Co-regulation of CYP3A4 and CYP3A5 and contribution to hepatic and intestinal midazolam metabolism

Population pharmacokinetics of blonanserin in Japanese adolescent and adult patients with schizophrenia

The second-generation antipsychotic blonanserin is a highly selective, full antagonist of dopamine D2 and D3 and serotonin 5-HT2A receptors. It is currently prescribed for patients with schizophrenia in Japan. We aimed to develop a population pharmacokinetic model of oral blonanserin, including data from 12 to 77 years old patients, to assess the covariates that influence blonanserin pharmacokinetics and evaluate appropriate dosage regimens in adolescents versus adults. The population pharmacokinetic analysis was conducted using plasma concentrations in 132 Japanese adolescent and 135 adult patients with schizophrenia (including 20 older adults [≥65 years] patients), and 49 healthy adults. The blonanserin population pharmacokinetics was described using a two-compartment model with first-order absorption with lag time. Relative bioavailability decreased in fasted conditions and with concomitant CYP3A4 inducer use. Apparent clearance in older adult was lower than adult and adolescent. Simulation revealed similar plasma exposures between adolescents and adults and slightly larger in older adults. Bayesian estimates of apparent clearance suggested no effects of age in adolescents between 12 and 18 years old. Together, these results reveal the pharmacokinetic characteristics of blonanserin over a wide age range and support the appropriateness of the approved dosing regimen for adolescent patients with schizophrenia in Japan.

Physiologically-based pharmacokinetic modelling to investigate the effect of CYP3A4/3A5 maturation on tacrolimus pharmacokinetics in paediatric HSCT patients

Tacrolimus (FK506) is a cornerstone of GVHD-prophylaxis treatment in paediatrics undergoing haematopoietic stem cell transplantation (HSCT). However, due to concerns about highly inter/intra-individual variability, precision dosing of FK506 is crucial. Cytochrome P450 (CYP) 3A4 and 3A5 are considered important sources of FK506 pharmacokinetic variability. Nevertheless, the impact of age-related maturation in hepatic and intestinal CYP3A4/3A5 enzymes remains unknown in paediatric HSCT patients. Physiologically-based pharmacokinetic (PBPK) models were developed and verified in adult volunteers and adult HSCT patients using GastroPlus™ (version 9.0), and then extrapolated to paediatric HSCT patients, taking into account the maturation of CYP3A4 and CYP3A5. Default CYP3A4 and CYP3A5 ontogeny profiles were updated based on the latest reports. The paediatric PBPK model was evaluated with independent data collected from Sun Yat-sen Memorial Hospital (86 paediatric HSCT patients, 1 to 16 -year-old). Simulations were performed to evaluate a reported FK506 dosing regimen in infants and children with different CYP3A5 genotypes. Extensive PBPK model validation indicated good predictability, with the predicted/observed (P/O) ratios within the range of 0.80-fold to 1.25-fold. Blood tacrolimus concentration-time curves were comparable between the real and virtual patients. Simulations showed that the higher levels of tacrolimus in 9-month-old to 3-year-old infants were mainly attributed to the CYP3A4/3A5 ontogeny profiles, which resulted in lower clearance and higher exposure relative to dose. The oral dosage of 0.1 mg/kg/day (q12 h) is considered appropriate for paediatric HSCT patients 9 months to 15 years of age with CYP3A5 *1/*1 genotypes. Lower doses were required for paediatric HSCT patients with CYP3A5 *1/*3 (0.08 mg/kg/day, q12h) or CYP3A5 *3/*3 genotypes (0.07 mg/kg/day, q12h), and analyses demonstrated 12.5-20 % decreases in ≤3-year-old patients. The study highlights the feasibility of PBPK modelling to explore age-related enzyme maturation in infants and children (≤3-year-old) undergoing HSCT and emphasizes the need to include hepatic and gut CYP3A4/3A5 maturation parameters.

Applying Physiologically Based Pharmacokinetic Modeling to Interpret Carbamazepine's Nonlinear Pharmacokinetics and Its Induction Potential on Cytochrome P450 3A4 and Cytochrome P450 2C9 Enzymes

Carbamazepine (CBZ) is commonly prescribed for epilepsy and frequently used in polypharmacy. However, concerns arise regarding its ability to induce the metabolism of other drugs, including itself, potentially leading to the undertreatment of co-administered drugs. Additionally, CBZ exhibits nonlinear pharmacokinetics (PK), but the root causes have not been fully studied. This study aims to investigate the mechanisms behind CBZ's nonlinear PK and its induction potential on CYP3A4 and CYP2C9 enzymes. To achieve this, we developed and validated a physiologically based pharmacokinetic (PBPK) parent-metabolite model of CBZ and its active metabolite Carbamazepine-10,11-epoxide in GastroPlus®. The model was utilized for Drug-Drug Interaction (DDI) prediction with CYP3A4 and CYP2C9 victim drugs and to further explore the underlying mechanisms behind CBZ's nonlinear PK. The model accurately recapitulated CBZ plasma PK. Good DDI performance was demonstrated by the prediction of CBZ DDIs with quinidine, dolutegravir, phenytoin, and tolbutamide; however, with midazolam, the predicted/observed DDI AUClast ratio was 0.49 (slightly outside of the two-fold range). CBZ's nonlinear PK can be attributed to its nonlinear metabolism caused by autoinduction, as well as nonlinear absorption due to poor solubility. In further applications, the model can help understand DDI potential when CBZ serves as a CYP3A4 and CYP2C9 inducer.

mRNA expression levels of cytochrome P450 CYP1A2, CYP3A4, and CYP3A5 in the epidermis: a focus on individual differences among Japanese individuals

Various cytochrome P450 enzymes (CYPs) that contribute to drug metabolism are expressed in the skin. However, variation among individuals in CYP expression profiles is not well-understood.To investigate CYPs related to the metabolism of transdermal preparations in Japan, multiple skin tissue specimens of individuals of Japanese descent were prepared, and the mRNA expression levels of CYP1A2, CYP3A4, and CYP3A5 were measured. Associations between the expression patterns of these CYPs and body mass index (BMI) were also investigated.There were considerable individual differences in epidermal CYP1A2 mRNA expression levels, and CYP1A2 showed a weak positive correlation with CYP3A4 mRNA expression levels. In contrast to previous results for other organs, epidermal CYP3A4 mRNA expression levels showed a weak positive correlation with BMI.CYP3A4 in the epidermis may have been locally enhanced as a defence mechanism against xenobiotics in response to impaired barrier function. These differences in mRNA expression in the skin may affect the transdermal absorption of drugs, such as lidocaine and fentanyl, which are metabolised by multiple overlapping CYPs.Our study provides new insights into drug metabolism in the skin. These results are valuable for predicting drug effects and transdermal drug transfer rates in Japanese patients.

Impact of pharmacogenomic profiles on post-surgical pain following laparotomy for gynecologic pathology

OBJECTIVES

The aim of this prospective study was to compare perioperative opioid use in women by status of CYP2D6, a highly polymorphic pharmacogene relevant to opioid metabolism.

METHODS

Patients undergoing laparotomy were prospectively recruited and provided a preoperative saliva swab for a pharmacogenomic (PGx) gene panel. Postoperative opioid usage and pain scores were evaluated via chart review and a phone survey. Pharmacogenes known to be relevant to opioid metabolism were genotyped, and opioid metabolizing activity predicted by CYP2D6 genotyping. Patient and procedural factors were compared using Fisher's exact and Kruskal-Wallis tests.

RESULTS

The 96 enrolled patients were classified as ultra-rapid (N = 3, 3%), normal (58, 60%), intermediate (27, 28%), and poor (8, 8%) opioid metabolizers. There was no difference in surgical complexity across CYP2D6 categories (p = 0.61). Morphine Milligram Equivalents (MME) consumed during the first 24 h after peri-operative suite exit were significantly different between groups: ultrarapid metabolizers had the highest median MME (75, IQR 45-88) compared to the other three groups (normal metabolizers 23 [8-45], intermediate metabolizers 48 [20-63], poor metabolizers 31 [12-53], p = 0.03). Opioid requirements were clinically greater in ultrarapid metabolizers during the second 24 h and last 24 h but were statistically similar (p = 0.07). There was no difference in MME prescribed at discharge (p = 0.22) or patient satisfaction with pain control (p = 0.64) between groups.

CONCLUSIONS

A positive association existed between increased CYP2D6 activity and in-hospital opioid requirements, especially in the first 24 h after surgery. This provides important information to further individualize opioid prescriptions for patients undergoing laparotomy for gynecologic pathology.

