Plasma and cerebrospinal fluid pharmacokinetics of imatinib after administration to nonhuman primates

Prophylactic treatment with the c-Abl inhibitor, neurotinib, diminishes neuronal damage and the convulsive state in pilocarpine-induced mice

The molecular mechanisms underlying seizure generation remain elusive, yet they are crucial for developing effective treatments for epilepsy. The current study shows that inhibiting c-Abl tyrosine kinase prevents apoptosis, reduces dendritic spine loss, and maintains N-methyl-d-aspartate (NMDA) receptor subunit 2B (NR2B) phosphorylated in in vitro models of excitotoxicity. Pilocarpine-induced status epilepticus (SE) in mice promotes c-Abl phosphorylation, and disrupting c-Abl activity leads to fewer seizures, increases latency toward SE, and improved animal survival. Currently, clinically used c-Abl inhibitors are non-selective and have poor brain penetration. The allosteric c-Abl inhibitor, neurotinib, used here has favorable potency, selectivity, pharmacokinetics, and vastly improved brain penetration. Neurotinib-administered mice have fewer seizures and improved survival following pilocarpine-SE induction. Our findings reveal c-Abl kinase activation as a key factor in ictogenesis and highlight the impact of its inhibition in preventing the insurgence of epileptic-like seizures in rodents and humans.

Phase I study using crenolanib to target PDGFR kinase in children and young adults with newly diagnosed DIPG or recurrent high-grade glioma, including DIPG

Background

Platelet-derived growth factor receptor (PDGFR) signaling has been directly implicated in pediatric high-grade gliomagenesis. This study evaluated the safety and tolerability of crenolanib, a potent, selective inhibitor of PDGFR-mediated phosphorylation, in pediatric patients with high-grade glioma (HGG).

Methods

We used a rolling-6 design to study the maximum tolerated dose (MTD) of once-daily crenolanib administered during and after focal radiation therapy in children with newly diagnosed diffuse intrinsic pontine glioma (DIPG) (stratum A) or with recurrent/progressive HGG (stratum B). Pharmacokinetics were studied during the first cycle at the first dose and at steady state (day 28). Alterations in PDGFRA were assessed by Sanger or exome sequencing and interphase fluorescence in situ hybridization or single nucleotide polymorphism arrays.

Results

Fifty evaluable patients were enrolled in the 2 strata, and an MTD of 170 mg/m² was established for both. Dose-limiting toxicities were primarily liver enzyme elevations and hematologic count suppression in both strata. Crenolanib AUC_0-48h and C _MAX did not differ significantly for crushed versus whole-tablet administration. Overall, PDGFRA alterations were observed in 25% and 30% of patients in stratum A and B, respectively. Neither crenolanib therapy duration nor survival outcomes differed significantly by PDGFRA status, and overall survival of stratum A was similar to that of historical controls.

Conclusions

Children tolerate crenolanib well at doses slightly higher than the established MTD in adults, with a toxicity spectrum generally similar to that in adults. Studies evaluating intratumoral PDGFR pathway inhibition in biomarker-enriched patients are needed to evaluate further the clinical utility of crenolanib in this population.

Isolated Ocular Manifestations in Chronic Myeloid Leukaemia

BACKGROUND

Chronic myeloid leukaemia (CML) presenting with only ocular manifestations either at the initial stage of diagnosis or at relapse is uncommon. We report two cases of CML presenting with isolated visual symptoms.

CASE SERIES

The first case is a 21-year-old healthy gentleman who presented with left eye painless loss of vision for a one-week duration. Visual acuity was 6/60 in the left eye and 6/6 in the right eye. There were scattered retinal haemorrhages in both eyes and a sub-macular bleed over the left eye. The full blood count revealed a high white cell count of 134.6 × 10⁹/L. Peripheral blood smear showed hyper-leucocytosis with absolute eosinophilia and basophilia and the presence of blasts suggestive of CML thus chemotherapy was commenced. The second case is a 28-year-old in haematological, molecular, and cytogenic remission from CML for the past two years, presented with left eye painless vision loss for five days duration. Vision in the left eye was counting fingers. There was a large subretinal mass involving the left optic disc. Magnetic resonance imaging of the brain and orbit showed an elliptical orbital mass at the left globe posteriorly with diffuse thickening of the optic nerve. The patient was diagnosed as CML relapsed to the left optic nerve. He underwent intrathecal chemotherapy and orbital irradiation.

CONCLUSION

Both these cases are unique since the manifestation of CML was with only ocular features at the time of presentation as per in the first case during the initial diagnosis and in the second case during relapse. This highlights that it is evident that the knowledge of ocular involvement in leukaemia is crucial since the eye is the only organ where leukemic infiltration to nerves and blood vessels can be observed directly. Recognizing fundus changes in leukaemia allows earlier diagnosis and prompt treatment. These case reports highlight the importance of recognizing early fundus changes, which should allow earlier diagnosis and treatment.

Isolated blast crisis relapse in the central nervous system of a patient treating for a chronic myelogenous leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative disorder associated with the Philadelphia chromosome t (9;22) and the BCR-ABL fusion gene. The condition is relatively rare, accounting for 2.0% to 3.0% of childhood leukemia cases. CML has historically been a triphasic disease. Most patients are diagnosed in chronic phase. Without treatment, it inevitably progresses into a more aggressive accelerated phase and blast crisis. Some proportion of CML cases of blastic transformation develop an extramedullary disease that involves rarely central nervous system. This report describe an extremely rare case of 13-year-old girl with CML and extramedullary blast crisis in the central nervous system. Treatment options and monitoring of disease response are discussed.

Ponatinib-induced cardiotoxicity: delineating the signalling mechanisms and potential rescue strategies

AIMS

Tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of chronic myelogenous leukaemia (CML). However, cardiotoxicity of these agents remains a serious concern. The underlying mechanism of these adverse cardiac effects is largely unknown. Delineation of the underlying mechanisms of TKIs associated cardiac dysfunction could guide potential prevention strategies, rescue approaches, and future drug design. This study aimed to determine the cardiotoxic potential of approved CML TKIs, define the associated signalling mechanism and identify potential alternatives.

METHODS AND RESULTS

In this study, we employed a zebrafish transgenic BNP reporter line that expresses luciferase under control of the nppb promoter (nppb:F-Luciferase) to assess the cardiotoxicity of all approved CML TKIs. Our in vivo screen identified ponatinib as the most cardiotoxic agent among the approved CML TKIs. Then using a combination of zebrafish and isolated neonatal rat cardiomyocytes, we delineated the signalling mechanism of ponatinib-induced cardiotoxicity by demonstrating that ponatinib inhibits cardiac prosurvival signalling pathways AKT and extra-cellular-signal-regulated kinase (ERK), and induces cardiomyocyte apoptosis. As a proof of concept, we augmented AKT and ERK signalling by administration of Neuregulin-1β (NRG-1β), and this prevented ponatinib-induced cardiomyocyte apoptosis. We also demonstrate that ponatinib-induced cardiotoxicity is not mediated by inhibition of fibroblast growth factor signalling, a well-known target of ponatinib. Finally, our comparative profiling for the cardiotoxic potential of CML approved TKIs, identified asciminib (ABL001) as a potentially much less cardiotoxic treatment option for CML patients with the T315I mutation.

