cgp-74588 and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

We measured intracellular accumulation of N-desmethyl imatinib (CGP 74588), the main pharmacologically active metabolite of imatinib (Gleevec or STI-571), in Bcr--Abl-positive cells. Using a sensitive and robust non-radioactive in vitro assay, we observed that CGP74588 accumulates in significantly higher amount than imatinib in sensitive K562 cells. In contrast, the intracellular level of CGP74588 was significantly lower than that of imatinib in K562/Dox cells, which represent a multidrug-resistant variant of K562 cells due to the P-glycoprotein (P-gp, ABCB1, MDR1) overexpression. An in vitro enzyme-based assay provided evidence that CGP74588 might serve as an excellent substrate for P-gp. Accordingly, we found that CGP74588 up to 20 μM concentration neither induced apoptosis nor inhibited substantially cell proliferation in resistant K562/Dox cells. In contrast, CGP74588 was capable to inhibit cell proliferation and induced apoptosis in sensitive K562 cells, although its effect was approximately three to four times lower than that of imatinib in the same cell line. Our results indicate that CGP74588 could hardly positively contribute to the treatment of chronic myeloid leukemia (CML) where ABCB1 gene overexpression represents a possible mechanism of resistance to imatinib in vivo.

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Apoptosis; ATP Binding Cassette Transporter, Subfamily B, Member 1; Benzamides; Cell Proliferation; Female; Humans; Imatinib Mesylate; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Middle Aged; Piperazines; Pyrimidines; Treatment Outcome

Imatinib mesylate (Gleevec) is a small molecule tyrosine kinase inhibitor approved for use in the management of chronic myeloid leukemia in adults and children and in gastrointestinal stromal tumors in adults. Population pharmacokinetic (PPK) studies evaluating the effect of population covariates on the pharmacokinetics of imatinib and its active metabolite have been developed in adults with chronic myeloid leukemia (CML) and gastrointestinal stromal tumor (GIST). However, this still remains to be described in children.. The objectives of the analysis were to develop a PPK model of imatinib and its active metabolite, CGP74588, to describe exposure in children and young adults and to identify covariates that are predictors of variability in disposition.. Plasma concentrations from 26 subjects with Philadelphia (Ph+) leukemia (Phase I study) and 15 subjects with refractory solid tumors (Phase II study), who received oral imatinib at doses ranging from 260 to 570 mg/m(2), were available for the PPK analysis in NONMEM. Blood samples were drawn prior to dosing and over 24-48 h on days 1 and 8 of the studies. Covariates studied included weight, age, albumin, alanine aminotransferase and the study population.. The pharmacokinetics of imatinib and CGP 74588 were well described by one and two compartment models, respectively. Total body weight was the only covariate found to significantly affect Cl/F and V/F. The final imatinib-CGP 74588 model is summarized as follows: CL/F (imatinib) (L/h) = 10.8 x (WT/70)(0.75), V/F (imatinib) (L) = 284 x (WT/70) and D1(duration of zero order absorption,imatinib) (h) = 1.67 and CL/F (CGP 74588) (L/h) = 9.65 x (WT/70)(0.75), V1/F (CGP 74588) (L) = 11.6 x (WT/70), Q (CGP 74588) (L/h) = 2.9 x (WT/70)(0.75) and V2/F (CGP 74588) (L) = 256*(WT/70). Model evaluation indicated that the final model was robust and satisfactory.. Current imatinib dosing guidelines in pediatrics is based on the achievement of exposures consistent with doses known to be safe and efficacious in adults. Dose adjustments in children are guided empirically by the observance of drug-related toxicities. While, the pharmacokinetics of imatinib and its active metabolite, CGP 74588 in children are consistent with prior knowledge in adults, the model will form the basis to support the design of future trials, particularly with a view to managing toxicities and exploring dosing in this population.

