A Phase 1 Open-Label, Fixed-Sequence Pharmacokinetic Drug Interaction Trial to Investigate the Effect of Cannabidiol on the CYP1A2 Probe Caffeine in Healthy Subjects.

This pharmacokinetic (PK) drug-interaction trial investigated the effects of repeated dosing of a plant-derived pharmaceutical formulation of highly purified cannabidiol (CBD; Epidiolex in the United States and Epidyolex in Europe; 100 mg/mL oral solution) on caffeine clearance via modulation of cytochrome P450 (CYP) 1A2 activity in healthy adults. In this phase 1 open-label, fixed-sequence trial, all subjects received a single 200 mg caffeine dose and placebo on day 1. Subjects then titrated CBD from 250 mg once daily to 750 mg twice daily between days 3 and 11 and took 750 mg CBD twice daily between days 12 and 27. On day 26, subjects received a single 200-mg caffeine dose with their morning CBD dose. Plasma concentrations of caffeine and its CYP1A2-mediated metabolite, paraxanthine, were determined on days 1 and 26 and PK parameters derived using noncompartmental analysis. Safety was monitored throughout. Sixteen subjects enrolled, and 9 completed treatment. When caffeine was administered with steady-state CBD, caffeine exposure increased by 15% for Cmax and 95% for AUC0-∞ , tmax increased from 1.5 to 3.0 hours, and t1/2 increased from 5.4 to 10.9 hours compared with caffeine administered with placebo. Under the same conditions, paraxanthine exposure decreased by 22% for Cmax and increased by 18% for AUC0-∞ , tmax increased from 8.0 to 14.0 hours, and t1/2 increased from 7.2 to 13.7 hours. Overall, there were no unexpected adverse events; diarrhea was most common, and 6 subjects discontinued because of elevated liver transaminases. These data suggest that CBD is an inhibitor of CYP1A2.

The inhibition of CYP1A2, CYP2C9, and CYP2D6 by pterostilbene in human liver microsomes.

This study used human liver microsomes to assess pterostilbene's effect on the metabolic activity of cytochrome P450 (CYP) 1A2, CYP2C9, and CYP2D6. The metabolism of their substrates (phenacetin, tolbutamide, and dextromethorphan) was assayed by quantifying their relevant metabolites by HPLC. The IC50 value was used to express the strength of inhibition, and the value of a volume per dose index (VDI) was used to indicate the metabolic ability of the enzyme. In this study, pterostilbene inhibited CYP1A2, CYP2C9, and CYP2D6's metabolic activities in vitro. CYP2C9's activity was most significantly inhibited by pterostilbene; its IC50 value was 0.12±0.04 µM. The IC50 value of CYP1A2 and CYP2D6 was 56.3±10.4 µM and 62.33±11.4 µM, respectively. The finding that suggests that pterostilbene has the potential to interact with CYP2C9 substrates in vivo. These results warrant clinical studies to assess the in vivo significance of these interactions.

Cimetidine-induced androgenic failure causes cell death and changes in actin, EGF and V-ATPase immunoexpression in rat submandibular glands.

Submandibular gland (SMG) is responsive to androgens via androgen receptor (AR). We verified whether cimetidine induces androgenic dysfunction in SMG, and evaluated the structural integrity, cell death and immunoexpression of actin, EGF and V-ATPase in androgen-deficient SMG. Male rats received cimetidine (CMTG) and control animals (CG) received saline. Granular convoluted tubules (GCTs) diameter and number of acinar cell nuclei were evaluated. TUNEL and immunofluorescence reactions for detection of AR, testosterone, actin, EGF and V-ATPase were quantitatively analysed. In CG, testosterone immunolabelling was detected in acinar and ductal cells cytoplasm. AR-immunolabelled nuclei were observed in acinar cells whereas ductal cells showed AR-immunostained cytoplasm, indicating a non-genomic AR action. In CMTG, the weak testosterone and AR immunoexpression confirmed cimetidine-induced androgenic failure. A high cell death index was correlated with decreased number of acinar cells, GCTs diameter and EGF immunoexpression under androgenic dysfunction. Actin immunofluorescence decreased in the SMG cells, but an increased and diffuse cytoplasmic V-ATPase immunolabelling was observed in striated ducts, suggesting a disruption in the actin-dependent V-ATPase recycling due to androgenic failure. Our findings reinforce the androgenic role in the maintenance of SMG histophysiology, and point to a potential clinical use of cimetidine against androgen-dependent glandular tumour cells.

