Membrane Activity and Transfection Ability of Amphipathic Polycations as a Function of Alkyl Group Size

Cationic membrane disruptive peptides such as melittin would appear to have attributes necessary for DNA delivery: DNA binding via electrostatic interactions and membrane lysis to enable cytoplasmic delivery. However, the relatively small overall charge of membrane disruptive peptides results in weak interactions with DNA. As a model of cationic membrane disruptive peptides, amphiphilic polyvinyl ethers were synthesized. The number of positively charged groups incorporated into these polymers is substantially greater than membrane-active peptides, which enables these polymers to form stable complexes with DNA. By varying the length of the hydrophobic groups incorporated into the polymer from one to four carbons, the dependence of membrane activity on side chain length was established. The ability of these polymers to transfect DNA in tissue culture was tested, and it was found that transfection efficiency is dependent upon the membrane disruptive activity of the polymer. Comparison of melittin and synthetic polymers suggests that transfection and toxicity appear to be dependent upon their affinity for DNA. This demonstration of relationships among membrane lysis, transfection, DNA binding, and polymer side-chain composition establishes a new class of transfection reagents and may guide in the design of polymers and formulations that will enable efficient in vivo transfection.