Phenotyping of drug-metabolizing enzymes in adults: a review of in-vivo cytochrome P450 phenotyping probes

The Use of Microdosing for In vivo Phenotyping of Cytochrome P450 Enzymes: Where Do We Stand? A Narrative Review

Cytochrome P450 (CYP) enzymes play a central role in the elimination of approximately 80% of all clinically used drugs. Differences in CYP enzyme activity between individuals can contribute to interindividual variability in exposure and, therefore, treatment outcome. In vivo CYP enzyme activity could be determined with phenotyping. Currently, (sub)therapeutic doses are used for in vivo phenotyping, which can lead to side effects. The use of microdoses (100 µg) for in vivo phenotyping for CYP enzymes could overcome the limitations associated with the use of (sub)therapeutic doses of substrates. The aim of this review is to provide a critical overview of the application of microdosing for in vivo phenotyping of CYP enzymes. A literature search was performed to find drug-drug interaction studies of CYP enzyme substrates that used microdoses of the respective substrates. A substrate was deemed sensitive to changes in CYP enzyme activity when the pharmacokinetics of the substrate significantly changed during inhibition and induction of the enzyme. On the basis of the currently available evidence, the use of microdosing for in vivo phenotyping for subtypes CYP1A2, CYP2C9, CYP2D6, and CYP2E1 is not recommended. Microdosing can be used for the in vivo phenotyping of CYP2C19 and CYP3A. The recommended microdose phenotyping test for CYP2C19 is measuring the omeprazole area-under-the-concentration-time curve over 24 h (AUC0-24) after administration of a single 100 µg dose. CYP3A activity could be best determined with a 0.1-75 µg dose of midazolam, and subsequently measuring AUC extrapolated to infinity (AUC∞) or clearance. Moreover, there are two metrics available for midazolam using a limited sampling strategy: AUC over 10 h (AUC0-10) and AUC from 2 to 4 h (AUC2-4).

Solanidine is a sensitive and specific dietary biomarker for CYP2D6 activity

BACKGROUND

Individual assessment of CYP enzyme activities can be challenging. Recently, the potato alkaloid solanidine was suggested as a biomarker for CYP2D6 activity. Here, we aimed to characterize the sensitivity and specificity of solanidine as a CYP2D6 biomarker among Finnish volunteers with known CYP2D6 genotypes.

RESULTS

Using non-targeted metabolomics analysis, we identified 9152 metabolite features in the fasting plasma samples of 356 healthy volunteers. Machine learning models suggested strong association between CYP2D6 genotype-based phenotype classes with a metabolite feature identified as solanidine. Plasma solanidine concentration was 1887% higher in genetically poor CYP2D6 metabolizers (gPM) (n = 9; 95% confidence interval 755%, 4515%; P = 1.88 × 10-11), 74% higher in intermediate CYP2D6 metabolizers (gIM) (n = 89; 27%, 138%; P = 6.40 × 10-4), and 35% lower in ultrarapid CYP2D6 metabolizers (gUM) (n = 20; 64%, - 17%; P = 0.151) than in genetically normal CYP2D6 metabolizers (gNM; n = 196). The solanidine metabolites m/z 444 and 430 to solanidine concentration ratios showed even stronger associations with CYP2D6 phenotypes. Furthermore, the areas under the receiver operating characteristic and precision-recall curves for these metabolic ratios showed equal or better performances for identifying the gPM, gIM, and gUM phenotype groups than the other metabolites, their ratios to solanidine, or solanidine alone. In vitro studies with human recombinant CYP enzymes showed that solanidine was metabolized mainly by CYP2D6, with a minor contribution from CYP3A4/5. In human liver microsomes, the CYP2D6 inhibitor paroxetine nearly completely (95%) inhibited the metabolism of solanidine. In a genome-wide association study, several variants near the CYP2D6 gene associated with plasma solanidine metabolite ratios.

CONCLUSIONS

These results are in line with earlier studies and further indicate that solanidine and its metabolites are sensitive and specific biomarkers for measuring CYP2D6 activity. Since potato consumption is common worldwide, this biomarker could be useful for evaluating CYP2D6-mediated drug-drug interactions and to improve prediction of CYP2D6 activity in addition to genotyping.

Circulating Biomarkers Instead of Genotyping to Establish Metabolizer Phenotypes

Pharmacogenomics (PGx) enables personalized treatment for the prediction of drug response and to avoid adverse drug reactions. Currently, PGx mainly relies on the genetic information of absorption, distribution, metabolism, and excretion (ADME) targets such as drug-metabolizing enzymes or transporters to predict differences in the patient's phenotype. However, there is evidence that the phenotype-genotype concordance is limited. Thus, we discuss different phenotyping strategies using exogenous xenobiotics (e.g., drug cocktails) or endogenous compounds for phenotype prediction. In particular, minimally invasive approaches focusing on liquid biopsies offer great potential to preemptively determine metabolic and transport capacities. Early studies indicate that ADME phenotyping using exosomes released from the liver is reliable. In addition, pharmacometric modeling and artificial intelligence improve phenotype prediction. However, further prospective studies are needed to demonstrate the clinical utility of individualized treatment based on phenotyping strategies, not only relying on genetics. The present review summarizes current knowledge and limitations.

Critical Assessment of Phenotyping Cocktails for Clinical Use in an African Context

Interethnic and interindividual variability in in vivo cytochrome P450 (CYP450)-dependent metabolism and altered drug absorption via expressed transport channels such as P-glycoprotein (P-gp) contribute to the adverse drug reactions, drug-drug interaction and therapeutic failure seen in clinical practice. A cost-effective phenotyping approach could be advantageous in providing real-time information on in vivo phenotypes to assist clinicians with individualized drug therapy, especially in resource-constrained countries such as South Africa. A number of phenotyping cocktails have been developed and the aim of this study was to critically assess the feasibility of their use in a South African context. A literature search on library databases (including AccessMedicine, BMJ, ClinicalKey, MEDLINE (Ovid), PubMed, Scopus and TOXLINE) was limited to in vivo cocktails used in the human population to phenotype phase I metabolism and/or P-gp transport. The study found that the implementation of phenotyping in clinical practice is currently limited by multiple administration routes, the varying availability of probe drugs, therapeutic doses eliciting side effects, the interaction between probe drugs and extensive sampling procedures. Analytical challenges include complicated sample workup or extraction assays and impractical analytical procedures with low detection limits, analyte sensitivity and specificity. It was concluded that a single time point, non-invasive capillary sampling, combined with a low-dose probe drug cocktail, to simultaneously quantify in vivo drug and metabolite concentrations, would enhance the feasibility and cost-effectiveness of routine phenotyping in clinical practice; however, future research is needed to establish whether the quantitative bioanalysis of drugs in a capillary whole-blood matrix correlates with that of the standard plasma/serum matrixes used as a reference in the current clinical environment.

Prediction of CYP2D6 poor metabolizers by measurements of solanidine and metabolites-a study in 839 patients with known CYP2D6 genotype

PURPOSE

Poor metabolizers (PMs) of the highly polymorphic enzyme CYP2D6 are usually at high risk of adverse effects during standard recommended dosing of CYP2D6-metabolized drugs. We studied if the metabolism of solanidine, a dietary compound found in potatoes, could serve as a biomarker predicting the CYP2D6 PM phenotype for precision dosing.

METHODS

The study included 839 CYP2D6-genotyped patients who were randomized by a 4:1 ratio into test or validation cohorts. Full-scan high-resolution mass spectrometry data files of previously analyzed serum samples were reprocessed for identification and quantification of solanidine and seven metabolites. Metabolite-to-solanidine ratios (MRs) of the various solanidine metabolites were calculated prior to performing receiver operator characteristic (ROC) and multiple linear regression analyses on the test cohort. The MR thresholds obtained from the ROC analyses were tested for the prediction of CYP2D6 PMs in the validation cohort.

