Phase II, open-label study of PTK787/ZK222584 for the treatment of metastatic gastrointestinal stromal tumors resistant to imatinib mesylate

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Abstract
Background: We evaluated safety and efficacy of PTK787/ZK222584 (PTK/ZK), a novel tyrosine kinase inhibitor of KIT, platelet-derived growth factor receptors and vascular endothelial cell growth factor receptors (VEGFRs), in patients with imatinib-resistant gastrointestinal stromal tumor (GIST). This is the first study of PTK/ZK in this population. Patients and methods: Patients with metastatic GIST that had progressed after ≥ 4-week treatment with imatinib mesylate were eligible. Prior VEGFR-2 inhibitor therapy was not permitted. PTK/ZK 1250 mg orally once-daily was administered to 15 patients (accrued as a two-stage procedure), most of whom (n = 11) had been unsuccessfully treated with imatinib 800 mg daily, until treatment failure. Patients were monitored at 4- to 8-week intervals. Results: All 15 patients enrolled were eligible; two (13%) achieved partial response (PR), eight (53%) had stable disease (SD) ≥3 months, and five (33%) progressed. The clinical benefit rate (PR + SD) was 67% (95% CI 38% to 86%). Median time to progression was 8.5 months (range 0.9–24.8+ months). Three patients had not progressed at the time of analysis, including one PR at 24.8 months and two SDs at 16.6 and 18.6 months on treatment. PTK/ZK was generally well tolerated. Conclusion: PTK/ZK 1250 mg p.o. once daily is active and well tolerated in patients with imatinib-resistant GIST.