A New in Vitro Model of Breast Cancer Metastasis to Bone

PUBLIC ABSTRACT

Breast cancer frequently metastasizes or spreads to other organs of the body. One of the favored sites is the skeleton. Once the breast cancer has begun to grow in the bone, it is very difficult to treat. The 5-year cure rate drops from 95% to 16%, and very seldom is breast cancer metastasized to bone totally eradicated. Breast cancer in the bone leads to bone degradation. This bone breakdown has serious consequences such as more bone fractures, bone pain, spinal cord compression, and high blood calcium levels that can affect the functions of other organs. The current evidence is that the cancer cells do not themselves break down the bone but the osteoclasts, the normal bone resorbing cells, are the culprits. In the presence of the breast cancer cells, the osteoclasts increase in number and become overly active. Drugs such as bisphosphnates (Alendronate, Pamidronate), which are aimed at blocking osteoclasts, slow down lesion formation and progression. However, the existing lesions do not heal. The evidence suggests that the bone-building cells, the osteoblasts, do not repair the bone. We are interested in why the osteoblasts so not seem to function to repair the bone. In addition to the clinical observations that the bone is not repaired, we have evidence from experiments carried out in cell culture that osteoblasts in the presence of breast cancer cells do not differentiate to make the proteins needed to repair bone. Instead, they begin to make factors that can attract and activate osteoclasts. These experiments are limited by conventional cell culture technology. There are no existing in vitro systems to study the interactions of breast cancer and bone long term under physiologically relevant conditions. We propose to use a bioreactor that we have developed as a tool to study the relationship of metastatic breast cancer cells with osteoblasts in a long-term culture system. We have already shown that we can grow osteoblast lines in this system for at least 120 days under conditions in which they form mineralized, collagenous connective tissue (synthetic bone). Now we plan to add metastatic breast cancer cells to the chamber to determine the fate of the osteoblasts. For the first aim, we will test osteoblast physiology in the presence of breast cancer cells. A battery of specialized osteoblast proteins and factors will be measured in the culture medium sampled from the chamber over time. The second aim will use several microscopic techniques to detect the morphology and cell interactions of the bone cells in co-culture with cancer cells. In the third aim, we propose to use the bioreactor to study how potential therapeutic agents affect both the cancer cells and the bone. This system offers a much needed bridge between conventional cell culture and in vivo animal studies. Furthermore, it has the potential to study bone:tumor cell interactions in other types of cancer as well.