Flavopiridol-induced growth inhibition and apoptosis of myeloid and myeloma cell lines and blasts

Survival following the diagnosis of Acute Myeloid Leukemia (AML) or Multiple Myeloma (MM) is among the worst for patients with hematologic malignancies. Recent success with the tyrosine kinase inhibitor ST1571 in Chronic Myeloid Leukemia provides a proof of principle for signal transduction therapy and challenges us to find other kinase inhibitors. Flavopiridol is an inhibitor of cyclin-dependent kinases (CDKʹs), currently in phase II trials for a variety of malignancies. We have studied the effects of Flavopiridol on myeloid cell lines HL-60, 32Dc13, and TF-1 and on myeloma cell lines U-266 and RPMI-8226. The G150 at 48 hr for Flavopiridol was HL-60 <100nM, TF-1 1uM, 32Dc13 100nM, and RPMI-8226 100 nM. We have also studied Flavopiridol effects on fresh leukemic blasts from patients. Growth inhibitory studies on these cells show that treated myeloid blast cells as a % of utreated blasts cells after 48 hr were: 0.02 mg/ml doxorubicin 35±25% 100 nM Flavopiridol 35± 19, 1 uM Flavopiridol 9±9, 10 uM Flavopiridol 6±9, and 100 nM Flavopiridol + 0.02 mg/ml doxorubicin 7±3. PI staining of cell lines showed an increase in the sub-GI region as early as 16 hr after treatment. Cells were stained with Annexin-V confirmed that Flavopiridol-induced apoptosis. Together these data suggest that trials to evaluate Flavopiridol in AML and MM are warranted.