A phase I study of ABT-751, an orally bioavailable tubulin inhibitor, administered daily for 21 days every 28 days in pediatric patients with solid tumors

Purpose: To determine the toxicity profile, close-limiting toxicities (DLT), and maximum tolerated dose (MTD) of ABT-751 administered orally once daily for 21 days, repeated every 28 days in a pediatric population. Experimental Design: Patients who were <= 18 years with relapsed or refractory solid tumors and who were able to swallow capsules were eligible. The starting dose was 75 mg/m(2)/d (n = 3) and was escalated to 100 (n = 6),130 (n = 5), and 165 (n = 3) mg/m(2)/d in cohorts of three to six patients. The MTD was determined from DLTs occurring during the first treatment cycle. Results: Nineteen children (median age, 13 years; range, 5-18 years) were enrolled, and 17 were evaluable for toxicity. Diagnoses included neuroblastoma (n = 9), sarcomas (n = 9), and other solid tumors (n = 1). DLTs included fatigue, sensory neuropathy, transient hypertension, neutropenia, thrombocytopenia, nausea, vomiting, dehydration, abdominal pain, and constipation. The MTD of ABT-751 administered daily for 21 days every 28 days was 100 mg/m(2)/d. Non-DLTat the MTD included bone marrow suppression, gastrointestinal toxicities (anorexia, abdominal pain, nausea, vomiting, and constipation), and sensory and motor neuropathies. The median number of cycles administered was one (range, one to five). Tolerance of repeated treatment cycles was poor. Conclusion: Fatigue, hematologic, and gastrointestinal toxicities limited the tolerability of ABT-751 administered to children on the once daily for 21 days every 28 days schedule. The MTD in children with solid tumors (100 mg/m(2)/d daily for 21 days) was similar to the recommended dose in adults with solid tumors (200 mg fixed dose) receiving the same dosing schedule.