Metabolism Of Imatinib Research Articles

Effect of recombinant CYP3A4 variants and interaction on imatinib metabolism in vitro

The aim of this study was to investigate the catalytic activity of 26 Cytochrome P450 3A4 (CYP3A4) variants and drug interactions on imatinib metabolism in recombinant insect microsomes. This study was designed with an appropriate incubation system and carried out in the constant temperature water. By using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) to measure the quantities of its metabolite N-desmethyl imatinib, to elucidate the impacts of the CYP3A4 genetic polymorphism and drug interactions on the metabolism of imatinib. Consequently, as compared to CYP3A4.1, the intrinsic clearance (CLint) values of the variations were dramatically changed, rising from 2.34 % to 120.57 %. CYP3A4.14 showed an increase in CLint in comparison to CYP3A4.1, and the remaining 24 variants demonstrated decreases in catalytic activity for the metabolism of imatinib. In addition, the metabolism of imatinib was decreased to varied degrees by ketoconazole, itraconazole, and fluconazole in CYP3A4.1 and CYP3A4.18. Moreover, most of CYP3A4 variants showed similar trend of enzyme activity under different substrates of imatinib and cabozantinib, except 6 variants (CYP3A4.3,.4,.10,.15,.29 and.31). The first study of the effects of 26 CYP3A4 variants on imatinib metabolism will contribute to the clinical evaluation of imatinib and help personalize therapy in clinical settings.

Evaluation of in vivo pharmacokinetic study of the anti-cancer drug imatinib using silkworms as an animal model.

Imatinib is an oral molecular targeted therapy that acts as a tyrosine kinase inhibitor. Silkworms present a promising experimental model for elucidating the pharmacokinetic and toxicity profiles of various compounds. This study aimed to establish an experimental paradigm for investigating the pharmacokinetics of imatinib in silkworms. A comparative analysis of imatinib pharmacokinetic parameters across silkworms, humans, mice, and rats revealed similarities in time to maximum concentration (Tmax) and apparent clearance values between silkworms and humans. However, differences in elimination half-life (t1/2) and apparent volume of distribution between silkworms and humans remained within 5- and 4-fold ranges, respectively. Importantly, mice demonstrated pharmacokinetic parameters closer to those of humans than rats during imatinib studies. Additionally, silkworms and mice exhibit similar Tmax and t1/2 values. This study highlights the potential of silkworms as valuable tools for investigating imatinib metabolism in pharmacokinetic studies. Furthermore, it underscores the applicability of silkworms in elucidating the pharmacokinetic parameters of various molecular-targeted drugs, thus facilitating advancements in drug development and evaluation.

Pharmacokinetic Interaction Between Imatinib and Metformin in Rats.

Imatinib is primarily transported into the liver by organic cation transporter 1 (OCT1), organic anion transporting polypeptide 1B3 (OATP1B3), and novel organic cation transporter 2 (OCTN2), which is the first step in the metabolic and elimination of imatinib. Patients taking imatinib may concurrently take metformin, a substrate for OCT1. Drug-drug interactions (DDI) may occur between imatinib and metformin, affecting the clinical efficacy of imatinib. This experiment aimed to investigate the pharmacokinetic effects of metformin on imatinib and its active metabolism of N-desmethyl imatinib in rats. Twenty healthy Sprague-Dawley rats were selected and randomly divided into control and experimental groups (10 rats per group). The control group was orally administered imatinib (30 mg/kg) for 14 days, and the experimental group was orally co-administered imatinib (30 mg/kg) and metformin (200 mg/kg) for 14 days. The plasma concentrations of imatinib and N-desmethyl imatinib in rats were determined by ultra-performance liquid chromatography-mass spectrometry. Pharmacokinetic parameters were calculated by DAS2.0 software. After single-dose co-administration of imatinib and metformin on day 1, the AUC0-24 (area under the plasma concentration-time curve) and Cmax (maximum concentration) of imatinib and the MRT (mean residence time) and Cmax of N-desmethyl imatinib in the experimental group were significantly decreased compared with the control group (P < 0.05). After multiple-dose co-administration of imatinib and metformin for 14 days, the AUC0-24 and Cmax of both imatinib and N-desmethyl imatinib were significantly decreased in the experimental group (P < 0.05). With both single and multiple co-administration doses, metformin significantly changed the pharmacokinetic parameters of imatinib and N-desmethyl imatinib. The results suggest that care should be taken when metformin and imatinib are co-administered.