Selective inhibitory effects of HYIpro-3-1 on CYP1A2 in human liver microsomes.

CYP1A2 is one of the main Cytochrome P450 enzymes in the human liver associated with the metabolism of several xenobiotics. CYP1A2 is especially involved in the metabolic activation of different procarcinogens. Therefore, the development of cancer may be inhibited by inhibiting CYP1A2 activity. Here, the inhibitory effect of HYIpro-3-1 and its derivatives on CYP1A2 activity in human liver microsomes (HLM) was studied through LC-MS/MS using a cocktail assay. Among the four compounds, HYIpro-3-1 showed the most selective and strongest inhibitory effect on CYP1A2 at IC50 values of 0.1 µM in HLMs and inhibition was confirmed using purified human CYP1A2. It was determined that inhibition is reversible because the inhibitory effect of HYIpro-3-1 is not dependent on preincubation time. HYIpro-3-1 showed a typical pattern of competitive inhibition for CYP1A2-catalyzed phenacetin O-deethylation, based on the Lineweaver-Burk plot, with a Ki value of 0.05 µM in HLMs; the secondary plot also showed a linear pattern. In our study, HYIpro-3-1 was proposed as a novel inhibitor with the capacity to selectively inhibit CYP1A activity in HLMs.

Metabolism and Mechanism of Human Cytochrome P450 Enzyme 1A2.

Human cytochrome P450 enzyme 1A2 (CYP1A2) is one of the most important cytochrome P450 (CYP) enzymes in the liver, accounting for 13% to 15% of hepatic CYP enzymes. CYP1A2 metabolises many clinical drugs, such as phenacetin, caffeine, clozapine, tacrine, propranolol, and mexiletine. CYP1A2 also metabolises certain precarcinogens such as aflatoxins, mycotoxins, nitrosamines, and endogenous substances such as steroids. The regulation of CYP1A2 is influenced by many factors. The transcription of CYP1A2 involves not only the aromatic hydrocarbon receptor pathway but also many additional transcription factors, and CYP1A2 expression may be affected by transcription coactivators and compression factors. Degradation of CYP1A2 mRNA and protein, alternative splicing, RNA stability, regulatory microRNAs, and DNA methylation are also known to affect the regulation of CYP1A2. Many factors can lead to changes in the activity of CYP1A2. Smoking, polycyclic aromatic hydrocarbon ingestion, and certain drugs (e.g., omeprazole) increase its activity, while many clinical drugs such as theophylline, fluvoxamine, quinolone antibiotics, verapamil, cimetidine, and oral contraceptives can inhibit CYP1A2 activity. Here, we review the drugs metabolised by CYP1A2, the metabolic mechanism of CYP1A2, and various factors that influence CYP1A2 metabolism. The metabolic mechanism of CYP1A2 is of great significance in the development of personalised medicine and CYP1A2 target-based drugs.

Metamizole is a Moderate Cytochrome P450 Inducer Via the Constitutive Androstane Receptor and a Weak Inhibitor of CYP1A2.

Metamizole is an analgesic and antipyretic drug used intensively in certain countries. Previous studies have shown that metamizole induces cytochrome (CYP) 2B6 and possibly CYP3A4. So far, it is unknown whether metamizole induces additional CYPs and by which mechanism. Therefore, we assessed the activity of 6 different CYPs in 12 healthy male subjects before and after treatment with 3 g of metamizole per day for 1 week using a phenotyping cocktail approach. In addition, we investigated whether metamizole induces CYPs by an interaction with the constitutive androstane receptor (CAR) or the pregnane X receptor (PXR) in HepaRG cells. In the clinical study, we confirmed a moderate induction of CYP2B6 (decrease in the efavirenz area under the plasma concentration time curve (AUC) by 79%) and 3A4 (decrease in the midazolam AUC by 68%) by metamizole. In addition, metamizole weakly induced CYP2C9 (decrease in the flurbiprofen AUC by 22%) and moderately CYP2C19 (decrease in the omeprazole AUC by 66%) but did not alter CYP2D6 activity. In addition, metamizole weakly inhibited CYP1A2 activity (1.79-fold increase in the caffeine AUC). We confirmed these results in HepaRG cells, where 4-MAA, the principal metabolite of metamizole, induced the mRNA expression of CYP2B6, 2C9, 2C19, and 3A4. In HepaRG cells with a stable knockout of PXR or CAR, we could demonstrate that CYP induction by 4-MAA depends on CAR and not on PXR. In conclusion, metamizole is a broad CYP inducer by an interaction with CAR and an inhibitor of CYP1A2. Regarding the widespread use of metamizole, these findings are of substantial clinical relevance.

