Utilizing miR-34a-Loaded HER2-Targeting Exosomes to Improve Breast Cancer Treatment: Insights From an Animal Model

Purpose: Exosomes, nanoscale vesicles with high biocompatibility, were engineered to express human epidermal growth factor receptor 2 (HER2)-binding peptides and carry miR-34a, targeting HER2 and programmed death-ligand 1 (PD-L1)-positive breast cancer cells. Methods: An in vivo xenograft breast cancer model was established by subcutaneously injecting breast cancer cells of both HER2 and PD-L1 positivity (SK-BR3 cells) into the buttocks of BALB/c nude mice. miR-34a-loaded HER2-targeting exosomes, termed tEx[34a], were engineered by transfecting human adipose-derived mesenchymal stem cells with the pDisplay vector to express HER2-binding peptides (P51 peptide). Purified exosomes were then loaded with miR-34a, a tumor-suppressor miRNA, using the Exo-Fect transfection kit, creating tEx[34a] for targeted cancer therapy. Results: Intravenous administration of miR-34a-loaded HER2-targeting exosomes, referred to as tEx[34a], demonstrated superior targetability compared to other materials, such as natural exosomes, miR-34a-loaded exosomes, and unloaded HER2-targeting exosomes. In vivo experiments using mouse breast cancer xenograft models revealed that the administration of tEx[34a] resulted in the smallest tumor size and lowest tumor weight when compared to all other groups. Notably, tEx[34a] treatment significantly reduced PD-L1 expression in breast cancer tissue compared to the other groups. Furthermore, tEx[34a] administration led to the highest upregulation of pro-apoptotic markers (Bax, PARP, and BIM) and the lowest downregulation of the anti-apoptotic marker Bcl-xL, as confirmed through various methods including RT-PCR, Western blot analysis, and immunofluorescence. Conclusion: MiR-34a-loaded HER2-targeting exosomes demonstrate strong anticancer efficacy by selectively binding to HER2-positive breast cancer cells and effectively suppressing PD-L1 expression.