Imatinib pharmacokinetics in patients with gastrointestinal stromal tumour: a retrospective population pharmacokinetic study over time. EORTC Soft Tissue and Bone Sarcoma Group

Gastrointestinal stromal tumors II: medical oncology and tumor response assessment

The finding of mutations of KIT in gastrointestinal stromal tumors (GISTs) and subsequent development of kinase-directed therapy in metastatic GIST serve as a touchstone for the translation of laboratory research into clinical therapeutics. A variety of novel developments have followed the discovery of clinical activity of kinase-directed therapy against GIST. Radiological assessment of GIST challenges the standard of care for assessing tumor responses, ie, Response Evaluation Criteria in Solid Tumors (RECIST). Furthermore, the determination of the relationship of specific KIT mutations and sensitivity and resistance to kinase-directed agents and the assessment of inhibitor levels and the quality of response to those agents have implications beyond the treatment of sarcomas. These discoveries and the next chapters in this developing story are discussed in this review.

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.

Pharmacological management of gastrointestinal stromal tumours: an update on the role of sunitinib

The efficacy and tolerability of the receptor tyrosine kinase inhibitor, sunitinib malate, have been demonstrated in phase I-III clinical trials of patients with imatinib-resistant or imatinib-intolerant gastrointestinal stromal tumours (GIST) as well as in a worldwide expanded-access study and in a continuous daily dosing (CDD) trial. Tumour genotype may have a significant influence on the activity of sunitinib in patients with imatinib-resistant GIST. Sunitinib activity was observed across different GIST genotypes and particularly in patients with wild-type and KIT exon 9 mutations (all relatively resistant to standard-dose imatinib) and in patients with secondary KIT exons 13 and 14 mutations. Adverse events with sunitinib were generally mild to moderate and easily managed by dose reduction, dose interruption or standard supportive measures. Treatment discontinuation can be avoided in most patients by close monitoring before and during treatment with appropriate adverse event management as necessary. The correlation between treatment exposure and clinical response is prompting the search for new approaches to treatment optimisation to ensure that patients derive maximum benefit from sunitinib therapy, including dose adjustments based on blood testing to ensure optimal drug exposure, and the use of the alternative CDD regimen to avoid treatment interruption.

Phase I dose escalation study of telatinib, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor 2 and 3, platelet-derived growth factor receptor beta, and c-Kit, in patients with advanced or metastatic solid tumors

PURPOSE

Telatinib (BAY 57-9352) is an orally available tyrosine kinase inhibitor of vascular endothelial growth factor receptor (VEGFR) -2, VEGFR-3, platelet-derived growth factor receptor-beta, and c-Kit. This phase I dose escalation study was conducted to evaluate the safety and tolerability of telatinib, with additional pharmacokinetic, pharmacodynamic, and efficacy assessments.

PATIENTS AND METHODS

Patients with solid tumors refractory to standard therapies or with no standard therapy available were enrolled. Doses of continuously administered telatinib were escalated from 20 mg once daily to 1,500 mg twice daily.

RESULTS

Fifty-three patients were enrolled. Most frequently observed drug-related adverse events were nausea (26.4%; grade >or= 3, 0%) and hypertension (20.8%; grade 3, 11.3%; grade 4, 0%). Two dose-limiting toxicities were observed: one poorly controlled hypertension (600 mg twice daily), and one grade 2 weight loss, anorexia, and fatigue (1,500 mg twice daily). A formal maximum-tolerated dose was not reached. Telatinib was rapidly absorbed, with median time to peak concentration (t(max)) lower than 3 hours after dose. A nearly dose-proportional increase in exposure was observed with substantial variability. Telatinib half-life averaged 5.5 hours. Biomarker analyses showed dose-dependent increase in VEGF levels and decrease in plasma soluble VEGFR-2 levels, with a plateau at 900 mg twice daily. A decrease in tumor blood flow (K(trans) and IAUC(60)) was observed with dynamic contrast-enhanced magnetic resonance imaging. Best tumor response was stable disease, observed in 50.9% of patients.

CONCLUSION

Telatinib was safe and well tolerated up to 1,500 mg twice daily. Based on pharmacodynamic and pharmacokinetic end points, telatinib 900 mg twice daily is the recommended dose for subsequent phase II studies.

Imatinib plasma levels are correlated with clinical benefit in patients with unresectable/metastatic gastrointestinal stromal tumors

PURPOSE To study the pharmacokinetics (PK) of imatinib (IM) in patients with advanced GI stromal tumors (GISTs) treated in a randomized phase II study and to explore the potential relationship between IM plasma levels and long-term clinical outcomes. PATIENTS AND METHODS Patients were randomly assigned to receive IM at 400 mg versus 600 mg daily. IM plasma levels were analyzed in a subset of patients (n = 73) for whom PK data on day 1 and at steady-state (SS, day 29) were available. IM PK was evaluated using a population PK approach. The relationship between IM plasma exposure and clinical outcome was explored by grouping patients into quartiles according to IM trough concentration (C(min)). The clinical outcome parameters evaluated include overall objective benefit rate (OOBR; complete response plus partial response plus stable disease) time to progression (TTP), and KIT genotyping. Results IM PK exposure showed a high inter-patient variability, and clinical outcomes were correlated with IM trough levels at SS. The median TTP was 11.3 months for patients in the lowest C(min) quartile (Q1, < 1,110 ng/mL) compared with more than 30 months for Q2 to Q4 (P = .0029). OOBR was also inferior in Q1 patients. In patients with GIST with KIT exon 11 mutations (n = 39), the OOBR was 67% for Q1 patients versus 100% for all others (P = .001). CONCLUSION In patients with advanced GIST, IM trough levels at SS were associated with clinical benefit. Patients with IM C(min) below 1,100 ng/mL showed a shorter TTP and lower rate of clinical benefit (OOBR). Further studies are justified to test whether monitoring IM plasma levels might optimize clinical outcomes for patients with GIST.

