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Inhibition of the cell mitotic pathway may provide a novel means for therapeutic intervention in chronic myeloid leukemia (CML). Kinesin spindle protein (KSP), a microtubule-associated motor protein which is essential for cell cycle progression, is overexpressed in bcr-abl+ CML cells. Retrovirus mediated bcr-abl transduction increases KSP expression in cord blood CD34 + cells. SB743921 is a selective KSP inhibitor which is being investigated in ongoing clinical trials for treatment of myeloma, leukemia and solid tumors. Treatment of CML cells with SB743921 resulted in reduced proliferation and colony forming cell (CFC) formation ability. SB743921 also actively blocked cell cycle progression, leading to apoptosis in both primary CML cells and cell lines. KSP inhibition sensitized CML cells to imatinib-induced apoptosis. Importantly, SB743921 inhibited the proliferation of various CML cells including T315I mutation-harboring cells. Furthermore, we demonstrated that SB743921 treatment suppressed ERK and AKT activity in CML cells. These data indicate that SB743921 may become a novel treatment agent for patients with CML. [ABSTRACT FROM AUTHOR]

Abstract: Spreds, a recently established class of negative regulators of the Ras–ERK (extracellular signal-regulated kinase) pathway, are involved in hematogenesises, allergic disorders and tumourigenesis. However, their role in hematologic neoplasms is largely unknown. Possible effects of Spreds on other signal pathways closely related to Ras–ERK have been poorly investigated. In this study, we investigated the in vitro effects of Spred2 on chronic myeloid leukemia (CML) cells. In addition to inhibiting the well-established Ras–ERK cascade, adenovirus-mediated Spred2 over-expression inhibits constitutive and stem cell factor (SCF)-stimulated sphingosine kinase-1 (SPHK1) and Mcl-1 expression, as well as inhibiting proliferation and inducing apoptosis in CML cells. In K562 cells and primary CML cells, imatinib induces endogenous Spred2 expression. Spred2 silencing by stable RNA interference partly protects K562 cells against imatinib-induced apoptosis. Together, these data implicate Spred2 in imatinib-induced cytotoxicity in CML cells, possibly by inhibiting the Ras–ERK cascade and the pro-survival signaling molecules SPHK1 and Mcl-1. These findings reveal potential targets for selective therapy of CML. [Copyright &y& Elsevier]

miR-17-92 cluster are overexpressed in hematological malignancies including chronic myeloid leukemia (CML). However, their roles and mechanisms that regulate BCR-ABL induced leukemogenesis remain unclear. In this study, we demonstrated that genomic depletion of miR-17-92 inhibited the BCR-ABL induced leukemogenesis by using a mouse model of transplantation of BCR-ABL transduced hematopoietic stem cells. Furthermore, we identified that miR-19b targeted A20 (TNFAIP3). A20 overexpression results in inactivation of NF-κB activity including decrease of phosphorylation of P65 and IκBα, leads to induce apoptosis and inhibit proliferation and cycle in CML CD34 + cells. Thus we proved that miR-17-92 is a critical contributor to CML leukemogenesis via targeting A20 and activation of NF-κB signaling. These findings indicate that miR-17-92 will be important resources for developing novel treatment strategies of CML and better understanding long-term disease control. [ABSTRACT FROM AUTHOR]

Abstract: Interactions between the proteasome inhibitor, bortezomib, and the sphingosine kinase (SPK1) inhibitor, SKI, were examined in BCR/ABL human leukemia cells. Coexposure of K562 or chronic myeloid leukemia (CML) cells from patients to subtoxic concentrations of SKI (10μM) and bortezomib (100nM) resulted in a synergistic increase in caspase-3 cleavage and apoptosis. These events were associated with the downregulation of BCR–ABL and Mcl-1, and a marked reduction in SPK1 expression. In imatinib mesylate-resistant K562 cells that displayed decreased BCR–ABL expression, bortezomib/SKI treatment markedly increased apoptosis and inhibited colony-formation in association with the downregulation of Mcl-1. Finally, the bortezomib/SKI regimen also potently induced the downregulation of BCR/ABL and Mcl-1 in human leukemia cells. Collectively, these findings suggest that combining SKI and bortezomib may represent a novel strategy in leukemia, including apoptosis-resistant BCR–ABL+ hematologic malignancies. [Copyright &y& Elsevier]