The pharmacogenetics of tacrolimus in renal transplant patients: association with tremors, new-onset diabetes and other clinical events

Our study is the first study to investigate the effect of SNPs in CYP3A5, CYP3A4, ABCB1 and POR genes on the incidence of tremors, nephrotoxicity, and diabetes mellitus. A total of 223 renal transplant patients receiving tacrolimus and mycophenolate mofetil (MMF) were recruited. Both adults and children patients participated in the study. Genotyping was performed using PROFLEX-PCR followed by RFLP. MPA and tacrolimus plasma concentrations were measured by immunoassay. The AUC0-12h of MMF was estimated by a Bayesian method. We found a statistically significant association between the CYP3A5*3 and CYP3A4*1B genotypes and the tacrolimus exposure. We found a lower occurrence of nephrotoxicity (p = 0.03), tremor (p = 0.01), and new-onset diabetes (p = 0.002) associated with CYP3A5*1 allele. The CYP3A4*1B allele was significantly associated with a lower occurrence of new-onset diabetes (p = 0.026). The CYP3A5*1 allele was significantly associated with an increased risk of acute and chronic rejection (p = 0.03 and p < 0.001, respectively). Our results support the usefulness of tacrolimus pharmacokinetics in pre-kidney transplant assessments.

An Integrative Approach to Elucidate Mechanisms Underlying the Pharmacokinetic Goldenseal-Midazolam Interaction: Application of In Vitro Assays and Physiologically Based Pharmacokinetic Models to Understand Clinical Observations

The natural product goldenseal is a clinical inhibitor of CYP3A activity, as evidenced by a 40%-60% increase in midazolam area under the plasma concentration versus time curve (AUC) after coadministration with goldenseal. The predominant goldenseal alkaloids berberine and (-)-β-hydrastine were previously identified as time-dependent CYP3A inhibitors using human liver microsomes. Whether these alkaloids contribute to the clinical interaction, as well as the primary anatomic site (hepatic vs. intestinal) and mode of CYP3A inhibition (reversible vs. time-dependent), remain uncharacterized. The objective of this study was to mechanistically assess the pharmacokinetic goldenseal-midazolam interaction using an integrated in vitro-in vivo-in silico approach. Using human intestinal microsomes, (-)-β-hydrastine was a more potent time-dependent inhibitor of midazolam 1'-hydroxylation than berberine (KI and kinact: 8.48 μM and 0.041 minutes-1, respectively, vs. >250 μM and ∼0.06 minutes-1, respectively). Both the AUC and Cmax of midazolam increased by 40%-60% after acute (single 3-g dose) and chronic (1 g thrice daily × 6 days) goldenseal administration to healthy adults. These increases, coupled with a modest or no increase (≤23%) in half-life, suggested that goldenseal primarily inhibited intestinal CYP3A. A physiologically based pharmacokinetic interaction model incorporating berberine and (-)-β-hydrastine successfully predicted the goldenseal-midazolam interaction to within 20% of that observed after both chronic and acute goldenseal administration. Simulations implicated (-)-β-hydrastine as the major alkaloid precipitating the interaction, primarily via time-dependent inhibition of intestinal CYP3A, after chronic and acute goldenseal exposure. Results highlight the potential interplay between time-dependent and reversible inhibition of intestinal CYP3A as the mechanism underlying natural product-drug interactions, even after acute exposure to the precipitant. SIGNIFICANCE STATEMENT: Natural products can alter the pharmacokinetics of an object drug, potentially resulting in increased off-target effects or decreased efficacy of the drug. The objective of this work was to evaluate fundamental mechanisms underlying the clinically observed goldenseal-midazolam interaction. Results support the use of an integrated approach involving established in vitro assays, clinical evaluation, and physiologically based pharmacokinetic modeling to elucidate the complex interplay between multiple phytoconstituents and various pharmacokinetic processes driving a drug interaction.

A pharmacogenetic precision medicine approach to analgesia and sedation optimization in critically ill adults

Precision medicine is a growing field in critical care. Research increasingly demonstrated pharmacogenomic variability to be an important determinant of analgesic and sedative drug response in the intensive care unit (ICU). Genome-wide association and candidate gene finding studies suggest analgesic and sedatives tailored to an individual's genetic makeup, environmental adaptations, in addition to several other patient- and drug-related factors, will maximize effectiveness and help mitigate harm. However, the number of pharmacogenetic studies in ICU patients remains small and no prospective studies have been published using pharmacogenomic data to optimize analgesic or sedative therapy in critically ill patients. Current recommendations for treating ICU pain and agitation are based on controlled studies having low external validity, including the failure to consider pharmacogenomic factors affecting response. Use of a precision medicine approach to individualize pharmacotherapy focused on optimizing ICU patient comfort and safety may improve the outcomes of critically ill adults. Additionally, benefits and risks of analgesic and/or sedative therapy in an individual may be informed with large, standardized datasets. The purpose of this review was to describe a precision medicine approach focused on optimizing analgesic and sedative therapy in individual ICU patients to optimize clinical outcomes and reduce safety concerns.

CYP3A4 and CYP3A5 Genotyping Recommendations: A Joint Consensus Recommendation of the Association for Molecular Pathology, Clinical Pharmacogenetics Implementation Consortium, College of American Pathologists, Dutch Pharmacogenetics Working Group of the Royal Dutch Pharmacists Association, European Society for Pharmacogenomics and Personalized Therapy, and Pharmacogenomics Knowledgebase

The goals of the Association for Molecular Pathology Clinical Practice Committee's Pharmacogenomics (PGx) Working Group are to define the key attributes of pharmacogenetic alleles recommended for clinical testing and a minimum set of variants that should be included in clinical PGx genotyping assays. This document series provides recommendations for a minimum panel of variant alleles (tier 1) and an extended panel of variant alleles (tier 2) that will aid clinical laboratories when designing assays for PGx testing. The Association for Molecular Pathology PGx Working Group considered functional impact of the variant alleles, allele frequencies in multiethnic populations, the availability of reference materials, and other technical considerations for PGx testing when developing these recommendations. The goal of this Working Group is to promote standardization of PGx gene/allele testing across clinical laboratories. This document will focus on clinical CYP3A4 and CYP3A5 PGx testing that may be applied to all CYP3A4- and CYP3A5-related medications. These recommendations are not to be interpreted as prescriptive but to provide a reference guide.

Safety, Tolerability, and Pharmacokinetics of the Novel Adenosine A2A Antagonist/Inverse Agonist KW-6356 Following Single and Multiple Oral Administration in Healthy Volunteers

KW-6356 is an adenosine A2A receptor-selective antagonist and inverse agonist. We conducted 2 studies: study 6356-001 (no NCT number), a randomized, double-blind, placebo-controlled phase 1 trial of single ascending (1, 3, 10 mg) and multiple (6 mg once daily) oral doses of KW-6356 in healthy Japanese subjects; and study 6356-004 (NCT03830528), including a randomized, double-blind, placebo-controlled phase 1 trial of single ascending (21, 42, 60 mg) and multiple (24 mg once daily) oral doses of KW-6356, and a phase 1 open-label trial of multiple oral doses (6 mg once daily) of KW-6356 in healthy Japanese and White subjects, to evaluate the safety, tolerability, and pharmacokinetics of KW-6356. KW-6356 was well tolerated after administration of single doses of up to 60 mg and multiple doses of up to 24 mg once daily for 14 days. The pharmacokinetics of KW-6356 were linear after a single dose of up to 60 mg KW-6356. The mean terminal elimination half-life of KW-6356 ranged from 18.4 to 43.1 hours following administration of single doses of 1-60 mg. There was no clear difference in the safety or pharmacokinetics of KW-6356 between healthy Japanese and White subjects.

Pharmacogenomics: Driving Personalized Medicine

Personalized medicine tailors therapies, disease prevention, and health maintenance to the individual, with pharmacogenomics serving as a key tool to improve outcomes and prevent adverse effects. Advances in genomics have transformed pharmacogenetics, traditionally focused on single gene-drug pairs, into pharmacogenomics, encompassing all "-omics" fields (e.g., proteomics, transcriptomics, metabolomics, and metagenomics). This review summarizes basic genomics principles relevant to translation into therapies, assessing pharmacogenomics' central role in converging diverse elements of personalized medicine. We discuss genetic variations in pharmacogenes (drug-metabolizing enzymes, drug transporters, and receptors), their clinical relevance as biomarkers, and the legacy of decades of research in pharmacogenetics. All types of therapies, including proteins, nucleic acids, viruses, cells, genes, and irradiation, can benefit from genomics, expanding the role of pharmacogenomics across medicine. Food and Drug Administration approvals of personalized therapeutics involving biomarkers increase rapidly, demonstrating the growing impact of pharmacogenomics. A beacon for all therapeutic approaches, molecularly targeted cancer therapies highlight trends in drug discovery and clinical applications. To account for human complexity, multicomponent biomarker panels encompassing genetic, personal, and environmental factors can guide diagnosis and therapies, increasingly involving artificial intelligence to cope with extreme data complexities. However, clinical application encounters substantial hurdles, such as unknown validity across ethnic groups, underlying bias in health care, and real-world validation. This review address the underlying science and technologies germane to pharmacogenomics and personalized medicine, integrated with economic, ethical, and regulatory issues, providing insights into the current status and future direction of health care. SIGNIFICANCE STATEMENT: Personalized medicine aims to optimize health care for the individual patients with use of predictive biomarkers to improve outcomes and prevent adverse effects. Pharmacogenomics drives biomarker discovery and guides the development of targeted therapeutics. This review addresses basic principles and current trends in pharmacogenomics, with large-scale data repositories accelerating medical advances. The impact of pharmacogenomics is discussed, along with hurdles impeding broad clinical implementation, in the context of clinical care, ethics, economics, and regulatory affairs.

