Contribution of the α1-Acid Glycoprotein in Drug Pharmacokinetics: The Usefulness of α1-Acid Glycoprotein-Knockout Mice.

α1-Acid glycoprotein (AGP) is a primary binding protein for many basic drugs in plasma. The number of drugs that bind to AGP, such as molecular target anticancer drugs, has been continuously increasing. Since the plasma level of AGP fluctuates under various pathological conditions such as inflammation, it is important to evaluate the contribution of AGP to drug pharmacokinetics. Here, we generated conventional AGP-knockout (AGP-KO) mice and used them to evaluate the contribution of AGP. The pharmacokinetics of drugs that bind to two AGP variants (F1*S or A variants) or albumin were evaluated. Imatinib (a F1*S-binding drug) and disopyramide (an A-binding drug) or ibuprofen (an albumin-binding drug) were administered to wild-type (WT) and AGP-KO. The plasma level of imatinib and disopyramide decreased rapidly in AGP-KO as compared to WT. In AGP-KO, AUC and t1/2 were decreased, then CLtot was increased. Compared with disopyramide, imatinib pharmacokinetics showed more marked changes in AGP-KO as compared to WT. The results seemed to be due to the difference in plasma level of each AGP variant (F1*S:A = 2-3:1). No differences were observed in ibuprofen pharmacokinetics between the WT and AGP-KO mice. In vitro experiments using plasma from WT and AGP-KO showed that unbound fractions of imatinib and disopyramide were higher in AGP-KO. These results suggest that the rapid elimination of imatinib and disopyramide in AGP-KO could be due to decreased protein binding to AGP. Taken together, the AGP-KO mouse could be a potential animal model for evaluating the contribution of AGP to the pharmacokinetics of various drugs.

Influence of genetic polymorphisms on imatinib concentration and therapeutic response in patients with chronic-phase chronic myeloid leukemia.

BACKGROUND: Diminished bioavailability of imatinib in leukemic cells contributes to poor clinical response. We examined the impact of genetic polymorphisms of imatinib on the pharmacokinetics and clinical response in 190 patients with chronic myeloid leukaemia (CML). METHODS: Single nucleotide polymorphisms were genotyped using pyrophosphate sequencing. Plasma trough levels of imatinib were measured using liquid chromatography-tandem mass spectrometry. RESULTS: Patients carrying the TT genotype for ABCB1 (rs1045642, rs2032582, and rs1128503), GG genotype for CYP3A5-rs776746 and AA genotype for ABCG2-rs2231142 polymorphisms showed higher concentration of imatinib. Patients with T allele for ABCB1 (rs1045642, rs2032582, and rs1128503), A allele for ABCG2-rs2231142, and G allele for CYP3A5-rs776746 polymorphisms showed better cytogenetic response and molecular response. In multivariate analysis, carriers of the CYP3A5-rs776746 G allele exhibited higher rates of complete cytogenetic response (CCyR) and major molecular response (MMR). Similarly, patients with the T allele of ABCB1-rs1045642 and rs1128503 demonstrated significantly increased CCyR rates. Patients with the A allele of ABCG2-rs2231142 were associated with higher MMR rates. The AA genotype for CYP3A5-rs776746, and the CC genotype for ABCB1-rs104562, and rs1128503 polymorphisms were associated with a higher risk of imatinib failure. Patients with the G allele for CYP3A5-rs776746 exhibited a higher incidence of anemia, and T allele for ABCB1-rs2032582 demonstrated an increased incidence of diarrhea. CONCLUSIONS: Genotyping of ABCB1, ABCG2, and CYP3A5 genes may be considered in the management of patients with CML to tailor therapy and optimize clinical outcomes.

Physiologically based pharmacokinetic modeling of imatinib and N-desmethyl imatinib for drug-drug interaction predictions.

The first-generation tyrosine kinase inhibitor imatinib has revolutionized the development of targeted cancer therapy and remains among the frontline treatments, for example, against chronic myeloid leukemia. As a substrate of cytochrome P450 (CYP) 2C8, CYP3A4, and various transporters, imatinib is highly susceptible to drug-drug interactions (DDIs) when co-administered with corresponding perpetrator drugs. Additionally, imatinib and its main metabolite N-desmethyl imatinib (NDMI) act as inhibitors of CYP2C8, CYP2D6, and CYP3A4 affecting their own metabolism as well as the exposure of co-medications. This work presents the development of a parent-metabolite whole-body physiologically based pharmacokinetic (PBPK) model for imatinib and NDMI used for the investigation and prediction of different DDI scenarios centered around imatinib as both a victim and perpetrator drug. Model development was performed in PK-Sim® using a total of 60 plasma concentration-time profiles of imatinib and NDMI in healthy subjects and cancer patients. Metabolism of both compounds was integrated via CYP2C8 and CYP3A4, with imatinib additionally transported via P-glycoprotein. The subsequently developed DDI network demonstrated good predictive performance. DDIs involving imatinib and NDMI were simulated with perpetrator drugs rifampicin, ketoconazole, and gemfibrozil as well as victim drugs simvastatin and metoprolol. Overall, 12/12 predicted DDI area under the curve determined between first and last plasma concentration measurements (AUClast) ratios and 12/12 predicted DDI maximum plasma concentration (Cmax) ratios were within twofold of the respective observed ratios. Potential applications of the final model include model-informed drug development or the support of model-informed precision dosing.