Kinase mutations and efficacy of imatinib in Korean patients with advanced gastrointestinal stromal tumors

PURPOSE

This study analyzed the relationship between treatment outcome and kinase mutational status in Korean patients with advanced gastrointestinal stromal tumors (GISTs).

EXPERIMENTAL DESIGN

Clinical data were collected from 113 consecutive patients with metastatic or unresectable GISTs treated with imatinib from June 2001 through June 2005 at five institutions in Korea. KIT exons 9, 11, 13, and 17 and PDGFRA exons 12 and 18 were examined.

RESULTS

The median patient age was 57 years (range, 31-82 years). The overall response rate was 67.2%. KIT mutations were found in exon 11 (n = 92, 81.4%) and exon 9 (n = 10, 8.8%). One patient had a PDGFRA exon 18 mutation. The overall mutation rate was 91.2%. Response rates were 68.4%, 50.0%, and 80.0% in patients with KIT exon 11 mutations, KIT exon 9 mutations, and no kinase mutations, respectively. With a median follow-up of 49.0 months, the median progression-free survival (PFS) time was 42.0 months and median overall survival (OS) time was not reached. PFS and OS times did not differ significantly according to KIT genotype.

CONCLUSION

This study was unable to find an association between KIT mutational status and clinical outcome of imatinib in Korean patients with advanced GISTs. There was a trend toward better outcomes for patients with wild-type KIT or exon 11 mutations compared with exon 9 mutations, although this was not statistically significant. Compared with previous studies in western populations, these results suggest that ethnic differences may influence the relationship between KIT genotype and clinical outcome to imatinib.

Dose escalation of imatinib after failure of standard dose in Korean patients with metastatic or unresectable gastrointestinal stromal tumor

OBJECTIVE

We evaluated the results of imatinib dose escalation in patients with advanced gastrointestinal stromal tumors (GISTs) after disease progression on standard-dose imatinib.

METHODS

Clinical data from patients with metastatic or unresectable GISTs whose dose of imatinib was increased after disease progression on imatinib 400 mg/day were retrospectively reviewed.

RESULTS

The 24 patients studied had a median age of 52 years. Imatinib dosing was escalated to 600 mg/day in 12 patients, then to 800 mg/day in four patients. The other 12 patients had dose escalation directly to 800 mg/day. Two patients (8.3%) achieved a partial response, and seven (29.2%) had stable disease. Six-month progression-free and overall survival rates were 33.3 and 70.7%, respectively. Dose escalation to 600 or 800 mg/day was generally well tolerated.

CONCLUSION

Imatinib dose escalation is feasible and well tolerated in patients with advanced GIST who progress on standard-dose therapy, producing clinical benefit in approximately 37% of patients.

Efficacy and safety profile of imatinib mesylate (ST1571) in Japanese patients with advanced gastrointestinal stromal tumors: a phase II study (STI571B1202)

BACKGROUND

Imatinib mesylate, an inhibitor of KIT, ABL protein, and platelet-derived growth factor receptor alpha (PDGFRalpha) tyrosine kinase, has recently been found to have a dramatic antitumor effect on gastrointestinal stromal tumor (GIST). The aim of this study was to assess the efficacy and safety of imatinib mesylate in Japanese patients with advanced GIST.

METHODS

Patients with measurable lesions were enrolled between April 1, 2002, and September 20, 2002, using a design based on previous phase II studies in the United States and the European Union. The diagnosis of GIST was proven histologically with positive immunostaining for KIT (CD117). Imatinib mesylate was administered at a dose of either 400 mg or 600 mg once a day. Pharmacokinetic parameters and mutation analysis of c-kit were also assessed in a subgroup of patients.

RESULTS

A total of 74 patients (28 receiving imatinib mesylate at 400 mg/day; 46 receiving 600 mg/day); median age, 56.0 years, were enrolled. No patient had a complete response, 51 patients (69%) had a partial response, and 19 patients (26%) had stable disease. The median progression-free survival time was 96 weeks. The estimated 3-year overall survival (Kaplan-Meier) rate for all patients was 73.6%. The most frequent adverse effects related to the drug were nausea (78%), diarrhea (70%), dermatitis (62%), facial edema (61%), edema of the lower limbs (58%), vomiting (54%), and eyelid edema (51%). Most of the adverse effects were mild and manageable.

CONCLUSION

Imatinib mesylate is generally safe and has significant activity in the treatment of advanced GIST in Japanese patients.

