Heat-preconditioned MSC-derived exosomal miR‑486‑5p reverses doxorubicin resistance in breast cancer

OBJECTIVE: Drug resistance remains a major obstacle to chemotherapy in breast cancer. human bone marrow-derived mesenchymal stem cells (MSC)-derived exosomes are promising drug-delivery nanocarriers, but their anticancer efficacy is limited by insufficient cargo loading. We aimed to engineer MSC-derived exosomes with enhanced anti-resistance activity via mild heat preconditioning. METHODS: MSCs were preconditioned at 41°C for 1 h (heat-preconditioned exosomes, HP-Exo) or at 37°C (non-heat-preconditioned exosomes, No HP-Exo). Exosome yield, stemness, and microRNA (miRNA) profiles were assessed. MCF-7/ADR doxorubicin (DOX)-resistant cells were cultured as three-dimensional (3D) spheroids and treated with HP-Exo or No HP-Exo with or without DOX; cell viability and apoptosis were evaluated. RESULTS: Heat preconditioning preserved MSC stemness and increased exosome secretion via Rab27b upregulation. HP-Exo, but not No HP-Exo, sensitized MCF-7/ADR spheroids to DOX, enhancing apoptosis. HP-Exo delivered microRNA-486-5p (miR-486-5p), which directly targeted high mobility group AT-hook 1 (HMGA1), downregulating breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp). miR-486-5p inhibition abrogated, and its mimic restored, this chemosensitizing effect. CONCLUSION: Mild heat preconditioning is a simple strategy to engineer MSC-derived exosomes with enriched tumor-suppressive microRNA cargo and enhanced chemosensitizing activity, offering a promising nanotherapeutic platform to overcome chemoresistance in breast cancer.