CONCLUSION

Herein, we used a combination of in vivo and in vitro methods to systematically screen CML TKIs for cardiotoxicity, identify novel molecular mechanisms for TKI cardiotoxicity, and identify less cardiotoxic alternatives.

How to Make Anticancer Drugs Cross the Blood-Brain Barrier to Treat Brain Metastases

The incidence of brain metastases has increased in the last 10 years. However, the survival of patients with brain metastases remains poor and challenging in daily practice in medical oncology. One of the mechanisms suggested for the persistence of a high incidence of brain metastases is the failure to cross the blood-brain barrier of most chemotherapeutic agents, including the more recent targeted therapies. Therefore, new pharmacological approaches are needed to optimize the efficacy of anticancer drug protocols. In this article, we present recent findings in molecular data on brain metastases. We then discuss published data from pharmacological studies on the crossing of the blood-brain barrier by anticancer agents. We go on to discuss future developments to facilitate drug penetration across the blood-brain barrier for the treatment of brain metastases among cancer patients, using physical methods or physiological transporters.

Preclinical pharmacokinetic evaluation to facilitate repurposing of tyrosine kinase inhibitors nilotinib and imatinib as antiviral agents

Background

Several tyrosine kinase inhibitors (TKIs) developed as anti-cancer drugs, also have anti-viral activity due to their ability to disrupt productive replication and dissemination in infected cells. Consequently, such drugs are attractive candidates for “repurposing” as anti-viral agents. However, clinical evaluation of therapeutics against infectious agents associated with high mortality, but low or infrequent incidence, is often unfeasible. The United States Food and Drug Administration formulated the “Animal Rule” to facilitate use of validated animal models for conducting anti-viral efficacy studies.

Methods

To enable such efficacy studies of two clinically approved TKIs, nilotinib, and imatinib, we first conducted comprehensive pharmacokinetic (PK) studies in relevant rodent and non-rodent animal models. PK of these agents following intravenous and oral dosing were evaluated in C57BL/6 mice, prairie dogs, guinea pigs and Cynomolgus monkeys. Plasma samples were analyzed using an LC-MS/MS method. Secondarily, we evaluated the utility of allometry-based inter-species scaling derived from previously published data to predict the PK parameters, systemic clearance (CL) and the steady state volume of distribution (Vss) of these two drugs in prairie dogs, an animal model not tested thus far.

Results

Marked inter-species variability in PK parameters and resulting oral bioavailability was observed. In general, elimination half-lives of these agents in mice and guinea pigs were much shorter (1–3 h) relative to those in larger species such as prairie dogs and monkeys. The longer nilotinib elimination half-life in prairie dogs (i.v., 6.5 h and oral, 7.5 h), facilitated multiple dosing PK and safety assessment. The allometry-based predicted values of the Vss and CL were within 2.0 and 2.5-fold, respectively, of the observed values.

Conclusions

Our results suggest that prairie dogs and monkeys may be suitable rodent and non-rodent species to perform further efficacy testing of these TKIs against orthopoxvirus infections. The use of rodent models such as C57BL/6 mice and guinea pigs for assessing pre-clinical anti-viral efficacy of these two TKIs may be limited due to short elimination and/or low oral bioavailability. Allometry-based correlations, derived from existing literature data, may provide initial estimates, which may serve as a useful guide for pre-clinical PK studies in untested animal models.

Autophagic and Apoptotic Pathways as Targets for Chemotherapy in Glioblastoma

Glioblastoma multiforme is the most malignant and aggressive type of brain tumor, with a mean life expectancy of less than 15 months. This is due in part to the high resistance to apoptosis and moderate resistant to autophagic cell death in glioblastoma cells, and to the poor therapeutic response to conventional therapies. Autophagic cell death represents an alternative mechanism to overcome the resistance of glioblastoma to pro-apoptosis-related therapies. Nevertheless, apoptosis induction plays a major conceptual role in several experimental studies to develop novel therapies against brain tumors. In this review, we outline the different components of the apoptotic and autophagic pathways and explore the mechanisms of resistance to these cell death pathways in glioblastoma cells. Finally, we discuss drugs with clinical and preclinical use that interfere with the mechanisms of survival, proliferation, angiogenesis, migration, invasion, and cell death of malignant cells, favoring the induction of apoptosis and autophagy, or the inhibition of the latter leading to cell death, as well as their therapeutic potential in glioma, and examine new perspectives in this promising research field.

Regulatory T cell-targeted hybrid nanoparticles combined with immuno-checkpoint blockage for cancer immunotherapy

Immunosuppression in tumor microenvironments induced by regulatory T (Treg) cells is regarded a critical mechanism of tumor immune escape and poses a major impediment to cancer immunotherapy. In this study, we developed tLyp1 peptide-conjugated hybrid nanoparticles for targeting Treg cells in the tumor microenvironment. The tLyp1 peptide-modified hybrid nanoparticles presented good stability and effective targeting to Treg cells, and they enhanced the effect of imatinib in downregulating Treg cell suppression through inhibition of STAT3 and STAT5 phosphorylation. In addition, an in vivo study revealed high tumor accumulation of the hybrid nanoparticle. Specifically, prolonged survival rate, enhanced tumor inhibition, reduced intratumoral Treg cells, and elevated intratumoral CD8⁺ T cells against tumor were observed when combined with checkpoint-blockade by using anti-cytotoxic T-lymphocyte antigen-4 antibody. This study provided groundwork for a repertoire of nanoparticle-based drugs for targeting and modulating Treg cell function in the tumor microenvironment and for improving antitumor immunotherapy.

BCR-ABL1 tyrosine kinase inhibitors for the treatment of chronic myeloid leukemia

The management of chronic myeloid leukemia with BCR-ABL1 tyrosine kinase inhibitors has evolved chronic myeloid leukemia into a chronic, manageable disease. A patient-centered approach is important for the appropriate management of chronic myeloid leukemia and optimization of long-term treatment outcomes. The pharmacist plays a key role in treatment selection, monitoring drug–drug interactions, identification and management of adverse events, and educating patients on adherence. The combination of tyrosine kinase inhibitors with unique safety profiles and individual patients with unique medical histories can make managing treatment difficult. This review will provide up-to-date information regarding tyrosine kinase inhibitor-based treatment of patients with chronic myeloid leukemia. Management strategies for adverse events and considerations for drug–drug interactions will not only vary among patients but also across tyrosine kinase inhibitors. Drug–drug interactions can be mild to severe. In instances where co-administration of concomitant medications cannot be avoided, it is critical to understand how drug levels are impacted and how subsequent dose modifications ensure therapeutic drug levels are maintained. An important component of patient-centered management of chronic myeloid leukemia also includes educating patients on the significance of early and regular monitoring of therapeutic milestones, emphasizing the importance of adhering to treatment in achieving these targets, and appropriately modifying treatment if these clinical goals are not being met. Overall, staying apprised of current research, utilizing the close pharmacist–patient relationship, and having regular interactions with patients, will help achieve successful long-term treatment of chronic myeloid leukemia in the age of BCR-ABL1 tyrosine kinase inhibitors.

