Phase I clinical and pharmacokinetic study of flavopiridol administered as a daily 1-hour infusion in patients with advanced neoplasms

Purpose: To define the maximum-tolerated dose (MTD), dose-limiting toxicity, and pharmacokinetics of the cyclin-dependent kinase inhibitor flavopiridol administered as a daily 1-hour infusion every 3 weeks. Patients and Methods: Fifty-five patients with advanced neoplasms were treated with flavopiridol at doses of 12, 17, 24, 30, 37.5, and 52.5 mg/m²/d for 5 days; doses of 50 and 62.5 mg/m²/d for 3 days; and doses of 62.5 and 78 mg/m²/d for 1 day. Plasma sampling was performed to characterize the pharmacokinetics of flavopiridol with these schedules. Results: Dose-limiting neutropenia developed at doses ≥ 52.5 mg/m²/d. Nonhematologic toxicities included nausea, vomiting, diarrhea, hypotension, and a proinflammatory syndrome characterized by anorexia, fatigue, fever, and tumor pain. The median peak concentrations of flavopiridol achieved at the MTDs on the 5-day, 3-day, and 1-day schedule were 1.7 μmol/L (range, 1.3 to 4.2 μmol/L), 3.2 μmol/L (range, 1.7 to 4.8 μmol/L), and 3.9 μmol/L (1.8 to 5.1 μmol/L), respectively. Twelve patients had stable disease for ≥ 3 months, with a median duration of 6 months (range, 3 to 11 months). Conclusion: The recommended phase II doses of flavopiridol as a 1-hour infusion are 37.5 mg/m²/d for 5 days, 50 mg/m²/d for 3 days, and 62.5 mg/m²/d for 1 day. Flavopiridol as a daily 1-hour infusion can be safely administered and can achieve concentrations in the micromolar range, sufficient to inhibit cyclin-dependent kinases in preclinical models. Further studies to determine the optimal schedule of flavopiridol as a single agent and in combination with chemotherapeutic agents are underway.