Triple-negative breast cancers (TNBCs) are aggressive and heterogeneous in nature with a recurrence rate observed in over 50% of patients treated with a primary round of conventional chemotherapy. Our previous studies showed that CD276 (also known as B7-H3), an immune checkpoint molecule that suppresses natural killer (NK) and T cells responses, is overexpressed in >80% of breast cancers. Mitochondria play a central role in cellular metabolism, proliferation, and apoptosis, making them a promising therapeutic target in cancer. The objective of this study was to develop a combined treatment strategy, i.e. antibody-drug conjugates (ADCs) and gene therapy, to effectively treat CD276+ TNBC. First, an anti-CD276 mAb (IgG2b/kappa) that targets the extracellular domain of surface receptor was developed and used to construct antibody-mertansine (DM1) conjugate. Further flow cytometry analysis, confocal microscopy imaging, and In Vivo Imaging System (IVIS) imaging demonstrated the TNBC specificity of our CD276 mAb. The high anti-cancer cytotoxicity and efficacy of CD276 ADC were revealed in three cell lines (MDA-MB-468, MDA-MB-231, 4T1) in vitro and in two TNBC xenografted mouse models in vivo, respectively. Second, we developed an advanced cancer mitochondrial-targeted luminoptogenetics technology (cmLumiOpto), and constructed a gene delivery vehicle, CD276-targeted monoclonal antibody-tagged exosome-associated adeno-associated virus (mAb-Exo-AAV). The cmLumiOpto reduced TNBC tumor burden and inhibited metastasis effectively by depolarizing cancer mitochondria and causing severe cancer cell death. Finally, we tested these therapies as monotherapies and in combination to evaluate their combined potency and synergy. Three models, including cell line-based xenograft models, metastasis model and patient-derived xenograft (PDX) models, were used for the in vivo evaluations. This study suggests that combining CD276-targeted ADC and cmLumiOpto could provide a promising targeted therapy for TNBC patients in future.
