Enhanced expression of foreign gene transferred to mammalian cells in vitro using chemically modified poly(L-lysine)s as gene carriers

Poly(L-lysine) (PL) is chemically modified on the basis of the commonly ess ential structures of effective gene carriers, which we previously found, in order to improve the insufficient gene-transferring efficacy of FL. The PL -derivatives were then subjected to gene transfer with the osmotic shock pr ocedure. Poly(N-epsilon-trimethyl-L-lysine-co-serine) (PtmLS) showed much h igher transient gene expression than PL with low cytotoxicity while poly(N- epsilon-trimethyl-L-lysine) and poly(l-lysine-co-serine) did not. These res ults strongly support the importance of both of the nonionic hydrophilic gr oups and quaternary ammonium groups of the gene carriers.