su-6656 and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

Src family protein tyrosine kinases play key roles in cell morphology, proliferation, motility, and survival in megakaryocytopoiesis. Six of Src family kinases (Fyn, Lyn, Fgr, Hck, Src and Yes), are present in megakaryocytes (Mks). Src kinases are negative factors of megakaryocytopoiesis induced by thrombopoietin. The inhibitors of Src kinases might be useful as agents inducing maturation of Mks. The experiments with inhibitors of Src kinases used in culture of Mk progenitors and potential megakaryocyte cell lines gave new information about the role of Src kinases in the development of Mks. The pyrrolo-pyrimidyne reagents family and highly selective inhibitor, SU6656, are known and used inhibitors of Src kinases. The presence of inhibitor in ex vivo culture of Mk progenitors blocks proliferation and simultaneously induces the changes in cell morphology, phenotype and ploidy level, indicating the maturation of the cells. The inhibitors of Src kinases also might play the therapeutic role. Dasatinib, dual Bcr-Abl/Src kinase inhibitor, is of high activity and induces hematologic and cytogenetic responses in patients with chronic myelogenous leukaemia in blast crisis.

Topics: Animals; Cell Proliferation; Humans; Indoles; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Megakaryocyte Progenitor Cells; Megakaryocytes; src-Family Kinases; Sulfonamides; Thrombopoiesis; Thrombopoietin

Once cleaved by caspases, the Lyn tyrosine kinase (LynDeltaN) is relocalized from the plasma membrane to the cytoplasm of apoptotic cells, but the function of such a cleavage is incompletely understood. We evaluated the effect of LynDeltaN overexpression on imatinib sensitivity of the chronic myelogenous leukemia (CML) cell line K562. Therefore, we generated stable cells that express plasmids encoding LynDeltaN or its catalytically inactive counterpart LynDeltaNKD. We established that Lyn is cleaved in imatinib-treated parental K562 cells in a caspase-dependent manner. Lyn cleavage also occurred following BCR-ABL silencing by specific short hairpin RNA (sh-RNA). Imatinib-induced apoptosis was abrogated in LynDeltaN-overexpressing cells, but not in cells overexpressing its inactive counterpart. Conversely, the overexpression of LynDeltaN failed to affect the differentiation of K562 cells. Importantly, the protective effect of LynDeltaN was suppressed by two inhibitors of Lyn activity. LynDeltaN also inhibits imatinib-mediated caspase-3 activation in the small proportion of nilotinib-resistant K562 cells overexpressing Lyn that can engage an apoptotic program upon imatinib stimulation. Finally, Lyn knockdown by sh-RNA altered neither imatinib-mediated apoptosis nor differentiation. Taken together, our data show that the caspase-cleaved form of Lyn exerts a negative feedback on imatinib-mediated CML cell apoptosis that is entirely dependent on its kinase activity and likely on the BCR-ABL pathway.

Topics: Antineoplastic Agents; Apoptosis; Benzamides; Caspase 3; Caspase 9; Caspase Inhibitors; Enzyme Activation; Erythropoiesis; Fusion Proteins, bcr-abl; Humans; Imatinib Mesylate; Indoles; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Neoplasm Proteins; Piperazines; Protein Kinase Inhibitors; Pyrimidines; Recombinant Fusion Proteins; RNA Interference; RNA, Small Interfering; Signal Transduction; src-Family Kinases; Structure-Activity Relationship; Sulfonamides