Tmic-68. sirpα blockade as an immunotherapeutic strategy to treat breast cancer brain metastasis

Triple-negative breast cancer (TNBC) has a high incidence of brain metastasis, with no standard therapeutic strategy for treatment. Therefore, new targets are urgently needed to overcome disease mortality. The CD47/SIRPα signaling pathway is implicated in tumor progression due to bypassing innate and adaptive immune surveillance. Most strategies targeting this pathway focus on targeting the receptor CD47; however, direct targeting SIRPα as a potential approach to mitigate metastatic burden remains understudied. Single-cell-RNA-sequencing indicates that SIRPα expression on basal epithelial cells, and TCGA data shows SIRPα expression is associated with a significant reduction in survival in basal-like breast cancer. Our immune staining against SIRPα in breast cancer patient biopsies shows a 3.5-fold increase in expression in metastatic lesions compared to the primary tumor (n=19; p ≤ 0.01). Staining of 4T1 parental and brain-trophic 4T1-Br3 cells showed an 84% increase in SIRPα in the metastatic cells (n=3; p ≤ 0.05). Furthermore, Real-time cell impedance analysis revealed that SIRPα blockade inhibits TNBC 4T1br3 cell migration (n=4; p≤0.01), suggesting a link between SIRPα expression and metastatic potential. Furthermore, in vivo SIRPα blockade reduced brain metastatic burden by approximately 90%, (n=4-7; p ≤ 0.05). Digital spatial profiling of tissues revealed that SIRPα blockade was associated with reductions in immune checkpoints, including CTLA-4, PD-1, PD-L1, and LAG3, and immunosuppressive T-cell/monocyte populations. Furthermore, our spatial analysis indicated that brain lesions of WT mice have increases in the extracellular matrix protein fibronectin in the immune enriched regions, potentially serving as a barrier for immune cell infiltration contributing to invasion, metastasis, and immune evasion, was reduced by 70% in SIRPα treated brain lesions (n-3-6; p ≤ 0.05). Thus, these data suggest that SIRPα blockade may influence the tumor microenvironment to limit brain metastatic breast cancer growth and potentially enhance patient survival to metastatic brain disease.