Screening of Human CYP1A2 and CYP3A4 Inhibitors from Seaweed In Silico and In Vitro.

Phenolic compounds and carotenoids are potential inhibitors of cytochrome P450s. Sixteen known compounds, phenolic compounds and carotenoids from seaweed were examined for potential inhibitory capacity against CYP1A2 and CYP3A4 in silico and in vitro. Morin, quercetin, and fucoxanthin inhibited the enzyme activity of CYP1A2 and CYP3A4 in a dose-dependent manner. The IC50 values of morin, quercetin, and fucoxanthin were 41.8, 22.5, and 30.3 µM for CYP1A2 and 86.6, 16.1, and 24.4 µM for CYP3A4, respectively. Siphonaxanthin and hesperidin did not show any significant effect on CYP1A2, but they slightly inhibited CYP3A4 activity at high concentrations. In silico modeling of CYP's binding site revealed that the potential inhibitors bound in the cavity located above the distal surface of the heme prosthetic group through the 2a or 2f channel of CYPs. This study presents an approach for quickly predicting CYP inhibitory activity and shows the potential interactions of compounds and CYPs through in silico modeling.

Interaction of Thalassia testudinum Metabolites with Cytochrome P450 Enzymes and Its Effects on Benzo(a)pyrene-Induced Mutagenicity.

The aim of the present work was to evaluate the effects of Thalassia testudinum hydroethanolic extract, its polyphenolic fraction and thalassiolin B on the activity of phase I metabolizing enzymes as well as their antimutagenic effects. Spectrofluorometric techniques were used to evaluate the effect of tested products on rat and human CYP1A and CYP2B activity. The antimutagenic effect of tested products was evaluated in benzo[a]pyrene (BP)-induced mutagenicity assay by an Ames test. Finally, the antimutagenic effect of Thalassia testudinum (100 mg/kg) was assessed in BP-induced mutagenesis in mice. The tested products significantly (p < 0.05) inhibit rat CYP1A1 activity, acting as mixed-type inhibitors of rat CYP1A1 (Ki = 54.16 ± 9.09 µg/mL, 5.96 ± 1.55 µg/mL and 3.05 ± 0.89 µg/mL, respectively). Inhibition of human CYP1A1 was also observed (Ki = 197.1 ± 63.40 µg/mL and 203.10 ± 17.29 µg/mL for the polyphenolic fraction and for thalassiolin B, respectively). In addition, the evaluated products significantly inhibit (p < 0.05) BP-induced mutagenicity in vitro. Furthermore, oral doses of Thalassia testudinum (100 mg/kg) significantly reduced (p < 0.05) the BP-induced micronuclei and oxidative damage, together with an increase of reduced glutathione, in mice. In summary, Thalassia testudinum metabolites exhibit antigenotoxic activity mediated, at least, by the inhibition of CYP1A1-mediated BP biotransformation, arresting the oxidative and mutagenic damage. Thus, the metabolites of T. testudinum may represent a potential source of chemopreventive compounds for the adjuvant therapy of cancer.

Nobiletin, sinensetin, and tangeretin are the main perpetrators in clementines provoking food-drug interactions in vitro.

For clementine juice, previous data indicate a possible food-drug interaction with substrates of key enzymes responsible for drug metabolism (i.e. cytochrome P450 [CYP] 3A4, CYP1A2). However, which compounds in clementine juice are responsible for these effects are unknown. Therefore, we aimed to identify the compounds in clementine juice provoking metabolic enzyme inhibition or induction. The results demonstrated that the flavonoid fraction of clementine juice provoked induction of several genes and inhibition of both CYP3A4 and CYP1A2, matching effects observed with whole clementine juice. CYP1A2 inhibition and induction can most likely be attributed to nobiletin, sinensetin, and tangeretin. Tangeretin was the only compound causing CYP3A4 induction while CYP3A4 inhibition was most likely the result of additive or synergistic effects caused by several compounds. Thus, whenever evaluating the clinical relevance of clementine interactions, flavonoid contents should be reported because these might explain differences between cultivars and harvests.

