ABSTRACT
Here we tested impact of Tris (dibenzylideneacetone) dipalladium (Tris-DBA) on chronic lymphocytic leukemia (CLL) B-cell survival. Indeed, treatment of CLL B-cells with Tris-DBA induced apoptosis in a dose-dependent manner irrespective of IgVH mutational status. Further analyses suggest that Tris-DBA-induced apoptosis involves reduced expression of the anti-apoptotic proteins Bcl-xL, and XIAP with an upregulation of the pro-apoptotic protein BIM in CLL B-cells. Our findings also indicate that Tris-DBA targets the ribosomal protein (rp)-S6, an essential component of the Akt/mTOR signaling axis in CLL B-cells. Of interest, CLL bone marrow stromal cells were unable to protect the leukemic B cells from Tris-DBA-induced apoptosis in an in vitro co-culture system. Finally, co-administration of Tris-DBA and the purine nucleoside analog fludarabine (F-ara-A) augmented CLL B-cell apoptosis levels in vitro showing synergistic effects. In total, Tris-DBA is effective at inducing apoptosis in CLL B-cells even in the presence of stromal cells likely by targeting directly the signal mediator, rpS6.
Subject(s)
Antineoplastic Agents/pharmacology , Apoptosis/drug effects , Organometallic Compounds/pharmacology , Cell Line, Tumor , Cell Survival/drug effects , Coculture Techniques , Dose-Response Relationship, Drug , Drug Synergism , Gene Expression Regulation, Neoplastic/drug effects , Humans , Leukemia, Lymphocytic, Chronic, B-Cell/genetics , Leukemia, Lymphocytic, Chronic, B-Cell/metabolism , Proto-Oncogene Proteins c-bcl-2/genetics , Proto-Oncogene Proteins c-bcl-2/metabolism , Ribosomal Protein S6/genetics , Ribosomal Protein S6/metabolism , Stromal Cells/drug effects , Stromal Cells/metabolism , Tumor Cells, CulturedSubject(s)
Antineoplastic Combined Chemotherapy Protocols/pharmacology , Heterocyclic Compounds, 3-Ring/pharmacology , Leukemia, Lymphocytic, Chronic, B-Cell/drug therapy , Nitrogen Mustard Compounds/pharmacology , Antineoplastic Agents, Alkylating/pharmacology , Apoptosis/drug effects , Bendamustine Hydrochloride , Cytokines/biosynthesis , Cytokines/immunology , Drug Synergism , Heterocyclic Compounds, 3-Ring/administration & dosage , Humans , Leukemia, Lymphocytic, Chronic, B-Cell/enzymology , Leukemia, Lymphocytic, Chronic, B-Cell/immunology , Leukemia, Lymphocytic, Chronic, B-Cell/pathology , Lymphocytes/drug effects , Lymphocytes/immunology , Nitrogen Mustard Compounds/administration & dosage , Proto-Oncogene Proteins c-akt/antagonists & inhibitors , Proto-Oncogene Proteins c-akt/metabolismABSTRACT
Recently, we detected that chronic lymphocytic leukemia (CLL) B-cell-derived microvesicles in CLL plasma carry a constitutively phosphorylated novel receptor tyrosine kinase (RTK), Axl, indicating that Axl was acquired from the leukemic B cells. To examine Axl status in CLL, we determined the expression of phosphorylated-Axl (P-Axl) in freshly isolated CLL B cells by Western blot analysis. We detected differential levels of P-Axl in CLL B cells, and further analysis showed that expression of P-Axl was correlated with the other constitutively phosphorylated kinases, including Lyn, phosphoinositide-3 kinase, SyK/ζ-associated protein of 70 kDa, phospholipase C γ2 in CLL B cells. We found that these intracellular signaling molecules were complexed with P-Axl in primary CLL B cells. When Axl and Src kinases were targeted by a Src/Abl kinase inhibitor, bosutinib (SKI-606), or a specific-inhibitor of Axl (R428), robust induction of CLL B-cell apoptosis was observed in both a dose- and time-dependent manner. Therefore, we have identified a novel RTK in CLL B cells which appears to work as a docking site for multiple non-RTKs and drives leukemic cell survival signals. These findings highlight a unique target for CLL treatment.
