Research Update
Authors: Robert M. Frederickson
Journal: Molecular Therapy (2003)

Efficient gene delivery continues to be a major challenge for practitioners of gene therapy. Although virus-based gene vectors have been used for many years, drawbacks such as immunogenicity and the potential for toxicity and adverse events have led some to explore non-viral vectors. Synthetic polypeptides represent a relatively new medium for gene delivery. In a recent issue of the Proceedings of the Academy of Science, Antoine Kichler and colleagues make use of histidinerich amphipathic peptide antibiotics to deliver genes to cultured mammalian cells. Previously, peptides have been used primarily as adjunct agents—providing receptor-targeting functions to a viral particle, for example, or a nuclear localization signal to direct a genetic payload to the nucleus. In the new study, the authors used peptides that mimic the “proton sponge” activity of polyethyl-eneimines (PEIs), by incorporating a number of histidine residues into a backbone of amphipathic peptides that were rich in alanine and leucine. The amphipathic stretch helps destabilize membranes, and the alanine/leucine rich region is required for binding DNA. They achieved gene transfer rates similar to commercially available reagents, with the best transfer mediated by peptides containing at least four or five histidine residues in the central region of the sequence. Interestingly, the DNA-bound peptides retained their antibacterial activity, leading the authors to suggest that such agents could be useful to treat genetic diseases such as cystic fibrosis, in which bacterial infection is a common problem—by simultaneously delivering a therapeutic gene and a bacteriocidal agent. Proceedings of the National Academy of Science, Online edition, doi: 10.1073/pnas.0337677100 Hepatitis C virus (HCV) is a major cause of chronic hepatitis and hepatocellular carcinoma. Unfortunately, current treatment—a combination of interferon and ribavirin—is unable to resolve disease in most patients. Furthermore, the lack of a tissue culture system for this virus has impeded research of the mechanism of viral replication—and potential therapeutic approaches to its inhibition. However, HCV replicons have been developed that replicate and synthesize HCV proteins in cultured human hepatoma cells. Using these cells, the mechanism of interferon action has been recently demonstrated, suggesting that these replicon might be useful to test therapeutic strategies to inhibit viral replication. In a recent issue of the Proceedings of the Academy of Sciences, Frank Chisari's group at the Scripps Research Institute made use of a subgenomic HCV replicon system to investigate the effects of short interfering RNA (siRNA) on HCV replication. RNA interference (RNAi), originally identified in plants, Caenorhabditis elegans and Drosophila, is an antiviral response initiated by dsRNA. The dsRNA is cleaved into siRNAs which then associate with a multiprotein complex to target homologous RNAs for degradation. The new study demonstrates that RNAi can block replication of subgenomic HCV replicons in transfected hepatoma cells. Further studies are necessary to determine whether the approach could inhibit full-length HCV replication. Proceedings of the National Academy of Science, Online edition, doi: 10.1073/pnas.252783999 A new vaccine against HIV developed by virologists at Emory University and the National Institutes of Health (NIH) entered a phase I clinical trial the last week of January 2003. The strategy comprises two inoculations of a DNA vaccine to prime the immune system to recognize the virus, and a booster vaccine based on a recombinant pox virus. Dr. Harriet Robinson and colleagues reported success of the strategy in 24 rhesus macaques in Science magazine in 2001. In a follow-up study in the Journal of Virology in October 2002, they showed that levels of viral RNA and DNA in these animals have declined to undetectable levels—reminiscent of the small subset of HIV-infected individuals termed long-term non-progressors. The experimental vaccine is licensed from Emory by GenVax, Inc., a company founded by Emory to manufactue the vaccine.