Calcium enhanced delivery of tetraarginine-PEG-lipid-coated DNA/protamine complexes

As we have previously reported the delivery of plasmid DNA (DNA) complexed with oligoarginine-PEG artificial lipids (oligoarginine/DNA complexes), we focused on tetra- and decaarginine (Arg4, Arg10) to improve transfection efficiency by both the formation of oligoarginine-coated DNA complexed with protamine (PD), and the addition of Ca2+ after formation of complexes. The efficiency of DNA condensation was determined by gel electrophoresis. Cellular uptake and transfection efficiency were evaluated in human cervical carcinoma HeLa cells using flow cytometry and luciferase assay. Oligoarginine-coated PD enhanced transfection efficiency significantly more than complexes where Arg10 in both vectors exhibited higher transfection efficiency than Arg4. As assessed by gel retardation assay, high gene expression by Arg10 may be explained by Arg4 binding DNA more strongly than Arg10. The addition of Ca2+ to incubation medium increased transfection efficiency of Arg4-coated PD 70-fold, similar to that of Arg10-coated PD alone without an increase of cellular uptake, suggesting that Ca2+ induced the release of DNA from complexes in endosomes. Only Arg4 with low cytotoxicity could gain an advantage from Ca2+ in transfection, but Arg10 with relatively high cytotoxicity could not. The present results demonstrate that Arg4-coated PD with Ca2+ has great potential as an efficient non-viral vector with low toxicity.