Topics: Administration, Oral; Adolescent; Aging; Antineoplastic Agents; Benzamides; Child; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Gastrointestinal Stromal Tumors; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Models, Biological; Multivariate Analysis; Piperazines; Pyrimidines; Young Adult

Imatinib mesylate, licensed to treat chronic myelogenous leukemia and gastrointestinal stromal tumors, is metabolized by means of cytochrome P450 3A and excreted primarily in the bile. Although the bioavailability of imatinib mesylate is more than 97%, the exact gastrointestinal site of its absorption is unknown. Liquid chromatography-mass spectrometry was used to quantitate imatinib and its metabolite CGP74588 in the plasma and jejunostomy output of a patient with newly diagnosed chronic myelogenous leukemia. She had previously lost most of her small bowel and all of her colon as a result of mesenteric artery thrombosis and radiation-induced colitis and/or proctitis. Imatinib pharmacokinetics in plasma indicated that approximately 20% of the patient's 400-mg dose was absorbed. The jejunostomy output contained 338 mg of imatinib, which was consistent with 320 mg of a nonabsorbed dose plus approximately 23% of the absorbed dose being excreted unchanged in the bile. These data indicate the importance of considering gastrointestinal anatomic abnormalities or disease states when oral imatinib is dosed.

Topics: Antineoplastic Agents; Benzamides; Female; Humans; Imatinib Mesylate; Jejunostomy; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Middle Aged; Piperazines; Pyrimidines; Short Bowel Syndrome

Cytochrome P450 3A (CYP3A) isoenzyme metabolic activity varies between individuals and is therefore a possible candidate of influence on the therapeutic outcome of the tyrosine kinase inhibitor imatinib in patients with chronic myeloid leukemia (CML). The aim of this study was to investigate the influence of CYP3A metabolic activity on the plasma concentration and outcome of imatinib in patients with CML.. Forty-three patients with CML were phenotyped for CYP3A activity using quinine as a probe drug and evaluated for clinical response parameters. Plasma concentrations of imatinib and its main metabolite, CGP74588, were determined using liquid chromatography-mass spectrometry.. Patients with optimal response to imatinib after 12 months of therapy did not differ in CYP3A activity compared to nonoptimal responders (quinine metabolic ratio of 14.69 and 14.70, respectively; P = 0.966). Neither the imatinib plasma concentration nor the CGP74588/imatinib ratio was significantly associated with CYP3A activity.. The CYP3A activity does not influence imatinib plasma concentrations or the therapeutic outcome. These results indicate that although imatinib is metabolized by CYP3A enzymes, this activity is not the rate-limiting step in imatinib metabolism and excretion. Future studies should focus on other pharmacokinetic processes so as to identify the major contributor to patient variability in imatinib plasma concentrations.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Child; Cytochrome P-450 CYP3A; Female; Humans; Imatinib Mesylate; Isoenzymes; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Middle Aged; Pilot Projects; Piperazines; Protein Kinase Inhibitors; Pyrimidines; Young Adult

The tyrosine kinase inhibitors (TKIs) used in the treatment of chronic myeloid leukemia are substrates for the efflux transport protein ATP-binding cassette subfamily G member 2 (ABCG2). Variations in ABCG2 activity might influence pharmacokinetics and therapeutic outcome of TKIs. The role of ABCG2 single-nucleotide polymorphisms (SNPs) in TKI treatment is not clear and functional in-vitro studies are lacking. The aim of this study was to investigate the consequences of ABCG2 SNPs for transport and efficacy of TKIs [imatinib, N-desmethyl imatinib (CGP74588), dasatinib, nilotinib, and bosutinib].. ABCG2 SNPs 34G>A, 421C>A, 623T>C, 886G>C, 1574T>G, and 1582G>A were constructed from ABCG2 wild-type cDNA and transduced to K562 cells by retroviral gene transfer. Variant ABCG2 expression in cell membranes was evaluated and the effects of ABCG2 SNPs on transport and efficacy of TKIs were measured as the ability of ABCG2 variants to protect against TKI cytotoxicity.. Wild-type ABCG2 had a protective effect against the cytotoxicity of all investigated compounds except bosutinib. It was found that ABCG2 expression provided better protection against CGP74588 than its parent compound, imatinib. ABCG2 421C>A, 623T>C, 886G>C, and 1574T>G reduced cell membrane expression of ABCG2 and the protective effect of ABCG2 against imatinib, CGP74588, dasatinib, and nilotinib cytotoxicity.. These findings show that the ABCG2 SNPs 421C>A, 623T>C, 886G>C, and 1574T>G increase the efficacy of investigated TKIs, indicating a reduced transport function that might influence TKI pharmacokinetics in vivo. Furthermore, the active imatinib metabolite CGP74588 is influenced by ABCG2 expression to a greater extent than the parent compound.

