Cytochrome P450 3A4 Activity Research Articles

Rational Design of a Two-Photon Fluorescent Probe for Human Cytochrome P450 3A and the Visualization of Mechanism-Based Inactivation.

Mechanism-based inactivation (MBI) can mediate adverse reactions and hepatotoxicity from drugs, which is a result of their conversion into highly reactive metabolites catalyzed by enzymes such as cytochrome P450 3A (CYP3A). In the present research, we optimized the key interaction domain of the fluorophore with the target protein to develop a two-photon fluorescent probe for CYP3A that is involved in the metabolism of more than half of all clinical drugs. The developed BN-1 probe exhibited appropriate selectivity and sensitivity for the semi-quantitative detection and imaging of endogenous CYP3A activity in various living systems, thereby providing a high-throughput screening system enabling evaluation of MBI-associated hepatotoxicity by CYP3A. Using BN-1 as a fluorescent molecular tool facilitates the efficient discovery and characterization of CYP3A-induced MBI in natural systems.

In Vitro Hepatic Assessment of Cineole and Its Derivatives in Common Brushtail Possums (Trichosurus vulpecula) and Rodents.

Simple SummaryFolivore marsupials can metabolise high levels of dietary terpenes compared to eutherian mammals, indicating that they possess highly efficient drug metabolising enzymes. However, two such highly efficient drug metabolising enzymes, cytochrome P450 3A and UDP-glucuronosyltransferase, are involved in terpene metabolism, evidence for inhibitory actions by these dietary terpenes on these enzymes are limited. Therefore, we investigated the effect of cineole, a major component of eucalyptus essential oils, and its derivatives on these hepatic drug metabolising enzymes in mice, rats, and possums. Our findings revealed no major inhibition on these drug metabolising enzymes by cineole and its derivatives at concentrations up to 50 µM. However, species-specific difference in their basal enzymatic activity was observed and may provide an avenue for developing future pest control strategies.Folivore marsupials, such as brushtail possum (Trichosurus Vulpecula) and koala (Phascolarctos cinereus), can metabolise higher levels of dietary terpenes, such as cineole, that are toxic to eutherian mammals. While the highly efficient drug metabolising enzymes, cytochrome P450 3A (CYP3A) and phase II conjugating enzymes (UDP-glucuronosyltransferase, UGT), are involved in the metabolism of high levels of dietary terpenes, evidence for inhibitory actions on these enzymes by these terpenes is scant. Thus, this study investigated the effect of cineole and its derivatives on catalytic activities of hepatic CYP3A and UGT in mice, rats, and possums. Results showed that cineole (up to 50 µM) and its derivatives (up to 25 µM) did not significantly inhibit CYP3A and UGT activities in mice, rats, and possums (both in silico and in vitro). Interestingly, basal hepatic CYP3A catalytic activity in the possums was ~20% lower than that in rats and mice. In contrast, possums had ~2-fold higher UGT catalytic activity when compared to mice and rats. Thus, these basal enzymatic differences may be further exploited in future pest management strategies.

Ocular metabolism and distribution of drugs in the rabbit eye: Quantitative assessment after intracameral and intravitreal administrations

Quantitation of ocular drug metabolism is important, but only sparse data is currently available. Herein, the pharmacokinetics of four drugs, substrates of metabolizing enzymes, was investigated in albino rabbit eyes after intracameral and intravitreal administrations. Acetaminophen, brimonidine, cefuroxime axetil, and sunitinib and their corresponding metabolites were quantitated in the cornea, iris-ciliary body, aqueous humor, lens, vitreous humor, and neural retina with LC-MS/MS analytics. Non-compartmental analysis was employed to estimate the pharmacokinetic parameters of the parent drugs and metabolites. The area under the curve (AUC) values of metabolites were 12–70 times lower than the AUC values of the parent drugs in the tissues with the highest enzymatic activity. The ester prodrug cefuroxime axetil was an exception because it was efficiently and quantitatively converted to cefuroxime in the ocular tissues. In contrast to the liver, sulfotransferases, aldehyde oxidase, and cytochrome P450 3A activities were low in the eye and they had negligible impact on ocular drug clearance. With the exception of esterase substrates, metabolism seems to be a minor player in ocular pharmacokinetics. However, metabolites might contribute to ocular toxicity, and drug metabolism in various eye tissues should be investigated and understood thoroughly.

