Using pharmacokinetic and pharmacodynamic data in early decision making regarding drug development: a phase I clinical trial evaluating tyrosine kinase inhibitor, AEE788.

PURPOSE: In this first-in-human study of AEE788, a tyrosine kinase inhibitor of epidermal growth factor receptor (EGFR), HER-2, and VEGFR-2, a comprehensive pharmacodynamic program was implemented in addition to the evaluation of safety, pharmacokinetics, and preliminary efficacy of AEE788 in cancer patients. EXPERIMENTAL DESIGN: Patients with advanced, solid tumors received escalating doses of oral AEE788 once daily. Primary endpoints were to determine dose-limiting toxicities (DLTs) and maximum-tolerated dose (MTD). A nonlinear model (Emax model) was used to describe the relationship between AEE788 exposure and target-pathway modulation in skin and tumor tissues. RESULTS: Overall, 111 patients were treated (25 to 550 mg/day). DLTs included rash and diarrhea; MTD was 450 mg/day. Effects on biomarkers correlated to serum AEE788 concentrations. The concentration at 50% inhibition (IC(50)) for EGFR in skin (0.033 µmol/L) and tumor (0.0125 µmol/L) were similar to IC(50) in vitro suggesting skin may be surrogate tissue for estimating tumor EGFR inhibition. No inhibition of p-MAPK and Ki67 was observed in skin vessels at ≤ MTD. Hence, AEE788 inhibited EGFR, but not VEGFR, at doses ≤ MTD. A total of 16 of 96 evaluable patients showed a >10% shrinkage of tumor size; one partial response was observed. CONCLUSION: Our pharmacodynamic-based study showed effective inhibition of EGFR, but not of VEGFR at tolerable AEE788 doses. Emax modeling integrated with biomarker data effectively guided real-time decision making in the early development of AEE788. Despite clinical activity, target inhibition of only EGFR led to discontinuation of further AEE788 development.

Efficacy and safety of motesanib, an oral inhibitor of VEGF, PDGF, and Kit receptors, in patients with imatinib-resistant gastrointestinal stromal tumors.

PURPOSE: This multicenter phase 2 study assessed the tolerability and efficacy of motesanib, an oral inhibitor of Kit, platelet-derived growth factor receptor (PDGFR), and vascular endothelial growth factor receptors (VEGFR), in patients with imatinib-resistant gastrointestinal stromal tumors (GIST). METHODS: Patients with advanced GIST who failed imatinib mesylate after ≥8 weeks of treatment with ≥600 mg daily received motesanib 125 mg orally once daily continuously for 48 weeks or until unacceptable toxicity or disease progression occurred. The primary endpoint was confirmed objective tumor response per RECIST and independent review. Secondary endpoints included progression-free survival (PFS), time to progression (TTP); objective response by (18)FDG-PET and by changes in tumor size and/or density (Choi criteria); pharmacokinetics and safety. RESULTS: In the patients evaluable for response (N = 102), the objective response rate was 3%; 59% of patients achieved stable disease, with 14% achieving durable stable disease ≥24 weeks; 38% had disease progression. Higher objective response rates were observed per (18)FDG-PET (N = 91) (30%) and Choi criteria (41%). The median PFS was 16 weeks (95% CI = 14-24 weeks); the median TTP was 17 weeks (95% CI = 15-24 weeks). The most common motesanib treatment-related grade 3 adverse events included hypertension (23%), fatigue (9%), and diarrhea (5%). Motesanib did not accumulate with daily dosing. CONCLUSIONS: In this study of patients with imatinib-resistant GIST, motesanib treatment resulted in acceptable tolerability and modest tumor control as evident in the proportion of patients who achieved stable disease and durable stable disease.

Imatinib mesylate in advanced dermatofibrosarcoma protuberans: pooled analysis of two phase II clinical trials.

