Synthetic gene transfer vectors could be an attractive alternative to biological vehicles for gene therapy. In an effort to improve the previously developed lipopolyamine-mediated transfection technique, various amphiphilic DNA-binding molecules have been synthesized. Besides Transfectam, several lipospermines display very high gene delivery levels. The structure-activity relationship obtained points to the central role played by the polyamine headgroup in condensing the plasmid and binding it to the cell surface, provided the hydrophobic moiety is capable to generate nonmicellar mesomorphic structures. It also highlights other favorable (albeit more speculative) properties shared by protonable lipospermines as compared to quaternary ammonium-bearing lipids, such as their ability to act as a buffer and their strong affinity for chromatin. The former property may prevent the pH decrease along the degradative lysosomial pathway. The ability to bind to chromatin even in the presence of endogeneous polyamines should have two consequences: a nuclear tropism of the transfecting particles and plasmid uncoating in the nucleus by competitive dilution of the lipopolyamine into an ocean of DNA.

Self-assembled cyclodextrin (CD)-DNA nanoparticles (CDplexes) exhibiting transfection efficiencies significantly higher than PEI-based polyplexes have been prepared from homogeneous seven-fold symmetric polyaminothiourea amphiphiles constructed on a beta-cyclodextrin scaffold.

A molecular-diversity-oriented approach for the preparation of well-defined polycationic amphiphilic cyclodextrins (paCDs) as gene-delivery systems is reported. The synthetic strategy takes advantage of the differential reactivity of primary versus secondary hydroxyl groups on the CD torus to regioselectively decorate each rim with cationic elements and lipophilic tails, respectively. Both the charge density and the hydrophobic-hydrophilic balance can be finely tuned in a highly symmetrical architecture that is reminiscent of both cationic lipids and cationic polymers, the two most prominent types of nonviral gene vectors. The monodisperse nature of paCDs and the modularity of the synthetic scheme are particularly well suited for structure-activity relationship studies. Gel electrophoresis revealed that paCDs self-assemble in the presence of plasmid DNA (pDNA) to provide homogeneous, stable nanoparticles (CDplexes) of 70-150 nm that fully protect pDNA from the environment. The transfection efficiency of the resulting CDplexes has been investigated in vitro on BNL-CL2 and COS-7 cell lines in the absence and presence of serum and found to be intimately dependent on architectural features. Facial amphiphilicity and the presence of a cluster of cationic and hydrogen-bonding centers for cooperative and reversible complexation of the polyanionic DNA chain is crucial to attain high transgene expression levels with very low toxicity profiles. Further enhancement of gene expression, eventually overcoming that of polyplexes from commercial polyethyleneimine (PEI) polymers (22 kDa), is achieved by building up space-oriented dendritic polycationic constructs.