Biodegradable branched polycationic polymers with varying hydrophilic spacers for nonviral gene delivery

Biodegradable branched polycationic polymers with varying hydrophilic spacer lengths were synthesized from different triacrylate monomers and the amine monomer 1-(2-aminoethyl)piperazine by Michael addition polymerization. The hydrophilic spacers were varied by the number of ethyleneoxy groups in the triacrylate monomer (E/M) that ranged from 0 to 14. The polymer degradation depended on the spacer length and pH; the amount of ester degraded as determined by (1)H NMR after 14 days was 43.4 +/- 2.1% (pH 5.0) and 89.7 +/- 1.3% (pH 7.4) for the polymer with 0 E/M compared to 55.7 +/- 2.6% (pH 5.0) and 98.5 +/- 1.6% (pH 7.4) for the polymer with 14 E/M. Cell viability of rat fibroblasts after exposure to polymer solutions of concentrations up to 1000 microg/mL remained high (above 66.9 +/- 12.1% compared to below 7.6 +/- 1.1% for polyethylenimine at a concentration of 50 microg/mL or higher) and increased with the spacer length. The polyplexes made with all the synthesized polymers showed higher transfection efficiency (4.5 +/- 1.7% to 9.4 +/- 2.0%, dependent on the polymer/pDNA weight ratio) with an enhanced green fluorescent protein reporter gene compared to naked pDNA (0.8 +/- 0.4%) as quantified by flow cytometry. This study demonstrates that hydrophilic spacers can be incorporated into polycationic polymers to reduce their cytotoxicity and enhance their degradability for nonviral gene delivery.