Dasatinib Promotes BIM Dependent Apoptosis Via MEK/ERK without Need for Permanent BCR-ABL Inhibition

Abstract 4472

Chronic myeloid leukaemia (CML) is a clonal disorder of haematopoietic stem cells, characterized by constitutively active BCR-ABL kinase. It was previously shown, that transient inhibition of BCR-ABL by tyrosin kinase inhibitor (TKI) dasatinib induces apoptosis in CML cells (Shah 2008). Dasatinib mediated apoptosis is accompanied by increasing expression level of proapoptotic protein BIM and inhibition of its degradation in proteasome.

Our aim is to find alterations in BCR-ABL downstream pathways and changes in BIM expression after pulse (wash-out after 20min) or continuous treatment with TKI dasatinib alone or in combination with proteasome inhibitor bortezomib in K562 cells.

Higher mRNA levels of BIM were confirmed in both transiently and continuously treated (100nM dasatinib) K562 cells compared to low dose continuous (1nM dasatinib) treatment. Western blot analysis of BCR-ABL induced signalling pathways activity revealed, among others, sustained inhibition of MEK/ERK pathway even in the case of re-activation of BCR-ABL after drug wash-out. MEK/ERK inhibition leads to activation of proapoptotic BIM expression and inhibition of its degradation. We used bortezomib, a reversible inhibitor of proteasome, in order to test the block of BIM degradation in dasatinib treated cells. However, we have not found any difference in cell viability caused by adding of 30nM bortezomib to dasatinib treated cells neither in continuous or transient exposure. These findings suggest that equal increase of BIM in the case of pulse and continuous dasatinib treatment is caused by MEK/ERK inhibition in cells with restored BCR-ABL activity.

This project is supported by grants from the Ministry of Education of Czech Republic NPVII (2B06052) and MSM-0021622430. The substance (dasatinib) for this project was supplied by BMS company.