PGP and breast carcinoma: To find out whether the aptamer labeling of the nanoparticles can enhance the silencing of P-gp and sustain the knockdown activity even at Dox exposure, Dox-resistant 4T1-R breast cancer cells were transfected with aptamer/non-aptamer labeled P-gp siRNA encapsulated nanoparticles for 24 hours followed by another 3 hours with/without Dox treatment.