Modified citrus pectin inhibits breast cancer development in mice by targeting tumor-associated macrophage survival and polarization in hypoxic microenvironment

Large amounts of tumor-associated macrophages (TAM), which are predominately localized in hypoxia area of the tumor tissue, are associated with the malignant progression of the tumor. In the present study, we investigated the inhibitory effects of modified citrus pectin (MCP), a natural dietary polysaccharide, on the survival and polarization of TAM in relation to its inhibition on the growth and migration of breast cancer. M2 macrophages polarized from human monocyte THP-1 were chosen as a model for TAM. We showed that MCP (0.06%–1%) concentration-dependently suppressed the survival of TAM through inhibiting glucose uptake with a greater extent in hypoxia than in normoxia. Furthermore, MCP treatment decreased ROS level in TAM through its reducibility and inhibiting galectin-3 expression, leading to inhibition of glucose transporter-1 expression and glucose uptake. In addition, MCP suppressed M2-like polarization via inhibiting STAT3 phosphorylation. Moreover, the tumor-promoting effect of TAM could be restrained by MCP treatment as shown in human breast cancer MDA-MB-231 cells in vitro and in mouse breast cancer 4T1-luc orthotopic and metastasis models. In both tumor tissue and lung tissue of the mouse tumor models, the number of TAM was significantly decreased after MCP treatment. Taken together, MCP may be a promising agent for targeting TAM in tumor hypoxic microenvironment for breast cancer treatment.