Marked transfection enhancement by the DPL (DNA/peptide/lipid) complex

A short peptide, corresponding to the nuclear localization signal of the human immunodeficiency virus-1 Tat protein, Arg-Lys-Lys-Arg-Arg-Gln-Arg-Arg-Arg, was modified by adding a cysteine residue at the COOH terminus. The peptide was mixed with a reporter plasmid, and then with cationic lipids, to form a tripartite complex, DNA/peptide/lipid (DPL). Various cell lines were treated with the DPL complex and compared for transfection efficiency with those of the conventional DNA/lipid (DL) complex. With the simple inclusion of the peptide, the DPL complex showed much enhanced transfection. Meanwhile, the plasmid DNA mixed only with the peptide exhibited some improvement but with much lower transfection than the DPL complex. When the DPL complex was formed with various cationic lipids, the DOSPA/DOPE exhibited superior transfection efficiency than the other cationic lipids tested at the optimal ratio of 1:3:5 (w:w:w) in many cell types. At the optimal ratio of the DPL components, transfection efficiency was routinely shown to be ≈10-fold higher for reporter gene expression than that of the conventional DL complex. Furthermore, when subcutaneous tumors of a colon cancer cell line (SW480) were treated intratumorally with antisense oligos, k-ras-RiAS, delivered as a DPL complex, tumor growth was markedly suppressed. This study shows that the DPL complex, which is easy to formulate by ordered mixing, can be employed for a much enhanced cellular uptake of a transgene both in vitro and in vivo.