Predicting drug-drug interactions by electrochemically driven cytochrome P450 3A4 reactions.

Human cytochrome P450 3A4 is the most abundant hepatic and intestinal Phase I enzyme that metabolizes approximately 60% marketed drugs. Simultaneous administration of several drugs may result in appearance of drug-drug interaction. Due to the great interest in the combination therapy, the exploration of the role of drug as "perpetrator" or "victim" is important task in pharmacology. In this work the model systems based on electrochemically driven cytochrome P450 3A4 for the analysis of drug combinations was used. We have shown that the analysis of electrochemical parameters of cytochrome P450 3A4 and especially, potential of the start of catalysis, Eonset, possess predictive properties in the determination of the leading ("perpetrator") properties of drug. Based on these experimental data, we concluded, that the more positive potential of the start of catalysis, Eonset, the more pronounced the role of drug as leading medication. Electrochemically driven cytochrome P450 3A4 was used as probe and measuring tool for the estimation of the role of interacting drugs. It is shown that the electrochemical non-invasive model systems for monitoring the catalytic activity of cytochrome P450 3A4 can be used as prognostic devise in assessment of drug/drug interacting medications. Cytochrome P450 3A4 activity was studied in electrochemically driven system. Method was implemented to monitor drug/drug interactions. Based on the obtained experimental data, we can conclude that electrochemical parameter such as potential of onset of catalysis, Eonset, has predictive efficiency in assessment of drug/drug interacting medications in the case of the co-administration.

Anti-inflammatory Effects in LPS-treated RAW 264.7 Cells and the Influences on Drug Metabolizing Enzyme Activities by the Traditional Herbal Formulas, Yongdamsagan-Tang and Paljung-san

Objectives: Yongdamsagan-tang (YST) and Paljung-san (PJS) in traditional medicine and finasteride in modern medicine are used to treat benign prostatic hyperplasia (BPH). In recent, the use of combination herbal remedies with conventional drugs has been increasing. Therefore, we investigated the anti-inflammatory effects of these drugs to treat BPH and the influence of herbal formulas on finasteride metabolism.Methods: The inhibitory effects of the herbal formulas and finasteride on the production of inflammatory mediators and cytokines were determined in lipopolysaccharide (LPS)-treated RAW 264.7 cells. Additionally, the influence of herbal formulas on activities of human drug metabolizing enzymes (DMEs) was assessed using human microsomal enzymes.Results: We observed that YST, PJS and finasteride inhibited the production of nitric oxide (NO), prostaglandin E2 (PGE2) and interleukin-6 (IL-6) in RAW 264.7 cells. The half maximal inhibitory concentration (IC50) of YST on PGE2 production was calculated to be below 25 μg/mL. YST inhibited the activity of uridine diphosphateglucuronosyltransterase (UGT) 1A4 with an IC50 value of 49.35 μg/mL. The activities of cytochrome P450 (CYP) 1A2, CYP2B6, CYP2C19, CYP3A4, and UGT1A1 were inhibited by PJS (IC50 < 100 μg/mL, each). Although PJS and YST inhibited the activities of CYP3A4 and UGT1A4, respectively, these formulas may not influence the metabolism of finasteride because the IC50 values of herbal formulas on DMEs are too high to affect metabolism.Conclusions: Our results suggest that the combination of finasteride and YST or PJS might not influence their drug metabolism and that the drugs may have synergistic effects against BPH.

Amiodarone, Verapamil, or Diltiazem Use With Direct Oral Anticoagulants and the Risk of Hemorrhage in Older Adults

