Cytochrome P450 3A Isoforms Research Articles

Effect of Itraconazole, a CYP3A4 Inhibitor, and Rifampin, a CYP3A4 Inducer, on the Pharmacokinetics of Vatiquinone.

Vatiquinone is a small molecule inhibitor of 15-lipoxygenase in development for patients with Friedreich's ataxia. The objective of this analysis was to determine the effect of a cytochrome P450 isoform 3A4 (CYP3A4) inhibitor and inducer on vatiquinone pharmacokinetics (PKs). The coadministration of 400mg of vatiquinone with 200mg of itraconazole (a CYP3A4 inhibitor) resulted in increased maximum observed concentration (Cmax) of vatiquinone and systemic exposure (AUC0-inf) by approximately 3.5- and 2.9-fold, respectively. The coadministration of 400mg of vatiquinone with 600mg of rifampin (a CYP3A4 inducer) resulted in decreased vatiquinone Cmax and AUC0-inf by approximately 0.64- and 0.54-fold, respectively. The terminal half-life of vatiquinone was not affected by itraconazole or rifampin. These clinical study results confirm the in vitro reaction phenotyping data that shows that CYP3A4 plays an important role in vatiquinone metabolism. The result of this analysis together with phase 3 efficacy and safety data, population PK analysis, and the exposure-response relationship will determine if the extent of vatiquinone changes in the presence of CYP3A4 inhibitors and inducers are considered clinically relevant.

Exploring the Regulation of Cytochrome P450 in SH-SY5Y Cells: Implications for the Onset of Neurodegenerative Diseases.

Human individual differences in brain cytochrome P450 (CYP) metabolism, including induction, inhibition, and genetic variation, may influence brain sensitivity to neurotoxins and thus participate in the onset of neurodegenerative diseases. The aim of this study was to explore the modulation of CYPs in neuronal cells. The experimental approach was focused on differentiating human neuroblastoma SH-SY5Y cells into a phenotype resembling mature dopamine neurons and investigating the effects of specific CYP isoform induction. The results demonstrated that the differentiation protocols using retinoic acid followed by phorbol esters or brain-derived neurotrophic factor successfully generated SH-SY5Y cells with morphological neuronal characteristics and increased neuronal markers (NeuN, synaptophysin, β-tubulin III, and MAO-B). qRT-PCR and Western blot analysis showed that expression of the CYP 1A1, 3A4, 2D6, and 2E1 isoforms was detectable in undifferentiated cells, with subsequent increases in CYP 2E1, 2D6, and 1A1 following differentiation. Further increases in the 1A1, 2D6, and 2E1 isoforms following β-naphthoflavone treatment and 1A1 and 2D6 isoforms following ethanol treatment were evident. These results demonstrate that CYP isoforms can be modulated in SH-SY5Y cells and suggest their potential as an experimental model to investigate the role of CYPs in neuronal processes involved in the development of neurodegenerative diseases.

Direct and Sequential Bioactivation of Pemigatinib to a Reactive Iminium Ion Intermediate Culminates in Mechanism‐Based Inactivation of Cytochrome P450 3A

