Phase I Dose Escalation Study of Flavopiridol in Combination with Fludarabine and Rituximab: Activity in Indolent B-Cell Lymphoproliferative Disorders and Mantle Cell Lymphoma.
Authors: Lin Thomas S. , Fischer Beth , Moran Mollie E. , Lucas David M. , Shank Roshini S. , Kraut Eric H. , Farag Sheriff S. , Lucas Margaret S. , Colevas Alexander D. , Grever Michael R. , Byrd John C. 
Published: April 2020

Abstract
The cyclin-dependent kinase inhibitor flavopiridol was inactive when administered as a 72-hour infusion, but a 1-hr IV bolus dosing schedule demonstrated clinical activity in mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). Flavopiridol induces apoptosis via a p53-independent mechanism. Thus, we hypothesized that flavopiridol may eliminate tumor cells resistant to fludarabine and rituximab. We report preliminary results of an ongoing phase I dose escalation study of flavopiridol in combination with fludarabine and rituximab in patients (pts) with MCL, CLL and other indolent B-cell lymphoproliferative disorders. Pts had adequate marrow function (ANC ≥ 1500, hemoglobin ≥ 9.0, platelets ≥ 100,000), organ function, and performance status (ECOG 0–2) and provided informed consent. Pts in all cohorts received fludarabine 25 mg/m2 IV on days 1–5 and rituximab 375 mg/m2 on day 1 of each 28-day cycle. The planned dose escalation of flavopiridol was 50 mg/m2 by 1-hr IV bolus on day 1 (cohort 1), days 1–2 (cohort 2), or days 1–3 (cohort 3) of each cycle. Treatment was for up to 6 cycles, and pts were placed on prophylactic Bactrim and Valtrex. Fifteen pts have been enrolled to date, and 9 pts are evaluable for toxicity and response. Median age of these 9 pts was 67 years (range, 43–72), and 4 pts were male. Pts had the following diagnoses: CLL (5), MCL (2) and follicular lymphoma (FL; 2). Four pts had received 1–2 prior therapies; 5 pts were previously untreated. CLL pts had Rai stage III/IV disease (2) or required treatment for Rai stage I/II disease (3) by NCI 96 criteria. MCL/FL pts were stage III/IV (3) or had progressive stage II disease (1). Three pts were treated in cohort 1; 2 pts completed 6 cycles, but 1 pt was removed from study after cycle 3 due to prolonged cytopenias. Six pts were treated in cohort 2. Two pts developed dose-limiting toxicity; 1 pt developed grade 3 confusion and grade 3 generalized seizures during cycle 2, and 1 pt developed nausea and diarrhea, which resulted in grade 3 acute renal failure. Infectious toxicity was limited to 1 pt who was hospitalized for 48 hrs with a grade 3 upper respiratory infection and febrile neutropenia. Three pts in cohort 2 were removed from study for prolonged cytopenias after 3, 3 and 4 cycles; only 1 pt in cohort 2 completed 6 cycles. Two of the 6 pts in cohort 2 did not receive flavopiridol after cycles 2 and 3, due to life threatening tumor lysis in our single agent flavopiridol study. Response was graded by NCI 96 criteria (CLL) or IWG criteria (MCL/FL). Overall response rate (ORR) was 100%; 7 pts (78%) achieved CR, and 2 pts achieved PR (22%). Two pts relapsed after 7 and 8 months; 7 pts remain in remission a median of 9 (range,7–12) months after therapy. Of note, all 4 MCL/FL pts remain in CR. An ongoing expansion of 12 pts at the cohort 1 dose level is being conducted, to better define toxicity and efficacy; 6 pts have been enrolled to date. In conclusion, flavopiridol, fludarabine and rituximab exhibited significant clinical activity in a small group of pts, with a 78% CR rate. This combination warrants further study, particularly with consideration to an altered flavopiridol schedule using our highly active 30-minute bolus followed by 4-hour infusion regimen.