Gene polymorphisms affect postoperative imatinib plasma levels and edema in adults with gastrointestinal stromal tumor.

Aim: To assess the role of genetic polymorphisms in postoperative imatinib concentrations and edema in patients with gastrointestinal stromal tumor. Methods: The relationships between genetic polymorphisms, imatinib concentrations and edema were explored. Results: Carriers of the rs683369 G-allele and rs2231142 T-allele had significantly higher imatinib concentrations. Grade ≥2 periorbital edemas were related to the carriership of two C-alleles in rs2072454 with an adjusted odds ratio of 2.85, two T-alleles in rs1867351 with an adjusted odds ratio of 3.42 and two A-alleles in rs11636419 with an adjusted odds ratio of 3.15. Conclusion: rs683369 and rs2231142 affect the metabolism of imatinib; rs2072454, rs1867351 and rs11636419 are related to grade ≥2 periorbital edemas.

A Study of the Identification, Fragmentation Mode and Metabolic Pathways of Imatinib in Rats Using UHPLC-Q-TOF-MS/MS.

In this study, The metabolites, metabolic pathways, and metabolic fragmentation mode of a tyrosine kinase inhibitor- (TKI-) imatinib in rats were investigated. The samples for analysis were pretreated via solid-phase extraction, and the metabolism of imatinib in rats was studied using ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS). Eighteen imatinib metabolites were identified in rat plasma, 21 in bile, 18 in urine, and 12 in feces. Twenty-seven of the above compounds were confirmed as metabolites of imatinib and 9 of them were newly discovered for the first time. Oxidation, hydroxylation, dealkylation, and catalytic dehydrogenation are the main metabolic pathways in phase I. For phase II, the main metabolic pathways were N-acetylation, methylation, cysteine, and glucuronidation binding. The fragment ions of imatinib and its metabolites were confirmed to be produced by the cleavage of the C-N bond at the amide bond. The newly discovered metabolite of imatinib was identified by UHPLC-Q-TOF-MS/MS. The metabolic pathway of imatinib and its fragmentation pattern were summarized. These results could be helpful to study the safety of imatinib for clinical use.

Physiologically-Based Pharmacokinetic Predictions of the Effect of Curcumin on Metabolism of Imatinib and Bosutinib: In Vitro and In Vivo Disconnect.

This study aimed to investigate the potential pharmacokinetic interactions between curcumin, imatinib and bosutinib, combining In Vitro and in silico methods. In Vitro metabolism of imatinib and bosutinib were investigated in pooled human liver microsomes and recombinant CYP3A4 enzyme in the presence and absence of curcumin and curcumin glucuronide using an LC-MS/MS assay for N-desmethyl metabolites. A physiologically-based pharmacokinetic (PBPK) model for curcumin formulated as solid lipid nanoparticles (SLN) was constructed using In Vitro glucuronidation kinetics and published clinical pharmacokinetic data. The potential effects of curcumin coadministration on systemic exposures of imatinib and bosutinib were predicted in silico using PBPK simulations. Curcumin demonstrated potent reversible inhibition of cytochrome P450 (CYP)3A4-mediated N-demethylation of imatinib and bosutinib and CYP2C8-mediated metabolism of imatinib with inhibitory constants (ki,u) of ≤1.5μmol. L-1. A confirmatory In Vitro study with paclitaxel, the 6α-hydroxylation of which is exclusively mediated by CYP2C8, was consistent with a potent inhibition of this enzyme by curcumin. Curcumin glucuronide also inhibited both CYP enzymes In Vitro, albeit to a lesser extent than that of curcumin. PBPK model simulations predicted that at recommended dosing regimens of SLN curcumin, coadministration would result in an increase in systemic exposures of imatinib and bosutinib of up to only 10%. A PBPK model for curcumin in a SLN formulation was successfully developed. Although curcumin possesses a strong In Vitro inhibitory activity towards CYP3A4 and CYP2C8 enzymes, its interactions with imatinib and bosutinib were unlikely to be of clinical importance due to curcumin's poor bioavailability.

