D6 and CYP3A4 in metabolizing clinically used drugs, and the inhibitory effects of berberine on these two CYP450 isoforms, it seems that the most important drug interaction of berberine that should be considered is related to its inhibitory effect on CYP2D6 and CYP3A4. In conclusion, due to the impact of barberry on multiple CYP450 isoforms, healthcare providers should conduct thorough consultations and investigations to ensure patient safety and prevent any potential adverse interactions before recommending the consumption of these herbs. Additional research, particularly clinical trials is crucial for preventing any potentially adverse interactions in patients who consume this herb.

Impacts of genetic polymorphisms and cancer cachexia on naldemedine pharmacokinetics and bowel movements in patients receiving opioid analgesics

BACKGROUND/OBJECTIVES

Clinical responses to naldemedine vary between individuals with advanced cancer. This is a prospective, single-center, observational study aimed to evaluate the influence of genetic polymorphisms and cachexia status on plasma naldemedine and clinical responses.

METHODS

Forty-eight patients being treated with naldemedine for opioid-induced constipation under treatment of cancer pain were enrolled. Plasma naldemedine concentrations were determined on the fourth day or later after administration of naldemedine, and the associations with genotypes, cachexia status, and clinical responses were assessed.

RESULTS

Cancer patients exhibited a large variation in the plasma naldemedine concentrations, and it was correlated with serum total protein level. Patients who were homozygous CYP3A5*3 had a higher plasma concentration of naldemedine than those with the *1 allele. ABCB1 genotypes tested in this study were not associated with plasma naldemedine. A negative correlation was observed between the plasma naldemedine concentration and 4β-hydroxycholesterol level. The plasma naldemedine concentration was lower in patients with refractory cachexia than in those with precachexia and cachexia. While serum levels of interleukin-6 (IL-6) and acute-phase proteins were higher in patients with refractory cachexia, they were not associated with plasma naldemedine. A higher plasma concentration of naldemedine, CYP3A5*3/*3, and an earlier naldemedine administration after starting opioid analgesics were related to improvement of bowel movements.

CONCLUSION

Plasma naldemedine increased under deficient activity of CYP3A5 in cancer patients. Cachectic patients with a higher serum IL-6 had a lower plasma naldemedine. Plasma naldemedine, related to CYP3A5 genotype, and the initiation timing of naldemedine were associated with improved bowel movements.

Cytochrome P450 activity in rheumatoid arthritis patients during continuous IL-6 receptor antagonist therapy

BACKGROUND

Inflammation suppresses cytochrome P450 (CYP) enzyme activity, and single-dose interleukin 6 receptor antagonists (anti-IL-6R) reverse this effect. Here, we assess the impact of continuous anti-IL-6R therapy in patients with rheumatoid arthritis.

METHODS

In a clinical pharmacokinetic trial, the Basel cocktail was administered before and after 3 and 12 weeks of anti-IL-6R therapy to assess CYP enzyme activity (registered in the ClinicalTrials.gov database (identifier NCT04842981) on April 13th, 2021). In a retrospective study, the 4β-hydroxycholesterol/cholesterol ratio was measured as a biomarker for CYP3A4 activity before and after 3 and 6 months of anti-IL-6R therapy. The control group was patients initiating a tumor necrosis factor alfa (TNF-α) inhibitor.

RESULTS

In the clinical pharmacokinetic trial (n = 3), midazolam metabolic ratio (CYP3A4) was inconclusive due to the limited sample size. Midazolam AUC and Cmax indicate a weak impact on CYP3A4 activity after 3 weeks of anti-IL-6R therapy compared to baseline (AUC geometric mean ratio (GMR): 0.80, 95% CI: 0.64-0.99 and Cmax GMR: 0.58, 95% CI: 0.37-0.91), which returns to baseline levels after 12 weeks of therapy (AUC GMR 1.02, 95% CI: 0.72-1.46 and Cmax GMR 1.03, 95% CI 0.72-1.47). No effect on the 4β-hydroxycholesterol/cholesterol ratio was observed in the retrospective study.

CONCLUSION

Based on sparse data from three patients, continuous anti-IL-6R therapy seems to cause an acute but transient increase in CYP3A4 activity in rheumatoid arthritis patients, which may be due to a normalization of the inflammation-suppressed CYP activity. Further studies are warranted to understand the mechanism behind this putative transient effect. Trial registration Registered in the ClinicalTrials.gov database (identifier NCT04842981) on April 13th, 2021.

Novel Approaches to Characterize Individual Drug Metabolism and Advance Precision Medicine

Interindividual variability in drug metabolism can significantly affect drug concentrations in the body and subsequent drug response. Understanding an individual's drug metabolism capacity is important for predicting drug exposure and developing precision medicine strategies. The goal of precision medicine is to individualize drug treatment for patients to maximize efficacy and minimize drug toxicity. While advances in pharmacogenomics have improved our understanding of how genetic variations in drug-metabolizing enzymes (DMEs) affect drug response, nongenetic factors are also known to influence drug metabolism phenotypes. This minireview discusses approaches beyond pharmacogenetic testing to phenotype DMEs-particularly the cytochrome P450 enzymes-in clinical settings. Several phenotyping approaches have been proposed: traditional approaches include phenotyping with exogenous probe substrates and the use of endogenous biomarkers; newer approaches include evaluating circulating noncoding RNAs and liquid biopsy-derived markers relevant to DME expression and function. The goals of this minireview are to 1) provide a high-level overview of traditional and novel approaches to phenotype individual drug metabolism capacity, 2) describe how these approaches are being applied or can be applied to pharmacokinetic studies, and 3) discuss perspectives on future opportunities to advance precision medicine in diverse populations. SIGNIFICANCE STATEMENT: This minireview provides an overview of recent advances in approaches to characterize individual drug metabolism phenotypes in clinical settings. It highlights the integration of existing pharmacokinetic biomarkers with novel approaches; also discussed are current challenges and existing knowledge gaps. The article concludes with perspectives on the future deployment of a liquid biopsy-informed physiologically based pharmacokinetic strategy for patient characterization and precision dosing.

Clinical Evaluation Based on a New Approach to Improve the Accuracy of 4β-Hydroxycholesterol Measurement as a Biomarker of CYP3A4 Activity

This study examines 4β-Hydroxycholesterol (4β-HC), which is considered to be a potential marker for the CYP3A4 induction of new chemical entities (NCEs) in drug development. To ensure the use of 4β-HC as a practical biomarker, it is necessary to accurately measure 4β-HC and demonstrate that CYP3A4 induction can be appropriately assessed, even for weak inducers. In clinical trials of NCEs, plasma is often collected with various anticoagulants, in some cases, the plasma is acidified, then stored for an extended period. In this study, we examined the effects of these manipulations on the measurement of 4β-HC, and based on the results, we optimized the plasma collection and storage protocols. We also found that a cholesterol oxidation product is formed when plasma is stored, and by monitoring the compound, we were able to identify when plasma was stored inappropriately. After evaluating the above, clinical drug-drug interaction (DDI) studies were conducted using two NCEs (novel retinoid-related orphan receptor γ antagonists). The weak CYP3A4 induction by the NCEs (which were determined based on a slight decline in the systemic exposure of a probe substrate (midazolam)), was detected by the significant increase in 4β-HC levels (more specifically, 4β-HC/total cholesterol ratios). Our new approach, based on monitoring a cholesterol oxidation product to identify plasma that is stored inappropriately, allowed for the accurate measurement of 4β-HC, and thus, it enabled the evaluation of weak CYP3A4 inducers in clinical studies without using a probe substrate.

The Role of CYP3A in Health and Disease

CYP3A is an enzyme subfamily in the cytochrome P450 (CYP) superfamily and includes isoforms CYP3A4, CYP3A5, CYP3A7, and CYP3A43. CYP3A enzymes are indiscriminate toward substrates and are unique in that these enzymes metabolize both endogenous compounds and diverse xenobiotics (including drugs); almost the only common characteristic of these compounds is lipophilicity and a relatively large molecular weight. CYP3A enzymes are widely expressed in human organs and tissues, and consequences of these enzymes' activities play a major role both in normal regulation of physiological levels of endogenous compounds and in various pathological conditions. This review addresses these aspects of regulation of CYP3A enzymes under physiological conditions and their involvement in the initiation and progression of diseases.

