Controlled DNA delivery systems

Genes are of increasing interest as pharmaceuticals, but current methods for long-term gene delivery are inadequate. Controlled release systems using biocompatible and/or biodegradable polymers offer many advantages over conventional gene delivery approaches. We have characterized systems for controlled delivery of DNA from implantable polymer matrices (EVAc: poly (ethylene-co-vinyl acetate)) and injectable microspheres (PLGA and PLA: poly (D, L-lactide-co-glycolide) copolymer and poly (L-lactide), respectively).

Herring sperm DNA and bacteria phage lambda DNA were encapsulated as a model system. Released DNA concentration was determined by fluoroassays. Agarose electrophoresis was used to determine the dependence of release rate on DNA size. The Green Fluorescent Protein (GFP) gene was used to determine the integrity and functionality of released DNA.

Both small and large DNA molecules (herring sperm DNA, 0.1-0.6 kb; GFP, 1.9 kb; lambda DNA, 48.5 kb) were successfully encapsulated and released from EVAc matrices, and PLGA or PLA microspheres. The release from DNA-EVAc systems was diffusion-controlled. When co-encapsulated in the same matrix, the larger lambda DNA was released more slowly than herring sperm; the rate of release scaled with the DNA diffusion coefficient in water. The chemical and biological integrity of released DNA was not changed.

These low cost, and adjustable, controlled DNA delivery systems, using FDA-approved biocompatible/biodegradable and implantable/injectable materials, could be useful for in vivo gene delivery, such as DNA vaccination and gene therapy.