PGP and breast cancer: The low expression profile of P-gp was maintained in aptamer-labeled siRNA-encapsulated nanoparticle transfection even after Dox exposure (lane 5; F31+Apt+Dox), whereas, the non-aptamer labeled siRNA-encapsulated nanoparticle transfection could not sustain the P-gp silencing, as presumably, the Dox can enhance the expression of P-gp in those Drug-resistant 4T1-R breast cancer cells (lane 4; F31-Apt+Dox in Fig. 8).