Muscular atrophy, impaired epithelial autophagy and UCHL1 increase in androgen-deficient cauda epididymis.

In epididymis, cimetidine induces androgenic failure due to reduced sex hormone-binding globulin stromal levels and blockade of androgen receptor (AR) nuclear import. UCHL1, a hydrolase of ubiquitin-proteasome system (UPS), seems to play a role in autophagy and apoptotic pathway. However, the role of UPS and autophagy in epididymis has not been clarified. We evaluated UCHL1 and autophagy in epididymal cauda epithelium under androgenic deficiency induced by cimetidine, focusing on the interplay among these processes and apoptosis. The integrity of epididymal muscular layer was also evaluated. Male rats received cimetidine (CMTG) or saline (CG). Seminal vesicles were weighed, the expression of androgen-responsive genes Crisp1 and connexin 43 (Cx43) in cauda epididymis was evaluated, and cauda fragments were processed for light and transmission electron microscopy. The epithelium height and muscular thickness were measured. TUNEL, immunohistochemistry for caspase-3 and Cx43, and immunofluorescence for AR, Bcl-2, UCHL1, MAP LC3A, and p62/SQSTM1 (autophagic markers) were performed. Bcl-2, UCHL1, and Cx43 were detected by Western blot. In CMTG, the reduction in seminal vesicles weight accompanied by downregulation of Crisp1 and Cx43 confirmed epididymal androgenic failure. These results were associated with muscular atrophy, apoptosis and weak Cx43 and AR immunoexpression, supporting the androgenic dependence of muscular integrity. The high UCHL1 levels and reduction in Bcl-2 reinforce UCHL1 role in epithelial cells death. The intense immunoexpression of LC3A and p62/SQSTM1 indicates autophagic disturb, which in association with high UCHL1 levels, points to a role of UPS and autophagy in the regulation of epididymal epithelial cells viability under androgenic control.

Comparison of the toxicity of sulfur mustard and its oxidation products in vitro.

The molecular toxicology of the chemical warfare agent sulfur mustard (SM) is still not completely understood. It has been suggested that in addition to SM itself also biotransformation products thereof mediate cytotoxicity. In the current study, we assessed this aspect by exposing a human hepatocyte cell line (HepG2) to SM or to its oxidation products sulfur mustard sulfoxide (SMO), sulfur mustard sulfone (SMO2), and divinyl sulfone (DVS). Cytotoxicity, determined with the XTT assay, revealed a significant higher toxicity of SMO2 and DVS compared to SM while SMO had no effect at any concentration. The exact biotransformation of SM leading to SMO, SMO2 and finally DVS is unknown so far. Involvement of the CYP450 system is discussed and was also investigated in the presented study. Modulation of CYP1A2 activity, taken as a model enzyme for CYP450, affected cytotoxicity of SM, SMO2 or DVS significantly. Induction of CYP1A2 with omeprazole led to decreased cytotoxicity for all compounds whereas inhibition with cimetidine resulted in an increased cytotoxicity for SM, but not for SMO2 and DVS. Our results indicate a distinctive role of the CYP450 system in SM poisoning. Future studies should address the metabolic conversion of SM in more detail. Our data may suggest the well-tolerated drug omeprazole as a potential co-treatment after contact to SM.

Effect of fluvoxamine augmentation and smoking on clozapine serum concentrations.

