CCFE - Center for Complex Fluid Engineering - Carnegie Mellon University

We are currently studying the self-assembly of DNA on neutrally charged liposome surfaces via hydrogen bonding interactions. By using these systems, we hope to avoid some of the complications in gene delivery brought about by cationic liposomes, such as their cytotoxicity and non-specific, ionic-strength-dependent DNA-binding properties. The systems that we are studying contain a small fraction of peptide nucleic acid (PNA), which is a synthetic mimic of DNA that replaces the negatively charged sugar-phosphate backbone with a charge-neutral, highly flexible peptide backbone. PNA binds DNA in a sequence-specific manner to form a double helix that is slightly more stable than its DNA counterpart due to the absence of electrostatic interactions. Using zeta potential measurements, we have quantified both the extent of PNA incorporation in the liposomes and the extent of DNA binding under various conditions.
Before the beginning of cell transfection with these novel gene delivery vectors, several research obstacles must be overcome. First, we must determine that self-assembly (i.e. sequence- specific PNA-DNA binding) is definitely occurring in the system.
For this, we can use circular dichroism spectroscopy, which provides information about the secondary structures produced by such binding. We must also examine the condensation and protection of longer DNA oligonucleotides by our liposomal system. An understanding of this condensation process should allow us to reduce the vulnerability of our system to nucleases. Finally, in a longer time frame, we will investigate the condensation of plasmid DNA and the incorporation of cellular signal receptors onto these novel liposomes.