The Role of New Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia

Imatinib mesylate was the first tyrosine kinase inhibitor (TKI) approved for the management of chronic myeloid leukemia. Imatinib produces acceptable responses in approximately 60% of patients, with approximately 20% discontinuing therapy because of intolerance and approximately 20% developing drug resistance. The advent of newer TKIs, such as nilotinib, dasatinib, bosutinib, and ponatinib, has provided multiple options for patients. These agents are more potent, have unique adverse effect profiles, and are more likely to achieve relevant milestones, such as early molecular responses (3-6 months) and optimal molecular responses (12 months). The acquisition of BCR-ABL kinase domain mutations is also reportedly lower with these drugs. Thus far, none of the randomized phase III clinical trials have shown a clinically significant survival difference between frontline imatinib versus newer TKIs. Cost and safety issues with the newer TKIs, such as vascular disease with nilotinib and ponatinib and pulmonary hypertension with dasatinib, have dampened the enthusiasm of using these drugs as frontline options. While the utility of new TKIs in the setting of imatinib failure or intolerance is clear, their use as frontline agents should factor in the age of the patient, additional comorbidities, risk stratification (Sokal score), and cost. Combination therapies and newer agents with potential to eradicate quiescent chronic myeloid leukemia stem cells offers future hope.

Blast phase transformation of chronic myelogenous leukemia presenting with central nervous system manifestation

Chronic myelogenous leukemia (CML) is the most common of all leukemia constituting 15–20% of all leukemia. The clinical course of the diseases runs in two to three phases, initial chronic phase followed by accelerated phase or blast phase. Blast phase most commonly presents clinically as fever, splenomegaly, and bone pain. Here, we present a case of CML in blast phase presenting with central nervous system manifestation in a 55-year-old patient with a brief review of the literature.

Potential mechanisms of disease progression and management of advanced-phase chronic myeloid leukemia

Despite vast improvements in the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML) in chronic phase (CP), advanced stages of CML, accelerated phase or blast crisis, remain notoriously difficult to treat. Treatments that are highly effective against CML-CP produce disappointing results against advanced disease. Therefore, a primary goal of therapy should be to maintain patients in CP for as long as possible, by (1) striving for deep, early molecular response to treatment; (2) using tyrosine kinase inhibitors that lower risk of disease progression; and (3) more closely observing patients who demonstrate cytogenetic risk factors at diagnosis or during treatment.

Inhibition of c-Kit signaling is associated with reduced heat and cold pain sensitivity in humans

The tyrosine kinase receptor c-Kit is critically involved in the modulation of nociceptive sensitivity in mice. Ablation of the c-Kit gene results in hyposensitivity to thermal pain, whereas activation of c-Kit produces hypersensitivity to noxious heat, without altering sensitivity to innocuous mechanical stimuli. In this study, we investigated the role of c-Kit signaling in human pain perception. We hypothesized that subjects treated with Imatinib or Nilotinib, potent inhibitors of tyrosine kinases including c-Kit but also Abl1, PDFGFRα, and PDFGFRβ, that are used to treat chronic myeloid leukemia (CML), would experience changes in thermal pain sensitivity. We examined 31 asymptomatic CML patients (14 male and 17 female) receiving Imatinib/Nilotinib treatment and compared them to 39 age- and sex-matched healthy controls (12 male and 27 female). We used cutaneous heat and cold stimulation to test normal and noxious thermal sensitivity, and a grating orientation task to assess tactile acuity. Thermal pain thresholds were significantly increased in the Imatinib/Nilotinib-treated group, whereas innocuous thermal and tactile thresholds were unchanged compared to those in the control group. In conclusion, our findings suggest that the biological effects of c-Kit inhibition are comparable in mice and humans in that c-Kit activity is required to regulate thermal pain sensitivity but does not affect innocuous thermal and mechanical sensation. The effect on experimental heat pain observed in our study is comparable to those of several common analgesics; thus modulation of the c-Kit pathway can be used to specifically modulate noxious heat and cold sensitivity in humans.

Phase I trial, pharmacokinetics, and pharmacodynamics of vandetanib and dasatinib in children with newly diagnosed diffuse intrinsic pontine glioma

PURPOSE

Testing of promising drug combinations is crucial in the treatment of diffuse intrinsic pontine glioma (DIPG). As the VEGF and platelet-derived growth factor (PDGF) pathways are critical in gliomas, we evaluated the safety, maximum tolerated dose (MTD), pharmacokinetics, and pharmacodynamics of vandetanib, a VEGFR-2 inhibitor, combined with dasatinib, a potent PDGFR inhibitor, during and after radiotherapy in children with newly diagnosed DIPG.

EXPERIMENTAL DESIGN

Dasatinib was started concurrently with radiotherapy. Vandetanib was started 8 days later. We tested increasing doses of vandetanib (65 and 85 mg/m(2) once daily) and dasatinib (65 and 85 mg/m(2) twice daily). Dose-limiting toxicities were evaluated during the first 6 weeks of therapy. Plasma pharmacokinetics was obtained on days 8 and 42 ± 3 in all patients and concomitantly with cerebrospinal fluid (CSF) when possible. Inhibition of targets of dasatinib in peripheral blood mononuclear cells (PBMC) was evaluated.

RESULTS

Twenty-five patients were treated. Treatment was well tolerated. The median duration of treatment was 184 days. Diarrhea was the most significant toxicity. Three patients experienced substantial myelosuppression. The steady-state plasma pharmacokinetics of vandetanib was comparable with previous studies. Although the plasma exposure to dasatinib decreased from days 8 to 42, it remained similar to adult studies. CSF to plasma exposure of vandetanib and dasatinib were approximately 2% in 2 patients. Phosphorylated 70S6K decreased during therapy in PBMCs.

CONCLUSIONS

The MTD of vandetanib and dasatinib in combination was 65 mg/m(2) for each drug. Other studies are underway to test dasatinib and other PDGFR inhibitors alone or in combination for this deadly cancer.

A neuropharmacokinetic assessment of bafetinib, a second generation dual BCR-Abl/Lyn tyrosine kinase inhibitor, in patients with recurrent high-grade gliomas

PURPOSE

The primary objective of this study was to use intracerebral microdialysis (ICMD) to determine the neuropharmacokinetics of bafetinib, a dual BCR-Abl/Lyn tyrosine kinase inhibitor that may have activity against gliomas.

