Abstract LB-307: Modeling the breast cancer metastatic niche

Mortality of breast cancer patients is due overwhelmingly to the metastatic spread of the disease. 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 (BM). In some of these patients the disseminated cells proliferate and generate metastases, typically in 3-5 years for ER negative tumors and 10-15 years for ER positive tumors. In other patients metastases never develop. These clinical characteristics offer the opportunity for intervention aimed to prevent metastasis development, provided the mechanisms underlying growth at the metastatic site are better understood. A challenge in this undertaking has been the lack of models for disseminated cells survival, dormancy and proliferation. We have established novel experimental systems that model the bone microenvironment of the breast cancer metastatic niche in vitro and in vivo. These models are based on 3D complex cultures of human BM stromal cells and breast cancer cell lines (BCCL) in biomatrices. In one of these systems all of the cell components are defined, represented by mesenchymal cell lines (HS-5), osteoblasts (hFOB) & endothelial cells (HUVEC) co-cultivated in a collagen 3D matrix (BM Niche Model I). The second system uses primary human BM stromal cells (BM Niche Model II). Small numbers of BCCLs are added to matrix pre-seeded to sub-confluency with niche cells in order to model conditions of disseminated tumor cells. The cell lines used in the niche models differentiate along osteogenic and adipogenic lineages, and support survival of hematopoietic stem cells. Our studies demonstrate that in BM Niche Model I, BCCLs remain dormant, but retain their ability to divide when re-plated in standard culture conditions. Whereas in BM Niche Model II, BCCLs proliferate. Importantly the proliferation of BCCLs in this model is similar to that observed in intratibial inoculation models in vivo. These matrices pre-seeded with cells can also be implanted subcutaneously, where they are readily vascularised. Comparing the profile of secreted cytokines and growth factors in these two BM niche models, we identified twenty factors (growth factors, cytokines, cognate receptors and metalloproteinases) necessary for survival and proliferation of disseminated breast cancer cells in the bone marrow microenvironment. Some of these factors have been previously associated with higher risk of metastasis development. We are currently validating these candidates in our in vitro culture systems, and using subcutaneous implantation and intratibial injection in vivo. These BM Niche model systems will be instrumental in understanding the biology of disseminated tumour cells and metastasis formation. They also have the potential application for in vitro drug screening to identify anti-metastatic treatments. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-307. doi:1538-7445.AM2012-LB-307