Correlations between 4β-hydroxycholesterol and hepatic and intestinal CYP3A4: protein expression, microsomal ex vivo activity, and in vivo activity in patients with a wide body weight range

PURPOSE

Variability in cytochrome P450 3A4 (CYP3A4) metabolism is mainly caused by non-genetic factors, hence providing a need for accurate phenotype biomarkers. Although 4β-hydroxycholesterol (4βOHC) is a promising endogenous CYP3A4 biomarker, additional investigations are required to evaluate its ability to predict CYP3A4 activity. This study investigated the correlations between 4βOHC concentrations and hepatic and intestinal CYP3A4 protein expression and ex vivo microsomal activity in paired liver and jejunum samples, as well as in vivo CYP3A4 phenotyping (midazolam) in patients with a wide body weight range.

METHODS

The patients (n = 96; 78 with obesity and 18 normal or overweight individuals) were included from the COCKTAIL-study (NCT02386917). Plasma samples for analysis of 4βOHC and midazolam concentrations, and liver (n = 56) and jejunal (n = 38) biopsies were obtained. The biopsies for determination of CYP3A4 protein concentration and microsomal activity were obtained during gastric bypass or cholecystectomy. In vivo CYP3A4 phenotyping was performed using semi-simultaneous oral (1.5 mg) and intravenous (1.0 mg) midazolam.

RESULTS

4βOHC concentrations were positively correlated with hepatic microsomal CYP3A4 activity (ρ = 0.53, p < 0.001), and hepatic CYP3A4 concentrations (ρ = 0.30, p = 0.027), but not with intestinal CYP3A4 concentrations (ρ = 0.18, p = 0.28) or intestinal microsomal CYP3A4 activity (ρ = 0.15, p = 0.53). 4βOHC concentrations correlated weakly with midazolam absolute bioavailability (ρ =  - 0.23, p = 0.027) and apparent oral clearance (ρ = 0.28, p = 0.008), but not with systemic clearance (ρ =  - 0.03, p = 0.81).

CONCLUSION

These findings suggest that 4βOHC concentrations reflect hepatic, but not intestinal, CYP3A4 activity. Further studies should investigate the potential value of 4βOHC as an endogenous biomarker for individual dose requirements of intravenously administered CYP3A4 substrate drugs.

TRIAL REGISTRATION

Clinical.

TRIALS

gov identifier: NCT02386917.

Recent advances in the translation of drug metabolism and pharmacokinetics science for drug discovery and development

Drug metabolism and pharmacokinetics (DMPK) is an important branch of pharmaceutical sciences. The nature of ADME (absorption, distribution, metabolism, excretion) and PK (pharmacokinetics) inquiries during drug discovery and development has evolved in recent years from being largely descriptive to seeking a more quantitative and mechanistic understanding of the fate of drug candidates in biological systems. Tremendous progress has been made in the past decade, not only in the characterization of physiochemical properties of drugs that influence their ADME, target organ exposure, and toxicity, but also in the identification of design principles that can minimize drug-drug interaction (DDI) potentials and reduce the attritions. The importance of membrane transporters in drug disposition, efficacy, and safety, as well as the interplay with metabolic processes, has been increasingly recognized. Dramatic increases in investments on new modalities beyond traditional small and large molecule drugs, such as peptides, oligonucleotides, and antibody-drug conjugates, necessitated further innovations in bioanalytical and experimental tools for the characterization of their ADME properties. In this review, we highlight some of the most notable advances in the last decade, and provide future perspectives on potential major breakthroughs and innovations in the translation of DMPK science in various stages of drug discovery and development.

Leveraging Human Plasma-Derived Small Extracellular Vesicles as Liquid Biopsy to Study the Induction of Cytochrome P450 3A4 by Modafinil

Preparations of plasma-derived small extracellular vesicles (sEVs) were deployed as liquid biopsy to study cytochrome P450 (CYP) 3A4 (CYP3A4) induction following modafinil 400 mg once daily × 14 days (young healthy volunteers, N = 10 subjects). Induction was confirmed using the 4β-hydroxycholesterol-to-cholesterol (4βHC/C) ratio, a plasma CYP3A4/5 biomarker, with a mean 2.1-fold increase (Day 15 vs. Day 1; 90% confidence interval (CI) = 1.8-2.3; P value = 0.0004). Proteomic analysis revealed the induction (mean Day 15 vs. Day 1 fold-increase (90% CI)) of both liver (1.3 (1.1-1.5), P value = 0.014) and nonliver (1.9 (1.6-2.2), P value = 0.04) sEV CYP3A4 protein expression. In CYP3A5 nonexpresser subjects, the baseline (pre-dose) 4βHC/C plasma ratio was more highly correlated with liver sEVs (r = 0.937, P value = 0.001) than nonliver sEVs (r = 0.619, P value = 0.101) CYP3A4 protein expression. When CYP3A5 expressers (CYP3A5*1/*3) were included, the correlation with liver sEVs (r = 0.761, P value = 0.011) and nonliver sEVs (r = 0.391, P value = 0.264) CYP3A4 protein was weaker. Although modafinil-induced changes in plasma 4βHC/C ratio did not correlate with sEVs CYP3A4 protein expression, the individual subject sEVs proteomic data were used successfully to predict victim drug (midazolam, triazolam, dextromethorphan, 17α-ethinylestradiol, and abemaciclib) area under the plasma concentration-time curve (AUC) ratios (AUCRs) following modafinil. Based on the AUCR values, modafinil was classified as a weak to moderate CYP3A4 inducer (vs. rifampicin). For the first time, it was possible to deploy plasma-derived sEVs to study CYP3A4 induction beyond rifampicin, a more potent CYP3A4 inducer.

Studies on CYP3A activity during the menstrual cycle as measured by urinary 6β-hydroxycortisol/cortisol

The 6β-OH-cortisol/cortisol ratio (6β-OHC/C) in urine is an endogenous marker of drug-metabolizing enzyme cytochrome P450 3A (CYP3A). The primary aim of this single center, prospective, non-interventional cohort study, was to investigate the variability of 6β-OHC/C during the menstrual cycle. In addition, possible associations between the CYP3A activity and sex hormones, gut microbiota metabolite trimethylamine-N-Oxide (TMAO) and microRNA-27b, respectively, were investigated. Serum and urinary samples from healthy, regularly menstruating women followed for two menstrual cycles were analyzed. Twenty-six complete menstrual cycles including follicular, ovulatory, and luteal phase were defined based on hormone analyses in serum. 6β-OHC/C were analyzed in urine and sex hormones, TMAO and miRNA-27b were analyzed in serum at the same time points. 6β-OHC/C did not vary between the follicular, ovulatory, or luteal phases. There was a difference in the relative miRNA-27b expression between the follicular and ovulatory phase (p = .03). A significant association was found between 6β-OHC/C and progesterone during the follicular (p = .005) and ovulatory (p = .01) phases (n = 26 for each phase). In addition, a significant association was found between the ratio and TMAO during the ovulatory (p = .02) and luteal (p = .002) phases. 6β-OHC/C and gut microbiota TMAO were significantly associated (p = .003) when evaluating all values, for all phases (n = 78). Interestingly, the finding of an association between 6β-OHC/C in urine and levels of TMAO in serum suggest that gut microbiota may affect CYP3A activity.

