Background: 70% of Breast Cancer patients develop metastatic bone deposits, predominantly spinal metasases. Adult Mesenchymal Stem Cells (MSCs) are multiprogenitor stem cells found within the bone marow which have the ability to self renew and differentiate into multiple cell types. MSCs home specifically to tumour sites, highlighting their potential as delivery vehicles for therapeutic agents. However studies show they may also increase tumour metastatic potential.

Aims: The aim of this study was to investigate interactions between MSCs and breast cancer cells to further elucidate their role in the tumour microenvironment and hence understand factors involved in stimulating the formation of bone metastases.

Methods: MSCs harvested from the iliac crest of healthy volunteers were grown for collection of conditioned medium (CM), containing all factors secreted by the cells. Breast cancer cell lines (T47D, SK-BR3) were then cultured in MSC CM +/− antibodies to TGFβ, VEGF, MCP-1 and CCL5 for 72hrs. Cell proliferation was assessed using an Apoglow^® assay and RNA harvested for analysis of changes in Epithelial Mesenchymal Transition specific gene expression: N-Cadherin, E-Cadherin, Vimentin, Twist, Snail.

Results: A significant down regulation of breast cancer cell proliferation in the presence of MSC secreted factors was observed (p< 0.05). There was a dramatic increase in expression of EMT specific genes in both cell lines following exposure to MSC-secreted factors. Inclusion of antibodies to TGF, VEGF, MCP-1 and CCL5 inhibited the effect seen, suggesting these paracrine factors played a role in the elevated expression levels.

Conclusion: MSCs clearly have a distinct paracrine effect on breast cancer epithelial cells, mediated at least in part through secretion of growth factors and chemokines. These factors play an important role in the metastatic cascade and may represent potential therapeutic targets to inhibit MSC-breast cancer interactions, helping to prevent the formation of bone metastases in cancer.