RESULTS

In the test cohort, the M414-to-solanidine MR attained the highest sensitivity and specificity parameters from the ROC analyses (0.98 and 1.00) and highest explained variance from the linear models (R² = 0.68). Below these thresholds, CYP2D6 PM predictions were tested in the validation cohort providing positive and negative predictive values of 100% for the MR of M414, while similar values for the other MRs ranged from 20.5 to 73.3% and 96.7 to 99.3%, respectively.

CONCLUSION

The M414-to-solanidine MR is an excellent predictor of the CYP2D6 PM phenotype. By measuring solanidine and metabolites using liquid chromatography-mass spectrometry in patient serum samples, CYP2D6 PMs can easily be identified, hence facilitating the implementation of precision dosing in clinical practice.

Simultaneous Determination of Cortisol and 6β-Hydroxycortisol in Human Plasma by Liquid Chromatography-Tandem Mass Spectrometry

The feasibility of taking the ratio of 6β-hydroxycortisol (6β-OHCOR) to cortisol (COR) in plasma as a biomarker to reflect CYP3A4 activity needs to be verified, but the low concentration of 6β-OHCOR which is an endogenous substance in plasma presents a challenge for determination. In this study, a Liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was established to simultaneously quantify the COR and 6β-OHCOR in plasma with COR-d4 and 6β-OHCOR-d4 as internal standards (ISs). Plasma samples were treated by protein precipitation using acetonitrile. Separation with a gradient elution within 5 min was achieved on C18+ column utilizing 5 mM ammonium formate and methanol. An API 4,000 MS in multiple reaction monitoring mode with transitions of 407.1 → 361.1 and 423.1 → 347.1 was utilized. Albumin solution was used as a surrogate matrix, with good linearities over the concentration of 1.20-300 ng/mL for COR and 0.0400-10.0 ng/mL for 6β-OHCOR. The precisions for intrarun and interrun were < 6.8%, and the accuracy was fell in the interval of -5.2 to 3.5%. Matrix effect was not found. Recovery was close to 100.0%. Stability was confirmed under the storage and processing conditions. The validated method was applied to evaluate the inhibitory effect of voriconazole to CYP3A by the ratio of 6β-OHCOR to COR.

What Is Known about Midazolam? A Bibliometric Approach of the Literature

Midazolam is a drug with actions towards the central nervous system producing sedative and anticonvulsants effects, used for sedation and seizures treatments. A better understanding about its effects in the different scenarios presented in the literature could be helpful to gather information regarding its clinical indications, pharmacological interactions, and adverse events. From this perspective, the aim of this study was to analyze the global research about midazolam mapping, specifically the knowledge of the 100 most-cited papers about this research field. For this, a search was executed on the Web of Science-Core Collection database using bibliometric methodological tools. The search strategy retrieved 34,799 articles. A total of 170 articles were evaluated, with 70 articles being excluded for not meeting the inclusion criteria. The 100 most-cited articles rendered 42,480 citations on WoS-CC, ranging from 253 to 1744. Non-systematic review was the most published study type, mainly from North America, during the period of 1992 to 2002. The most frequent keywords were midazolam and pharmacokinetics. Regarding the authors, Thummel and Kunze were the ones with the greatest number of papers included. Our findings showed the global research trends about midazolam, mainly related to its different effects and uses throughout the time.

Simultaneous separation of naproxen and 6-O-desmethylnaproxen metabolite in saliva samples by liquid chromatography-tandem mass spectrometry: Pharmacokinetic study of naproxen alone and associated with esomeprazol-Results

After performing liquid-liquid extraction with ethyl acetate and HCl, samples from 12 volunteers who performed sequential collections after taking a tablet of naproxen alone (n = 6) or associated with esomeprazole (n = 6) were analyzed in a triple quadrupole mass spectrometer 8040 LC MS/MS Shimadzu. Separation of naproxen and its main metabolite 6-O-desmethylnaproxen was performed in a Shim-Pack XR-ODS 75Lx2.0 column and C18 pre-column at 40°C using a mixture of methanol and ammonium acetate 10 mM (70:30, v/v) with an injection rate of 0.3 ml/min. The total analytical run time for each sample was 5 min. The association of naproxen with esomeprazole take considerably longer time to reach the maximum concentration [Tmax 0.17 h (interquartile range, 0.13-1.95) for naproxen alone and 13.18*h (interquartile range, 10.12-27.15) for naproxen with esomeprazole, p = 0.002], also to be eliminated [T1/2 0.12 h (interquartile range, 0.09-1.35) for naproxen alone and 9.16*h (interquartile range, 7.16-41.40) for naproxen with esomeprazole, p = 0.002] and lower maximum concentrations (Cmax 4.6 ± 2.5 ug/mL for naproxen alone and 2.04 ± 0.78* μg/mL, p = 0.038). The association of naproxen with esomeprazole showed increased values of AUC0-t [82.06* h*μg/mL (interquartile range, 51.90-157.00) with esomeprazole and 2.97 h*μg/mL (interquartile range, 1.82-7.84) naproxen alone, p = 0.002] in drug concentrations in relation to the naproxen tablet alone, probably, such differences are due to the delay in the absorption of naproxen when it is associated with the drug proton pump inhibitor, esomeprazole. As well as reduced values of full clearance when naproxen is combined with esomeprazole (0.07* μg/h (interquartile range, 0.005-0.01) with esomeprazole and 7.29 μg/h (interquartile range, 3.17-16.23) in naproxen alone, p = 0.002). Both naproxen and 6-O-desmethylnaproxen in saliva samples can be effectively quantified using LC-MS/MS, this methodology proved to be rapid, sensitive, accurate and selective for each drug and allows for the analysis of their pharmacokinetic parameters, in both situations.

Evaluation of Zuo-Gui Yin Decoction Effects on Six CYP450 Enzymes in Rats Using a Cocktail Method by UPLC-MS/MS

Background. Zuo-Gui Yin Decoction (ZGYD), a traditional Chinese prescription, is mainly used in various kinds of andrology and gynecology diseases. However, the study on the interaction of ZGYD and drugs has not been reported. Therefore, evaluating the interaction between ZGYD and metabolic enzymes is helpful to guide rational drug use. Objective. This study was conducted to explore the effects of ZGYD on the activity and mRNA expressions of six Cytochrome P450 (CYP450) enzymes in rats and to provide a basis for its rational clinical use. Methods. Sprague-Dawley rats were randomly divided into control, ZGYD high, medium, and low-dose group ( $n=6$ ). The concentrations of six probe substrates in plasma of rats in each group were determined by UPLC-MS/MS. In addition, RT-PCR and Western blot were used to determine the effects of ZGYD on the expression of CYP450 isoforms in the liver. Results. Compared with the control group, the main pharmacokinetic parameters AUC(0-t), AUC (0~∞), of omeprazole, dextromethorphan, and midazolam in the high-dose group were significantly decreased, while the CL of these were significantly increased. The gene expressions of CYP2C11 and CYP3A1 were upregulated in the ZGYD medium, high-dose group. The protein expression of CYP2C11 was upregulated in the high-dose group, and the protein expression of CYP3A1 was upregulated in the medium, high-dose group. Conclusion. The results showed that ZGYD exhibited the induction effects on CYP2C11 and CYP3A1 (CYP2C19 and CYP3A4 in humans) in rats. However, no significant change in CYP1A2, CYP2B1, CYP2C7, and CYP2D2 activities was observed. It would be useful for the safe and effective usage of ZGYD in clinic.

