Validation of 4β-hydroxycholesterol and evaluation of other endogenous biomarkers for the assessment of CYP3A activity in healthy subjects

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.

Differences in the Serum 4β-hydroxycholesterol Levels of Patients with Chronic Hepatitis C Virus (HCV) Infection: A Possible Impact on the Efficacy and Safety of Interferon (IFN)-free Treatment

Objective Since the majority of direct-acting antivirals (DAAs) that are used in the treatment of hepatitis C virus (HCV) infection are mainly metabolized by CYP3A4, it is hypothesized that inter-individual differences in CYP3A4 activity may be associated with the bioavailability of these agents. Methods The level of serum 4β-hydroxycholesterol (4βHC), a surrogate marker of CYP3A4 activity, was determined by LC-MS/MS in samples obtained from patients with HCV infection (CHCs) as well as healthy control subjects (CTLs). Serum samples obtained from patients treated with either asunaprevir/daclatasvir (ASV/DCV) or ombitasvir/paritaprevir/ritonavir (OTV/PTV/r) were used for additional assays. Results The serum 4βHC level in CHCs was significantly higher than that in CTLs, and a gender difference was seen among CHCs. In patients treated with OTV/PTV/r, the serum 4βHC level was observed to gradually decrease during the treatment period. In the cohort treated with ASV/DCV, 4 of 83 patients showed virological treatment failure. In pretreatment testing, an Invader assay detected a low prevalence of resistance-associated variants in these four patients. The average serum concentration of DCV/ASV in the treatment-failed group tended to be lower than that in the sustained virological response (SVR) group. The pretreatment serum 4βHC level in patients with treatment failure was significantly higher than that in patients with an SVR but in whom the prevalence of resistance-associated variants was low in the pretreatment setting. Conclusion The evaluation of CYP3A4 activity by measuring 4βHC before treatment may provide additional information that can potentially be used to select cost- and efficacy-optimized treatment of HCV.

Sterol 27-hydroxylase gene dosage and the antiatherosclerotic effect of Rifampicin in mice

Sterol 27-hydroxylase (CYP27A1) catalyzes the hydroxylation of cholesterol to 27-hydroxycholesterol (27-OHC) and regulates cholesterol homeostasis. In Cyp27a1/ Apolipoprotein E (ApoE) double knockout (KO) mice fed with Western diet (WD), the atherosclerotic phenotype found in ApoE KO mice was reversed. As protective mechanism, up-regulation of Cyp3a11 and Cyp7a1 was proposed. Cyp27a1 heterozygote/ApoE KO (het) mice, with reduced Cyp27a1 expression and normal levels of Cyp7a1 and Cyp3a11, developed more severe lesions than ApoE KO mice. To analyze the contribution of Cyp3a11 to the protection of atherosclerosis development, Cyp3a11 was induced by Rifampicin (RIF) in ApoE KO and het mice. Males were fed with WD and treated daily with RIF (10 mg/kg ip) or vehicle for 4 weeks. Atherosclerosis was quantified in the aortic valve. Plasma lipids and 27-hydroxycholesterol (27-OHC), expression of cytochromes P450 and genes involved in cholesterol transport and bile acids (BAs) signaling in liver and intestine, and intestinal cholesterol absorption were analyzed. RIF increased expression of hepatic but not intestinal Cyp3a11 4-fold in both genotypes. In ApoE KO mice treated with RIF, we found a 2-fold decrease in plasma cholesterol, and a 2-fold increase in high-density lipoprotein/low-density lipoprotein ratio and CY27A1 activity. Intestinal cholesterol absorption remained unchanged and atherosclerotic lesions decreased approximately 3-fold. In het mice, RIF had no effect on plasma lipids composition, CYP27A1 activity, and atherosclerotic plaque development, despite a reduction in cholesterol absorption. In conclusion, the antiatherogenic effect of Cyp3a11 induction by RIF was also dependent on Cyp27a1 expression.

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).

First-in-human phase I study of oral S49076, a unique MET/AXL/FGFR inhibitor, in advanced solid tumours

BACKGROUND AND OBJECTIVES

S49076 is a novel ATP-competitive tyrosine kinase inhibitor of MET, AXL and FGFR with a unique selectivity profile. A phase I open-label study was undertaken to establish the tolerability profile and determine the recommended dose (RD) and administration schedule.

MATERIALS AND METHODS

Patients with advanced solid tumours received S49076 orally once-daily (qd) or twice-daily (bid) in continuous 21-day cycles at escalating doses guided by a 3 + 3 design and followed by an expansion phase at the RD. Pharmacokinetic (PK) parameters were assessed and pharmacodynamic end-points were evaluated in pre- and post-treatment tumour biopsies. Preliminary anti-tumour activity was evaluated as per the Response Evaluation Criteria In Solid Tumours 1.1 criteria.