Relationship of imatinib-free plasma levels and target genotype with efficacy and tolerability

Imatinib has revolutionised the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumours (GIST). Using a nonlinear mixed effects population model, individual estimates of pharmacokinetic parameters were derived and used to estimate imatinib exposure (area under the curve, AUC) in 58 patients. Plasma-free concentration was deduced from a model incorporating plasma levels of alpha₁-acid glycoprotein. Associations between AUC (or clearance) and response or incidence of side effects were explored by logistic regression analysis. Influence of KIT genotype was also assessed in GIST patients. Both total (in GIST) and free drug exposure (in CML and GIST) correlated with the occurrence and number of side effects (e.g. odds ratio 2.7±0.6 for a two-fold free AUC increase in GIST; P<0.001). Higher free AUC also predicted a higher probability of therapeutic response in GIST (odds ratio 2.6±1.1; P=0.026) when taking into account tumour KIT genotype (strongest association in patients harbouring exon 9 mutation or wild-type KIT, known to decrease tumour sensitivity towards imatinib). In CML, no straightforward concentration–response relationships were obtained. Our findings represent additional arguments to further evaluate the usefulness of individualising imatinib prescription based on a therapeutic drug monitoring programme, possibly associated with target genotype profiling of patients.

The effect of P-gp (Mdr1a/1b), BCRP (Bcrp1) and P-gp/BCRP inhibitors on the in vivo absorption, distribution, metabolism and excretion of imatinib

Imatinib is transported by P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP), however, the exact impact of these transporters on absorption, distribution, metabolism and excretion (ADME) of imatinib is not fully understood due to incomplete data. We have performed a comprehensive ADME study of imatinib given as single agent or in combination with the well known BCRP/P-gp inhibitors, elacridar and pantoprazole, in wild-type and P-gp and/or BCRP knockout mice. The absence of P-gp and BCRP together resulted in a significantly higher area under the plasma concentration-time curve (AUC) after i.v. administration, whereas the AUC after oral dosing was unaltered. Both elacridar and pantoprazole significantly increased the AUC of orally administered imatinib in wild-type but also in P-gp/BCRP knockout mice. This lower clearance was not due to a (further) reduction in biliary excretion. Fecal excretion was significantly reduced in P-gp and P-gp/BCRP knockout but not in BCRP knockout mice, whereas the brain penetration was significantly higher in P-gp/BCRP knockout mice compared to single P-gp or BCRP knockout or wild-type mice. In conclusion, P-gp and BCRP have only a modest effect on the ADME of imatinib in comparison to metabolic elimination. P-gp is the most prevalent factor for systemic clearance and limiting the brain penetration. The considerable drug-drug interaction observed with elacridar or pantoprazole is only partly mediated by inhibition of P-gp and BCRP and far more by the inhibition of other elimination pathways.

Imatinib for hepatocellular cancer--focus on pharmacokinetic/pharmacodynamic modelling and liver function

The effects of imatinib are partly mediated by the inhibition of platelet-derived growth factor (PDGF), which is highly expressed in the liver. In this phase-I/II trial pharmacokinetic parameters of imatinib given for hepatocellular cancer were similar to those previously derived from CML patients. The AUC of N-desmethyl-imatinib depended on liver function; the metabolism of imatinib was otherwise comparable to other populations. During short-termed imatinib treatment (4 weeks, 400 mg/d), plasma PDGF significantly decreased. The AUC of N-desmethyl-imatinib could best be attributed to the pharmacodynamic effect of PDGF inhibition (r=-0.679 [95% CI: -0.917 to -0.0868], p=0.031).

Drug Insight: gastrointestinal stromal tumors (GIST)--the solid tumor model for cancer-specific treatment

We are living in an exciting era in the treatment of cancer, using drugs that target specific proteins rather than agents that cause more general cytotoxic effects. The identification of proteins and signal transduction pathways that play crucial roles in the pathogenesis of cancer has allowed treatments to be designed that target these tumor-driven events. Gastrointestinal stromal tumors (GIST) are rare mesenchymal tumors and were among the first solid tumor types for which such a novel treatment (in this case imatinib) became available. The tyrosine kinase inhibitor imatinib targets the human KIT receptor and the platelet-derived growth factor receptor-alpha. This drug exhibits impressive antitumor effects against GIST and has become the first-line therapy for advanced disease. Major insights into the mechanism of action of this drug, drug resistance, and patient management issues have been gleaned. Additionally, new drugs developed for the treatment of GIST have been identified. As a consequence, lessons learned from GIST are widely applicable to other tumor entities, thereby rendering GIST the paradigm of solid tumors treated with tyrosine kinase inhibitors. This Review discusses the pathogenesis of GIST, treatment strategies, mechanisms accounting for drug resistance, and potential future perspectives.

Influence of CYP3A4 inhibition on the steady-state pharmacokinetics of imatinib

PURPOSE

To evaluate the effects of ritonavir, a potent inhibitor of CYP3A4, on the steady-state pharmacokinetics of imatinib.

EXPERIMENTAL DESIGN

Imatinib pharmacokinetics were evaluated in cancer patients receiving the drug for at least 2 months, after which ritonavir (600 mg) was administered daily for 3 days. Samples were obtained on the day before ritonavir (day 1) and on the third day (day 4). The in vitro metabolism of imatinib with or without ritonavir and the effect of imatinib on 1-OH-midazolam formation rate, a probe for CYP3A4 activity, were evaluated with human CYP3A4 and pooled liver microsomes.