Isolation and Identification of 3,4-Seco-Solanidine-3,4-dioic acid (SSDA) as a Urinary Biomarker of Cytochrome P450 2D6 (CYP2D6) Activity

Cytochrome P450 2D6 (CYP2D6), is responsible for the metabolism and elimination of approximately 25% of clinically used drugs, including antidepressants and antipsychotics, and its activity varies considerably on a population basis primary due to genetic variation. CYP2D6 phenotype can be assessed in vivo following administration of an exogenous probe compound, such as dextromethorphan or debrisoquine, but use of a biomarker that does not require administration of an exogenous compound (i.e., drug) has considerable appeal for assessing CYP2D6 activity in vulnerable populations, such as children. The goal of this study was to isolate, purify and identify an "endogenous" urinary biomarker (M1; m/z 444.3102) of CYP2D6 activity reported previously. Several chromatographic separation techniques (reverse phase HPLC, cation exchange and analytical reverse phase UPLC) were used to isolate and purify 96 μg of M1 from 40 L of urine. Subsequently, 1D and 2D NMR, and functional group modification reactions were used to elucidate its structure. Analysis of mass spectrometry and NMR data revealed M1 to have similar spectroscopic features to the nitrogen-containing steroidal alkaloid, solanidine. 2D NMR characterization by HMBC, COSY, TOCSY, and HSQC-TOCSY proved to be invaluable in the structural elucidation of M1; derivatization of M1 revealed the presence of two carboxylic acid moieties. M1 was determined to be a steroidal alkaloid with a solanidine backbone that had undergone C-C bond scission to yield 3,4-seco-solanidine-3,4-dioic acid (SSDA). SSDA may have value as a dietary biomarker of CYP2D6 activity in populations where potato consumption is common. Significance Statement Endogenous biomarkers of processes involved in drug disposition and response may allow improved individualization of drug treatment, especially in vulnerable populations, such as children. Given that several CYP2D6 substrates are commonly used in pediatrics and the ubiquitous nature of potato consumption in western diets, SSDA has considerable appeal as non-invasive biomarker of CYP2D6 activity to guide treatment with CYP2D6 substrates in children and adults.

Evaluation of a six-probe cocktail (caffeine, tolbutamide, omeprazole, dextromethorphan, midazolam, and digoxin) approach to estimate hepatic drug detoxification capability and dosage requirements after a single oral dosing in healthy Chinese volunteers

The primary objectives of this study were to investigate the suitability of a 6-probe cocktail (caffeine, tolbutamide, omeprazole, dextromethorphan, midazolam, and digoxin) to be used as a tool for assessing the activity of drug metabolizing enzymes and transporters, and examine differences in the way drugs are handled among groups with different genetic regulation of these processes. This was a single-center, open-label, phase I clinical study involving 20 young, healthy Chinese volunteers (equal gender distribution). The subjects were administered a single, oral dose of the 6-probe cocktail and serum samples were collected to assess the disposition of the different probe substrates and produced metabolites. The serum samples were analyzed using ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry technology. The DNA samples were subjected to whole exome sequencing. Nineteen healthy volunteers completed the study. The 6-probe cocktail was safe and well-tolerated by all the subjects. The parent substrates and metabolites-caffeine (paraxanthine), dextromethorphan (dextrorphan), digoxin, midazolam (1-hydroxy-midazolam), omeprazole (5-hydroxy-omeprazole), and tolbutamide (4-hydroxy-tolbutamide)-were within the detectable window. Genetic variations known to alter drug metabolism (CYP2D6*10, CYP2C19*2, CYP2C19*3, and CYP2C9*3) were identified and generally correlated with phenotypic status. The 6-probe cocktail appeared to be suitable for assessing drug metabolizing activities. This, in conjunction with individual genetics, will pave the way for the implementation of personalized medicine in clinical practice. This will hopefully improve efficacy and reduce the incidence of adverse drug reactions.

Oral Yohimbine as a New Probe Drug to Predict CYP2D6 Activity: Results of a Fixed-Sequence Phase I Trial

Objective

Yohimbine pharmacokinetics were determined after oral administration of a single oral dose of yohimbine 5 mg and a microdose of yohimbine 50 µg in relation to different cytochrome P450 (CYP) 2D6 genotypes. The CYP2D6 inhibitor paroxetine was used to investigate the influence on yohimbine pharmacokinetics. Microdosed midazolam was applied to evaluate a possible impact of yohimbine on CYP3A activity and the possibility of combining microdosed yohimbine and midazolam to simultaneously determine CYP2D6 and CYP3A activity.

Methods

In a fixed-sequence clinical trial, 16 healthy volunteers with a known CYP2D6 genotype [extensive (10), intermediate (2) and poor (4) metaboliser] received an oral dose of yohimbine 50 µg, yohimbine 5 mg at baseline and during paroxetine as a CYP2D6 inhibitor. Midazolam (30 µg) was co-administered to determine CYP3A activity at each occasion. Plasma concentrations of yohimbine, its main metabolite 11-OH-yohimbine, midazolam and paroxetine were quantified using validated liquid chromatography-tandem mass spectrometry assays.

Results

Pharmacokinetics of yohimbine were highly variable and a CYP2D6 genotype dependent clearance was observed. After yohimbine 5 mg, the clearance ranged from 25.3 to 15,864 mL/min and after yohimbine 50 µg, the clearance ranged from 39.6 to 38,822 mL/min. A more than fivefold reduction in clearance was caused by paroxetine in CYP2D6 extensive metabolisers, while the clearance in poor metabolisers was not affected. Yohimbine did not alter CYP3A activity as measured by microdosed midazolam.

Conclusions

The pharmacokinetics of yohimbine were highly correlated with CYP2D6, which was further supported by the clearance inhibition caused by the CYP2D6 inhibitor paroxetine. With these data, yohimbine is proposed to be a suitable probe drug to predict CYP2D6 activity. In addition, the microdose can be used in combination with microdosed midazolam to simultaneously evaluate CYP2D6 and CYP3A activity without any interaction between the probe drugs and because the microdoses exert no pharmacological effects.

Clinical Trial Registration

EudraCT2017-001801-34.

Electronic supplementary material

The online version of this article (10.1007/s40262-020-00862-6) contains supplementary material, which is available to authorized users.

A simple method to measure sulfonation in man using paracetamol as probe drug

Sulfotransferase enzymes (SULT) catalyse sulfoconjugation of drugs, as well as endogenous mediators, gut microbiota metabolites and environmental xenobiotics. To address the limited evidence on sulfonation activity from clinical research, we developed a clinical metabolic phenotyping method using paracetamol as a probe substrate. Our aim was to estimate sulfonation capability of phenolic compounds and study its intraindividual variability in man. A total of 36 healthy adult volunteers (12 men, 12 women and 12 women on oral contraceptives) received paracetamol in a 1 g-tablet formulation on three separate occasions. Paracetamol and its metabolites were measured in plasma and spot urine samples using liquid chromatography-high resolution mass spectrometry. A metabolic ratio (Paracetamol Sulfonation Index—PSI) was used to estimate phenol SULT activity. PSI showed low intraindividual variability, with a good correlation between values in plasma and spot urine samples. Urinary PSI was independent of factors not related to SULT activity, such as urine pH or eGFR. Gender and oral contraceptive intake had no impact on PSI. Our SULT phenotyping method is a simple non-invasive procedure requiring urine spot samples, using the safe and convenient drug paracetamol as a probe substrate, and with low intraindividual coefficient of variation. Although it will not give us mechanistic information, it will provide us an empirical measure of an individual’s sulfonator status. To the best of our knowledge, our method provides the first standardised in vivo empirical measure of an individual’s phenol sulfonation capability and of its intraindividual variability. EUDRA-CT 2016-001395-29, NCT03182595 June 9, 2017.

Pharmacokinetics of docetaxel and ritonavir after oral administration of ModraDoc006/r in patients with prostate cancer versus patients with other advanced solid tumours

PURPOSE

ModraDoc006 is a novel oral formulation of docetaxel. The clearance of intravenous docetaxel is higher in medically castrated prostate cancer patients as compared to patients with other types of solid tumours. Oral docetaxel requires co-administration ritonavir (r), which might further impact the pharmacokinetics (PK). We now compare the PK of docetaxel and ritonavir between patients with Hormone Sensitive Prostate Cancer (HSPC), metastatic Castration-Resistant Prostate Cancer (mCRPC) and other metastatic solid tumours, treated on the same dose and weekly schedule of ModraDoc006/r.

