OBJECTIVETo synthesize a biodegradable and minimally cytotoxic amphiphilic block copolymer of PLGA-b-(PEI-co- PEG) and study its micellization behavior.

METHODSPLGA was synthesized by ring-opening polymerization. The cross-linked copolymer of PEI-co-PEG was synthesized from the low-molecular-weight polyethyleneimine (PEI, 1800 D) and hydrophilic poly(ethylene glycol) (PEG, 2000 D). PLGA-b-(PEI-co-PEG) was synthesized by dehydration condensation reaction of PLGA and water soluble PEI-co-PEG. The biodegradability of PEI-co-PEG was evaluated according to the molecular weight change after incubation at 37 ℃ for different time. The cytotoxicity of PLGA- b-(PEI-co-PEG) and PEI-co-PEG in MCF-7 cells was determined by MTT assay. The cationic PLGA-b-(PEI-co-PEG) micelles were prepared by standard dialysis method. The particle size and Zeta potential of the micelles were measured by a Malvern laser particle size analyzer. Micelle/insulin complexes were prepared by simple mixing method and their morphology were characterized by transmission electron microscopy (TEM). The fluorescence quenching method was used to determine the stability of the micelle/insulin complexes at different salt concentrations.

RESULTSAmphiphilic block copolymer of PLGA-b-(PEI-co-PEG) was successfully synthesized. The half-life of PEI-co-PEG degradation in PBS at 37 ℃ was about 48 h. The 50% cell inhibiting concentration (IC) of PLGA-b-(PEIco- PEG) and PEI-co-PEG in MCF-7 cells were 1375.7 μg/mL and 425.1 μg/mL, respectively. The micelles of PLGA-b-(PEI-co- PEG) (particle size: 99.5±2.61 nm, Zeta potential: 52.9±2.38 mV) were complexed with insulin electrostatic interaction and formed nanoscale micelle/insulin complexes. The dissociation rate of micelle/insulin complexes in 150 mmol/L NaCl solution was 27.6%.

CONCLUSIONSThe synthesized PEI-co-PEG shows good degradability . The cytotoxicity of PLGA-b-(PEI-co- PEG) is significantly lower than PEI-co-PEG, and PLGA-b-(PEI-co-PEG) micelle/insulin complexes have good salt- resistant stability in physiological condition.