Synthesis of Bifunctional Integrin‐Binding Peptides Containing PEG Spacers of Defined Length for Non‐Viral Gene Delivery

Improving the buffer and serum stability of non-viral gene delivery vectors, and increasing their circulation time in vivo, is an important focus of current research in gene therapy. The most successful strategies to date have involved shielding the complexes with large polydisperse PEG adducts. However, this approach is accompanied by a fall in transfection efficiency. In this paper we describe the solid-phase synthesis of a series of bifunctional peptides bearing short PEG spacers of defined structure as components of lipopolyplex gene delivery vectors. Short, high-yielding routes to a series of PEG-amino acids are described: these PEG-amino acids can be used in varying combinations to afford bifunctional peptides with varying lengths of PEG spacers by using standard solid-phase synthesis techniques. A series of lipopolyplexes were formulated using these bifunctional peptides, and their transfection properties assessed. Dynamic light scattering measurements on the complex with the best transfection properties showed that in phosphate-buffered saline this complex was considerably more stable, and aggregated more slowly, than a complex formulated using a similar peptide lacking the short PEG spacer. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.