BackgroundRoutinely used cardiac medications, based on pharmacokinetics, are hypothesized to increase drug levels of direct oral anticoagulants (DOACs), with the potential to increase the risk of hemorrhage. We set out to compare the risk for hemorrhage following initiation of amiodarone, verapamil, or diltiazem (moderate cytochrome P450 3A4 and/or P-glycoprotein activity) vs metoprolol or amlodipine (weak or no activity), among older adults prescribed DOACs. MethodsWe conducted a population-based, retrospective cohort study of all adults (aged ≥ 66 years) on a DOAC (dabigatran, apixaban, rivaroxaban; n = 295,038) who were newly prescribed amiodarone (n = 4872), verapamil (n = 1284), or diltiazem (n = 14,638), compared with metoprolol or amlodipine, from Ontario, Canada (2009-2016). The outcome was hospital admission or emergency room visit with a major hemorrhage (upper or lower gastrointestinal tract, intracranial), examined using weighted models. ResultsA total of 1737 hemorrhage events occurred (amiodarone, 80 [1.6%] vs metoprolol 503 [2.3%]; verapamil, 32 [2.5%] vs amlodipine, 406 [1.6%]; diltiazem, 312 [2.1%] vs amlodipine, 404 [1.5%]). The weighted risk of major hemorrhage was not elevated with amiodarone, verapamil, or diltiazem initiation in DOAC users, compared to metoprolol or amlodipine, during the full follow-up period (hazard ratio [HR; 95% confidence interval]: amiodarone HR 0.77 [0.61-0.97]; verapamil HR 1.32 [0.88-1.98]; diltiazem HR 0.99 [0.85-1.15]). This finding was consistent with a broader definition of bleeding, adjusting for kidney function, by DOAC type or dosage. ConclusionsHemorrhage risk with amiodarone, verapamil, and diltiazem was similar to that with comparators, among DOAC users aged > 66 years.

Co-Administration of Vonoprazan, Not Tegoprazan, Affects the Pharmacokinetics of Atorvastatin in Healthy Male Subjects.

Potassium-competitive acid blocker is a new class of drugs inhibiting gastric acid. It is controversial that vonoprazan showed the inhibitory activities of cytochrome P450 3A4. This study aimed to evaluate the pharmacokinetics (PK) of atorvastatin and safety when atorvastatin was administered alone and co-administered with vonoprazan or tegoprazan. An open-label, multiple-dose, 3-intervention, 4-sequence, 4-period, partial replicate crossover study was conducted, and three interventions were; one is orally administered atorvastatin 40 mg alone once daily for 7 days, another is atorvastatin co-administered with vonoprazan 20 mg, and the other is atorvastatin co-administered with tegoprazan 50 mg. PK blood samples were collected up to 24 h after the last dose, and PK parameters for atorvastatin, 2-hydroxyatorvastatin and atorvastatin lactone were estimated by a non-compartmental method. Safety was evaluated, including adverse events and clinical laboratory tests. A total of 28 subjects completed the study. When atorvastatin was co-administered with vonoprazan, the systemic exposures of atorvastatin and atorvastatin lactone significantly increased, and the metabolic ratio of 2-hydroxyatorvastatin significantly decreased. Hypergastrinemia only occurred when atorvastatin was co-administered with vonoprazan. However, the plasma concentration profiles of atorvastatin, 2-hydroxyatorvastatin and atorvastatin lactone were similar when atorvastatin was administered alone or co-administered with tegoprazan. In conclusion, after multiple doses of atorvastatin co-administered with vonoprazan in healthy subjects, the systemic exposure of atorvastatin and the incidence of hypergastrinemia increased. With tegoprazan, however, those interactions were not observed.

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

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

Quantification of CYP3A and Drug Transporters Activity in Healthy Young, Healthy Elderly and Chronic Kidney Disease Elderly Patients by a Microdose Cocktail Approach.

Background: Ageing and chronic kidney disease (CKD) affect pharmacokinetic (PK) parameters. Since mechanisms are related and remain unclear, cytochrome P450 (CYP) 3A and drug transporter activities were investigated in the elderly with or without CKD and compared to healthy adults using a microdose cocktail.Methods: Healthy young participants (n = 20), healthy elderly participants (n = 16) and elderly patients with CKD (n = 17) received, in study period 1, a single dose of microdose cocktail probe containing 30 µg midazolam, 750 µg dabigatran etexilate, 100 µg atorvastatin, 10 µg pitavastatin, and 50 µg rosuvastatin. After a 14-day wash-out period, healthy young participants continued to study period 2 with the microdose cocktail plus rifampicin. PK parameters including area under the plasma concentration-time curve (AUC), maximum plasma drug concentration (Cmax), and half-life were estimated before making pairwise comparisons of geometric mean ratios (GMR) between groups.Results: AUC and Cmax GMR (95% confidence interval; CI) of midazolam, a CYP3A probe substrate, were increased 2.30 (1.70–3.09) and 2.90 (2.16–3.88) fold in healthy elderly and elderly patients with CKD, respectively, together with a prolonged half-life. AUC and Cmax GMR (95%CI) of atorvastatin, another CYP3A substrate, was increased 2.14 (1.52–3.02) fold in healthy elderly and 4.15 (2.98–5.79) fold in elderly patients with CKD, indicating decreased CYP3A activity related to ageing. Associated AUC changes in the probe drug whose activity could be modified by intestinal P-glycoprotein (P-gp) activity, dabigatran etexilate, were observed in patients with CKD. However, whether the activity of pitavastatin and rosuvastatin is modified by organic anion transporting polypeptide 1B (OATP1B) and of breast cancer resistance protein (BCRP), respectively, in elderly participants with or without CKD was inconclusive.Conclusions: CYP3A activity is reduced in ageing. Intestinal P-gp function might be affected by CKD, but further confirmation appears warranted.Clinical Trial Registration:http://www.thaiclinicaltrials.org/ (TCTR 20180312002 registered on March 07, 2018)