METHODS

A microdialysis catheter was placed into either peritumoural or enhancing brain tissue of seven patients at the time of tumour resection or biopsy. Twenty-four hours later, bafetinib was administered, 240 or 360 mg po, repeating the same dose 12 h later. Dialysate samples were continuously collected for 24h, with plasma samples obtained in parallel. One to two weeks after finishing ICMD, patients were allowed to resume taking bafetinib continuously while being observed for toxicity and tumour response.

RESULTS

Twenty-six dialysate samples per patient were collected (n=6) and analysed for bafetinib by tandem mass spectrometry. Bafetinib concentrations in the brain were below the lower limit of detection of the assay (0.1 ng/ml) in all samples except one from a single subject that was 0.52 ng/ml. The mean plasma bafetinib maximum concentrations after dose 1 and 2 were 143±99 and 247±73 ng/ml, respectively. Only one patient remained on treatment past two cycles, and no radiographic responses were seen.

CONCLUSIONS

Bafetinib does not sufficiently cross intact or disrupted blood-brain barrier, and therefore, systemic administration of bafetinib is not recommended when investigating this drug as a treatment for brain tumours. ICMD can be a valuable research tool in early drug development. Lead-in ICMD studies can be performed relatively quickly, requiring only a small number of patients, and without significantly disrupting standard cancer care.

Interspecies scaling and prediction of human clearance: comparison of small- and macro-molecule drugs

Human clearance prediction for small- and macro-molecule drugs was evaluated and compared using various scaling methods and statistical analysis. Human clearance is generally well predicted using single or multiple species simple allometry for macro- and small-molecule drugs excreted renally. The prediction error is higher for hepatically eliminated small-molecules using single or multiple species simple allometry scaling, and it appears that the prediction error is mainly associated with drugs with low hepatic extraction ratio (Eh). The error in human clearance prediction for hepatically eliminated small-molecules was reduced using scaling methods with a correction of maximum life span (MLP) or brain weight (BRW). Human clearance of both small- and macro-molecule drugs is well predicted using the monkey liver blood flow method. Predictions using liver blood flow from other species did not work as well, especially for the small-molecule drugs.

Metronidazole leads to enhanced uptake of imatinib in brain, liver and kidney without affecting its plasma pharmacokinetics in mice

Objectives

The pharmacokinetic interaction between metronidazole, an antibiotic–antiparasitic drug used to treat anaerobic bacterial and protozoal infections, and imatinib, a CYP3A4, P-glycoprotein substrate kinase inhibitor anticancer drug, was evaluated.

Methods

Male imprinting control region mice were given 50 mg/kg imatinib PO (control group) or 50 mg/kg imatinib PO, 15 min after 40 mg/kg PO metronidazole (study group). Imatinib plasma, brain, kidney and liver concentrations were measured by HPLC and non-compartmental pharmacokinetic parameters estimated.

Key findings

Metronidazole coadministration resulted in a double-peak imatinib disposition profile. The maximum concentration (Cmax) decreased by 38%, the area under the curve (AUC0–∞) decreased by 14% and the time to Cmax (Tmax) was earlier (50%) in plasma. Apparent volume of distribution (VSS/F) and oral clearance (Cl/F) increased by 21% and 17%, respectively. Imatinib tissue penetration was higher after metronidazole coadministration, with 1.7 and 2.1-fold AUC0–∞ increases in liver and kidney, respectively. Metronidazole increased imatinib's tissue-to-plasma AUC0–∞ ratio in liver from 2.29 to 4.53 and in kidney from 3.04 to 7.57, suggesting higher uptake efficiency. Brain Cmax was 3.9-fold higher than control and AUC0–t last was 2.3-fold greater than plasma (3.5% in control group). No tissue-plasma concentration correlation was found.

Conclusions

Metronidazole slightly decreased imatinib systemic exposure but enhanced liver, kidney and brain penetration, probably due to metronidazole-mediated inhibition of P-glycoprotein and other efflux transporters. The high brain exposure opens possibilities for treatment of glioma and glioblastoma. Renal and hepatic functions may need to be monitored due to potential renal and hepatic toxicity.

Central nervous system blast crisis in chronic myeloid leukemia on imatinib mesylate therapy: report of two cases

Chronic myeloid leukaemia is a chronic myeloproliferative disorder characterised by a reciprocal translocation between chromosomes 9 and 22 and thereby formation of the Philadelphia chromosome. Imatinib mesylate (STI-571) is a potent and selective inhibitor of BCR-ABL tyrosine kinase and has emerged as a treatment of choice in chronic myeloid leukaemia (CML) patients in chronic phase. It has shown activity in CML patients in the chronic phase or blastic phase. However there is poor penetration of the central nervous system (CNS) by the drug or its active metabolites. Therefore the CNS acts as a sanctuary site for malignant cells for CML patients treated with Imatinib. We report cases of two CML patients on Imatinib therapy, who were in haematological remission but developed CNS disease.

Chemotherapeutic agents circumvent emergence of dasatinib-resistant BCR-ABL kinase mutations in a precise mouse model of Philadelphia chromosome-positive acute lymphoblastic leukemia

The introduction of cultured p185(BCR-ABL)-expressing (p185+) Arf (-/-) pre-B cells into healthy syngeneic mice induces aggressive acute lymphoblastic leukemia (ALL) that genetically and phenotypically mimics the human disease. We adapted this high-throughput Philadelphia chromosome-positive (Ph(+)) ALL animal model for in vivo luminescent imaging to investigate disease progression, targeted therapeutic response, and ALL relapse in living mice. Mice bearing high leukemic burdens (simulating human Ph(+) ALL at diagnosis) entered remission on maximally intensive, twice-daily dasatinib therapy, but invariably relapsed with disseminated and/or central nervous system disease. Although relapse was frequently accompanied by the eventual appearance of leukemic clones harboring BCR-ABL kinase domain (KD) mutations that confer drug resistance, their clonal emergence required prolonged dasatinib exposure. KD P-loop mutations predominated in mice receiving less intensive therapy, whereas high-dose treatment selected for T315I "gatekeeper" mutations resistant to all 3 Food and Drug Administration-approved BCR-ABL kinase inhibitors. The addition of dexamethasone and/or L-asparaginase to reduced-intensity dasatinib therapy improved long-term survival of the majority of mice that received all 3 drugs. Although non-tumor-cell-autonomous mechanisms can prevent full eradication of dasatinib-refractory ALL in this clinically relevant model, the emergence of resistance to BCR-ABL kinase inhibitors can be effectively circumvented by the addition of "conventional" chemotherapeutic agents with alternate antileukemic mechanisms of action.

Efficacy of erlotinib for brain and leptomeningeal metastases in patients with lung adenocarcinoma who showed initial good response to gefitinib

INTRODUCTION

The efficacy of high-dose (1250 mg/d) gefitinib for the treatment of leptomeningeal metastasis in a patient with lung cancer harboring a mutation in the epidermal growth factor receptor (EGFR) gene was previously reported. We speculate that erlotinib, instead of high dose of gefitinib, may be also effective for the treatment of central nervous system (CNS) lesions, as trough serum concentration of erlotinib is nine times higher than that of gefitinib.