Potential for pharmacokinetic interactions between Schisandra sphenanthera and bosutinib, but not imatinib: in vitro metabolism study combined with a physiologically-based pharmacokinetic modelling approach.

This study aimed to investigate the potential interaction between Schisandra sphenanthera, imatinib and bosutinib combining in vitro and in silico methods. In vitro metabolism of imatinib and bosutinib using recombinant enzymes and human liver microsomes were investigated in the presence and absence of Schisandra lignans. Physiologically-based pharmacokinetic (PBPK) models for the lignans accounting for reversible and mechanism-based inhibitions and induction of CYP3A enzymes were built in the Simcyp Simulator (version 17) and evaluated for their capability to predict interactions with midazolam and tacrolimus. Their potential effect on systemic exposures of imatinib and bosutinib were predicted using PBPK in silico simulations. Schisantherin A and schisandrol B, but not schisandrin A, potently inhibited CYP3A4-mediated metabolism of imatinib and bosutinib. All three compounds showed a strong reversible inhibition on CYP2C8 enzyme with ki of less than 0.5 μmol L-1 . The verified PBPK models were able to describe the increase in systemic exposure of midazolam and tacrolimus due to co-administration of S. sphenanthera, consistent with the reported changes in the corresponding clinical interaction study (AUC ratio of 2.0 vs 2.1 and 2.4 vs 2.1, respectively). The PBPK simulation predicted that at recommended dosing regimens of S. sphenanthera, co-administration would result in an increase in bosutinib exposure (AUC ratio 3.0) but not in imatinib exposure. PBPK models for Schisandra lignans were successfully developed. Interaction between imatinib and Schisandra lignans was unlikely to be of clinical importance. Conversely, S. sphenanthera at a clinically-relevant dose results in a predicted three-fold increase in bosutinib systemic exposure.

The impact of azole antifungal drugs on imatinib metabolism in human liver microsomes

1. Imatinib is widely used for the treatment of hematologic malignancies. It is common that imatinib is clinically co-prescribed with azole antifungal agents since these patients are more prone to invasive antifungal infection. The present study was to investigate the effects of azole antifungal drugs, including ketoconazole, fluconazole, voriconazole, itraconazole and posaconazole on imatinib metabolism.2. The main metabolites, 1-OH midazolam and N-desmethyl imatinib, were determined in the absence and in the presence of various levels of ketoconazole, fluconazole, voriconazole, itraconazole and posaconazole. The relevant assay was also performed to screen mechanism-based inhibitors (MBI).3. The inhibition ability of 1-OH midazolam formation from midazolam based on IC50 values was ketoconazole (0.09 µM)>itraconazole (0.31 µM)> posaconazole (0.68 µM)>voriconazole (2.10 µM) > fluconazole (8.90 µM). Similarly, the rank order of inhibitory effects on formation of N-desmethyl imatinib from imatinib was ketoconazole (4.58 µM)>itraconazole (17.45 µM)> posaconazole (31.02 µM)> voriconazole (367.9 µM) >fluconazole (1.11 mM). Posaconazole and itraconazole displayed evidence of MBI. Additionally, imatinib was also shown as a MBI of CYP3A with IC50 value of 5.40 µM against the midazolam.4. The significant difference in IC50 values of midazolam and imatinib inhibited by azole antifungal agents was observed. The role of CYP2C8 in imatinib metabolism and imatinib autoinhibits CYP3A activity may explain this difference. Our findings suggest that the azole antifungal agents might have limited impacts on imatinib exposure by CYP3A activity.