METHODS

The docetaxel and ritonavir PK were compared between four patient groups from three clinical phase I trials, including eight male and eight female patients with different types of solid tumours (study 1), seven patients with HSPC (study 2) and five patients with mCRPC (study 3). All patients were treated with ModraDoc006 30 mg and ritonavir 100 mg in the morning, followed by ModraDoc006 20 mg and ritonavir 100 mg in the evening (ModraDoc006/r 30-20/100-100). For comparative purposes, the PK of six mCRPC patients that received 30-20/200-100 in study 3 were also evaluated.

RESULTS

The maximum plasma concentration (C_max) was significantly lower for both docetaxel and ritonavir in the prostate cancer patients as compared to the patients with other types of solid tumours treated at ModraDoc006/r 30-20/100-100. The docetaxel area under the plasma concentration versus time curve (AUC) was significantly different at this dose, with a mean AUC_0-48 of 1359 ± 374 ng/mL*h (N = 8) in female patients and 894 ± 223 ng/mL*h (N = 8) in male patients with different solid tumours (study 1), 321 ± 81 (N = 7) in HSPC (study 2) and 367 ± 182 ng/mL*h (N = 5) in mCRPC (study 3). A similar pattern was observed for ritonavir. ModraDoc006/r 30-20/200-100 in six mCRPC patients led to a comparable ritonavir exposure as compared to the patients at 30-20/100-100 in study 1 and increased the docetaxel AUC_0-48 to 1266 ± 473 ng/mL*h (N = 6).

CONCLUSION

The exposure to docetaxel and ritonavir was significantly lower in prostate cancer patients as compared to patients with other types of solid tumours, treated on ModraDoc006/r 30-20/100-100. An increase of the ritonavir dose increased the docetaxel exposure in mCRPC patients. Therefore, a different RP2D of ModraDoc006/r is pursued in castrated prostate cancer patients as compared to patients with other types of solid tumours.

TRIAL REGISTRATION

Study 1: ClinicalTrials.gov Identifier NCT01173913, date of registration August 2, 2010. Study 2: ClinicalTrials.gov Identifier NCT03066154, date of registration February 28, 2017. Study 3: ClinicalTrials.gov Identifier NCT03136640, date of registration May 2, 2017.

Immunization and Drug Metabolizing Enzymes: Focus on Hepatic Cytochrome P450 3A

OBJECTIVE

Infectious disease emergencies like the 2013-2016 Ebola epidemic and the 2009 influenza and current SARS-CoV-2 pandemics illustrate that vaccines are now given to diverse populations with preexisting pathologies requiring pharmacological management. Many natural biomolecules (steroid hormones, fatty acids, vitamins) and ~60% of prescribed medications are processed by hepatic cytochrome P450 (CYP) 3A4. The objective of this work was to determine the impact of infection and vaccines on drug metabolism.

METHODS

The impact of an adenovirus-based vaccine expressing Ebola glycoprotein (AdEBO) and H1N1 and H3N2 influenza viruses on hepatic CYP 3A4 and associated nuclear receptors was evaluated in human hepatocytes (HC-04 cells) and in mice.

RESULTS

CYP3A activity was suppressed by 55% in mice 24 h after administration of mouse-adapted H1N1, while ˂10% activity remained in HC-04 cells after infection with H1N1 and H3N2 due to global suppression of cellular translation capacity, indicated by reduction (70%, H1N1, 56%, H3N2) of phosphorylated eukaryotic translation initiation factor 4e (eIF4E). AdEBO suppressed CYP3A activity in vivo (44%) and in vitro (26%) 24 hours after infection.

CONCLUSION

As the clinical evaluation of vaccines for SARS-CoV-2 and other global pathogens rise, studies to evaluate the impact of new vaccines and emerging pathogens on CYP3A4 and other metabolic enzymes are warranted to avoid therapeutic failures that could further compromise the public health during infectious disease emergencies.

The Oral Bioavailability and Metabolism of Midazolam in Stable Critically Ill Children: A Pharmacokinetic Microtracing Study

Midazolam is metabolized by the developmentally regulated intestinal and hepatic drug-metabolizing enzyme cytochrome P450 (CYP) 3A4/5. It is frequently administered orally to children, yet knowledge is lacking on the oral bioavailability in term neonates up until 1 year of age. Furthermore, the dispositions of the major metabolites 1-OH-midazolam (OHM) and 1-OH-midazolam-glucuronide (OHMG) after oral administration are largely unknown for the entire pediatric age span. We aimed to fill these knowledge gaps with a pediatric [14 C]midazolam microtracer population pharmacokinetic study. Forty-six stable, critically ill children (median age 9.8 (range 0.3-276.4) weeks) received a single oral [14 C]midazolam microtracer (58 (40-67) Bq/kg) when they received a therapeutic continuous intravenous midazolam infusion and had an arterial line in place enabling blood sampling. For midazolam, in a one-compartment model, bodyweight was a significant predictor for clearance (0.98 L/hour) and volume of distribution (8.7 L) (values for a typical individual of 5 kg). The typical oral bioavailability in the population was 66% (range 25-85%). The exposures of OHM and OHMG were highest for the youngest age groups and significantly decreased with postnatal age. The oral bioavailability of midazolam, largely reflective of intestinal and hepatic CYP3A activity, was on average lower than the reported 49-92% for preterm neonates, and higher than the reported 21% for children> 1 year of age and 30% for adults. As midazolam oral bioavailability varied widely, systemic exposure of other CYP3A-substrate drugs after oral dosing in this population may also be unpredictable, with risk of therapy failure or toxicity.

Differential pulse voltammetric determination of homovanillic acid as a tumor biomarker in human urine after hollow fiber-based liquid-phase microextraction

Novel method for the determination of a tumor marker homovanillic acid (HVA) in human urine was developed. Combination of hollow fiber - based liquid-phase microextraction (HF-LPME) and differential pulse voltammetry (DPV) at a cathodically pre-treated boron doped diamond electrode (BDDE) was applied for these purposes. Optimum conditions were: butyl benzoate as supported liquid membrane (SLM) formed on polypropylene HF, 0.1 mol L^-1 HCl as donor phase, 0.1 mol L^-1 sodium phosphate buffer of pH 6 as acceptor phase, and 30 min extraction time. HF-LPME-DPV concentration dependence was linear in the range from 1.2 to 100 μmol L^-1. Limits of quantification (LOQ) and detection (LOD) were 1.2 and 0.4 μmol L^-1, respectively. The applicability of the developed method was verified by analysis of human urine. Standard addition method was used, found HVA concentration was 13.5 ± 1.3 μmol L^-1, RSD = 9.3% (n=5).

Composite midazolam and 1'-OH midazolam population pharmacokinetic model for constitutive, inhibited and induced CYP3A activity

CYP3A plays an important role in drug metabolism and, thus, can be a considerable liability for drug-drug interactions. Population pharmacokinetics may be an efficient tool for detecting such drug-drug interactions. Multiple models have been developed for midazolam, the typical probe substrate for CYP3A activity, but no population pharmacokinetic models have been developed for use with inhibition or induction. The objective of the current analysis was to develop a composite parent-metabolite model for midazolam which could adequately describe CYP3A drug-drug interactions. As an exploratory objective, parameters were assessed for potential cut-points which may allow for determination of drug-drug interactions when a baseline profile is not available. The final interaction model adequately described midazolam and 1′-OH midazolam concentrations for constitutive, inhibited, and induced CYP3A activity. The model showed good internal and external validity, both with full profiles and limited sampling (2, 2.5, 3, and 4 h), and the model predicted parameters were congruent with values found in clinical studies. Assessment of potential cut-points for model predicted parameters to assess drug-drug interaction liability with a single profile suggested that midazolam clearance may reasonably be used to detect inhibition (4.82–16.4 L/h), induction (41.8–88.9 L/h), and no modulation (16.4–41.8 L/h), with sensitivities for potent inhibition and induction of 87.9% and 83.3%, respectively, and a specificity of 98.2% for no modulation. Thus, the current model and cut-points could provide efficient and accurate tools for drug-drug liability detection, both during drug development and in the clinic, following prospective validation in healthy volunteers and patient populations.