BACKGROUND: Clozapine (CLZ) is metabolized via cytochrome P450 CYP1A2 to N-desmethylclozapine (NCLZ). Smoking induces CYP1A2 thereby increasing clozapine metabolism whereas fluvoxamine inhibits CYP1A2. Studies suggest that the beneficial effect of fluvoxamine augmentation in raising serum clozapine concentrations also occurs when serum concentrations are low due to smoking. Yet, little is known about the influence of fluvoxamine augmentation on clozapine serum concentrations in smoking versus non-smoking patients. METHODS: A TDM database was analyzed. Serum concentrations of CLZ, NCLZ, dose-adjusted serum concentrations (C/D) and metabolite-to-parent ratios (MPR) were compared using non-parametrical tests in four groups: clozapine-monotherapy in non-smokers (VNS, n = 28) and smokers (VS, n = 43); combined treatment with clozapine and fluvoxamine in non-smokers (VNS+F, n = 11) and smokers (VS+F, n = 43). RESULTS: The CLZ monotherapy smoking group showed lower values of C/D CLZ of -38.6% (p < 0.001), C/D NCLZ -35.6% (p < 0.001) and a higher MPR (p = 0.021) than in the non-smoking group. The combination of CLZ and fluvoxamine in non-smoking patients led to higher C/D values: C/D CLZ +117.9% (p < 0.001), C/D NCLZ +60.8% (p = 0.029) while the MPR did not differ between groups (p = 0.089). Changes were comparable to fluvoxamine augmentation in the smoking group with increased C/D CLZ of +120.1% (p < 0.001), C/D NCLZ of +85.8% (p < 0.001) and lower MPR (p = 0.006). CONCLUSIONS: Smoking in clozapine monotherapy reduced median dose-adjusted serum concentrations more than a third. Combined treatment with fluvoxamine and clozapine led to higher median C/D values in both, smokers and non-smokers. The opposing effects of CYP1A2 induction by smoking and inhibition by fluvoxamine on clozapine serum concentrations balanced out.

Enoxacin extends lifespan of C. elegans by inhibiting miR-34-5p and promoting mitohormesis.

Alterations in microRNA (miRNA) processing have been previously linked to aging. Here we used the small molecule enoxacin to pharmacologically interfere with miRNA biogenesis and study how it affects aging in C. elegans. Enoxacin extended worm lifespan and promoted survival under normal and oxidative stress conditions. Enoxacin-induced longevity required the transcription factor SKN-1/Nrf2 and was blunted by the antioxidant N-acetyl-cysteine, suggesting a prooxidant-mediated mitohormetic response. The longevity effects of enoxacin were also dependent on the miRNA pathway, consistent with changes in miRNA expression elicited by the drug. Among these differentially expressed miRNAs, the widely conserved miR-34-5p was found to play an important role in enoxacin-mediated longevity. Enoxacin treatment down-regulated miR-34-5p and did not further extend lifespan of long-lived mir-34 mutants. Moreover, N-acetyl-cysteine abrogated mir-34(gk437)-induced longevity. Evidence also points to double-stranded RNA-specific adenosine deaminases (ADARs) as new targets of enoxacin since ADAR loss-of-function abrogates enoxacin-induced lifespan extension. Thus, enoxacin increases lifespan by reducing miR-34-5p levels, interfering with the redox balance and promoting healthspan.

In Vivo Assessment of the Effect of CYP1A2 Inhibition and Induction on Pomalidomide Pharmacokinetics in Healthy Subjects.

Pomalidomide is an immunomodulatory drug, and the dosage of 4 mg per day taken orally on days 1-21 of repeated 28-day cycles has been approved in the European Union and the United States to treat patients with relapsed/refractory multiple myeloma. In vitro data showed that pomalidomide is a substrate of multiple cytochrome P450 (CYP) isozymes and that its oxidative metabolism is mediated primarily by CYP1A2 and CYP3A4, with minor contributions from CYP2C19 and CYP2D6. The effect of CYP1A2 inhibition by fluvoxamine (a strong CYP1A2 inhibitor) and CYP1A2 induction by smoking on pomalidomide pharmacokinetics in healthy subjects has been assessed in 2 separate phase 1 open-label, single-dose studies. Following administration of a single oral dose of 4 mg pomalidomide, the plasma exposure when coadministered with fluvoxamine was 225.1% and 123.7% of that when administered alone for the total plasma exposure (AUC0-inf ) and the plasma peak exposure (Cmax ), respectively. In smokers with elevated CYP1A2 activity demonstrated by high caffeine clearance (a marker of CYP1A2 induction), the AUC0-inf was 32.3% lower, whereas the Cmax was 14.4% higher than that in nonsmokers. In addition, pomalidomide was safe and well tolerated as a single oral dose of 4 mg in healthy male smokers and nonsmokers ≥ 40 to ≤ 80 years old, and a single oral dose of 4 mg pomalidomide coadministered with multiple oral 50-mg doses of the CYP1A2 inhibitor fluvoxamine compared with pomalidomide alone was safe and well tolerated by the healthy male subjects.

Evaluation of Strategies for the Assessment of Drug-Drug Interactions Involving Cytochrome P450 Enzymes.

