Novel reduction-sensitive pullulan-based micelles with good hemocompatibility for efficient intracellular doxorubicin delivery

A novel intracellular reduction-sensitive delivery system of doxorubicin (DOX), based on pullulan-stearic acid (P-ss-SA) conjugates with disulfide bonds as reduction-sensitive bonds, was successfully developed. The conjugates could self-assemble into micelles in aqueous media and encapsulate DOX. The properties of blank and DOX-loaded micelles were studied in detail. The results showed that the mean size of the blank and DOX-loaded micelles was around 187.7 nm and 194.4 nm, respectively. The drug loading content and encapsulation efficiency of the P-ss-SA micelles were around 6.19% and 65.53%, respectively. The mean size of reduction-sensitive P-ss-SA micelles increased dramatically under reductive conditions. The drug release of P-ss-SA micelles under reductive conditions was much faster than that under non-reductive conditions. The confocal laser microscopy and flow cytometry measurements indicated that the intracellular reductive conditions broke the disulfide bonds in P-ss-SA micelles and triggered the fast release of DOX. The in vitro IC50 of the DOX-loaded P-ss-SA micelles was lower than that of DOX-loaded micelles without reduction-sensitivity against HepG2 and MCF-7 cells. The blank micelles showed negligible cytotoxicity, and possessed excellent hemocompatibility without causing undesirable hemolysis. These results indicated that the biocompatible reduction-sensitive P-ss-SA micelles can be used as potential carrier systems for the intracellular delivery of DOX.