Preparation and characterization of poly (D,L-lactide-co-glycolide) microspheres for controlled release of poly(L-lysine) complexed plasmid DNA

Purpose. To produce and characterize controlled release formulations of pla smid DNA (pDNA) loaded in poly (D,L-lactide-co-glycolide) (PLGA) microspher es both in free form and as a complex with poly (L-lysine). Methods. Poly (L-lysine) (PLL) was used to form pDNA/PLL complexes with com plexation ratio of 1:0.125 and 1:0.333 w/w to enhance the stability of pDNA during microsphere preparation and protect pDNA from nuclease attack. pDNA structure, particle size, zeta potential, drug loading, in vitro release p roperties, and protection from DNase I were studied. Results. The microspheres were found to be spherical with average particle size of 3.1-3.5 mu m Drug loading of 0.6% was targeted. Incorporation effic iencies of 35.1% and 29.4-30.6% were obtained for pDNA and pDNA/PLL loaded microspheres respectively. Overall, pDNA release kinetics following the ini tial burst did not correlate with blank microsphere polymer degradation pro file suggesting that pDNA release is convective diffusion controlled. The p ercentage of supercoiled pDNA in the pDNA and pDNA/PLL loaded microspheres was 16.6% and 76.7-85.6% respectively. Unencapsulated pDNA and pDNA/PLL deg raded completely within 30 minutes upon the addition of DNase I. Encapsulat ion of DNA/PLL in PLGA microspheres protected pDNA from enzymatic degradati on. Conclusions. The results show that using a novel process, pDNA can be stabi lized and encapsulated in PLGA microspheres to protect pDNA from enzymatic degradation.