Topics: Aniline Compounds; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Benzamides; Cell Line; Cell Membrane; Dasatinib; Genetic Variation; Genotype; Humans; Imatinib Mesylate; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mutation; Neoplasm Proteins; Nitriles; Piperazines; Polymorphism, Single Nucleotide; Protein Kinase Inhibitors; Pyrimidines; Quinolines; Thiazoles; Transduction, Genetic

Multidrug resistance (MDR) is often associated with overexpression of the P-glycoprotein (P-gp, ABCB1). It was demonstrated that the P-gp mediated efflux decreases the drug concentration in cancer cells which results in the failure of chemotherapy. However, the MDR phenotype in cancer cells obviously involves various mechanisms. Therefore, if we want to estimate a contribution of the P-gp expression to the MDR phenotype, a clear quantitative relationship between the intracellular drug level and cell sensitivity must be established. To achieve this goal, a sensitive and non-radioactive assay for precise determination of intracellular levels of imatinib and its main metabolite N-desmethyl imatinib (CGP 74588) has been developed. The assay is based on an optimised extraction of cells with 4% formic acid after their separation from the growth medium by centrifugation through a layer of silicone oil. Cell extracts are subsequently analyzed by LC/MS/MS. Calibration curves were linear from 1 to 500 nmol/l for imatinib and from 2 to 500 nmol/l for CGP 74588, with correlation coefficients (r(2)) better than 0.998 and 0.996, respectively. The limit of quantitation (LOQ) was 1 nmol/l for imatinib and 2 nmol/l for CGP 74588. Our method has been successfully applied to the determination of intracellular levels of imatinib in sensitive K562 and their resistant variant, K562/Dox cells.

Topics: Antineoplastic Agents; Benzamides; Biological Assay; Gas Chromatography-Mass Spectrometry; Humans; Imatinib Mesylate; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Limit of Detection; Piperazines; Pyrimidines

Imatinib is currently used for the treatment of chronic myeloid leukemia (CML). The main metabolite CGP74588 has similar potency to that of imatinib and is a product of CYP3A4 and CYP3A5 metabolism. However, the clinical significance of the metabolism on therapeutic response and pharmacokinetics is still unclear. We designed this study to investigate the role of the CYP3A activity in the response to imatinib therapy.. Fourteen CML patients were phenotyped for in vivo CYP3A activity using quinine as a probe drug. The plasma concentration ratio of quinine and its CYP3A metabolite was used for assessing CYP3A activity. The patients were divided into complete molecular responders with undetectable levels of BCR-ABL transcripts after 12 months of therapy and into partial molecular responders who had failed to achieve a complete molecular response.. Patients that achieved complete molecular response showed significantly (Mann-Whitney U-test, p=0.013) higher in vivo CYP3A activity (median quinine metabolic ratio = 10.1) than patients achieving partial molecular response (median = 15.9).. These results indicate a clinical significance of the CYP3A activity and its metabolic products in CML patients treated with imatinib.

Topics: Benzamides; Cytochrome P-450 CYP3A; Fusion Proteins, bcr-abl; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Pilot Projects; Piperazines; Pyrimidines; Remission Induction

Treatment of maternal chronic myeloid leukemia with imatinib mesylate is avoided because of potential fetal effects. Two women with progression of disease during pregnancy required imatinib therapy. Concentrations of imatinib in maternal blood, placenta, umbilical cord blood and breast milk were 886, 2452, 0 to 157, and 596 ng/ml, respectively. Concentrations of the active metabolite CGP74588 in maternal blood, placenta, umbilical cord blood and breast milk were 338, 1462, 0 and 1513 ng/ml, respectively. As Imatinib and CGP74588 cross the mature placenta poorly, use of the drug after the first trimester may be reasonable under some circumstances. Imatinib and CGP74588 are found in breast milk, and therefore avoidance of breastfeeding is advisable.