Role of pharmacogenetics in personalised imatinib dosing

Imatinib is the original tyrosine kinase inhibitor specifically designed and clinically used for the molecularly targeted treatment of chronic myeloid leukaemia (CML). It remains one of the most widely used first-line treatments for CML, and is now also indicated in multiple other BCR-ABL-, c-KIT- and PDGFR-driven cancers. Imatinib is orally administered, predominantly hepatically cleared with a low hepatic extraction ratio, is 95% bound to plasma proteins, and has an intracellular site of action. In the CML setting, treatment outcomes correlate with plasma imatinib concentrations, which show large interpatient variability. Treatment outcomes also correlate with markers of drug transporter variability considered to influence imatinib distribution into CML cells. Personalised imatinib dosing is therefore expected to improve treatment outcomes compared to a “one-dose-fits-all” approach, with a potential additional role for pharmacogenetics. Imatinib is metabolised by CYPs 2C8 and 3A4 in vitro . CYP2C8 genotype significantly affects imatinib metabolism, and consequently imatinib systemic exposure in CML patients. Conversely, there is no consistent evidence that CYP3A4 or CYP3A5 inhibitors, inducers or genetics alter imatinib metabolism and pharmacokinetics clinically. Imatinib is also a substrate for uptake and efflux transporters expressed in the liver and/or CML cells, although exactly which transporters is an area of open debate. The clear majority of studies indicate no significant effect of transporter genotypes on plasma imatinib concentrations or clearance, and any positive findings to date have not been replicated. Various measures of CML treatment outcome have been correlated with transporter genotype, and from this implied an effect of transporter genetics on imatinib distribution into CML cells. However, due to study design limitations it is unclear if these observations are due to genetic effects on imatinib clearance, intracellular distribution, or possibly neither. Other potentially novel genetic factors influencing imatinib disposition, such as xenobiotic-responsive receptor gene polymorphisms, remain to be thoroughly investigated. In summary, studies to date indicate a potential genetic influence on imatinib disposition, however evidence is still lacking to support a pharmacogenomic approach to personalised imatinib dosing. Whether pharmacogenomic information might be complementary to potential therapeutic drug monitoring or target concentration intervention for imatinib is an ongoing question. Improved study designs are required to gain greater mechanistic understanding of the factors governing variable imatinib intracellular distribution and its relationship to response, and move toward improved tools for personalised imatinib dosing.

Impact of pharmacogenomics on imatinib toxicity in gastrointestinal stromal tumors.

11043 Background: Imatinib-induced side effects are common, although most of these side effects are mild, some will be severe and lead to disruption of Imatinib treatment in gastrointestinal stromal tumor (GIST). It is necessary to explore a biological predictors to predict and optimal therapeutic strategy. But there were few studied conducted to explore the mechanisms of Imatinib-induced side effects. The present study comprehensively investigated the effects of genetic polymorphisms of cytokines involved in cell proliferation and metabolic enzymes and transporters involved in Imatinib metabolism on these side effects. Methods: A total of 154 GSIT patients treated with Imatinib were enrolled. 22 SNPs (single nucleotide polymorphisms) in KIT/ PDGFRA/ PDGFRB/ SHC1/ FLT1/ MAPK1/ EGFR/ CCL5/ CXCL14were detected using Agena Massarray matrix-assisted laser desorption / ionization-time of flight (MALDI-TOF) platform. Logistic regression analyses were performed to evaluate their effects on Imatinib-induced toxicities. This study was approved by the ethical committee of Sun Yat-Sen University Cancer Center. Results: Imatinibdose, FLT1 rs9951465, MAPK1 rs13515, PDGFRB rs55712339 and SHC1 rs3766920 were found to be correlated with the incidence of myelosuppression ( P= 0.027, 0.009, 0.002, 0.008, &lt; 0.001, respectively), moreover, FLT1 rs9554314 was correlated with severe myelosuppression (Grade 0,1 vs. 2+, P= 0.009, OR (95%CI) = 3.042 (1.314-7,042)). Meanwhile, EGFR rs10228436 was found to be correlated with the incidence of skin rash ( P= 0.027), moreover, CCL5 rs4796120 and CXCL14 rs7716492 were correlated with severe skin rash (Grade 0,1 vs. 2+), with OR (95%CI) and p value were 8.542 (0.934-78.107), 13.504 (2.308-79.004) and 0.057, 0.020, respectively. Conclusions: This is the first comprehensive report on the biomarkers for Imatinib toxicities. These biomarkers might be able to distinguish patients with mild or more severe forms of Imatinib toxicities, thus enabling the optimization of Imatinib therapy and lead patients benefit from Imatinib treatment in a long-term.

