Sterically stabilized polyplex: ligand-mediated activity

Synthetic vectors have been considered as a safer and more versatile altern ative to viral-based gene delivery systems. A variety of very simple synthe tic vector systems, e.g., cationic lipid- and polymer-complexed plasmid DNA have activity in vivo but it appears to be mediated by non-specific electr ostatic interactions limiting targeting. In order to avoid these problems, we designed a sterically stabilized layered colloidal system. The steric po lymer coating reduces non-specific interactions. We have synthesized a PEG conjugate of PEI that complexes DNA to form small, stable colloids with a s teric polymer coat on their surface. The polymer enhances colloidal stabili ty and reduces non-specific binding and toxicity. It also renders the compl ex inactive presumably due to reduced binding. Ligands are then appended to the distal end of the steric polymer to restore cell binding and expressio n at target cells. We prepared conjugates with RGD peptide ligands appended to the distal end of the steric polymer. The resulting conjugates also for m complexes but with ligands exposed on their surface restoring binding and activity. Labeled oligonucleotides and DNA were used to measure intracellu lar distribution. Oligonucleotides are found localized in the nucleus. wher eas the labeled plasmid DNA remained in the cytoplasm. Import of plasmid DN A into the nucleus appears to be very inefficient yet sufficient for expres sion. (C) 2001 Elsevier Science B.V. All rights reserved.