CYP3A Activity in End-of-Life Cancer Patients Measured by 4β-Hydroxycholesterol/cholesterol Ratio, in Men and Women

Simple Summary

The elimination of drugs by enzymes in the liver may be impaired in cancer patients that are close to death (end-of-life). This could cause unwanted side effects or lack of effect of drugs and compromise the quality of life in patients. Blood samples collected in 137 deceased end-of-life cancer patients were analyzed for the marker 4β-hydroxycholesterol/cholesterol (4β-OHC/C), representing the activity of the most important drug eliminating enzyme, CYP3A. In addition, samples from young (n = 280) and elderly (n = 30) controls were analyzed for 4β-OHC/C. The average 4β-OHC/C was higher in male and female end-of-life cancer patients than in young and elderly controls without cancer. This finding may suggest that the ability to eliminate drugs by CYP3A is maintained until end of life and that drugs metabolized by CYP3 may not need dose adjustment or discontinuation in cancer patients close to death.

Abstract

More than 50% of all drugs are metabolized by the cytochrome P450 3A enzyme (CYP3A). The aim of this study was to investigate if the CYP3A activity, measured by the endogenous marker 4β-hydroxycholesterol/cholesterol ratio (4β-OHC/C), is changed during the last weeks and days of life in men and women. To this end, serum samples from 137 deceased patients (median age 70 years) collected at a single time point 1–60 days before death, were analyzed and compared to 280 young (median 27 years), and 30 elderly (median age 70 years) non-cancer controls. There were no significant differences in the 4β-OHC/C ratio between men and women in end-of-life patients (p < 0.25). The median 4β-OHC/C was significantly higher in end-of-life male patients compared to both young (p < 0.0001) and elderly (p < 0.05) male controls. In a similar manner, 4β-OHC/C in end-of-life female patients was significantly higher compared to young and elderly female controls, p < 0.0001 and p < 0.001, respectively. There was no significant correlation between 4β-OHC/C and survival time. The results from this study suggest maintained CYP3A activity to the very last days of life and even a capacity of induction of the enzyme in end-of-life cancer patients.

Evaluation of Methods to Assess CYP3A Induction Risk in Clinical Practice Using in Vitro Induction Parameters

Established guidelines have recommended a number of methods based on in vitro data to assess the CYP3A induction risk of new chemical entities in clinical practice. In this study, we evaluated the predictability of various assessment methods. We collected in vitro parameters from a variety of literature that includes data on 19 batches of hepatocytes. Clinical CYP3A induction was predicted using 3 direct approaches-the fold-change, basic model, and mechanistic static models-as well as 5 correlation approaches, including the relative induction score (RIS) and the relative factor (RF) method. These predictions were then compared with data from 30 clinical inductions. Collected in vitro parameters varied greatly between hepatocyte batches. Direct assessment methods using fixed cut-off values provided a lot of false predictions due to hepatocyte variability, which can overlook induction risk or lead to needless clinical drug-drug interaction (DDI) studies. On the other hand, correlation methods with the cut-off values set for each batch of hepatocytes accurately predicted the induction risk. Among these, the AUC_u/inducer concentrations for half the maximum induction (EC₅₀) and the RF methods which use the area under the curve (AUC) of the unbound inducers for calculating induction potential showed an especially good correlation with clinical induction. Correlation methods were better at predicting clinical induction risk than the other methods, regardless of hepatocyte variability. The AUC_u/EC₅₀ and the RF methods in particular had a small number of false predictions, and can therefore be used to assess induction risk along with the other correlation methods recommended in guidelines.

Early or deferred initiation of efavirenz during rifampicin-based TB therapy has no significant effect on CYP3A induction in TB-HIV infected patients

Background and Purpose

In TB‐HIV co‐infection, prompt initiation of TB therapy is recommended but anti‐retroviral treatment (ART) is often delayed due to potential drug–drug interactions between rifampicin and efavirenz. In a longitudinal cohort study, we evaluated the effects of efavirenz/rifampicin co‐treatment and time of ART initiation on CYP3A induction.

Experimental Approach

Treatment‐naïve TB‐HIV co‐infected patients (n = 102) were randomized to efavirenz‐based‐ART after 4 (n = 69) or 8 weeks (n = 33) of commencing rifampicin‐based anti‐TB therapy. HIV patients without TB (n = 94) receiving efavirenz‐based‐ART only were enrolled as control. Plasma 4β‐hydroxycholesterol/cholesterol (4β‐OHC/Chol) ratio, an endogenous biomarker for CYP3A activity, was determined at baseline, at 4 and 16 weeks of ART.

Key Results

In patients treated with efavirenz only, median 4β‐OHC/Chol ratios increased from baseline by 269% and 275% after 4 and 16 weeks of ART, respectively. In TB‐HIV patients, rifampicin only therapy for 4 and 8 weeks increased median 4β‐OHC/Chol ratios from baseline by 378% and 576% respectively. After efavirenz/rifampicin co‐treatment, 4β‐OHC/Chol ratios increased by 560% of baseline (4 weeks) and 456% of baseline (16 weeks). Neither time of ART initiation, sex, genotype nor efavirenz plasma concentration were significant predictors of 4β‐OHC/Chol ratios after 4 weeks of efavirenz/rifampicin co‐treatment.

Conclusion and Implications

Rifampicin induced CYP3A more potently than efavirenz, with maximum induction occurring within the first 4 weeks of rifampicin therapy. We provide pharmacological evidence that early (4 weeks) or deferred (8 weeks) ART initiation during anti‐TB therapy has no significant effect on CYP3A induction.

LINKED ARTICLES

This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc

Serum 4β-hydroxycholesterol increases during fluconazole treatment

PURPOSE

The antifungal drugs ketoconazole and itraconazole reduce serum concentrations of 4β-hydroxycholesterol, which is a validated marker for hepatic cytochrome P450 (CYP) 3A4 activity. We tested the effect of another antifungal triazole agent, fluconazole, on serum concentrations of different sterols and oxysterols within the cholesterol metabolism to see if this inhibitory reaction is a general side effect of azole antifungal agents.

METHODS

In a prospective, double-blind, placebo-controlled, two-way crossover design, we studied 17 healthy subjects (nine men, eight women) who received 400 mg fluconazole or placebo daily for 8 days. On day 1 before treatment and on day 8 after the last dose, fasting blood samples were collected. Serum cholesterol precursors and oxysterols were measured by gas chromatography-mass spectrometry-selected ion monitoring and expressed as the ratio to cholesterol (R_sterol).

RESULTS

Under fluconazole treatment, serum R_lanosterol and R_24,25-dihydrolanosterol increased significantly without affecting serum cholesterol or metabolic downstream markers of hepatic cholesterol synthesis. Serum R_4β-, R_24S-, and R_27-hydroxycholesterol increased significantly.

CONCLUSION

Fluconazole inhibits the 14α-demethylation of lanosterol and 24,25-dihydrolanosterol, regulated by CYP51A1, without reduction of total cholesterol synthesis. The increased serum level of R_4β-hydroxycholesterol under fluconazole treatment is in contrast to the reductions observed under ketoconazole and itraconazole treatments. The question, whether this increase is caused by induction of CYP3A4 or by inhibition of the catabolism of 4β-hydroxycholesterol, must be answered by mechanistic in vitro and in vivo studies comparing effects of various azole antifungal agents on hepatic CYP3A4 activity.

The Effects of Weak and Strong CYP3A Induction by Rifampicin on the Pharmacokinetics of Five Progestins and Ethinylestradiol Compared to Midazolam

It is known that co‐administration of CYP3A inducers may decrease the effectiveness of oral contraceptives containing progestins as mono‐preparations or combined with ethinylestradiol. In a randomized clinical drug‐drug interaction study, we investigated the effects of CYP3A induction on the pharmacokinetics of commonly used progestins and ethinylestradiol. Rifampicin was used to induce CYP3A. The progestins chosen as victim drugs were levonorgestrel, norethindrone, desogestrel, and dienogest as mono‐products, and drospirenone combined with ethinylestradiol. Postmenopausal women (n = 12–14 per treatment group) received, in fixed sequence, a single dose of the victim drug plus midazolam without rifampicin, with rifampicin 10 mg/day (weak induction), and with rifampicin 600 mg/day (strong induction). The effects on progestin exposure were compared with the effects on midazolam exposure (as a benchmark). Unbound concentrations were evaluated for drugs binding to sex hormone binding globulin. Weak CYP3A induction, as confirmed by a mean decrease in midazolam exposure by 46%, resulted in minor changes in progestin exposure (mean decreases: 15–37%). Strong CYP3A induction, in contrast, resulted in mean decreases by 57–90% (mean decrease in midazolam exposure: 86%). Namely, the magnitude of the observed induction effects varied from weak to strong. Our data might provide an impetus to revisit the currently applied clinical recommendations for oral contraceptives, especially for levonorgestrel and norethindrone‐containing products, and they might give an indication as to which progestin could be used, if requested, by women taking weak CYP3A inducers—although it is acknowledged that the exact exposure‐response relationship for contraceptive efficacy is currently unclear for most progestins.

