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P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) is a major obstacle in achieving the therapeutic benefits of paclitaxel (PTX) in the treatment of human ovarian carcinoma.This study is aimed to develop an efficient PTX drug delivery approach to overcome MDR.Redox-responsive micelles consisting of amphiphilic polymers containing disulfide linkages,ie,poly (phosphate ester)-SS-D-α-tocopheryl succinate (POPEA-SS-TOS,PSST) were prepared.PTX-loaded PSST micelles (PTX/PSST-M) designed to display synergistic functions,including reversible inhibition of P-gp,intracellular redox-sensitive release and potent anticancer activities.The average size of PTX/PSST-M was 68.1±4.9 nm.The encapsulated PTX was released quickly through redox-triggered dissociation of micelles.The inhibition of P-gp activity and enhanced cellular accumulation of the PSST micelles were validated.PTX/PSST-M showed significantly increased cytotoxicity against PTX-resistant human ovarian cancer A2780/PTX cells:when the cells were treated with PTX/PSST-M for 48 h,the equivalent IC50 value of PTX was reduced from 61.51 to 0.49 μmol/L.The enhanced cytotoxic effects of PTX/PSST-M against A2780/PTX cells were attributed to their synergistic effects on reducing the mitochondrial transmembrane potential,ATP depletion,ROS production,and activation of apoptotic pathways.Furthermore,PTX/PSST-M significantly increased cell apoptosis/necrosis and cell cycle arrest at the G2/M phase in A2780/PTX cells.These results demonstrate that the redox-responsive PSST micelles inhibit P-gp activity and have a good potential to effectively reverse PTX resistance in human ovarian carcinoma cells by activating intrinsic apoptotic pathways.