Chitosan as a nonviral gene delivery system. Structure-property relationships and characteristics compared with polyethylenimine in vitro and after lung administration in vivo

Chitosan is a natural cationic linear polymer that has recently emerged as an alternative nonviral gene delivery system. We have established the relat ionships between the structure and the properties of chitosan-pDNA polyplex es in vitro. Further, we have compared polyplexes of ultrapure chitosan (UP C) of preferred molecular structure with those of optimised polyethylenimin e (PEI) polyplexes in vitro and after intratracheal administration to mice in vivo. Chitosans in which over two out of three monomer units carried a p rimary amino group formed stable colloidal polyplexes with pDNA. Optimized UPC and PEI polyplexes protected the pDNA from serum degradation to approxi mately the same degree, and they gave a comparable maximal transgene expres sion in 293 cells. In contrast to PEI, UPC was non toxic at escalating dose s. After intratracheal administration, both polyplexes distributed to the m id-airways, where transgene expression was observed in virtually every epit helial cell, using a sensitive pLacZ reporter containing a translational en hancer element. However, the kinetics of gene expression differed - PEI pol yplexes induced a more rapid onset of gene expression than UPC. This was at tributed to a more rapid endosomal escape of the PEI polyplexes. Although t his resulted in a more efficient gene expression with PEI polyplexes, UPC h ad an efficiency comparable to that of commonly used cationic lipids. In co nclusion, this study provides insights into the use of chitosan as a gene d elivery system. It emphasises that chitosan is a nontoxic alternative to ot her cationic polymers and it forms a platform for further studies of chitos an-based gene delivery systems.