Reversing multidrug resistance by intracellular delivery of Pluronic® P85 unimers

Pluronics have been demonstrated as excellent multidrug resistance (MDR) reversal agent in the form of unimers rather than micelles. However, the effective intracellular delivery of Pluronic (R) unimers to MDR cancer cells still remains a big challenge. To address this issue, a mixed micellar system based mainly on the pH-sensitive copolymer of poly (L-histidine)-poly (D,L-lactide)-polyethyleneglycol-poly (D,L-lactide)poly (L-histidine) (PHis-PLA-PEG-PLA-PHis) and Pluronic (R) F127, some of which was conjugated with folate, was constructed to intracellularly deliver the unimers of Pluronic (R) P85 to MDR cells. The folate-mediated endosomal pH-sensitive mixed micelles (PHendoSM-P85/f) were prepared by a thin-film hydration method, by which Pluronic (R) P85 unimers and doxorubicin (DOX) were incoporated into the mixed micelles. The incorporation of Pluronic (R) P85 unimers was investigated by the surface tension test. The results indicated that the Pluronic (R) P85 unimers probably first inserted into the binary mixed micelles and then formed a triple-component mixed micelles with Pluronic (R) F127 and PHis-PLA-PEG-PLA-PHis as the loading content increased. Further analyzed with flow cytometry, confocal laser scanning microscopy (CLSM) and MIT assay, the micelles with inserted Pluronic (R) P85 unimers demonstrated much more cellular uptake and higher cytotoxicity against MDR cells than the triple-component mixed micelles and plain Pluronic (R) micelles. The enhanced MDR reversal effect was attributed to the successful intracellular delivery of Pluronic (R) P85 unimers to the MDR cells, which was confirmed by the subcellular colocalization of Pluronic (R) P85 unimers with mitochondria, the decreased ATP energy and mitochondrial membrane potential (MP) in the MCF-7/ADR cells. The pH(endo)SM-P85/f/DOX also demonstrated more dramatic antitumor efficiency and remarkable reduction of ATP energy in the MDR cells in tumors than the control formulations. The intracellular delivery of Pluronic (R) P85 unimers to the MDR cells based on the targeted and endosomal pH triggerd release mixed micelles has been demonstrated as a promising approach to reverse MDR. (C) 2013 Elsevier Ltd. All rights reserved.