BACKGROUND AND OBJECTIVES: Drug-drug interactions (DDIs) can occur when one drug alters the metabolism of another drug. Drug metabolism mediated by cytochrome P450 enzymes (CYPs) is responsible for the majority of metabolism of known drugs and inhibition of CYP enzymes is a well-known cause of DDIs. In the current study, the use of various human liver microsomes (HLM)-based methods to determine occurrence of CYP-mediated metabolism-dependent inhibition (MDI) and possible follow-up studies were evaluated. METHODS: Human CYP inhibition was studied using the following methodologies: direct inhibition and (non-diluted) IC50-shift assays, a ferricyanide-based reversibility assay, a spectrophotometric metabolic intermediate complex (MIC) assay, and recording of reduced carbon monoxide (CO)-difference spectra. HLM incubations in the presence and absence of NADPH and glutathione (GSH) were performed to study the possible formation of CYP-dependent GSH adducts. HLM incubations with the radiolabeled inhibitors mifepristone and paroxetine were performed to study CYP-mediated covalent binding. RESULTS: Dihydralazine and furafylline displayed irreversible MDI of CYP1A2. Paroxetine displayed both quasi-irreversible and irreversible MDI of CYP2D6, formation of CYP-dependent GSH adducts was observed, while CYP-mediated covalent binding occurred which was decreased in the presence of GSH. Mifepristone displayed irreversible MDI of CYP3A4, formation of CYP-dependent GSH adducts was observed, while CYP-mediated covalent binding occurred which was decreased in the presence of GSH. Troleandomycin and verapamil displayed quasi-irreversible MDI of CYP3A4; MIC formation was observed, while no formation of CYP-dependent GSH adducts occurred. CONCLUSIONS: This study gives a representative overview of current methodologies that can be used to study CYP inhibition. The here presented strategy can be applied as a tool during risk evaluation of CYP-mediated DDIs.

Nanofractionation Platform with Parallel Mass Spectrometry for Identification of CYP1A2 Inhibitors in Metabolic Mixtures.

With early assessment of inhibitory properties of drug candidates and their circulating metabolites toward cytochrome P450 enzymes, drug attrition, especially later in the drug development process, can be decreased. Here we describe the development and validation of an at-line nanofractionation platform, which was applied for screening of CYP1A2 inhibitors in Phase I metabolic mixtures. With this platform, a metabolic mixture is separated by liquid chromatography (LC), followed by parallel nanofractionation on a microtiter well plate and mass spectrometry (MS) analysis. After solvent evaporation, all metabolites present in the nanofractionated mixture are assayed utilizing a fluorescence CYP1A2 inhibition bioassay performed on the plate. Next, a bioactivity chromatogram is constructed from the bioassay results. By peak shape and retention time correlation of the bioactivity peaks with the obtained MS data, CYP1A2-bioactive inhibiting metabolites can be identified. The method correctly evaluated the potency of five CYP1A2 inhibitors. Mixtures comprising potent inhibitors of CYP1A2 or in vitro-generated metabolites of ellipticine were evaluated for their inhibitory bioactivities. In both cases, good LC separation of all compounds was achieved and bioactivity data could be accurately correlated with the parallel recorded MS data. Generation and evaluation of Phase II metabolites of hydroxylated ellipticine was also pursued.

Variation in the Response of Clozapine Biotransformation Pathways in Human Hepatic Microsomes to CYP1A2- and CYP3A4-selective Inhibitors.

The atypical antipsychotic agent clozapine (CLZ) is effective in many patients who are resistant to conventional antipsychotic drugs. Cytochromes P450 (CYPs) 1A2 and 3A4 oxidize CLZ to norCLZ and CLZ N-oxide in human liver. Concurrent treatment with inducers and inhibitors of CYP1A2 modulates CLZ elimination that disrupts therapy. Drug-drug interactions involving CYP3A4 are also significant but less predictable. To further characterize the factors underlying these interactions, we used samples from a cohort of human livers to assess variation in CLZ oxidation pathways in relation to intrinsic CYP3A4 and CYP1A2 activities and the effects of the corresponding selective inhibitors ketoconazole (0.2 and 2 µM) and fluvoxamine (1 and 10 µM). The CYP3A4-selective inhibitor ketoconazole (2 µM) impaired CLZ N-oxide formation in all 14 of the livers used in inhibition studies (≥50% inhibition) while the CYP1A2-selective inhibitor fluvoxamine (10 µM) decreased norCLZ formation in nine. Ketoconazole effectively inhibited CLZ metabolism in five of seven livers that catalysed CYP3A4-dependent testosterone 6ß-hydroxylation at or above the median rate and in four other livers with lower intrinsic CYP3A4 activity. Similarly, fluvoxamine (10 µM) readily inhibited CLZ oxidation in seven livers with high CYP1A2-mediated 7-ethoxyresorufin O-deethylation activity (at or above the median) and three livers with lower intrinsic CYP1A2 activity. In three livers, CLZ biotransformation was impaired by both ketoconazole and fluvoxamine, consistent with a major role for both CYPs. These findings suggest that the intrinsic activities of CYPs 1A2 and 3A4 are unrelated to the response to CYP-selective inhibitors and that assessment of the activities in vivo may not assist the prediction of drug-drug interactions.