RESULTS

In 11 evaluable patients, the geometric mean (95% confidence interval) area under the curve of imatinib on days 1 and 4 were 42.6 (33.0-54.9) microg.h/mL and 41.2 (32.1-53.1) microg.h/mL, respectively (P = 0.65). A population analysis done in NONMEM with a time-dependent covariate confirmed that ritonavir did not influence the clearance or bioavailability of imatinib. In vitro, imatinib was metabolized to the active metabolite CGP74588 by CYP3A4 and CYP3A5 and, to a lesser extent, by CYP2D6. Ritonavir (1 micromol/L) completely inhibited CYP3A4-mediated metabolism of imatinib to CGP74588 but inhibited metabolism in microsomes by only 50%. Imatinib significantly inhibited CYP3A4 activity in vitro.

CONCLUSION

At steady state, imatinib is insensitive to potent CYP3A4 inhibition and relies on alternate elimination pathways. For agents with complex elimination pathways that involve autoinhibition, interaction studies that are done after a single dose may not be applicable when drugs are administered chronically.

Pharmacokinetic investigation of imatinib using accelerator mass spectrometry in patients with chronic myeloid leukemia

PURPOSE

To investigate the potential use of accelerator mass spectrometry (AMS) in the study of the clinical pharmacology of imatinib.

EXPERIMENTAL DESIGN

Six patients who were receiving imatinib (400 mg/d) as part of their ongoing treatment for chronic myeloid leukemia (CML) received a dose containing a trace quantity (13.6 kBq) of (14)C-imatinib. Blood samples were collected from patients before and at various times up to 72 h after administration of the test dose and were processed to provide samples of plasma and peripheral blood lymphocytes (PBL). Samples were analyzed by AMS, with chromatographic separation of parent compound from metabolites. In addition, plasma samples were analyzed by liquid chromatography/mass spectrometry (LCMS).

RESULTS

Analysis of the AMS data indicated that imatinib was rapidly absorbed and could be detected in plasma up to 72 h after administration. Imatinib was also detectable in PBL at 24 h after administration of the (14)C-labeled dose. Comparison of plasma concentrations determined by AMS with those derived by LCMS analysis gave similar average estimates of area under plasma concentration time curve (26 +/- 3 versus 27 +/- 11 microg/mL.h), but with some variation within each individual.

CONCLUSIONS

Using this technique, data were obtained in a small number of patients on the pharmacokinetics of a single dose of imatinib in the context of chronic dosing, which could shed light on possible pharmacologic causes of resistance to imatinib in CML.

Phase I clinical study of AZD2171, an oral vascular endothelial growth factor signaling inhibitor, in patients with advanced solid tumors

PURPOSE

AZD2171 is a highly potent oral selective inhibitor of vascular endothelial growth factor (VEGF) signaling. This phase I study was designed to evaluate the safety and tolerability of increasing doses of AZD2171, with additional assessments of pharmacokinetics, pharmacodynamics, and efficacy.

PATIENTS AND METHODS

In part A, 36 patients with solid tumors and liver metastases refractory to standard therapies received once-daily oral AZD2171 (0.5 to 60 mg). Doses were escalated in successive cohorts until the maximum-tolerated dose was identified. In part B, patients with (n = 36) or without (n = 11) liver metastases were randomly assigned to receive once-daily AZD2171 (20, 30, or 45 mg). In both parts, treatment continued until tumor progression or dose-limiting toxicity (DLT) was observed.

RESULTS

Eighty-three patients received AZD2171, which was generally well tolerated at doses of 45 mg/d or less; the most frequently reported dose-related adverse events were diarrhea, dysphonia, and hypertension. The most common DLT was hypertension (n = 7), which occurred at AZD2171 doses of 20 mg and higher. After a single dose, maximum plasma (peak) drug concentration after single-dose administration (Cmax) was achieved 1 to 8 hours postdosing with an arithmetic mean half-life associated with terminal slope of a semilogarithmic concentration-time curve (t1/2 lamda(z)) of 22 hours. Pharmacodynamic assessments demonstrated time-, dose-, and exposure-related decreases in initial area under the curve, defined over 60 seconds post-contrast arrival in the tissue (iAUC60) using dynamic contrast-enhanced magnetic resonance imaging, as well as dose- and time-dependent reductions in soluble VEGF receptor 2 levels. Preliminary evidence of efficacy included two confirmed partial responses and 22 patients with stable disease; effects on tumor size appeared to be dose related.

CONCLUSION

Once-daily oral AZD2171 at doses of 45 mg or less was generally well tolerated and was associated with encouraging antitumor activity in patients with a broad range of advanced solid tumors.

Imatinib-refractory gastrointestinal stromal tumors: the clinical problem and therapeutic strategies

Treatment of gastrointestinal stromal tumor (GIST) is a paradigm for targeted therapy. These mesenchymal tumors are refractory to standard chemotherapy and radiation therapy. Targeted therapy has successfully exploited the oncologic drivers of GIST--the tyrosine kinases, KIT, and the platelet-derived growth factor receptor. Therapy with imatinib has dramatically altered the natural history of patients with advanced GIST. However, patients are developing resistance to imatinib and thus presenting with a major clinical challenge. Alternative approaches to imatinib-refractory disease are needed. Newer approaches using biologic data regarding the mechanisms of resistance are being tested alone or in combination with imatinib and are the focus of this review. Effective novel agents for imatinib-refractory GIST used as single agents or in combination with imatinib will likely become future regimens to be tested in first-line metastatic disease and in the adjuvant setting.

