Inhibiting synergy with both chlorambucil and fludarabine in inducing apoptosis of CLL cells

Inhibiting synergy with both chlorambucil and fludarabine in inducing apoptosis of CLL cells in vitro , dasatinib has been shown to chemosensitize CLL cells to fludarabine when cocultured with stromal cells alone , or following coculture with stromal cells expressing CD154 . We sought to compare the ability of dasatinib to and its’ inhibition with the Syk inhibitor R406 induced apoptosis of Vascular Disrupting Agent DLBCL cell lines. Of note, recent studies in DLBCL cell lines have also shown dasatinib sensitivity to correlate with the inhibition of BCR signal transduction . Yang et al demonstrated dasatinib to inhibit Srcfamily kinase activity in all cell lines assessed, however apoptosis correlated with the level of inhibition of both Syk and phospholipase Cc2 phosphorylation .
That Lyn is overexpressed Rapamycin in CLL, and related to increased global tyrosine phosphorylation and survival of CLL cells , suggests that exaggerated tonic BCR signalling may also be an important survival mechanism for CLL cells. Moreover, a number of groups have recently shown Syk to be overexpressed in CLL , and constitutively phosphorylated on activating tyrosines . We demonstrated appreciable SykY348 phosphorylation in the absence of BCR stimulation in CLL cells, which was significantly inhibited by dasatinib, resulting in apoptosis. Furthermore, we observed a significant negative correlation between the basal level of SykY348 phosphorylation and the sensitivity of individual patient samples to dasatinib, and established that dasatinib rarely completely inhibited SykY348 phosphorylation in vitro.
Our results are supported by a recent study which found that the apoptotic response unicellular of CLL cells to dasatinib correlated with the activities of both Syk and PLCc2 , suggesting their potential clinical utility as biomarkers of response. Song et al concluded that Syk inhibitors may have more therapeutic potential than dasatinib in CLL. However, as the level of apoptosis observed with small molecule Syk inhibitors in CLL cells in vitro positively correlated with Syk expression, with CLL samples expressing low levels of Syk demonstrating little apoptosis on treatment with Syk inhibitors , it is reasonable to suggest that separate subgroups of CLL patients may particularly benefit from each class of kinase inhibitor. As CLL cells have geneexpression patterns of antigenexperienced B lymphocytes , blockade of antigeninduced signalling is also desirable.
Dasatinib has previously been reported to inhibit BCR signalling following ligation of surface IgM and IgG in primary DLBCL cells . We show that dasatinib also inhibits key downstream signalling events following BCR crosslinking in CLL cells, including calcium mobilization, PI3K and MAPK activation. As dasatinib targets other Src kinases and Btk, in addition to Lyn and cabl , it is possible that these effects contribute to signal inhibition. The physiological significance of these data is underscored by the ability of dasatinib to block Mcl1 upregulation through an Aktmediated pathway , and the corresponding increase in CLL cell viability on prolonged IgM stimulation in vitro. In contrast to Hallaert et al , we found dasatinib to have no inhibitory effect on Mcl1 and BclxL expression in the CD154L IL4 system. Although the level of CD154 expression.