Predictive performance of population pharmacokinetic models of imatinib in chronic myeloid leukemia patients.

BACKGROUND AND AIM: Chronic myeloid leukemia is a myeloproliferative neoplasm associated with the specific chromosomal translocation known as the Philadelphia chromosome. Imatinib is a potent BCR-ABL tyrosine kinase inhibitor, which is approved as the first line therapy for CML patients. There are various population pharmacokinetic studies available in the literature for this population. However, their use in other populations outside of their cohort for the model development has not been evaluated. This study was aimed to perform the predictive performance of the published population pharmacokinetic models for imatinib in CML population and propose a dosing nomogram. METHODS: A systematic review was conducted through PubMed, and WoS databases to identify PopPK models. Clinical data collected in adult CML patients treated with imatinib was used for evaluation of these models. Various prediction-based metrics were used for assessing the bias and precision of PopPK models using individual predictions. RESULTS: Eight imatinib PopPK model were selected for evaluating the model performance. A total of 145 plasma imatinib samples were collected from 43 adult patients diagnosed with CML and treated with imatinib. The PopPK model reported by Menon et al. had better performance than all other PopPK models. CONCLUSION: Menon et al. model was able to predict well for our clinical data where it had the relative mean prediction error percentage ≤ 20%, relative median absolute prediction error ≤ 30% and relative root mean square error close to zero. Based on this final model, we proposed a dosing nomogram for various weight groups, which could potentially help to maintain the trough concentrations in the therapeutic range.

Imatinib pharmacokinetics and creatine kinase levels in chronic myeloid leukemia patients: implications for therapeutic response and monitoring.

BACKGROUND: Imatinib treatment for certain cancers can lead to elevated creatine kinase (CK) levels, potentially indicating muscle injury, and ongoing research aims to understand the correlation between imatinib levels and creatine kinase to assess its impact on treatment response. METHODS: This single-center observational study involved 76 chronic myeloid leukemia (CML) patients receiving imatinib treatment, focusing on evaluating drug and metabolite levels using liquid chromatography-mass spectrometry (LC-MS-MS) instrumentation. Serum CK and creatine kinase-MB (CK-MB) levels were assessed using Colorimetric kits. RESULTS: CK and CK-MB levels were measured, CK showed a median value of 211.5 IU/l and CK-MB showed a median value of 4.4 IU/l. Comparing low and high CK groups, significant differences were found in peak and trough plasma concentrations of imatinib and its metabolites. Correlations between CK levels and pharmacokinetic parameters were explored, with notable associations identified. Binary logistic regression revealed predictors influencing the therapeutic response to imatinib and categorized expected CK levels into high or low, with peak levels of imatinib emerging as a significant predictor for CK level categorization. CONCLUSION: The study highlights the link between imatinib's pharmacokinetics and elevated CK levels, indicating a possible correlation between specific metabolites and improved treatment response. Individualized monitoring of CK levels and imatinib pharmacokinetics could enhance care for CML patients.

Analytical Validation of a Volumetric Absorptive Microsampling Method for Therapeutic Drug Monitoring of the Oral Targeted Anticancer Agents, Abiraterone, Alectinib, Cabozantinib, Imatinib, Olaparib, and Sunitinib, and Metabolites.

