Diblock copolymers that consist of poly(2-ethyl-2-oxazoline) (PEOz) and linear polyethylenimine (LPEI) wereprepared for use as nonviral gene carriers. The PEOz-
b-LPEI copolymers were synthesized by coupling PEOzwith LPEI in a thiol-disulfide exchange reaction between the sulfhydryl and pyridyl disulfide terminal groups.A polymer/DNA weight ratio (P/D) of over 12 was required to enable PEOz-
b-LPEI to condense DNA completely.The DNA-condensing capability of the diblock copolymers was increased with increasing the hydrolytic degrees of the LPEI segment. The PEOz-
b-LPEI polyplexes were stable in 150 mM NaCl aqueous solution andhad a mean diameter around 190 nm, whereas BPEI and LPEI polyplexes formed large aggregates in the range300-500 nm. In addition, these polyplexes exhibited the sensitivity to solution pH and were dissociated in theacidic buffers (pH
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5.5). The results of in vitro cell viability and luciferase assay indicated that PEOz-
b-LPEIs
howed not only low cytotoxicity but also high transfection efficiency in gene expression.