ALBERT

Description: Janus kinases (JAK) are tyrosine kinases associated with both cytokine receptors and downstream signal transducer and activator of transcription (Stat) proteins. Upon activation of JAK by a variety of cytokines and growth factors, Stats translocate to the nucleus and promote transcription of target genes. Constitutive activation of Stat proteins in AML has been associated with poor prognosis and AG490, an inhibitor of this pathway, was shown to suppress AML cell proliferation in vitro. WP-1066 represents a further development of AG490 with biological activity at significantly lower concentrations. Therefore, we studied the effects of WP-1066 on the AML cell lines OCIM2 and K562 and on fresh bone marrow aspirates obtained from five newly diagnosed AML patients. We found that WP-1066 inhibited the proliferation of OCIM2 and K562 cells and of fresh marrow AML blast colony-forming cells in a dose-dependent fashion at concentrations ranging from 0.5 to 3 μM. WP-1066 completely abrogated the growth of leukemia cells at a concentration of 3 μM. Furthermore, WP-1066 induced a cell cycle arrest of OCIM2 and K562 cells. Incubation of AML cells with 2 μM of WP-1066 resulted in a time-dependent accumulation of OCIM2 and K562 cells in the sub-G0 phase of the cell cycle. Those leukemia cells underwent apoptotic cell death as assessed by annexin V-FITC. Incubation of OCIM2 cells with 0.5 to 3 μM WP-1066 for 2 hours induced a dose-dependent apoptosis in 52% of the cells. A 4 hour exposure of either OCIM2 or K562 cells to 2 μM of WP-1066 induced caspase 3 activation and PARP cleavage. As expected, WP-1066 inhibited Stat3 and Stat5 phosphorylation in K562 and OCIM2 cells both in a time- and dose-dependent manner, confirming that inhibition of the JAK-Stat pathway is its mechanism of action. Overall, our data showing that WP-1066 inhibits the JAK-Stat pathway, suppresses proliferation, induces cell cycle arrest and apoptosis of AML cells, suggest that the activity of this compound warrants further exploitation aimed at developing WP-1066 for future therapy of AML.