Improved Insight into Resistance Mechanisms to Imatinib in Gastrointestinal Stromal Tumors: A Basis for Novel Approaches and Individualization of Treatment

Gastrointestinal stromal tumor (GIST) is one of the first solid tumor types in which a tyrosine kinase inhibitor, imatinib, has become standard of care for patients with advanced disease. Although imatinib yields antitumor activity in the vast majority of patients, it is likely that all patients eventually experience progressive disease given enough time. In recent years, major progress has been made in the elucidation of mechanisms conferring resistance to imatinib that result in progressive disease. Insight into these resistance mechanisms has already resulted in the availability of strategies that can be applied in cases of progressive disease and it is likely that more approaches will be defined in the next years. Additionally, it can be anticipated that in the near future treatment will be guided according to factors determining sensitivity to imatinib. This review focuses on the factors inducing imatinib resistance that have been elucidated so far, the currently available and potential novel treatment options for patients with progressive disease, and how insight into resistance mechanisms may allow individualized treatment in the near future for patients with advanced GISTs.

Predictive factors for long-term effects of imatinib therapy in patients with inoperable/metastatic CD117(+) gastrointestinal stromal tumors (GISTs)

THE PURPOSE

To analyze the outcomes of treatment and factors predicting effects of imatinib (IM) therapy in inoperable/metastatic gastrointestinal stromal tumors (GIST) CD117(+) patients.

MATERIALS AND METHODS

We identified 232 patients in a prospectively collected Clinical GIST Registry with advanced inoperable/metastatic GIST treated with IM 400-800 mg daily (129 males and 103 females and median age 56 years). Median follow-up time was 26 months.

RESULTS

The estimated 3-year progression-free survival (PFS; calculated from the date of the start of IM) was 54% and median PFS was 40.5 months. The following factors significantly and negatively influenced PFS in univariate analysis: poor baseline World Health Organization (WHO) performance status > or = 2 (P < 0.00001), tumor genotype indicating other than KIT exon 11 isoform (P = 0.005), baseline high neutrophils count (P < 0.00001), age <45 years at the diagnosis (P = 0.04), mitotic index >10/50 high-power fields (HPF) (P = 0.001), GIST histological type other than spindle-cell (P = 0.03), baseline low albumin level (P = 0.0005), low baseline hemoglobin level (P < 0.00001), and primary overtly malignant tumors (unresectable and/or metastatic lesions at presentation) (P = 0.05). We identified four factors negatively affecting PFS, statistically significant (P < 0.05) in multivariate analysis: baseline poor WHO performance status > or = 2, high baseline neutrophils count (>5 x 10(9)/l), tumor genotype indicating the presence of non-exon 11 KIT mutant and mitotic index >10/50 HPF.

CONCLUSIONS

We confirmed that many advanced GIST patients benefit from IM therapy for a prolonged time, although resistance to therapy is observed. We identified four independent biological factors influencing the PFS during long-term IM therapy.

Prospective multicentric randomized phase III study of imatinib in patients with advanced gastrointestinal stromal tumors comparing interruption versus continuation of treatment beyond 1 year: the French Sarcoma Group

PURPOSE

Imatinib is the standard treatment of advanced GI stromal tumors (GISTs). It is not known whether imatinib may be stopped in patients in whom disease is controlled.

METHODS

This prospective, randomized, multicentric phase III study was designed to compare continuous (CONT) compared with interrupted (INT) imatinib beyond 1 year of treatment in patients with advanced GIST. The primary end point was progression-free survival. Secondary end points included overall survival, response rate after reinitiation of imatinib, and quality of life. Early stopping rules in cases of rapid progression of disease were defined, with preplanned interim analyses.

RESULTS

Between May 2002 and April 2004, 182 patients with advanced GIST were enrolled. Between May 2003 and April 2004, 98 patients in response or stable disease under imatinib reached more than 1 year of follow-up. Forty were not eligible for randomization, and 58 patients were randomly assigned, 32 and 26 patients in the INT and CONT arms, respectively. As of October 15, 2005, eight of 26 patients in the CONT group and 26 of 32 patients in the INT group had documented disease progression (P < .0001). Twenty-four of 26 patients with documented progression in the INT arm responded to imatinib reintroduction. No differences in overall survival or imatinib resistance were observed between the two arms. Quality of life evaluated 6 months after random assignment using the 30-item Quality of Life Questionnaire was not significantly different between the two groups of randomly assigned patients.

CONCLUSION

Imatinib interruption results in rapid progression in most patients with advanced GIST, and cannot be recommended in routine practice unless patient experience significant toxicity

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Pharmacocinétique (PK) et pharmacodynamie (PD) de l’imatinib (Glivec®)

Imatinib (Glivec) is a specific inhibitor of tyrosine kinase receptor, in particular of the proto-oncogene c-kit. Proto-oncogene c-kit is expressed or mutated in stromal digestive tumors (GIST). Pharmacokinetic (PK) analysis showed that imatinib displayed linear PK in patients with advanced GIST. Imatinib is extensively metabolized by the cytochrome P450 enzyme system. Alpha-1-acid glycoprotein (AAG), a protein involved in the acute phase of inflammation, is implicated in protein binding of imatinib and seems to play a key role in imatinib PK.

