Flavopiridol Administered as a Pharmacologically-Derived Schedule Demonstrates Marked Clinical Activity in Refractory, Genetically High Risk, Chronic Lymphocytic Leukemia (CLL).
Authors: Byrd John C. , Lin Thomas S. , Dalton James T. , Wu Di , Fischer Beth , Moran Mollie E. , Blum Kristie A. , Shank Roshini S. , Lucas David M. , Lucas Margaret S. , Suarez Jose-Ramon , Grever Michael R. 
Published: October 2019

Flavopiridol is a broad cyclin dependent kinase inhibitor that induces p53/IL4 independent apoptosis in CLL cells. Despite potent pre-clinical activity, phase I/II studies of both a 24 and 72-hour continuous IV (CI) schedule demonstrated no activity in CLL or other cancers. Discordant binding of flavopiridol to human plasma proteins as compared to fetal calf serum prompted us to perform pharmacokinetic modeling from the Aventis-sponsored CI studies. This suggested optimal dosing would be a 30-minute IV bolus followed by 4-hour infusion. We report a mature phase I dose escalation study of flavopiridol with this schedule. We enrolled 23 pts (median age 61, range 44–84, 8 female) previously treated for CLL (median prior therapies 3, range 2–13) . At study entry, 21 pts had no response to their last therapy, 9 had intermediate risk disease, and 14 were stage III/IV. Pts received 50% of the flavopiridol dose IV over 30 minutes, the remaining 50% followed over 4 hours. This was repeated weekly 4 times on a 6-week cycle. Six pts in cohort 1 received 60 mg/m2/dose with 1 dose limiting toxicity (DLT, neutropenic fever) and 3 pts in cohort 2 received 80 mg/m2/dose. The maximally tolerated dose was exceeded in cohort 2. Acute tumor lysis syndrome (TLS) following the first flavopiridol dose was the DLT. One pt developed TLS that was controlled with aggressive medical management. The 2nd pt with TLS died with hyperkalemia before dialysis could be initiated, and on autopsy had extensive apoptosis/necrosis of diffuse intra-abdominal lymphadenopathy. No additional pts were treated at this dose, but a 3rd pt previously without TLS at the 80 mg/m2/dose developed TLS on day 1,cycle 2 at the 60 mg/m2 dose. An inpatient management plan to prevent further life-threatening TLS was initiated. We enrolled 14 additional pts. Several pts developed transient tumor lysis upon initial treatment, with increased serum potassium, phosphate, and LDH, but only 1 pt required temporary dialysis. Other manageable toxicities observed included neutropenia, anemia, thrombocytopenia, fatigue, nausea, diarrhea, and anorexia. Twenty-two patients have been followed long enough for NCI 96 response assessment. Nine pts achieved a PR (41%); 7 pts remain in remission (3–11+ months), and 2 pts relapsed at 7 and 12 months, respectively. Of the 9 responding pts, 8 were fludarabine refractory or intolerant, 8 had bulky LN (> 5cm), and 8 had del(11q) [n=6] or del(17p) [n=3] abnormalities. Additionally, opportunistic infections have not been noted to date. Eight of 9 responding pts with enlarged LN had a 50% reduction with the 1st treatment, compared to 2 of 10 who did not ultimately achieve a PR. The AUC of flavopiridol did not increase proportionally with dose, but pharmacologic data support our hypothesis that the clinical activity and toxicity of flavopiridol may be directly related to the Cmax, AUC, and Css. In summary, single agent flavopiridol given with this novel, pharmacologically modeled schedule has significant clinical activity in pts with fludarabine-refractory, genetically high-risk CLL. Further study of flavopiridol in CLL and other B-cell diseases using this pharmacokinetically modeled schedule is warranted.