Establishment and Characterization of a Novel Gill Cell Line, LG-1, from Atlantic Lumpfish (Cyclopterus lumpus L.).

The use of lumpfish (Cyclopterus lumpus) as a cleaner fish to fight sea lice infestation in farmed Atlantic salmon has become increasingly common. Still, tools to increase our knowledge about lumpfish biology are lacking. Here, we successfully established and characterized the first Lumpfish Gill cell line (LG-1). LG-1 are adherent, homogenous and have a flat, stretched-out and almost transparent appearance. Transmission electron microscopy revealed cellular protrusions and desmosome-like structures that, together with their ability to generate a transcellular epithelial/endothelial resistance, suggest an epithelial or endothelial cell type. Furthermore, the cells exert Cytochrome P450 1A activity. LG-1 supported the propagation of several viruses that may lead to severe infectious diseases with high mortalities in fish farming, including viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV). Altogether, our data indicate that the LG-1 cell line originates from an epithelial or endothelial cell type and will be a valuable in vitro research tool to study gill cell function as well as host-pathogen interactions in lumpfish.

Development of a 3D Cell Culture System Using Amphiphilic Polydepsipeptides and Its Application to Hepatic Differentiation.

Various three-dimensional (3D) culture systems are available to provide more accurate in vivo mimicry than two-dimensional (2D) cultures. Synthetic and/or xeno-free biomaterials are desired, as they would provide lower batch-to-batch variability and high repeatability. Here, we introduce a 3D culture system using nanofibers composed of an amphiphilic polydepsipeptide-based polymer named HYDROX, which turns into 3D nanofibers after hydration. Our system produces a large amount of cell aggregates and requires only the seeding of a cell mixture. In addition, cells cultured with HYDROX can be collected with only a centrifugation procedure, and analytical assays can then be performed. Here, we applied HYDROX to hepatic differentiation from induced pluripotent stem cells. The cells cultured with HYDROX formed aggregates and HYDROX strongly promoted hepatic differentiation and maturation in terms of functions such as the positive ratio of alpha-1 antitrypsin, the production of albumin, the cytochrome P450 (CYP) 3A4 activity, and the low-density-lipoprotein uptake ability. In addition, primary human hepatocytes cultured with HYDROX showed significantly improved CYP3A4 gene expression and activity. The viscoelasticity and stiffness of HYDROX can be modulated by varying the concentration of the synthetic polymer, thereby providing a suitable microenvironment for the differentiation of cells with various characteristics toward a target cell type. Our findings demonstrated that HYDROX is a promising biomaterial for 3D cultures in research fields ranging from basic cell research to drug discovery.

Interaction study of engeletin toward cytochrome P450 3A4 and 2D6 by multi-spectroscopy and molecular docking

The inhibitory effects of engeletin on the activities of human cytochrome P450 3A4 and 2D6 (CYP3A4 and CYP2D6) were investigated by enzyme kinetics, multi-spectroscopy and molecular docking. Engeletin was found to strongly inhibit CYP3A4 and CYP2D6, with the IC50 of 1.32 μM and 2.87 μM, respectively. The inhibition modes of engeletin against CYP3A4 and CYP2D6 were a competitive type and a mixed type, respectively. The fluorescence of the two CYPs was quenched statically by engeletin, which was bound to CYP3A4 stronger than to CYP2D6 at the same temperature. Circular dichroism spectroscopy, three-dimensional fluorescence, ultraviolet–visible spectroscopy and synchronous fluorescence confirmed that the conformation and micro-environment of the two CYPs protein were changed after binding with engeletin. Molecular docking, ultraviolet–visible spectroscopy and the fluorescence data revealed that engeletin had strong binding affinity to the two CYPs through hydrogen and van der Waals forces. The findings here suggested that engeletin may cause the herb-drug interactions for its inhibition of CYP3A4 and CYP2D6 activities.