Mechanism‐based inactivation (MBI) is a unique phenomenon in drug metabolism that arises when an enzyme metabolically activates a drug to a chemically reactive intermediate and primes it for irreversible binding, leading to an irrevocable loss of catalytic activity that is only restored upon de novo synthesis of the implicated enzyme. Our laboratory recently established the MBI of cytochrome P450 3A (CYP3A) by the fibroblast growth factor receptor (FGFR) inhibitors erdafitinib and infigratinib. Serendipitously, our preliminary data has also revealed that pemigatinib (PEM) – another clinically approved FGFR1‐3 inhibitor – similarly elicited time‐dependent inhibition of CYP3A. This was rather unexpected as it was previously purported that PEM did not pose any metabolism‐dependent liabilities due to the absence of glutathione‐related conjugates in metabolic profiling experiments conducted in human liver microsomes. Consequently, we posited that PEM is bioactivated by CYP3A to a hard electrophile, thereby allowing it to elude glutathione trapping and detection in the aforementioned reactive metabolite screen. Here, we confirmed that PEM inhibited both CYP3A isoforms in a time‐, concentration‐, and cofactor‐dependent manner consistent with MBI – with KI, kinact, and partition ratio of 8.69 and 11.95 μM, 0.108 and 0.042 min−1, and ~44 and ~47 for CYP3A4 and CYP3A5 respectively, when rivaroxaban was employed as the probe substrate. While the rate of inactivation was diminished by coincubation with an alternative substrate (testosterone) or direct inhibitor of CYP3A (ketoconazole), the inclusion of nucleophilic trapping agents afforded no such protection. Furthermore, the lack of catalytic activity recovery following dialysis and oxidation with potassium ferricyanide coupled with the absence of a spectrally resolvable peak in the Soret region collectively implied that the underlying mechanism of inactivation was not elicited via the formation of pseudoirreversible metabolite‐intermediate complexes. Utilizing cyanide trapping and high‐resolution mass spectrometry, we illuminated the direct and sequential oxidative bioactivation of PEM and its major O‐desmethylated metabolite at its distal morpholine moiety to a reactive iminium ion intermediate that could covalently modify the CYP3A apoprotein and/or prosthetic heme and culminate in its MBI. Finally, structural determinants gleaned from our in silicocovalent docking simulations suggested that the discrepancies in MBI potencies between both CYP3A isoforms might be alluded to the propensity for PEM to interact more favourably with an accessible active‐site serine residue in position 312 of CYP3A4 as compared to CYP3A5. Further physiologically based pharmacokinetic modelling studies are currently underway to better discern the clinical implications of our findings.

Reevaluate In Vitro CYP3A Index Reactions of Benzodiazepines and Steroids between Humans and Dogs.

Cytochrome P450 3A (CYP3A), the most important class of drug-metabolizing enzymes, participates in the metabolism of half of clinically used drugs. The CYP3A index reactions of dogs, one of the most widely used preclinical nonrodent species, are still poorly understood. This work evaluated the activity and selectivity of 10 CYP3A index reactions, including midazolam (MDZ) 1'- and 4-hydroxylation, alprazolam (APZ) and triazolam (TRZ) α- and 4-hydroxylation, testosterone (T) 6β-hydroxylation, lithocholate (LCA) 6α-hydroxylation, deoxycholate (DCA) 1β- and 5β-hydroxylation, with quantitative reaction phenotyping and kinetic analysis in human and canine recombinant CYP enzymes (rCYPs). In human studies, all reactions are reconfirmed as mixed index reactions of CYP3A with minor contributions from non-CYP3A isoforms. In canine studies, all reactions are also primarily catalyzed by CYP3A12 with lower contributions from CYP3A26. However, the canine CYP2B11 appreciably contributes to the hydroxylation of benzodiazepines except for APZ 4-hydroxylation. The canine CYP3A isoforms have lower activity than human isoforms toward T 6β-hydroxylation and LCA 6α-hydroxylation and both substrates undergo non-CYP3A catalyzed side reactions. DCA 1β- and 5β-hydroxylation are validated as the CYP3A index reactions in both humans and dogs with limited non-CYP3A contributions and side reactions. In conclusion, this work provides a comprehensive overview for the selectivity and activity of in vitro CYP3A index reactions in humans and dogs. The validated CYP3A index reactions between humans and dogs may benefit future practices in drug metabolism and drug interaction studies. SIGNIFICANCE STATEMENT: Dogs are one of the most important nonrodent animals with limited studies of cytochrome P450 enzymes than humans. This work provides the most comprehensive quantitative data to date for the selectivity and activity of CYP3A index reactions in humans and dogs. The canine CYP2B11 was found to appreciably contribute to hydroxylation of midazolam, alprazolam and triazolam, the well-known probes for human CYP3A. Deoxycholate 1β- and 5β-hydroxylation are validated as the CYP3A index reactions in both humans and dogs.

Direct and Sequential Bioactivation of Pemigatinib to Reactive Iminium Ion Intermediates Culminates in Mechanism-Based Inactivation of Cytochrome P450 3A.