No alteration of Cyp3A4 activity after major hepatectomy in the early postoperative period - A prospective before-after study

BACKGROUND

The impact of major liver resection (LR) on the detoxifying function of the remaining liver tissue as represented by CYP3A activity has yet to be assessed. Therefore, this study evaluates the changes in CYP3A activity between preoperative values and after liver resection.

MATERIAL AND METHODS

To determine CYP3A activity, midazolam (MDZ) was used as a marker substance, 3 μg were applied intravenously one day before surgery and on the 3rd day after surgery. Subsequently blood was withdrawn at 0, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4 and 6 h post application of the study drug. Plasma MDZ and 1-OH-MDZ concentration was assessed using a LC-MS/MS method. Volumetric analysis of the resected liver was done by syngo.CT liver analysis software (Siemens Healthineers) using preoperative multidetector computed tomography.

RESULTS

N = 13 (8 male/5 female) patients were included in this study and received preoperative evaluation, 11 patients were studied also after liver resection. The mean age was 62 (±15.3) years with a mean BMI of 23.6 ± 4.8 kg/m². No patient suffered from acute liver dysfunction postoperatively. None of the pharmacokinetic parameters assessed were significantly altered by liver resection. CYP3A activity over time was not significantly reduced by major liver resection.

CONCLUSION

This study gives first time data on the impact of major liver resection on CYP3A activity. It was shown that MDZ clearance representing in vivo CYP3A activity is not altered by major liver resection. This suggests no dose adjustment of commonly applied drugs which are CYP3A substrates needs to be carried out.

Clobetasol Propionate Is a Heme-Mediated Selective Inhibitor of Human Cytochrome P450 3A5

The human cytochrome P450 (CYP) enzymes CYP3A4 and CYP3A5 metabolize most drugs and have high similarities in their structure and substrate preference. Whereas CYP3A4 is predominantly expressed in the liver, CYP3A5 is upregulated in cancer, contributing to drug resistance. Selective inhibitors of CYP3A5 are, therefore, critical to validating it as a therapeutic target. Here we report clobetasol propionate (clobetasol) as a potent and selective CYP3A5 inhibitor identified by high-throughput screening using enzymatic and cell-based assays. Molecular dynamics simulations suggest a close proximity of clobetasol to the heme in CYP3A5 but not in CYP3A4. UV-visible spectroscopy and electron paramagnetic resonance analyses confirmed the formation of an inhibitory type I heme-clobetasol complex in CYP3A5 but not in CYP3A4, thus explaining the CYP3A5 selectivity of clobetasol. Our results provide a structural basis for selective CYP3A5 inhibition, along with mechanistic insights, and highlight clobetasol as an important chemical tool for target validation.

Toward precision medicine in pediatric population using cytochrome P450 phenotyping approaches and physiologically based pharmacokinetic modeling

The activity of drug-metabolizing enzymes (DME) shows high inter- and intra-individual variability. Genetic polymorphisms, exposure to drugs, and environmental toxins are known to significantly alter DME expression. In addition, the activity of these enzymes is highly age-dependent due to maturation processes that occur during development. Currently, there is a vast choice of phenotyping methods in adults using exogenous probes to characterize the activity of these enzymes. However, this can hardly be applied to children since it requires the intake of non-therapeutic xenobiotics. In addition, sampling may be challenging in the pediatric population for a variety of reasons: limited volume (e.g., blood), inappropriate sampling methods for age (e.g., urine), and metric requiring invasive or multiple blood samples. This review covers the main existing methods that can be used in the pediatric population to determine DME activity, with a particular focus on cytochrome P450 enzymes. Less invasive tools are described, including phenotyping using endogenous probes. Finally, the potential of pediatric model-informed precision dosing using physiologically based pharmacokinetic modeling is discussed.

Use of Cocktail Probe Drugs for Indexing Cytochrome P450 Enzymes in Clinical Pharmacology Studies - Review of Case Studies

BACKGROUND

The cocktail approach of probing drug metabolizing enzymes, in particular cytochrome P450 (CYP) enzymes, is a cornerstone in clinical pharmacology studies. The first report of the famous "Pittsburg cocktail" has led the way for the availability of numerous cocktail substrate mixtures that provide options for indexing of CYP enzymes and/or evaluating the perpetrator capacity of the drug.

OBJECTIVE

The key objectives were: 1) To collate, tabulate, and discuss the various cocktail substrates to determine specific CYP enzyme activity in clinical pharmacology studies with specific case studies; 2) To introspect on how the cocktail approach has withstood the test of time and evolved for enabling key decision(s); 3) To provide some futuristic views on the use of cocktail in drug discovery and development.

METHOD

The review was compiled after consultation with databases such as PubMed (NCBI database) and Google scholar to source various published literature on cocktail approaches in drug development.

RESULTS

In the reviewed case studies, CYP indexing was achieved using a single time point (differing for specific CYP enzyme) plasma determination of the metabolite to parent ratio for all CYP enzymes with the exception of CYP3A4/5, where multiple time points were required for exposure measurement of midazolam and its metabolite. Likewise, a single void of urine, for a specific time duration, has been utilized for the recovery measurements of parent and metabolite for CYP indexing purposes.

CONCLUSION

The review provides a comprehensive list of various types of cocktail approaches and discusses some key considerations including the evolution of the cocktail approaches over time, perspectives and futuristic views for the use of probe drugs to aid the execution of clinical pharmacology studies and data interpretation.

Food-Drug Interaction between the Adlay Bran Oil and Drugs in Rats

Adlay (Coix lachryma-jobi L. var. ma-yuen Stapf) contains various phytonutrients for treating many diseases in Asia. To investigate whether orally administered adlay bran oil (ABO) can cause drug interactions, the effects of ABO on the pharmacokinetics of five cytochrome P450 (CYP) probe drugs were evaluated. Rats were given a single oral dose (2.5 mL/kg BW) of ABO 1 h before administration of a drug cocktail either orally or intravenously, and blood was collected at various time points. A single oral dose of ABO administration did not affect the pharmacokinetics of five probe drugs when given as a drug cocktail intravenously. However, ABO increased plasma theophylline (+28.4%), dextromethorphan (+48.7%), and diltiazem (+46.7%) when co-administered an oral drug cocktail. After 7 days of feeding with an ABO-containing diet, plasma concentrations of theophylline (+45.4%) and chlorzoxazone (+53.6%) were increased after the oral administration of the drug cocktail. The major CYP enzyme activities in the liver and intestinal tract were not affected by ABO treatment. Results from this study indicate that a single oral dose or short-term administration of ABO may increase plasma drug concentrations when ABO is given concomitantly with drugs. ABO is likely to enhance intestinal drug absorption. Therefore, caution is needed to avoid food–drug interactions between ABO and co-administered drugs.

The influence of bariatric surgery on oral drug bioavailability in patients with obesity: A systematic review

Anatomical changes in the gastrointestinal tract and subsequent weight loss may influence drug disposition and thus drug dosing following bariatric surgery. This review systematically examines the effects of bariatric surgery on drug pharmacokinetics, focusing especially on the mechanisms involved in restricting oral bioavailability. Studies with a longitudinal before-after design investigating the pharmacokinetics of at least one drug were reviewed. The need for dose adjustment following bariatric surgery was examined, as well as the potential for extrapolation to other drugs subjected to coinciding pharmacokinetic mechanisms. A total of 22 original articles and 32 different drugs were assessed. The majority of available data is based on Roux-en-Y gastric bypass (RYGBP) (18 of 22 studies), and hence, the overall interpretation is more or less limited to RYGBP. In the case of the majority of studied drugs, an increased absorption rate was observed early after RYGBP. The effect on systemic exposure allows for a low degree of extrapolation, including between drugs subjected to the same major metabolic and transporter pathways. On the basis of current understanding, predicting the pharmacokinetic change for a specific drug following RYGBP is challenging. Close monitoring of each individual drug is therefore recommended in the early postsurgical phase. Future studies should focus on the long-term effects of bariatric surgery on drug disposition, and they should also aim to disentangle the effects of the surgery itself and the subsequent weight loss.

