PGP and cancer: The developed Dox-Mel PL drug delivery system could effectively control MDR cancer cells and provide the following advantages: (1) synergistic effect of the co-delivery of doxorubicin and melittin via a biocompatible polymersome; (2) reduced side effects of doxorubicin and melittin; and (3) prevention of drug resistance through P-gp downregulation by melittin.