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Two biodegradable polycations based on hexanediol diacrylate linked oligoethylenimine (OEI) were synthesized by applying different reaction temperatures, 20 degrees C (LT-OEI-HD) and 60 degrees C (HT-OEI-HD). Their structural properties were analyzed by NMR, FTIR, and SEC/MALLS (size exclusion chromatography coupled with multiangle laser light scattering detection). Reaction temperature strongly influenced molecular weight and ester/amide ratio and thus resulted in polycations with different biological activities and degradation profiles. LT-OEI-HD was an ester-based polycation of 8.7 kDa which degraded rapidly at pH 7 and pH 9 respectively. HT-OEI-HD had a molecular weight of 26.6 kDa, was mainly based on amides, and degraded more slowly than LT-OEI-HD. Both polymers mediated gene transfer as efficiently as linear polyethylenimine of 22 kDa in two cell lines while being less toxic at their optimal conjugate/plasmid (C/P) ratios. LT-OEI-HD needed higher C/P ratios for gene delivery; however, it was significantly less toxic than HT-OEI-HD.

Epidermal growth factor receptor (EGFR) targeted DNA polyplexes, containing polyethylenimine (PEI) conjugated with EGF protein as cell-binding ligand for endocytosis and polyethylene glycol (PEG) for masking the polyplex surface charge, mediated a 3- to 30-fold higher luciferase gene expression in HUH7, HepG2 and A431 cell transfections than analogous untargeted PEG-PEI polyplexes. Transfection levels can be further enhanced by treatment of cells with amphiphilic photosensitizers followed by illumination. In this process photosensitizers localized in membranes of endocytic vesicles are activated by light, resulting in the destruction of endocytic membrane structures and releasing co-endocytosed polyplexes into the cell cytosol. Photochemical enhanced gene expression was observed in all cell lines, with the magnitude of enhancement depending on the particular PEI polyplex formulation and cell line, ranging between 2- and 600-fold. Importantly, improved gene transfer retained EGF receptor specificity, as demonstrated by comparison with ligand-free polyplexes and by receptor antibody or ligand competition experiments. These results suggest that this combined procedure enables a dual mode of targeting polyplexes: biological targeting via EGFR interaction, combined with physical targeting with light to direct a photochemical delivery of therapeutic genes to a desired location.