Publications

Abstract

The bone microenvironment and its modification by cancer and host cell interactions is a key driver of skeletal metastatic growth. Interleukin-6 (IL-6) stimulates RANKL expression in bone cells, and serum IL-6 levels are associated with poor clinical outcomes in cancer patients. We investigated the effects of RANKL on cancer cells and the role of tumor-derived IL-6 within the bone microenvironment. Using human breast cancer cell lines to induce tumors in the bone of immune-deficient mice, we first determined whether RANKL released by cells of the osteoblast lineage directly promotes IL-6 expression by cancer cells in-vitro and in-vivo. We then disrupted of IL-6 signaling in-vivo either via knock-down of IL-6 in tumor cells or through treatment with specific anti-human or anti-mouse IL-6 receptor antibodies to investigate the tumor effect. Finally, we tested the effect of RANK knockdown in cancer cells on cancer growth. We demonstrate that osteoblast lineage-derived RANKL up-regulates secretion of IL-6 by breast cancers in-vivo and in-vitro. IL-6 in turn induces expression of RANK by cancer cells, which sensitizes the tumor to RANKL and significantly enhances cancer IL-6 release. Disruption in-vivo of this auto-amplifying crosstalk by knockdown of IL-6 or RANK in cancer cells, or via treatment with anti-IL-6 receptor antibodies, significantly reduces tumor growth in bone but not in soft tissues. RANKL and IL-6 mediate direct paracrine-autocrine signaling between cells of the osteoblast lineage and cancer cells significantly enhancing the growth of metastatic breast cancers within bone. (c) 2014 American Society for Bone and Mineral Research.