Poly(diallyldimethylammonium chlorides) and their N-methyl-N-vinylacetamide copolymer-based DNA-polyplexes:: role of molecular weight and charge density in complex formation, stability, and in vitro activity

Poly(diallyldimethylammonium chlorides) (pDADMAC) of different molecular weights (5-244 kDa) and DADMAC/N-methyl-N-vinylacetamide (NMVA) copolymers (coDADMAC) with different composition (24-75 mol%) and therefore varying cationic charge densities were used to investigate the relationship between polymer structure, polyplex formation and stability, as well as their biological activity. All polymers interacted electrostatically with DNA to form polyplexes as detected by electrophoresis. Complexation and condensation of DNA by the polycations as well as protection of DNA against mechanical and enzymatic degradation were found to increase with higher molecular weights and charge densities of the polymers as well as increasing charge ratios of the complexes. Static and dynamic light scattering revealed for all DNA/polymer complexes sphere-like structures of about 100-150 nm forming more compact structures with increasing charge ratios which were stable over 24 h. The in vitro cytotoxicity of the free polymers determined by MTT-assay was directly correlated to molecular weight and charge density of the polycations which was also confirmed for polymer/DNA complexes quantifying the membrane toxic effects by LDH-release. The transfection efficiency of the complexes was low independent from different charge ratios, presence or absence of serum and lysosomotropic agents. In conclusion, the DADMACs are an interesting tool to study structure-function-relationships due to the specific adjustment of molecular weight as well as number and density of charges. (C) 2004 Elsevier B.V. All rights reserved.