e16576 Background: Prostate cancer is the second most common cancer in men worldwide. Lethality is normally associated with the consequences of metastasis rather than the primary tumor. In particular, bone is the most frequent site of metastasis and once prostate tumor cells are engrafted in the skeleton, curative therapy is no longer possible. Bone morphogenetic proteins (BMPs) play a critical role in bone physiology and pathology. However, little is known about the role of BMP9 and its signaling receptors, ALK1 and ALK2, in prostate cancer and bone metastasis. In this context, we investigate the impact of BMP9 on primary prostate cancer and derived bone metastasis. Methods: The human ALK1 extracellular domain (ECD) binds BMP9 and BMP10 with high affinity. In order to study the effect of BMP9 in vitro and in vivo we use a soluble chimeric protein, consisting of ALK1 ECD fused to human Fc (ALK1Fc), for preventing the activation of endogenous signaling. ALK1Fc sequesters BMP9 and BMP10, preserving the activation of ALK1 through other ligands. Results: We show that ALK1Fc reduces BMP9-mediated signaling and decreases proliferation of highly metastatic and tumor initiating human prostate cancer cells in vitro. In line with these observations, we demonstrate that ALK1Fc reduces tumor growth in vivo in an orthotopic transplantation model. The propensity of the primary prostate cancer to metastasize to the bone is also investigated. In particular, we report how the ALK1Fc influences the prostate cancer cells in vitro and in vivo when these are probed in different bone settings (co-culture with bone cells and intraosseous transplantation in mice). Conclusions: Our study provides the first demonstration that ALK1Fc inhibits prostate cancer cells growth identifying BMP9 as a putative therapeutic target and ALK1Fc as a potential therapy. All together, these findings justify the ongoing clinical development of drugs blocking ALK1 and ALK2 receptor activity.
48. Increased Potency of Engineered FasL-Expressing T Cells Is Modified in Primary Prostate Cancer Cells by Common Chemotherapeutic Agents
