Other cationic polymers used for gene delivery include cationic peptides and their derivatives (e.g., polylysine, polyornithine), linear or branched synthetic polymers (e.g., polybrene, polyethyleneimine), polysaccharide-based delivery molecules (e.g., cyclodextrin, chitosan), natural polymers (e.g., histone, collagen), and activated and non-activated dendrimers.

Cationic polymers differ from cationic lipids in that they do not contain a hydrophobic moiety and are completely soluble in water. Although they differ dramatically in their degree of transfection efficiency and cytotoxicity, all cationic polymers work in a similar fashion by allowing the formation of nucleic acid-polymer complexes, which adhere to the cell membrane through electrostatic interactions and are taken up by the cell via endocytosis. The efficiency of uptake can be improved by conjugating cell-targeting ligands or nuclear localization signals onto the polymer.

While cationic polymers can offer increased complex stability, more reproducible results, and higher transfection efficiencies when compared to DEAE‑dextran, their main limitations continue to be cytotoxicity and their limitation to transient transfection studies. While higher molecular weight (MW) cationic polymers tend to be non-biodegradable and more cytotoxic than lower MW polymers, they show higher transfection efficiencies due to their increased polymer-to nucleic acid-charge ratio. However, the higher toxicity of larger MW polymers can be reduced by biodegradable cross-linking of small polymers into larger polymeric structures.

Mix nucleic acid with cationic polymer solution in transfection medium or phosphate-buffered saline solution. Nucleic acid-cationic polymer complexes are formed via electrostatic interactions between the polymer and phosphate backbone of the nucleic acid.

Add the nucleic acid-cationic polymer complexes to the cells. The complexes bind to the cell surface via electrostatic interactions. Nucleic acid-cationic polymer complexes are taken up by the cell via endocytosis and are released into the cytoplasm.

Assay cells for transient gene expression.

Cationic polymer-mediated transfection workflow.