We recently established the mechanism-based inactivation (MBI) of cytochrome P450 3A (CYP3A) by the fibroblast growth factor receptor (FGFR) inhibitors erdafitinib and infigratinib. Serendipitously, our preliminary data have also revealed that pemigatinib (PEM), another clinically approved FGFR1-3 inhibitor, similarly elicited time-dependent inhibition of CYP3A. This was rather unexpected, as it was previously purported that PEM did not pose any metabolism-dependent liabilities due to the absence of glutathione-related conjugates in metabolic profiling experiments conducted in human liver microsomes. Here, we confirmed that PEM inhibited both CYP3A isoforms in a time-, concentration-, and cofactor-dependent manner consistent with MBI, with inactivator concentration at half-maximum rate constant, maximum inactivation rate constant, and partition ratio of 8.69 and 11.95 μM, 0.108 and 0.042 min-1, and approximately 44 and approximately 47 for CYP3A4 and CYP3A5, respectively. Although the rate of inactivation was diminished by coincubation with an alternative substrate or direct inhibitor of CYP3A, the inclusion of nucleophilic trapping agents afforded no such protection. Furthermore, the lack of catalytic activity recovery following dialysis and oxidation with potassium ferricyanide coupled with the absence of a spectrally resolvable peak in the Soret region collectively implied that the underlying mechanism of inactivation was not elicited via the formation of pseudo-irreversible metabolite-intermediate complexes. Finally, utilizing cyanide trapping and high-resolution mass spectrometry, we illuminated the direct and sequential oxidative bioactivation of PEM and its major O-desmethylated metabolite at its distal morpholine moiety to reactive iminium ion hard electrophilic species that could covalently inactivate CYP3A via MBI. SIGNIFICANCE STATEMENT: This study reports for the first time the covalent MBI of CYP3A by PEM and deciphered its bioactivation pathway involving the metabolic activation of PEM and its major O-desmethylated metabolite to reactive iminium ion intermediates. Following which, a unique covalent docking methodology was harnessed to unravel the structural and molecular determinants underpinning its inactivation. Findings from this study lay the foundation for future investigation of clinically relevant drug-drug interactions between PEM and concomitant substrates of CYP3A.

Spectroscopic observations of β-eudesmol binding to human cytochrome P450 isoforms 3A4 and 1A2, but not to isoforms 2C9, 2C19, and 2D6

β-Eudesmol (BEU) is a sesquiterpenoid component of Atractylodes lancea with cytotoxic activity against cholangiocarcinoma. Its lipophilic nature makes BEU a likely substrate of human cytochrome P450 (P450) enzymes. Using ligand-binding difference spectroscopy, the affinities of this compound to recombinant CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 were investigated in Escherichia coli membrane preparations. CYP3A4 showed a type I spectral change, with a binding constant Ks of 77 ± 23 (mean ± SD) μM at 0.5 μM P450 (Ks/[P450] ≈ 155). The reference substrate testosterone (TES) and the inhibitor fluconazole bound to the enzyme with apparent affinities of 86 ± 4 μM (type I) and 21 μM (type II), respectively. BEU was bound by CYP3A4 in a non-cooperative manner (Hill coefficient n ≈ 0.8). CYP1A2 showed reverse type I difference spectra with either BEU or caffeine (CAF). The CYP1A2 affinity for BEU was higher (0.23 mM) than for CAF (0.37 mM) but lower than for phenacetin (0.11 mM, type I). BEU did not bind significantly to CYP2C9, CYP2C19, and CYP2D6. Confirmation of metabolic activity and studies on the involvement of other human P450 isoforms are required. Double-beam spectrometry is needed to validate Ks measurements made with a microplate reader.

Effects of Aspirin on the Bioavailability and Pharmacokinetics of Repaglinide: Possible Role of Cytochrome P450 3A Isoforms Inhibition by Aspirin

Effects of Aspirin on the Bioavailability and Pharmacokinetics of Repaglinide: Possible Role of Cytochrome P450 3A Isoforms Inhibition by Aspirin

Variation in Expression of Cytochrome P450 3A Isoforms and Toxicological Effects: Endo- and Exogenous Substances as Regulatory Factors and Substrates.