Imatinib

Imatinib (Gleevec, Glivec is a small molecule inhibitor of tyrosine kinase that has been evaluated for efficacy in patients with gastrointestinal stromal tumours (GIST). The drug is approved for the treatment of unresectable and/or metastatic, KIT-positive GIST in the US, Europe and many other countries. Imatinib has had a significant impact on the management of advanced GIST, which has traditionally had a poor prognosis, and has quickly become the first choice of treatment in the medical therapy of unresectable and/or metastatic, KIT-positive GIST. In randomised, nonblind trials, imatinib 400-800 mg/day produced complete or partial responses in up to two-thirds of patients, with long-term efficacy, and substantially prolonged progression-free and overall survival. The drug was generally well tolerated in GIST patients, including during long-term treatment. Imatinib dosages higher than 400 mg/day (up to 800 mg/day) may improve progression-free survival, with an increase in dosage benefiting some patients who show disease progression at the lower dosage, particularly in those with exon 9 mutation; however, there is also a dose-related increase in imatinib toxicity. Mutational genotype and other, non-biomolecular factors may aid in guiding imatinib therapy and predicting prognosis in GIST patients. Further data are required to evaluate the use of imatinib in adjuvant and neoadjuvant settings. Nevertheless, imatinib currently provides the most effective treatment option in the management of advanced GIST.

Polyclonal evolution of multiple secondary KIT mutations in gastrointestinal stromal tumors under treatment with imatinib mesylate

Gastrointestinal stromal tumors (GIST) are characterized by a strong KIT receptor activation most often resulting from KIT mutations. In a smaller subgroup of tumors without KIT mutations, analogous activating mutations are found in the platelet-derived growth factor receptor alpha (PDGFRalpha) gene. Both PDGFRalpha and KIT receptors are targets of the tyrosine kinase inhibitor imatinib (Glivec) which has improved the treatment of advanced GISTs significantly. However, a subgroup of tumors show a secondary progress under therapy with imatinib after initial response. One possible mechanism of secondary resistance is the development of newly acquired KIT mutations. In the present study, we evaluated the frequency of such secondary KIT mutations in a series of GIST patients in which tumor tissue was resected under treatment. We examined one to seven different tumor areas in 32 cases (total of 104 samples) and found up to four newly acquired KIT mutations in 14 patients (43.8%). These were always located in exons encoding the first or second tyrosine kinase domain (exon 13, 14, or 17). Mutations were found only in a subset of samples analyzed from each case whereas others retained the wild-type sequence in the same region. There was never more than one new mutation in the same sample. Consistent with a secondary clonal evolution, the primary mutation was always detectable in all samples from each tumor. According to our results, the identification of newly acquired KIT mutations in addition to the primary mutation is dependent on the number of tissue samples analyzed and has high implications for further therapeutic strategies.

Pharmacokinetic-Pharmacodynamic Relationships of Imatinib and Its Main Metabolite in Patients with Advanced Gastrointestinal Stromal Tumors

PURPOSE

This study explored factors affecting the pharmacokinetic variability of imatinib and CGP 74588, and the pharmacokinetic-pharmacodynamic correlations in patients with advanced gastrointestinal stromal tumors.

EXPERIMENTAL DESIGN

Thirty-five patients with advanced gastrointestinal stromal tumors received 400 mg of imatinib daily. Six blood samples were drawn: before intake, during 1- to 3- and 6- to 9-hour intervals after intake on day 1, and before intake on days 2, 30, and 60. Plasma imatinib and CGP 74588 concentrations were quantified by reverse-phase high-performance liquid chromatography coupled with tandem mass spectrometry, and analyzed by the population pharmacokinetic method (NONMEM program). The influence of 17 covariates on imatinib clearance (CL) and CGP 74588 clearance (CLM/fm) was studied. These covariates included clinical and biological variables and occasion (OCC = 0 for pharmacokinetic data corresponding to the first administration, or OCC = 1 for the day 30 or 60 administrations).

RESULTS

The best regression formulas were: CL (L/h) = 7.97 (AAG/1.15)(-0.52), and CLM/fm (L/h) = 58.6 (AAG/1.15)(-0.60) x 0.55(OCC), with the plasma alpha1-acid glycoprotein (AAG) levels indicating that both clearance values decreased at a higher AAG level. A significant time-dependent decrease in CLM/fm was evidenced with a mean (+SD) CGP 74588/imatinib area under the curve (AUC) ratio of 0.25 (+/-0.07) at steady state, compared with 0.14 (+/-0.03) on day 1. Hematologic toxicity was correlated with pharmacokinetic variables: the correlation observed with the estimated unbound imatinib AUC at steady-state (r = 0.56, P < 0.001) was larger than that of the total imatinib AUC (r = 0.32, NS).

CONCLUSIONS

The plasma AAG levels influenced imatinib pharmacokinetics. A protein-binding phenomenon needs to be considered when exploring the correlations between pharmacokinetics and pharmacodynamics.