BACKGROUND: Volumetric Absorptive Microsampling (VAMS) is a useful tool for therapeutic drug monitoring (TDM) of oral targeted anticancer agents. VAMS aims to improve safety and efficacy by enabling at-home blood sample collection by patients. This study aimed to develop and validate an ultra-high performance liquid chromatography-tandem mass spectrometry method for the quantitative determination of abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and the metabolites, Δ(4)-abiraterone (D4A), alectinib-M4, imatinib-M1, and N -desethyl sunitinib, in dried whole blood samples using VAMS to support TDM. METHODS: After the collection of 10 µL of whole blood sample using the VAMS device, the analytes were extracted from the tip using methanol with shaking, evaporated, and reconstituted in acetonitrile:0.1 mol/L ammonium hydroxide in water (1:1, vol/vol). The extracts were then analyzed using ultra-high performance liquid chromatography-tandem mass spectrometry. Validation experiments based on the ICH M10 guideline were carried out, and stability was evaluated under shipping and storage conditions. VAMS specimens were collected in the outpatient clinic to demonstrate the applicability of the assay. RESULTS: The validated range of the method was considered accurate and precise for all analytes. Accordingly, the validation experiments met the relevant requirements, except for cross-analyte interference. Based on the stability data, shipment can be performed at room temperature within 14 days after sample collection and the VAMS specimen can be stored up to 9 months at -20 and -70°C. Samples from 59 patients were collected at the hospital. CONCLUSIONS: The developed method could be used to successfully quantify the concentrations of abiraterone, D4A, alectinib, alectinib-M4, cabozantinib, imatinib, imatinib-M1, olaparib, sunitinib, and N -desethyl sunitinib within the validated range using VAMS. Therefore, the method can be used to estimate the dried whole blood-to-plasma ratios for TDM in the clinic.

Correlation Between N-Demethyl Imatinib Trough Concentration and Serious Adverse Reactions in Patients with Gastrointestinal Stromal Tumors: A Retrospective Cohort Study.

BACKGROUND: Imatinib is the first-line treatment for gastrointestinal stromal tumors; however, the clinical prognosis and adverse reactions of patients vary owing to individualized discrepancies in plasma exposure. METHODS: To determine the safe interval for steady-state plasma trough concentrations (C min ) of imatinib and its active metabolite, N-demethyl imatinib (NDI), 328 plasma samples from 273 patients treated with imatinib were retrospectively analyzed. Imatinib C min and NDI C min were tested, and adverse reactions were recorded. The association between imatinib C min , NDI C min , and serious adverse reactions was evaluated. RESULTS: The C min range of imatinib was 209.5-4950.0 ng/mL, with the mean value and SD of 1491.8 ± 731.4 ng/mL. The C min range of NDI was 80.0-2390.0 ng/mL with the mean value and SD of 610.8 ± 281.5 ng/mL. NDI C min was positively correlated with imatinib C min , whereas the ratio of NDI C min to imatinib C min (NDI C min /imatinib C min ) was negatively correlated with imatinib C min . Univariate logistic regression analysis demonstrated that the treatment objective, daily dose, imatinib C min , NDI C min , and imatinib C min + NDI C min were significantly associated with serious adverse reactions. Multivariate logistic regression analysis showed that NDI C min was an independent risk factor for serious adverse reactions, with a threshold of 665 ng/mL. CONCLUSIONS: NDI C min was an independent risk factor for serious adverse reactions, with a threshold of 665 ng/mL. Monitoring NDI C min was beneficial for the rational application of imatinib and individualized treatment of patients with gastrointestinal stromal tumors.

Application of physiologically based pharmacokinetic modeling to understand real-world outcomes in patients receiving imatinib for chronic myeloid leukemia.

We aimed to use physiologically based pharmacokinetic (PBPK) modeling and simulation to predict imatinib steady-state plasma exposure in patients with chronic myeloid leukemia (CML) to investigate variability in outcomes. A validated imatinib PBPK model (Simcyp Simulator) was used to predict imatinib AUCss , Css,min and Css,max for patients with CML (n = 68) from a real-world retrospective observational study. Differences in imatinib exposure were evaluated based on clinical outcomes, (a) Early Molecular Response (EMR) achievement and (b) occurrence of grade ≥3 adverse drug reactions (ADRs), using the Kruskal-Wallis rank sum test. Sensitivity analyses explored the influence of patient characteristics and drug interactions on imatinib exposure. Simulated imatinib exposure was significantly higher in patients who achieved EMR compared to patients who did not (geometric mean AUC0-24,ss 51.2 vs. 42.7 µg h mL-1 , p < 0.05; Css,min 1.1 vs. 0.9 µg mL-1 , p < 0.05; Css,max 3.4 vs. 2.8 µg mL-1 , p < 0.05). Patients who experienced grade ≥3 ADRs had a significantly higher simulated imatinib exposure compared to patients who did not (AUC0-24,ss 56.1 vs. 45.9 µg h mL-1 , p < 0.05; Css,min 1.2 vs. 1.0 µg mL-1 , p < 0.05; Css,max 3.7 vs. 3.0 µg mL-1 , p < 0.05). Simulations identified a range of patient (sex, age, weight, abundance of hepatic CYP2C8 and CYP3A4, α1 -acid glycoprotein concentrations, liver and kidney function) and medication-related factors (dose, concomitant CYP2C8 modulators) contributing to the inter-individual variability in imatinib exposure. Relationships between imatinib plasma exposure, EMR achievement and ADRs support the rationale for therapeutic drug monitoring to guide imatinib dosing to achieve optimal outcomes in CML.

