Synthesis and comparison of cationic polymers for structural effects of backbones and grafted side chains on their DNA transfection for efficient gene delivery

Many cationic polymers with varied architectures either in backbones or in side chains have been used for gene delivery. However, these polymers yielding different DNA transfection efficiency cannot answer whether backbones or side chains have more influence on DNA delivery. In this research, polyurethanes (PUs) made from the reaction of l-lysine diisocyanate and 1,4-piperazinediethanol were synthesized. Together with poly(l-lysine) (PLL), these polymers were further modified to carry side chains by connecting to low-molecular-weight polyethylenimine (PEI) via imine linkages. The PEI was either linear (423 Da) or branched (600 Da) and grafted to the backbone representing two distinct shapes (i.e. a twig with needle-leaves or round-leaves). In addition, one PU derivative was synthesized to have shorter side chains (as PU-PEI S₄₂₃) than PU-PEI₄₂₃ by aminolysis reaction. These synthesized polymers were compared for their transfection potential as gene vectors into cells. Electrophoretic mobility, dynamic light scattering and zeta potential analyses of polymer/DNA complexes confirmed that, after grafting of PEI (PEI₄₂₃ or PEI₆₀₀), PLL-PEIs and PU-PEIs were able to self-assemble with plasmid DNA to form nano-scaled (ca 200 nm) and positively charged (ca +25 mV) complexes. These cationic polymers hardly showed any cytotoxicity on COS-7 cells. The outcome of fluorescence imaging and flow cytometry verified that the order of greater transfection efficiency is PLL-PEI₆₀₀ = PU-PEI₆₀₀ > PLL-PEI₄₂₃ = PU-PEI₄₂₃ > PEI_25K (commercial standard) = PU-PEI S₄₂₃ >> PLL > PEI₄₂₃ = PEI₆₀₀ (starting materials). These results reveal that the polymers with longer side chains or higher charge density have positive influence on transfection efficiency. Nevertheless, different polymer backbones may reflect their biodegradability and cytotoxicity, but their effect on transfection efficiency is less significant. © 2024 Society of Chemical Industry.