PGP and cancer: Confocal analysis indicates a cytoplasmic localization of Dox in MDA-MB-231 when delivered through Fol-Apt-NC (Figure S6), as previously shown for Fol-NC in HeLa cells [9], which suggests that the receptor-mediated entry enables Dox to escape the recognition by P-gp proteins on the cell membrane enhancing Dox accumulation in resistant cancer cells without efflux [9,38].