PATIENTS AND METHODS

Patients with lung cancer in whom CNS lesions developed after an initial good response to gefitinib for extra CNS lesions were enrolled in the study. Tumor response, performance status, neurologic symptoms, and survival were retrospectively evaluated.

RESULTS

All seven patients had EGFR mutations in their primary tumors except one patient. The median interval between gefitinib withdrawal and erlotinib administration was 5 days. Three patients showed partial response, three had stable disease, and one had progressive disease. Performance status and symptoms improved in five patients. The overall survival from the initiation of erlotinib treatment ranged from 15 to 530 days (median, 88 days).

CONCLUSIONS

Erlotinib was a reasonable option for the treatment of CNS diseases that appeared after a good initial response of extra CNS disease to gefitinib.

Intratumoral concentrations of imatinib after oral administration in patients with glioblastoma multiforme

Imatinib, an orally administered tyrosine kinase inhibitor of PDGF receptor, c-abl and c-kit, is currently in clinical trials to assess its efficacy in malignant gliomas. Although imatinib does not readily penetrate an intact blood-brain barrier (BBB), the extent to which it distributes into regions of high grade gliomas where the BBB is compromised has not been determined. Patients with recurrent high-grade gliomas for whom repeat surgical tumor debulking was clinically indicated received imatinib mesylate 600 mg orally once a day for seven days prior to surgery. Tissue samples were collected from different regions of the tumor and the approximate location of these samples was determined using frameless stereotactic neuronavigation. Plasma samples were obtained immediately before and after the resection. The concentration of imatinib in the plasma and tumor samples was determined using high performance liquid chromatography with mass spectrometric detection. Eleven tumor samples were obtained from three patients with recurrent glioblastoma multiforme. The median concentration of imatinib in these 11 tumor specimens was 1.34 microg/g (range 0.21-4.31 microg/g) and the median tumor-to-plasma ratio was 0.71 (range 0.28-3.03). These findings suggest that imatinib can reach intratumoral concentrations similar to those or higher than in plasma in regions of glioblastoma where the BBB is disrupted as indicated by contrast enhancement on magnetic resonance imaging.

Clinical pharmacokinetics of tyrosine kinase inhibitors

In the recent years, eight tyrosine kinase inhibitors (TKIs) have been approved for cancer treatment and numerous are under investigation. These drugs are rationally designed to target specific tyrosine kinases that are mutated and/or over-expressed in cancer tissues. Post marketing study commitments have been made upon (accelerated) approval such as additional pharmacokinetic studies in patients with renal- or hepatic impairment, in children, additional interactions studies and studies on the relative or absolute bioavailability. Therefore, much information will emerge on the pharmacokinetic behavior of these drugs after their approval. In the present manuscript, the pharmacokinetic characteristics; absorption, distribution, metabolism and excretion (ADME), of the available TKIs are reviewed. Results from additional studies on the effect of drug transporters and drug-drug interactions have been incorporated. Overall, the TKIs reach their maximum plasma levels relatively fast; have an unknown absolute bioavailability, are extensively distributed and highly protein bound. The drugs are primarily metabolized by cytochrome P450 (CYP) 3A4 with other CYP-enzymes playing a secondary role. They are predominantly excreted with the feces and only a minor fraction is eliminated with the urine. All TKIs appear to be transported by the efflux ATP binding-cassette transports B1 and G2. Additionally these drugs can inhibit some of their own metabolizing enzymes and transporters making steady-state metabolism and drug-drug interactions both complex and unpredictable. By understanding the pharmacokinetic profile of these drugs and their similarities, factors that influence drug exposure will be better recognized and this knowledge may be used to limit sub- or supra-therapeutic drug exposure.

Extracellular fluid concentrations of cisplatin, carboplatin, and oxaliplatin in brain, muscle, and blood measured using microdialysis in nonhuman primates

PURPOSE

Cisplatin, carboplatin, and oxaliplatin are chemically reactive anticancer drugs with modest activity in brain tumors. Previously, we have demonstrated that drug exposure in cerebrospinal fluid (CSF) for these platinum analogs is <5% of the plasma ultrafiltrate (UF) drug exposure in nonhuman primates. Microdialysis is a minimally invasive in vivo method for sampling small molecules in the blood and tissue extracellular fluid (ECF). The purpose of this study was to estimate the penetration of platinum analogs into the brain ECF.

METHODS

We measured free concentrations of cisplatin, carboplatin, and oxaliplatin in ECF of brain, muscle, and blood of nonhuman primates using microdialysis and compared ECF platinum concentrations in blood and brain to plasma UF and CSF concentrations obtained using conventional sampling methods.

RESULTS

For all three platinum analogs, AUC(0-4h) for microdialysis sampling from the vein was similar to standard plasma UF sampling. The median AUC(0-4h) ratio for vein to plasma UF was 1.1 (range, 0.9-1.4). The platinum analogs had limited distribution (<5%) to the CSF and brain ECF. CSF penetration predicts for the limited penetration of the platinum analogs into brain ECF, but concordance between CSF and brain ECF measurements was poor. CSF oxaliplatin concentrations (AUC(0-4h), 0.4-0.9 microM h) were substantially lower than brain ECF concentrations (AUC(0-4h), 2.0-8.6 microM h).

CONCLUSIONS

The penetration of platinum analogs into CSF and brain is limited. The differences in the CNS penetrations among the three platinum analogs are not clinically significant. For cisplatin and carboplatin, CSF penetration appears to be a surrogate for brain extracellular free drug exposure.

P-glycoprotein and breast cancer resistance protein influence brain distribution of dasatinib

The novel tyrosine kinase inhibitor dasatinib (Sprycel; BMS-354825) is approved for use in imatinib (Gleevec; STI 571)-resistant or -intolerant chronic myelogenous leukemia and may be useful for other tumors in the central nervous system (CNS). The objective of this study was to investigate the role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in modulating the CNS penetration of dasatinib. Results from the in vitro studies indicate that cellular delivery of dasatinib is significantly limited by active efflux due to both P-gp and BCRP. Permeability studies indicated greater permeability in the basolateral-to-apical direction than in the apical-to-basolateral direction due to active efflux by P-gp or BCRP. Selective inhibitors of P-gp and BCRP, such as (R)-4-((1aR,6R,10bS)-1,2-difluoro-1,1a,6,10b-tetrahydrodibenzo-(a,e)cyclopropa(c) cycloheptan-6-yl)-alpha-((5-quinoloyloxy)methyl)-1-piperazineethanol, trihydrochloride (zosuquidar; LY335979) and 3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12alpha-octahydropyrazino1',2': 1,6pryrido3,4-bindol-3-yl)-propionic acid tert-butyl ester (Ko143), were able to restore the intracellular accumulation and abolish the directionality in net flux of dasatinib. In vivo brain distribution studies showed that the CNS distribution of dasatinib is limited, with the brain-to-plasma concentration ratios less than 0.12 in wild-type mice, which increased approximately 8-fold in Mdr1a/b(-/-) Bcrp1(-/-) mice. Dasatinib brain distribution was significantly increased in Mdr1a/b(-/-) mice and when wild-type mice were pretreated with LY335979. Simultaneous inhibition of P-gp and BCRP by elacridar [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide] (GF120918) resulted in a 5-fold increase in brain concentration. These in vitro and in vivo studies demonstrate that dasatinib is a substrate for the important efflux transporters p-glycoprotein and BCRP. These transport systems play a significant role in limiting the CNS delivery of dasatinib and may have direct implications in the treatment of primary and metastatic brain tumors.

