pH-responsive release of paclitaxel from hydrazone-containing biodegradable micelles

Many tumor cells have acidic microenvironment that can be exploited for the design of pH-responsive drug delivery systems. In this work, well-defined pH-sensitive and biodegradable polymeric micelles were prepared and evaluate as carrier of paclitaxel (PTX). A diblock copolymer constituting of a poly(ethylene glycol) (PEG) and a polycaprolactone (PCL) segment linked by a pH-sensitive hydrazone bond (Hyd), which was denoted as mPEG-Hyd-PCL, was synthesized. The copolymer was assembled to micelles with mean diameters about 100 nm. The mean diameters and size distribution of the hydrazone-containing micelles increased obviously in mildly acidic environments while kept unchanged in the neutral. No significant change in size was found on polymeric micelles without hydrazone (mPEG-PCL). PTX was loaded into micelles, and the anticancer drug released from mPEG-Hyd-PCL micelles was promoted by the increased acidity. In vitro cytotoxicity study showed that the PTX-loaded mPEG-Hyd-PCL micelles exhibited significantly enhanced cytotoxicity against HepG2 cells compared to the non-sensitive mPEG-PCL micelles. These results suggest that hydrazone-containing copolymer micelles with pH sensitivity and biodegradability show excellent potential as carriers of anticancer drugs.