Design and synthesis of pH-responsive polymeric carriers that target uptake and enhance the intracellular delivery of oligonucleotides

The delivery of biomolecular therapeutics that function intracellularly remains a significant challenge in the field of biotechnology. In this report, a new family of polymeric drug carriers that combine cell targeting, a pH-responsive membrane-disruptive component, and serum-stabilizing polyethylene glycol (PEG) grafts, is shown to direct the uptake and endosomal release of oligonucleotides in a primary hepatocyte cell line. These polymers are called encrypted polymers and are graft terpolymers that consist of a hydrophobic, membrane-disruptive backbone onto which hydrophilic PEG chains have been grafted through acid-degradable linker acetal linkages. In this report, the ability of the encrypted polymers to deliver rhodamine-labeled oligonucleotides or PEG-FITC (a model macromolecular drug) (5 kDa) into the cytoplasm of hepatocytes was investigated by fluorescence microscopy. Two new encrypted polymer derivatives (polymers E2 and E3) were synthesized that contained lactose for targeting to hepatocytes. Polymer E2 also has PEG-FITC conjugated to it, as a model macromolecular drug, and polymer E3 contains a pendant hexalysine moiety for complexing oligonucleotides. The results of the fluorescence microscopy experiments show that the encrypted polymers direct vesicular escape and efficiently deliver oligonucleotides and macromolecules into the cytoplasm of hepatocytes. (C) 2003 Elsevier Science B.V. All rights reserved.