Transfection and physical properties of various saccharide, poly(ethylene glycol), and antibody-derivatized polyethylenimines (PEI)

Background The ideal non-viral vector should be cell-type directed and form complexes with DNA that are physically stable, small and electrically neut ral. Methods We have synthesized several PEI derivatives that coat the PEI/DNA c omplexes with. water-soluble residues able to stabilize the particles, to m ask their surface charge and eventually to direct them to a particular tiss ue. The morphologies and sizes of the complexes were observed by TEM and DL S techniques, and their apparent surface charge was quantitated by zeta pot ential measurements; in vitro transfection efficacies were determined in se rum-containing cell culture medium. Results When compared to DNA complexes formed with the unmodified PEI, exte nsive grafting with maltose (15-25% of the amine functions) led to benefici al electrostatic shielding of the particle surface, but was unable to preve nt aggregation in physiological salt concentration. More extended hydrophil ic residues were therefore explored as a mean of physical repulsion between the particles. Low grafting (2.7%) with a linear dextran non-asaccharide l ed to small and stable toroids having no apparent surface charge, yet still reaching effective transfection levels. Electron microscopy of complexes w ith a higher extent of grafting showed worm-like structures unsuited for ce ll entry. Conjugation of PEI with as little as 0.5% of a terminally galacto se-derivatized polyethyleneglycol (PEG)-3400 also gave neutral complexes of another worm-like structure that failed to transfect receptor-expressing h epatocytes. Conclusion These results show that conjugation of large and flexible hydrop hilic residues to PEI, while protecting the complexes from parasitic intera ctions also interfere with DNA condensation. PEG conjugation after PEI/DNA complex formation may avoid this problem, provided intracomplex reorganizat ion is slow. Finally an anti-GD2 antibody (mAb) grafted with PEI was synthe sized. The corresponding protein-coated DNA complexes were compact and smal l (50-60 nm), yet did not enhance transfection of GD2 ganglioside-expressin g cells. Copyright (C) 1999 John Wiley & Sons, Ltd.