Dasatinib (BMS-354825) inhibits Stat5 signaling associated with apoptosis in chronic myelogenous leukemia cells

Abstract

Dasatinib (BMS-354825) is a novel, oral, potent, multitargeted kinase inhibitor of Bcr-Abl and Src family kinases (SFK) and is a promising cancer therapeutic agent. Preclinical data indicate that dasatinib is 325-fold more potent than imatinib against cells expressing wild-type Bcr-Abl, and that dasatinib is active against 18 of 19 Bcr-Abl mutations known to cause imatinib resistance. Phase I clinical data show that dasatinib is well tolerated and highly effective for the treatment of imatinib-resistant/ imatinib-intolerant chronic myelogenous leukemia (CML) and Philadelphia chromosome -positive acute lymphoblastic leukemia. However, the molecular mechanism of action of dasatinib is not fully understood. In this study, we confirm that dasatinib inhibits tyrosine phosphorylation of SFKs, including Src, Hck, and Lyn, in K562 human CML cells. Significantly, downstream signal transducer and activator of transcription 5 (Stat5) signaling is also blocked by dasatinib as shown by decreases in levels of phosphorylated Stat5 and Stat5 DNA-binding activities. In addition, dasatinib down-regulates expression of Stat5 target genes, including Bcl-x, Mcl-1, and cyclin D1. Consistent with these results, blockade of Stat5 signaling by dasatinib is accompanied by inhibition of cell proliferation and induction of apoptosis. Surprisingly, Stat5 DNA-binding activities are enhanced with increasing cell density, which is associated with resistance to apoptosis by dasatinib. Our findings indicate that inhibition of Stat5 signaling downstream of Bcr-Abl/SFKs contributes to the action of dasatinib, and, conversely, that increasing cell density up-regulates Stat5 activation and confers resistance to dasatinib. Moreover, the level of phosphorylated Stat5 in CML cells represents a mechanistically relevant biomarker for monitoring inhibition of Bcr-Abl signaling by dasatinib in CML patients using convenient immunocytochemical assays.

BCR-ABL mutants spread resistance to non-mutated cells through a paracrine mechanism

“…13 Reduction of MCL1, BCL2 and BCL-xL has been observed in some studies but not in others. [31][32][33][34] Our data confirm the essential role of Bim, and also indicate a possible role for MCL1, BCL-xL, Bad and Bax. We observed that apoptosis of resistant cells, induced through JAK2 blocking, was characterized by overexpression of Bim, while MEK1/2 blocking had little effect.…”

Bcr-Abl induces autocrine IGF-1 signaling

“…Dasatinib, a multi-targeted inhibitor of Bcr-Abl and Src kinases, shows activity in imatinib resistant or intolerant CML in accelerated phase (Guilhot et al, 2007). Dasatinib inhibits tyrosine phosphorylation of Src kinases Src, Hck and Lyn and decreases Stat5 phosphorylation in K562 cells (Nam et al, 2007). The most compelling evidence for the role of Src kinases in CML is their involvement in the transformation of CP CML to lymphoid BC (Hu et al, 2006).…”

Lyn Kinase-Dependent Regulation of miR181 and Myeloid Cell Leukemia-1 Expression: Implications for Drug Resistance in Myelogenous Leukemia

“…Lyn kinase (Lyn) has been implicated in imatinib resistance in both CML cells and patient samples. Overexpression of Lyn, the most abundant SFK in hematopoietic cells, may contribute to drug resistance through increased signal transducer and activator of transcription 5 phosphorylation, Bcl-2 expression, and other prosurvival responses (Donato et al, 2003;Dai et al, 2004;Nam et al, 2007). Inhibition of Lyn with SFK inhibitors reduced prosurvival signaling and reversed imatinib resistance in CML cells (Ito et al, 2007;Nam et al, 2007).…”