PURPOSE: Dermatofibrosarcoma protuberans (DFSP) is a dermal sarcoma typically carrying a translocation between chromosomes 17 and 22 that generates functional platelet-derived growth factor B (PDGFB). PATIENTS AND METHODS: Two distinct phase II trials of imatinib (400 to 800 mg daily) in patients with locally advanced or metastatic DFSP were conducted and closed prematurely, one in Europe (European Organisation for Research and Treatment of Cancer [EORTC]) with 14-week progression-free rate as the primary end point and the other in North America (Southwest Oncology Group [SWOG]) with confirmed objective response rate as the primary end point. In the EORTC trial, confirmation of PDGFB rearrangement was required, and surgery was undertaken after 14 weeks if feasible. The SWOG study confirmed t(17;22) after enrollment. RESULTS: Sixteen and eight patients were enrolled onto the EORTC and SWOG trials, respectively. Tumor size ranged from 1.2 to 49 cm. DFSP was located on head/neck, trunk, and limb in seven, 11, and six patients, respectively, and was classic, pigmented, and fibrosarcomatous DFSP in 13, one, and nine patients, respectively. Metastases were present in seven patients (lung involvement was present six patients). Eleven patients (4%) had partial response as best response, and four patients had progressive disease as best response. Median time to progression (TTP) was 1.7 years. Imatinib was stopped in 11 patients because of progression, one patient because of toxicity, and two patients after complete resection of disease. Median overall survival (OS) time has not been reached; 1-year OS rate was 87.5%. CONCLUSION: Imatinib is active in DFSP harboring t(17;22) including fibrosarcomatous DFSP, with objective response rate approaching 50%. Response rates and TTP did not differ between patients taking 400 mg daily versus 400 mg twice a day.

Phase II study of plitidepsin 3-hour infusion every 2 weeks in patients with unresectable advanced medullary thyroid carcinoma.

OBJECTIVES: To evaluate the antitumor response, time-to-event efficacy endpoints and toxicity of plitidepsin (Aplidin) 5 mg/m as a 3-hour intravenous (i.v.) infusion every 2 weeks in patients with unresectable advanced medullary thyroid carcinoma (MTC). METHODS: Sixteen patients with MTC and disease progression or large tumor burden received plitidepsin. Tumor response and time-related parameters were evaluated according to Response Evaluation Criteria in Solid Tumors. Secondary efficacy endpoints were marker response (calcitonin and carcinoembryonic antigen), clinical benefit and quality of life. Safety was assessed using the National Cancer Institute Common Toxicity Criteria. RESULTS: A total of 141 cycles (median, 9 per patient; range, 1-24) were administered. No complete responses or partial responses (PR) were found, and 12 patients had stable disease for >8 weeks. Median follow-up was 15.0 months. Median time to progression was 5.3 months. Median overall survival could not be calculated, but 86.7% and 66.0% of patients were alive at 6 and 12 months. Marker response included 1 unconfirmed PR and 2 stabilizations for calcitonin, and 1 unconfirmed PR and 4 stabilizations for calcitonin and carcinoembryonic antigen. One patient showed clinical benefit. Quality of life scores generally decreased during the study. Most treatment-related adverse events were mild or moderate. Grade 3 lymphopenia was the only severe hematological toxicity found (2 patients). Severe nonhematological toxicities were grade 3 creatine phosphokinase increase (2 patients, with no myalgia or muscular weakness) and transient grade 3 alanine aminotransferase increase (5 patients). CONCLUSIONS: Single-agent plitidepsin given as 3-hour i.v. infusions every 2 weeks was generally well tolerated but showed limited clinical activity in patients with unresectable advanced MTC.

Effect of cigarette smoking on imatinib in patients in the soft tissue and bone sarcoma group of the EORTC.