A Proof-of-Concept Study Evaluating the Phosphodiesterase 10A Inhibitor PF-02545920 in the Adjunctive Treatment of Suboptimally Controlled Symptoms of Schizophrenia

BACKGROUND

Effective treatments for managing suboptimal clinical responses to current therapy for schizophrenia remain a critical unmet need. Phosphodiesterase 10A (PDE10A) inhibition represents a mechanistically novel approach to the treatment of schizophrenia, with preclinical studies suggesting improvements in partially responsive symptoms could be achieved via adjunctive use of the PDE10A inhibitor PF-02545920. Therefore, the adjunctive safety, tolerability, pharmacokinetics, and efficacy of multiple repeat doses of PF-02545920 were investigated in a phase 1b study and subsequent phase 2 study.

METHODS

The phase 1b study randomized 37 adult patients with stable symptomatology and stable antipsychotic regimens within 3 cohorts. Study participants received ascending doses of PF-02545920 or placebo for 10 to 18 days. The phase 2 study randomized 240 outpatients with stable symptomatology but suboptimal response to current antipsychotic regimens 1:1:1 to PF-02545920 5 mg, PF-02545920 15 mg, or placebo every 12 hours for 12 weeks. The primary efficacy end point of the phase 2 study was change in the Positive and Negative Syndrome Scale total score from baseline to week 12, with changes in other clinical assessments as secondary end points.

RESULTS

Treatment was well tolerated, and observed PF-02545920 exposures were within the range predicted to be adequate for demonstrating efficacy. However, no significant differences in the prespecified efficacy end points between the 2 PF-02545920 treatment arms and placebo were observed.

CONCLUSIONS

Current data and results of a prior monotherapy study in which PF-02545920 failed to differentiate from placebo refute the hypothesis that PDE10A inhibitors have use as antipsychotic agents for schizophrenia.

Quantitative evaluation of hepatic and intestinal induction of CYP3A in clinical practice

This is the first report quantitatively evaluating the clinical induction of CYP3A in the liver and the intestine.To evaluate hepatic induction, we collected literature data on endogenous biomarkers of hepatic CYP3A induction which we then used to calculate the fold-induction (inducer-mediated change in biomarker level). Literature data on decreases in the area under the curve (AUC) of alfentanil, a CYP3A substrate, caused by CYP3A inducers were also collected. We used the hepatic intrinsic clearance of alfentanil to calculate the hepatic induction ratio (inducer-mediated change in intrinsic clearance). For intestinal induction, the intestinal bioavailability (F_g) of alfentanil was used to calculate the intestinal induction ratio. We determined in vivo maximum induction (E_max) and the average unbound plasma concentration (C_av,u) required for half the maximum induction (EC₅₀) for inducers using an E_max model analysis.In our results, fold-induction was comparable to the induction ratio at several inducer concentrations, and almost the maximum induction was achieved by a therapeutic dose. Induction ratios in the intestine were similar to the liver.Our findings suggest that, by knowing only hepatic induction ratios for common inducers, we can quantitatively predict the decreases in the AUC of substrates by CYP3A induction.

Validation of a 3-h Sampling Interval to Assess Variability in Cytochrome P450 3A Phenotype and the Impact of Induction and Mechanism-Based Inhibition Using Midazolam as a Probe Substrate

Background: Drug probe phenotyping is used extensively in academic and industry research to evaluate cytochrome P450 (CYP) phenotype in order to account for sources of between- and within- subject variability in metabolic clearance. In terms of application, CYP3A is the most important drug metabolizing enzyme the most frequently studied. Currently, phenotyping studies for CYP3A involve the administration of midazolam and collection of timed blood samples up to 24-48 hours in order to determine an area under the plasma concentration time curve (AUC). The key challenge that limits the use of midazolam-based phenotyping for CYP3A in academic research settings and preclude the use of this approach in a clinical setting is the logistical burden of collecting frequent blood samples for up to 48 h post dose following the administration of a probe drug ± an interacting drug. Aim: The current study sought to validate if a reduced sampling interval could be used to accurately define both between-subject variability in CYP3A phenotype and the magnitude of changes in CYP3A activity due to either induction or mechanism-based inhibition. Methods: The area under the curve (AUC) for midazolam was assessed under baseline, induction (7 days rifampin, 300 mg daily) and, following a washout period of 4 days, mechanism based inhibition (3 days clarithromycin, 250 mg daily) conditions in a cohort of 30 health males. The capacity of normalized reduced sampling interval AUCs measured over 0 to 1, 0 to 2, 0 to 3, and 0 to 4 h to accurately define the AUC_0-6 was evaluated with respect to precision (R2 for correlation), bias (slope of normalized correlation), agreement (Bland Altman analysis) and proportional bias (linear regression of Bland Altman parameters). Results: Robust concordance was observed between the AUC calculated from PK collection intervals of 0 to 3 and 0 to 6 h in terms of both the measurement of between-subject variability in midazolam AUC and changes in midazolam AUC due to induction and mechanism-based inhibition of CYP3A4. Conclusion: On this basis, it is proposed that a 3-h assessment of midazolam AUC (AUC_0-3) represents a viable strategy to reduce the logistical burden associated with the assessment of CYP3A phenotype.

Use of 4β-Hydroxycholesterol Plasma Concentrations as an Endogenous Biomarker of CYP3A Activity: Clinical Validation in Individuals With Type 2 Diabetes

The relevance of endogenous 4β-hydroxycholesterol (4β-OHC) plasma concentrations or of the 4β-OHC/total cholesterol concentration ratio (4β-OHC ratio) as surrogate markers of cytochrome P450 3A (CYP3A) activity was evaluated in individuals with (n = 38) or without (n = 35) type 2 diabetes (T2D). Midazolam was used as a comparator to validate exploratory measures of phenotypic CYP3A activity. Metabolic ratios of orally administered midazolam in nondiabetic and diabetic populations correlated significantly with 4β-OHC (r_s  = 0.64 and 0.48; P ≤ 0.003) and 4β-OHC ratio (r_s  = 0.69 and 0.46; P ≤ 0.003), respectively. Activity of CYP3A was lower in the T2D population compared with nondiabetic subjects; this decrease was reflected in 4β-OHC concentrations (24.33 vs. 12.58 ng/mL; P < 0.0001) and 4β-OHC ratio (0.13 vs. 0.09 (× 10⁴ ); P < 0.0002). These results suggest that 4β-OHC should be considered as a valid, convenient, and easy to use endogenous biomarker of CYP3A activity in patients.

Identification of the caffeine to trimethyluric acid ratio as a dietary biomarker to characterise variability in cytochrome P450 3A activity

PURPOSE

Cytochrome P450 (CYP) 3A plays an important role in the metabolism of many clinically used drugs and exhibits substantial between-subject variability (BSV) in activity. Current methods to assess variability in CYP3A activity have limitations and there remains a need for a minimally invasive clinically translatable strategy to define CYP3A activity. The purpose of this study was to evaluate the potential for a caffeine metabolic ratio to describe variability in CYP3A activity.

METHODS

The metabolic ratio 1,3,7-trimethyluric acid (TMU) to caffeine was evaluated as a biomarker to describe variability in CYP3A activity in a cohort (n = 28) of healthy 21 to 35-year-old males. Midazolam, caffeine, and TMU concentrations were assessed at baseline and following dosing of rifampicin (300 mg daily) for 7 days.

