Macrophage mediated elimination of cancer cells is critical for control of tumor growth. Cancer cells evade immune recognition by expressing receptors that send inhibitory signals to prevent macrophage mediated cytotoxicity. Clinical studies show that overexpression of the cell surface receptor CD47 is a poor prognostic factor in cancer, allowing tumors to bypass immunosurveillance and activation pro-growth pathways. Prior studies have described that CD47 cell surface expression on cancer cells inhibits phagocytic activity through engagement of its counter receptor SIRPα on macrophages. However, the role of CD47 expression on macrophage function is not known. Here, we show that CD47 is expressed on primary mouse macrophages, RAW 264.7 and the U937 cell lines. Moreover, knockdown of CD47 on macrophages enhanced the tumoricidal capacity against melanoma and breast cancer cells as measured by cell impedance and LDH release. Blockade of CD47 enhanced the macrophage-mediated cytotoxicity against B16 melanoma and 4T1 cells when compared to untreated effector/target pairs. Blockade of CD47 on differentiated U937 human monocytes also enhanced tumoricidal activity against the triple-negative breast cancer cell line MDA-MB-231 by over 50% when compared to untreated co-cultures. This indicates that expression of CD47 on macrophages may play a role in polarization and macrophage tumoricidal capacity against cancer cells beyond the known interactions with SIRPα. Our previous studies show that blockade of CD47 preserves T cell viability under stress by increasing glycolytic flux. Activation of M1 cytotoxic macrophages requires a shift in metabolism from oxidative phosphorylation to glycolysis. Our data shows that blockade of CD47 on RAW 264.7 macrophages increases glycolytic flux when compared to untreated controls as measured by extracellular acidification rate (ECAR) using a Seahorse© XF analyzer. The increase in glycolysis was associated with a significant elevation of glucose uptake by macrophages treated with anti-sense CD47 morpholino, indicating that targeting this receptor regulates glucose metabolism to improve macrophage tumoricidal activity. Interestingly, blockade of CD47 in the 4T1 breast cancer cell line reduced ECAR and reduced glucose uptake indicating that targeting CD47 reverses Warburg metabolism in cancer cells. Overall, these results show a new role of CD47 expression that extends beyond suppressing macrophage mediated killing through engagement of SIRPα. Therefore, anti-CD47 immunotherapy may regulate immunometabolism to improve clinical outcomes of cancer patients.
Citation Format: Ashley A. Smith, Adam S. Wilson, David R. Soto-Pantoja. Targeting CD47 expression on macrophages regulates immunometabolism enhancing tumoricidal activity against cancer cells [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 5661. doi:10.1158/1538-7445.AM2017-5661