Novel sulphur-containing imatinib metabolites found by untargeted LC-HRMS analysis

Untargeted metabolite profiling using high-resolution mass spectrometry coupled with liquid chromatography (LC-HRMS), followed by data analysis with the Compound Discoverer 2.0™ software, was used to study the metabolism of imatinib in humans with chronic myeloid leukemia. Plasma samples from control (drug-free) and patient (treated with imatinib) groups were analyzed in full-scan mode and the unknown ions occurring only in the patient group were then, as potential imatinib metabolites, subjected to multi-stage fragmentation in order to elucidate their structure. The application of an untargeted approach, as described in this study, enabled the detection of 24 novel structurally unexpected metabolites. Several sulphur-containing compounds, probably originating after the reaction of reactive intermediates of imatinib with endogenous glutathione, were found and annotated as cysteine and cystine adducts. In the proposed mechanism, the cysteine adducts were formed after the rearrangement of piperazine moiety to imidazoline. On the contrary, in vivo S-N exchange occurred in the case of the cystine adducts. In addition, N-O exchange was observed in the collision cell in the course of the fragmentation of the cystine adducts. The presence of sulphur in the cysteine and cystine conjugates was proved by means of ultra-high resolution measurements using Orbitrap Elite. The detection of metabolites derived from glutathione might improve knowledge about the disposition of imatinib towards bioactivation and help to improve understanding of the mechanism of its hepatotoxicity or nephrotoxicity in humans.

CYP2C8 Genotype Significantly Alters Imatinib Metabolism in Chronic Myeloid Leukaemia Patients

The aims of this study were to determine the effects of the CYP2C8*3 and *4 polymorphisms on imatinib metabolism and plasma imatinib concentrations in chronic myeloid leukaemia (CML) patients. We genotyped 210 CML patients from the TIDELII trial receiving imatinib 400-800mg/day for CYP2C8*3 (rs11572080, rs10509681) and *4 (rs1058930). Steady-state trough total plasma N-desmethyl imatinib (major metabolite):imatinib concentration ratios (metabolic ratios) and trough total plasma imatinib concentrations were compared between genotypes (one-way ANOVA with Tukey post hoc). CYP2C8*3 (n=34) and *4 (n=15) carriers had significantly higher (P<0.01) and lower (P<0.01) metabolic ratios, respectively, than CYP2C8*1/*1 (n=147) patients (median ± standard deviation: 0.28±0.08, 0.18±0.06 and 0.22±0.08, respectively). Plasma imatinib concentrations were consequently>50% higher for CYP2C8*1/*4 than for CYP2C8*1/*1 and CYP2C8*3 carriers (2.18 ± 0.66 vs. 1.45 ± 0.74 [P<0.05] and 1.36 ± 0.98μg/mL [P<0.05], respectively). CYP2C8 genotype significantly alters imatinib metabolism in patients through gain- and loss-of-function mechanisms.

Imatinib metabolism and disposition in isolated rat perfused liver

Imatinib is an orally administered tyrosine kinase inhibitor which inhibits the Bcr-Abl protein-tyrosine kinase with high selectivity. Imatinib is rapidly absorbed from the gut, after oral intake and has an almost absolute bioavailability of 98%. The metabolism of imatinib is mediated by the cytochrome P450 (CYP) isoenzymes in the liver and gut wall. CGP74588 is a major active metabolite of imatinib. The study was performed on Male Sprague-Dawley rats (250-300 g) housing under artificial light on a 12-h light/dark cycle with free access to standard laboratory chow and water. Re-circulating (at imatinib concentration of 1 and 5 µg/ml) and single-pass (imatinib dose of 1mg) perfusion modes in the presence and absence of BSA were tested. Throughout the experiment, perfusate temperature (37±0.5 C°), pH (7.4±0.2) and liver viability (ALT and AST) were monitored. The concentrations of imatinib and its main metabolite in perfusion buffer and liver homogenate were determined by a validated HPLC method. No metabolite was detected in outlet perfusate in all conditions. However negligible amounts of metabolite were found in liver homogenate at 1 and 5 µg/ml imatinib concentrations in re-circulating perfusion mode. The rapid and remarkable disappearance of imatinib from perfusate was related to its accumulation in liver. Statistical moment definition was used to calculate some pharmacokinetic parameters. These calculations also confirmed liver accumulation and slow and sustained dissociation of imatinib from liver.

