Poly(
ethylene glycol)-b-poly(γ-benzyl
L-glutamate)s bearing the
disulfide bond (
PEG-SS-PBLGs), which is specifically cleavable in intracellular compartments, were prepared via a facile synthetic route as a potential carrier of
camptothecin (
CPT). Diblock copolymers with different lengths of PBLG were synthesized by ring-opening polymerization of benzyl
glutamate N-carboxy
anhydride in the presence of a PEG macroinitiator (PEG-SS-NH(2)). Owing to their amphiphilic nature, the copolymers formed spherical
micelles in an aqueous condition, and their particle sizes (20-125 nm in diameter) were dependent on the block length of PBLG. Critical
micelle concentrations of the copolymers were in the range 0.005-0.065 mg/mL, which decreased as the block length of PBLG increased.
CPT, chosen as a model anticancer
drug, was effectively encapsulated up to 12 wt % into the hydrophobic core of the
micelles by the
solvent casting method. It was demonstrated by the in vitro optical imaging technique that the fluorescence signal of
doxorubicin, quenched in the
PEG-SS-PBLG
micelles, was highly recovered in the presence of
glutathione (GSH), a tripeptide reducing
disulfide bonds in the cytoplasm. The
micelles released
CPT completely within 20 h under 10 mM GSH, whereas only 40% of
CPT was released from the
micelles in the absence of GSH. From the in vitro cytotoxicity test, it was found that
CPT-loaded
PEG-SS-PBLG
micelles showed higher toxicity to SCC7
cancer cells than
CPT-loaded PEG-b-PBLG
micelles without the
disulfide bond. Microscopic observation demonstrated that the
disulfide-containing
micelle could effectively deliver the
drug into nuclei of SCC7 cells. These results suggest that
PEG-SS-PBLG diblock copolymer is a promising carrier for intracellular delivery of
CPT.