RESULTS

At baseline, correlation coefficients for the relationship between apparent oral midazolam clearance (CL/F) with caffeine/TMU ratio measured at 3, 4, and 6 h post dose were 0.82, 0.79, and 0.65, respectively. The strength of correlations was retained post rifampicin dosing; 0.72, 0.87, and 0.82 for the ratios at 3, 4, and 6 h, respectively. Weaker correlations were observed between the change in midazolam CL/F and change in caffeine/TMU ratio post/pre-rifampicin dosing.

CONCLUSION

BSV in CYP3A activity was well described by caffeine/TMU ratios pre- and post-induction. The caffeine/TMU ratio may be a convenient tool to assess BSV in CYP3A activity, but assessment of caffeine/TMU ratio alone is unlikely to account for all sources of variability in CYP3A activity.

Genotyping and phenotyping CYP3A4\CYP3A5: no association with antiplatelet effect of clopidogrel

The objective of this study was to determine the impact of polymorphism of CYP3A subfamily isoenzymes (allelic variants of CYP3A4*22 and CYP3A5*3) on the efficacy clopidogrel in patients with an acute coronary syndrome (ACS), who have undergone percutaneous coronary intervention (PCI). Platelet activity was determined on a VerifyNow P2Y12 test system in 81 patients with ACS aged 37-91 who had PCI. The activity of CYP3A4/5 was expressed as the ratio of the concentrations of cortisol and 6β-hydroxycortisol was performed by using high performance liquid chromatography. Genotyping was performed by using real-time polymerase real-time chain reaction. The frequencies for the CYP3A5 gene, rs 776746, were identified as follows: 77 (95.1%)-CC, 4 (4.9%)-CT; the allele frequencies by loci for the CYP3A4, rs rs35599367, were as follows: 78 (96.3%)-GG, 3 (3.7%)-AG. There was no statistically significant genotype-dependent difference between the presence of a minor T and G alleles and the presence of clopidogrel resistance (OR 3.53; 95% CI 0.46-26.94; p = 0.233 and p = 0.443, respectively). The average level of the metabolic relationship (6β-hydroxycortisol/cortisol) between the clopidogrel-resistant group and the normal platelet reactivity group was not statistically significantly different: 3.3 ± 2.8 versus 3.2 ± 3.2; p = 0.947. So, the activity of CYP3A4/5 was not related to platelet aggregation rates in this model. Genotyping and phenotyping CYP3A4\CYP3A5 does not predict the antiplatelet effect of clopidogrel. More extensive research is required to establish their clinical relevance.

Effect of Grapefruit Juice Intake on Serum Level of the Endogenous CYP3A4 Metabolite 4β-Hydroxycholesterol-an Interaction Study in Healthy Volunteers

4β-Hydroxycholesterol (4βOHC) is an endogenous CYP3A4 metabolite. However, it is unclear whether circulating levels of 4βOHC may reflect hepatic CYP3A4 activity or both hepatic and intestinal enzyme activity. The aim of this study was to investigate the effect of grapefruit juice, regarded to be a selective intestinal CYP3A4 inhibitor, on serum 4βOHC levels in healthy volunteers. The participants (n = 22) consumed grapefruit juice twice daily for 3 weeks followed by a 2-week washout period. Blood samples for measurements of 4βOHC and the non-CYP3A4-derived oxysterols 24-hydroxycholesterol (24OHC) and 27-hydroxycholesterol (27OHC), as well as lathosterol and total cholesterol, were drawn on days 0, 7, 21, and 35. Median individual changes (ratios) in cholesterol-corrected 4βOHC levels from baseline to weeks 1, 3, and 5 were 0.94 (P = 0.2), 0.98 (P = 0.3), and 0.97 (P = 0.9), respectively. In comparison, median changes (ratios) in cholesterol-corrected levels of 24OHC at the same points were 1.01 (P = 0.6), 0.98 (P = 0.3), and 0.99 (P = 0.5), and of 27OHC 1.01 (P = 0.8), 0.97 (P = 0.5), and 0.99 (P = 0.2). Surprisingly, serum concentration of cholesterol was significantly reduced by approximately 5% after 1 week (P = 0.03), while median cholesterol-corrected levels of lathosterol increased significantly and persistently by approximately 15% during the whole 5-week period (P < 0.04). In conclusion, the present findings suggest that intestinal CYP3A4 is not relevant for the overall formation of 4βOHC in healthy volunteers. The fact that grapefruit juice altered cholesterol homeostasis should be further investigated.

Modeling and simulation of the endogenous CYP3A induction marker 4β-hydroxycholesterol during enasidenib treatment

Background

Enasidenib (IDHIFA^®, AG-221) is a first-in-class, targeted inhibitor of mutant IDH2 proteins for treatment of relapsed or refractory acute myeloid leukemia. This was a Phase I/II study evaluating safety, efficacy, and pharmacokinetics/pharmacodynamics (PK/PD) of orally administered enasidenib in subjects with advanced hematologic malignancies with an IDH2 mutation.

Methods

Blood samples for PK and PD assessment were collected. A semi-mechanistic nonlinear mixed effect PK/PD model was successfully developed to characterize enasidenib plasma PK and to assess enasidenib-induced CYP3A activity.

Results

The PK model showed that enasidenib plasma concentrations were adequately described by a one-compartment model with first-order absorption and elimination; the PD model showed a high capacity to induce CYP3A (E_max=7.36) and a high enasidenib plasma concentration to produce half of maximum CYP3A induction (EC₅₀ =31,400 ng/mL). Monte Carlo simulations based on the final PK/PD model showed that at 100 mg once daily dose there was significant drug accumulation and a maximum of three-fold CYP3A induction after multiple doses. Although the EC₅₀ value for CYP3A induction by enasidenib is high, CYP3A induction was observed due to significant drug accumulation.

Conclusion

CYP3A induction following enasidenib dosing should be considered when prescribing concomitant medication metabolized via this pathway.

4β-Hydroxycholesterol as an Endogenous Biomarker for CYP3A Activity: Literature Review and Critical Evaluation

A number of cytochrome P450 (CYP)3A phenotyping probes have been used to characterize the drug interaction potential of new molecular entities; of these, midazolam has emerged as the gold standard. Recently, plasma 4β-hydroxycholesterol (4β-OHC), the metabolite of CYP3A-mediated cholesterol metabolism, has been championed as an endogenous biomarker for CYP3A, particularly during chronic conditions where CYP3A activity is altered by disease and in long-term treatment studies where midazolam administration is not optimal. Multiple studies in humans have shown that 4β-OHC can qualitatively differentiate among weak, moderate, and potent CYP3A induction when an inducer, typically rifampin, is administered for up to 2 weeks. Conversely, longer durations of CYP3A inhibitor administration (≥1 month) appear to be necessary to differentiate among weak, moderate, and potent CYP3A inhibitors. A number of studies have reported statistically significant linear relationships between 4β-OHC plasma concentrations (and 4β-OHC:cholesterol ratios) and midazolam clearance. However, sufficiently powered studies assessing the ability of 4β-OHC or 4β-OHC:cholesterol ratios to measure CYP3A activity (ie, predictive performance) have not been conducted to date. Additional limitations associated with 4β-OHC phenotyping include inability to detect acute changes in CYP3A activity, uncertainty with regard to its intestinal formation, ambiguity surrounding the role of CYP3A5 in its metabolism, and lack of clarity regarding the role of transporters in its disposition. As such, the data do not support the use of 4β-OHC or 4β-OHC:cholesterol ratios as an endogenous biomarker for CYP3A activity.

Effect of multiple-dose osimertinib on the pharmacokinetics of simvastatin and rosuvastatin

AIM

We report on two Phase 1, open-label, single-arm studies assessing the effect of osimertinib on simvastatin (CYP3A substrate) and rosuvastatin (breast cancer resistance protein substrate [BCRP] substrate) exposure in patients with advanced epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer who have progressed after treatment with an EGFR tyrosine kinase inhibitor, to determine, upon coadministration, whether osimertinib could affect the exposure of these agents.

