Canadian scientists have taken a fresh look at the processes behind DNA delivery into cells. The group, led by Ronald Verrall at the University of Saskatchewan in Saskatoon, says that a more detailed understanding of the mechanism is needed to build better DNA carriers, key synthetic targets for gene therapy.

Gemini surfactants (red) can form several different complexes with DNA (green).

The concept of gene therapy is to replace defective or missing genes with healthy DNA delivered into cells by a carrier, called a vector, in a process called transfection. Typical vectors have a positive charge to allow the negatively-charged DNA to pass through the hydrophobic membranes. However, predicting how efficient a vector will be has been difficult. Verrall set out to investigate how this could be improved.

The group studied the complexes formed between synthetic vectors called gemini surfactants and DNA. Gemini surfactants are lipids with two hydrocarbons, each connected to an ionic group, chemically linked by a spacer. These doubled-up surfactants have high transfection efficiencies; each lipid molecule has twice the positive charge of a single surfactant, allowing binding to DNA at lower concentrations.

Verrall's group found that DNA is packed tightly by the surfactants and that the form of the surfactant-DNA complexes depends upon the surfactant structure. They also showed that there is a correlation between a complex's structure and the gemini surfactant's transfection efficiency.

The group used a range of techniques to study the surfactant-DNA complexes. Whilst atomic force microscopy was used to examine complexes bound on surfaces, light scattering experiments were used to provide additional information about their properties in solution. Martin Feiters from the Radboud University, Nijmegen, The Netherlands, who also works on transfection using cationic lipids, explained that 'the combination of techniques allowed Verrall and his group to extrapolate their results from surface to solution where they are relevant for the transfection.'

Laura Howes