CYP2D6 and CYP2C8 pharmacogenetics and pharmacological interactions to predict imatinib plasmatic exposure in GIST patients.

AIMS: Patients on treatment with oral fixed dose imatinib are frequently under- or overexposed to the drug. We investigated the association between the gene activity score (GAS) of imatinib-metabolizing cytochromes (CYP3A4, CYP3A5, CYP2D6, CYP2C9, CYP2C19, CYP2C8) and imatinib and nor-imatinib exposure. We also investigated the impact of concurrent drug-drug-interactions (DDIs) on the association between GAS and imatinib exposure. METHODS: Serial plasma samples were collected from 33 GIST patients treated with imatinib 400 mg daily within a prospective clinical trial. Imatinib and nor-imatinib Ctrough were quantified by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Genetic polymorphisms with a functional impact on imatinib-metabolizing cytochromes were identified and a GAS was calculated for each gene. A DDI-adjusted GAS was also generated. RESULTS: Imatinib and nor-imatinib Ctrough were measured in 161 plasma samples. CYP2D6 GAS and metabolizer status based on genotype were associated with imatinib and (imatinib + nor-imatinib) Ctrough . CYP2D6 poor and intermediate metabolizers were predicted to have a lower nor-imatinib/imatinib metabolic ratio than normal metabolizers (0.197 and 0.193 vs. 0.247, P = .0205), whereas CYP2C8*3 carriers had a higher ratio than CYP2C8*1/*1 patients (0.263 vs. 0.201, P = .0220). CYP2C9 metabolizer status was inversely related to the metabolic ratio with an effect probably driven by the linkage disequilibrium between CYP2C9*2 and CYP2C8*3. The CYP2D6 DDI-adjusted GAS was still predictive of imatinib exposure. CONCLUSIONS: These findings highlight that CYP2D6 plays a major role in imatinib pharmacokinetics, but other players (i.e., CYP2C8) may influence imatinib exposure. These findings could drive the selection of patients more susceptible to imatinib under- or overexposure who could be candidates for personalized treatment and intensified monitoring strategies.

Role of ADME gene polymorphisms on imatinib disposition: results from a population pharmacokinetic study in chronic myeloid leukaemia.

PURPOSE: Imatinib is a substrate of CYP3A4, ABCB1 and ABCG2, and is known to have wide variability in pharmacokinetics (PK). At the same time, a clear relationship between drug levels and response also exists for imatinib in chronic myeloid leukaemia (CML). Therefore, pharmacogenetic-based dosing of imatinib is an attractive proposition. This study aims to characterize the population pharmacokinetics of imatinib in order to identify significant covariates including pharmacogenetic variants. METHODS: Forty-nine patients with CML were enrolled in the study after being on imatinib for at least 4 consecutive weeks. Steady-state pharmacokinetic sampling was performed either in a sparse (4 samples each, n = 44) or intensive manner (9 samples each, n = 5). An additional pharmacogenetic sample was also collected from all patients. Plasma imatinib levels were estimated using a validated HPLC method. Pharmacogenetic variants were identified using the PharmacoScan array platform. Population pharmacokinetic analysis was carried out using NONMEM v7.2. Seven SNPs within CYP3A4, ABCB1 and ABCG2 genes were evaluated for covariate effect on the clearance of imatinib. RESULTS: Imatinib PK was well characterized using a one-compartment model with zero-order absorption. The clearance and volume of distribution were found to be 10.2 L/h and 389 L respectively. Only SNP rs1128503 of the ABCB1 gene had a small but insignificant effect on imatinib clearance, with a 25% reduction in clearance observed in patients carrying the polymorphism. Twenty-three out of forty-nine patients (47%) carried the polymorphic allele, of whom 17 were heterozygous and six were homozygous. CONCLUSION: Our study conclusively proves that genetic polymorphisms in the CYP3A4 and ABC family of transporters do not have any role in the personalized dosing of imatinib in CML.

