Abstract LB-285: Pro-tumor N2 neutrophils contribute to the pre-metastatic niche.

Abstract

Abstract Metastasis is the primary cause of cancer-related mortalities and the tissue microenvironment that supports tumor cell attachment and growth at metastatic sites has become an active area of investigation. Here we present evidence that pro-tumor N2 neutrophils are one of the bone marrow-derived cell types that establish this pre-metastatic niche. In the murine Lewis Lung adenocarcinoma (LLC) in vivo metastasis model, tumor cells metastasize to the lungs with increasing primary tumor growth over time. In these studies, immunocompetent mice injected subcutaneously with syngeneic LLC cells are sacrificed sequentially 10-32 days later, before and after established lung metastases. Neutrophil chemoattractants KC/CXCL1 and MIP-2/CXCL2 are significantly elevated in pre-metastatic tissue compared to normal lungs of healthy contemporary controls. MCP-1/CCL2, a marker of pro-tumor N2 neutrophils, increases steadily over time in pre-metastatic lung tissue of study mice and is significantly elevated in pre-metastatic tissue and in metastases compared to normal lung tissue. Isolated lung-infiltrating neutrophils also express N2 markers. In contrast, TNF-alpha, a marker for anti-tumor N1 cells, remains low or undetectable in lung tissue throughout metastatic tumor development. Neither active nor total TGF-beta, the putative control switch for a pro-tumor phenotype, is elevated in pre-metastatic tissue. Notably, levels of all cytokines are low or undetectable in normal lungs from naïve mice and in other organs of tumor-bearing mice (non-metastatic sites). Ly6G+ neutrophils were detected at a higher density in the lungs of pre-metastatic and metastatic mice compared to normal lungs, although the density of myeloperoxidase (MPO)-stained cells was similar in all groups. These data are consistent with recent reports that MPO activity is low or absent from tumor-associated neutrophils, although high in MDSC and naïve neutrophils. Neutrophil distribution in metastatic lung tissue is most concentrated around the tumor foci and tumor vasculature. Finally, studies of lung tissue from mice bearing LLC variants with different metastatic capacities are also consistent with our premise that neutrophils help establish the pre-metastatic niche. Understanding the factors that regulate the development and growth of malignant cells at metastatic sites is critical for improved clinical strategies in the prevention, diagnosis and treatment of metastases. Citation Format: Jered Cope Meyers, H. Keith Pittman, Hunter Story, Dare M. Imes, George A. Howard, Kathryn M. Verbanac. Pro-tumor N2 neutrophils contribute to the pre-metastatic niche. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-285. doi:10.1158/1538-7445.AM2013-LB-285