The relative role of CYP3A4 and CYP3A5 in eplerenone metabolism

Cytochrome P450 mediated metabolism is the rate-limiting step of elimination for many drugs. CYP3A4 is the most abundant hepatic isoform and CYP3A4/5 metabolize the largest fraction of drugs. Pharmacogenetic studies have not been able to characterize population variability in CYP3A4 activity because few variant alleles associated with aberrant enzyme activity have been found. Substrate probes such as midazolam and testosterone have been utilized in-vivo and in-vitro to determine catalytic activity of these enzymes, but they suffer from several limitations. Eplerenone, an aldosterone antagonist, is also metabolized by CYP3A enzymes, and it has the potential to be an excellent substrate probe for CYP3A4/5. Eplerenone's primary metabolite, 6 beta-hydroxyeplerenone is formed preferentially via CYP3A4, however, the relative contribution of CYP3A5 to the 21-hydroxyeplerenone metabolite formation is unknown. Through in-vitro microsomal incubations with recombinant CYP3A4 and CYP3A5 enzymes, we identified their relative contributions to 21-hydroxyeplerenone metabolism. The 21-hydroxy metabolite is formed preferentially via CYP3A5 V_max/K_M (3.3) versus CYP3A4 V_max/K_M (1.9). Based on these findings, eplerenone has the potential to serve as an in-vivo substrate probe for CYP3A4 by monitoring 6-beta-hydroxy metabolite formation as well as CYP3A4/5 by monitoring 21-hydroxy metabolite formation.

Dose-linearity of the pharmacokinetics of an intravenous [14 C]midazolam microdose in children

Aims

Drug disposition in children may vary from adults due to age‐related variation in drug metabolism. Microdose studies present an innovation to study pharmacokinetics (PK) in paediatrics; however, they should be used only when the PK is dose linear. We aimed to assess dose linearity of a [¹⁴C]midazolam microdose, by comparing the PK of an intravenous (IV) microtracer (a microdose given simultaneously with a therapeutic midazolam dose), with the PK of a single isolated microdose.

Methods

Preterm to 2‐year‐old infants admitted to the intensive care unit received [¹⁴C]midazolam IV as a microtracer or microdose, followed by dense blood sampling up to 36 hours. Plasma concentrations of [¹⁴C]midazolam and [¹⁴C]1‐hydroxy‐midazolam were determined by accelerator mass spectrometry. Noncompartmental PK analysis was performed and a population PK model was developed.

Results

Of 15 infants (median gestational age 39.4 [range 23.9–41.4] weeks, postnatal age 11.4 [0.6–49.1] weeks), 6 received a microtracer and 9 a microdose of [¹⁴C]midazolam (111 Bq kg⁻¹; 37.6 ng kg⁻¹). In a 2‐compartment PK model, bodyweight was the most significant covariate for volume of distribution. There was no statistically significant difference in any PK parameter between the microdose and microtracer, nor in the area under curve ratio [¹⁴C]1‐OH‐midazolam/[¹⁴C]midazolam, showing the PK of midazolam to be linear within the range of the therapeutic and microdoses.

Conclusion

Our data support the dose linearity of the PK of an IV [¹⁴C]midazolam microdose in children. Hence, a [¹⁴C]midazolam microdosing approach may be used as an alternative to a therapeutic dose of midazolam to study developmental changes in hepatic CYP3A activity in young children.

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.

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.

Evaluating metronidazole as a novel, safe CYP2A6 phenotyping probe in healthy adults

AIMS

CYP2A6 is a genetically polymorphic enzyme resulting in differential substrate metabolism and health behaviours. Current phenotyping probes for CYP2A6 exhibit limitations related to procurement (deuterated cotinine), toxicity (coumarin), specificity (caffeine) and age-appropriate administration (nicotine, NIC). In vitro, CYP2A6 selectively forms 2-hydroxymetronidazole (2HM) from metronidazole (MTZ). The purpose of this study was to evaluate MTZ as a CYP2A6 phenotyping probe drug in healthy adults against the well-established method of measuring trans-3-hydroxycotinine (3HC)/cotinine (COT).

METHODS

A randomized, cross-over, pharmacokinetic study was completed in 16 healthy, nonsmoking adults. Separated by a washout period of at least 2 weeks, MTZ 500 mg and NIC gum 2 mg were administered and plasma was sampled over 48 hours and 8 hours, respectively. Correlations of plasma metabolite/parent ratios (2HM/MTZ; 3HC/COT) were assessed by Pearson coefficient. CYP2A6 genotyping was conducted and incorporated as a variable of plasma ratio response.

RESULTS

Correlations between the plasma ratio 2HM/MTZ and 3HC/COT were ≥ 0.9 at multiple time points (P < 0.001), demonstrating a wide window during which 2HM/MTZ can be queried post-MTZ dose. CYP2A6 genotype had significant impacts on both MTZ and NIC phenotyping ratios with decreased activity predicted phenotypes demonstrating 2HM/MTZ ratios ≤58% and 3HC/COT ratios ≤56% compared with extensive activity predicted phenotypes at all time points examined in the study (P < 0.05). No adverse events were reported in the MTZ arm while 38% (n = 6) of participants reported mild adverse events in the NIC arm.

CONCLUSIONS

Metronidazole via 2HM/MTZ performed well as a novel, safe phenotyping probe for CYP2A6 in healthy adults.

Inhibition of CYP3A4 and CYP3A5 expression by scutellarin is not mediated via the regulation of hsa-miR-27a, 27b, 148a, 298 and 451a levels

1. Scutellarin is a flavonoid glycoside widely used in the treatment of cardio-cerebrovascular diseases in China. In this study, we investigated the effect of scutellarin on cytochrome P450 3A4 (CYP3A4) and CYP3A5 expression. Furthermore, we studied the expression of hsa-miR-27a, hsa-miR-27b, hsa-miR-148a, hsa-miR-298 and hsa-miR-451a in humans to determine whether scutellarin regulated CYP3A4 and CYP3A5 expression by altering levels of those micro-ribonucleic acids (miRNAs). 2. In vitro CYP3A4 and CYP3A5 expression was measured in Chang liver cells via quantitative real-time polymerase chain reaction (qPCR) and western blot. In vivo CYP3A4 and CYP3A5 expression was evaluated through the metabolism of their substrate midazolam (MID), and detected via ultra-performance liquid chromatography-mass spectrometry. The relative miRNA levels in the plasma of study participants were investigated via qPCR. 3. Results showed that scutellarin significantly inhibited the CYP3A4 and CYP3A5 expression both in vitro and in vivo. However, the levels of hsa-miR-27a, hsa-miR-27b, hsa-miR-148a, hsa-miR-298 and hsa-miR-451a in scutellarin group did not show significant changes when compared with those of the placebo group (p > 0.05), suggesting that the expression of these miRNAs is not relevant to the scutellarin-induced down-regulation of CYP3A4 and CYP3A5.

Dietary effects of Sideritis scardica "mountain tea" on human in vivo activities of xenobiotic metabolizing enzymes in healthy subjects

Sideritis scardica(S. scardica) is an endemic plant of the Balkan Peninsula traditionally used as herbal tea for inflammation and gastric disorders. Aqueous herbal extracts may affect the activity of Phase I and II enzymes involved in xenobiotic metabolism. The purpose of the present study was to determine whether S. scardica decoction alters the activity of CYP1A2, CYP2A6, XO, NAT2 and UGT1A1/1A6 enzymes in humans. Fourteen healthy subjects consumed S. scardica decoction for six days. Enzyme phenotyping was assessed in saliva and urine using caffeine and paracetamol metabolite ratios as follows: CYP1A2: 17X/137X (saliva) and (AFMU+1U+1X)/17U, CYP2A6: 17U/(17U + 17X), XO: 1U/(1U+1X), NAT2: AFMU/(AFMU+1U+1X) and UGT1A1/1A6: glucuronidated/total paracetamol (urine). After S. scardica intake, CYP1A2 index was reduced by ∼16% and ∼8% in saliva (before: 0.54 ± 0.18, after: 0.46 ± 0.09; p = 0.08) and urine (before: 3.59 ± 0.52, after: 3.67 ± 0.78; p = 0.12), respectively. CYP2A6 index was significantly reduced only in males (before: 0.76 ± 0.08, after: 0.67 ± 0.07; p = 0.004), suggesting sexual dimorphism in CYP2A6 inhibition. There was no effect of Sideritis scardica treatment on XO, NAT2 or UGT1A1/1A6 indices. Usual consumption of the aerial parts of S. scardica decoction is unlikely to result in herb-drug interactions involving the enzymes studied, with the exception of potential herb-CYP2A6 substrate interaction in males.

