Abstract 4019: Examining mechanisms by which macrophages enhance intravasation in breast cancer

Breast cancer is the most common invasive malignancy and a leading cause of cancer-associated deaths in women worldwide. Metastasis is the major cause of morbidity and mortality in women afflicted with breast cancer. In the metastatic process, intravasation is an important step and largely dependent on interactions between tumor cells and stromal cells in the tumor microenvironment (TME). Tumor-associated macrophages (TAMs), an integral component of the TME, have been found to associate and co-migrate with tumor cells during intravasation. Invasive TAMs that co-migrate with tumor cells in response to epidermal growth factor display a unique transcriptome in comparison to the general TAM population found in the TME. Furthermore, intercellular signaling between tumor cells and TAMs generates a positive feedback loop that promotes tumor cell invasion and intravasation. Chemokines play a major role in cell migration and are an important component of the TME. In particular, chemokine (C-X-C motif) receptor 2 (CXCR2) has been shown to be important in tumor growth and angiogenesis. MIF and IL8, two ligands of CXCR2, correlate with poor outcome in breast cancer. Our objective is to elucidate the role of macrophage CXCR2 in tumor cell intravasation. We have used flow cytometry to characterize the basal expression of CXCR2 in a murine macrophage cell line, BAC-1.2F5 (BAC). We have also analyzed mRNA expression of CXCR2 in BAC and primary TAMs isolated from a murine model of breast cancer, the polyoma middle T oncoprotein (PyMT), by qRT-PCR. To test the functional significance of CXCR2 in intravasation, we have examined the effects of an inhibitor of CXCR2 on the ability of tumor cells to migrate through the endothelium using an in vitro transendothelial migration assay (iTEM). In this assay, MDA-MB-231 tumor cells, a human breast cancer cell line, are co-cultured with BAC cells and subsequently placed in an environment that is in contact with the basal surface of endothelial cells. We have observed that BAC cells produce CXCR2 mRNA and express surface CXCR2. We have also found elevated expression of CXCR2 in invasive TAMs as compared to the general TAM population. When MDA-MB-231 cells are co-cultured with BAC cells in the iTEM assay in the presence of SB265610, an inhibitor of CXCR2, we have found a significant reduction (p Citation Format: Serena Chiang, Zhenni Zhou, Jeffrey E. Segall. Examining mechanisms by which macrophages enhance intravasation in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4019. doi:10.1158/1538-7445.AM2015-4019