PGP and breast cancer: For example, based on the high overexpression of Y-1 receptor (Y1R) protein and P-gp in the multidrug-resistant breast cancer cell line, a selective Y1R ligand, [Asn(6), Pro(34)]-NPY (AP) was employed to stabilize the chemotherapeutic drug DOX and P-gp inhibitor tariquidar (Tar) co-loaded nanomicelles at the physiological level.