A small, synthetic peptide for gene delivery via the serpin-enzyme complex receptor

The serpin-enzyme complex receptor (SECR) has previously been successfully targeted for gene delivery using synthetic peptide ligands covalently linked in fluid phase to commercially available polylysine preparations (approximately 10-54kDa). The objective of the present study was to improve this approach by the use of small, bifunctional, and easily standardised synthetic peptides.

Two synthetic peptides designated polylysine antitrypsin 1 (PAT1) (K16 FNKPFVFLI) and PAT2 (K16 CSIPPEVKFNKPFVFLI) were evaluated for gene delivery to the HUH7 human hepatocyte cell line. The K16 moiety binds DNA electrostatically, while the FVFLM motif of human alpha1-antitrypsin targets the SECR.

Both PAT1 and PAT2 bind to and condense DNA into small particles as shown by laser scattering techniques. However, only PAT2 is effective for gene delivery, presumably on account of the greater distance between the K16 chain and the FVFLM motif. Gene delivery by PAT2/DNA complexes is chloroquine-dependent, can be blocked completely by free ligand (CSIPPEVKFNKPFVFLI), and is highly efficient (e.g. approximately five-fold more effective than lipofectamine). At physiological salt concentrations, PAT2/DNA complexes formed at 4 microg/ml DNA are approximately 350 nm in diameter and highly effective for gene transfer, but at 100 microg/ml DNA the complexes are aggregated (diameter > 4 microm) and inactive.

A small (33 amino acid), bifunctional, synthetic peptide represents a highly efficient and readily standardised DNA vector for the SECR. The effectiveness of this peptide depends on the distance of the K16 moiety from the targeting ligand. High salt concentrations are not required to form effective vector/DNA complexes.