Extracellular vesicles from chemoresistant breast cancer cells reprogram macrophages toward an M2-like phenotype in an ABCC1-dependent manner

Triple-negative breast cancer is characterized by high rates of chemoresistance and poor clinical outcomes. Although ATP-binding cassette (ABC) transporters are well-established mediators of drug efflux, their role in tumor–immune communication remains poorly defined. Here, we investigated whether the acquisition of doxorubicin resistance alters extracellular vesicle (EV) biogenesis and cargo content. We report that the doxorubicin-resistant MDA-MB-231 cell line exhibits significantly higher rates of EV production, without changes in particle size distribution, compared to the parental cell line. At the cellular level, we observed a significant increase in the number of multivesicular bodies present in doxorubicin-resistant cells. Proteomic and Western blot analysis of isolated EVs derived from the doxorubicin-resistant MDA-MB-231 cell line, compared to the parental MDA-MB-231 cell line, revealed an enrichment of ABCC1, accompanied by enrichment of vesicle-associated pathways. Cellular ABCC1 localized to CD63-positive compartments and was validated to be enriched in resistant cell line-derived EVs. Functionally, EVs from resistant cells promoted M2-like polarization of primary human macrophages, characterized by decreased CD86⁺ and increased CD206⁺ populations in addition to a decrease in IL-6, IL-8 and TNFα levels. Knocking down ABCC1 in resistant cells significantly attenuated this effect. Together, these findings suggest EV-associated ABCC1 might be a contributor to macrophage polarization and immune modulation in breast cancer.