Dose and time dependency and specificity of SFK inhibition by dasatinib in CLL cells. Lysates of CLL cells and of prolymphocytic cell lines were analyzed for general tyrosine phosphorylation (pTyr) or specifically for the positive regulatory phosphotyrosine in SFKs (p-Src). Before phosphorylation analysis, freshly prepared purified CLL cells were cultivated either for various times in the presence of 100 nM dasatinib (A) or for 2 or 16 hours in the presence of different concentrations of dasatinib (B). After 2 hours incubation without (−) and with (+) 100 nM dasatinib, cells were analyzed for the activation of specific SFKs by probing immunoprecipitated Lyn or Lck protein for tyrosine phosphorylation (C).