Modeling the breast cancer bone metastatic niche in complex three-dimensional cocultures.

Despite advances in early detection, prevention and treatment of breast cancer, the mortality of breast cancer patients did not decrease considerably in the last years. Metastatic breast cancer remains incurable. There is compelling evidence that dissemination of breast cancer cells at distant sites is an early event. At the time of detection and diagnosis, patients have disseminated breast cancer cells in the bone marrow. Only in half of these patients the disseminated cells proliferate and generate metastases, typically in 3-5 years for ER negative breast tumors and 10-15 years for ER positive breast tumors. In other patients metastases never develop. The ability to predict which patients will develop metastases and to devise strategies to interfere with this process hinges on understanding the mechanisms underlying growth at the metastatic site. In turn, this requires novel experimental systems that model in vitro the survival, dormancy and proliferation of disseminated cancer cells.We have established such experimental systems that model the bone microenvironment of the breast cancer metastatic niche. These systems are based on 3D complex cultures of human bone marrow stromal cells and breast cancer cell lines in collagen biomatrices. We identified conditions in which cancer cells are dormant, and conditions in which they proliferate and we validated the results in vivo. Dormant cancer cells were able to proliferate upon transfer into supportive microenvironment or upon manipulation of signaling pathways that control dormancy. These experimental systems will be instrumental in screening new compounds for metastasis studies and particularly in studying the pathways that control cellular dormancy. We provide in this chapter detailed protocols for these complex 3D coculture systems.