Targeted minicircle DNA delivery using folate–poly(ethylene glycol)–polyethylenimine as non-viral carrier

Targeted gene delivery systems have attracted great attention due to their potential in directing the therapeutic genes to the target cells. However, due to their low efficiency, most of the successful applications of polymeric vectors have been focused on genes which can achieve robust expression. Minicircle DNA (mcDNA) is a powerful candidate in terms of improving gene expression and prolonging the lifespan of gene expression. In this study, we have combined folate/poly(ethylene glycol) modified polyethylenimine and mcDNA as a new tumor gene delivery system. We found that folate-labeled polyplexes were homogenous, with a size ranging from 60 to 85 nm. mcDNA increased folate-labeled vector based gene expression 2–8 fold in folate receptor-positive cells. Results of folic acid competition assay indicated that mcDNA mediated by folate-labeled vector were internalized into cells through receptor-mediated endocytosis. The investigation of the endocytosis pathway of the polyplexes showed that a large portion of them escaped from endo/lysosome and the polyplexes were associated before being separated in the nucleus. Furthermore, in vivo optical imaging and luciferase assays demonstrated that systemic delivery of the folate-labeled polyplexes resulted in preferential accumulation of transgenes in folate receptor-positive tumors, and mcDNA mediated approach achieved 2.3 fold higher gene expressions in tumors than conventional plasmid. Cytotoxicity assays showed that PEG-shielding of the polyplexes reduced the toxicity of PEI.