88 Review Received: 21 July 2010 Revised: 22 September 2010 Accepted: 22 September 2010 Published online in Wiley Online Library: 23 November 2010 (wileyonlinelibrary.com) DOI 10.1002/psc.1318 A new family of peptide – nucleic acid nanostructures with potent transfection activities ‡ Burkhard Bechinger, a* Verica Vidovic, a Philippe Bertani a and Antoine Kichler b,c A family of His-rich peptides has been shown to complex DNA and efficiently deliver these nucleic acids into eukaryotic cells. Therefore, these nanoscale complexes have potential applications in gene therapy. Here, we review a number of spectroscopic and biophysical investigations aimed at characterizing the supramolecular interactions of the peptides with the nucleic acids and when overcoming the membrane barriers of the cell. Furthermore, solid-state NMR distance measurements for the first time reveal close interatomic distances between the amino acid side chains and the DNA phosphates within the transfection complex. A recent study indicates that the peptides are also potent transfectants of siRNAs and they could thereby be of potential interest for gene silencing therapies using these compounds. Copyright c  2010 European Peptide Society and John Wiley & Sons, Ltd. Keywords: solid-state NMR; isothermal titration calorimetry; siRNA; DNA; histidine-rich peptide; antimicrobial peptide; membrane interaction; cell-penetrating peptide Introduction The capacity to deliver nucleic acids into cells has profoundly changed fundamental and applied research. Indeed, besides allowing one to investigate the effect of expression of a given protein in a cell, it has also allowed the concept of gene therapy to emerge. The objective of the latter is to deliver a therapeutic gene into cells for the treatment of acquired and genetic diseases. However, as DNA is a negatively charged macromolecule that does not enter cells, the success of gene therapy will depend on our capacity to develop efficient and safe DNA vehicles. One delivery approach consists in exploiting the properties of viruses such as adeno-associated virus (AAV), which corresponds to a protein/DNA supramolecular assembly about 25 nm in size. This is currently the most widely used system, including in clinical trials. However, these viral vectors are not devoid of limitations: for ex- ample, the maximal size of DNA fragment they can introduce into a cell is <5 kb. All other approaches are collectively summarized under the term ‘nonviral gene delivery systems’ and use designed molecules. The approach that has attracted the greatest attention consists in using synthetic cationic compounds [1 – 3]. The rationale of this strategy was simple, namely, mimicking the properties of hi- stones, i.e. condensing the DNA in order to obtain nanometric par- ticles. Indeed, most cationic compounds are able to compact DNA. However, DNA condensation is not sufficient for efficient transfec- tion of eukaryotic cells. In fact, the (ideal) transport system should, in addition, be able to protect DNA against enzymatic degradation, allow for the cellular uptake of the complexes, facilitate the endo- somal escape of the plasmid and lastly, favor the nuclear delivery. In the last 20 years, a great variety of molecules have been syn- thesized, ranging from polypeptides such as polylysine to synthetic lipids, polymers, dendrimers, nanoparticles and peptides. Notably, among all, the latter family is the least explored, although peptides allow product identification and quality control as well as the pos- sibility of a reproducible and scalable production process, which are all important properties for future biomedical applications. Cationic Peptides for Gene Delivery In the 1990s, one of the most popular transfection agent was polylysine, although this homopolymer performed poorly when mixed only with DNA [4]. But pioneering work by Ernst Wagner’s group showed that the transfection efficiency can be greatly enhanced by adding fusogenic anionic peptides to the polylysine–DNA complexes. In particular, these authors used peptides derived from the N-terminal segment of the HA-2 subunit ∗ Correspondence to: Burkhard Bechinger, Facult´ e de chimie, Institut le Bel, 4, rue Blaise Pascal, 67070 Strasbourg, France. E-mail: bechinger@chimie.u-strasbg.fr a Universit´ e de Strasbourg/CNRS, UMR7177, Institut de Chimie, 4, rue Blaise Pascal, 67070 Strasbourg, France b Genethon, BP60, 91002 Evry, France c CNRS UMR 8151, Inserm U1022, Universit´ e Ren´ e Descartes, Chimie-Paristech, Paris, France ‡ Special issue devoted to contributions presented at the E-MRS Symposium C ‘Peptide-based materials: from nanostructures to applications’, 7–11 June 2010, Strasbourg, France. Abbreviations used: ITC, isothermal titration calorimetry; MAS, magic angle spinning; POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; POPE, 1- palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine; POPG, 1-palmitoyl-2- oleoyl-sn-glycero-3-phospho-(1 ′ -rac-glycerol); POPS, 1-palmitoyl-2-oleoyl-sn- glycero-3-phospho-L-serine; REDOR, rotational echo double resonance. J. Pept. Sci. 2011; 17: 88–93 Copyright c  2010 European Peptide Society and John Wiley & Sons, Ltd.