Development of a three-dimensional in vitro model to study the effect of vitamin D on bone metastatic breast cancer

Breast cancer has a high prevalence among women and most patients suffer from metastasis to bone. The mechanisms involved in breast cancer bone metastasis are poorly understood. Three-dimensional (3D) tissue culture systems are becoming a focus of biomedical engineering. The 3D cultures can mimic the in vivo microenvironment and have much greater biological relevance than the traditional two-dimensional (2D) monolayer cell culture systems. There is a need for developing reliable in vitro models to study the mechanism of bone metastasis in breast cancer. We established a 3-dimensional (3D) collagen matrix tissue culture model to study metastatic breast cancer. Calcitriol or 1, 25 dihydroxyvitamin D3 has anti-tumor effects by inhibiting cancer cell proliferation and inducing differentiation. There are few research studies investigating its role in metastasis. None of the research studies were based on bio-mimetic 3D models. We used this novel 3D tissue culture system to test 1, 25 dihydroxyvitamin D3¡¯s role in breast cancer bone metastasis. Our results demonstrate vitamin D pretreated breast cancer cells had significantly decreased (p ¡Ü 0.0001) migration rate, in association with significantly decreased (p ¡Ü 0.05) cell surface expression of CXCR4. This result proved the hypothesis vitamin D inhibits breast cancer bone metastasis by down regulating CXCR4 expression. Our data showed in the 3D system, breast cancer migration rate increased significantly compared with those in 2D system. In our pilot study, CXC12 expression data suggest that the decrease in migration was not due to the CXCR4-CXCL12 axis because there was no significant difference (p ¡Ý 0.05) of CXCL12 expression between 3D and 2D osteoblast cells. The CXC12 studies needs to be validated with a larger sample size. Alternatively, this observation suggests that there are other signaling pathways which influence the migration of breast cancer cells towards osteoblast cells and bone matrix