Atypical Chemokine Receptor 1 (Ackr1/Darc) Expressing Tumors Are Associated With Distinct Recruitment Of Immune Cells And Increased Proinflammatory Chemokines

Interactions between chemokines and their receptors can improve a host’s anti-tumor response by influencing the targeted migration of immune cells via a chemokine gradient. Atypical Chemokine Receptor 1 (ACKR1/DARC), a genetically diverse transmembrane GPCR, acts as a decoy receptor for a variety of CXC and CC chemokines, including those with pro-malignant and pro-inflammatory effects, such as CCL2 (MCP-1, MCAF, JE) and CXCL8 (IL-8). The purpose of this study is to determine if the migration of tumor-associated immune cells is unique based on epithelial ACKR1 expression on breast cancer cells, and if this association is correlated to an increase in pro-malignant chemokines, better survival odds, and differences in race. Immunohistochemistry techniques were used to determine expression levels of ACKR1 on primary breast tumors, along with relative expression of T-cells, B-cells, dendritic cells, and macrophages. Concentrations of pro-inflammatory chemokines in circulation were determined using a Luminex-based immunoassay and matched patient peripheral blood samples. In silco analyses were performed to determine associations between ACKR1 tumor expression status, race, and survival. Finally, using human breast cancer cell lines and immunofluorescence techniques, co-localization between ACKR1 and selected pro-inflammatory chemokines was investigated. Results from these tests indicate that there is differential expression of immune cell types in tumors expressing ACKR1, and this difference was associated with the migration of B-cells and dendritic cells, which were not detected in ACKR1 negative tumors. Significantly increased circulating CCL2 and CXCL8 chemokine levels we also determined to be positively correlated with ACKR1 expression in primary breast tumors. Survival analyses showed a significantly increased relapse free survival in patients having tumors with high ACKR1 expression, while investigations into racial differences revealed a significant race effect, with Caucasians having higher ACKR1 levels on their tumors than African-Americans. Finally, co-localization between ACKR1 with CCL2 and CXCL8 is observed in cultured human breast cancer cells. Given that the data collected shows a tendency for those tumors positively expressing ACKR1 to have a more favorable prognosis, we suggest that a partial role of ACKR1 on breast tumor cells is to sequester pro-inflammatory chemokines in the tumor microenvironment, indirectly recruiting a distinct subset of tumor-associated immune cells. Citation Format: Brittany D. Jenkins, Rupali Hire, Elizabeth Howerth, Michele Monteil, Rachel Martini, Melissa B. Davis. Atypical chemokine receptor 1 (ACKR1/DARC) expressing tumors are associated with distinct recruitment of immune cells and increased pro-inflammatory chemokines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 953. doi:10.1158/1538-7445.AM2017-953