Differential effect of imatinib and synergism of combination treatment with chemotherapeutic agents in malignant glioma cells

Imatinib mesylate (STI571, Gleevec) is a signal transduction inhibitor and novel anti-cancer agent. It selectively inhibits aberrantly activated tyrosine kinases in malignant cells, for example, bcr-abl in leukaemia, platelet-derived growth factor receptor and stem cell factor receptor (c-Kit) in solid cancers including malignant glioma. However, recently published clinical studies with imatinib monotherapy in patients with malignant glioma demonstrated only very modest anti-tumour activity. The aim of this study was to investigate the biological activity of imatinib, its cellular mechanisms of action and its synergism with other chemotherapeutic agents in human malignant glioma cells in culture. Expression of PDGF/R and c-Kit was analyzed by RT-PCR. Proliferation was measured by MTT assays and drug synergy was assessed by the Chou-Talalay method. Cell cycle and apoptosis were analyzed by flow cytometry and migration by monolayer migration assays. Multi-immunoblot was performed on imatinib-treated and control malignant glioma cells. Results indicate that imatinib is more effective in inhibiting cell colony formation and migration rather than proliferation. Imatinib treatment caused cell cycle arrest of glioma cells in G0-G1 or G2/M, with significant elevation of a few cyclin-dependent kinases. Furthermore, imatinib acted synergistically with chemotherapy agents, such as the DNA alkylating agent, temozolomide, and riboneucleotide reductase inhibitors, for example, hydroxyurea at varied effective dose levels. In conclusion, imatinib exerts varied biological effects on malignant glioma cells in culture. Synergistic interaction of imatinib with chemotherapy agents may be related to cell cycle control mechanisms and could be potentially important in a clinical setting.

A phase II study of imatinib mesylate in children with refractory or relapsed solid tumors: a Children's Oncology Group study

BACKGROUND

Imatinib mesylate is a small molecule inhibitor of certain tyrosine kinases, most notably the chimeric bcr-abl fusion protein found in CML. It also inhibits KIT and PDGF receptor tyrosine kinases in vitro. Ewing sarcoma, osteosarcoma, neuroblastoma, desmoplastic small round cell, and synovial sarcomas often overexpress KIT or the PDGF receptor. A phase II study of imatinib in children and young adults with select solid tumors was performed.

PROCEDURE

Patients less than 30 years of age with refractory or recurrent Ewing sarcoma, osteosarcoma, neuroblastoma, desmoplastic small round cell, synovial sarcomas or GIST were eligible. Imatinib was administered daily for 28 day courses at a dose of 440 mg/m(2)/day. Responses were assessed according to Response Evaluation Criteria in Solid Tumor (RECIST).

RESULTS

Seventy eligible patients, 48 male and 22 female, were enrolled and 59 were evaluable for response. Only one partial response was seen among 24 patients with Ewing sarcoma. There were no other objective responses. Hemorrhagic pleural effusions occurred in seven patients with pulmonary lesions, four of whom had progressive disease at the time of the hemorrhage. Intratumoral bleeding was reported in three additional patients.

CONCLUSION

Imatinib as a single agent at a dose of 440 mg/m(2)/day demonstrated little or no activity as a single agent in children with relapsed or refractory Ewing sarcoma, osteosarcoma, neuroblastoma, or desmoplastic small round cell tumors.

Flying under the radar: the new wave of BCR-ABL inhibitors

The introduction of the BCR-ABL kinase inhibitor imatinib mesylate (Gleevec; Novartis) revolutionized the treatment of chronic myeloid leukaemia (CML). However, most patients with CML receiving imatinib still harbour molecular residual disease and some develop resistance associated with ABL kinase domain mutations. The second-generation BCR-ABL inhibitors nilotinib (Tasigna; Novartis) and dasatinib (Sprycel; Bristol-Myers Squibb) have shown significant activity after imatinib failure in clinical trials, but still face similar obstacles to imatinib, including negligible activity against the frequent BCR-ABL T315I mutation and modest effects in advanced phases of CML. Various medicinal chemistry efforts, in part aided by structural studies of the ABL kinase-imatinib complex have resulted in the synthesis of a new generation of BCR-ABL inhibitors, some of which have shown encouraging preliminary activity in clinical trials, including against T315I mutants. Here, we discuss these emerging therapies, which have the potential to improve the outcome of patients with CML.

Influence of breast cancer resistance protein (Abcg2) and p-glycoprotein (Abcb1a) on the transport of imatinib mesylate (Gleevec) across the mouse blood-brain barrier

Imatinib, a protein tyrosine kinase inhibitor, may prevent the growth of glioblastoma cells. Unfortunately, its brain distribution is restricted by p-glycoprotein (p-gp or multidrug resistance protein Mdr1a), and probably by breast cancer resistance protein (Bcrp1), two efflux pumps expressed at the blood-brain barrier (BBB). We have used in situ brain perfusion to investigate the mechanisms of imatinib transport across the mouse BBB. The brain uptake of imatinib in wild-type mice was limited by saturable efflux processes. The inhibition of p-gp, by valspodar and zosuquidar, increased imatinib uptake (2.5-fold), as did the deficiency of p-gp in Mdr1a/1b(-/-) mice (5.5-fold). Perfusing imatinib with the p-gp/Bcrp1 inhibitor, elacridar, enhanced the brain uptake of imatinib in wild-type (4.1-fold) and Mdr1a/1b(-/-) mice (1.2-fold). However, the brain uptake of imatinib was similar in wild-type and Bcrp1(-/-) mice when it was perfused at a non-saturating concentration. The brain uptake of CGP74588, an active metabolite of imatinib, was low. It was increased by perfusion with elacridar (twofold), but not with valspodar and zosuquidar. CGP74588 uptake was 1.5 times greater in Bcrp1(-/-) mice than in wild-type mice. These data suggest that imatinib transport at the mouse BBB is limited by p-gp and probably by Bcrp1, and that CGP74588 transport is restricted by Bcrp1.

