Chitosan and depolymerized chitosan oligomers as condensing carriers for in vivo plasmid delivery

Chitosan is a polysaccharide that demonstrates much potential as a gene del ivery system. The ability of a commercially available chitosan and depolyme rized chitosan oligomers to condense plasmid was determined using TEM and m icrotitration calorimetry, while the diameter and stability of the resultan t complexes were measured using laser light scattering. Selected complexes were physically stable to challenge with both serum and salt solutions. Par ameters such as chitosan molecular weight, plasmid concentration and charge ratio influenced such stability. The effect of including a pH-sensitive en dosomolytic peptide on the physicochemical properties of the complex was de termined. The presence of a pH-sensitive endosomolytic peptide enhanced the levels of reporter gene expression in Cos-l cells 4-fold. A selected compl ex containing a lyric peptide was administered in the upper small intestine and colon of rabbits, and reporter gene expression was measured in defined intestinal tissues. Reporter gene expression was enhanced in defined intes tinal tissues, although levels of expression remained low. The combination of strong complex stability and low in vivo expression levels suggest that uptake and/or decomplexation, but not endosomal release, may be the critica l rate-limiting steps in the uptake process. (C) 1998 Elsevier Science B.V. All rights reserved.