Abstract TMIM-076: OMENTAL MACROPHAGES REGULATE OVARIAN CANCER METASTATIC COLONIZATION THROUGH THE CCL6-CCR1 SIGNALING AXIS

BACKGROUND: Metastatic ovarian cancer remains an urgent clinical problem. The homing and invasion of cancer cells into the omental adipose tissue, which is the preferred site of ovarian cancer metastasis, is a critical step in disease progression. Omental adipose tissue contains adipocytes, blood vessels, and clusters of leukocytes known as milky spots. We have previously demonstrated in several mouse models that intraperitoneally injected ovarian cancer cells localize to the omentum and specifically to the milky spots. However, we found that B, T, or NK cells were not required for omental colonization. We hypothesize that macrophages within the milky spots play a crucial role in promoting ovarian cancer progression. METHODS AND RESULTS: Depleting macrophages disrupts cancer cells9 localization to the omentum. This result supports our hypothesis that macrophages play an essential role in attracting ovarian cancer cells to the omental milky spots. Correspondingly, factors secreted by omental macrophages promote ovarian cancer migration in vitro, in contrast to factors secreted by macrophages isolated from other peritoneal adipose tissues. In order to understand the specific mechanism(s) that regulate metastatic colonization of the omentum, we performed RNA-Seq of CD45+CD11b+F4/80+ flow-sorted macrophages from the omentum and the mesenteric fat of naive and cancer-bearing mice. We found that omental macrophages have a distinct and dynamic gene expression pattern even when compared to a very similar cell type. The chemokine CCL6 is one of the most highly upregulated genes during metastatic colonization. The human homolog of CCL6 is CCL23 and is also expressed by human omental macrophages. Genomic inactivation of CCR1, the gene encoding receptor for CCL6 in mice and CCL23 in humans, in mouse ovarian cancer cells abolishes their ability to home to omental milky spots. Our findings establish a role for chemokine signaling in the early colonization of the omentum by ovarian cancer. CONCLUSION: We demonstrate that omental milky spots are the preferential sites for cancer colonization of peritoneal adipose. Further, we have identified omental macrophages as the critical mediators of colonization via the CCL6/CCR1 chemokine axis. Future studies are focused on understanding the cancer cell-macrophage interactions that can be targeted therapeutically to disrupt metastatic growth and extend disease-free survival. Citation Format: Venkatesh Krishnan, Supreeti Tallapragada, Bruce Schaar, Anita Chanana, Carrie Rinker-Schaeffer, Oliver Dorigo. OMENTAL MACROPHAGES REGULATE OVARIAN CANCER METASTATIC COLONIZATION THROUGH THE CCL6-CCR1 SIGNALING AXIS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-076.