Genetic chemistry: Tools for gene therapy coming from unexpected directions

Overcoming the limitations of foreign gene delivery to eukaryotic cells is a crucial path toward human gene therapy. Over the last 5 years, this challenge has been approached in different ways. The design and synthesis of novel cationic lipids for gene delivery was a central preoccupation to obtain increased transgene expression. Significant progress was achieved for in vitro and in vivo gene delivery by designing a series of geometrically differing lipopolyamines. First, the geometry of lipopolyamines affects the final transgene expression. Second, introduction of DNA complexing peptides into lipopolyamine/DNA complexes is advantageous for transgene expression in the presence of serum. In a third approach, the introduction of different cationic entities such as polyguanidinium or polycyclic guanidinium instead of the polyamine head group may favor tissue-specific gene delivery. In a fourth approach, introduction of a reduction-sensitive group in lipopolyamines lead to increased transgene expression as compared to nonreducible lipopolyamines. Finally, the design and synthesis of novel nonelectrostatic DNA complexing agents represent a new promising approach for in vivo DNA delivery. The last exciting challenge to be faced was the site-specific chemical ligation to plasmid DNA as a tool for plasmid DNA targeting and intracellular localization of complexes. Together with the development of the different approaches, the physicochemical characterization of the different gene delivery systems, as well as their intracellular fate, were studied. These studies are of great importance for understanding the differing transfection efficiency obtained for different types of DNA complexes, thus a more rational base can be used for designing new generations of highly efficient nonviral self-assembling systems for gene delivery. (C) 2000 Wiley-Liss, Inc.