Abstract
The presence of cell surface protein CD47 allows cancer cells to evade innate and adaptive immune surveillance resulting in metastatic spread. CD47 binds to and activates SIRPα on the surface of myeloid cells, inhibiting their phagocytic activity. On the other hand, CD47 binds the matricellular protein Thrombospondin-1, limiting T-cell activation. Thus, blocking CD47 is a potential therapeutic strategy for preventing brain metastasis. To test this hypothesis, breast cancer patient biopsies were stained with antibodies against CD47 to determine differences in protein expression. An anti-CD47 antibody was used in a syngeneic orthotopic triple-negative breast cancer model, and CD47 null mice were used in a breast cancer brain metastasis model by intracardiac injection of the E0771-Br-Luc cell line. Immunohistochemical staining of patient biopsies revealed an 89% increase in CD47 expression in metastatic brain tumors compared to normal adjacent tissue (p ≤ 0.05). Anti-CD47 treatment in mice bearing brain metastatic 4T1br3 orthotopic tumors reduced tumor volume and tumor weight by over 50% compared to control mice (p ≤ 0.05) and increased IBA1 macrophage/microglia marker 5-fold in tumors compared to control (p ≤ 0.05). Additionally, CD47 blockade increased the M1/M2 macrophage ratio in tumors 2.5-fold (p ≤ 0.05). CD47 null mice had an 89% decrease in metastatic brain burden (p ≤ 0.05) compared to control mice in a brain metastasis model. Additionally, RNA sequencing revealed several uniquely expressed genes and significantly enriched genes related to tissue development, cell death, and cell migration tumors treated with anti-CD47 antibodies. Thus, demonstrating that CD47 blockade affects cancer cell and tumor microenvironment signaling to limit metastatic spread and may be an effective therapeutic for triple-negative breast cancer brain metastasis.