Tirapazamine Plus Cyclophosphamide in Treating Children With Refractory Solid Tumors

OBJECTIVES: I. Determine the maximum tolerated dose and the dose limiting toxicity of tirapazamine when administered with cyclophosphamide as intravenous infusions to children with refractory solid tumors. II. Determine the incidence and severity of other toxicities of tirapazamine and cyclophosphamide in these patients. III. Determine a safe and tolerable dose of tirapazamine administered with cyclophosphamide for a phase II study for the same indications. IV. Determine the pharmacokinetics of tirapazamine in children and adolescents receiving the combination of tirapazamine and cyclophosphamide. V. Determine the preliminary evidence of antitumor activity of tirapazamine and cyclophosphamide. OUTLINE: This is a dose escalation study. Patients receive tirapazamine by 2 hour intravenous infusion (hours 0-2) followed 2 hours later by a 30 minute intravenous infusion of cyclophosphamide. This course is repeated every 3 weeks in patients with partial/complete response or stable disease for a maximum of 1 year. Cohorts of 3-6 patients each are treated at each dose level of tirapazamine. Dose escalation of tirapazamine occurs when 0 of 3 patients or 1 of 6 patients has experienced dose limiting toxicity (DLT). If DLT is experienced in 1 of 3 patients at a given dose level, up to 3 additional patients are treated at that same dose level. If none of the 3 additional patients at that dose level experiences DLT, the dose is escalated. If DLT is experienced in 1 or more of the additional 3 patients, the maximum tolerated dose (MTD) has been exceeded and 3 patients are treated at the next lower dose level (defined as the MTD). A total of six patients are treated at the MTD. If DLT is proved to be neutropenia, patients must then also meet the additional eligibility criteria listed for stratum 2. If neutropenia continues to be the DLT in stratum 2, then additional patients receive subcutaneous filgrastim (granulocyte colony-stimulating factor; G-CSF) beginning 24 hours after cyclophosphamide. A second MTD may be determined for chemotherapy with G-CSF. Patients are followed every 6 months for 4 years, and then annually thereafter.