Application of Physiologically Based Pharmacokinetic Modeling to Predict Drug-Drug Interactions between Elexacaftor/Tezacaftor/Ivacaftor and Tacrolimus in Lung Transplant Recipients

Elexacaftor/tezacaftor/ivacaftor (ETI) treatment has potential benefits in lung transplant recipients, including improvements in extrapulmonary manifestations, such as gastrointestinal and sinus disease; however, ivacaftor is an inhibitor of cytochrome P450 3A (CYP3A) and may, therefore, pose a risk for elevated systemic exposure to tacrolimus. The aim of this investigation is to determine the impact of ETI on tacrolimus exposure and devise an appropriate dosing regimen to manage the risk of this drug-drug interaction (DDI). The CYP3A-mediated DDI of ivacaftor-tacrolimus was evaluated using a physiologically based pharmacokinetic (PBPK) modeling approach, incorporating CYP3A4 inhibition parameters of ivacaftor and in vitro enzyme kinetic parameters of tacrolimus. To further support the findings in PBPK modeling, we present a case series of lung transplant patients who received both ETI and tacrolimus. We predicted a 2.36-fold increase in tacrolimus exposure when co-administered with ivacaftor, which would require a 50% dose reduction of tacrolimus upon initiation of ETI treatment to avoid the risk of elevated systemic exposure. Clinical cases (N = 13) indicate a median 32% (IQR: -14.30, 63.80) increase in the dose-normalized tacrolimus trough level (trough concentration/weight-normalized daily dose) after starting ETI. These results indicate that the concomitant administration of tacrolimus and ETI may lead to a clinically significant DDI, requiring the dose adjustment of tacrolimus.

Newly identified cytochrome P450 3A genes of tree shrews and pigs are expressed and encode functional enzymes

Novel cytochrome P450 3A5 (CYP3A5) cDNA in tree shrews (which are non-rodent primate-like species) and pig CYP3A227 cDNA were identified, along with known pig CYP3A22, CYP3A29, and CYP3A46 cDNAs. All five cDNAs contained open reading frames encoding a polypeptide of 503 amino acids that shared high sequence identity (72-78 %) with human CYP3A4 and were more closely related to human CYP3As than rat CYP3As by phylogenetic analysis. CYP3A5 was the only CYP3A in the tree shrew genome, but pig CYP3A genes formed a CYP3A gene cluster in the genomic region corresponding to that of human CYP3A genes. Tree shrew CYP3A5 mRNA was predominantly expressed in liver and small intestine, among the tissues analyzed, whereas pig CYP3A227 mRNA was most abundantly expressed in jejunum, followed by liver. Metabolic assays established that tree shrew CYP3A5 and pig CYP3A proteins heterologously expressed in Escherichia coli metabolized typical human CYP3A4 substrates nifedipine and midazolam. These results suggest that novel tree shrew CYP3A5 and pig CYP3A227 were functional enzymes able to metabolize human CYP3A4 substrates in liver and small intestine, similar to human CYP3A4, although pig CYP3A227 mRNA was minimally expressed in all tissues analyzed.

CYP3A4 and CYP3A5 Expression is Regulated by CYP3A4*1G in CRISPR/Cas9-Edited HepG2 Cells

Functional CYP3A4*1G (G>A, rs2242480) in cytochrome P450 3A4 (CYP3A4) regulates the drug-metabolizing enzyme CYP3A4 expression. The objective of this study was to investigate whether CYP3A4*1G regulates both basal and rifampicin (RIF)-induced expression and enzyme activity of CYP3A4 and CYP3A5 in gene-edited human HepG2 cells. CYP3A4*1G GG and AA genotype HepG2 cells were established using the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) single nucleotide polymorphism technology and homology-directed repair in the CYP3A4*1G GA HepG2 cell line. In CYP3A4*1G GG, GA, and AA HepG2 cells, CYP3A4*1G regulated expression of CYP3A4 and CYP3A5 mRNA and protein in an allele-dependent manner. Of note, significantly decreased expression level of CYP3A4 and CYP3A5 was observed in CYP3A4*1G AA HepG2 cells. Moreover, the results after RIF treatment showed that CYP3A4*1G decreased the induction level of CYP3A4 and CYP3A5 mRNA expression in CYP3A4*1G AA HepG2 cells. At the same time, CYP3A4*1G decreased CYP3A4 enzyme activity and tacrolimus metabolism, especially in CYP3A4*1G GA HepG2 cells. In summary, we successfully constructed CYP3A4*1G GG and AA homozygous HepG2 cell models and found that CYP3A4*1G regulates both basal and RIF-induced expression and enzyme activity of CYP3A4 and CYP3A5 in CRISPR/Cas9 CYP3A4*1G HepG2 cells. SIGNIFICANCE STATEMENT: Cytochrome P450 (CYP) 3A4*1G regulates both basal and rifampicin (RIF)-induced expression and enzyme activity of CYP3A4 and CYP3A5. This study successfully established CYP3A4*1G (G>A, rs2242480), GG, and AA HepG2 cell models using CRISPR/Cas9, thus providing a powerful tool for studying the mechanism by which CYP3A4*1G regulates the basal and RIF-induced expression of CYP3A4 and CYP3A5.

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.

The Impact of Suboptimal 25-Hydroxyvitamin D Levels and Cholecalciferol Replacement on the Pharmacokinetics of Oral Midazolam in Control Subjects and Patients With Chronic Kidney Disease

The aim of this study was to investigate the impact of suboptimal 25-hydroxyvitamin D (25-VitD) and cholecalciferol (VitD3 ) supplementation on the pharmacokinetics of oral midazolam (MDZ) in control subjects and subjects with chronic kidney disease (CKD). Subjects with CKD (n = 14) and controls (n = 5) with suboptimal 25-VitD levels (<30 ng/mL) were enrolled in a 2-phase study. In phase 1 (suboptimal), subjects were administered a single oral dose of VitD3 (5000 IU) and MDZ (2 mg). In phase 2 (replete) subjects who achieved 25-VitD repletion after receiving up to 16 weeks of daily cholecalciferol were given the identical single oral doses of VitD3 and MDZ as in phase 1. Concentrations of MDZ and metabolites, 1'-hydroxymidazolam (1'-OHMDZ), and 1'-OHMDZ glucuronide (1'-OHMDZ-G) were measured by liquid chromatography-tandem mass spectrometry and pharmacokinetic analysis was performed. Under suboptimal 25-VitD, reductions in MDZ clearance and renal clearance of 47% and 87%, respectively, and a 72% reduction in renal clearance of 1'-OHMDZ-G were observed in CKD vs controls. In phase 1 versus phase 2, MDZ clearance increased in all control subjects, with a median (interquartile range) increase of 10.5 (0.62-16.7) L/h. No changes in MDZ pharmacokinetics were observed in subjects with CKD between phases 1 and 2. The effects of 25-VitD repletion on MDZ disposition was largely observed in subjects without kidney disease. Impaired MDZ metabolism and/or excretion alterations due to CKD in a suboptimal 25-VitD state may not be reversed by cholecalciferol therapy. Suboptimal 25-VitD may augment the reductions in MDZ and 1'-OHMDZ-G clearance values observed in patients with CKD.

Transcription Factors and ncRNAs Associated with CYP3A Expression in Human Liver and Small Intestine Assessed with Weighted Gene Co-Expression Network Analysis

CYP3A4, CYP3A5, and CYP3A7, which are located in a multigene locus (CYP3A), play crucial roles in drug metabolism. To understand the highly variable hepatic expression of CYP3As, regulatory network analyses have focused on transcription factors (TFs). Since long non-coding RNAs (lncRNAs) likely contribute to such networks, we assessed the regulatory effects of both TFs and lncRNAs on CYP3A expression in the human liver and small intestine, main organs of CYP3A expression. Using weighted gene co-expression network analysis (WGCNA) of GTEx v8 RNA expression data and multiple stepwise regression analysis, we constructed TF-lncRNA-CYP3A co-expression networks. Multiple lncRNAs and TFs displayed robust associations with CYP3A expression that differed between liver and small intestines (LINC02499, HNF4A-AS1, AC027682.6, LOC102724153, and RP11-503C24.6), indicating that lncRNAs contribute to variance in CYP3A expression in both organs. Of these, HNF4A-AS1 had been experimentally demonstrated to affect CYP3A expression. Incorporating ncRNAs into CYP3A expression regulatory network revealed additional candidate TFs associated with CYP3A expression. These results serve as a guide for experimental studies on lncRNA-TF regulation of CYP3A expression in the liver and small intestines.