The CYP3A subfamily, which includes isoforms CYP3A4, CYP3A5, and CYP3A7 in humans, plays important roles in the metabolism of various endogenous and exogenous substances. Gene and protein expression of CYP3A4, CYP3A5, and CYP3A7 show large inter-individual differences, which are caused by many endogenous and exogenous factors. Inter-individual differences can cause negative outcomes, such as adverse drug events and disease development. Therefore, it is important to understand the variations in CYP3A expression caused by endo- and exogenous factors, as well as the variation in the metabolism and kinetics of endo- and exogenous substrates. In this review, we summarize the factors regulating CYP3A expression, such as bile acids, hormones, microRNA, inflammatory cytokines, drugs, environmental chemicals, and dietary factors. In addition, variations in CYP3A expression under pathological conditions, such as coronavirus disease 2019 and liver diseases, are described as examples of the physiological effects of endogenous factors. We also summarize endogenous and exogenous substrates metabolized by CYP3A isoforms, such as cholesterol, bile acids, hormones, arachidonic acid, vitamin D, and drugs. The relationship between the changes in the kinetics of these substrates and the toxicological effects in our bodies are discussed. The usefulness of these substrates and metabolites as endogenous biomarkers for CYP3A activity is also discussed. Notably, we focused on discrimination between CYP3A4, CYP3A5, and CYP3A7 to understand inter-individual differences in CYP3A expression and function.

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.

In silico and in vitro studies on interaction of novel non-imidazole histamine H3R antagonists with CYP3A4

The paper presents in silico study to explain differences in the influence of the series of non-imidazole histamine receptor H3 ligands on the activity of cytochrome P-450 3A4 isoform, which was verified in in vitro tests. The compounds appeared to induce broad range of effects – from significant inhibition (-61% reduction of CYP3A4 control activity) to extreme activation (+713% of control activity). Structure-activity relationship for examined compounds was analyzed, with special attention paid to the influence of substituent and the chain length. Docking, molecular dynamics studies, and their statistical analysis allowed to identify those interactions that can be responsible for determination of particular activity type of a compound toward CYP3A4 (activation/inhibition). It resulted in indication of several amino acid residues, which should be carefully analyzed during estimation of compound effects on CYP3A4 activity.

Smallest Maximum Intramolecular Distance: A Novel Method to Mitigate Pregnane Xenobiotic Receptor Activation

Induction of cytochrome P450 isoform 3A4 via activation of the pregnane xenobiotic receptor (PXR) is a concern for pharmaceutical discovery and development, as it can lead to drug-drug interactions. We present a novel molecular descriptor, the smallest maximum intramolecular distance (SMID), which is correlated with PXR activation, and a method for using the SMID descriptor to guide discovery chemists in modifying lead compounds to decrease PXR activation.

Ligand-Free Estrogen Receptor α (ESR1) as Master Regulator for the Expression of CYP3A4 and Other Cytochrome P450 Enzymes in the Human Liver.

