PGP and breast cancer: Meng et al. constructed 50 nm mesoporous silica nanoparticles to transport doxorubicin and Pgp siRNA, which are protected via a polyethyleneimine-polyethylene glycol copolymer, resulting in an 8% increase in doxorubicin and Pgp siRNA permeability by 8%, ultimately reversing the resistance of breast cancer to doxorubicin.