Chain length of the polylysine in receptor-targeted gene transfer complexes affects duration of reporter gene expression both in vitro and in vivo

Complexes composed of peptide ligand for the serpin enzyme complex receptor covalently coupled to poly-L-lysine condensed by charge interaction with p lasmid DNA direct gene transfer into receptor bearing cells, We compared in tensity and duration of reporter gene expression in vitro and in vivo from serpin-enzyme receptor-directed gene transfer complexes prepared with poly- L-lysine of different chain lengths. When substituted with linker and ligan d to comparable extents, DNA complexes containing short chain poly-L-lysine were larger and gave higher peak expression but significantly shorter dura tion of expression than those containing long chain poly-L-lysine. Both pea k expression and duration of expression exceeded that observed with Lipofec tin, Neither naked DNA nor DNA complexed with unsubstituted polylysine was effective in gene transfer. For in vivo experiments, complexes containing o ptimal ligand and degree of substitution (based on in vitro data, peptide C 105Y, 11 ligands/plasmid DNA molecule) were prepared with either short chai n or long chain polylysine and a beta-galactosidase expression plasmid. Fol lowing injection into the tail veins of mice, longer chain complexes gave s ignificantly higher expression of reporter gene in lung and spleen that las ted for a significantly longer period of time than the shorter chain comple xes. The short chain poly-L-lysine-DNA complexes were larger in diameter, a s assessed by electron microscopy or atomic force microscopy, and gave less protection against DNase digestion in, vitro than longer chain complexes. Thus, for gene transfer complexes directed at the serpin enzyme complex rec eptor, longer chain poly-L-lysine gave a much longer duration of expression both in vitro and in vivo, We speculate that this may be due to protection against degradation afforded the plasmid DNA by the tighter compaction pro duced by long chain poly-L-lysine.