Physiologically Based Pharmacokinetic Modeling Approaches for Patients With SARS-CoV-2 Infection: A Case Study With Imatinib.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which causes coronavirus disease 2019 (COVID-19), manifests as mild respiratory symptoms to severe respiratory failure and is associated with inflammation and other physiological changes. Of note, substantial increases in plasma concentrations of α1 -acid-glycoprotein and interleukin-6 have been observed among patients admitted to the hospital with advanced SARS-CoV-2 infection. A physiologically based pharmacokinetic (PBPK) approach is a useful tool to evaluate and predict disease-related changes on drug pharmacokinetics. A PBPK model of imatinib has previously been developed and verified in healthy people and patients with cancer. In this study, the PBPK model of imatinib was successfully extrapolated to patients with SARS-CoV-2 infection by accounting for disease-related changes in plasma α1 -acid-glycoprotein concentrations and the potential drug interaction between imatinib and dexamethasone. The model demonstrated a good predictive performance in describing total and unbound imatinib concentrations in patients with SARS-CoV-2 infection. PBPK simulations highlight that an equivalent dose of imatinib may lead to substantially higher total drug concentrations in patients with SARS-CoV-2 infection compared to that in patients with cancer, while the unbound concentrations remain comparable between the 2 patient populations. This supports the notion that unbound trough concentration is a better exposure metric for dose adjustment of imatinib in patients with SARS-CoV-2 infection, compared to the corresponding total drug concentration. Potential strategies for refinement and generalization of the PBPK modeling approach in the patient population with SARS-CoV-2 are also provided in this article, which could be used to guide study design and inform dose adjustment in the future.

In vitro Measurement and In vivo Prediction of Time-Dependent Inhibitory Effects of Three Tyrosine Kinase Inhibitors on CYP3A Activity.

BACKGROUND: Imatinib, sunitinib, and gefitinib are the three most common tyrosine kinase inhibitors (TKIs). However, their quantitative drug-drug interaction potentials In vivo and the relationship between their structure and inhibitory activity remain unknown. OBJECTIVE: This study aimed to investigate the potential drug-drug interaction risk of three TKIs based on CYP3A. METHODS: 6ß-Hydroxylated testosterone formation was selected to probe the CYP3A activity in human liver microsomes. A molecular docking simulation was performed to explore the potential structural alerts. RESULTS: Imatinib exhibited the strongest inhibitory effect towards CYP3A, while the inhibitory potential of gefitinib and sunitinib were comparable to each other but weaker than imatinib. IC50 shift assays demonstrated that the inhibitory potential of all three TKIs was significantly increased after a 30-min preincubation with NADPH. The KI and Kinact values of imatinib, sunitinib, and gefitinib were 3.75 µM and 0.055 min-1, 1.96 µM and 0.037 min-1, and 9.94 µM and 0.031 min-1, respectively. IVIVE results showed that there was a 1.3- to 43.1-fold increase in the AUC of CYP3A-metabolizing drugs in the presence of the TKIs. CONCLUSION: All three TKIs exhibited a typical irreversible inhibitory effect towards CYP3A. The presence of more N-heterocycles and the resulting better binding confirmation of imatinib may have been responsible for its stronger inhibitory effect than sunitinib and gefitinib. Therefore, caution should be taken when CYP3A-metabolizing drugs are co-administrated with imatinib, sunitinib, or gefitinib.

Development of Imatinib Mesylate-Loaded Liposomes for Nose to Brain Delivery: In Vitro and In Vivo Evaluation.

Neurodegenerative diseases like Alzheimer's disease require treatment where it is essential for drug to reach brain. Nose to brain delivery of drugs enables direct transport to brain bypassing blood brain barrier. Imatinib mesylate, an anti-cancer agent, was found to have potential anti-Alzheimer's activity and thus repurposed for the same. However, the drug has severe side effects, poor brain bioavailability which may hinder effective treatment of Alzheimer's disease. In the current work, imatinib mesylate-loaded liposomes were prepared with particle size below 150 nm with sustained drug release up to 96 h. The liposomal drug formulation was compared with plain drug solution for cytotoxicity on N2a cells and did not show any kind of toxicity at concentrations up to 25 µg/mL. The nanocarrier formulation was then evaluated for brain deposition by nose to brain administration in comparison with drug solution in rats. The liposomes effectively improved the brain deposition of drug in brain from formulation compared to pure drug solution as indicated by AUC from in vivo experiments. These results indicate that the nose to brain delivery of liposomal imatinib mesylate improved the drug deposition and residence time in brain compared to drug solution administered through oral and intranasal routes.

In vivo Pharmacokinetics and in vitro Release of Imatinib Mesylate-Loaded Liposomes for Pulmonary Delivery.

