A Novel Mechanism of Tumour Communication: Malignant Extracellular Vesicles-Induced Aggressiveness in Benign Cells and Melatonin-Driven Reversal.

Extracellular vesicles (EVs/EV) are key mediators of intercellular communication and influence proliferation, migration, and metabolic reprogramming. In breast cancer, EVs released by malignant cells carry bioactive molecules capable of altering the behaviour of surrounding cells. However, it remains uncertain whether these vesicles can directly induce a more aggressive phenotype in benign mammary cells. Melatonin, known for its oncostatic properties, regulates proliferation, metabolism, and signalling pathways associated with tumour progression and may modulate EV-mediated intercellular communication. This study evaluated whether EVs derived from four breast cancer cell lines (MCF-7, MDA-MB-231, MDA-MB-453 and HCC70), treated or not with melatonin, can modify the phenotype of benign MCF10A cells. EVs were isolated from conditioned media and co-cultured with benign cells. Assays of proliferation, viability, colony formation, migration, lactate production and immunofluorescence were performed to assess EV-mediated effects. EVs derived from malignant cells promoted a more aggressive phenotype in benign cells, as evidenced by increased proliferation, migration, and phenotypic remodelling. In contrast, EVs derived from melatonin-treated malignant cells were associated with reduced lactate production and attenuation of pro-tumoural features. Overall, these findings demonstrate that tumour-derived EVs can induce aggressive traits in benign mammary cells and suggest that melatonin exposure in donor cells modulates EV-mediated effects, attenuating their pro-tumoural influence.