PROJECT SUMMARY Metastatic dissemination is a leading cause of death from cancer with metastasis to bone represents a particularly poor prognosis. Unfortunately, metastasis to bone is one of the most common sites of metastases in cancers such as breast, prostate and lung. In lung cancer, near half of advanced cases develop metastasis to the bone significantly impacting morbidity and survival. The underlying mechanisms are incompletely understood limiting treatment options to reducing pain and fracture risk after diagnosis. Therefore, studies addressing this underserved area would mark a significant advance in preventing and treating bone metastasis. Increasingly different components of the tumor microenvironment have been identified as modulators of cancer progression. Ourselves and others have identified one such component to be inorganic phosphate (Pi), which is elevated in the American diet due to processed foods. High dietary Pi has putatively been linked to cancer progression and aggression. Our data suggests that high Pi could increase local invasion, angiogenesis and bone turnover potentially driving tumor dissemination and priming the metastatic niche in bone. Further, using a FRET-based Pi sensor we have observed marked differences in cytosolic Pi levels within individual lung cancer cells. Suggesting that tumor cells have varying degrees to which they can sense and respond to changes in Pi levels. Thus, leading to the postulation that a subpopulation of tumor cells is more sensitive to fluctuations in Pi and as a result drive tumor progression and metastasis to the bone. Studies proposed herein will use a state-of-the-art mouse metastasis model and a fluorescent Pi sensor to monitor Pi metabolism in real-time to examine the role of phosphate availability in promoting lung cancer invasion and colonization of the bone. Specifically, we will test the hypothesis that high Pi availability in lung cancer is pro-invasion and pro-metastatic, and specifically influences the metastatic burden in the bone. Further, we will examine if heterogeneity in Pi transport within lung cancer cell lines promotes tumor cell homing to bone. To test this hypothesis, we will: 1) Determine if serum phosphate levels promote lung cancer invasion and bone metastasis and 2) Determine the cellular requirement of phosphate for tumor invasion and metastasis to bone. Results from the current proposal will provide new information about the role of Pi in altering cell behavior and mechanisms underlying tumor dissemination and colonization of the skeleton.