Abstract 1469: Mechanisms of oncostatin M (OSM)-mediated breast cancer metastasis to bone: Evidence for a role in osteoclastogenesis

Oncostatin M (OSM) is an interleukin-6 (IL-6)-family cytokine that has been implicated in a number of biological processes including the induction of inflammation and modulation of the extracellular matrix. OSM was initially shown to inhibit the proliferation of breast cancer cell lines in vitro and has been evaluated as a potential cancer therapy. However, evidence in the literature and our data suggest that OSM may actually promote tumor invasion and metastasis. Using the orthotopic 4T1.2 mouse mammary model of metastasis, we have investigated the ability of OSM to enhance the formation of metastases in organs such as lung and bone in vivo. OSM expression was knocked down using shRNA in 4T1.2 cells, which endogenously express both OSM and its receptor. These 4T1.2-OSM cells were orthotopically injected into Balb/c mice and resulted in a 98% decrease in metastasis to bone and a 55% decrease in metastasis to lung compared to that of 4T1.2-Lac Z control cells. Metastases were quantified using qPCR to detect the vector neomycin resistance gene in post-mortem organ samples. In this study we investigate the specific cellular mechanisms that might be important for tumor cell-derived OSM promotion of metastasis to bone, such as hypoxia-inducible factor 1 alpha (HIF1α) and vascular endothelial growth factor (VEGF). An in vitro model was developed using the pre-osteoclast cell line (RAW 264.7) co-cultured with 4T1.2 mouse mammary tumor cells treated with and without recombinant OSM. Osteoclastogenesis of co-cultured RAW 264.7 cells was measured by staining for differentiated osteoclasts using the TRAP (tartrate-resistant acid phosphatase) assay and was found to increase with OSM treatment. Additionally, suppression of HIF1α expression by siRNA resulted in a 76% decrease in OSM-induced osteoclastogenesis. As RAW 264.7 cells do not express the OSM receptor beta (OSMRβ) necessary for OSM signaling, we suggest that this inhibition of osteoclast differentiation is via an autocrine signaling mechanism in the 4T1.2 cells that initiates the secretion of osteoclast differentiation factors including VEGF. Currently, we are investigating what these secreted factors from 4T1.2 cells are that affect RAW 264.7 cell differentiation and activity. Our results suggest that OSM might be an important therapeutic target in the prevention of metastatic breast cancer invasion of bone. Funded by ACS RSG-09-276-01-CSM, Susan G Komen for the Cure KG100513, and NIH/NCRR P20RR016454. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1469. doi:10.1158/1538-7445.AM2011-1469