Predicting toxicities for patients with advanced gastrointestinal stromal tumours treated with imatinib: A study of the European Organisation for Research and Treatment of Cancer, the Italian Sarcoma Group, and the Australasian Gastro-Intestinal Trials Group (EORTC–ISG–AGITG)

The aim of this study was to identify prognostic factors for toxicity to treatment with imatinib. The study was based on 942 patients with gastrointestinal stromal tumours (GIST) randomised to receive imatinib at different doses. The correlation between toxicities occurring with a Common Toxicity Criteria (CTC) grade 2 or more (non-haematological) or grade 3 or 4 (haematological) and imatinib dose, age, sex, performance status, original disease site, site and size of lesions at trial entry, baseline haematological and biological parameters was investigated. Anaemia was correlated with dose and baseline haemoglobin level, and neutropaenia with baseline neutrophil count and haemoglobin level. The risk of non-haematological toxicities was dose dependent and higher in females (oedema, nausea, diarrhoea), and in patients of advanced age (oedema, rash fatigue), poor performance status (fatigue and nausea), prior chemotherapy (fatigue), tumour of identified gastrointestinal origin (diarrhoea) and small lesions (rash). A multivariate risk calculator that can be used in the clinic for individual patients is proposed.

Gastrointestinal stromal tumor (GIST)

Gastrointestinal stromal tumors (GISTs) may be defined as morphologically spindle cell, epithelioid, or occasionally pleomorphic mesenchymal tumours of the gastrointestinal tract that usually express the KIT protein and harbour mutation of a gene that encodes for a type III receptor tyrosine kinase (either KIT or PDGFRA). In Caucasian populations their annual incidence is 10 to 15 cases per million. Approximately 80% of GISTs have mutated KIT and 5% mutated PDGFRA. Most KIT mutations occur in untreated GISTs in the juxtamembrane exon 11 and only rarely in the kinase domain, whereas in imatinib-treated patients secondary mutations are frequent in exons encoding for the ATP/imatinib binding pocket or the kinase activation loop. Surgery is the standard treatment of local GIST. Tyrosine kinase inhibitor imatinib is the standard treatment for metastatic disease with few exceptions. A majority (80-90%) of patients with metastatic disease respond to imatinib or achieve durable tumour growth stabilisation with continuous therapy using a daily dose of 400 mg to 600 mg. Treatment with imatinib increases survival of patients with advanced disease with a few years and is associated with only moderate toxicity. Imatinib is being evaluated as adjuvant treatment following surgery, and other tyrosine kinase inhibitors as treatments of advanced GIST.

Phase II study of imatinib mesylate plus hydroxyurea in adults with recurrent glioblastoma multiforme

PURPOSE

We performed a phase II study to evaluate the combination of imatinib mesylate, an adenosine triphosphate mimetic, tyrosine kinase inhibitor, plus hydroxyurea, a ribonucleotide reductase inhibitor, in patients with recurrent glioblastoma multiforme (GBM).

PATIENTS AND METHODS

Patients with GBM at any recurrence received imatinib mesylate plus hydroxyurea (500 mg twice a day) orally on a continuous, daily schedule. The imatinib mesylate dose was 500 mg twice a day for patients on enzyme-inducing antiepileptic drugs (EIAEDs) and 400 mg once a day for those not on EIAEDs. Assessments were performed every 28 days. The primary end point was 6-month progression-free survival (PFS).

RESULTS

Thirty-three patients enrolled with progressive disease after prior radiotherapy and at least temozolomide-based chemotherapy. With a median follow-up of 58 weeks, 27% of patients were progression-free at 6 months, and the median PFS was 14.4 weeks. Three patients (9%) achieved radiographic response, and 14 (42%) achieved stable disease. Cox regression analysis identified concurrent EIAED use and no more than one prior progression as independent positive prognostic factors of PFS. The most common toxicities included grade 3 neutropenia (16%), thrombocytopenia (6%), and edema (6%). There were no grade 4 or 5 events. Concurrent EIAED use lowered imatinib mesylate exposure. Imatinib mesylate clearance was decreased at day 28 compared with day 1 in all patients, suggesting an effect of hydroxyurea.

CONCLUSION

Imatinib mesylate plus hydroxyurea is well tolerated and associated with durable antitumor activity in some patients with recurrent GBM.

Clinical factors affecting acquired resistance to gefitinib in previously treated Japanese patients with advanced nonsmall cell lung cancer

BACKGROUND

The risk factors for the development of acquired resistance in nonsmall cell lung cancer (NSCLC) patients responding to gefitinib are unclear. The current study assessed clinicopathologic factors affecting acquired resistance to gefitinib in previously treated patients with advanced NSCLC.

METHODS

Between 2000 and 2004, 197 consecutive Japanese patients with advanced NSCLC underwent treatment with gefitinib. Of these patients, 56 who had continued gefitinib treatment without disease progression for at least 6 months were included in the study.