Kronik Miyeloid Lösemi Hastalarında İmatinib ve Norimatinib Plazma Düzeyi Ölçümleri

Objective: Imatinib is the first line treatment in chronic myeloid leukemia (CML). Imatinib metabolism depends primarily on the presence of cytochrome P450 enzymes, its active metabolite being norimatinib (N-desmethyl imatinib). Norimatinib accumulates in plasma 10-30%. The aim of this study was to analyze certain parameters which maintain the importance in clarifying the pharmacologic effects of imatinib. Material and Methods: To investigate plasma concentrations, 41 CML patients on minimum 400 mg imatinib daily were included to the study. Pharmacokinetic analysis was performed by tandem mass spectrometry (LC-MS/MS). Mean plasma imatinib and norimatinib levels were statistically calculated as 4.038±1.290 ppm (min. 0.576 ppm, max. 6.795 ppm) and 1.150±0.733 ppm (min. 0.08 ppm, max. 3.835 ppm), respectively. Results: Limit of detection (LOD) values for imatinib and norimatinib were 30 ppb and 25 ppb, whereas limit of quantification (LOQ) values were 99 ppb and 82.5 ppb, and recovery of imatinib and norimatinib were 98.45% and 92.47%, respectively. Average percentage of imatinib transformation to norimatinib was 22.16%. Variation of this percentage from one patient to another suggested the possibility of interindividual differences in drug response. Conclusion: Individual results have shown that pharmacologic effects of imatinib may differentiate among patients. In this study, we standardized and justified the applicability of our analysis method. Patients' plasma drug levels can be measured using this method. Thus optimal treatment efficacy can be ensured.

Human hepatocyte assessment of imatinib drug-drug interactions - complexities in clinical translation.

Inducers and inhibitors of CYP3A, such as ritonavir and efavirenz, may be used as part of the highly active antiretroviral therapy (HAART) to treat HIV patients. HIV patients with chronic myeloid leukemia or gastrointestinal stromal tumour may need imatinib, a CYP3A4 substrate with known exposure response-relationships. Administration of imatinib to patients on ritonavir or efavirenz may result in altered imatinib exposure leading to increased toxicity or failure of therapy, respectively. We used primary human hepatocyte cultures to evaluate the magnitude of interaction between imatinib and ritonavir/efavirenz. Hepatocytes were pre-treated with vehicle, ritonavir, ketoconazole, efavirenz or rifampicin, and the metabolism of imatinib was characterized over time. Concentrations of imatinib and metabolite were quantitated in combined lysate and medium, using LC-MS. The predicted changes in imatinib CLoral (95% CI) with ketoconazole, ritonavir, rifampicin and efavirenz were 4.0-fold (0, 9.2) lower, 2.8-fold (0.04, 5.5) lower, 2.9-fold (2.2, 3.5) higher and 2.0-fold (0.42, 3.5) higher, respectively. These predictions were in good agreement with clinical single dose drug-drug interaction studies, but not with reports of imatinib interactions at steady-state. Alterations in metabolism were similar after acute or chronic imatinib exposure. In vitro human hepatocytes predicted increased clearance of imatinib with inducers and decreased clearance with inhibitors of CYP enzymes. The impact of HAART on imatinib may depend on whether it is being initiated or has already been dosed chronically in patients. Therapeutic drug monitoring may have a role in optimizing imatinib therapy in this patient population.

Impact of CYP2C8*3 polymorphism on in vitro metabolism of imatinib to N-desmethyl imatinib

1. Imatinib is metabolized to N-desmethyl imatinib by CYPs 3A4 and 2C8. The effect of CYP2C8*3 genotype on N-desmethyl imatinib formation was unknown.2. We examined imatinib N-demethylation in human liver microsomes (HLMs) genotyped for CYP2C8*3, in CYP2C8*3/*3 pooled HLMs and in recombinant CYP2C8 and CYP3A4 enzymes. Effects of CYP-selective inhibitors on N-demethylation were also determined.3. A single-enzyme Michaelis–Menten model with autoinhibition best fitted CYP2C8*1/*1 HLM (n = 5) and recombinant CYP2C8 kinetic data (median ± SD Ki = 139 ± 61 µM and 149 µM, respectively). Recombinant CYP3A4 showed two-site enzyme kinetics with no autoinhibition. Three of four CYP2C8*1/*3 HLMs showed single-enzyme kinetics with no autoinhibition. Binding affinity was higher in CYP2C8*1/*3 than CYP2C8*1/*1 HLM (median ± SD Km = 6 ± 2 versus 11 ± 2 µM, P=0.04). CYP2C8*3/*3 (pooled HLM) also showed high binding affinity (Km = 4 µM) and single-enzyme weak autoinhibition (Ki = 449 µM) kinetics. CYP2C8 inhibitors reduced HLM N-demethylation by 47–75%, compared to 0–30% for CYP3A4 inhibitors.4. In conclusion, CYP2C8*3 is a gain-of-function polymorphism for imatinib N-demethylation, which appears to be mainly mediated by CYP2C8 and not CYP3A4 in vitro in HLM.

