Insulin-like growth factor-1 acts as a chemoattractant factor for 5T2 multiple myeloma cells

The chemotactic and growth-stimulatory effect of insulin-like growth factor 1 (IGF-1) was investigated in the experimental mouse 5T2 multiple myeloma (MM) model. Chemotaxis was analyzed by classical checkerboard analysis. Bone marrow fibroblasts-conditioned medium exhibited a chemotactic effect on 5T2 MM cells that could be neutralized by adding a blocking antibody to IGF-1. On the other hand, exogenously added IGF-1 also had a chemotactic effect on the 5T2 MM cells. Moreover, in vitro analysis demonstrated that transmigrated 5T2 MM cells have a higher expression of IGF-1 receptor, both in bone marrow-conditioned medium and in IGF-1-induced chemotaxis, in comparison to cells before migration. When analyzed in vivo, 18 hours after injection of the heterogeneous 5T2 MM population, 5T2 MM cells present in the bone marrow show a higher expression of the IGF-1 receptor than their counterparts before injection. When the proliferative effect of IGF-1 was analyzed, no stimulation was observed, which is in contrast to the influence of bone marrow-conditioned medium and interleukin-6. Our results suggest a causal relationship between the presence of IGF-1 in the bone marrow and the chemotaxis of MM cells to and their subsequent presence in the bone marrow.