BACKGROUND: Pulmonary arterial hypertension (PAH) is characterized by abnormal proliferation of vascular endothelial and smooth muscle cells and causes occlusion of pulmonary arterioles that eventually results in right heart failure and death. The platelet-derived growth factor (PDGF) plays a prominent role in abnormal remodeling of pulmonary resistance vessels. Imatinib mesylate (IM), a PDGF-receptor tyrosine kinase inhibitor, was able to ameliorate PAH by reversing pulmonary vascular remodeling. METHODS: In the present study, IM-loaded liposomes (IM-LPs) were developed and administered via the pulmonary route to delay the drug release and improve patient compliance for the treatment of PAH. The IM-LPs were prepared by the transmembrane gradient method with the spherical vesicles. The compatibility of the IM-LPs was studied by determining the viability of pulmonary arterial smooth muscle cells (PASMCs). Particle uptake by rat PASMCs was evaluated by incubating the particles with rat PASMCs. Pharmacokinetic studies were performed in male SD rats. RESULTS: The IM-LPs showed an average size of 101.6 ± 50.80 nm with a zeta potential value of 19.66 ± 0.55 mV, a PDI of 0.250 and 81.96% ± 0.98% drug entrapment efficiency, meanwhile displayed a sustained release profile. Liposomes obviously increased intracellular accumulation of Rhodamine B by PASMCs using the fluorescence microscopic. Following intratracheal administration to rats, IM-LPs not only extended the half-life of IM, but also prolonged retention of IM compared with plain IM solution after intratracheal and intravenous administration. CONCLUSION: The study show potential applications of the LPs for pulmonary delivery of IM and the method for the development of LPs in sustained release of IM for better therapeutic outcomes. Conclusively, the prepared IM-LPs were well designed in nanosized ranges and may be a promising formulation for pulmonary delivery of IM.

The effect of grape seed and green tea extracts on the pharmacokinetics of imatinib and its main metabolite, N-desmethyl imatinib, in rats.

BACKGROUND: Imatinib is mainly metabolized by CYP3A4 and to a lesser extent by other isoenzymes, with N-desmethyl imatinib being its major equipotent metabolite. Being a CYP3A4 substrate, imatinib co-administration with CYP3A4 modulators would change its pharmacokinetic profile. The cancer chemoprevention potential and anticancer efficacy of many herbal products such as grape seed (GS) and green tea (GT) extracts had led to an increase in their concomitant use with anticancer agents. GS and GT extracts were demonstrated to be potent inhibitors of CYP3A4. The aim of this study is to investigate the effect of standardized GS and/or GT extracts at two different doses on the pharmacokinetics of imatinib and its metabolite, N-desmethyl imatinib, in SD-rats. METHODS: Standardized GS and/or GT extracts were administered orally once daily for 21 days, at low (l) and high (h) doses, 50 and 100 mg/kg, respectively, before the administration of a single intragastric dose of imatinib. Plasma samples were collected and analyzed for imatinib and N-desmethyl imatinib concentrations using LC-MS/MS method, then their non-compartmental pharmacokinetic parameters were determined. RESULTS: h-GS dose significantly decreased imatinib's Cmax and the [Formula: see text] by 61.1 and 72.2%, respectively. Similar effects on N-desmethyl imatinib's exposure were observed as well, in addition to a significant increase in its clearance by 3.7-fold. l-GT caused a significant decrease in imatinib's Cmax and [Formula: see text] by 53.6 and 63.5%, respectively, with more significant effects on N-desmethyl imatinib's exposure, which exhibited a significant decrease by 79.2 and 81.1%, respectively. h-GT showed similar effects as those of l-GT on the kinetics of imatinib and its metabolite. However, when these extracts were co-administered at low doses, no significant effects were shown on the pharmacokinetics of imatinib and its metabolite. Nevertheless, increasing the dose caused a significant decrease in Cmax of N-desmethyl imatinib by 71.5%. CONCLUSIONS: These results demonstrated that the pharmacokinetics of imatinib and N-desmethyl imatinib had been significantly affected by GS and/or GT extracts, which could be partially explained by the inhibition of CYP3A-mediated metabolism. However, the involvement of other kinetic pathways such as other isoenzymes, efflux and uptake transporters could be involved and should be characterized.

Relationship between trough level of tyrosine kinase inhibitor (imatinib and nilotinib) and BCR-ABL ratios in an Indonesian chronic-phase chronic myeloid leukemia (CML) population.