GRWR Correlates with the Metabolism of Tacrolimus after Pediatric Living Donor Liver Transplantation According to Donor CYP3A5 Polymorphism

Objectives

Tacrolimus is characterized by high pharmacokinetic variability in combination with a narrow therapeutic range. However, influence of donor CYP3A5 genotype and graft-to-recipient body weight ratio (GRWR) on tacrolimus' pharmacokinetics after pediatric living donor liver transplantation (LDLT) remains unclear.

Methods

A total of 174 LDLT recipients (<6 y) were grouped according to donor CYP3A5 genotypes (nonexpressor (NEX) or expressor (EX)) and GRWR (<3.0% (SS, small-size) or ≥3.0% (LS, large-size)): SS/NEX (n = 40), SS/EX (n = 38), LS/NEX (n = 48), and LS/EX (n = 48). Pharmacokinetics of tacrolimus and clinical outcomes were analyzed.

Results

The relationships between the concentration-dose ratio and donor CYP3A5 genotypes and graft size were examined 3, 7, 14, and 30 days after the transplantation. Tacrolimus C0 levels varied greatly among groups, although recipients started with the same initial dosage. LS/EX recipients had significantly lower C0 levels in comparison with those of other groups. The use of CYP3A5-EX-grafts and a greater GRWR both resulted in significantly higher TAC dose requirements and lower C/D ratios. However, the significance of GRWR no longer exists 3 months after transplantation. The multivariate generalized linear mixed model analysis showed that donor CYP3A5 genotypes (F = 11.876; P = 0.01) and GRWR (F = 4.631; P = 0.033) were independent impact factors for C/D ratios 3, 7, 14, and 30 days after transplantation. Donor CYP3A5-EX genotype was associated with significantly increasing risks of infectious complications and significantly lower Cylex ATP values. However, no significant difference was observed in acute rejections among 4 groups.

Conclusions

Monitoring of C0 levels alone is not reliable to guide tacrolimus administration. Donor CYP3A5 and GRWR both significantly affect tacrolimus pharmacokinetics after pediatric LDLT. The use of Cylex ATP tests would be helpful to avoid overimmunosuppression.

The Role of CYP3A in Health and Disease

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

Prediction of pyrotinib exposure based on physiologically-based pharmacokinetic model and endogenous biomarker

Pyrotinib, a novel irreversible epidermal growth factor receptor dual tyrosine kinase inhibitor, is mainly (about 90%) eliminated through cytochrome P450 (CYP) 3A mediated metabolism in vivo. Meanwhile, genotype is a key factor affecting pyrotinib clearance and 4β-hydroxycholesterol is an endogenous biomarker of CYP3A activity that can indirectly reflect the possible pyrotinib exposure. Thus, it is necessary to evaluate the clinical drug-drug interactions (DDI) between CYP3A perpetrators and pyrotinib, understand potential exposure in specific populations including liver impairment and geriatric populations, and explore the possible relationships among pyrotinib exposure, genotypes and endogenous biomarker. Physiologically-based pharmacokinetic (PBPK) model can be used to replace prospective DDI studies and evaluate external and internal factors that may influence system exposure. Herein, a basic PBPK model was firstly developed to evaluate the potential risk of pyrotinib coadministration with strong inhibitor and guide the clinical trial design. Subsequently, the mechanistic PBPK model was established and used to quantitatively estimate the potential DDI risk for other CYP3A modulators, understand the potential exposure of specific populations, including liver impairment and geriatric populations. Meanwhile, the possible relationships among pyrotinib exposure, genotypes and endogenous biomarker were explored. With the help of PBPK model, the DDI clinical trial of pyrotinib coadministration with strong inhibitor has been successfully completed, some DDI clinical trials may be waived based on the predicted results and clinical trials in specific populations can be reasonably designed. Moreover, the mutant genotypes of CYP3A4*18A and CYP3A5*3 were likely to have a limited influence on pyrotinib clearance, and the genotype-independent linear correlation coefficient between endogenous biomarker and system exposure was larger than 0.6. Therefore, based on the reliable predicted results and the linear correlations between pyrotinib exposure and endogenous biomarker, dosage adjustment of pyrotinib can be designed for clinical practice.

Atypical kinetics of cytochrome P450 enzymes in pharmacology and toxicology

Atypical kinetics are observed in metabolic reactions catalyzed by cytochrome P450 enzymes (P450). Yet, this phenomenon is regarded as experimental artifacts in some instances despite increasing evidence challenging the assumptions of typical Michaelis-Menten kinetics. As P450 play a major role in the metabolism of a wide range of substrates including drugs and endogenous compounds, it becomes critical to consider the impact of atypical kinetics on the accuracy of estimated kinetic and inhibitory parameters which could affect extrapolation of pharmacological and toxicological implications. The first half of this book chapter will focus on atypical non-Michaelis-Menten kinetics (e.g. substrate inhibition, biphasic and sigmoidal kinetics) as well as proposed underlying mechanisms supported by recent insights in mechanistic enzymology. In particular, substrate inhibition kinetics in P450 as well as concurrent drug inhibition of P450 in the presence of substrate inhibition will be further discussed. Moreover, mounting evidence has revealed that despite the high degree of sequence homology between CYP3A isoforms (i.e. CYP3A4 and CYP3A5), they have the propensities to exhibit vastly different susceptibilities and potencies of mechanism-based inactivation (MBI) with a common drug inhibitor. These experimental observations pertaining to the presence of these atypical isoform- and probe substrate-specific complexities in CYP3A isoforms by several clinically-relevant drugs will therefore be expounded and elaborated upon in the second half of this book chapter.

Individualized medication based on pharmacogenomics and treatment progress in children with IgAV nephritis

Immunoglobulin A vasculitis (IgAV) nephritis, also known as Henoch-Schönlein purpura nephritis (HSPN), is a condition in which small blood vessel inflammation and perivascular IgA deposition in the kidney caused by neutrophil activation, which more often leads to chronic kidney disease and accounts for 1%–2% of children with end-stage renal disease (ESRD). The treatment principles recommended by the current management guidelines include general drug treatment, support measures and prevention of sequelae, among which the therapeutic drugs include corticosteroids, immunosuppressive agents and angiotensin system inhibitors. However, the concentration range of immunosuppressive therapy is narrow and the individualized difference is large, and the use of corticosteroids does not seem to improve the persistent nephropathy and prognosis of children with IgAV. Therefore, individualized maintenance treatment of the disease and stable renal prognosis are still difficult problems. Genetic information helps to predict drug response in advance. It has been proved that most gene polymorphisms of cytochrome oxidase P450 and drug transporter can affect drug efficacy and adverse reactions (ADR). Drug therapy based on genetics and pharmacogenomics is beneficial to providing safer and more effective treatment for children. Based on the pathogenesis of IgAV, this paper summarizes the current therapeutic drugs, explores potential therapeutic drugs, and focuses on the therapeutic significance of corticosteroids and immunosuppressants in children with IgAV nephritis at the level of pharmacogenomics. In addition, the individualized application of corticosteroids and immunosuppressants in children with different genotypes was analyzed, in order to provide a more comprehensive reference for the individualized treatment of IgAV nephritis in children.

Why We Need to Take a Closer Look at Genetic Contributions to CYP3A Activity

Cytochrome P450 3A (CYP3A) subfamily enzymes are involved in the metabolism of 40% of drugs in clinical use. Twin studies have indicated that 66% of the variability in CYP3A4 activity is hereditary. Yet, the complexity of the CYP3A locus and the lack of distinct drug metabolizer phenotypes has limited the identification and clinical application of CYP3A genetic variants compared to other Cytochrome P450 enzymes. In recent years evidence has emerged indicating that a substantial part of the missing heritability is caused by low frequency genetic variation. In this review, we outline the current pharmacogenomics knowledge of CYP3A activity and discuss potential future directions to improve our genetic knowledge and ability to explain CYP3A variability.

Interindividual Variability in Cytochrome P450 3A and 1A Activity Influences Sunitinib Metabolism and Bioactivation

Sunitinib is an orally administered tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity; however, the mechanisms of this toxicity remain unclear. We have previously shown that cytochromes P450 1A2 and 3A4 catalyze sunitinib metabolic activation via oxidative defluorination leading to a chemically reactive, potentially toxic quinoneimine, trapped as a glutathione (GSH) conjugate (M5). The goals of this study were to determine the impact of interindividual variability in P450 1A and 3A activity on sunitinib bioactivation to the reactive quinoneimine and sunitinib N-dealkylation to the primary active metabolite N-desethylsunitinib (M1). Experiments were conducted in vitro using single-donor human liver microsomes and human hepatocytes. Relative sunitinib metabolite levels were measured by liquid chromatography-tandem mass spectrometry. In human liver microsomes, the P450 3A inhibitor ketoconazole significantly reduced M1 formation compared to the control. The P450 1A2 inhibitor furafylline significantly reduced defluorosunitinib (M3) and M5 formation compared to the control but had minimal effect on M1. In CYP3A5-genotyped human liver microsomes from 12 individual donors, M1 formation was highly correlated with P450 3A activity measured by midazolam 1'-hydroxylation, and M3 and M5 formation was correlated with P450 1A2 activity estimated by phenacetin O-deethylation. M3 and M5 formation was also associated with P450 3A5-selective activity. In sandwich-cultured human hepatocytes, the P450 3A inducer rifampicin significantly increased M1 levels. P450 1A induction by omeprazole markedly increased M3 formation and the generation of a quinoneimine-cysteine conjugate (M6) identified as a downstream metabolite of M5. The nonselective P450 inhibitor 1-aminobenzotriazole reduced each of these metabolites (M1, M3, and M6). Collectively, these findings indicate that P450 3A activity is a key determinant of sunitinib N-dealkylation to the active metabolite M1, and P450 1A (and potentially 3A5) activity influences sunitinib bioactivation to the reactive quinoneimine metabolite. Accordingly, modulation of P450 activity due to genetic and/or nongenetic factors may impact the risk of sunitinib-associated toxicities.

