pH and reduction dual-sensitive copolymeric micelles for intracellular doxorubicin delivery

This study develops novel pH and reduction dual-sensitive micelles for the anticancer drug doxorubicin (DOX) delivery owing to the fact that the tumor tissues show low pH and high reduction environment. These sub-100 nm micelles present a core-shell structure under physiological conditions, but quickly release the loaded drugs responding to acidic and reductive stimuli. With disulfide bonds in each repeat unit of poly(β-amino ester)s, the novel copolymer was synthesized via Michael addition polymerization from 2,2'-dithiodiethanol diacrylate, 4,4'-trimethylene dipiperidine, and methoxy-PEG-NH(2). DOX released faster from micelles in a weakly acidic environment (pH 6.5) than at pH 7.4 or in the presence of a higher concentration (5 mM) of reducing agent (DTT). The release is even more effective in a scenario of both stimuli (pH 6.5 and 5 mM DTT). MTT assay showed that the DOX-loaded micelles had a higher cytotoxicity for HepG2 tumor cells than DOX at higher concentrations, and that blank micelles had a very low cytotoxicity to the tumor cells. Confocal microscopy observation showed that the micelles can be quickly internalized, effectively deliver the drugs into nuclei, and inhibit cell growth. These results present the copolymer as a novel and effective pH and reduction dual-responsive nanocarrier to enhance drug efficacy for cancer cells.