The Src-Abl Kinase Inhibitor Dasatinib (BMS-354825) Shows Anti-Proliferative and Anti-Apoptotic Effects in Chronic Lymphocytic Leukemia (CLL) Cells In Vitro.

Introduction: Dasatinib is an ATP competitive, dual-specific Src-Abl kinase inhibitor used for the treatment of imatinib-resistant Bcr-Abl-positive leukemias. Originally it was developed from the aminothiazole scaffold as an inhibitor of Src family kinases (SFKs). Since the aberrant expression and activity of the SFK Lyn seems to enhance the survival of CLL cells, dasatinib is currently tested in clinical studies for CLL. In order to explore the anti-leukemic potential of dasatinib we tested its effects on freshly isolated CLL cells and on CLL cell lines.

Methods and Results: In freshly isolated CLL cells, dasatinib showed a dose and time dependent reduction of global tyrosine phosphorylation which was paralleled by a decreased phosphorylation of the activating tyrosine residue of SFKs. The comparison of the inhibitory effect of several protein tyrosine kinase inhibitors on overall tyrosine phosphorylation in cellular lysates of freshly isolated CLL cells showed that 0.1 μM dasatinib had a more pronounced effect than 5 μM of nilotinib, or 10 μM of PP1 or imatinib. In the CLL cell lines, Mec1 and JVM-3, 0.1 μM of dasatinib appeared to interfere with survival signaling, since decreased levels of the activated phosphorylated forms of Akt, Erk1/2 and p38 were observed after exposure to dasatinib for 2 hours. In these cell lines, dasatinib treatment increased p53 protein levels and induced PARP cleavage and caspase activity. Pro-apoptotic effects of dasatinib were observed by an increase of annexin V-positive cells and a decrease of metabolic activity measured as XTT reduction, alone and in combination with fludarabine. Among six patient samples, two clones were particularly sensitive to dasatinib and fludarabine-resistant. While in these two samples the apoptosis induction by 5 μM dasatinib surpassed that by 5 μM fludarabine, the same dose of the two drugs led to similar apoptosis induction in the fludarabine-sensitive samples. Dasatinib treatment sensitized CLL cells for fludarabine-induced apoptosis. This enhancement of apoptosis induction was more pronounced in fludarabine-resistant patient samples and JVM-3 cells than in Mec1 and fludarabine-sensitive CLL cells.

Conclusion: The Src-Abl kinase inhibitor dasatinib shows potent inhibitory effects on the survival of CLL cells in vitro.