A three-dimensional osteogenic tissue model for the study of metastatic tumor cell interactions with bone.

A specialized bioreactor based on the principle of simultaneous growth and dialysis permits growth of three-dimensional (3D), multiple-cell-layer osteogenic tissue from isolated osteoblasts over long, continuous-culture intervals (tested up to 10 months with no sign of necrosis). The resulting tissue recapitulates the stages of bone development observed in vivo, including phenotypic maturation of cobblestone-shaped osteoblasts into stellate-shaped osteocytes interconnected by many intercellular processes. Gene expression profiles parallel cell-morphologic changes with time, ultimately leading to increased expression of osteocyte-associated molecules such as E11, DMP1, and sclerostin. Contiguous, cm(2)-scale macroscopic mineral deposits that form within the bioreactor are consistent with bone hydroxyapatite. The simple to use bioreactor system provides an in vitro model that permits the study and manipulation of cancer cell interactions with bone tissue in real time. Metastatic human breast cancer cells, MDA-MB-231(GFP), introduced into the model grow and colonize osteoblastic tissue in a manner reflecting various characteristics of pathologic tissue observed in the clinic. Specifically, MDA-MB-231(GFP) cells are observed to penetrate the thick extracellular matrix in which osteoblasts are embedded and to form chains reminiscent of "Indian files," described for infiltrating lobular or metaplastic breast carcinomas. Osteoblasts appear to be marshaled into a parallel alignment with cancer cells, followed by erosion of extracellular matrix structural integrity. Tissue degradation appears to be accompanied by increased expression of osteoblast inflammatory cytokines.