The thrombolytic activity of tPA is regulated by specific inhibitors of activated platelets

This difference might translate into a low diagnostic sensitivity for residual TKI activity in vitro, if CRKLphosphorylation is used as a sole test for BCR-ABL tyrosine kinase activity. The apparent contradiction in our finding, that BCR-ABL phosphorylation does not correlate with BCR-ABL substrate phosphorylation is supported by recent publications. While BCR-ABL has been shown to play a crucial role for leukemic transformation capacity of BCR-ABL, kinase activity of BCR-ABL and downstream signaling is mainly regulated by BCR-ABL -phosphorylation. Along this line, a recent paper purchase 220551-92-8 demonstrated that BCR-ABL is phosphorylated by JAK2, and not by ABL. It has been Darapladib proposed that BCR-ABL -phosphorylation provides finetuning of BCR-ABL downstream signaling rather than switching BCR-ABL signaling on and off. In our hands, STAT5 is a useful surrogate parameter to monitor immediate effects of BCRABL kinase activity as its phosphorylation positively correlates with cell survival. Moreover, it has been demonstrated that STAT5 signaling is indispensable for initiation and maintenance of BCR-ABL mediated leukemic transformation.. Results obtained by employing successive rounds of drug washout suggested prolonged intracellular TKI exposure to be the critical mechanism involved in induction of apoptosis upon HDTKI pulse-treatment. Dose-dependent intracellular accumulation of TKI upon imatinib exposure has already been reported previously. Along this line, we hypothesized that pronounced intracellular TKI-accumulation might be responsible for the observed results. Indeed, measurements of intracellular imatinib and dasatinib uncovered remarkable intracellular TKI accumulation upon HD-TKI pulse-exposure. Moreover, intracellular TKI accumulation is characterized by a slow time-dependent decrease in intracellular TKI levels upon drug wash-out. This was paralleled by a time-dependent increase of TKI concentrations in extracellular media upon washing and re-plating of cells, indicating release of TKI from an intracellular compartment into the cell culture media. Consistent with this, we demonstrated that HD-TKI pulse-exposure with imatinib was ineffective at inducing apoptosis in cells expressing the ABC-family transporters ABCB1 or ABC