Preparation and biological characterization of pH-responsive PASP-g-PEG-DDA-Hyd-ADR

Abstract

This research aimed to develop a biodegradable and biocompatible polymeric micelle system to solubilize ADR and release this anticancer agent in a pH-dependent manner. To achieve the purpose above, the pH-responsive amphiphilic centipede-like polymer conjugate p(aspartate)-graft-p(ethylene glycol)-dodecylamine-hydrazone-adriamycin (PASP-g-PEG-DDA-Hyd-ADR) was successfully synthesized. Adriamycin (ADR) was conjugated to the polymer backbone through an acid-labile hydrazone bond. The product was found to form spherical micelles in aqueous media due to its amphiphilic nature with an average particle size of 25 nm measured by dynamic light scattering (DLS) and AFM imaging. The drug release curve shows that the amount of released ADR gradually increased with a decrease in pH and that almost no ADR was released under normal physiological conditions (pH 7.4). This result showed that the micelles can stably preserve drugs under physiological conditions (pH 7.4) and selectively release them by sensing the intracellular pH decrease in endosomes and lysosomes (pH 4–6). An MTT assay showed that the acute cytotoxicity to HepG2 decreased compared with free ADR and that the released ADR from the conjugate kept its pharmaceutical activity. Remarkably, confocal laser scanning microscopy (CLSM) revealed that the localized fluorescence is dot-shaped within the cytoplasm, suggesting the presence of the micelles trapped in vesicular entities after 2 h incubation. The time-dependent increase in fluorescence intensity, which was also observed by flow cytometry, indicated that the polymer–drug micelles were taken up by the cancer cells through an endocytic process.