PURPOSE: Smoking is a potent inducer of cytochrome P450 (CYP) 1A2 and may affect the pharmacokinetics of CYP1A2 metabolized drugs. The effect of smoking on the pharmacokinetics of imatinib, which is metabolized by CYP3A4 and partly by CYP1A2, is unknown. We studied the effect of smoking on imatinib pharmacokinetics, safety, and efficacy. EXPERIMENTAL DESIGN: Imatinib pharmacokinetics, safety, and efficacy was analyzed in 45 patients with gastrointestinal stromal tumors (GIST) or soft-tissue sarcoma included in two European Organisation for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group trials, including 15 smokers and 30 nonsmokers. Apparent oral clearance, distribution volume, elimination half-life, and dose-standardized area under the concentration curve (AUC) were assessed in 34 patients using nonlinear mixed-effect modeling. RESULTS: Mean +/- SD pharmacokinetic variables in smokers (n = 9) versus nonsmokers (n = 25) groups were 9.6 +/- 5.5 versus 9.2 +/- 4.6 L/h (apparent oral clearance), 216.5 +/- 114.3 versus 207.0 +/- 116.9 L (distribution volume), 16.1 +/- 6.0 versus 16.5 +/- 6.0 h (elimination half-life), and 133.6 +/- 71.0 versus 142.3 +/- 84.0 ng h/mL mg area under the concentration curve; P > 0.05. Smokers experienced more grade 2/3 anemia (P = 0.010) and fatigue (P = 0.011) and those with GIST had a significantly shorter overall survival (P = 0.037) and time to progression (P = 0.052). CONCLUSIONS: This retrospective study suggests that the pharmacokinetics of imatinib is not affected by smoking. However, smokers have an increased risk of anemia and fatigue. Smokers with GIST have a shorter overall survival and time to progression.

Clinical impact of trabectedin (ecteinascidin-743) in advanced/metastatic soft tissue sarcoma.

BACKGROUND: Patients with advanced or metastatic non-gastrointestinal stromal tumour soft tissue sarcoma (STS) whose disease progresses during or after chemotherapy with doxorubicin or ifosfamide have few options and very limited life expectancy. In this setting, the DNA and transcription interacting agent trabectedin (ecteinascidin-743), isolated originally from the tunicate Ecteinascidia turbinata, has encouraging activity and is now approved in the European Union. OBJECTIVE: To review evidence for the efficacy of trabectedin in STSs. METHODS: This review includes material known to the authors through preclinical and clinical work with trabectedin, and information from relevant papers and abstracts. RESULTS: Pooled analysis of Phase II studies suggests that around 50% of STS patients, failing conventional chemotherapy, experienced long lasting tumour control (either objective response or stabilization of disease) when treated with trabectedin. Twenty-nine per cent of patients were alive at 2 years, and median overall survival was 10.3 months. Leiomyosarcomas and liposarcomas appear particularly sensitive to the drug. In myxoid and round-cell liposarcomas trabectedin seems exceptionally active. A link between specific translocations underlying this disease and the drug's mechanism of action is being explored. Trabectedin is also active in synovial, ewing sarcoma and other translocation-related STSs. Trabectedin is not cardio- or neurotoxic. The neutropenia and hepatic toxicity that occur are non-cumulative, reversible, and lessened by steroid premedication. The lack of cumulative toxicities could make trabectedin appropriate for prolonged treatment. CONCLUSION: The potential of trabectedin should be further explored in STSs in general and in specific subtypes, both in combination with other cytotoxic agents and with modulators of intracellular signalling.

Phase II, open-label study evaluating the activity of imatinib in treating life-threatening malignancies known to be associated with imatinib-sensitive tyrosine kinases.

PURPOSE: To evaluate the activity of imatinib in treating advanced, life-threatening malignancies expressing one or more imatinib-sensitive tyrosine kinases. EXPERIMENTAL DESIGN: This was a phase II, open-label, single arm study. Patients > or = 15 years old with malignancies showing histologic or molecular evidence of expression/activation of imatinib-sensitive tyrosine kinases were enrolled. Patients were treated with 400 or 800 mg/d imatinib for hematologic malignancy and solid tumors, respectively. Treatment was continued until disease progression or unacceptable toxicity. The primary objective was to identify evidence of imatinib activity with tumor response as the primary end point. RESULTS: One hundred eighty-six patients with 40 different malignancies were enrolled (78.5% solid tumors, 21.5% hematologic malignancies). Confirmed response occurred in 8.9% of solid tumor patients (4 complete, 9 partial) and 27.5% of hematologic malignancy patients (8 complete, 3 partial). Notable activity of imatinib was observed in only five tumor types (aggressive fibromatosis, dermatofibrosarcoma protuberans, hypereosinophilic syndrome, myeloproliferative disorders, and systemic mastocytosis). A total of 106 tumors were screened for activating mutations: five KIT mutations and no platelet-derived growth factor receptor mutations were found. One patient with systemic mastocytosis and a partial response to therapy had a novel imatinib-sensitive KIT mutation (D816T). There was no clear relationship between expression or activation of wild-type imatinib-sensitive tyrosine kinases and clinical response. CONCLUSION: Clinical benefit was largely confined to diseases with known genomic mechanisms of activation of imatinib target kinases. Our results indicate an important role for molecular characterization of tumors to identify patients likely to benefit from imatinib treatment.