Objectives Among Chronic Myeloid Leukemia (CML) patients treated with Tyrosine Kinase Inhibitor (TKI-imatinib-nilotinib), some showed a suboptimal response. Based on pharmacokinetic studies, TKI trough level ( C m i n ∞ ${C}_{min}\hat{\infty }$ ) is associated with clinical outcomes, reflected by the BCR-ABL ratio. However, the interindividual pharmacokinetic variability of imatinib and nilotinib is found to be moderate-high. This study aims to analyze the relationship between TKI C m i n ∞   ${C}_{min}\hat{\infty }$ and BCL-ABL ratio in chronic-phase CML patients. Methods Cross-sectional study to CML chronic-phase patients treated with imatinib 400 mg daily or nilotinib 400 or 800 mg daily for ≥12 months. The exclusion criteria were therapy discontinuation within 29 days (imatinib) or 8 days (nilotinib) before the sampling day. Blood samples were drawn 1 h before the next dose. Imatinib-nilotinib C m i n ∞ ${C}_{min}\hat{\infty }$ and BCR-ABL ratio were measured using HPLC and RT-qPCR. The relationship was analyzed using bivariate correlation Spearman's rho test. Results Twenty-three imatinib and 11 nilotinib patients met the inclusion criteria. The mean imatinib and nilotinib C m i n ∞ ${C}_{min}\hat{\infty }$ were 1,065.46 ± 765.71 and 1,445 ± 1,010.35 ng/mL respectively. There were large interindividual variations in both groups (71.87% vs. 69.88%). Half of the patients in each group were found to reach C m i n ∞ ${C}_{min}\hat{\infty }$ target (≥1.000 ng/mL, imatinib; ≥800 ng/mL nilotinib), but only 12 (35,29%) of them result in BCR-ABL ratio ≤0.1%. C m i n ∞   ${C}_{min}\hat{\infty }$ imatinib was found to be significantly associated with BCR-ABL ratio. But, not with the nilotinib group. Conclusions There were high interindividual variations of imatinib and nilotinib correlated with BCR-ABL ratio, but no correlation in nilotinib.

Therapeutic drug monitoring of imatinib in patients with gastrointestinal stromal tumours - Results from daily clinical practice.

AIM: Higher imatinib exposure is correlated with longer time to progression, while the variability in exposure is high. This provides a strong rationale for therapeutic drug monitoring, which has therefore been implemented in routine clinical practice in our institute. The aim of this study is to evaluate whether pharmacokinetically (PK)-guided dose increases are feasible in daily clinical practice and result in an improved exposure (Cmin≥1100 ng/mL) and longer progression-free survival (PFS). METHODS: This retrospective study included all patients with a gastrointestinal stromal tumour (GIST) in the Netherlands Cancer Institute who started imatinib treatment at a dose of 400 mg and of whom PK plasma samples were available. Of these patients, minimum plasma concentrations (Cmin) of imatinib, frequency and successfulness of PK-guided dose increases and PFS in the palliative treatment setting were analysed. RESULTS: In total, 169 consecutive patients were included, of whom 1402 PK samples were collected. In 126 patients (75%), Cmin was below the efficacy threshold of 1100 ng/mL. In 78 of these patients (62%), a PK-guided dose increase was performed, which was successful in 49 patients (63%). PFS was similar in patients with and without imatinib dose increase. However, due to the small number of patients with progressive disease, no definite conclusions on the effect on PFS could yet be drawn. CONCLUSION: This is the largest cohort evaluating PK-guided dose increases of imatinib in patients with GIST in routine clinical practice and demonstrating its feasibility. PK-guided dose increases should be applied to optimise exposure in the significant subset of patients with a low Cmin.

Melanoma Cancer Immunotherapy Using PD-L1 siRNA and Imatinib Promotes Cancer-Immunity Cycle.

PURPOSE: Cancer-Immunity Cycle is a cascade of anticancer immune responses in the body that continues and fights against the cancer expansion. The Cancer-Immunity Cycle is halted by tumor cell immunosuppression of host T cell through programmed cell death receptor 1 (PD-1) and programmed cell death ligand 1 (PD-L1) interactions that induce the functional suppression of tumor-reactive cytotoxic T cells and actively promotes the tumorigenesis via the mTOR signaling pathway. METHODS: Here, we demonstrated that this Cycle could be enhanced by the synergistic knock down of PD-L1 through co-delivery of siRNA-PD-L1 (siPD-L1) and imatinib (IMT) in a liposomal nanoparticle. RESULTS: The siPDIN effectively downregulated the protein expressions of PD-L1 and significantly knocked down the expression of p-S6k protein at in vitro and in vivo conditions which inhibited tumorigenic mTOR pathway. The combination-based siPDIN exhibited a significantly higher cytotoxic effect compared to that of individual anticancer agents. B16F10 cells treated with siPDIN exhibited a significantly higher cancer cell apoptosis (~60%) compared to cocktail combination of siRNA+IMT (~35%) analyzed by flow cytometer. Importantly, siPDIN significantly delayed the tumor growth with significantly lower tumor-specific growth rate than the animals treated with individual free IMT or siRNA. siPDIN produced a 3-fold higher IFN-γ compared to control in DLNs and 4-fold higher IFN-γ in spleens. CONCLUSION: Overall, results revealed that the tumors treated with siPDIN restored the immunity of CTLs by potentially inhibiting the immune checkpoint interactions, suppressed the mTOR signaling pathway and exhibited an enhanced anticancer efficacy in melanoma.

