Effects of protein kinase inhibitors on chronic lymphocytic leukemia (CLL) cells

B cell Chronic lymphocytic leukemia (B-CLL) is a neoplastic disorder characterized by accumulation of B lymphocytes due to uncontrolled growth and resistance to apoptosis. Src family kinases (SFKs) are non receptor tyrosine kinases present in the cytosol, which couple with downstream B cell receptor signaling and thus mediate growth, survival, proliferation and antiapoptosis. In CLL cells SFKs are remarkably overexpressed, especially Lyn kinase. This gives the rational to use SFKs inhibitor to treat CLL. Addition of the specific pharmacological inhibitors of SFKs, bosutinib and saracatinib, inhibited the global tyrosine phosphorylation as well as the basal auto-phosphorylation of SFKs. Mechanistically, inhibition of SFKs is coupled to apoptosis induction via decreased protein levels of the anti-apoptotic proteins Bcl-2, Mcl-1 and survivin, which were demonstrated by Western blotting. To assess apoptosis induction, annexin V binding to freshly isolated CLL cells with or without treatment with kinase inhibitors was measured flow cytometrically. Using the inhibitors at a concentration of 10 μM the average percentages of annexin V-positive, apoptotic cells in 11 CLL samples increased from 24 % in untreated controls to 55 %, 45 % and 37 % after treatment with bosutinib, saracatinib and dasatinib, respectively. The response to each of the inhibitors showed a high but comparable degree of variation among the investigated CLL samples. On the average bosutinib induced apoptosis with significantly higher efficiency than dasatinib, which calls for further investigation of its pre-clinical potential for treatment of CLL