A phase II trial of docetaxel (Taxotere) as second-line chemotherapy in patients with metastatic breast cancer.

The efficacy and tolerability of docetaxel 100 mg/m(2) every 3 weeks as second-line chemotherapy in patients with metastatic breast cancer was investigated. In addition, the efficacy of a 3-day prophylaxis against cumulative dose-related fluid retention was examined with methylprednisolone 32 mg twice daily for 3 days starting 12 and 3 h before the docetaxel infusion together with oral cetirizine 10 mg 12 and 3 h before start of docetaxel for prevention of acute hypersensitivity reactions. According to the intent to treat-analysis 35% (95%CI: 25; 46) of the 94 patients entered responded to therapy. Their median survival was 12 months (range 0-20 months). The respective response rate for the 87 patients eligible for response evaluation was 37% (95%CI: 27; 48). Their median duration of response was 8 months (range 3-12 months), their median time to progression was 4 months (range 1-12 months). The corresponding response rate in the eligible patient cohort with anthracycline-resistant disease was 28% (95%CI: 15; 45) and increased to 44% (95%CI: 30; 59) in the cohort with non-anthracycline-resistant disease. Patients with visceral metastases responded in 36% and patients with > or = 3 organs involved in 33%. In a retrospective analysis, the 3-day premedication of corticosteroids and antihistamines proved to be as effective as the established but more toxic 5-day regimen in delaying and preventing the occurrence of docetaxel derived toxicities especially the cumulative fluid retention. In conclusion, docetaxel represents one of the most active agents for second-line treatment of metastatic breast cancer, especially for anthracycline-resistant patients. Due to comparable effectiveness of the 5-day regimen which is widely used by others and the 3-day premedication tested in this trial the latter proved to be more favourable and was therefore recommended for future therapies.

Intra-hepatic Mitomycin C bolus infusion in the treatment of extensive liver metastases of breast cancer.

BACKGROUND: In the treatment of extensive liver metastasis of breast cancer (LMBC), locally administered Mitomycin C (MMC) to the liver might be an effective approach with limited toxicity. PATIENTS AND METHODS: We retrospectively reviewed the records of 30 patients with LMBC treated with intra-hepatic MMC at our institution. MMC (12 mg) was administered by transcatheter bolus infusion into the hepatic arteries every 4 weeks. Tumour response according to RECIST criteria, progression free survival (PFS), overall survival (OS) and duration of response (DR) were used to evaluate efficacy. RESULTS: There was a local response in the liver and a global response in respectively 33 and 26%. The median PFS, DR and OS were 3, 4 and 7 months, respectively. There was more benefit in patients without documented metastases outside the liver and without severe liver dysfunction. Thrombocytopenia, leucocytopenia and an allergic reaction were observed after MMC administration in 20 (67%), 12 (40%) and 4 patients (13%), respectively. CONCLUSION: Intra-hepatic MMC bolus infusion as treatment of extensive LMBC is associated with limited toxicity and has a significant response rate in the liver. Prospective investigations are required to define the place of this modality for treating patients with breast cancer liver metastases.

Imatinib does not induce cardiac left ventricular failure in gastrointestinal stromal tumours patients: analysis of EORTC-ISG-AGITG study 62005.

Recent publications have suggested that imatinib (Glivec) may be cardiotoxic. We have therefore assessed the largest study on the agent performed in patients with gastrointestinal stromal tumours, randomising a daily dose of 400mg versus 800 mg. 946 Patients were entered, 942 patients received at least one dose of imatinib. The median time on treatment was 24 months. A total of 24,574 exposure months could be analysed. We could not identify an excess of cardiac events in the study population. In 2 patients (0.2%) a possible cardiotoxic effect of imatinib could not fully be excluded. The current analysis of a large randomised prospective study could not confirm previous suggestions of imatinib induced cardiac toxicity.

