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.