Phase I Study Of The Cyclin-Dependent Kinase Inhibitor Flavopiridol In Combination With Paclitaxel In Patients With Advanced Solid Tumors
PURPOSE: Preclinical studies indicate that the cyclin-dependent kinase inhibitor flavopiridol potentiates the induction of apoptosis by paclitaxel, provided paclitaxel is followed by flavopiridol. We therefore designed a phase I clinical trial of sequential paclitaxel and flavopiridol.
PATIENTS AND METHODS: Paclitaxel was administered at a fixed dose, as either a 24- or 3-hour infusion on day 1, followed by a 24-hour infusion of flavopiridol on day 2. Doses of flavopiridol were escalated in successive cohorts according to a modified Fibonacci design. Flavopiridol pharmacokinetics were obtained on all patients.
RESULTS: Dose-limiting neutropenia developed with 24-hour paclitaxel doses of 135 and 100 mg/m2 and flavopiridol doses of 10 and 20 mg/m2, respectively. With 3-hour paclitaxel at 100 mg/m2, flavopiridol could be escalated to 70 mg/m2 without dose-limiting toxicity. With 3-hour paclitaxel next escalated to 135 mg/m2, dose-limiting neutropenia and pulmonary toxicity occurred when flavopiridol was escalated to 94 mg/m2. This did not correlate with any change in flavopiridol or paclitaxel pharmacokinetics. At a 3-hour paclitaxel dose of 175 mg/m2, dose-limiting pulmonary toxicity occurred in only one patient at flavopiridol doses under 94 mg/m2. Clinical activity was observed in patients with esophagus, lung, and prostate cancer, including patients who had progressed on paclitaxel.
CONCLUSION: The recommended phase II doses will be a 3-hour infusion of paclitaxel at 175 mg/m2 on day 1 followed by a 24-hour infusion of flavopiridol at 70 mg/m2 on day 2. Flavopiridol dose escalations to 80 mg/m2 are possible. At these doses, toxicities are manageable and clinical activity is promising.