Simultaneous determination of AMN107 and Imatinib (Gleevec, Glivec, STI571) in cultured tumour cells using an isocratic high-performance liquid chromatography procedure with UV detection.

A reversed phase high-performance liquid chromatographic (HPLC) method with UV detection was developed for the simultaneous determination of imatinib (Gleevec, Glivec, STI571) and AMN107 in cultured tumour cells, using clozapine as an internal standard. The compounds of interest were extracted by liquid-liquid extraction using TOXI-TUBES((R)) A extraction tubes. Chromatographic separation was performed on a Phenomenex Gemini C18 reversed phase column (150 mm x 2.0 mm, 5 microm particle size), using a mixture of 65% CH(3)OH (methanol) and 35% NH(4)Ac (Ammonium acetate) buffer (20mM, pH 10). Separation was achieved under isocratic conditions at a flow rate of 0.5 ml/min. Imatinib, clozapine and AMN107 are detected by UV detection at 260 nm. Calibration curves were linear from 50 to 7500 ng/ml with correlation coefficients (r(2)) better than 0.998. The limit of quantitation (LOD) was 50 ng/ml. The method has been successfully applied to a cellular kinetics study.

A phase I and pharmacokinetic study of LAF389 administered to patients with advanced cancer.

LAF389 is a synthetic analogue of bengamide B, a natural product isolated from Jaspidae sponges. LAF389 has both antiproliferative and antiangiogenetic properties, and preclinical investigations showed a broad antitumour activity. This clinical trial aimed to determine the safety and pharmacokinetic profile of LAF389 administered as a slow intravenous injection for 3 consecutive days every 3 weeks in patients with advanced solid tumours. Eight dose levels were tested: 1, 2.5, 5, 10, 15, 30, 25 and 20 mg/day. A total of 33 patients, median age 52 years (range 33-72), with refractory solid tumours were enroled, 19 men and 14 women with a median World Health Organization performance status of 1 (0-4). Seventy-eight cycles of treatment have been administered (mean 2.5, range 1-10). Four cardiovascular dose-limiting toxicities were reported at 30 mg (2/2 patients) and 25 mg (2/9 patients), eight additional patients at various dose levels had (cardio)vascular toxicity, probably drug related, and one patient died owing to pulmonary embolism at the 5 mg dose. No objective responses were recorded. Pharmacokinetic parameters were variable, although linear and without obvious accumulation from cycle I to cycle II. LAF389 dose escalation was terminated owing to occurrence of unpredictable cardiovascular events. This, associated with the lack of clinical activity, did not warrant further investigation of this agent.

Docetaxel and gemcitabine combination therapy in advanced transitional cell carcinoma of the urothelium: results of a phase II and pharmacologic study.

Our objective was to determine the response to gemcitabine plus docetaxel in advanced urothelial transitional cell carcinoma in a phase II trial, and gemcitabine distribution between plasma and erythrocytes, following docetaxel administration. Patients with locally advanced or metastatic transitional cell carcinoma, following a maximum of one prior chemotherapy regimen, were given gemcitabine 800 mg/m on days 1 and 8 plus docetaxel 85 mg/m on day 8, every 21 days. Gemcitabine was measured in the plasma and erythrocytes of nine patients before and after docetaxel administration. Thirty-four patients (median 63 years; range 49-79 years), of whom seven had prior chemotherapy and 27 were chemotherapy-naive, received a median of six cycles (range 1-6). Complete and partial remissions were observed in two and 16 (including three pretreated) patients, respectively, for an overall response rate of 53%. Median response duration was 5 months (range 1-39+). Haematoxicity was manageable, despite grade 3 infections in 24% of patients, but other toxicities were mostly mild. An apparent shift of gemcitabine from plasma to erythrocytes occurred after docetaxel in five of six patients evaluable for this analysis. We conclude gemcitabine plus docetaxel is tolerable and highly active in treated and untreated patients with advanced transitional cell carcinoma.

Efficacy and safety of sunitinib in patients with advanced gastrointestinal stromal tumour after failure of imatinib: a randomised controlled trial.

