Nuclear localization signal-containing PLGA nanospheres and PLGA-graft-PEI copolymers for delivery of plasmid DNA

Abstract

Polymeric nanospheres formulated from the biodegradable poly(L-lactide-co-glycolide) (PLGA) have been extensively investigated for the applications in controlled drug delivery and gene delivery. In this study, we developed a nuclear localization signal (NLS, SV40 peptide)-conjugated PLGA nanospheres to enhance gene transfection efficiency. The conjugation of an NLS peptide to PLGA nanospheres could improve nuclear localization of PLGA/plasmid DNA nanospheres and thereby improve transfection efficiency of PLGA nanospheres gene delivery system. Gene transfection efficiency was tested using nanospheres encapsulating the luciferase gene in vitro on human embryonic kidney 293 (HEK293) cells. The plasmid DNA release from PLGA nanospheres was sustained over 15 days. The NLS conjugation enhanced the gene transfection efficacy of PLGA nanospheres in vitro by 2.2 fold at day 3. Although the in vitro gene transfection efficiency of NLS-conjugated PLGA nanospheres was lower than that of lipofectamine, duration of the gene expression was more sustained. This study showed that NLS conjugation enhanced the gene transfection efficiency of PLGA nanospheres and prolonged the gene expression in vitro. In the second part of our study, we synthesized a new type of grafting copolymers of PLGA onto polyethylenimine (PEI). We investigated the feasibility of using these copolymers to design more desirable gene delivery systems in terms of gene transfection efficiency and cytotoxicity. Zeta-potential of PLGA-g-PEI copolymers was measured at pH 4, 7 and 10. Cytotoxicity of the copolymers was assayed using MTT assay and lactate dehydrogenase release assay at various polymer concentrations. Transfection studies were conducted using human HEK 293 cells. A reasonable concentration dependency was found for all samples, the cell viability of the polymers decreased with increasing polymer concentration. Transfection with PEI-g-PLGA copolymers yielded variable results depending on the PLGA content, and the N/P ratio. The transfection efficiency decreased as the PLGA contents in copolymer increased. Transfection efficiency was the highest level at N/P ratio 5 for all samples. PLGA-g-PEI copolymer can be used as delivery systems for DNA but further optimization is necessary to exploit their full potential.