Cytochrome P450 3A4 isoform (CYP3A4) transcription is controlled by hepatic transcription factors (TFs), but how TFs dynamically interact remains uncertain. We hypothesize that several TFs form a regulatory network with nonlinear, dynamic, and hierarchical interactions. To resolve complex interactions, we have applied a computational approach for estimating Sobol's sensitivity indices (SSI) under generalized linear models to existing liver RNA expression microarray data (GSE9588) and RNA-seq data from genotype-tissue expression (GTEx), generating robust importance ranking of TF effects and interactions. The SSI-based analysis identified TFs and interacting TF pairs, triplets, and quadruplets involved in CYP3A4 expression. In addition to known CYP3A4 TFs, estrogen receptor α (ESR1) emerges as key TF with the strongest main effect and as the most frequently included TF interacting partner. Model predictions were validated using small interfering RNA (siRNA)/short hairpin RNA (shRNA) gene knockdown and clustered regularly interspaced short palindromic repeats (CRISPR)-mediated transcriptional activation of ESR1 in biliary epithelial Huh7 cells and human hepatocytes in the absence of estrogen. Moreover, ESR1 and known CYP3A4 TFs mutually regulate each other. Detectable in both male and female hepatocytes without added estrogen, the results demonstrate a role for unliganded ESR1 in CYP3A4 expression consistent with unliganded ESR1 signaling reported in other cell types. Added estrogen further enhances ESR1 effects. We propose a hierarchical regulatory network for CYP3A4 expression directed by ESR1 through self-regulation, cross regulation, and TF-TF interactions. We also demonstrate that ESR1 regulates the expression of other P450 enzymes, suggesting broad influence of ESR1 on xenobiotics metabolism in human liver. Further studies are required to understand the mechanisms underlying role of ESR1 in P450 regulation. SIGNIFICANCE STATEMENT: This study focuses on identifying key transcription factors and regulatory networks for CYP3A4, the main drug metabolizing enzymes in liver. We applied a new computational approach (Sobol's sensitivity analysis) to existing hepatic gene expression data to determine the role of transcription factors in regulating CYP3A4 expression, and used molecular genetics methods (siRNA/shRNA gene knockdown and CRISPR-mediated transcriptional activation) to test these interactions in life cells. This approach reveals a robust network of TFs, including their putative interactions and the relative impact of each interaction. We find that ESR1 serves as a key transcription factor function in regulating CYP3A4, and it appears to be acting at least in part in a ligand-free fashion.

Secukinumab Treatment Does Not Alter the Pharmacokinetics of theCytochrome P450 3A4 Substrate Midazolam in Patients With Moderate to Severe Psoriasis.

This open‐label disease‐drug–drug interaction study assessed whether blockade of the interleukin (IL)‐17A pathway by secukinumab and subsequent downregulation of inflammatory cytokines like IL‐6 or high‐sensitivity C‐reactive protein affects the pharmacokinetics (PKs) of a sensitive probe substrate of the cytochrome P450 3A4 isoform (CYP3A4). The PKs of midazolam, metabolized by CYP3A4, was evaluated before and after 7 and 35 days of treatment initiation of subcutaneous secukinumab at a dose of 300 mg weekly in 24 patients with moderate‐to‐severe psoriasis. Although demonstrating the expected decrease in downstream inflammatory cytokines, secukinumab had no clinically relevant effects on the PKs of midazolam, provided substantial clinical benefit, and was generally well tolerated. In summary, blockade of IL‐17A signaling in patients with moderate‐to‐severe psoriasis does not significantly affect CYP3A4 enzyme activities and, therefore, the use of secukinumab is unlikely to influence the PKs of CYP3A4 substrates.

Effects of catalpol on the activity of human liver cytochrome P450 enzymes

1. Catalpol possesses numerous pharmacological activities, and however, little data available for the effects of catalpol on the activity of human liver cytochrome P450 (CYP) enzymes.2. This study investigates the inhibitory effects of catalpol on the main human liver CYP isoforms. In this study, the inhibitory effects of catalpol on the eight human liver CYP isoforms 1A2, 2A6, 2E1, 2D6, 2C9, 2C19, 2C8 and 3A4 were investigated in human liver microsomes.3. The results indicated that catalpol could inhibit the activity of CYP3A4, CYP2E1 and CYP2C9, with IC50 values of 14.27, 22.4 and 14.69 μM, respectively, but those other CYP isoforms were not affected. Enzyme kinetic studies showed that catalpol was not only a noncompetitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP2E1 and CYP2C9, with Ki values of 7.40, 10.75 and 7.37 μM, respectively. In addition, catalpol is a time-dependent inhibitor for CYP3A4, with maximum inactivation (kinact) and 50% maximum inactivation (KI) values of 0.02 min−1 and 1.86 μM, respectively.4. The in vitro studies of catalpol with CYP isoforms suggest that catalpol has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP3A4, CYP2E1 and CYP2C9. Further in vivo studies are needed in order to evaluate the significance of this interaction.

