Synergistic effects of A-B-C-type amphiphilic copolymer on reversal of drug resistance in MCF-7/ADR breast carcinoma

P-glycoprotein (P-gp) overexpression has become the most common cause of occurrence of multidrug resistance in clinical settings. We aimed to construct a micellar polymer carrier to sensitize drug-resistant tumors to doxorubicin (DOX). This A-B-C-type amphiphilic copolymer was prepared by the sequential linkage of β-cyclodextrin, hydrophobic poly(d,l-lactide), and hydrophilic poly(ethylene glycol). Upon incubation of the DOX-loaded micelles with DOX-resistant human breast carcinoma MCF-7/ADR cells, significantly enhanced cytotoxicity and apoptosis were achieved. A series of studies on the action mechanism showed that the polymer components such as β-cyclodextrin, hydrophobic poly(d,l-lactide) segment, and poly(ethylene glycol) coordinatively contributed to the improved intracellular ATP depletion and ATPase activity, increased intracellular uptake of P-gp substrates via competitive binding to P-gp, and decreased P-gp expression in MCF-7/ADR cells. More interestingly, a similar phenomenon was observed in the zebrafish xenograft model, resulting in ~64% inhibition of MCF-7/ADR tumor growth. These results implied that the polymeric micelles displayed great potentials as P-gp modulators to reverse DOX resistance in MCF-7/ADR breast carcinoma.