Liposomes are spherical vesicles composed of natural or artificial lipids and are used as drug carriers. However, their surface needs modification with ligands to target specific tissues. Cell- derived Vesicles (CVs) are bioinspired drug carriers, as they derive from whole cells by physical methods. One of their most striking characteristics is the ability to preserve the topology and composition of the molecules present in the plasma membrane of the parental cell, enabling in vivo organotropism and specific drug delivery. The aim of this study is the investigation of the mechanisms by which liposomes and autologous CVs are internalized by 3 different breast cancer cell lines. Two of the selected cell lines, 4T1 and MDA-MB-231, are triple negative breast cancer cell lines, and the third one, MCF-7, is negative only for the protein HER2. The elucidation of the mechanism is likely to result to the optimization of specific drug delivery and comprehension of their sub- cellular fate. More specifically, liposomes and CVs were produced, characterized and loaded with the fluorescent dye FITC-dextran. Uptake experiments were performed using inhibitors of the clathrin dependent or caveolin dependent endocytic pathways and after incubating the cells at 4°C, where the active processes are inactivated. The results indicate that the endocytosis of CVs is active, mainly via the caveolin pathway, whereas liposomes are internalized actively by both pathways and also passively, as their uptake at 4°C is not significantly hampered.

Acknowledgements: This research has been co‐financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH – CREATE - INNOVATE (project code: MIS 5031802).