Phase I and pharmacologic study of oral ZD9331, a novel nonpolyglutamated thymidylate synthase inhibitor, in adult patients with solid tumors.

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PURPOSE: To assess the toxicity profile and dose-limiting toxicities (DLTs), to determine the maximum-tolerated dose, and to study the pharmacokinetics of ZD9331 when administered orally to patients with advanced solid tumors. PATIENTS AND METHODS: Patients were treated with oral ZD9331 given once daily (od) or twice daily (bid) for 5, 7, or 10 days; cycles were repeated every 21 days at doses ranging from 2.5 to 40 mg. For pharmacokinetic analysis, plasma sampling was performed during the first course and assayed using a validated liquid chromatographic-tandem mass spectrometry assay. Plasma levels of 2'-deoxyuridine were measured as a surrogate marker for TS inhibition. RESULTS: Forty-two patients received a total of 166 courses. The DLTs were myelosuppression and skin rash. Dose escalation of oral ZD9331 from 2.5 to 40 mg, as a single daily dose, resulted in a less than proportional increase in the plasma area under the concentration-time curve of ZD9331. The plasma drug exposure per cycle for the schedules 20 mg od for 5 days, 10 mg od for 10 days, and 10 mg bid for 5 days, all resulting in a total dose per cycle of 100 mg, were comparable. One partial response was noted in a patient with gastric cancer. CONCLUSION: DLTs in this phase I study of oral ZD9331 were myelosuppression and skin toxicity. The recommended dose for phase II studies of oral ZD9331 is 20 mg od for 5 consecutive days, every 3 weeks.