Determination of the absolute bioavailability of oral imatinib using a stable isotopically labeled intravenous imatinib-d8 microdose.

PURPOSE: The aim of this study was to ascertain whether the absolute bioavailability of oral imatinib (Glivec®) during steady state plasma pharmacokinetics in cancer patients could be determined through a concomitant intravenous administration of a single 100 µg microdose of deuterium labeled imatinib (imatinib-d8). Secondly, the usefulness of liquid chromatography-tandem mass spectrometry (LC-MS/MS) was investigated for simultaneous analysis of orally and intravenously administered imatinib. METHODS: Included patients were on a stable daily dose of 400 mg oral imatinib prior to study participation. On day 1, patients received a 100 µg intravenous imatinib-d8 microdose 2.5 h after intake of the oral dose. Plasma samples were collected for 48 h. Imatinib and imatinib-d8 concentrations were simultaneously quantified using a validated LC-MS/MS assay. The absolute bioavailability was calculated by comparing the dose-normalized exposure with unlabeled and stable isotopically labeled imatinib in plasma. RESULTS: A total of six patients were enrolled. All patients had a history of gastrointestinal stromal tumors (GIST). The median absolute bioavailability of oral imatinib at steady state was 76% (range 44-106%). Imatinib and imatinib-d8 plasma concentrations were quantified in all collected plasma samples, with no samples below the limit of quantification for imatinib-d8. CONCLUSION: The absolute bioavailability of imatinib was successfully estimated at steady state plasma pharmacokinetics using the stable isotopically labeled microdose trial design. This study exhibits the use of a stable isotopically labeled intravenous microdose to determine the absolute bioavailability of an oral anticancer agent in patients with LC-MS/MS as the analytical tool.

Effect of Cytochrome P450 and ABCB1 Polymorphisms on Imatinib Pharmacokinetics After Single-Dose Administration to Healthy Subjects.

BACKGROUND: Validated genomic biomarkers for oncological drugs are expanding to improve targeted therapies. Pharmacogenetics research focusing on the mechanisms underlying imatinib suboptimal response might help to explain the different treatment outcomes and drug safety profiles. OBJECTIVE: To investigate whether polymorphisms in genes encoding cytochrome P450 (CYP) enzymes and ABCB1 transporter affect imatinib pharmacokinetic parameters. METHODS: A prospective, multicenter, pharmacogenetic pilot study was performed in the context of two separate oral imatinib bioequivalence clinical trials, which included 26 healthy volunteers. DNA was extracted in order to analyze polymorphisms in genes CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5 and ABCB1. Imatinib plasma concentrations were measured by HPLC-MS/MS. Pharmacokinetic parameters were calculated by non-compartmental methods using WinNonlin software. RESULTS: Volunteers (n = 26; aged 24 ± 3 years; 69% male) presented regular pharmacokinetic imatinib data (concentration at 24 h, 436 ± 140 ng/mL and at 72 h, 40 ± 26 ng/mL; AUC0-72 32,868 ± 10,713 ng/mL⋅h; and Cmax 2074 ± 604 ng/mL). CYP2B6 516GT carriers showed a significant reduction of imatinib concentration at 24 h (23%, 391 ng/dL vs 511 ng/dL in 516GG carriers, p = 0.005) and elimination half-life (11%, 12.6 h vs 14.1 h in 516GG carriers, p = 0.041). Carriers for CYP3A4 (*22/*22, *1/*20 and *1/*22 variants) showed a reduced frequency of adverse events compared to *1/*1 carriers (0 vs 64%, p = 0.033). The other polymorphisms analyzed did not influence pharmacokinetics or drug toxicity. CONCLUSION: CYP2B6 G516T and CYP3A4 *20,*22 polymorphisms could influence imatinib plasma concentrations and safety profile, after single-dose administration to healthy subjects. This finding needs to be confirmed before it is implemented in clinical practice in oncological patients under treatment with imatinib.