RESULTS

A total of 103 patients were treated: 79 in the dose-escalation and 24 in the expansion. Doses from 15 to 900 mg were evaluated. Dose-limiting toxicities were reported in 9 patients and occurred at 30, 760 and 900 mg in the qd arm and at 180, 225 and 285 mg in the bid arm. The RD was defined at 600 mg qd. Adverse events (AEs) occurred with similar frequency in both regimens at an equivalent total daily dose. Overall, 83 patients (81.4%) had drug-related AEs, the majority (93%) of which were grade I-II (National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0) and only 3% led to drug discontinuation. Intratumoural PK analysis at the RD suggested hitting of MET, AXL and FGFR.

CONCLUSION

S49076 demonstrated a tolerable safety profile with limited single-agent activity. PK/pharmacodynamic readouts of S49076 are encouraging for further investigation of S49076 in combination therapies.

TRIAL REGISTRATION NUMBER

ISRCTN00759419.

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.

UHPLC-MS/MS bioanalysis of urinary DHEA, cortisone and their hydroxylated metabolites as potential biomarkers for CYP3A-mediated drug-drug interactions

AIM

A UHPLC-MS/MS assay was developed to quantify urinary dehydroepiandrosterone (DHEA), 7β-hydroxy-DHEA, cortisone and 6β-hydroxycortisone as potential biomarkers to predict CYP3A activity.

RESULTS

A sensitive assay at LLOQ of 0.500 ng/ml with good accuracy and precision was developed for the four analytes in human urine. This UHPLC-MS/MS assay was optimized by eliminating nonspecific loss of the analytes in urine, ensuring complete hydrolysis of the conjugates to unconjugated forms and use of the product ions of [M+H-H₂O]⁺ for multiple reaction monitoring detection of DHEA and 7β-hydroxy-DHEA.

CONCLUSION

This assay was successfully applied to a pilot clinical study. It is also suitable for future drug-drug interaction studies to continue evaluating the potential of these steroids as biomarkers for CYP3A inhibition and induction.

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.

Oxysterols: From cholesterol metabolites to key mediators

Oxysterols are cholesterol metabolites that can be produced through enzymatic or radical processes. They constitute a large family of lipids (i.e. the oxysterome) involved in a plethora of physiological processes. They can act through GPCR (e.g. EBI2, SMO, CXCR2), nuclear receptors (LXR, ROR, ERα) and through transporters or regulatory proteins. Their physiological effects encompass cholesterol, lipid and glucose homeostasis. Additionally, they were shown to be involved in other processes such as immune regulatory functions and brain homeostasis. First studied as precursors of bile acids, they quickly emerged as interesting lipid mediators. Their levels are greatly altered in several pathologies and some oxysterols (e.g. 4β-hydroxycholesterol or 7α-hydroxycholestenone) are used as biomarkers of specific pathologies. In this review, we discuss the complex metabolism and molecular targets (including binding properties) of these bioactive lipids in human and mice. We also discuss the genetic mouse models currently available to interrogate their effects in pathophysiological settings. We also summarize the levels of oxysterols reported in two key organs in oxysterol metabolism (liver and brain), plasma and cerebrospinal fluid. Finally, we consider future opportunities and directions in the oxysterol field in order to gain a better insight and understanding of the complex oxysterol system.

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.

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.

An Exposure-Response Modeling Approach to Examine the Relationship Between Potency of CYP3A Inducer and Plasma 4β-Hydroxycholesterol in Healthy Subjects

The objectives of this analysis were to establish the exposure-response relationship between plasma rifampicin and 4β-hydroxycholesterol (4βHC) concentration and to estimate the effect of weak, moderate, and potent CYP3A induction. Plasma rifampicin and 4βHC concentration-time data from a drug-drug interaction study with rifampicin 600 mg were used for model development. An indirect response model with an effect compartment described the relationship between rifampicin and 4βHC concentrations. The model predicted that the equilibration t_1/2 and 4βHC t_1/2 were 72.8 and 142 hours, respectively. EM₅₀ and E_max of rifampicin induction were 32.6 μg and 8.39-fold, respectively. The population PK-PD model was then used to simulate the effects of rifampicin 10, 20, and 100 mg on plasma 4βHC for up to 21 days, in which rifampicin 10, 20, and 100 mg were used to represent weak, moderate, and strong inducers, respectively. The model-predicted median (5th, 95th percentiles) 1.13 (1.04, 1.44)-, 1.28 (1.10, 1.71)-, and 2.10 (1.45, 3.49)-fold increases in plasma 4βHC after 14-day treatment with rifampicin 10, 20, and 100 mg, respectively. A new drug candidate can likely be classified as a weak, moderate, or strong inducer if baseline-normalized plasma 4βHC increases by <1.13-, 1.13- to 2.10-, or >2.10-fold, respectively, after 14 days of dosing.