Sensitive and simultaneous quantitation of 6β-hydroxycortisol and cortisol in human plasma by LC-MS/MS coupled with stable isotope dilution method

CYP3A phenotyping provides a means for personalized drug therapy. We focused our attention on the plasma 6β-hydroxycortisol (6β-OHF) to cortisol ratio as an index for CYP3A phenotyping. In the present study, we developed a sensitive and reliable method for the simultaneous determination of 6β-OHF and cortisol in human plasma using high-performance liquid chromatography/tandem mass spectrometry together with picolinylester derivatization or nonderivatization methods and 6β-[9,11,12,12-² H₄ ]hydroxycortisol and [1,2,4,19-¹³ C₄ ]cortisol as internal standards for in vivo CYP3A phenotyping in humans. The lower limits of quantification were 38.513 pg/mL for 6β-OHF and 38.100 pg/mL for cortisol. The relative error and relative standard deviation of the lower limits of quantification were <5% for both methods. The intra-day and inter-day assay reproducibilities of the determined 6β-OHF and cortisol concentrations were consistent with the actual amounts added as relative errors and relative standard deviations for both methods, which were <5.4% and <3.9%, respectively. Both methods were applied for the quantification of plasma 6β-OHF and cortisol concentrations in healthy subjects taking oral contraceptives. The absolute concentrations and time course of 6β-OHF and cortisol were found to be consistent when measured using the 2 methods. The ratio as an index for in vivo CYP3A activity decreased after 21 days of taking oral contraceptives for both methods. To the best of our knowledge, this is the first study reporting the detailed investigation of accuracy and precision in the simultaneous measurement of 6β-OHF and cortisol in human plasma using liquid chromatography/tandem mass spectrometry coupled with stable isotope dilution method, which can be applied to CYP3A phenotyping.

Evaluation of Omeprazole Limited Sampling Strategies to Estimate Constitutive Cytochrome P450 2C19 Activity in Healthy Adults

BACKGROUND

Limited sampling strategy (LSS) is a validated method to estimate pharmacokinetic (PK) parameters from a reduced number of samples. Omeprazole is used to phenotype in vivo cytochrome P450 (CYP) 2C19 activity. This study examined an LSS using 2 estimation methods to determine apparent oral clearance (CL/F) and thus CYP2C19 activity.

METHODS

Data from 7 previously published studies included healthy subjects receiving a single, oral dose of omeprazole with intensive PK sampling. CL/F was estimated using noncompartmental analysis (NCA) and population PK modeling. LSS was simulated by selecting the 1, 2, 4, and/or 6-hour postdose time points. Linear regression was performed to assess whether CL/F estimated from limited sampling could accurately predict CL/F from the full PK profile.

RESULTS

Median CL/F was 23.7 L/h by NCA and 19.3 L/h by population PK modeling. In comparing the LSS NCA estimated versus observed CL/F, all evaluated linear regression models had unacceptable coefficients of determination (r, range: 0.14-0.81). With the population PK approach, 737 plasma concentrations (n = 71) and CYP2C19 genotype data were described with a 1-compartment structural model with mixed zero and first-order absorption and lag time. In comparing the population PK LSS estimated versus observed CL/F, all evaluated linear regression models had unacceptable r (range: 0.02-0.74). Post hoc comparison of CYP2C19 poor metabolizers versus CYP2C19 extensive metabolizers resulted in significantly lower CL/F in poor metabolizers versus extensive metabolizers.

CONCLUSIONS

Omeprazole LSS performed poorly in estimating CL/F using 2 separate estimation approaches and does not seem to be a suitable method for determining CYP2C19 activity.

Quantitative Evaluation of Cytochrome P450 3A4 Inhibition and Hepatotoxicity in HepaRG 3-D Spheroids

Predicting drug–drug interactions (DDIs) is an important step during drug development to avoid unexpected side effects. Cytochrome P450 (CYP) 3A4 is the most abundant human hepatic phase I enzyme, which metabolizes >50% of therapeutic drugs. Therefore, it is essential to test the potential of a drug candidate to induce CYP3A4 expression or inhibit its activity. Recently, 3-dimensional (3-D) mammalian cell culture models have been adopted in drug discovery research to assess toxicity, DDIs, and pharmacokinetics. In this study, we applied a human 3-D spheroid culture protocol using HepaRG cells combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to assess its ability to predict CYP3A4 inhibition. Levels of midazolam, a specific substrate of CYP3A4, were used to determine the long-term metabolic capacity of CYP3A4. Midazolam was decreased in the 3-D HepaRG culture system by ∼80% over 7 days, whereas its primary metabolite, 1-hydroxymidazolam, increased by ∼40%. Next, we assessed hepatotoxicity by determining the cytotoxicity of known hepatotoxicants in HepaRG spheroids, HepG2 cells, and primary human hepatocytes. Significant differences in cytotoxicity were detected in the system using 3-D HepaRG spheroids. These results suggest that 3-D HepaRG spheroids are a good model for prediction of CYP inhibition and hepatotoxicity in screening of early drug candidates.

Drug Interaction Potential of Osilodrostat (LCI699) Based on Its Effect on the Pharmacokinetics of Probe Drugs of Cytochrome P450 Enzymes in Healthy Adults

BACKGROUND AND OBJECTIVES

Osilodrostat (LCI699) is an adrenal steroidogenesis inhibitor currently in late-phase clinical development as a potential treatment for Cushing's disease. This study evaluated the inhibitory effect of osilodrostat on the pharmacokinetics of probe substrates of the cytochrome P450 (CYP) enzymes CYP1A2, CYP2C19, CYP2D6, and CYP3A4.

METHODS

Healthy adult volunteers received single-dose cocktail probe substrates [caffeine (100 mg), omeprazole (20 mg), dextromethorphan (30 mg), and midazolam (2 mg)] followed by a 6-day washout. Subjects then received a single dose of osilodrostat 50 mg followed by a single dose of cocktail probe substrates.

RESULTS

Nineteen of twenty subjects (ten were male) completed the study. Mean age, body weight, and body mass index were 41.8 years, 73.0 kg, and 24.4 kg/m². Geometric mean ratio of the area under the concentration-time curve from time zero to the last measureable concentration and 90% confidence intervals of probe substrate exposure with osilodrostat were: caffeine (CYP1A2 probe substrate), 2.33 (2.10-2.59); omeprazole (CYP2C19), 1.91 (1.74-2.11); dextromethorphan (CYP2D6), 1.48 (1.34-1.63); and midazolam (CYP3A4/5), 1.50 (1.41-1.60). Corresponding values for geometric mean ratio of maximum plasma concentration (90% confidence interval) for the change in substrate exposure were 1.07 (0.988-1.15), 1.61 (1.40-1.84), 1.35 (1.21-1.50), and 1.47 (1.32-1.62).

CONCLUSIONS

Osilodrostat is a moderate inhibitor of CYP1A2 and CYP2C19 and a weak inhibitor of CYP2D6 and the most clinically important CYP enzyme, CYP3A4. Osilodrostat is unlikely to significantly increase the exposures of other medications cleared by CYP3A4. These findings are clinically relevant given that Cushing's disease is a chronic condition often requiring multiple medications and that most other therapies have significant drug interaction potential.