METHODS

Fifty-two patients in the CYP3A study (pharmacokinetic [PK] analysis, n = 49), and 44 patients in the BCRP study were dosed (PK analysis, n = 44). In the CYP3A study, patients received single doses of simvastatin 40 mg on Days 1 and 31, and osimertinib 80 mg once daily on Days 3-32. In the BCRP study, single doses of rosuvastatin 20 mg were given on Days 1 and 32, and osimertinib 80 mg once daily on Days 4-34.

RESULTS

Geometric least squares mean (GLSM) ratios (90% confidence intervals) of simvastatin plus osimertinib for area under the plasma concentration-time curves from zero to infinity (AUC) were 91% (77-108): entirely contained within the predefined no relevant effect limits, and C_max of 77% (63, 94) which was not contained within the limits. GLSM ratios of rosuvastatin plus osimertinib for AUC were 135% (115-157) and C_max were 172 (146, 203): outside the no relevant effect limits.

CONCLUSIONS

Osimertinib is unlikely to have any clinically relevant interaction with CYP3A substrates and has a weak inhibitory effect on BCRP. No new safety concerns were identified in either study.

The effect of itraconazole and rifampicin on the pharmacokinetics of osimertinib

AIMS

We investigated the effects of a strong CYP3A4 inhibitor (itraconazole) or inducer (rifampicin) on the pharmacokinetics of the epidermal growth factor receptor-tyrosine kinase inhibitor osimertinib, in patients with advanced non-small cell lung cancer in two Phase I, open-label, two-part clinical studies. Part one of both studies is reported.

METHODS

In the itraconazole study (NCT02157883), patients received single-dose osimertinib 80 mg on Days 1 and 10 and itraconazole (200 mg twice daily) on Days 6-18 orally. In the rifampicin study (NCT02197247), patients received osimertinib 80 mg once daily on Days 1-77 and rifampicin 600 mg once daily on Days 29-49.

RESULTS

In the itraconazole study (n = 36), the geometric least squares mean (GMLSM) ratios (osimertinib plus itraconazole/osimertinib alone) for Cmax and AUC were 80% (90% CI 73, 87) and 124% (90% CI 115, 135), respectively, below the predefined no-effect upper limit of 200%. In the rifampicin study (n = 40), the GMLSM ratios (osimertinib plus rifampicin/osimertinib alone) for Css,max and AUCτ were 27% (90% CI 24, 30) and 22% (90% CI 20, 24), respectively, below the predefined no-effect lower limit of 50%. The induction effect of rifampicin was apparent within 7 days of initiation; osimertinib Css,max and AUCτ values returned to pre-rifampicin levels within 3 weeks of rifampicin discontinuation. No new osimertinib safety findings were observed.

CONCLUSIONS

Osimertinib can be co-administered with CYP3A4 inhibitors, but strong CYP3A inducers should be avoided if possible.

Population Pharmacokinetic Modeling of JNJ-53718678, a Novel Fusion Inhibitor for the Treatment of Respiratory Syncytial Virus: Results from a Phase I, Double-Blind, Randomized, Placebo-Controlled First-in-Human Study in Healthy Adult Subjects

BACKGROUND

JNJ-53718678 is a potent small-molecule inhibitor of the F-glycoprotein-mediated complex membrane fusion process of the respiratory syncytial virus. Here, we report the pharmacokinetics, the population pharmacokinetic modeling, and the safety and tolerability of JNJ-53718678 from the first-in-human, double-blind, randomized, placebo-controlled phase I study.

METHODS

Healthy subjects were randomized (6:3) into five single-dose groups (25-1000 mg) or three multiple-dose groups [250 mg every 24 h (q24h), 500 mg q24h, 250 mg every 12 h; fed conditions for 8 days] to receive JNJ-53718678 or placebo. Blood and urine samples were collected at several timepoints up to 72 h after intake of JNJ-53718678 and analyzed using validated liquid chromatography-mass spectrometry methods. A population pharmacokinetic model was developed and validated.

RESULTS

Peak plasma concentrations of JNJ-53718678 increased with increasing single (159 ± 54.9 to 6702 ± 1733 ng/mL) and multiple (on day 8, 1528 ± 256 to 2655 ± 591 ng/mL) doses. Steady-state conditions were reached on day 2 of the 8-day dosing regimen. Less than 4% of JNJ-53718678 was excreted in urine across all dose groups. Mean exposure of JNJ-53718678 was 7% lower in the fed state compared with the fasted state at the same dose. A two-compartment model with first-order absorption with parallel linear and non-linear elimination best described the pharmacokinetics of JNJ-53718678. No covariate effects were observed.

CONCLUSIONS

A population pharmacokinetic model that describes the concentration data well with good precision of all parameter estimates was developed and validated. JNJ-53718678 was well tolerated at all single and multiple doses studied.

The cytochrome P450 isoenzyme and some new opportunities for the prediction of negative drug interaction in vivo

Cytochrome (CYP) 450 isoenzymes are the basic enzymes involved in Phase I biotransformation. The most important role in biotransformation belongs to CYP3A4, CYP2D6, CYP2C9, CYP2C19 and CYP1A2. Inhibition and induction of CYP isoenzymes caused by drugs are important and clinically relevant pharmacokinetic mechanisms of drug interaction. Investigation of the activity of CYP isoenzymes by using phenotyping methods (such as the determination of the concentration of specific substrates and metabolites in biological fluids) during drug administration provides the prediction of negative side effects caused by drug interaction. In clinical practice, the process of phenotyping of CYP isoenzymes and some endogenous substrates in the ratio of cortisol to 6β-hydroxycortisol in urine for the evaluation of CYP3A4 activity has been deemed to be a quite promising, safe and minimally invasive method for patients nowadays.

Identification of ω- or (ω-1)-Hydroxylated Medium-Chain Acylcarnitines as Novel Urinary Biomarkers for CYP3A Activity

Quantitative models of endogenous metabolites are useful in predicting CYP3A-mediated drug-drug interactions. This study aimed to identify novel predictive markers for the magnitude of CYP3A induction and inhibition in male and female subjects using an untargeted metabolomics approach. Here we report five ω- or (ω-1)-hydroxylated medium-chain acylcarnitines as novel CYP3A4 markers. As CYP4 catalyzes the ω- or (ω-1)-hydroxylation of various medium-chain fatty acids (MCFAs), recombinant enzyme assays were used to determine the ω- and (ω-1)-hydroxylation activities of CYP3A4, CYP4A11, and CYP4F2. CYP3A4 catalyzed ω- and (ω-1)-hydroxylated MCFAs with the lowest K_m and highest V_max /K_m values. Finally, we derived a model to predict midazolam clearance using these markers and demonstrated that the predictive model including three ω- or (ω-1)-hydroxylated medium-chain acylcarnitines, 6β-OH cortisol, and gender as covariates shows reliable predictability (r² = 0.894).

4β-Hydroxycholesterol level significantly correlates with steady-state serum concentration of the CYP3A4 substrate quetiapine in psychiatric patients

AIM

4β-Hydroxycholesterol (4βOHC) is sensitive towards induction or inhibition of CYP3A4, but its potential usefulness as a dosing biomarker remains to be demonstrated. The aim of this study was to investigate the correlation between 4βOHC levels and steady-state concentrations (Css) of quetiapine, a CYP3A4 substrate with high presystemic metabolism, in psychiatric patients.

METHODS

Serum samples from 151 patients treated with quetiapine as immediate release (IR; n = 98) or slow release (XR; n = 53) tablets were included for analysis of 4βOHC. In all patients, Css of quetiapine had been measured at trough level, i.e. 10-14 and 17-25 h post-dosing for IR and XR tablets, respectively. Correlations between 4βOHC levels and dose-adjusted Css (C/D ratios) of quetiapine were tested by univariate (Spearman's) and multivariate (multiple linear regression) analyses. Gender, age (≥60 vs. <60 years) and tablet formulation were included as potential covariates in the multivariate analysis.

