Tissue-Engineered Bone Serves as a Target for Metastasis of Human Breast Cancer in a Mouse Model

The high frequency and mortality associated with breast cancer metastasis to bone has motivated efforts to elucidate tumor-stroma interactions in the bone microenvironment contributing to invasion and proliferation of metastatic cells. The development of engineered tissues has prompted the integration of engineered bone scaffolds into animal models as potential targets for metastatic spread. Silk scaffolds were coupled with bone morphogenetic protein-2 (BMP-2), seeded with bone marrow stromal cells (BMSC), and maintained in culture for 7 weeks, 4 weeks, and 1 day before s.c. implant in a mouse model of human breast cancer metastasis from the orthotopic site. Following injection of SUM1315 cells into mouse mammary fat pads, tumor burden of implanted tissues was observed only in 1-day scaffolds. Scaffold development and implantation was then reinitiated to identify the elements of the engineered bone that contribute to metastatic spread. Untreated scaffolds were compared with BMP-2-coupled, BMSC-seeded, or BMP-2/BMSC-combined treatment. Migration of SUM1315 cells was detected in four of four mice bearing scaffolds with BMP-2 treatment and with BMSC treatment, respectively, whereas only one of six mice of the BMP-2/BMSC combination showed evidence of metastatic spread. Histology confirmed active matrix modeling and stromal cell/fibroblast infiltration in scaffolds positive for the presence of metastasis. These results show the first successful integration of engineered tissues in a model system of human breast cancer metastasis. This novel platform now can be used in continued investigation of the bone environment and stem cell contributions to the process of breast cancer metastasis.