Interaction of Astramol poly(propyleneimine) dendrimers with DNA and poly(methacrylate) anion in water and water-salt solutions.

Interaction of poly(propyleneimine) dendrimers DAB-dendr-(NH2)x of five generations (x = 4, 8, 16, 32, and 64) with either calf thymus DNA or tagged by pyrenyl groups poly(methacrylate) anion (PMA*) as well as destruction of formed polyelectrolyte complexes by the added sodium chloride were studied by fluorescence quenching techniques. DNA-containing complexes (dendriplexes) were investigated by ethidium bromide assay, whereas formation of PMA* complexes was estimated by fluorescence of the pyrenyl groups that remained free of contact with the dendrimers-quenchers. The ion pairing with DNA phosphate groups was pH-sensitive and accompanied by inaccessibility of a part of the dendrimer amino groups even in slightly acidic media. The growth of the generation number resulted in successive stabilization of the dendriplexes against the added salt. The dendriplexes of all dendrimers except DAB-dendr-(NH2)4 were stable at physiological ionic strength. In contrast to the highly charged cationic polymer poly(N-ethyl-4-vinylpyridinium) bromide of different degrees of polymerization, the dendrimers formed more stable complexes with flexible PMA* rather than with DNA, proving the inaccessibility of a part of the amino groups for the rigid double helix. The revealed regularities appear to be a platform for design of dendriplexes with controllable stability, in particular fulfilling the requirements imposed for gene delivery vehicles.