Imatinib (Im), a rationally designed inhibitor of the Bcr/Abl kinase as well as other kinases, represents the standard treatment for Bcr/Abl+ malignancies. Im as a single agent, however, is not curative. Flavopiridol (Fl), an investigational cyclin dependent kinase inhibitor, is broadly active in vitro against human leukemia cells (

Blood
91
:
2482
,
1998
). Previously we have shown that simultaneous disruption of a survival signaling pathway and a cell cycle regulatory pathway results in a pronounced increase in leukemic cell death (
Cancer Res.
61
:
5106
,
2001
) and in more recent preclinical studies demonstrated synergistic interactions between Im and Fl in Bcr/Abl+ leukemia cells, including some that were resistant to Im (
Clin Cancer Res
8
;
2976
,
2002
). Based on these considerations, we have initiated a phase I trial to identify appropriate doses of Im+Fl for further investigation. Eligible patients (pts) have CML with a suboptimal response to prior Im, CML in blast crisis, or Bcr/Abl+ acute lymphocytic leukemia (ALL). CML-BC and ALL patients may be Im-naïve. Pts receive Im by continuous daily oral dosing and Fl by 1 hour intravenous infusion weekly x 3 repeated every 4 weeks. Targeted dose levels are (Fl/Im; mg/m2): 30/400, 30/600, 45/600, 60/600, 60/800, 60/1000. Patients are divided into 2 strata based upon blast percentage in peripheral blood or bone marrow: stratum 1, <15%; and stratum 2, ≥15%. For stratum 1 dose limiting toxicity (DLT) is defined as NCI CTCAE grade 4 ANC/platelet for > 1 week or grade ≥ 3 non-heme toxicity; for stratum 2, DLT is profound marrow hypoplasia in the absence of persistent leukemia. In stratum 1, 16 pts have been treated at 4 dose levels; in stratum 2, 5 pts in the 1st and 3rd dose level. In stratum 1, 1 DLT has occurred at dose level 4 (cholecystitis requiring cholecystectomy); in stratum 2, 1 DLT has occurred at dose level 3 (sepsis/multi-organ failure which was not clearly related to treatment). The only frequent toxicities have been hematological. 4 pts have experienced objective responses including complete hematological remissions in 2 pts in stratum 1 treated with Im/Fl 30/600 who had been previously treated with Im 800 and complete hematological remissions in 2 pts in stratum 2 (who had not received prior Im). Preliminary studies indicate no Fl impact upon Im pharmacokinetics, and variable post-treatment effects on signaling pathways in CML cells. These findings indicate that a regimen consisting of Fl and Im is tolerable and active in at least some patients with Bcr/Abl+ hematologic malignancies, including some with Im-resistant disease. Pending identification of the MTD and the recommended Phase II dose (RPTD), Phase II trials will be necessary to assess the activity of this strategy more definitively.

Topics:
flavopiridol, hematologic neoplasms, imatinib mesylate, brachial plexus neuritis, cancer, leukemia, toxic effect, disease remission, phosphotransferases, acute lymphocytic leukemia

Author notes

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2005, The American Society of Hematology
2005
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