Zeta potential changing phosphorylated nanocomplexes for pDNA delivery

The objective of this study was to evaluate the suitability of a zeta potential changing system as gene delivery system. The phosphate ester bearing ligand 6-phosphogluconic acid (6-PGA) was attached to linear and branched polyethyleneimine (PEI) via a carbodiimide-mediated reaction whereby 287 mu mol and 413 mmol 6-PGA could be coupled per gram polymer. Nanocomplexes of these modified polymers with pDNA showed a zeta potential of +12 mV for nanocomplexes with the linear PEI-6PGA and +16 mV in case of the branched derivative. By the addition of carboxymethylcellulose (CMC), zeta potentials of the complexes were reduced to +2.86 and +3.25, respectively. Phosphate release studies on Caco 2 cells and HEK-293 cells demonstrated the ability to cleave the phosphate ester. Compared to HEK-293 cells, enzymatic degradation of the phosphate ester in Caco 2 cells was 2.3-fold higher from nanocomplexes comprising linear PEI and 4.3-fold higher from those with branched PEI. Furthermore, incubation with alkaline phosphatase led to an increase in the zeta potential of nanocomplexes based on linear PEI-6PGA to +6.96 mV and +8.26 mV in nanocomplexes comprising branched PEI-6PGA. Studying transfection efficiency in Caco 2 cells and HEK-293 cells, a higher expression of the green fluorescent protein (GFP) could be detected in HEK-293 cells. In presence of a phosphate inhibitor, transfection efficiencies were decreased in both cells lines, due to a lacking shift of the zeta potential of the tested pDNA complexes. According to these results, zeta potential changing systems seem to be a promising strategy for future gene delivery systems, as this concept allows the in situ generation of positive charges in close proximity to the cellular surface. (C) 2015 Elsevier B.V. All rights reserved.