BACKGROUND: No effective therapeutic options for patients with unresectable imatinib-resistant gastrointestinal stromal tumour are available. We did a randomised, double-blind, placebo-controlled, multicentre, international trial to assess tolerability and anticancer efficacy of sunitinib, a multitargeted tyrosine kinase inhibitor, in patients with advanced gastrointestinal stromal tumour who were resistant to or intolerant of previous treatment with imatinib. METHODS: Blinded sunitinib or placebo was given orally once daily at a 50-mg starting dose in 6-week cycles with 4 weeks on and 2 weeks off treatment. The primary endpoint was time to tumour progression. Intention-to-treat, modified intention-to-treat, and per-protocol analyses were done. This study is registered at ClinicalTrials.gov, number NCT00075218. FINDINGS: 312 patients were randomised in a 2:1 ratio to receive sunitinib (n=207) or placebo (n=105); the trial was unblinded early when a planned interim analysis showed significantly longer time to tumour progression with sunitinib. Median time to tumour progression was 27.3 weeks (95% CI 16.0-32.1) in patients receiving sunitinib and 6.4 weeks (4.4-10.0) in those on placebo (hazard ratio 0.33; p<0.0001). Therapy was reasonably well tolerated; the most common treatment-related adverse events were fatigue, diarrhoea, skin discolouration, and nausea. INTERPRETATION: We noted significant clinical benefit, including disease control and superior survival, with sunitinib compared with placebo in patients with advanced gastrointestinal stromal tumour after failure and discontinuation of imatinab. Tolerability was acceptable.

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.

Association of enzyme and transporter genotypes with the pharmacokinetics of imatinib.

OBJECTIVE: Our objective was to explore the relationships between imatinib pharmacokinetics and 9 allelic variants in 7 genes coding for adenosine triphosphate-binding cassette transporters (ABCB1 and ABCG2) and enzymes (cytochrome P450 [CYP] 2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5) of putative relevance for imatinib. METHODS: Imatinib transport in vitro was studied by use of human embryonic kidney 293 cells transfected with wild-type ABCG2 and an ABCG2 Q141K clone. Steady-state pharmacokinetics of imatinib was obtained in 82 patients with gastrointestinal stromal tumors treated with oral imatinib at doses ranging from 100 to 1000 mg/d. Genotyping was carried out via direct sequencing or restriction fragment length polymorphism-based techniques. RESULTS: Human embryonic kidney 293 cells transfected with ABCG2 Q141K exhibited greater drug accumulation in vitro in comparison with cells expressing wild-type ABCG2 (P = .028). However, pharmacokinetic parameters of imatinib in vivo were not statistically significantly different in 16 patients who were heterozygous for ABCG2 421C>A compared with 66 patients carrying the wild-type sequence (P = .479). The apparent oral clearance of imatinib was potentially reduced in individuals with at least 1 CYP2D6*4 allele (median, 7.78 versus 10.6 L/h; P = .0695). Pharmacokinetic parameters were not related to any of the other multiple-variant genotypes (P >or= .230), possibly because of the low allele frequencies. CONCLUSIONS: This study indicates that common genetic variants in the evaluated genes have only a limited impact on the pharmacokinetics of imatinib. Further investigation is required to quantitatively assess the clinical significance of homozygous variant ABCG2 and CYP2D6 genotypes in patients treated with imatinib.

Everolimus alters imatinib blood partition in favour of the erythrocyte.

The signal transduction inhibitor imatinib is one of the latest breakthroughs in cancer pharmacotherapy. It is administered orally over prolonged periods of time for the treatment of gastro-intestinal stromal tumours. Routine therapeutic drug monitoring of blood plasma versus red blood cells over several years by liquid chromatography coupled tandem mass spectrometry has high-lighted a very intriguing phenomenon. Imatinib plasma availability decreases dramatically owing to a significant shift in the partition ratio of red blood cells versus plasma. The shift is enforced by combination with everolimus, another signal transduction inhibitor. These data warrant routine erythrocyte versus plasma monitoring to prevent unexpected alterations in drug efficacy during long-term treatment.

KIT mutations and dose selection for imatinib in patients with advanced gastrointestinal stromal tumours.