Exploration and application of a liver-on-a-chip device in combination with modelling and simulation for quantitative drug metabolism studies

Microphysiological systems (MPS) are complex and more physiologically realistic cellular in vitro tools that aim to provide more relevant human in vitro data for quantitative prediction of clinical pharmacokinetics while also reducing the need for animal testing. The PhysioMimix liver-on-a-chip integrates medium flow with hepatocyte culture and has the potential to be adopted for in vitro studies investigating the hepatic disposition characteristics of drug candidates. The current study focusses on liver-on-a-chip system exploration for multiple drug metabolism applications. Characterization of cytochrome P450 (CYP), UDP-glucuronosyl transferase (UGT) and aldehyde oxidase (AO) activities was performed using 15 drugs and in vitro to in vivo extrapolation (IVIVE) was assessed for 12 of them. Next, the utility of the liver-on-a-chip for estimation of the fraction metabolized (f_m) via specific biotransformation pathways of quinidine and diclofenac was established. Finally, the metabolite identification opportunities were also explored using efavirenz as an example drug with complex primary and secondary metabolism involving a combination of CYP, UGT and sulfotransferase enzymes. A key aspect of these investigations was the application of mathematical modelling for improved parameter calculation. Such approaches will be required for quantitative assessment of metabolism and/or transporter processes in systems where medium flow and system compartments result in non-homogeneous drug concentrations. In particular, modelling was used to explore the effect of evaporation from the medium and it was found that the intrinsic clearance (CL_int) might be underestimated by up to 40% for low clearance compounds if evaporation is not accounted for. Modelling of liver-on-a-chip in vitro data also enhanced the approach to f_m estimation allowing objective assessment of metabolism models of different complexity. The resultant diclofenac f_m,UGT of 0.64 was highly comparable with values reported previously in the literature. The current study demonstrates the integration of mathematical modelling with experimental liver-on-a-chip studies and illustrates how this approach supports generation of high quality of data from complex in vitro cellular systems.

Cytochrome P450 3A5 polymorphism affects the metabolism of sorafenib and its toxicity for hepatocellular carcinoma cells in vitro

OBJECTIVE

Cytochrome P450 3A5 (CYP3A5) is a highly polymorphic gene and the encoded protein variants differ in catalytic activity, leading to inter-individual variation in metabolic ability. The aim of the current study was to investigate the effects of seven allelic variants on the ability of CYP3A5 to metabolize sorafenib in vitro and further explore the impacts of CYP3A5 polymorphism on the proliferation and apoptosis of hepatocellular carcinoma cell line (HepG2) induced by sorafenib.

METHODS

Wild-type and variant CYP3A5 enzymes were expressed in Spodoptera frugiperda insect cells using a baculovirus dual-expression system, and protein expression was checked by western blot. The enzymes were incubated with sorafenib at 37°C for 30 min, and formation of the major metabolite sorafenib N-oxide was assayed using ultra-performance liquid chromatography and tandem mass spectrometry. Intrinsic clearance values (V_max/K_m) were calculated for each enzyme. Additionally, recombinant HepG2 cells transfecting with CYP3A5 variants were used to investigate the effects of sorafenib on the proliferation of HepG2 cells.

RESULTS

Intrinsic clearance of the six variants CYP3A5*2, CYP3A5*3A, CYP3A5*3C, CYP3A5*4, CYP3A5*5, and CYP3A5*7 was 26.41-71.04% of the wild-type (CYP3A5*1) value. In contrast, the clearance value of the variant CYP3A5*6 was significantly higher (174.74%). Additionally, the decreased ATP levels and cell viability and the increased cell apoptosis in HepG2 cells transfected with CYP3A5*2, CYP3A5*3A, CYP3A5*3C, CYP3A5*4, CYP3A5*5, and CYP3A5*7 were observed, whereas, the increased ATP levels and cell viability and the reduced cell apoptosis in HepG2 cells transfected with CYP3A5*6 were also investigated when compared to CYP3A5*1.

CONCLUSION

Our results suggest that CYP3A5 polymorphism influences sorafenib metabolism and pharmacotherapeutic effect in hepatic carcinomas. These data may help explain differential response to drug therapy for hepatocellular carcinoma, and they support the need for individualized treatment.

Regulation of CYP3A4 and CYP3A5 by a lncRNA: a potential underlying mechanism explaining the association between CYP3A4*1G and CYP3A metabolism

The cytochrome P450 3A4 (CYP3A4) enzyme is the most abundant drug-metabolizing enzyme in the liver, displaying large inter-person variability with unknown causes. In this study, we found that the expression of CYP3A4 is negatively correlated with AC069294.1 (ENSG00000273407, ENST00000608397.1), a lncRNA generated antisense to CYP3A4. Knockdown of AC069294.1 in Huh7 cells increased CYP3A4 mRNA ~3-fold, whereas overexpression of AC069294.1 decreased CYP3A4 mRNA by 89%. We also observed changes in CYP3A5 expression when AC069294.1 was knocked down or overexpressed, indicating dual effects of AC069294.1 on both CYP3A4 and CYP3A5 expression. Consistently, the expression level of CYP3A5 is also negatively correlated with AC069294.1. Previous studies have shown associations between an intronic single nucleotide polymorphism CYP3A4*1G (rs2242480) and CYP3A metabolism, but the results are inconsistent and the underlying mechanism is unclear. We show here that CYP3A4*1G (rs2242480) is associated with 1.26-fold increased expression of AC069294.1 (P < 0.0001), and decreased expression of CYP3A4 by 31% (P = 0.008) and CYP3A5 by 39% (P = 0.004). CYP3A4*1G is located ~2.7 kb upstream of AC069294.1 and has been previously reported to have increased transcriptional activity in reporter gene assays. Taken together, our results demonstrate the regulation of CYP3A4 and CYP3A5 by a novel lncRNA AC069294.1. Our results also indicate that the clinically observed CYP3A4*1G associations may be caused by its effect on the expression of AC069294.1, and thereby altered expression of both CYP3A4 and CYP3A5. Furthermore, because CYP3A4*1G is in high linkage disequilibrium with CYP3A5*1, increased AC069294.1 expression caused by CYP3A4*1G may decrease expression of the normal-functioning CYP3A5*1, explaining additional inter-person variability of CYP3A5.

Cytochrome P450 3A5 polymorphism affects the metabolism of sorafenib and its toxicity for hepatocellular carcinoma cells in vitro

OBJECTIVE

Cytochrome P450 3A5 (CYP3A5) is a highly polymorphic gene and the encoded protein variants differ in catalytic activity, leading to inter-individual variation in metabolic ability. The aim of the current study was to investigate the effects of seven allelic variants on the ability of CYP3A5 to metabolize sorafenib in vitro and further explore the impacts of CYP3A5 polymorphism on the proliferation and apoptosis of hepatocellular carcinoma cell line (HepG2) induced by sorafenib.

METHODS

Wild-type and variant CYP3A5 enzymes were expressed in Spodoptera frugiperda insect cells using a baculovirus dual-expression system, and protein expression was checked by western blot. The enzymes were incubated with sorafenib at 37°C for 30 min, and formation of the major metabolite sorafenib N-oxide was assayed using ultra-performance liquid chromatography and tandem mass spectrometry. Intrinsic clearance values (V_max/K_m) were calculated for each enzyme. Additionally, recombinant HepG2 cells transfecting with CYP3A5 variants were used to investigate the effects of sorafenib on the proliferation of HepG2 cells.

RESULTS

Intrinsic clearance of the six variants CYP3A5*2, CYP3A5*3A, CYP3A5*3C, CYP3A5*4, CYP3A5*5, and CYP3A5*7 was 26.41-71.04% of the wild-type (CYP3A5*1) value. In contrast, the clearance value of the variant CYP3A5*6 was significantly higher (174.74%). Additionally, the decreased ATP levels and cell viability and the increased cell apoptosis in HepG2 cells transfected with CYP3A5*2, CYP3A5*3A, CYP3A5*3C, CYP3A5*4, CYP3A5*5, and CYP3A5*7 were observed, whereas, the increased ATP levels and cell viability and the reduced cell apoptosis in HepG2 cells transfected with CYP3A5*6 were also investigated when compared to CYP3A5*1.

