Abstract C09: The collagen-dense tumor microenvironment recruits tumor promoting Ly6G+Ly6C+ neutrophils in mouse mammary carcinoma

The breast tumor microenvironment (TME) is a diverse area where complex interactions between the extra-cellular matrix (ECM) and multiple cell types (tumor epithelial, endothelial, and inflammatory cells, fibroblasts, and adipocytes) occur resulting in tumor promotion, invasion and metastasis. Changes in breast tissue density have been correlated with a 4-6-fold increased risk for developing breast cancer, and are associated with increased stromal deposition of the ECM protein, collagen I. In a transgenic mouse model of increased collagen (Col1A1Tm1Jae), there is a 3-fold increase in MMTV-PyMT tumor formation and lung metastases compared to control, wild type mice. Of the non-malignant cells in the TME, tumor-associated macrophages (TAMs) and tumor-associated neutrophils (TANs) have been shown by several investigators to alter the TME and ECM, enhance tumor cell migration and invasion, stimulate angiogenesis, and suppress antitumor immunity. The direct interaction of both increased collagen and immune (myeloid) cell recruitment leading to increased cancer progression and metastasis has not been characterized. We hypothesized that a collagen-dense tumor microenvironment recruits an abnormal population of myeloid cells, which promotes tumor progression and metastasis. Flow cytometry analysis of cells from collagen-dense mouse tumors at late stages showed an increase in the number of Ly6G+Ly6C+ neutrophils recruited compared to wild type tumors, while the number of F4/80+ macrophages did not seem to be affected. The increased Ly6G+Ly6C+ neutrophil recruitment is a global immune response also observed in the spleens and circulating blood of collagen-dense mice. Using a cytokine/chemokine ELISA plate array, we found that the collagen-dense TME cytokine cross talk supports neutrophil and monocyte recruitment and maturation via increased GM-CSF signaling. Depleting neutrophils with anti-Ly6G (1A8) reduces the number of tumors and tumor burden in collagen-dense mice compared to anti-IgG control mice. These effects are not seen in treated wild type mice compared to control mice. Neutrophil depletion reduces metastasis in over 80% of treated collagen-dense mice compared to control mice. In contrast, wild type mice show an increase in metastasis with anti-Ly6G treatment. Our study supports the idea that the ECM, collagen I, can manipulate other cells in the TME, specifically the pro and anti-tumor functions of Ly6G+ neutrophils in mammary carcinoma. Experiments are underway to determine the exact mechanism by which the collagen-dense tumor microenvironment enhances the tumor promoting activities of Ly6G+ neutrophils in the primary and metastatic sites of this mouse model. Citation Format: Maria Gracia Garcia Mendoza, David R. Inman, Justin J. Jeffery, Patricia J. Keely. The collagen-dense tumor microenvironment recruits tumor promoting Ly6G+Ly6C+ neutrophils in mouse mammary carcinoma. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr C09.