Multidrug resistance (MDR) of tumor cells is becoming the main reason for the failure of chemotherapy and P-glycoprotein (P-gp) mediated drug efflux has demonstrated to be the key factor for MDR. To address this issue, a novel pH-responsive mixed micelles drug delivery system composed of dextran-g-poly(lactide-co-glycolide)-g-histidine (HDP) and folate acid-D-α-tocopheryl polyethylene glycol 2000 (FA-TPGS2K) copolymers has been designed for the delivery of antitumor agent, paclitaxel (PTX) via FA-receptor mediated cell endocytosis, into PTX-resistant breast cancer MCF-7 cells (MCF-7/PTX). PTX-loaded FA-TPGS2K/HDP mixed micelles were characterized to have a small size distribution, high loading content and excellent pH-responsive drug release profiles. Compared with HDP micelles, FA-TPGS2K/HDP mixed micelles showed a higher cytotoxicity against MCF-7 and MCF-7/PTX cells due to the synergistic effect of FA-receptor mediated cell endocytosis, pH-responsive drug release and TPGS mediated P-gp inhibition. P-gp expression level, ATP content and mitochondrial membrane potential change have been measured, the results indicated blank FA-TPGS2K/HDP mixed micelles could inhibit the P-gp activity by reducing the mitochondrial membrane potential and depleting ATP content but not down-regulating the P-gp expression. In vivo antitumor activities demonstrated FA-TPGS2K/HDP mixed micelles could reach higher antitumor activity compared with HDP micelles for MCF-7/PTX tumor cells. Histological assay also indicated that FA-TPGS2K/HDP mixed micelles showed strongly apoptosis inducing effect, anti-proliferation effect and anti-angiogenesis effect. All these evidences demonstrated this pH-sensitive FA-TPGS2K/HDP micelle-based drug delivery system is a promising approach for overcoming MDR.Statement of SignificanceIn this work, a novel FA-TPGS2K copolymer has been synthesized and used it to construct mixed micelles with HDP copolymer to overcome MDR effect. Furthermore, a series in vitro and in vivo evaluations have been made, which supported enough evidences for the efficient delivery of antitumor drug to MDR cells.Download high-res image (242KB)Download full-size image

Over the last few decades pH-sensitive drug delivery systems have been successfully developed for the treatment of cancers by improving the therapeutical effect. In this study, a novel pH-sensitive conjugate glycyrrhetinic acid–polyethylene glycol–Schiff bond–cholesterol (GPSC) has been synthesized successfully and used to construct doxorubicin (DOX)-loaded liposomes (GPSLP/DOX) with both pH-sensitive features and active targeting ability. DOX was incorporated into liposomes using a thin-film hydration method with a relatively high encapsulation efficiency (EE%) and drug loading content (LC%). Physicochemical characteristics, in vitro release behavior, cellular toxicity and cellular uptake, in vivo biodistribution as well as in vivo antitumor activities of GPSLP/DOX were investigated. GPSLP/DOX showed significantly pH-sensitive features in the in vitro release assay. All the blank liposomes were nontoxic in the in vitro cytotoxicity assay. In the MTT assay, GPSLP/DOX showed the highest cell cytotoxicity among all the groups. A cellular uptake study revealed that GPSLP/DOX could be taken up efficiently via receptor-mediated endocytosis and pH-responsive drug release of DOX into cytoplasm, which resulted in a higher cytotoxicity and therapeutical effect. An in vivo NIR fluorescence image study showed that GPSLP/DOX could specifically accumulate in the liver and tumor sites via receptor mediated endocytosis. In vivo antitumor activity results showed that this novel GPSLP/DOX could significantly inhibit tumor growth and prolong survival time due to its pH-responsive behaviour and GA-mediated endocytosis, resulting in a lower systematic toxicity and higher therapeutical effect. All these results confirm that this GA-mediated pH-sensitive GPSLP/DOX is a novel nanocarrier for the delivery of the antitumor agent DOX to reach higher toxicity effects against tumor tissue.