Kam Leong Abstract :

Nonviral Gene Transfer Mediated by DNA Nanoparticles

Cationic polymers that condense plasmid DNA through electrostatic interactions to form nanocomplexes have emerged as safer, though less efficient, options than viral vectors for gene transfer. We have studied the complexation of DNA with natural biopolymers such as gelatin and chitosan, and biodegradable synthetic polymers, such as poly(phosphoester)s in forming nanospheres.

Gene transfer has been observed in vivo in the lung, muscle, bladder, spinal cord, and gastrointestinal tissues in animal models. However, the gene transfection efficiency has been poor. One of the possible rate-limiting steps in non-viral gene transfer is release of the DNA from the cationic carrier-complex. However, a tight binding of the DNA by the carrier is presumably required to condense the DNA to a compact size for cell internalization and to protect the DNA from enzymatic degradation.

While it might be able to achieve the balance of stability by chance, a more elegant solution would be to design a biodegradable gene carrier that initially condenses the DNA efficiently and then gradually releases the DNA.

Such a gene delivery system for extracellular sustained release of plasmid DNA should prove valuable in gene medicine and genetic immunization applications. We have synthesized gene carriers that are rendered biodegradable by a phosphoester bond in the backbone.

The cationic character imparted by amino functionalities is placed in the backbone or the sidechain of the polymer, in the latter case via a phosphate or a phosphoramidate bond. We have developed a sensitive optical technique based on quantum dot-mediated fluorescence resonance energy transfer to examine the intracellular transport and unpacking of these polymeric DNA nanocomplexes intracellularly. In this presentation, we will discuss the most recent results on the use of both chitosan and poly(phosphoester)s as gene carriers.