Plasma pharmacokinetics and CYP3A12-dependent metabolism of c-kit inhibitor imatinib in dogs

Imatinib is a highly selective tyrosine kinase inhibitor, and is used for the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumours (GISTs) in humans. The aim of this study is to determine the in vitro and in vivo pharmacokinetics of imatinib in dogs and which cytochrome P450 (CYPs) contribute to its metabolism. Imatinib was administered orally or intravenously to dogs and the time of the peak concentration (T(max)) of imatinib was 4-9 h. The mean half-life was 622 +/- 368 min, and the AUC was 1256 +/- 809 microM * min after oral administration. The range of C0 of intravenously injected dogs was 12-24 microM. The half-life and AUC after intravenous injection were 206 +/- 112 min and 1026 +/- 371 microM * min, respectively. Recombinant system of dog CYP3A12 and CYP2C21 showed that CYP3A12 contributed to the metabolism of imatinib. The inhibition of CYP3A-dependent activity using a rat anti-CYP3A antibody or ketoconazole revealed that CYP3A12 plays a major role in the metabolism of imatinib in dog liver microsomes.

Pharmacokinetic considerations in the treatment of CNS tumours

Despite aggressive therapy, the majority of primary and metastatic brain tumour patients have a poor prognosis with brief survival periods. This is because of the different pharmacokinetic parameters of systemically administered chemotherapeutic agents between the brain and the rest of the body. Specifically, before systemically administered drugs can distribute into the CNS, they must cross two membrane barriers, the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB). To some extent, these structures function to exclude xenobiotics, such as anticancer drugs, from the brain. An understanding of these unique barriers is essential to predict when and how systemically administered drugs will be transported to the brain. Specifically, factors such as physiological variables (e.g. blood flow), physicochemical properties of the drug (e.g. molecular weight), as well as influx and efflux transporter expression at the BBB and BCB (e.g. adenosine triphosphate-binding cassette transporters) determine what compounds reach the CNS. A large body of preclinical and clinical research exists regarding brain penetration of anticancer agents. In most cases, a surrogate endpoint (i.e. CSF to plasma area under the concentration-time curve [AUC] ratio) is used to describe how effectively agents can be transported into the CNS. Some agents, such as the topoisomerase I inhibitor, topotecan, have high CSF to plasma AUC ratios, making them valid therapeutic options for primary and metastatic brain tumours. In contrast, other agents like the oral tyrosine kinase inhibitor, imatinib, have a low CSF to plasma AUC ratio. Knowledge of these data can have important clinical implications. For example, it is now known that chronic myelogenous leukaemia patients treated with imatinib might need additional CNS prophylaxis. Since most anticancer agents have limited brain penetration, new pharmacological approaches are needed to enhance delivery into the brain. BBB disruption, regional administration of chemotherapy and transporter modulation are all currently being evaluated in an effort to improve therapeutic outcomes. Additionally, since many chemotherapeutic agents are metabolised by the cytochrome P450 3A enzyme system, minimising drug interactions by avoiding concomitant drug therapies that are also metabolised through this system may potentially enhance outcomes. Specifically, the use of non-enzyme-inducing antiepileptic drugs and curtailing nonessential corticosteroid use may have an impact.

Modulation of the brain distribution of imatinib and its metabolites in mice by valspodar, zosuquidar and elacridar

PURPOSE

The selective protein tyrosine kinase inhibitor, imatinib, inhibits the growth of glioma cells in preclinical models, but its poor brain distribution limits its efficacy in patients. P-glycoprotein (P-gp, rodent Mdr1a/1b or Abcb1a/1b) and Breast cancer resistance protein (rodent Bcrp1 or Abcg2) were suggested to restrict the delivery of imatinib to the brain. This study evaluates the effect of administering selective inhibitors of these transporters together with imatinib on the systemic and cerebral disposition of imatinib in mice.

MATERIALS AND METHODS

Wild-type, Mdr1a/1b(-/-) and Bcrp1(-/-) mice were given imatinib intravenously, either alone, or with valspodar, zosuquidar (P-gp inhibitors), or elacridar (a P-gp and Bcrp1 inhibitor). The blood and brain concentrations of [(14)C]imatinib and its radioactive metabolites were determined.

RESULTS

The blockade of P-gp by valspodar or zosuquidar (>3 mg/kg) enhanced the brain uptake of imatinib ( approximately 4-fold) in wild-type mice, but not that of its metabolites. Blockade of both P-gp and Bcrp1 by elacridar (>3 mg/kg) produced significantly greater brain penetration of imatinib (9.3-fold) and its metabolites (2.8-fold). In contrast, only the lack of P-gp enhanced imatinib brain penetration (6.4-fold) in knockout mice. These results of brain uptake correlated reasonably well with those obtained previously by our group using in situ brain perfusion.

CONCLUSIONS

Imatinib and its metabolites penetrate into the brain poorly and their penetration is limited by P-gp and (probably) Bcrp1. Administering imatinib together with P-gp (and Bcrp1) transporter inhibitors such as elacridar may improve the delivery of imatinib to the brain, making it potentially more effective against malignant gliomas.

Imatinib mesylate and nilotinib (AMN107) exhibit high-affinity interaction with ABCG2 on primitive hematopoietic stem cells

The majority of chronic phase chronic myeloid leukemia (CML) patients treated with the tyrosine kinase inhibitor (TKI) imatinib mesylate maintain durable responses to the drug. However, most patients relapse after withdrawal of imatinib and advanced stage patients often develop drug resistance. As CML is considered a hematopoietic stem cell cancer, it has been postulated that inherent protective mechanisms lead to relapse in patients. The ATP binding-cassette transporters ABCB1 (MDR-1; P-glycoprotein) and ABCG2 are highly expressed on primitive hematopoietic stem cells (HSCs) and have been shown to interact with TKIs. Herein we demonstrate a dose-dependent, reversible inhibition of ABCG2-mediated Hoechst 33342 dye efflux in primary human and murine HSC by both imatinib and nilotinib (AMN107), a novel aminopyrimidine inhibitor of BCR-ABL. ABCG2-transduced K562 cells were protected from imatinib and nilotinib-mediated cell death and from downregulation of P-CRKL. Moreover, photoaffinity labeling revealed interaction of both TKIs with ABCG2 at the substrate binding sites as they compete with the binding of [(125)I] IAAP and also stimulate the transporter's ATPase activity. Therefore, our evidence suggests for the role of ABC transporters in resistance to TKI on primitive HSCs and CML stem cells and provides a rationale how TKI resistance can be overcome in vivo.

INNO-406, a novel BCR-ABL/Lyn dual tyrosine kinase inhibitor, suppresses the growth of Ph+ leukemia cells in the central nervous system, and cyclosporine A augments its in vivo activity

Central nervous system (CNS) relapse accompanying the prolonged administration of imatinib mesylate has recently become apparent as an impediment to the therapy of Philadelphia chromosome–positive (Ph+) leukemia. CNS relapse may be explained by limited penetration of imatinib mesylate into the cerebrospinal fluid because of the presence of P-glycoprotein at the blood-brain barrier. To overcome imatinib mesylate–resistance mechanisms such as bcr-abl amplification, mutations within the ABL kinase domain, and activation of Lyn, we developed a dual BCR-ABL/Lyn inhibitor, INNO-406 (formerly NS-187), which is 25 to 55 times more potent than imatinib mesylate in vitro and at least 10 times more potent in vivo. The aim of this study was to investigate the efficacy of INNO-406 in treating CNS Ph+ leukemia. We found that INNO-406, like imatinib mesylate, is a substrate for P-glycoprotein. The concentrations of INNO-406 in the CNS were about 10% of those in the plasma. However, this residual concentration was enough to inhibit the growth of Ph+ leukemic cells which expressed not only wild-type but also mutated BCR-ABL in the murine CNS. Furthermore, cyclosporine A, a P-glycoprotein inhibitor, augmented the in vivo activity of INNO-406 against CNS Ph+ leukemia. These findings indicate that INNO-406 is a promising agent for the treatment of CNS Ph+ leukemia.