Differences in CYP3A genotypes of a liver transplant recipient and the donor liver graft and adjustment of tacrolimus dose

Tacrolimus (Tac) is well established as main immunosuppressant in most immunosuppressive regimens in solid organ transplantation. Due to the narrow therapeutic window, pre dose Tac levels (C0) are monitored in all patients receiving Tac to reach optimal therapeutic levels. Tac is metabolized in the liver and intestine by the cytochrome P450 3A (CYP3A) isoforms CYP3A4 and CYP3A5. We present a case of an African American woman who underwent a liver transplantation in which adequate Tac levels were difficult to accomplish due to differences in cytochrome P450 3A4/5 (CYP3A4/5) polymorphisms of the transplant recipient and the donor liver graft. This case report highlights that genotyping the liver transplant recipient and the donor liver graft might provide data which could be used to predict the tacrolimus metabolism post transplantation.

7-Hydroxymitragynine Is an Active Metabolite of Mitragynine and a Key Mediator of Its Analgesic Effects.

Mitragyna speciosa, more commonly known as kratom, is a plant native to Southeast Asia, the leaves of which have been used traditionally as a stimulant, analgesic, and treatment for opioid addiction. Recently, growing use of the plant in the United States and concerns that kratom represents an uncontrolled drug with potential abuse liability, have highlighted the need for more careful study of its pharmacological activity. The major active alkaloid found in kratom, mitragynine, has been reported to have opioid agonist and analgesic activity in vitro and in animal models, consistent with the purported effects of kratom leaf in humans. However, preliminary research has provided some evidence that mitragynine and related compounds may act as atypical opioid agonists, inducing therapeutic effects such as analgesia, while limiting the negative side effects typical of classical opioids. Here we report evidence that an active metabolite plays an important role in mediating the analgesic effects of mitragynine. We find that mitragynine is converted in vitro in both mouse and human liver preparations to the much more potent mu-opioid receptor agonist 7-hydroxymitragynine and that this conversion is mediated by cytochrome P450 3A isoforms. Further, we show that 7-hydroxymitragynine is formed from mitragynine in mice and that brain concentrations of this metabolite are sufficient to explain most or all of the opioid-receptor-mediated analgesic activity of mitragynine. At the same time, mitragynine is found in the brains of mice at very high concentrations relative to its opioid receptor binding affinity, suggesting that it does not directly activate opioid receptors. The results presented here provide a metabolism-dependent mechanism for the analgesic effects of mitragynine and clarify the importance of route of administration for determining the activity of this compound. Further, they raise important questions about the interpretation of existing data on mitragynine and highlight critical areas for further research in animals and humans.

Population Pharmacokinetic Analysis of Bisoprolol in Patients With Acute Coronary Syndrome.

To date, many questions about the extent and cause of pharmacokinetic (PK) variability of even the most widely studied and prescribed β1-adrenergic receptor blockers, such as metoprolol and bisoprolol, remain unanswered. Given that there are still no published population pharmacokinetic (PopPK) analyses of bisoprolol in routinely treated patients with acute coronary syndrome (ACS), the aim of this study was to determine its PK variability in 71 Serbian patients with ACS. PopPK analysis was conducted using a nonlinear mixed-effects model (NONMEM), version 7.3.0 (Icon Development Solutions). In each patient, the same formulation of bisoprolol was administered once or twice daily at a total daily dose of 0.625-7.5 mg. We separately assessed the effects of 31 covariates on the PKs of bisoprolol, and our results indicated that only 2 covariates could have possible influence on the variability of the clearance of bisoprolol: the mean daily dose of the drug and smoking habits of patients. These findings suggest that possible autoinduction of drug metabolism by higher total daily doses and induction of cytochrome P450 isoform 3A4 (CYP3A4) by cigarette smoke in liver could be the potential causes of increased total clearance of bisoprolol in patients with ACS.

