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Blood, 15 September 2008, Vol. 112, No. 6, pp. 2450-2462. Prepublished online as a Blood First Edition Paper on June 26, 2008; DOI 10.1182/blood-2007-10-114348.
NEOPLASIA Targeting MEK/MAPK signal transduction module potentiates ATO-induced apoptosis in multiple myeloma cells through multiple signaling pathways1 Department of Clinical Sciences, University of Parma, Parma; 2 Unit of Hematology and Bone Marrow Transplantation, University Hospital of Parma, Parma; 3 Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna Bruno Ubertini, Brescia; 4 Department of Animal Health, Pathology Unit, Faculty of Veterinary Medicine, University of Parma, Parma; 5 Department of Hematology, Oncology and Molecular Medicine, Italian Institute of Public Health, Rome; 6 Department of Dermatology, University of Rome Tor Vergata, Rome; 7 Department of Internal Medicine, University of Rome La Sapienza, Rome; and 8 Laboratory of Gene Expression, Fondazione Andrea Cesalpino, University of Rome La Sapienza, Rome, Italy We demonstrate that blockade of the MEK/ERK signaling module, using the small-molecule inhibitors PD184352 or PD325901 (PD), strikingly enhances arsenic trioxide (ATO)–induced cytotoxicity in human myeloma cell lines (HMCLs) and in tumor cells from patients with multiple myeloma (MM) through a caspase-dependent mechanism. In HMCLs retaining a functional p53, PD treatment greatly enhances the ATO-induced p53 accumulation and p73, a p53 paralog, cooperates with p53 in caspase activation and apoptosis induction. In HMCLs carrying a nonfunctional p53, cotreatment with PD strikingly elevates the (DR4 + DR5)/(DcR1 + DcR2) tumor necrosis factor (TNF)–related apoptosis-inducing ligand (TRAIL) receptors ratio and caspase-8 activation of ATO-treated cells. In MM cells, irrespective of p53 status, the combined PD/ATO treatment increases the level of the proapoptotic protein Bim (PD-mediated) and decreases antiapoptotic protein Mcl-1 (ATO-mediated). Moreover, Bim physically interacts with both DR4 and DR5 TRAIL receptors in PD/ATO-treated cells, and loss of Bim interferes with the activation of both extrinsic and intrinsic apoptotic pathways in response to PD/ATO. Finally, PD/ATO treatment induces tumor regression, prolongs survival, and is well tolerated in vivo in a human plasmacytoma xenograft model. These preclinical studies provide the framework for testing PD325901 and ATO combination therapy in clinical trials aimed to improve patient outcome in MM.
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