Phase I/II Study of Imatinib Mesylate for Recurrent Malignant Gliomas: North American Brain Tumor Consortium Study 99-08

PURPOSE

Phase I: To determine the maximum tolerated doses, toxicities, and pharmacokinetics of imatinib mesylate (Gleevec) in patients with malignant gliomas taking enzyme-inducing antiepileptic drugs (EIAED) or not taking EIAED. Phase II: To determine the therapeutic efficacy of imatinib.

EXPERIMENTAL DESIGN

Phase I component used an interpatient dose escalation scheme. End points of the phase II component were 6-month progression-free survival and response.

RESULTS

Fifty patients enrolled in the phase I component (27 EIAED and 23 non-EIAED). The maximum tolerated dose for non-EIAED patients was 800 mg/d. Dose-limiting toxicities were neutropenia, rash, and elevated alanine aminotransferase. EIAED patients received up to 1,200 mg/d imatinib without developing dose-limiting toxicity. Plasma exposure of imatinib was reduced by approximately 68% in EIAED patients compared with non-EIAED patients. Fifty-five non-EIAED patients (34 glioblastoma multiforme and 21 anaplastic glioma) enrolled in the phase II component. Patients initially received 800 mg/d imatinib; 15 anaplastic glioma patients received 600 mg/d after hemorrhages were observed. There were 2 partial response and 6 stable disease among glioblastoma multiforme patients and 0 partial response and 5 stable disease among anaplastic glioma patients. Six-month progression-free survival was 3% for glioblastoma multiforme and 10% for anaplastic glioma patients. Five phase II patients developed intratumoral hemorrhages.

CONCLUSIONS

Single-agent imatinib has minimal activity in malignant gliomas. CYP3A4 inducers, such as EIAEDs, substantially decreased plasma exposure of imatinib and should be avoided in patients receiving imatinib for chronic myelogenous leukemia and gastrointestinal stromal tumors. The evaluation of the activity of combination regimens incorporating imatinib is under way in phase II trials.

EGFR mutations in patients with brain metastases from lung cancer: association with the efficacy of gefitinib

Gefitinib--a specific inhibitor of epidermal growth factor receptor (EGFR)-associated tyrosine kinase--has demonstrated efficacy in a subgroup of patients with non-small-cell lung carcinoma (NSCLC) who fail conventional chemotherapy. It is also reported to have an antitumor effect in brain metastases from NSCLC. Additionally, EGFR mutations have shown a strong association with gefitinib sensitivity for NSCLC. Here, we assessed the efficacy of gefitinib in brain metastases from NSCLC and evaluated the association of this efficacy with EGFR mutations. We retrospectively reviewed eight cases in which patients were suffering from brain metastases before the initiation of gefitinib treatment. Brain tumor response could be evaluated by MRI in these patients; EGFR gene analyses were also available. We evaluated whether objective tumor response was observed after gefitinib treatment and assessed the efficacy of gefitinib as effective, noneffective, or not assessable in consideration of the influence of previous radiotherapy. Of the eight patients, the efficacy of gefitinib was assessed as effective in three and as noneffective in three. All three patients demonstrating effective efficacy had EGFR mutations in the tyrosine kinase domain (deletion mutation in two patients and point mutation in one patients), whereas none of the three patients demonstrating noneffective efficacy had EGFR mutations. Gefitinib appears to be effective in treating brain metastases in a subgroup of patients. Our data suggested a possible association between the efficacy of gefitinib in the treatment of brain metastases and EGFR mutations.

Breast cancer resistance protein in pharmacokinetics and drug–drug interactions

Breast cancer resistance protein (BCRP), also known as ABCG2, ABCP and MXR, is a member of the ATP-binding cassette transporter G family. BCRP functions as a biological barrier that extrudes xenobiotics out of cells. The broad substrate specificity and tissue distributions of BCRP in the body make this transporter one of the major efflux transporters in chemotherapy. Recent studies have demonstrated that BCRP exerts a great impact on drug absorption and disposition. This review focuses on the role of BCRP in pharmacokinetics as well as in vitro and in vivo strategies to evaluate hepatic/intestinal BCRP-mediated drug transports and drug-drug interactions. The impacts of polymorphism and gender difference of BCRP are also discussed.

The effect of Bcrp1 (Abcg2) on the in vivo pharmacokinetics and brain penetration of imatinib mesylate (Gleevec): implications for the use of breast cancer resistance protein and P-glycoprotein inhibitors to enable the brain penetration of imatinib in patients

Imatinib mesylate (signal transduction inhibitor 571, Gleevec) is a potent and selective tyrosine kinase inhibitor, which was shown to effectively inhibit platelet-derived growth factor-induced glioblastoma cell growth preclinically. However, in patients, a limited penetration of imatinib into the brain has been reported. Imatinib is transported in vitro and in vivo by P-glycoprotein (P-gp; ABCB1), which thereby limits its distribution into the brain in mice. Previously, imatinib was shown to potently inhibit human breast cancer resistance protein (BCRP; ABCG2). Here, we show that imatinib is efficiently transported by mouse Bcrp1 in transfected Madin-Darby canine kidney strain II (MDCKII) monolayers. Furthermore, we show that the clearance of i.v. imatinib is significantly decreased 1.6-fold in Bcrp1 knockout mice compared with wild-type mice. At t = 2 hours, the brain penetration of i.v. imatinib was significantly 2.5-fold increased in Bcrp1 knockout mice compared with control mice. We tested the hypothesis that P-gp and BCRP inhibitors, such as elacridar and pantoprazole, improve the brain penetration of imatinib. Firstly, we showed in vitro that pantoprazole and elacridar inhibit the Bcrp1-mediated transport of imatinib in MDCKII-Bcrp1 cells. Secondly, we showed that co-administration of pantoprazole or elacridar significantly reduced the clearance of i.v. imatinib in wild-type mice by respectively 1.7-fold and 1.5-fold. Finally, in wild-type mice treated with pantoprazole or elacridar, the brain penetration of i.v. imatinib significantly increased 1.8-fold and 4.2-fold, respectively. Moreover, the brain penetration of p.o. imatinib increased 5.2-fold when pantoprazole was co-administered in wild-type mice. Our results suggest that co-administration of BCRP and P-gp inhibitors may improve delivery of imatinib to malignant gliomas.