A recent randomized EORTC phase III trial, comparing two doses of imatinib in patients with advanced gastrointestinal stromal tumours (GISTs), reported dose dependency for progression-free survival. The current analysis of that study aimed to assess if tumour mutational status correlates with clinical response to imatinib. Pre-treatment samples of GISTs from 377 patients enrolled in phase III study were analyzed for mutations of KIT or PDGFRA by combination of D-HPLC and direct sequencing of tumour genomic DNA. Mutation types were correlated with patients' survival data. The presence of exon 9-activating mutations in KIT was the strongest adverse prognostic factor for response to imatinib, increasing the relative risk of progression by 171% (P<0.0001) and the relative risk of death by 190% (P<0.0001) when compared with KIT exon 11 mutants. Similarly, the relative risk of progression was increased by 108% (P<0.0001) and the relative risk of death by 76% (P=0.028) in patients without detectable KIT or PDGFRA mutations. In patients whose tumours expressed an exon 9 KIT oncoprotein, treatment with the high-dose regimen resulted in a significantly superior progression-free survival (P=0.0013), with a reduction of the relative risk of 61%. We conclude that tumour genotype is of major prognostic significance for progression-free survival and overall survival in patients treated with imatinib for advanced GISTs. Our findings suggest the need for differential treatment of patients with GISTs, with KIT exon 9 mutant patients benefiting the most from the 800 mg daily dose of the drug.

Efficacy of the kinase inhibitor SU11248 against gastrointestinal stromal tumor mutants refractory to imatinib mesylate.

PURPOSE: The majority of gastrointestinal stromal tumors harbor mutations in the receptor tyrosine kinases KIT or platelet-derived growth factor receptor A (PDGFRA), and respond to treatment with the tyrosine kinase inhibitor imatinib. Some tumors, however, show primary resistance to imatinib treatment, and most others become resistant during treatment. The most common mechanism of imatinib resistance involves specific mutations in the kinase domains of KIT or PDGFRA. We tested the activity of SU11248, an orally active small-molecule tyrosine kinase inhibitor, to inhibit important imatinib-resistant KIT and PDGFRA mutants. EXPERIMENTAL DESIGN: Primary imatinib-resistant tumor cells and cell lines expressing clinically identified imatinib-resistant KIT-V654A, KIT-T670I, or PDGFRA-D842V mutant isoforms were evaluated for sensitivity to SU11248 by Western immunoblotting and proliferation assays. Three patients with the KIT-V654A mutation were treated with SU11248. RESULTS: Based on ex vivo assays, SU11248 potently inhibits KIT kinase activity of V654A and T670I mutants and suppresses proliferation of the cells expressing these mutations. Sensitivity of KIT-V654A and KIT-T670I mutants to SU11248 was confirmed using cell lines expressing these mutants. In contrast, SU11248 did not potently inhibit the PDGFRA-D842V mutant. In agreement with these results, two of the three imatinib-resistant patients with the KIT-V654A mutation responded to SU11248 treatment. CONCLUSIONS: These studies suggest that SU11248 may be a useful therapeutic agent to treat gastrointestinal stromal tumors harboring the imatinib-resistant KIT-V654A or KIT-T670I mutations, but it has no effect on the activity of the PDGFRA-D842V mutant. Specific kinase inhibitors should be designed to inhibit the constitutive activating PDGFRA mutation at codon 842.

Establishment of a mouse gastrointestinal stromal tumour model and evaluation of response to imatinib by small animal positron emission tomography.

BACKGROUND: Gastrointestinal stromal tumours (GIST) predominantly express activating mutations of the KIT tyrosine kinase receptor and are successfully treated with imatinib mesylate, a KIT inhibitor. As resistance to imatinib causes therapy failure, our aim was to develop an in vivo GIST model to evaluate KIT inhibitors and monitor therapy with small animal positron emission tomography (PET). MATERIALS AND METHODS: The first mouse model of GIST xenografts was successfully established by injecting GIST882 cells subcutaneously into nude mice. RESULTS: Using the small animal PET, FDG up-take in xenografts was significantly decreased after 24 h of treatment with imatinib, which correlated with a response to treatment, e.g., with a decrease in tumour volume, the inhibition of KIT and downstream intermediate phosphorylation and arrest of tumour cell proliferation as evaluated after 7 days of treatment. CONCLUSION: This model is useful to study imatinib resistance and to evaluate novel targeted therapies.