Novel reducible linear L-lysine-modified copolymers as efficient nonviral vectors

The development of biodegradable gene delivery systems with high transfection efficiencies is paramount to the clinical translation of nonviral gene carriers. Therefore, to produce a biocompatible, reducible, effective and non-toxic gene delivery system, we have designed and synthesized novel reducible linear L-lysine modified copolymers (LLCs) as an alternative to high molecular weight poly(L-lysine) (PLL). The molecular weight (MW) of the copolymers was found to be ∼ 3.2 kDa with a polydispersity index of ∼ 1.2. Gel retardation assays showed complete condensation of DNA at N/P ratios greater than 20/1 and exceptional LLC/pDNA polyplex stability during incubation with DNase I. Release of DNA from the polyplexes only occurred in the presence of the reducing agent dithiothreitol (DTT). The particle sizes of LLC/pDNA polyplexes were found to be between 100 and 231 nm with surface charges of 0.8–17 mV respectively. The transfection efficiencies of the polyplexes as determined with a luciferase assay showed that LLC polyplexes produced five times higher transfection efficiencies in HDF cells, three times higher transfection efficiencies in MCF-7 cells, and four times higher transfection efficiencies in MA cells as compared to the optimal PLL control. The LLC/pDNA polyplexes showed significantly lower cytotoxicities as compared to the control in HDF, MCF-7 and MA cells at certain N/P ratios. Therefore, these results suggest that these novel LLCs are efficient, reducible and biocompatible polymers for nonviral gene delivery.

Schematic diagram of the DNA release inside the cytosol from the LLC (L-lysine modified copolymers)/pDNA polyplexes upon the reduction of the disulfide bonds within the polymer backbone due to the difference in redox potential between the intracellular and extracellular environment.Figure optionsDownload as PowerPoint slide