NEPA (netupitant + palonosetron) Administration Is Safe and Effective in cHL Patients Receiving ABVD Regimen: A Single-Center Real Life Experience

BACKGROUNDIn the setting of cHL, ABVD (adriamycin, bleomycin, vinblastine, dacarbazine) is the most widely used first line chemotherapeutic treatment and it is well known that this regimen is associated with a high emetic risk (HEC). Palonosetron (PALO) currently represents one of the most effective and implemented drug for CINV prevention, but after many ABVD cycles patients (pts) frequently need to add other antiemetic drugs to obtain a good control of their symptoms. Netupitant (NETU) is the NK1-RA (neurokinin receptor antagonist) component of NEPA, the first antiemetic drug available as oral fixed combination: NETU (300mg) + PALO (0.5mg). Both ABVD drugs and NETU are metabolized by cytochrome P-450 isoform 3A4 (CYP3A4), but respect to other NK1-receptor antagonist available, NETU has demonstrated to have no clinical relevant interaction with chemotherapy drugs like etoposide, cyclophosphamide and docetaxel. However, no data are currently available about the safety profile of NETU in the setting of ABVD treatment; for that reason we started the use of this drug as salvage therapy after PALO failure.METHODSWe retrospectively analyzed the cHL pts treated with ABVD at our Center from September 2016 to January 2018. We used PALO + dexamethasone as first-line anti-CINV prophylaxis, while NEPA was introduced as salvage drug for those pts with inadequately controlled CINV.We collected data regarding demographics; diagnosis; planned chemotherapeutic treatment; performed chemotherapeutic treatment; acute, delayed and anticipatory CINV (before and after NEPA); laboratory findings including transaminases, creatinine and electrolytes (before and after NEPA); adverse reactions (before and after NEPA).The primary endpoint of the study was safety of NEPA in ABVD treated pts, while CINV control (no nausea or vomiting) was the secondary endpoint. NEPA-related safety data have been compared to the same data collected at the moment of the last previous PALO-containing regimen.RESULTSAmong the 32 pts treated with ABVD during the study period, 13 (41%) received NEPA.Three pts were males and 10 females, and median age was 33 years (range 18-61). According to disease characteristics at diagnosis the planned ABVD administrations were 12 (6 cycles) in 9 pts, 8 (4 cycles) in 3 pts and 4 (2 cycles) in 1 pt. Nine pts completed the planned chemotherapy, 1 pt skipped the last cycle for personal decision, 3 pts are ongoing treatment at the time of analysis.Reasons for shift to NEPA are as follows: acute (grade 2) CINV alone in 3/13 pts; late (grade 2) CINV alone in 3/13 pts; combined acute (4 grade 2, 1 grade 1) and late (4 grade 2, 1 grade 1) CINV in 5/13 pts; combined anticipatory (grade 1), acute (grade 1) and late (grade 2) CINV in 2/13 pts.NEPA was started after a median of 4 ABVD administrations (range 1-10). Globally 53 NEPA administrations were delivered during subsequent cycles (median number of 3 NEPA administrations for each pt, range 1-11).With regard to the primary endpoint, the observed adverse events are listed in Table 1.With regard to the secondary endpoint, anticipatory, acute and delayed CINV were detected in 15%, 77%, 77%, of PALO pts and 15%, 46% and 15% of NEPA pts, respectively (see Table 2)CONCLUSIONIn our experience NETU did not show drug-drug interaction with ABVD chemotherapy agents, and NEPA administration was globally well tolerated with mild and transient adverse events. Furthermore, in cHL ABVD treated pts who experienced nausea and/or vomiting after failure of PALO + dexamethasone antiemetic prophylaxis, NEPA has demonstrated to be effective in CINV control. In 4 out of 13 cases, after an initial improvement in CINV control, pts subsequently required to shift to anti-CINV third line treatments. On the other hand, the 9 pts who continued on NEPA administration could experience an optimal CINV control immediately after the first administration.At our knowledge no data have been published regarding NEPA toxicities in the ABVD setting. Our safety and efficacy data come from a real life experience of consecutive pts treated homogeneously at a single center and would suggest the use of NEPA as primary anti-CINV prophylaxis in previously untreated cHL pts. DisclosuresRusconi:Celgene: Research Funding.