Pharmacogenetic testing revisited: 5' nuclease real-time polymerase chain reaction test panels for genotyping CYP2D6 and CYP2C19

Due to their involvement in the metabolization of commonly prescribed psychopharmaceutical drugs, the cytochrome oxidase genes CYP2D6 and CYP2C19 are extensive targets for pharmacogenetic testing. The existence of common allelic variants allows the prediction of a metabolic phenotype based on a genotype result, hereby supplying a clinical tool for optimizing prescription and minimizing adverse effects. In this study, we present the development of two 5' nuclease real-time polymerase chain reaction (PCR) test panels, capable of detecting eight of the most clinically relevant alleles of the CYP2D6 gene (*2, *3, *4, *6, *9, *10, 17, *41) and the three most common nonfunctional alleles of CYP2C19 (*2, *3, *4). The assays have been thoroughly validated using a large collection of reference samples, by parallel testing and by DNA sequencing. The reanalysis of reference samples provided the calculation of the frequency of the CYP2D6*4K allele in a population, not previously reported. Furthermore, original test results from CYP2D6*41, generated based on the presence of the 2850T and the lack of the -1584G single-nucleotide polymorphism (SNP), were compared with genotyping based on the current acknowledged founder SNP 2988G of this allele. These results indicate that up to 17.7% of the patients originally tested as carriers of the CYP2D6*41 allele may have had an incorrect phenotypic result assigned. The two 5' nuclease real-time PCR test panels have subsequently been optimized for use in the clinical laboratory, using a standard real-time PCR instrument and software.

A highly sensitive method for the simultaneous UHPLC-MS/MS analysis of clonidine, morphine, midazolam and their metabolites in blood plasma using HFIP as the eluent additive

In intensive care units, the precise administration of sedatives and analgesics is crucial in order to avoid under- or over sedation and for appropriate pain control. Both can be harmful to the patient, causing side effects or pain and suffering. This is especially important in the case of pediatric patients, and dose-response relationships require studies using pharmacokinetic-pharmacodynamic modeling. The aim of this work was to develop and validate a rapid ultra-high performance liquid chromatographic-tandem mass spectrometric method for the analysis of three common sedative and analgesic agents: morphine, clonidine and midazolam, and their metabolites (morphine-3-glucuronide, morphine-6-glucuronide and 1'-hydroxymidazolam) in blood plasma at trace level concentrations. Low concentrations and low sampling volumes may be expected in pediatric patients; we report the lowest limit of quantification for all analytes as 0.05ng/mL using only 100μL of blood plasma. The analytes were separated chromatographically using the C18 column with the weak ion-pairing additive 1,1,1,3,3,3-hexafluoro-2-propanol and methanol. The method was fully validated and a matrix matched calibration range of 0.05-250ng/mL was attained for all analytes In addition, between-day accuracy for all analytes remained within 93-108%, and precision remained within 1.5-9.6% for all analytes at all concentration levels over the calibration range.

The CYP3A biomarker 4β-hydroxycholesterol does not improve tacrolimus dose predictions early after kidney transplantation

AIMS

Tacrolimus is a cornerstone in modern immunosuppressive therapy after kidney transplantation. Tacrolimus dosing is challenged by considerable pharmacokinetic variability, both between patients and over time after transplantation, partly due to variability in cytochrome P450 3A (CYP3A) activity. The aim of this study was to assess the value of the endogenous CYP3A marker 4β-hydroxycholesterol (4βOHC) for tacrolimus dose individualization early after kidney transplantation.

METHODS

Data were obtained from 79 adult kidney transplant recipients who contributed a total of 625 4βOHC measurements and 1999 tacrolimus whole blood concentrations during the first 2 months after transplantation. The relationships between 4βOHC levels and individual estimates of tacrolimus apparent plasma clearance (CL/F_plasma ) at different time points after transplantation were investigated using scatterplots and population pharmacokinetic modelling.

RESULTS

There was no significant correlation between pre-transplant 4βOHC levels and tacrolimus CL/F_plasma the first week (r = 0.19 [95% CI -0.03-0.40]) or between 4βOHC and tacrolimus CL/F_plasma 1 week (r = 0.20 [-0.11-0.47]), 4 weeks (r = 0.21 [-0.07-0.46]) or 2 months (r = 0.24 [-0.03-0.48]) after transplantation (P ≥ 0.06). In the population analysis, time-varying 4βOHC was not a statistically significant covariate on tacrolimus CL/F_plasma , neither in terms of absolute values (P = 0.11) nor in terms of changes from baseline (P = 0.17). 4βOHC values increased between 1 week and 2 months after transplantation (median change +57% [IQR +22-83%], P < 0.001), indicating increasing CYP3A activity. Contradictorily, tacrolimus CL/F_plasma decreased over the same period (median change -13% [IQR -3 to -26%], P < 0.001).

CONCLUSIONS

4βOHC does not appear to have a clinical potential to improve individualization of tacrolimus doses early after kidney transplantation.

CRISPR knockout rat cytochrome P450 3A1/2 model for advancing drug metabolism and pharmacokinetics research

Cytochrome P450 (CYP) 3A accounts for nearly 30% of the total CYP enzymes in the human liver and participates in the metabolism of over 50% of clinical drugs. Moreover, CYP3A plays an important role in chemical metabolism, toxicity, and carcinogenicity. New animal models are needed to investigate CYP3A functions, especially for drug metabolism. In this report, Cyp3a1/2 double knockout (KO) rats were generated by CRISPR-Cas9 technology, and then were characterized for viability and physiological status. The Cyp3a1/2 double KO rats were viable and fertile, and had no obvious physiological abnormities. Compared with the wild-type (WT) rat, Cyp3a1/2 expression was completely absent in the liver of the KO rat. In vitro and in vivo metabolic studies of the CYP3A1/2 substrates indicated that CYP3A1/2 was functionally inactive in double KO rats. The Cyp3a1/2 double KO rat model was successfully generated and characterized. The Cyp3a1/2 KO rats are a novel rodent animal model that will be a powerful tool for the study of the physiological and pharmacological roles of CYP3A, especially in drug and chemical metabolism in vivo.

An ultra-sensitive LC–MS/MS method to determine midazolam levels in human plasma: development, validation and application to a clinical study

Aim: Midazolam is a commonly used marker substrate for the in vivo assessment of CYP3A activity. Reliable pharmacokinetic assessment at sub-pharmacological doses of midazolam requires an ultra-sensitive analytical method. Methods: A new, ultra-sensitive LC–MS/MS method for the determination of midazolam in human plasma using SPE was developed and fully validated. The lowest limit of quantitation is 0.1 pg/ml with a sample volume of 500 μl. Results/conclusion: The following parameters were validated: sensitivity, assay accuracy and precision, linearity, selectivity, and stability of midazolam at pertinent analytical and storage conditions. The validated method was utilized successfully for the sample assay during a midazolam microdosing study for the evaluation of CYP3A4 activity of a clinical candidate.

Optimized Cocktail Phenotyping Study Protocol Using Physiological Based Pharmacokinetic Modeling and In silico Assessment of Metabolic Drug-Drug Interactions Involving Modafinil

In vivo cocktail pathway phenotyping (ICPP) is routinely used to assess the metabolic drug-drug interaction (mDDI) potential of new drug candidates (NDC) during drug development. However, there are a number of potential limitations to this approach and the use of validated drug cocktails and study protocols is essential. Typically ICPP mDDI studies assess only the impact of interactions following multiple postulated perpetrator doses and hence the emphasis in terms of validation of these studies has been ensuring that there are no interactions between probe substrates. Studies assessing the comparative impact of single and multiple doses of the postulated perpetrator have the potential to provide richer information regarding both the clinical impact and mechanism of mDDIs. Using modafinil as a model compound, we sought to develop an optimized ICPP mDDI study protocol to evaluate the potential magnitude and clinical relevance of mDDIs using a physiologically based pharmacokinetic modeling approach.