Mifamurtide and TAM-like macrophages: effect on proliferation, migration and differentiation of osteosarcoma cells

Tumor-associated macrophages and their alternative activation states together with cytokines and growth factors trapped in tumor microenvironment contribute to the progression of OS. In contrast to other tumor types, M2 polarized macrophages, reduce metastasis and improve survival in osteosarcoma patients. Mifamurtide is an immunomodulatory drug given together with standard adjuvant chemotherapy in high-grade osteosarcoma to improve outcome. Macrophages obtained from peripheral blood mononucleated cells of healthy donors and MG63 cells were cultured alone and together, and treated with Mifamurtide. We analyzed the effects of Mifamurtide on macrophage polarization and on MG63 proliferation, migration and differentiation, evaluating the expression of M1/M2 and osteoblast markers and molecules involved in metastasis and proliferation pathways. Our data suggest that Mifamurtide, switching macrophage polarization towards a TAM-like intermediate M1/M2 phenotype, may modulate the delicate balance between pro-inflammatory and immunomodulatory macrophage functions. Moreover, Mifamurtide may inhibit the cellular proliferation and induce the tumor cell differentiation, probably through the down regulation of pSTAT3, pAKT and IL-17R.