Novel Synthetic Analogues of 19(S/R)-Hydroxyeicosatetraenoic Acid Exhibit Noncompetitive Inhibitory Effect on the Activity of Cytochrome P450 1A1 and 1B1.

Cytochrome P450 (CYP) 1A1 and CYP1B1 enzymes play a significant role in the pathogenesis of cancer and cardiovascular diseases (CVD) such as cardiac hypertrophy and heart failure. Previously, we have demonstrated that R- and S-enantiomers of 19-hydroxyeicosatetraenoic acid (19-HETE), an arachidonic acid endogenous metabolite, enantioselectively inhibit CYP1B1. The current study was conducted to test the possible inhibitory effect of novel synthetic analogues of R- and S-enantiomers of 19-HETE on the activity of CYP1A1, CYP1A2, and CYP1B1. The O-dealkylation rate of 7-ethoxyresorufin (EROD) by recombinant human CYP1A1 and CYP1B1, in addition to the O-dealkylation rate of 7-methoxyresorufin (MROD) by recombinant human CYP1A2, were measured in the absence and presence of varying concentrations (0-40 nM) of the synthetic analogues of 19(R)- and 19(S)-HETE. Also, the possible inhibitory effect of both analogues on the catalytic activity of EROD and MROD, using RL-14 cells and human liver microsomes, was assessed. The results showed that both synthetic analogues of 19(R)- and 19(S)-HETE exhibited direct inhibitory effects on the activity of CYP1A1 and CYP1B1, while they had no significant effect on CYP1A2 activity. Nonlinear regression analysis and comparisons showed that the mode of inhibition for both analogues is noncompetitive inhibition of CYP1A1 and CYP1B1 enzymes. Also, nonlinear regression analysis and Dixon plots showed that the R- and S-analogues have KI values of 15.7 ±4.4 and 6.1 ±1.5 nM for CYP1A1 and 26.1 ±2.9 and 9.1 ±1.8 nM for CYP1B1, respectively. Moreover, both analogues were able to inhibit EROD and MROD activities in a cell-based assay and human liver microsomes. Therefore, the synthetic analogues of 19-HETE could be considered as a novel therapeutic approach in the treatment of cancer and CVD.

Structural Dynamics of Cytochrome P450 3A4 in the Presence of Substrates and Cytochrome P450 Reductase.

Cytochrome P450 3A4 (CYP3A4) is the most important drug-metabolizing enzyme in humans and has been associated with harmful drug interactions. The activity of CYP3A4 is known to be modulated by several compounds and by the electron transfer partner, cytochrome P450 reductase (CPR). The underlying mechanism of these effects, however, is poorly understood. We have used hydrogen-deuterium exchange mass spectrometry to investigate the impact of binding of CPR and of three different substrates (7-benzyloxy-4-trifluoromethyl-coumarin, testosterone, and progesterone) on the conformational dynamics of CYP3A4. Here, we report that interaction of CYP3A4 with substrates or with the oxidized or reduced forms of CPR leads to a global rigidification of the CYP3A4 structure. This was evident from the suppression of deuterium exchange in several regions of CYP3A4, including regions known to be involved in protein-protein interactions (helix C) and substrate binding and specificity (helices B' and E, and loop K/β1). Furthermore, the bimodal isotopic distributions observed for some CYP3A4-derived peptides were drastically impacted upon binding to CPR and/or substrates, suggesting the existence of stable CYP3A4 conformational populations that are perturbed by ligand/CPR binding. The results have implications for understanding the mechanisms of ligand binding, allostery, and catalysis in CYP enzymes.

Genome-wide association study of letrozole plasma concentrations identifies non-exonic variants that may affect CYP2A6 metabolic activity.