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.

Effect of Statin Treatment on Plasma 4β-Hydroxycholesterol Concentrations

The endogenous oxysterol 4β-hydroxycholesterol may be used as a marker for the drug-metabolizing enzymes cytochrome P450 3A (CYP3A). The primary aim of this study was to investigate the effect of statin treatment on plasma 4β-hydroxycholesterol concentrations. Plasma samples from a previously performed clinical study where gallstone patients had been treated with placebo (n = 6), 20 mg fluvastatin (n = 9) or 80 mg atorvastatin (n = 9) daily for 4 weeks were analysed. Hepatic CYP3A mRNA levels had previously been shown to be unchanged in all three treatment groups. Plasma 4β-hydroxycholesterol did not change significantly (p = 0.92) in the placebo group, but treatment with low-dose fluvastatin or high-dose atorvastatin resulted in reductions in plasma concentration of 10.7% (p < 0.05) and 36.5% (p < 0.01), respectively. However, the 4β-hydroxycholesterol/cholesterol ratio did not change significantly for the patients receiving placebo or patients receiving low-dose fluvastatin. The ratio for patients receiving high-dose atorvastatin increased by 12% (p < 0.05). In conclusion, the total plasma cholesterol level is an important determinant for the plasma 4β-hydroxycholesterol level.

miRNA-27b levels are associated with CYP3A activity in vitro and in vivo

Previous in vitro studies have shown that microRNA‐27b (miR‐27b) may regulate mRNA levels of CYP3A4, vitamin D receptor (VDR), and Peroxisome proliferator‐activated receptor α (PPARα) as well as CYP3A4 protein expression and activity. In vitro studies have also shown that vitamin D may affect the expression of CYP3A4. The primary aim of this pilot study was to investigate the association between miR‐27b and CYP3A expression and activity. The secondary aim was to investigate the association between 25‐hydroxy vitamin D in serum and CYP3A activity. Mi‐RNA‐27b was quantified using real‐time PCR in serum samples (n = 28) and 25‐hydroxyvitamin D was measured and correlated with the levels of the endogenous CYP3A activity marker 4β‐hydroxycholesterol. In addition, the correlation between miR‐27b and CYP3A activity, measured by dextromethorphan N‐demethylation and 6β‐hydroxylation of testosterone and the gene expression of CYP3A4, VDR and PPARα were assessed in 20 human liver samples. A significant association between circulatory miR‐27b levels and 4β‐hydroxycholesterol ratio was found; P = 0.04, and between hepatic miR‐27b levels and CYP3A activity, measured by dextromethorphan N‐demethylation in human liver (P = 0.04). There was no association between hepatic miR‐27b and mRNA levels of CYP3A4, VDR or PPARα. There was a significant association between serum 25‐hydroxyvitamin D levels and 4β‐hydroxycholesterol ratio, P = 0.002. In conclusion, this pilot‐study supports the hypothesis that miR‐27b levels as well as 25‐hydroxyvitamin D may affect CYP3A activity in vivo. The results indicate that miR‐27b exerts its inhibitory effect on a translational level rather than affecting mRNA levels.

Ritonavir is the best alternative to ketoconazole as an index inhibitor of cytochrome P450-3A in drug-drug interaction studies

AIMS

The regulatory prohibition of ketoconazole as a CYP3A index inhibitor in drug-drug interaction (DDI) studies has compelled consideration of alternative inhibitors.

METHODS

The biomedical literature was searched to identify DDI studies in which oral midazolam (MDZ) was the victim, and the inhibitory perpetrator was either ketoconazole, itraconazole, clarithromycin, or ritonavir. The ratios (RAUC ) of total area under the curve (AUC) for MDZ with inhibitor divided by MDZ AUC in the control condition were aggregated across individual studies for each inhibitor.

RESULTS

Mean (± SE) RAUC values were: ketoconazole (15 studies, 131 subjects), 11.5 (±1.2); itraconazole (five studies, 48 subjects), 7.3 (±1.0); clarithromycin (five studies, 73 subjects), 6.5 (±10.9); and ritonavir (13 studies, 159 subjects), 14.5 (±2.0). Differences among inhibitors were significant (F = 5.31, P < 0.005). RAUC values were not significantly related to inhibitor dosage or to duration of inhibitor pre-exposure prior to administration of MDZ.

CONCLUSIONS

Ritonavir produces CYP3A inhibition equivalent to or greater than ketoconazole, and is the best index CYP3A inhibitor alternative to ketoconazole. Cobicistat closely resembles ritonavir in structure and function, and can also be considered. Itraconazole and clarithromycin are not suitable alternatives since they do not produce inhibition comparable with ketoconazole or ritonavir, and have other significant disadvantages as well.