Dependence of the cellular internalization and transfection efficiency on the structure and physicochemical...

Control of the structure and physicochemical properties of DNA complexed with nonviral vectors is essential for efficient biodistribution and gene delivery to cells. Cationic liposomes interact with DNA giving transfection competent but large and heterogeneous aggregates. On the other hand, cationic detergents condense DNA into small homogeneous but reversible complexes inefficient for transfection.

In order to combine the favorable features of both vectors, ternary complexes were prepared by adding cationic liposomes to plasmid DNA condensed by cationic detergents. The structure and physicochemical properties of these complexes were investigated by electron microscopy, quasi-elastic light scattering, gel electrophoresis and fluorescence techniques. These data were then correlated with the transfection efficiency and intracellular trafficking of the ternary complexes determined by luciferase gene expression and confocal microscopy, respectively.

The ternary complexes were found to form small, homogeneous, globular, stable and positively charged particles with a highly dense and packed lamellar internal structure differing from the multilamellar structure (L(alpha)(C)) of the corresponding lipoplexes. In the presence of serum, the ternary complexes were more efficiently internalized into cells, less toxic and showed 20-fold higher transfection efficiency than lipoplexes.

This study showed that small, monodisperse and highly stable complexes could be obtained by precompaction of DNA with cetyltrimethylammonium bromide, followed by addition of cationic lipids. The higher efficiency of the ternary complexes with respect to their corresponding lipoplexes was related to their internal structure which prevents their dissociation by serum proteins and allows efficient internalization in the target cells.