RESULTS

Correlations between 4βOHC levels and quetiapine C/D ratios were highly significant both for IR- and XR-treated patients (P < 0.0001). Estimated Spearman r values were -0.47 (95% confidence interval -0.62, -0.30) and -0.56 (-0.72, -0.33), respectively. The relationship between 4βOHC level and quetiapine C/D ratio was also significant in the multiple linear regression analysis (P < 0.001), including gender (P = 0.023) and age (P = 0.003) as significant covariates.

CONCLUSIONS

The present study shows that 4βOHC level is significantly correlated with steady-state concentration of quetiapine. This supports the potential usefulness of 4βOHC as a phenotype biomarker for individualized dosing of quetiapine and other drugs where systemic exposure is mainly determined by CYP3A4 metabolism.

Pretransplant 4β-hydroxycholesterol does not predict tacrolimus exposure or dose requirements during the first days after kidney transplantation

AIMS

The CYP3A metric 4β-hydroxycholesterol (4βOHC) has been shown to correlate with tacrolimus steady-state apparent oral clearance (CL/F). Recently, pretransplant 4βOHC was shown not to predict tacrolimus CL/F after transplantation in a cohort of renal recipients (n = 79). The goal of the current study was determine whether these findings could be validated in a substantially larger cohort.

METHODS

In a retrospective analysis of 279 renal recipients, tacrolimus trough concentrations (C0), daily dose, haematocrit and other relevant covariates were registered every day for the first 14 days after transplantation. 4βOHC and cholesterol were quantified on plasma collected immediately pretransplant using liquid chromatography tandem-mass spectrometry. Patients were genotyped for CYP3A5*1 and CYP3A4*22.

RESULTS

A total of 3551 tacrolimus C0 concentrations were registered. In a linear mixed model for the 14-day period, determinants of tacrolimus C0 were CYP3A5 genotype, haematocrit, age and weight (overall R²  = 0.179). Determinants of daily dose were CYP3A5 genotype, age, methylprednisolone dose, tacrolimus formulation, ALT and estimated glomerular filtration rate (overall R²  = 0.242). Considering each of the first 5 days separately, 4βOHC had a limited effect on tacrolimus C0 on day 3 only (-1.00 ng ml^-1 per ln, P = 0.035) but not on any other day, and no effect on dose or C0/dose. During the first 5 days, haematocrit and age, which were previously established as determinants of tacrolimus disposition under steady-state conditions, never explained more than 17.7% of between-subject variability in tacrolimus C0/dose.

CONCLUSIONS

The CYP3A metric 4βOHC cannot be used to predict tacrolimus dose requirements in the first days after transplantation.

Examination of the Human Cytochrome P4503A4 Induction Potential of PF-06282999, an Irreversible Myeloperoxidase Inactivator: Integration of Preclinical, In Silico, and Biomarker Methodologies in the Prediction of the Clinical Outcome

The propensity for CYP3A4 induction by 2-(6-(5-chloro-2-methoxyphenyl)-4-oxo-2-thioxo-3,4-dihydropyrimidin-1(2H)-yl)acetamide (PF-06282999), an irreversible inactivator of myeloperoxidase, was examined in the present study. Studies using human hepatocytes revealed moderate increases in CYP3A4 mRNA and midazolam-1'-hydroxylase activity in a PF-06282999 dose-dependent fashion. At the highest tested concentration of 300 μM, PF-06282999 caused maximal induction in CYP3A4 mRNA and enzyme activity ranging from 56% to 86% and 47% t0 72%, respectively, of rifampicin response across the three hepatocyte donor pools. In a clinical drug-drug interaction (DDI) study, the mean midazolam C_max and area under the curve (AUC) values following 14-day treatment with PF-06282999 decreased in a dose-dependent fashion with a maximum decrease in midazolam AUC_0-inf and C_max of ∼57.2% and 41.1% observed at the 500 mg twice daily dose. The moderate impact on midazolam pharmacokinetics at the 500 mg twice daily dose of PF-06282999 was also reflected in statistically significant changes in plasma 4β-hydroxycholesterol/cholesterol and urinary 6β-hydroxycortisol/cortisol ratios. Changes in plasma and urinary CYP3A4 biomarkers did not reach statistical significance at the 125 mg three times daily dose of PF-06282999, despite a modest decrease in midazolam systemic exposure. Predicted DDI magnitude based on the in vitro induction parameters and simulated pharmacokinetics of perpetrator (PF-06282999) and victim (midazolam) using the Simcyp (Simcyp Ltd., Sheffield, United Kingdom) population-based simulator were in reasonable agreement with the observed clinical data. Since the magnitude of the 4β-hydroxycholesterol or 6β-hydroxycortisol ratio change was generally smaller than the magnitude of the midazolam AUC change with PF-06282999, a pharmacokinetic interaction study with midazolam ultimately proved important for assessment of DDI via CYP3A4 induction.

Impact of genetic and nongenetic factors on interindividual variability in 4β-hydroxycholesterol concentration

PURPOSE

Individual variability in the endogenous CYP3A metabolite 4β-hydroxycholesterol (4βOHC) is substantial, but to which extent this is determined by genetic and nongenetic factors remains unclear. The aim of the study was to evaluate the explanatory power of candidate genetic variants and key nongenetic factors on individual variability in 4βOHC levels in a large naturalistic patient population.

METHODS

We measured 4βOHC concentration in serum samples from 655 patients and used multiple linear regression analysis to estimate the quantitative effects of CYP3A4*22, CYP3A5*3, and POR*28 variant alleles, comedication with CYP3A inducers, inhibitors and substrates, sex, and age on individual 4βOHC levels.

RESULTS

4βOHC concentration ranged >100-fold in the population, and the multiple linear regression model explained about one fourth of the variability (R ² = 0.23). Only comedication with inducers or inhibitors, sex, and POR genotype were significantly associated with individual variability in 4βOHC level. The estimated quantitative effects on 4βOHC levels were greatest for inducer comedication (+>313%, P < 0.001), inhibitor comedication (-34%, P = 0.021), and female sex (+30%, P < 0.001), while only a modestly elevated 4βOHC level was observed in carriers vs. noncarriers of POR*28 (+11%, P = 0.023).

CONCLUSIONS

These findings suggest that the CYP3A4*22, CYP3A5*3, and POR*28 variant alleles are of limited importance for overall individual variability in 4βOHC levels compared to nongenetic factors.

Managing the Risk of CYP3A Induction in Drug Development: A Strategic Approach

Induction of cytochrome P450 (P450) can impact the efficacy and safety of drug molecules upon multiple dosing with coadministered drugs. This strategy is focused on CYP3A since the majority of clinically relevant cases of P450 induction are related to these enzymes. However, the in vitro evaluation of induction is applicable to other P450 enzymes; however, the in vivo relevance cannot be assessed because the scarcity of relevant clinical data. In the preclinical phase, compounds are screened using pregnane X receptor reporter gene assay, and if necessary structure-activity relationships (SAR) are developed. When projects progress toward the clinical phase, induction studies in a hepatocyte-derived model using HepaRG cells will generate enough robust data to assess the compound's induction liability in vivo. The sensitive CYP3A biomarker 4β-hydroxycholesterol is built into the early clinical phase I studies for all candidates since rare cases of in vivo induction have been found without any induction alerts from the currently used in vitro methods. Using this model, the AstraZeneca induction strategy integrates in vitro assays and in vivo studies to make a comprehensive assessment of the induction potential of new chemical entities. Convincing data that support the validity of both the in vitro models and the use of the biomarker can be found in the scientific literature. However, regulatory authorities recommend the use of primary human hepatocytes and do not advise the use of sensitive biomarkers. Therefore, primary human hepatocytes and midazolam studies will be conducted during the clinical program as required for regulatory submission.

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.

Comparative performance of oral midazolam clearance and plasma 4β-hydroxycholesterol to explain interindividual variability in tacrolimus clearance

AIMS

We compared the CYP3A4 metrics weight-corrected midazolam apparent oral clearance (MDZ Cl/F/W) and plasma 4β-hydroxycholesterol/cholesterol (4β-OHC/C) as they relate to tacrolimus (TAC) Cl/F/W in renal transplant recipients.