A drug-drug interaction study to assess the effect of the CYP1A2 inhibitor fluvoxamine on the pharmacokinetics of dovitinib (TKI258) in patients with advanced solid tumors.

PURPOSE: Dovitinib is an orally available multi tyrosine kinase inhibitor which inhibits VEGFR 1-3, FGFR 1-3, and PDGFR. This study was performed to investigate the potential drug-drug interaction of dovitinib with the CYP1A2 inhibitor fluvoxamine in patients with advanced solid tumors. METHODS: Non-smoking patients of ≥ 18 years with advanced solid tumors, excluding breast cancer, were included. Patients were treated with a dose of 300 mg in 5 days on/2 days off schedule. Steady-state pharmacokinetic assessments of dovitinib were performed with or without fluvoxamine. RESULTS: Forty-five patients were enrolled; 24 were evaluable for drug-drug interaction assessment. Median age was 60 years (range 30-85). At steady state the geometric mean for dovitinib (coefficient of variation%) of the area under the plasma concentration-time curve (AUC0-72h) and maximum concentration (C max) were 2880 ng/mL h (47%) and 144 ng/mL (41%), respectively. Following administration of dovitinib in combination with fluvoxamine the geometric mean of dovitinib AUC0-72h and C max were 8290 ng/mL h (60%) and 259 ng/mL (45%), respectively. The estimated geometric mean ratios for dovitinib AUC0-72h and C max (dovitinib + fluvoxamine vs. dovitinib alone) were 2.88 [90% confidence interval (CI) 2.58, 3.20] and 1.80 (90% CI 1.66, 1.95). This effect is considered a moderate drug-drug interaction. CONCLUSIONS: Fluvoxamine co-administration resulted in a 80% increase in C max and a 188% increase in AUC0-72h of dovitinib. Given the increase in exposure to dovitinib observed, patients are at risk of dovitinib related toxicity. Dovitinib should, therefore, not be co-administered with moderate and strong CYP1A2 inhibitors, without dose reduction.

In vitro metabolism of 4, 5-dimethoxycanthin-6-one by human liver microsomes and its inhibition on human CYP1A2.

AIMS: P. quassioides is a traditional Chinese medicine used for the treatment of gastroenteritis, snakebite, infection and hypertension in China. 4, 5-dimethoxycanthin-6-one is one of the main active canthinone alkaloid isolated from P. quassioides. The aim of this work was to identify the cytochrome P (CYP) 450 enzymes responsible for the metabolism of 4, 5-dimethoxycanthin-6-one (DCO) and to evaluate the inhibitory effect of DCO on CYP activity in human liver microsomes (HLM) in vitro. MATERIALS AND METHODS: the CYP isoforms responsible for DCO metabolism and the inhibitory effects of DCO on CYP activity was studied in HLM. KEY FINDINGS: The in vitro metabolic enzyme of DCO was CYP3A4 (mediated the formation of metabolites M1-M5), CYP2C9 (mediated the formation of metabolites M1-M3, M6 and M8) and CYP2D6 (mediated the formation of metabolite M3) in HLM. Furthermore, the present work found that DCO uncompetitively inhibited CYP1A2-mediated phenacetin O-deethylation with an IC50 value of 1.7µM and a Ki value of 2.6µM. SIGNIFICANCE: The results suggested that the metabolic interaction should be existed when the substrate drugs of CYP1A2 were co-administered with DCO or traditional Chinese medicine containing it, such as the extract of P. quassioides and Kumu injection.