Targeted Delivery of miR-34a via Anti-CD47 Antibody Conjugates for Enhanced Cancer Immunotherapy in Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer that lacks estrogen receptor, progesterone receptor, and HER2 expression, which limits the efficacy of targeted therapies. MicroRNA-34a-5p (miR-34a), a tumor-suppressor miRNA known for regulating oncogenic pathways, initially appeared promising as a therapeutic avenue. However, the clinical translation of miR-34a has been hindered by challenges such as poor stability, inefficient cytoplasmic delivery, and immune-related toxicities, as evidenced by the failure of MRX34 in trials. To address these limitations, this study developes a novel antibody-oligonucleotide conjugate (AOC) platform anti-CD47-miR-34a conjugate (aCD47-C-miR34a). The aCD47-C-miR34a system combines the anti-CD47 antibodies with miR-34a using a bioreducible linker, ensuring targeted cytoplasmic delivery via CD47-mediated endocytosis and endosomal escape. CD47, an immune checkpoint protein overexpressed in TNBC, facilitates immune evasion, making it an attractive therapeutic target. In preclinical TNBC models, aCD47-C-miR34a successfully restored miR-34a's tumor-suppressive functions by downregulating oncogenic pathways including PD-L1, while modulating the tumor microenvironment. This dual mechanism promoted macrophage phagocytosis, enhanced CD8⁺ T-cell activation, and induced apoptosis, resulting in significant tumor inhibition without systemic toxicity. These findings demonstrate the transformative potential of aCD47-C-miR34a in overcoming TNBC's oncogenic and immune-evasive mechanisms, paving the way for innovative treatments in TNBC and other heterogeneous, aggressive cancers.