Topics: Antineoplastic Agents; Benzamides; Female; Fetal Blood; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Milk, Human; Piperazines; Placenta; Pregnancy; Pregnancy Complications, Neoplastic; Pyrimidines

Hematologic toxicity is reported as one of the most important problems connected with imatinib mesylate (IM) treatment in patients with chronic myelogenous leukemia (CML). Withholding the drug or application of growth factors is recommended in this situation. This study introduced a novel approach using intermittent dosage of IM in order to avoid prolonged interruptions in therapy, to allow spontaneous recovery in blood count and, simultaneously, to achieve intermittently therapeutic plasma drug levels. A retrospective analysis of intermittent therapy (iT) in 12 patients with CML is presented. All patients had intermediate-to-high prognostic scores. Two patients had history of autologous stem cell transplantation. Initial standard therapy with IM was indicated for resistance to interferon (eight subjects) and for accelerated phase in four cases (one of them cytogenetic) and lasted for 1 - 6 months. iT with 300 - 600 mg of IM 1 - 5 times a week was started after significant hematologic toxicity occurred. In three patients treated 3 - 5 times a week, hematologic recovery allowed reintroduction of full dose after 3 - 7 (mean 4.6) months. In three patients, one-to-three doses per week were sufficient to maintain the cytogenetic response for a mean of 30.6 months (range 29 - 33). Six patients tolerated more frequent dosage of 4 - 5 times a week for a mean of 17.8 months (range 3 - 28). Five patients improved their cytogenetic response during iT, while hematologic progression occurred in one patient. Development of a cytogenetic abnormality in a Ph-negative clone was observed in one patient. Overall, two complete and five major cytogenetic responses were achieved. The sensitivity of Bcr/Abl kinase to inhibition by IM was proved in seven patients tested by Crkl phosphorylation assay. Measurement of plasma IM concentrations in three subjects showed concentrations fully compatible with the dosage applied suggesting normal intestinal absorption. iT with IM is a feasible and safe strategy for short-time 'bridging' management of patients with significant hematologic toxicity after standard daily dosing. Long-term iT with IM does not seem to compromise the cytogenetic response in patients with sensitivity of Bcr/Abl kinase to IM and should be considered as a plausible treatment option in patients with persistent signs of myelotoxicity.

Topics: Adenosine Triphosphate; Antineoplastic Agents; Benzamides; Chromosome Aberrations; Cytogenetics; Drug Administration Schedule; Fusion Proteins, bcr-abl; Humans; Imatinib Mesylate; In Situ Hybridization, Fluorescence; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Phosphorylation; Piperazines; Protein Binding; Pyrimidines; Retrospective Studies; Time Factors

Despite the remarkable clinical response rates to imatinib in the treatment of bcr-abl leukemic patients, pharmacokinetic data on this relatively novel substance are needed to improve our understanding of the emergence of resistance, the interindividual variations of clinical response and the clinical and biologic relevance of its main metabolite N-desmethyl-imatinib. We present here pharmacokinetic data obtained with a newly designed HPLC approach in 97 patients with chronic myeloid leukemia or acute lymphatic leukemia (ALL) under treatment with imatinib that allowed us to calculate the AUC (39.5 microg.h/ml for an oral dose of 400 mg daily), the t(1/2) (18.2 h) and the peak concentration (1.92 micro/ml for an oral dose of 400 mg daily) of imatinib in plasma. In a subgroup of patients, the same parameters were analyzed for N-desmethyl-imatinib. We also provide data on the imatinib concentration in the cerebrospinal fluid (CSF) of ALL patients and demonstrate that oral administration of imatinib resulted only in a marginal flux across the blood-brain barrier. Finally, in an in vitro setting, we determined cellular concentrations of imatinib in HL-60 cells and showed an over-proportional uptake both in RPMI medium and in human plasma. Using an arithmetical approach combining all parameters obtained in imatinib-treated patients, we finally provide a conclusive approximation of basic pharmacokinetic data for both imatinib and its main metabolite N-desmethyl-imatinib.

Topics: Administration, Oral; Aged; Benzamides; Biological Availability; Chromatography, High Pressure Liquid; Half-Life; HL-60 Cells; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Metabolic Clearance Rate; Piperazines; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Pyrimidines