Inhibition of p38A Mitogen-Activated Protein Kinase Prevents the Development of Osteolytic Bone Disease, Reduces Tumor Burden, and Increases Survival in Murine Models of Multiple Myeloma Karin Vanderkerken, 1 Satya Medicherla, 2 Les Coulton, 3 Hendrik De Raeve, 4 Angelo Willems, 1 Michelle Lawson, 3 Ben Van Camp, 1 Andrew A. Protter, 2 Linda S. Higgins, 2 Eline Menu, 1 and Peter I. Croucher 3 1 Department of Hematology and Immunology, Vrije Universiteit Brussel (VUB), Brussels, Belgium; 2 Scios, Inc., Fremont, California; 3 Academic Unit of Bone Biology, University of Sheffield School of Medicine and Biomedical Science, Sheffield, United Kingdom; and 4 Department of Pathology, University Hospital Antwerp, Antwerp, Belgium Abstract The bone microenvironment plays a critical role in supporting the growth and survival of multiple myeloma as well as in the development of osteolytic bone disease. Signaling through p38A mitogen-activated protein kinase (MAPK) mediates synthesis of multiple myeloma cell growth factors, and its inhibition reduces proliferation in vitro . However, it is unclear whether targeting p38A MAPK prevents multiple myeloma growth and the development of bone disease in vivo . In this study, we determined whether SCIO-469, a selective p38A MAPK inhibitor, inhibits multiple myeloma growth and prevents bone disease in the 5T2MM and 5T33MM models. SCIO-469 decreased constitutive p38A MAPK phosphorylation of both 5T2MM and 5T33MM cells in vitro. This was associated with decreased DNA synthesis and an induction of apoptosis when the cells were cultured with bone marrow stromal cells. Treatment of C57Bl/KaLwRij mice bearing 5T33MM cells with SCIO-469 inhibited p38A MAPK phosphorylation and was associated with a significant decrease in serum paraprotein, an almost complete reduction in tumor cells in the bone marrow, a decrease in angiogenesis, and a significant increase in disease-free survival. Injection of 5T2MM murine myeloma cells into C57Bl/KaLwRij mice resulted in myeloma bone disease characterized by increased osteoclast occupation of the bone surface, reduced cancellous bone, and the develop- ment of osteolytic bone lesions. Treatment of 5T2MM-injected mice with SCIO-469 reduced this development of bone disease. Together, these data show that targeting p38A MAPK with SCIO-469 decreases myeloma burden in vivo , in addition to preventing the development of myeloma bone disease. [Cancer Res 2007;67(10):4572–7] Introduction Multiple myeloma is a plasma cell cancer characterized by the clonal expansion of malignant cells that accumulate in the bone marrow, leading to osteoclast and endothelial cell activation, which, in turn, results in bone destruction and angiogenesis. Despite the progress achieved in the last few years with high-dose chemotherapy and stem cell transplantation resulting in a higher success rate of remission, patients eventually develop drug- resistant disease and relapse. New therapies targeting both multiple myeloma cells and their microenvironment are urgently required. Mitogen-activated protein kinase (MAPK) p38a, a member of the MAPK family and activated by cytokines and growth factors, has been reported to be involved in the production of tumor- promoting factors by the multiple myeloma bone marrow microenvironment. Activation of p38a in bone marrow stromal cells enhanced the production of interleukin (IL)-6, which is critical for multiple myeloma growth and survival (1). The p38a MAPK inhibitor decreased IL-6 secretion in the bone marrow stromal cells of patients with multiple myeloma, decreasing proliferation of multiple myeloma cells adherent to bone marrow stromal cells and IL-6 secretion by the bone marrow stromal cells triggered by adherence of multiple myeloma cells to bone marrow stromal cells in vitro (1). The p38a MAPK inhibitor SCIO-469 prevented tumor necrosis factor-a–induced adhesion of multiple myeloma cells to bone marrow stromal cells through an intercellular adhesion molecule 1– and vascular cell adhesion molecule-1–independent mechanism (2). Furthermore, SCIO-469 enhanced PS-341 (borte- zomib)–induced cytotoxicity against multiple myeloma cell lines and patient’s multiple myeloma cells (3) by inhibiting transient expression and phosphorylation of heat shock protein 27, a downstream target of p38. SCIO-469 also enhanced bortezomib- induced multiple myeloma apoptosis by up-regulation of p53 and down-regulation of Bcl-X L and Mcl-1. In a xenograft model for plasmacytosis, it was furthermore shown that inhibiting p38 augments the effects of bortezomib in decreasing multiple myeloma tumor growth in vivo (4). SCIO-469 also inhibits secretion and expression of the osteoclast-activating factors IL-11, receptor activator of NF-nB ligand, and macrophage inflammatory protein 1a, and prevents human osteoclast activation in vitro . Recently, two articles report on the effect of inhibiting p38 on the restoration of dendritic cell function both in murine and human multiple myeloma (5, 6). In the present work, we investigated the role of p38 MAPK in the development of multiple myeloma disease in vivo using the specific p38a MAPK inhibitor SCIO-469 in a fully immunocompetent murine multiple myeloma model. Materials and Methods The 5T2MM and 5T33MM murine models of myeloma. The 5T2MM and 5T33MM murine models of myeloma originated spontane- Note: K. Vanderkerken is a postdoctoral fellow of Fonds voor Wetenschappelijk Onderzoek-Vlaanderen. Requests for reprints: Karin Vanderkerken, Department of Hematology and Immunology, Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, B-1090 Brussels, Belgium. Phone: 32-2-477-44-18; Fax: 32-2-477-44-05; E-mail: Karin.Vanderkerken@ vub.ac.be. I2007 American Association for Cancer Research. doi:10.1158/0008-5472.CAN-06-4361 Cancer Res 2007; 67: (10). May 15, 2007 4572 www.aacrjournals.org Priority Report Research. on August 23, 2021. © 2007 American Association for Cancer cancerres.aacrjournals.org Downloaded from Published OnlineFirst May 10, 2007; DOI: 10.1158/0008-5472.CAN-06-4361