CONCLUSION

Our results suggest that CYP3A5 polymorphism influences sorafenib metabolism and pharmacotherapeutic effect in hepatic carcinomas. These data may help explain differential response to drug therapy for hepatocellular carcinoma, and they support the need for individualized treatment.

Cytochrome P450 3A4 (CYP3A4) protein quantification using capillary western blot technology and total protein normalization

The western blot (WB) is the predominate method for protein quantification, frequently used in pharmacological and toxicological studies. To control for technical variation, WB signals are normalized through immunodetection of an internal standard "house-keeping" gene or total protein quantification via staining of the same blot or a duplicate, sister blot. Increasing evidence suggests that house-keeping genes are subject to change after drug treatment or under disease states, causing protein quantification errors in WB. Recent advances in automated capillary-based WB technologies enable measurement of the protein of interest, internal standards, and total protein in a single capillary. Using this approach, we quantified cytochrome P450 3A4 (CYP3A4) across 179 liver samples and compared normalization by both β-actin and total protein to determine which better functions as an internal standard. CYP3A4 is responsible for metabolism of a wide array of xenobiotics and is known to exhibit large inter-person variation, making it a good candidate to evaluate protein quantification. We observed significant differences in β-actin protein levels between liver samples (~20-fold) and found better correlation between CYP3A4 protein and mRNA using total protein normalization than β-actin, indicating total protein normalization to be less error prone for estimation of CYP3A4. Furthermore, by using total protein normalization, we confirmed significant association between CYP3A4 protein expression and the functional CYP3A4 variant CYP3A4*22, which contains two linked SNPs rs35599367 and rs62471956. Our results indicate that the automatic capillary WB instrument combined with total protein normalization provides a high throughput and robust approach for protein quantification.

In vitro assessments predict that CYP3A4 contributes to a greater extent than CYP3A5 to prednisolone clearance

Because several steroid hormones are metabolized to their respective 6β-hydroxy forms by CYP3A4 and CYP3A5, these isoenzymes have been assumed to metabolize the immunosuppressive drug prednisolone, with conflicting results in the literature with respect to their relative importance. A direct study of the metabolism of prednisolone by microsomal CYP3A4 and CYP3A5 is missing. The aim of this in vitro study was to investigate the relative importance of recombinant CYP3A4 and recombinant CYP3A5 in the metabolism of prednisolone and to compare the extent of formation of 6β-OH-prednisolone by the two enzymes. Through in vitro incubations using rCYP3A4 and rCYP3A5 enzymes, intrinsic clearance (CL_int ) of prednisolone was determined by the substrate depletion approach. Formation of the metabolite 6β-OH-prednisolone by rCYP3A4 and rCYP3A5, respectively, were compared. Prednisolone concentrations were measured and its metabolite 6β-OH-prednisolone was identified using a HPLC-MS/MS in-house method. CL_int for prednisolone by rCYP3A5 was less than 26% relative to rCYP3A4. Formation of 6β -OH-prednisolone by rCYP3A5 was less than 11% relative to rCYP3A4. The study indicates that 6β-hydroxylation of prednisolone assessed in vitro in recombinant CYP enzymes depends on rCYP3A4 rather than rCYP3A5, and that CYP3A5 may be responsible for the formation of other prednisolone metabolite(s) in addition to 6β-OH-prednisolone.

CYP3A4∗22 Genotyping in Clinical Practice: Ready for Implementation?

Cytochrome P450 3A4 (CYP3A4) is the most important drug metabolizing enzyme in the liver, responsible for the oxidative metabolism of ∼50% of clinically prescribed drugs. Therefore, genetic variation in CYP3A4 could potentially affect the pharmacokinetics, toxicity and clinical outcome of drug treatment. Thus far, pharmacogenetics for CYP3A4 has not received much attention. However, the recent discovery of the intron 6 single-nucleotide polymorphism (SNP) rs35599367C > T, encoding the CYP3A4^∗22 allele, led to several studies into the pharmacogenetic effect of CYP3A4^∗22 on different drugs. This allele has a relatively minor allele frequency of 3-5% and an effect on CYP3A4 enzymatic activity. Thus far, no review summarizing the data published on several drugs is available yet. This article therefore addresses the current knowledge on CYP3A4^∗22. This information may help in deciding if, and for which drugs, CYP3A4^∗22 genotype-based dosing could be helpful in improving drug therapy. CYP3A4^∗22 was shown to significantly influence the pharmacokinetics of several drugs, with currently being most thoroughly investigated tacrolimus, cyclosporine, and statins. Additional studies, focusing on toxicity and clinical outcome, are warranted to demonstrate clinical utility of CYP3A4^∗22 genotype-based dosing.

Differential Reversible and Irreversible Interactions between Benzbromarone and Human Cytochrome P450s 3A4 and 3A5

Mounting evidence has revealed that despite the high degree of sequence homology between cytochrome P450 3A isoforms (i.e., CYP3A4 and CYP3A5), they have the propensities to exhibit vastly different irreversible and reversible interactions with a single substrate. We have previously established that benzbromarone (BBR), a potent uricosuric agent used in the management of gout, irreversibly inhibits CYP3A4 via mechanism-based inactivation (MBI). However, it remains unelucidated if CYP3A5-its highly homologous counterpart-is susceptible to inactivation by BBR. Using three structurally distinct probe substrates, we consistently demonstrated that MBI was not elicited in CYP3A5 by BBR. Our in silico covalent docking models and molecular dynamics simulations suggested that disparities in the susceptibilities toward MBI could be attributed to the specific effects of BBR covalent adducts on the F-F' loop. Serendipitously, we also discovered that BBR reversibly activated CYP3A5-mediated rivaroxaban hydroxylation wherein apparent V _max increased and K _m decreased with increasing BBR concentration. Fitting data to the two-site model yielded interaction factors α and β of 0.44 and 5.88, respectively, thereby confirming heterotropic activation of CYP3A5 by BBR. Furthermore, heteroactivation was suppressed by the CYP3A inhibitor ketoconazole in a concentration-dependent manner and decreased with increasing preincubation time, implying that activation was incited via binding of parent BBR molecule within the enzymatic active site. Finally, noncovalent docking revealed that CYP3A5 can more favorably accommodate both BBR and rivaroxaban in concert as compared with CYP3A4, which further substantiated our experimental observations. SIGNIFICANCE STATEMENT: Although it has been previously demonstrated that benzbromarone (BBR) inactivates CYP3A4, it remains uninterrogated whether it also elicits mechanism-based inactivation in CYP3A5, which shares ∼85% sequence similarity with CYP3A4. This study reported that BBR exhibited differential irreversible and reversible interactions with both CYP3A isoforms and further unraveled the molecular determinants underpinning their diverging interactions. These data offer important insight into differential kinetic behavior of CYP3A4 and CYP3A5, which potentially contributes to interindividual variabilities in drug disposition.

Mechanism-Based Inactivation of Cytochrome P450 3A4 and 3A5 by the Fibroblast Growth Factor Receptor Inhibitor Erdafitinib

Erdafitinib (ERD) is a first-in-class pan inhibitor of fibroblast growth factor receptor 1-4 that has garnered global regulatory approval for the treatment of advanced or metastatic urothelial carcinoma. Although it has been previously reported that ERD elicits time-dependent inhibition (TDI) of cytochrome P450 (P450) 3A4 (CYP3A4), the exact biochemical nature underpinning this observation remains obfuscated. Moreover, it is also uninterrogated if CYP3A5-its highly homologous counterpart-could be susceptible to such interactions. Mechanism-based inactivation (MBI) of P450 is a unique subset of TDI that hinges on prior bioactivation of the drug to a reactive intermediate and possesses profound clinical and toxicological implications due to its irreversible nature. Here, we investigated and confirmed that ERD inactivated both CYP3A isoforms in a time-, concentration-, and NADPH-dependent manner with K_I, k_inact, and partition ratio of 4.01 and 10.04 μM, 0.120 and 0.045 min^-1, and 32 and 55 for both CYP3A4 and CYP3A5, respectively, when rivaroxaban was employed as the probe substrate. Co-incubation with an alternative substrate or direct inhibitor of CYP3A attenuated the rate of inactivation, whereas the addition of glutathione or catalase did not induce such protection. The lack of enzyme activity recovery following dialysis for 4 h and oxidation with potassium ferricyanide combined with the lack of a Soret peak in spectral scans collectively substantiated that ERD is an irreversible covalent MBI of CYP3A. Finally, glutathione trapping and high-resolution mass spectrometry experiments illuminated a plausible bioactivation mechanism of ERD by CYP3A arising from metabolic epoxidation of its quinoxaline ring.

