Phase I and pharmacokinetic study of the oral farnesyltransferase inhibitor lonafarnib administered twice daily to pediatric patients with advanced central nervous system tumors using a modified continuous reassessment method: A pediatric brain tumor consortium study

Purpose: A dose-escalation phase I and pharmacokinetic study of the famesyltransferase inhibitor lonafarnib (SCH66336) was conducted in children with recurrent or progressive CNS tumors. Primary objectives were to estimate the maximum-tolerated dose (MTD) and to describe the dose-limiting toxicities (DLTs) and pharmacokinetics of lonafarnib. Farnesylation inhibition of HDJ-2 in peripheral blood was also measured. Patients and Methods: Lonafarnib was administered orally twice daily at dose levels of 70, 90, 115, 150, and 200 mg/m²/dose bid. A modified continual reassessment method (CRM) was used to estimate the MTD based on actual dosages of lonafarnib administered and toxicities observed during the initial 4 weeks of treatment. Results: Fifty-three children with progressive or recurrent brain tumors were enrolled, with a median age of 12.2 years (range, 3.9 to 19.5 years). Dose-limiting pneumonitis or myelosuppression was observed in three of three patients at the 200 mg/m²/dose level. A relatively constant DLT rate at the 70, 90, and 115 mg/m²/dose levels resulted in a recommended phase II dose of 115 mg/m²/dose. Significant diarrhea did not occur with prophylactic loperamide. Both radiographic response (one anaplastic astrocytoma) and stable disease (one medulloblastoma, two high-grade and four low-grade gliomas, one ependymoma, and one sarcoma) were noted, and seven patients remained on treatment for 1 year or longer. Conclusion: Although the estimated MTD by the CRM model was 98.5 mg/m²/dose, because of the relatively constant observed DLT rate at the lower four dose levels, the recommended phase II dose of lonafarnib is 115 mg/m²/dose administered twice daily by mouth with concurrent loperamide.