Abstract 68: Targeting macrophage that forms a chemotherapy-induced niche significantly reduces cancer stem cells and tumors

Failure in cancer therapy is often caused by relapse resulting largely from chemo-resistant cancer stem cells (CSCs). Most colorectal cancer patients, after receiving chemoradiotherapy, still harbor treatment-resistant residual tumor cells that are akin to colorectal adenoma. We therefore exploited the APC Min adenoma model that allowed us to study the natural and dynamic interaction between CSCs and their microenvironment in vivo following therapeutic stress. We observed that macrophages were directly recruited from blood vessel to the CSC niche in response to chemotherapy, playing a role in protecting and further promoting activation of CSCs. Reduction in the Ly6c - CD11b int CX3CR1 + MHCII + population of tumor associated macrophages (TAMs) by celecoxib or clodrosome was correlated with a decline in slow-cycling drug-resistant CSCs and tumorigenesis. Molecularly, we found that COX-2 inhibitor celecoxib suppressed Akt and Wnt signaling, downstream of macrophage-dependent PGE2-EP pathway, thus reducing CSC survival and activation. Taken together, in the naturally formed adenoma reflecting human familial adenomatous polyposis, Chemotherapy-induced recruitment of TAMs to the CSC niche protected and promoted activation of surviving CSCs via PGE2-EP mediated Akt-Wnt signaling, leading to tumor regrowth. Targeting the TAMs will benefit clinical treatment of colorectal cancer. Citation Format: Xi He, Paloma I. Giles, Edward H. Lin, Linheng Li. Targeting macrophage that forms a chemotherapy-induced niche significantly reduces cancer stem cells and tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 68.