Letrozole is a nonsteroidal aromatase inhibitor used to treat hormone-receptor-positive breast cancer. Variability in letrozole efficacy and toxicity may be partially attributable to variable systemic drug exposure, which may be influenced by germline variants in the enzymes responsible for letrozole metabolism, including cytochrome P450 2A6 (CYP2A6). The objective of this genome-wide association study (GWAS) was to identify polymorphisms associated with steady-state letrozole concentrations. The Exemestane and Letrozole Pharmacogenetics (ELPh) Study randomized postmenopausal patients with hormone-receptor-positive nonmetastatic breast cancer to letrozole or exemestane treatment. Germline DNA was collected pretreatment and blood samples were collected after 1 or 3 months of treatment to measure steady-state letrozole (and exemestane) plasma concentrations via HPLC/MS. Genome-wide genotyping was conducted on the Infinium Global Screening Array (>650 000 variants) followed by imputation. The association of each germline variant with age- and BMI-adjusted letrozole concentrations was tested in self-reported white patients via linear regression assuming an additive genetic model. There were 228 patients who met the study-specific inclusion criteria and had both DNA and letrozole concentration data for this GWAS. The association for one genotyped polymorphism (rs7937) with letrozole concentration surpassed genome-wide significance (P = 5.26 × 10-10), explaining 13% of the variability in untransformed steady-state letrozole concentrations. Imputation around rs7937 and in silico analyses identified rs56113850, a variant in the CYP2A6 intron that may affect CYP2A6 expression and activity. rs7937 was associated with age- and BMI-adjusted letrozole levels even after adjusting for genotype-predicted CYP2A6 metabolic phenotype (P = 3.86 × 10-10). Our GWAS findings confirm that steady-state letrozole plasma concentrations are partially determined by germline polymorphisms that affect CYP2A6 activity, including variants near rs7937 such as the intronic rs56113850 variant. Further research is needed to confirm whether rs56113850 directly affects CYP2A6 activity and to integrate nonexonic variants into CYP2A6 phenotypic activity prediction systems.

Structure-based virtual screening of CYP1A1 inhibitors: towards rapid tier-one assessment of potential developmental toxicants

Cytochrome P450 1A1 (CYP1A1) metabolizes estrogens, melatonin, and other key endogenous signaling molecules critical for embryonic/fetal development. The enzyme has increasing expression during pregnancy, and its inhibition or knockout increases embryonic/fetal lethality and/or developmental problems. Here, we present a virtual screening model for CYP1A1 inhibitors based on the orthosteric and predicted allosteric sites of the enzyme. Using 1001 reference compounds with CYP1A1 activity data, we optimized the decision thresholds of our model and classified the training compounds with 68.3% balanced accuracy (91.0% sensitivity and 45.7% specificity). We applied our final model to 11 known CYP1A1 orthosteric binders and related compounds, and found that our ranking of the known orthosteric binders generally agrees with the relative activity of CYP1A1 in metabolizing these compounds. We also applied the model to 22 new test compounds with unknown/unclear CYP1A1 inhibitory activity, and predicted 16 of them are CYP1A1 inhibitors. The CYP1A1 potency and modes of inhibition of these 22 compounds were experimentally determined. We confirmed that most predicted inhibitors, including drugs contraindicated during pregnancy (amiodarone, bicalutamide, cyproterone acetate, ketoconazole, and tamoxifen) and environmental agents suspected to be endocrine disruptors (bisphenol A, diethyl and dibutyl phthalates, and zearalenone), are indeed potent inhibitors of CYP1A1. Our results suggest that virtual screening may be used as a rapid tier-one method to screen for potential CYP1A1 inhibitors, and flag them out for further experimental evaluations.

Tumor Microenvironment Alters Chemoresistance of Hepatocellular Carcinoma Through CYP3A4 Metabolic Activity.

Variations in tumor biology from patient to patient combined with the low overall survival rate of hepatocellular carcinoma (HCC) present significant clinical challenges. During the progression of chronic liver diseases from inflammation to the development of HCC, microenvironmental properties, including tissue stiffness and oxygen concentration, change over time. This can potentially impact drug metabolism and subsequent therapy response to commonly utilized therapeutics, such as doxorubicin, multi-kinase inhibitors (e.g., sorafenib), and other drugs, including immunotherapies. In this study, we utilized four common HCC cell lines embedded in 3D collagen type-I gels of varying stiffnesses to mimic normal and cirrhotic livers with environmental oxygen regulation to quantify the impact of these microenvironmental factors on HCC chemoresistance. In general, we found that HCC cells with higher baseline levels of cytochrome p450-3A4 (CYP3A4) enzyme expression, HepG2 and C3Asub28, exhibited a cirrhosis-dependent increase in doxorubicin chemoresistance. Under the same conditions, HCC cell lines with lower CYP3A4 expression, HuH-7 and Hep3B2, showed a decrease in doxorubicin chemoresistance in response to an increase in microenvironmental stiffness. This differential therapeutic response was correlated with the regulation of CYP3A4 expression levels under the influence of stiffness and oxygen variation. In all tested HCC cell lines, the addition of sorafenib lowered the required doxorubicin dose to induce significant levels of cell death, demonstrating its potential to help reduce systemic doxorubicin toxicity when used in combination. These results suggest that patient-specific tumor microenvironmental factors, including tissue stiffness, hypoxia, and CYP3A4 activity levels, may need to be considered for more effective use of chemotherapeutics in HCC patients.

