Comparison of the effects of two kinase inhibitors, sorafenib and dasatinib, on chronic lymphocytic leukemia cells.

BACKGROUND: With sorafenib displaying the highest affinities for Flt3, VEGFR (vascular endothelial growth factor receptor) and Raf and dasatinib for Abl and Src kinases, the profiles of kinases targeted by these inhibitors differ strongly. MATERIALS AND METHODS: Dose-dependent effects of the inhibitors on freshly isolated chronic lymphocytic leukemia (CLL) cells were assessed as increased phosphatidylserine exposure. Inhibition by sorafenib and dasatinib of survival and anti-apoptotic signaling in CLL cells was examined by Western blot analysis. RESULTS: Sorafenib uniformly induced apoptosis in CLL lymphocytes with a concentration inhibiting by 50% (IC50) of 8 mM, whereas the response to dasatinib was heterogeneous with the onset of inhibition at submicromolar concentrations but with IC50 values below 25 mM in only a few samples. At the respective pharmacologically achievable plasma concentrations, the inhibitors showed more efficient apoptosis induction by sorafenib than by dasatinib and less than additive mutual enhancement in combination. Co-culture with the bone marrow stroma cell line HS-5 increased the viability of untreated CLL cells but did not protect from sorafenib-induced apoptosis. CONCLUSIONS: Sorafenib or dasatinib displayed sigmoidal or saturation-type dose-response relationships for apoptosis induction, which were uniform or highly divergent, respectively, among individual CLL samples and therefore might complement each other in their clinical potential for CLL.

The kinase inhibitor dasatinib induces apoptosis in chronic lymphocytic leukemia cells in vitro with preference for a subgroup of patients with unmutated IgVH genes.

Src family kinases (SFKs) were described to be overexpressed in chronic lymphocytic leukemia (CLL). We wished to examine the effects of the Src and Abl kinase inhibitor dasatinib on the intracellular signaling and survival of CLL cells. Dasa-tinib showed a dose- and time-dependent reduction of global tyrosine phosphorylation and of activating phosphotyrosine levels of SFKs. Treatment with 100 nM dasatinib led to decreased levels of the activated, phosphorylated forms of Akt, Erk1/2, and p38, and induced PARP cleavage through caspase activity. In Mec1 and JVM-3 cell lines, dasatinib increased p53 protein levels and inhibited proliferation. In freshly isolated CLL cells, dasatinib reduced the expression of Mcl-1 and Bcl-x(L). Combination of 5 microM dasatinib and fludarabine increased the apoptosis induction of each by approximately 50%. In 15 primary CLL samples, cells with unmutated immunoglobulin variable heavy chain (IgV(H)) genes were more sensitive to dasatinib than those with mutated IgV(H) genes (P = .002). In summary, dasatinib shows potent inhibitory effects on the survival of CLL cells in vitro, most prominently in samples obtained from patients with unfavorable prognostic features.

Erufosine, a novel alkylphosphocholine, induces apoptosis in CLL through a caspase-dependent pathway.

The alkylphosphocholine (APC) erufosine is a synthetic phospholipid analogue with antineoplastic activity. APC are known to interact with lipid metabolism and modulate cellular signaling pathways, particularly the phosphorylation of Akt. Here, in primary CLL cells induction of apoptosis was detected with an IC50 of 22muM whereas healthy donor PBMC were less sensitive towards erufosine. Treatment with erufosine caused dose-dependent cleavage of PARP, co-incubation with caspase inhibitor z-VAD almost completely abrogated the cytotoxic effect of erufosine indicating a caspase-dependent mechanism of erufosine. Erufosine was shown to induce apoptosis in primary CLL cells and merits further investigation regarding therapeutic options in CLL.