METHODS

For a cohort of 147 patients, 8 h area under the curve (AUC) values for TAC and oral MDZ were calculated besides measurement of 4β-OHC/C. A subgroup of 70 patients additionally underwent intravenous erythromycin breath test (EBT) and were administered the intravenous MDZ probe. All patients were genotyped for common polymorphisms in CYP3A4, CYP3A5 and P450 oxidoreductase, among others.

RESULTS

MDZ Cl/F/W, 4β-OHC/C/W, EBT and TAC Cl/F/W were all moderately correlated (r = 0.262-0.505). Neither MDZ Cl/F/W nor 4β-OHC/C/W explained variability in TAC Cl/F/W in CYP3A5 expressors (n = 29). For CYP3A5 non-expressors (n = 118), factors explaining variability in TAC Cl/F/W in a MDZ-based model were MDZ Cl/F/W (R²  = 0.201), haematocrit (R²  = 0.139), TAC formulation (R²  = 0.107) and age (R²  = 0.032; total R²  = 0.479). In the 4β-OHC/C/W-based model, predictors were 4β-OHC/C/W (R²  = 0.196), haematocrit (R²  = 0.059) and age (R²  = 0.057; total R²  = 0.312). When genotype information was ignored, predictors of TAC Cl/F/W in the whole cohort were 4β-OHC/C/W (R²  = 0.167), MDZ Cl/F/W (R²  = 0.045); Tac QD formulation (R²  = 0.036), and haematocrit (R²  = 0.032; total R²  = 0.315). 4β-OHC/C/W, but not MDZ Cl/F/W, was higher in CYP3A5 expressors because it was higher in CYP3A4*1b carriers, which were almost all CYP3A5 expressors.

CONCLUSIONS

A MDZ-based model explained more variability in TAC clearance in CYP3A5 non-expressors. However, 4β-OHC/C/W was superior in a model in which no genotype information was available, likely because 4β-OHC/C/W was influenced by the CYP3A4*1b polymorphism.

Rapid LC-MS/MS method for the determination of 4-hydroxycholesterol/cholesterol ratio in serum as endogenous biomarker for CYP3A activity in human and foals

Cytochrome P450 3A (CYP) enzymes are involved in the elimination of many drugs and are known to be regulated by several environmental factors. Thus, it was the aim of this study to develop and validate an analytical method allowing estimation of the hepatic CYP3A enzyme activity using the 4-hydroxycholesterol to cholesterol ratio as an endogenous biomarker in serum. Both compounds were isolated from the biological matrix by liquid-liquid extraction using n-hexane after saponification with ethanolic sodium methoxide solution (2M) to cleave the steroids from their esterified forms without any kind of further derivatization. Chromatographic separation was achieved on a reversed-phase column (SupelcoAcsentis(®), C8) within 7min using an isocratic elution with ammonium acetate 5mM (pH=3.8, 10%) and acetonitrile (90%) at a flow rate of 300μl/min. d6-cholesterol and d7-4β-hydroxycholesterol were used as internal standards. Detection was done on a triple quadrupole mass spectrometer using the following mass transitions: 369.3/161.5, 369.3/147.1 and 369.3/95.2 for cholesterol; 385.2/367.4, 385.2/109.1 for 4-hydroxycholesterol; 374.4/152.7 and 392.2/108.9 for d6-cholesterol and d7-4-hydroxycholesterol, respectively as the internal standards. The method was validated according to current bioanalytical guidelines considering selectivity, linearity, accuracy, precision, recovery, stability. The analytical range was 5-250 and 50-1000ng/ml, for 4-hydroxycholesterol and cholesterol, respectively. The method was shown to be selective for both compounds with good linearity over the selected range (r>0.99) as well as good within- and between day accuracy (error: -1.2-3.7% for 4-hydroxycholesterol and -7.7-9.5% for cholesterol) and within- and between day precision (2.1-14.6% for 4-hydroxycholesterol and 1.1-14.9% for cholesterol). Recovery was found to be over 80% for both analytes while significant stability issues could not be observed. Finally, the validated assay was applied to measure 4-hydroxycholesterol and cholesterol in serum samples of clinical studies in humans and foals that could verify induction of hepatic CYP3A4 (human) and CYP3A89 (foals) after premedication with the known enzyme inducer rifampicin.

Coadministration of Rifampin Significantly Reduces Odanacatib Concentrations in Healthy Subjects

This open-label 2-period study assessed the effect of multiple-dose administration of rifampin, a strong cytochrome P450 3A (CYP3A) and P-glycoprotein inducer, on the pharmacokinetics of odanacatib, a cathepsin K inhibitor. In period 1, 12 healthy male subjects (mean age, 30 years) received a single dose of odanacatib 50 mg on day 1, followed by a 28-day washout. In period 2, subjects received rifampin 600 mg/day for 28 days; odanacatib 50 mg was coadministered on day 14. Blood samples for odanacatib pharmacokinetics were collected at predose and on day 1 of period 1 and day 14 of period 2. Coadministration of odanacatib and rifampin significantly reduced odanacatib exposure. The odanacatib AUC_0-∞ geometric mean ratio (90% confidence interval) of odanacatib + rifampin/odanacatib alone was 0.13 (0.11-0.16). The harmonic mean ± jackknife standard deviation apparent terminal half-life (t_½ ) was 71.6 ± 10.2 hours for odanacatib alone and 16.0 ± 3.4 hours for odanacatib + rifampin, indicating greater odanacatib clearance following coadministration with rifampin. Samples were collected in period 2 during rifampin dosing (days 1, 14, and 28) and after rifampin discontinuation (days 35, 42, and 56) to evaluate the ratio of plasma 4β-hydroxycholesterol to total serum cholesterol as a CYP3A4 induction biomarker; the ratio increased ∼5-fold over 28 days of daily dosing with 600 mg rifampin, demonstrating sensitivity to CYP3A4 induction.

CYP3A Specifically Catalyzes 1β-Hydroxylation of Deoxycholic Acid: Characterization and Enzymatic Synthesis of a Potential Novel Urinary Biomarker for CYP3A Activity

The endogenous bile acid metabolite 1β-hydroxy-deoxycholic acid (1β-OH-DCA) excreted in human urine may be used as a sensitive CYP3A biomarker in drug development reflecting in vivo CYP3A activity. An efficient and stereospecific enzymatic synthesis of 1β-OH-DCA was developed using a Bacillus megaterium (BM3) cytochrome P450 (P450) mutant, and its structure was confirmed by nuclear magnetic resonance (NMR) spectroscopy. A [(2)H4]-labeled analog of 1β-OH-DCA was also prepared. The major hydroxylated metabolite of deoxycholic acid (DCA) in human liver microsomal incubations was identified as 1β-OH-DCA by comparison with the synthesized reference analyzed by UPLC-HRMS. Its formation was strongly inhibited by CYP3A inhibitor ketoconazole. Screening of 21 recombinant human cytochrome P450 (P450) enzymes showed that, with the exception of extrahepatic CYP46A1, the most abundant liver P450 subfamily CYP3A, including CYP3A4, 3A5, and 3A7, specifically catalyzed 1β-OH-DCA formation. This indicated that 1β-hydroxylation of DCA may be a useful marker reaction for CYP3A activity in vitro. The metabolic pathways of DCA and 1β-OH-DCA in human hepatocytes were predominantly via glycine and, to a lesser extent, via taurine and sulfate conjugation. The potential utility of 1β-hydroxylation of DCA as a urinary CYP3A biomarker was illustrated by comparing the ratio of 1β-OH-DCA:DCA in a pooled spot urine sample from six healthy control subjects to a sample from one patient treated with carbamazepine, a potent CYP3A inducer; 1β-OH-DCA:DCA was considerably higher in the patient versus controls (ratio 2.8 vs. 0.4). Our results highlight the potential of 1β-OH-DCA as a urinary biomarker in clinical CYP3A DDI studies.