Pharmacokinetics interaction between imatinib and genistein in rats.

The objective of this work was to investigate the effect of orally administered genistein on the pharmacokinetics of imatinib and N-desmethyl imatinib in rats. Twenty-five healthy male SD (Sprague-Dawley) rats were randomly divided into five groups: A group (control group), B group (multiple dose of 100 mg/kg genistein for consecutive 15 days), C group (multiple dose of 50 mg/kg genistein for consecutive 15 days), D group (a single dose of 100 mg/kg genistein), and E group (a single dose of 50 mg/kg genistein). A single dose of imatinib is administered orally 30 min after administration of genistein (100 mg/kg or 50 mg/kg). The pharmacokinetic parameters of imatinib and N-desmethyl imatinib were calculated by DAS 3.0 software. The multiple dose of 100 mg/kg or 50 mg/kg genistein significantly (P < 0.05) decreased the AUC0−t and C max of imatinib. AUC0−t and the C max of N-desmethyl imatinib were also increased, but without any significant difference. However, the single dose of 100 mg/kg or 50 mg/kg genistein has no effect on the pharmacokinetics of imatinib and N-desmethyl imatinib. Those results indicated that multiple dose of genistein (100 mg/kg or 50 mg/kg) induces the metabolism of imatinib, while single dose of genistein has no effect.

Impact of Drug Transporters ABCB1 and ABCG2 and Regulators of Xenobiotic Transport and Metabolism Pxr and CAR Gene Polymorphisms on Clinical Efficacy of Imatinib in Chronic Myeloid Leukemia (CML)

Background: Inherited background in mechanisms regulating cellular uptake, elimination and metabolism of imatinib and other BCR-ABL tyrosine kinase inhibitors may influence treatment outcome in chronic myeloid leukemia (CML). Despite good efficacy of imatinib in CML therapy, a proportion of patients show suboptimal responses or even primary resistance. Imatinib is a well-established substrate of ABC-superfamily xenobiotic transporters ABCB1 (MDR1, Pg-P) and ABCG2 (BCRP). However, the results of published studies regarding impact of ABCB1 and ABCG2 single nucleotide polymorphisms (SNPs) on imatinib treatment outcome have shown discrepant results. Moreover, little is known on the potential role of polymorphisms of regulators of xenobiotic transport and metabolism, pregnane X receptor (PXR, NR1|2) and constitutive androstane receptor (CAR, NR1|3) in imatinib efficacy.Aim: In this study we verified whether 61 tagging SNPs in drug transporters genes (ABCB1 and ABCG2) and regulators of xenobiotic transport and metabolism gene (PXR and CAR) genes affect imatinib therapy outcomes in CML.Methods: Genotyping was performed in 256 patients of Polish Caucasian origin (141 men and 117 women) treated with imatinib as first line treatment (229; 89.5%) or after second-line after interferon therapy (27; 10.5%). Tagging SNP approach was used to select the genetic variants and resulted in a selection of 61 tagging SNPs including 26 SNPs for ABCB1, 17 SNPs for ABCG2, 11 SNPs for PXR and 7 SNPs for CAR gene. Complete clinical data on imatinib treatment outcome were assessable for analyses of associations with tested SNPs. The influence of SNPs on imatinib outcomes including achievement of complete cytogenetic response (CCyR) at 12 months, achievement of major molecular response (MMR) at 18 months, progression-free survival (PFS), time to treatment failure (TTF) and overall survival (OS) were tested in regard to established clinical and laboratory predictive factors using logistic regression and proportional-hazards regression models. Three inheritance models (co-dominant, dominant and recessive) were tested for all allelic variants.Results: In this study we found that carriers of minor allele of CAR rs4073054A>C SNP significantly associated with shorter TTF on imatinib therapy (OR=2.42, 95%CI 1.41 - 4.17; p=0.0014; Bonferroni corrected p=0.048). In contrast, no impact of other tested allelic variants in ABCB1, ABCG2, PXR and CAR genes on proportion of patients who achieved CCyR at 12 months, MMR at 18 months as well as on probability of PFS, TTF and OS was observed.Conclusion: Our data suggest that inherited variants in the regulator of xenobiotic transport and metabolism CAR gene may modify results of imatinib therapy in CML patients. In contrast, the results of this relatively large study indicate that polymorphic variants in ABCB1, ABCG2 and PXR genes do not seem to play major role as determinants of response to imatinib in CML. DisclosuresRobak:MorphoSys AG: Research Funding.

