Abstract The skeleton is the most common site of prostate cancer metastasis, which often results in osteoblastic lesions. The associated fractures and pain are major causes of morbidity and mortality in prostate cancer patients. Transforming growth factor-beta (TGFβ) signaling has been shown to developmentally regulate bone mass and bone matrix properties. It has also been shown to promote osteolytic metastasis induced by breast cancer through its regulation of some secreted proteins that are involved in bone resorption. However, its role in prostate cancer-induced osteoblastic metastasis is much less clear. This is in part due to a lack of prostate cancer cell lines that can efficiently induce bone metastasis and osteoblastic lesions in animal models. We found that a newly established human prostate cancer PacMetUT1 cell line produces copious amounts of active TGFβ1 and induces extensive bone metastases in calvaria, rib, femur, and tibia when inoculated in the left cardiac ventricle of male nude mice. Histology revealed extensive bone formation in the metastatic lesions of the calvaria and femur with some areas showing bone resorption. Stable knockdown of TGFβ1 with a shRNA in the PacMetUT1 cells resulted in significantly reduced TGFβ1 secretion and decreased tumor incidence when the cells were directly injected into the tibiae of male nude mice. Systemic administration of either a small inhibitor of TGFβ type I receptor kinase or a pan TGFβ binding protein also decreased osteoblastic intratibial tumor incidence and growth. PacMetUT1 is a novel prostate cancer cell line for the investigation of mechanisms that regulate formation of metastatic osteoblastic bone lesions. Future studies will reveal whether targeting the TGFβ signaling pathway is feasible for the prevention and treatment of prostate cancer-induced bone metastasis. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B108.