Concomitant Use of Midostaurin with Strong CYP3A4 Inhibitors: An Analysis from the Ratify Trial

Introduction: Midostaurin is an oral multikinase inhibitor with activity in FMS-like tyrosine kinase 3 (FLT3 )-mutated acute myeloid leukemia (AML), including internal tandem duplications and tyrosine kinase domain mutations. The phase 3, double-blind, placebo-controlled, randomized RATIFY/CALGB (Alliance) 10603 trial investigated the effect of midostaurin in combination with standard chemotherapy and as single-agent maintenance therapy on outcomes in patients with newly diagnosed FLT3 -mutated AML. When added to standard chemotherapy, midostaurin improved both event-free survival (EFS) and overall survival (OS) (Stone et al, N Engl J Med. 2017 Jun 23. [Epub ahead of print]). Midostaurin is metabolized into 2 metabolites (CGP62221 and CGP52421) by cytochrome P450 3A4 (CYP3A4). We evaluated the effects of strong CYP3A4 inhibitors on midostaurin exposure, activity, and safety based on clinical data from the RATIFY trial.Methods: Patients received placebo or midostaurin 50 mg twice daily on days 8 to 21 of each 28-day induction or consolidation cycle, followed by 50 mg twice daily as a single agent on days 1 to 28 during the 12-cycle maintenance phase. Concomitant medication use was recorded for patients throughout all 3 treatment phases (induction, consolidation, and maintenance). Plasma levels of midostaurin and its metabolites were measured in a subset of 188 patients. Data on grade ≥3 adverse events (AEs) were collected at all sites; all grade 1/2 AE data were collected by sites outside the United States while only 13 prespecified grade 1/2 AEs were recorded at North American sites. The effect of CYP3A4 on efficacy was assessed using multiple endpoints including complete response, EFS, and OS.Results: Concomitant medication use was balanced between the midostaurin and placebo groups. Strong CYP3A4 inhibitors concurrently administered most frequently were the antifungal medications posaconazole and voriconazole. Strong CYP3A4 inhibitors were used in 60.8%, 45.6%, and 10.8% of patients during induction, consolidation, and maintenance, respectively.A 1.44-fold increase in midostaurin exposure (Cmin) was observed in patients receiving coadministration of strong CYP3A4 inhibitors compared with patients not receiving strong CYP3A4 inhibitors (number of patients: n=55 vs n=112, respectively). No relevant effect was observed with CGP62221 and CGP52421. Because the protocol did not include any recommendations for dose modifications when strong CYP3A4 inhibitors were administered, the median relative dose intensity of midostaurin was >94% of the intended dose in both treatment arms. There was no notable increase in midostaurin-related AEs in patients receiving strong CYP3A4 inhibitors. Exposure-safety analyses showed a slightly shorter time to occurrence of grade 3 or 4 clinically notable AEs with increasing exposure, with an overall acceptable safety profile for midostaurin. Exposure-response analyses indicated that a higher dose intensity was associated with a larger benefit to patients, namely through complete response, EFS and OS. This observation was generally not affected by demographic covariates or presence/absence of CYP3A4 perpetrators during the cycle where the PK sample was used for the analysis.Conclusions: Overall, co-administration of midostaurin with strong CYP3A4 inhibitors, without midostaurin dose adjustment, led to a balanced safety and efficacy profile. Because strong CYP3A4 inhibitors can increase the plasma concentration of midostaurin, caution is required when concomitantly prescribing these with midostaurin. Alternative medicinal products that do not strongly inhibit CYP3A4 activity should be considered. In situations in which satisfactory therapeutic alternatives do not exist, patients should be closely monitored for midostaurin-related toxicity.Support: U10CA180821, U10CA180882, U24CA196171; ClinicalTrials.gov identifier, NCT00651261. DisclosuresOuatas:Novartis: Employment. Duval:Novartis: Employment. Sinclair:Novartis: Employment. Berkowitz:Novartis: Employment.

