PROJECT SUMMARY The long-term objective of this NCI R03 project (Effect of skeletal compression on tumor growth and migration) is to contribute to developing guidelines for physical therapies that most effectively reduce the risk of cancer induction and relapse. The specific goal of this project is to evaluate the role of skeletal compression (bone loading) in regulating tumor growth and epithelial-to-mesenchymal transition (EMT) in the bone microenvironment. Focusing on bone metastasis associated with breast cancer, we will evaluate interactions of tumor cells with osteocytes, the most abundant type of cells in bone matrix, in the presence and absence of mechanical stimulation. One out of eight women suffers breast cancer in her lifetime, and bone is one of the most frequent sites of metastasis. Currently, we know little about the impact of osteocyte-driven mechanotransduction in tumor-bone interactions and bone metastasis. Preliminary studies suggest that osteocytes act as an attractant of tumor cells, but application of fluid flow shear stress reverses the attraction and leads to EMT. An intriguing question is whether mechanical stimulation to osteocytes may act as a regulatory switch of tumor EMT. Our working hypothesis is: Mechanical stimulation inhibits proliferation and stimulates migration of tumor cells in the loaded bone by regulating Src in tumor-osteocyte interactions. To test this hypothesis, we will conduct two specific aims: Aim 1: Evaluate the effect of skeletal compression in tumor growth and invasion using a mouse model. Aim 2: Determine the mechanism of action of mechanical stimulation in tumor-osteocyte interactions. In Aim 1, we will use a mouse model of skeletal loading to determine tumor growth and migration associated with breast cancer (mammary tumor) in the bone microenvironment. In Aim 2, we will employ monolayer cell cultures and 3D spheroids to evaluate tumor-osteocyte interactions in the presence and absence of oscillatory fluid flow shear stress. We will focus on genes involved in EMT and mechanotransduction of bone such as TGFβ and Src, as well as mechano-sensitive factors (e.g., fibronectin, heat shock protein, nucleolin) that were identified by mass spectrometry in osteocyte-derived conditioned mediums. We expect that this project will contribute to a basic understanding of the role of skeletal compression in tumor growth and invasion in the bone microenvironment. We also expect that the results will contribute to the provision of risk-benefit analysis of loading-linked physical activities, such as walking and jogging, as well as the establishment of a therapeutic guideline for bone metastasis.