The critical role of porcine cytochrome P450 3A46 in the bioactivation of aflatoxin B1

Aflatoxin B1 (AFB1) is bioactivated by cytochrome P450 (CYP) 3A isoforms in humans to generate the highly reactive epoxide intermediate AFB1-8,9-epoxide (AFBO), causing hepatotoxicity and hepatocarcinoma. Due to the unavoidable contamination in their feed, pigs are more likely to be exposed to AFB1 and indirectly harm human health. Therefore, identifying the porcine CYP3A isoforms involved in AFB1-8,9-epoxidation is critical. In this study, we used codon optimization and N-terminal coding sequence modification to modify a CYP3A46 recombinant protein that exhibits good structure and catalytic activities and revealed its strong AFB1-8,9-epoxidase activity for the first time. Site-directed mutagenesis, kinetics and docking analyses were performed and demonstrated that residues Phe-108, Ser-119, Phe-215, Phe-304 and Thr-309 play important roles in AFB1-8,9-epoxidation and its responsiveness to α-naphthoflavone. Interestingly, we uncovered the dual and reverse roles of Phe-304 in CYP3A46, CYP3A5 and CYP3A4 in AFB1 oxidation. Unlike the π-π interaction between the Phe-304 phenyl of CYP3A4 and the AFB1 aromatic ring, Phe-304 of CYP3A46 may function to provide steric hindrance to bind AFB1. Phe-108 and Phe-215 could stabilize AFB1 with a potentially productive orientation through van der Waals interactions with AFB1. Ser-119 and Thr-309 are likely to function to form H-bonds with AFB1. This study broadens our knowledge of AFB1 bioactivation in pigs and may contribute to reduce the deleterious effects of AFB1 in pigs and humans.

Identification of the enzyme isoforms responsible for the N‐oxide detoxification pathway in tobacco specific nitrosamines (TSNAs)

Tobacco‐specific nitrosamines (TSNAs), are among the most potent carcinogens found in tobacco products. Among them are N′‐nitrosonornicotine (NNN), N′‐nitrosoanabasine (NAB), N′‐nitrosoanabatine (NAT), 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) and 4‐ (methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL), a major metabolite of NNK. TSNAs are detoxified by a number of metabolic pathways, including glucuronidation by the UDP‐glucuronosyltransferase (UGT) family of enzymes, as well as N‐oxidation by an as yet unidentified enzyme or family of enzymes. TSNAs share a pyridine ring in their chemical structure that can be further metabolized to a detoxification N‐oxide product. TSNA‐N‐oxides have been identified in the urine of rodents exposed to TSNAs and NNAL‐N‐oxide was found in the urine of smokers, however, the enzymes responsible for this conversion have not yet been determined. To identify enzymes that catalyze TSNA‐N‐oxide formation, we used specific inhibitors for the major hepatic cytochrome P450 (CYP) enzymes (CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4) in oxidation reactions with pooled human liver microsomes, including phenacetin, coumarin, bupropion, amodiaquine, diclofenac, omeprazole, dextrometrphan, chlorzoxazone and midazolam. Inhibition of NNK‐N‐oxide and NNAL‐N‐oxide formation was observed when using inhibitors for CYPs 1A2, 2A6, 2E1, 2C19 and 3A4. To confirm results from these inhibition studies, NNK‐N‐oxide and NNAL‐N‐oxide formation was examined using microsomal fractions from CYP over‐expressing HEK293 cells. Microsomes from cells over‐expressing CYPs 1A2, 2C19, 2E1 and 3A4 isoforms exhibited TSNA‐N‐oxide formation. The isoforms 2C19 and 2E1 presented an approximate two‐fold higher activity than the other active isoforms. These data suggest that several cytochrome P450 enzymes may play an important role in the N‐oxidation of TSNAs, and that inter‐individual variability in the activity of these enzymes could potentially be important in TSNA‐induced cancer risk.Support or Funding Information National Institutes of Health, National Institutes of Environmental Health Sciences [Grant R01‐ES025460] Health Sciences and Services Authority of Spokane, WA [Grant WSU002292] This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.