Inhibitory effect of silybin on pharmacokinetics of imatinib in vivo and in vitro.

The objective of this work was to investigate the effect of orally administered silybin on the pharmacokinetics of imatinib in rats and the metabolism of imatinib in human liver microsome and rat liver microsomes. Eighteen healthy male SD rats were randomly divided into 3 groups: group A (control group), group B (received multiple doses of 50 mg·kg(-1) silybin for 15 consecutive days), and group C (received a single dose of 50 mg·kg(-1) silybin). A single dose of imatinib was administered orally 30 min after administration of silybin (50 mg·kg(-1)). Imatinib plasma levels were measured by UPLC-MS/MS, and pharmacokinetic parameters were calculated by DAS 3.0 software (Bontz Inc., Beijing, China). In addition, human and rat liver microsome were performed to determine the effects of silybin metabolism of imatinib in vitro. The multiple doses or single dose of 50 mg·kg(-1) silybin significantly decreased the area under the curve (0-t) of imatinib (p < 0.01). And the half-life (t1/2) of imatinib is significantly increased (p < 0.05 and p < 0.01, respectively). Also, silybin showed inhibitory effect on human and rat microsomes, the IC50 of silybin were 26.42 μmol·L(-1) and 49.12 μmol·L(-1) in human and rat liver microsomes, respectively. These results indicate that more attention should be paid to when imatinib is administrated combined with silybin.

Phase II Trial of Imatinib in AIDS-Associated Kaposi's Sarcoma: AIDS Malignancy Consortium Protocol 042

Kaposi's sarcoma (KS) is a disease of multifocal vascular proliferation that requires infection with KS herpes virus (KSHV/HHV-8). Activation of the c-kit and platelet-derived growth factor (PDGF) receptors by autocrine/paracrine mechanisms follows endothelial cell KSHV infection. In a pilot study, imatinib, a c-kit/PDGF-receptor inhibitor, induced partial regression of AIDS-associated KS (AIDS-KS) in five of 10 patients. This multicenter phase II study was designed to estimate the response rate to imatinib in AIDS-KS. Secondary objectives included investigation of predictors of response and imatinib pharmacokinetics in patients on antiretrovirals. Patients received imatinib 400 mg/day by mouth for up to 12 months with dose escalation up to 600 mg/day at 3 months if their disease was stable. Thirty patients were treated at 12 AIDS Malignancy Consortium sites. Ten patients (33.3%) achieved partial response, six (20%) had stable disease, and seven (23.3%) exhibited KS progression. Nine patients completed 52 weeks of imatinib therapy. The median treatment duration was 22.5 weeks. Only five patients (16.7%) discontinued therapy owing to adverse events. Antiretroviral regimens did not significantly alter imatinib metabolism. Activating mutations in PDGF-R and c-kit were not found at baseline or at disease progression. We found no correlation with response with changes in any of the candidate cytokines. Imatinib has activity in AIDS-KS. Pharmacokinetic interactions with antiretroviral drugs did not correlate with toxicity. Thirty percent of patients showed long-term clinical benefit and remained on imatinib for the entire year. These results suggest imatinib is well tolerated and may be an alternative therapy for some patients with AIDS-KS.