Antisense oligonucleotide development for the selective modulation of CYP3A5 in renal disease

CYP3A5 is the primary CYP3A subfamily enzyme expressed in the human kidney and its aberrant expression may contribute to a broad spectrum of renal disorders. Pharmacogenetic studies have reported inconsistent linkages between CYP3A5 expression and hypertension, however, most investigators have considered CYP3A5*1 as active and CYP3A5*3 as an inactive allele. Observations of gender specific differences in CYP3A5*3/*3 protein expression suggest additional complexity in gene regulation that may underpin an environmentally responsive role for CYP3A5 in renal function. Reconciliation of the molecular mechanism driving conditional restoration of functional CYP3A5*3 expression from alternatively spliced transcripts, and validation of a morpholino-based approach for selectively suppressing renal CYP3A5 expression, is the focus of this work. Morpholinos targeting a cryptic splice acceptor created by the CYP3A5*3 mutation in intron 3 rescued functional CYP3A5 expression in vitro, and salt-sensitive cellular mechanisms regulating splicing and conditional expression of CYP3A5*3 transcripts are reported. The potential for a G-quadruplex (G4) in intron 3 to mediate restored splicing to exon 4 in CYP3A5*3 transcripts was also investigated. Finally, a proximal tubule microphysiological system (PT-MPS) was used to evaluate the safety profile of morpholinos in proximal tubule epithelial cells, highlighting their potential as a therapeutic platform for the treatment of renal disease.

Identifying the Dominant Contribution of Human Cytochrome P450 2J2 to the Metabolism of Rivaroxaban, an Oral Anticoagulant

PURPOSE

Rivaroxaban, an oral anticoagulant, undergoes the metabolism mediated by human cytochrome P450 (CYP). The present study is to quantitatively analyze and compare the contributions of multiple CYPs in the metabolism of rivaroxaban to provide new information for medication safety.

METHODS

The metabolic stability of rivaroxaban in the presence of human liver microsomes (HLMs) and recombinant CYPs was systematically evaluated to estimate the participation of various CYP isoforms. Furthermore, the catalytic efficiency of CYP isoforms was compared via metabolic kinetic studies of rivaroxaban with recombinant CYP isoenzymes, as well as via CYP-specific inhibitory studies. Additionally, docking simulations were used to illustrate molecular interactions.

RESULTS

Multiple CYP isoforms were involved in the hydroxylation of rivaroxaban, with decreasing catalytic rates as follows: CYP2J2 > 3A4 > 2D6 > 4F3 > 1A1 > 3A5 > 3A7 > 2A6 > 2E1 > 2C9 > 2C19. Among the CYPs, 2J2, 3A4, 2D6, and 4F3 were the four major isoforms responsible for rivaroxaban metabolism. Notably, the intrinsic clearance of rivaroxaban catalyzed by CYP2J2 was nearly 39-, 64-, and 100-fold that catalyzed by CYP3A4, 2D6, and 4F3, respectively. In addition, rivaroxaban hydroxylation was inhibited by 41.1% in the presence of the CYP2J2-specific inhibitor danazol, which was comparable to the inhibition rate of 43.3% by the CYP3A-specific inhibitor ketoconazole in mixed HLMs. Furthermore, molecular simulations showed that rivaroxaban is principally bound to CYP2J2 by π-alkyl bonds, carbon-hydrogen bonds, and alkyl interactions.

CONCLUSION

CYP2J2 dominated the hydroxylation of rivaroxaban, which may provide new insight into clinical drug interactions involving rivaroxaban.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

Cis-acting regulatory elements regulating CYP3A4 transcription in human liver

The CYP3A4 enzyme is the most abundant drug-metabolizing enzyme in the liver, metabolizing ~50% of commonly used medications. CYP3A4 displays large interperson variability in expression and enzyme activity with unknown causes. This study aims to identify cis-acting regulatory elements controlling the transcription of CYP3A4, using chromatin conformation capture (4C and 3C assays), chromatin immunoprecipitation followed by quantitative PCR (ChIP-qPCR), clustered regularly interspaced short palindromic repeats (CRISPR)-mediated deletions of genomic regions and reporter gene assays in primary culture human hepatocytes and hepatic cell lines. 4C assays identified four regions (R1-R4) interacting with the CYP3A4 promoter, one of which overlaps with the previously identified upstream enhancers CLEM4/XREM (R2) while the other three are novel. ChIP-qPCR, reporter gene assays and CRISPR-mediated deletion experiments indicate regulatory roles for both R2 and R4. Interestingly, the deletion of R4 increased CYP3A4 while decreasing CYP3A43 expression, possibly due to competitive domain-domain interactions within the CYP3A cluster, supported by deletion of R4 increasing interaction between the CYP3A4 promoter and R2. We also identified a single nucleotide polymorphism rs62471956 within R4, with the variant allele A having increased transcriptional activity in a reporter gene assay. The rs62471956 A allele is associated with higher CYP3A43 expression and lower CYP3A4 expression in a cohort of 136 liver samples, further supporting the opposing effects of R4 on CYP3A4 and CYP3A43. rs62471956 is in complete linkage disequilibrium with CYP3A4*22, potentially contributing to reduced expression of CYP3A4*22. These results validate previously identified enhancers (CLEM4 and XREM) of CYP3A4 and demonstrate additional regulatory mechanisms underlying CYP3A4 transcriptional control via competitive domain-domain interactions within the CYP3A cluster.

Transchromosomic technology for genomically humanized animals

"Genomically" humanized animals are invaluable tools for generating human disease models and for biomedical research. Humanized animal models have generally been developed via conventional transgenic technologies; however, conventional gene delivery vectors such as viruses, plasmids, bacterial artificial chromosomes, P1 phase-derived artificial chromosomes, and yeast artificial chromosomes have limitations for transgenic animal creation as their loading gene capacity is restricted, and the expression of transgenes is unstable. Transchromosomic (Tc) techniques using mammalian artificial chromosomes, including human chromosome fragments, human artificial chromosomes, and mouse artificial chromosomes, have overcome these limitations. These tools can carry multiple genes or Mb-sized genomic loci and their associated regulatory elements, which has facilitated the creation of more useful and complex transgenic models for human disease, drug development, and humanized animal research. This review describes the history of Tc animal development, the applications of Tc animals, and future prospects.

Effect of CYP3A5*3 genetic variant on the metabolism of direct-acting antivirals in vitro: a different effect on asunaprevir versus daclatasvir and beclabuvir

Direct-acting antivirals, asunaprevir (ASV), daclatasvir (DCV), and beclabuvir (BCV) are known to be mainly metabolized by CYP3A enzymes; however, the differences in the detailed metabolic activities of CYP3A4 and CYP3A5 on these drugs are not well clarified. The aim of the present study was to elucidate the relative contributions of CYP3A4 and CYP3A5 to the metabolism of ASV, DCV, and BCV, as well as the effect of CYP3A5*3 genetic variant in vitro. The amount of each drug and their major metabolites were determined using LC-MS/MS. Recombinant CYP3As and CYP3A5*3-genotyped human liver microsomes (CYP3A5 expressers or non-expressers) were used for the determination of their metabolic activities. The contribution of CYP3A5 to ASV metabolism was considerable compared to that of CYP3A4. Consistently, ASV metabolic activity in CYP3A5 expressers was higher than those in CYP3A5 non-expresser. Moreover, CYP3A5 expression level was significantly correlated with ASV metabolism. In contrast, these observations were not found in DCV and BCV metabolism. To our knowledge, this is the first study to directly demonstrate the effect of CYP3A5*3 genetic variants on the metabolism of ASV. The findings of the present study may provide basic information on ASV, DCV, and BCV metabolisms.

Quantitative Prediction of CYP3A4- and CYP3A5-Mediated Drug Interactions

We verified a physiologically-based pharmacokinetic (PBPK) model to predict cytochrome P450 3A4/5-mediated drug-drug interactions (DDIs). A midazolam (MDZ)-ketoconazole (KTZ) interaction study in 24 subjects selected by CYP3A5 genotype, and liquid chromatography and mass spectroscopy quantification of CYP3A4/5 abundance from independently acquired and genotyped human liver (n = 136) and small intestinal (N = 12) samples, were conducted. The observed CYP3A5 genetic effect on MDZ systemic and oral clearance was successfully replicated by a mechanistic framework incorporating the proteomics-informed CYP3A abundance and optimized small intestinal CYP3A4 abundance based on MDZ intestinal availability (F_G ) of 0.44. Furthermore, combined with a modified KTZ PBPK model, this framework recapitulated the observed geometric mean ratio of MDZ area under the curve (AUCR) following 200 or 400 mg KTZ, which was, respectively, 2.7-3.4 and 3.9-4.7-fold in intravenous administration and 11.4-13.4 and 17.0-19.7-fold in oral administration, with AUCR numerically lower (P > 0.05) in CYP3A5 expressers than nonexpressers. In conclusion, the developed mechanistic framework supports dynamic prediction of CYP3A-mediated DDIs in study planning by bridging DDIs between CYP3A5 expressers and nonexpressers.

