PGP and cancer: MDR arises from various complex mechanisms, including abnormal expression of topoisomerase regulated by apoptosis-related genes, as well as the overexpression of P-glycoprotein (P-gp).37–39 Key strategy to overcome cancer MDR is through combination therapy by utilizing NPs for targeted delivery to specific subcellular organelles, and implementing multimodal combination therapy.36,40,41 The overexpressed P-gp levels in resistant cancer cells are particularly crucial, as they efflux chemotherapeutic agents out of the cells.