A New In Vitro Model of Breast Cancer Metastasis to Bone

Breast cancer frequently metastasizes to the bone where it disrupts the balance between osteoblasts and osteoclasts and leads to osteolytic degradation. The objective of this study was to test the hypothesis that osteolytic bone metastases results partly from the effect of the cancer cells on the osteoblasts, i.e., the cancer cells prevent osteoblasts from accreting mineralized tissue, ultimately leading to accelerated skeletal degradation. To test this idea, we proposed to develop an existing three-dimensional culture system into an in vitro test system for studying the interactions between osteoblasts and metastatic breast cancer cells. The objectives were to characterize the morphology and physiology of osteoblasts MC3T3-E1 cultured as a 3D osteoid in a bioreactor and determine how they reacted to the presence of human metastatic breast cancer cells MDA-MB-231. In addition, we proposed to determine how this interaction was affected by changing the oxidative state of the microenvironment with selenium supplementation. We also used this system to determine how the currently used drugs, zoledronic acid and doxetaxel, affected osteoblasts and cancer cells in the 3D model. Osteoblasts OB grew into bone-like tissue in a 3D model system. Pre-OB matured to OB and eventually to osteocyte-like cells. These cells met the criteria of osteocytes based on shape and protein expression. In addition, the density was similar to that reported for calvaria bone. The 3-D system was used to examine the interaction of metastatic breast cancer cells, MDA-MB-231, with OB. The cancer cells brought about profound effects on the osteoid tissue. The OB changed from cuboidal to spindle shape. The cancer cells aligned into an Indian filing pattern, and penetrated the osteoid. Using RT-PCR, we found that cancer cells downregulated OB differentiation proteins but increased inflammatory cytokines.