Functional assessment of the effects of CYP3A4 variants on acalabrutinib metabolism in vitro

AimWe aimed (i) to study the effects of genetic polymorphism of cytochrome P450 3A4 (CYP3A4) and drug interactions on acalabrutinib (ACA) metabolism and (ii) to investigate the mechanisms underlying the effects of CYP3A4 variants on the differential kinetic profiles of ACA and ibrutinib. MethodRecombinant human CYP3A4 and variants were expressed using a Bac-to-Bac baculovirus expression system. The cell microsome was prepared and subjected to kinetic study. The analyte concentrations were determined by UPLC-MS/MS. A molecular docking assay was employed to investigate the mechanisms leading to differences in kinetic profiles. ResultsThe kinetic parameters of ACA, catalyzed by CYP3A4 and 28 of its variants, were determined, including Vmax, Km, and Ksi. CYP3A4.6–8, 12, 13, 17, 18, 20, and 30 lost their catalytic function. No significant differences were found for CYP3A4.4, 5, 10, 15, 31, and 34 compared with CYP3A4.1 with respect to intrinsic clearance (Vmax/Km, Clint). However, the Clint values of CYP3A4.9, 14, 16, 19, 23, 24, 28, 32 were obviously decreased, ranging from 0.02 to 0.05 μL/min/pmol. On the contrary, the catalytic activities of CYP3A4.2, 3, 11, 29, and 33 were increased dramatically. The Clint value of CYP3A4.11 was 5.95 times as high as that of CYP3A4.1. Subsequently, CYP3A4.1, 3, 11, 23, and 28 were chosen to study the kinetic changes in combination with ketoconazole. Interestingly, we found the inhibitory potency of ketoconazole varied in different variants. In addition, the kinetic parameters of ibrutinib and ACA were accordingly compared in different CYP3A4 variants. Significant differences in relative clearance were observed among variants, which would probably influence the distance between the redox site and the heme iron atom. ConclusionGenetic polymorphism of CYP3A4 extensively changes its ACA-metabolizing enzymatic activity. In combination with a CYP inhibitor, its inhibitory potency also varied among different variants. Even the same variants exhibited different capabilities catalyzing ACA. Its enzymatic capabilities are probably determined by the distance between the substrate and the heme iron atom, which could be impacted by mutation.

Identification of the contact region responsible for the formation of the homomeric CYP1A2•CYP1A2 complex.

Previous studies showed that cytochrome P450 1A2 (CYP1A2) forms a homomeric complex that influences its metabolic characteristics. Specifically, CYP1A2 activity exhibits a sigmoidal response as a function of NADPH-cytochrome P450 reductase (POR) concentration and is consistent with an inhibitory CYP1A2•CYP1A2 complex that is disrupted by increasing [POR] (Reed et al. (2012) Biochem. J. 446, 489-497). The goal of this study was to identify the CYP1A2 contact regions involved in homomeric complex formation. Examination of X-ray structure of CYP1A2 implicated the proximal face in homomeric complex formation. Consequently, the involvement of residues L91-K106 (P1 region) located on the proximal face of CYP1A2 was investigated. This region was replaced with the homologous region of CYP2B4 (T81-S96) and the protein was expressed in HEK293T/17 cells. Complex formation and its disruption was observed using bioluminescence resonance energy transfer (BRET). The P1-CYP1A2 (CYP1A2 with the modified P1 region) exhibited a decreased BRET signal as compared with wild-type CYP1A2 (WT-CYP1A2). On further examination, P1-CYP1A2 was much less effective at disrupting the CYP1A2•CYP1A2 homomeric complex, when compared with WT-CYP1A2, thereby demonstrating impaired binding of P1-CYP1A2 to WT-CYP1A2 protein. In contrast, the P1 substitution did not affect its ability to form a heteromeric complex with CYP2B4. P1-CYP1A2 also showed decreased activity as compared with WT-CYP1A2, which was consistent with a decrease in the ability of P1-CYP1A2 to associate with WT-POR, again implicating the P1 region in POR binding. These results indicate that the contact region responsible for the CYP1A2•CYP1A2 homomeric complex resides in the proximal region of the protein.