Optimization of factors influencing the transfection efficiency of folate-PEG-folate-graft-polyethylenimine

Folate-poly(ethylene glycol)-folate-grafted-polyethylenimine (FPF-g-PEI) was synthesized over a range of grafting ratios of folate-poly(ethylene glycol)-folate (FPF) to polyethylenimine (PEI). The conjugation was determined using the absorbance at 363 nm for each polymer. FPF-g-PEIs were determined to have 2.3, 5.2, 9.3 and 20 FPF linear polymers grafted to each PEI. The average molecular weight was calculated to be ∼34,848, 47,266, 64,823 and 110,640 Da, respectively. The pH profiles of FPF-g-PEIs suggest that the polymers have endosomal disruption capacity, and the gel electrophoretic band retardation showed efficient condensation of DNA. The transfection efficiency, determined using plasmid encoding luciferase, was dependent on the cell type and was different for CT-26 colon adenocarcinoma, KB oral epidermoid, and normal smooth muscle cells (SMC). The relative toxicity of polymer/plasmid complexes was determined using the MTT colorimetric assay. At neutral charge ratio, FPF-g-PEI/pLuc complexes were less toxic to cells and showed higher transfection in cancer cells compared to PEI/pLuc complexes. Smooth muscle cells showed no specificity for FPF-g-PEI/pLuc complexes, whereas PEI/pLuc complexes showed a higher transfection efficiency. The transfection efficiency increased when neutral polymer/DNA complex concentrations increased, but decreased when positively charged polymer/DNA complex concentrations increased. There was little increase in toxicity when FPF-5.2g-PEI/pLuc complex concentrations increased.