Inhibition of bone-derived insulin-like growth factors toy a ligand-specific antibody suppresses the growth of human multiple myeloma in the human adult bone explanted in NOD/SCID mouse

Multiple myeloma (MM) is a fatal disease that affects plasma cells. Patients with MM have I or more osteolytic lesions in their bone tissues, where insulin-like growth factors (IGFs; IGF-I and IGF-II) are mainly stored. The role of bone-derived IGFs in the development of MM has not been extensively studied because reliable animal models are lacking. We established an animal model using a human MM cell line, RPMI8226, in nonobese diabetic/severe-combined immunodeficient (NOD/SCID) mice implanted with human adult bone (HAB) fragments. Treatment with an antihuman IGF-neutralizing monoclonal antibody, KM1468, inhibited the IGF-I-stimulated phosphorylation of type-I IGF receptors (IGF-IR) in RPM18226 cells and the activation of the downstream P13-K/Akt signaling pathway in vitro. KM1468 inhibited IGF-I-mediated RPM18226 cell growth in a dose-dependent manner. In the NOD/SCID-HAB model, treatment with KM1468 significantly inhibited the growth of RPM18226 cells (p < 0.02). These results indicated that the growth of MM cells was predominantly stimulated not by serum-derived IGFs, but by bone-derived IGFs. Furthermore, the targeting of bone-derived IGFs, using a neutralizing antibody, may offer a new therapeutic strategy for MM. (c) 2005 Wiley-Liss, life.