PS1173 PROTEIN CASEIN KINASE 2 IS INVOLVED IN CHRONIC MYELOID LEUKEMIA RESISTANCE TO IMATINIB AND ALSO TO DASATINIB

Abstract

Background:Protein casein kinase 2 (CK2) is a Ser/Thr kinase, which is ubiquitously expressed in eukaryotic cells. It phosphorylates a broad number of proteins, regulates a number of key signaling pathways and promotes cell proliferation and survival. Although CK2 does not belong to the “oncogenic kinases”, it is overexpressed in many solid tumours and also in hematological malignancies. Previous results by Donella‐Deana et al. indicated CK2 association with resistance to imatinib in CML cell lines. In our study, we explored the role of CK2 in cell resistance to imatinib as well as to dasatinib, both in CML cell lines and in patient samples.Aims:We aimed 1) to verify the involvement of CK2 kinase in the resistance to imatinib, in cell line model and in patient samples and 2) to investigate possible role of CK2 in the resistance to dasatinib.Methods:Sublines resistant to either 2 nM dasatinib or 2 μM imatinib were derived from established CML cell lines JURL‐MK1, MOLM‐7, and K562. Sensitive and resistant cells were then treated with the CK2 inhibitor CX‐4945, imatinib, or dasatinib, individually or in selected combinations. Alternatively, siRNAs against CK2 subunits were used. Cell viability was determined using Alamar test. Protein levels and phosphorylation were measured using western blots. CK2 activity was assessed through phosphorylation of its substrates [(pS/pT)DXE] and of its natural target, Cdc37. To evaluate the extent of apoptosis, PARP and caspase 3 cleavage was analysed.Results:We have successfully established JURL‐MK1, MOLM‐7 and K562 sublines resistant to either 2 nM dasatinib or 2 μM imatinib. We found increased protein levels of CK2 kinase and increased phosphorylation levels of CK2 substrates in all resistant cells as compared to sensitive cells. All cells were treated with imatinib, dasatinib and CK2 inhibitor CX‐4945 and their combinations. Despite the loss of response to TKIs, the resistant cells remained sensitive to CK2 inhibition. CX‐4945 reduced CK2 substrates phosphorylation and also cell proliferation in both type of resistant cells. It also increased apoptotic indicators (cleaved PARP, caspase 3) and the dead cell fraction. Preliminary results showed a decrease of cell viability and/or apoptosis induction also in primary cells from four patients resistant to imatinib or dasatinib. Leukocytes from healthy donors were not affected by any of the inhibitors tested.Summary/Conclusion:Altogether, our results suggest that CK2 kinase is involved in CML resistance to both imatinib and dasatinib. Further research is necessary to fully understand the role of CK2 in CML and its potential to become a new target of therapy.