The crosstalk between
tumor cells and bone cells in the bone microenvironment is crucial to understanding the mechanism of bone
metastasis formation. We developed an in vitro fully human preclinical model of a co-culture of
breast cancer cells and monocytes undergoing differentiation towards osteoclasts. We optimized a model of osteoclastogenesis starting from a sample of peripheral blood collected from healthy donors. Peripheral blood mononuclear cells (PBMCs) were first separated by density gradient centrifugation, seeded at a high density and induced to differentiate by adding two
growth factors (GFs): receptor activator of nuclear factor-κB
ligand (RANKL) and
macrophage colony-stimulating factor (MCSF). The cells were left in culture for 14 days and then fixed and analyzed by downstream analysis. In osteolytic bone
metastases, one of the effects of
cancer cell arrival in bone is the induction of osteoclastogenesis. We thus challenged our model with co-cultures of
breast cancer cells to study the differentiation power of
cancer cells with respect to GFs. A straightforward way of studying
cancer cell-osteoclast interaction is to perform indirect co-cultures based on the use of
conditioned medium collected from
breast cancer cell cultures and mixed with fresh medium. This mixture is then used to induce osteoclast differentiation. We also optimized a method of direct co-culture in which
cancer cells and monocytes undergoing differentiation share the medium and exchange secreted factors. This is a significant improvement over the original indirect co-culture method as researchers can observe the reciprocal interactions of the two cell types and perform downstream analyses for both
cancer cells and osteoclasts. This method enables us to study the effect of drugs on the metastatic bone microenvironment and to seed cell lines other than those derived from
breast cancer. The model can also be used to study other diseases such as
osteoporosis or other bone conditions.