RESULTS

At a median follow-up time of 21.6 months (range, 7.7-59.7 months), the median time to disease progression was 19.5 months, with progression-free survival rates of 68.5% at 1 year, 33.6% at 2 years, and 21.2% at 3 years. In a multivariate analysis using a Cox regression model, baseline brain metastasis was the strongest prognostic factor affecting acquired resistance to gefitinib (hazards ratio, 2.14; 95% confidence interval, 1.10- 4.17 [P = .025]). In addition, a decreased baseline hemoglobin level (P = .074) and the administration of >1 chemotherapy regimen before gefitinib treatment (P = .069) tended to be significant negative prognostic factors.

CONCLUSIONS

In patients undergoing treatment with gefitinib, the presence of brain metastasis was strongly associated with the emergence of acquired resistance in the current series of NSCLC patients. The finding requires confirmation in a large cohort of patients with advanced NSCLC, including a non-Japanese/Asian population.

Outcome of patients with advanced gastro-intestinal stromal tumours crossing over to a daily imatinib dose of 800 mg after progression on 400 mg

In the EORTC-ISG-AGITG trial 946 patients with advanced gastro-intestinal stromal tumours (GIST) were randomised to receive 400 or 800 mg of imatinib daily. An increase in progression free survival (PFS) was demonstrated for patients randomised to the high-dose arm. Patients randomised to low-dose could cross-over to high-dose upon progression. We evaluated the feasibility, safety and efficacy of this policy. Of the 241 patients available for follow-up, 133 patients (55%) crossed over to high-dose imatinib according to the protocol. Of these patients, 92% had not had a prior dose reduction. The cumulative incidence of subsequent dose reductions after cross-over was 17% after six months with 51% discontinuing therapy without requiring a dose reduction. The extent of anaemia and fatigue increased significantly after cross-over, whilst neutropenia was less severe than during low-dose treatment. Objective responses after cross-over included three patients (2%) with a partial response and 36 (27%) with stable disease. The median PFS after cross-over was 81 days, although 18.1% of patients were still alive and progression free one year after cross-over. We conclude that a cross-over to high-dose imatinib is feasible and safe in GIST patients who progress on low-dose therapy.

Population pharmacokinetics of imatinib mesylate in patients with chronic-phase chronic myeloid leukaemia: results of a phase III study

AIMS

This study was designed to investigate the biochemical and physiological covariates or comedications that affect the pharmacokinetics of imatinib mesylate in patients with chronic-phase chronic myeloid leukaemia (CP CML).

METHODS

Pharmacokinetic data were analyzed in 371 patients receiving 400 mg imatinib once daily during a phase III trial of imatinib vs interferon-alfa plus cytarabine for the treatment of newly diagnosed CP CML. Covariates included age, weight, sex, ethnicity, haemoglobin (Hb) concentration, white blood cell (WBC) count, liver function, and creatinine concentration. Blood samples for imatinib analysis were taken on treatment days 1 and 29. Nonlinear mixed effects modelling was used for the population pharmacokinetic analysis.

RESULTS

Population mean estimates (95% confidence interval) at day 1 for apparent clearance (CL) and apparent volume of distribution (V) of imatinib were 14 (13-15) l h(-1) and 252 (237-267) l, respectively. Modelling suggested that CL decreased by 4 (3-5) l h(-1) from day 1 to day 29, whereas V remained unchanged. Interindividual variability in CL and V was 32% and 31%, respectively. Weight, Hb, and WBC count demonstrated small effects on CL and V. Doubling body weight or Hb or halving the WBC count was associated with a 12%, 86% and 8% increase in CL, respectively, and a 32%, 60% and 5% increase in V, respectively. Comedications showed no clear effects on imatinib CL.

CONCLUSIONS

Population covariates and coadministered drugs minimally affected imatinib pharmacokinetics in newly diagnosed CP CML patients.

Initial and late resistance to imatinib in advanced gastrointestinal stromal tumors are predicted by different prognostic factors: a European Organisation for Research and Treatment of Cancer-Italian Sarcoma Group-Australasian Gastrointestinal Trials Group study

PURPOSE

The aim of this study was to identify factors predicting initial and late resistance of GI stromal tumor (GIST) patients to imatinib and to document the dose-response relationship in the prognostic subgroups. This study is based on the European Organisation for Research and Treatment of Cancer-Italian Sarcoma Group-Australasian Gastrointestinal Trials Group randomized trial comparing two doses of imatinib in advanced disease.

PATIENTS AND METHODS

Initial resistance was defined as progression within 3 months of randomization, and late resistance was defined as progression beyond 3 months. Investigated cofactors include imatinib dose, age, sex, performance status, original disease site, site and size of lesions at trial entry, and baseline hematologic and biologic parameters.

RESULTS

Initial resistance was recorded for 116 (12%) of 934 assessable patients and was independently predicted by the presence of lung and absence of liver metastases, low hemoglobin level, and high granulocyte count. Among 818 patients who were alive and progression free at 3 months, 347 subsequent progressions were recorded, and late resistance was independently predicted by high baseline granulocyte count, primary tumor outside of the stomach, large tumor size, and low initial imatinib dose. The impact of initial dose on late resistance was mainly significant in patients with a high baseline granulocyte count (> 5.10(9)/L) and in patients with tumors of GI origin outside of the stomach and small intestine.

CONCLUSION

Our study identifies patients for whom initial and/or long-term treatment needs to be improved and patients who require a high initial dose. Correlation of these results with immunohistochemistry and molecular parameters may further help to understand the biologic mechanisms of resistance.