Phase i dose escalation and pharmacokinetic study of oral gefitinib and irinotecan in children with refractory solid tumors

Purpose: This phase I study endeavored to estimate the maximum tolerated dose and describe the dose-limiting toxicities (DLTs) of oral irinotecan with gefitinib in children with refractory solid tumors. Methods: Oral irinotecan was administered on days 1-5 and 8-12 with oral gefitinib (fixed dose, 150 mg/m²/day) on days 1-12 of a 21-day course. The escalation with overdose control method guided irinotecan dose escalation (7 dose levels, range 5-40 mg/m²/day). Results: Sixteen of 19 patients were evaluable, with serial pharmacokinetic studies in ten patients. Diagnoses included osteosarcoma (N = 5), neuroblastoma (N = 3), sarcoma (N = 3), and others (N = 5). Patients received a median of two courses (range 1-20), with at least two patients treated on dose levels 2-7. Three patients had five DLTs; the most common being metabolic (hypokalemia, N = 2 and hypophosphatemia, N = 1) at dose levels two (10 mg/m²) and four (20 mg/m²). One patient experienced grade 3 diarrhea (40 mg/m²). Irinotecan bioavailability was 2.5-fold higher when co-administered with gefitinib, while the conversion rate of irinotecan to SN-38 lactone was unaffected. The study closed due to poor accrual before evaluation of the next recommended irinotecan dose level (35 mg/m²). Of 11 patients receiving at least two courses of therapy, three had stable disease lasting two to four courses and one patient maintained a complete response through 18 courses. Conclusions: The combination of oral gefitinib and irinotecan has acceptable toxicity and anti-tumor activity in pediatric patients with refractory solid tumors. Pharmacokinetic analysis confirms that co-administration of gefitinib increases irinotecan bioavailability leading to an increased SN-38 lactone systemic exposure.