Interindividual Variation in CYP3A Activity Influences Lapatinib Bioactivation

Lapatinib is a dual tyrosine kinase inhibitor associated with rare but potentially severe idiosyncratic hepatotoxicity. We have previously shown that cytochromes P450 CYP3A4 and CYP3A5 quantitatively contribute to lapatinib bioactivation, leading to formation of a reactive, potentially toxic quinone imine. CYP3A5 is highly polymorphic; however, the impact of CYP3A5 polymorphism on lapatinib metabolism has not been fully established. The goal of this study was to determine the effect of CYP3A5 genotype and individual variation in CYP3A activity on the metabolic activation of lapatinib using human-relevant in vitro systems. Lapatinib metabolism was examined using CYP3A5-genotyped human liver microsomes and cryopreserved human hepatocytes. CYP3A and CYP3A5-selective activities were measured in liver tissues using probe substrates midazolam and T-5 (T-1032), respectively, to evaluate the correlation between enzymatic activity and lapatinib metabolite formation. Drug metabolites were measured by high-performance liquid chromatography-tandem mass spectrometry. Further, the relative contributions of CYP3A4 and CYP3A5 to lapatinib O-debenzylation were estimated using selective chemical inhibitors of CYP3A. The results from this study demonstrated that lapatinib O-debenzylation and quinone imine-GSH conjugate formation were highly correlated with hepatic CYP3A activity, as measured by midazolam 1'-hydroxylation. CYP3A4 played a dominant role in lapatinib bioactivation in all liver tissues evaluated. The CYP3A5 contribution to lapatinib bioactivation varied by individual donor and was dependent on CYP3A5 genotype and activity. CYP3A5 contributed approximately 20%-42% to lapatinib O-debenzylation in livers from CYP3A5 expressers. These findings indicate that individual CYP3A activity, not CYP3A5 genotype alone, is a key determinant of lapatinib bioactivation and likely influences exposure to reactive metabolites. SIGNIFICANCE STATEMENT: This study is the first to examine the effect of CYP3A5 genotype, total CYP3A activity, and CYP3A5-selective activity on lapatinib bioactivation in individual human liver tissues. The results of this investigation indicate that lapatinib bioactivation via oxidative O-debenzylation is highly correlated with total hepatic CYP3A activity, and not CYP3A5 genotype alone. These findings provide insight into the individual factors, namely, CYP3A activity, that may affect individual exposure to reactive, potentially toxic metabolites of lapatinib.

Global Investigation of Cytochrome P450 Genes in the Chicken Genome

Cytochrome P450 (CYP) superfamily enzymes are broadly involved in a variety of physiological and toxicological processes. However, genome-wide analysis of this superfamily has never been investigated in the chicken genome. In this study, genome-wide analyses identified 45 chicken CYPs (cCYPs) from the chicken genome, and their classification and evolutionary relationships were investigated by phylogenetic, conserved protein motif, and gene structure analyses. The comprehensive evolutionary data revealed several remarkable characteristics of cCYPs, including the highly divergent and rapid evolution of the cCYPs, and the loss of cCYP2AF in the chicken genome. Furthermore, the cCYP expression profile was investigated by RNA-sequencing. The differential expression of cCYPs in developing embryos revealed the involvement of cCYPs in embryonic development. The significantly regulated cCYPs suggested its potential role in hepatic metabolism. Additionally, 11 cCYPs, including cCYP2AC1, cCYP2C23a, and cCYP2C23b, were identified as estrogen-responsive genes, which indicates that these cCYPs are involved in the estrogen-signaling pathway. Meanwhile, an expression profile analysis highlights the divergent role of different cCYPs. These data expand our view of the phylogeny and evolution of cCYPs, provide evolutionary insight, and can help elucidate the roles of cCYPs in physiological and toxicological processes in chicken.

Biotransformation and bioactivation reactions - 2018 literature highlights

In the past three decades, ADME sciences have become an integral component of the drug discovery and development process. At the same time, the field has continued to evolve, thus, requiring ADME scientists to be knowledgeable of and engage with diverse aspects of drug assessment: from pharmacology to toxicology, and from in silico modeling to in vitro models and finally in vivo models. Progress in this field requires deliberate exposure to different aspects of ADME; however, this task can seem daunting in the current age of mass information. We hope this review provides a focused and brief summary of a wide array of critical advances over the past year and explains the relevance of this research ( Table 1 ). We divided the articles into categories of (1) drug optimization, (2) metabolites and drug metabolizing enzymes, and (3) bioactivation. This annual review is the fourth of its kind (Baillie et al. 2016 ; Khojasteh et al. 2017 , 2018 ). We have followed the same format we used in previous years in terms of the selection of articles and the authoring of each section. This effort in itself also continues to evolve. I am pleased that Rietjens, Miller, and Mitra have again contributed to this annual review. We would like to welcome Namandjé N. Bumpus, James P. Driscoll, and Donglu Zhang as authors for this year's issue. We strive to maintain a balance of authors from academic and industry settings. We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. Cyrus Khojasteh, on behalf of the authors.

A Minimal Physiologically-Based Pharmacokinetic Model for Tacrolimus in Living-Donor Liver Transplantation: Perspectives Related to Liver Regeneration and the cytochrome P450 3A5 (CYP3A5) Genotype

In adult patients after living‐donor liver transplantation, postoperative days and the cytochrome P450 3A5 (CYP3A5) genotype are known to affect tacrolimus pharmacokinetics. In this study, we constructed a physiologically‐based pharmacokinetic model adapted to the clinical data and evaluated the contribution of liver regeneration as well as hepatic and intestine CYP3A5 genotypes on tacrolimus pharmacokinetics. As a result, liver function recovered immediately and affected the total body clearance of tacrolimus only during a limited period after living‐donor liver transplantation. The clearance was about 1.35‐fold higher in the recipients who had a liver with the CYP3A5*1 allele than in those with the CYP3A5*3/*3 genotype, whereas bioavailability was ~0.7‐fold higher in the recipients who had intestines with the CYP3A5*1 allele than those with CYP3A5*3/*3. In conclusion, the constructed physiologically‐based pharmacokinetic model clarified that the oral clearance of tacrolimus was affected by the CYP3A5 genotypes in both the liver and intestine to the same extent.

Improved predictions of time-dependent drug-drug interactions by determination of cytosolic drug concentrations

The clinical impact of drug-drug interactions based on time-dependent inhibition of cytochrome P450 (CYP) 3A4 has often been overpredicted, likely due to use of improper inhibitor concentration estimates at the enzyme. Here, we investigated if use of cytosolic unbound inhibitor concentrations could improve predictions of time-dependent drug-drug interactions. First, we assessed the inhibitory effects of ten time-dependent CYP3A inhibitors on midazolam 1′-hydroxylation in human liver microsomes. Then, using a novel method, we determined the cytosolic bioavailability of the inhibitors in human hepatocytes, and used the obtained values to calculate their concentrations at the active site of the enzyme, i.e. the cytosolic unbound concentrations. Finally, we combined the data in mechanistic static predictions, by considering different combinations of inhibitor concentrations in intestine and liver, including hepatic concentrations corrected for cytosolic bioavailability. The results were then compared to clinical data. Compared to no correction, correction for cytosolic bioavailability resulted in higher accuracy and precision, generally in line with those obtained by more demanding modelling. The best predictions were obtained when the inhibition of hepatic CYP3A was based on unbound maximal inhibitor concentrations corrected for cytosolic bioavailability. Our findings suggest that cytosolic unbound inhibitor concentrations improves predictions of time-dependent drug-drug interactions for CYP3A.

Influence of CYP3A4/5 and ABC transporter polymorphisms on lenvatinib plasma trough concentrations in Japanese patients with thyroid cancer

Lenvatinib is a substrate of cytochrome P450 (CYP) 3A and ATP-binding cassette (ABC) transporters. In this study, we aimed to evaluate how CYP3A4/5 and ABC transporter polymorphisms affected the mean steady-state dose-adjusted plasma trough concentrations (C₀) of lenvatinib in a cohort of 40 Japanese patients with thyroid cancer. CYP3A4 20230G > A (*1G), CYP3A5 6986A > G (*3), ABCB1 1236C > T, ABCB1 2677G > T/A, ABCB1 3435C > T, ABCC2 −24C > T, and ABCG2 421C > A genotypes were determined using polymerase chain reaction-restriction fragment length polymorphism. In univariate analysis, there were no significant differences in the mean dose-adjusted C₀ values of lenvatinib between the ABCB1, ABCG2, and CYP3A5 genotypes. However, the mean dose-adjusted C₀ values of lenvatinib in patients with the CYP3A4*1/*1 genotype and ABCC2 −24T allele were significantly higher than those in patients with the CYP3A4*1G allele and −24C/C genotype, respectively (P = 0.018 and 0.036, respectively). In multivariate analysis, CYP3A4 genotype and total bilirubin were independent factors influencing the dose-adjusted C₀ of lenvatinib (P = 0.010 and 0.046, respectively). No significant differences were found in the incidence rates of hypertension, proteinuria, and hand-foot syndrome following treatment with lenvatinib between the genotypes of CYP3A4/5 and ABC transporters. Lenvatinib pharmacokinetics were significantly influenced by the CYP3A4*1G polymorphism. If the target plasma concentration of lenvatinib for efficacy or toxicity is determined, elucidation of the details of the CYP3A4*1G genotype may facilitate decision-making related to the appropriate initial lenvatinib dosage to achieve optimal plasma concentrations.