Water-soluble lipopolymers and
lipopeptides are nonviral gene-transfer
reagents that combine the advantages of
lipids, which increase permeability of
DNA through cell membranes, with the
DNA-condensing and enhanced endosomal release properties of
polycations. This protocol describes the synthesis and characterization of
water-soluble lipopolymer/
lipopeptide-
DNA complexes and their use in transfection of cultured cells and injection into
tumor-bearing mice. Lipopolymers are formed by conjugating cholesteryl chloroformate with the primary or secondary
amines of 1800-Da branched
polyethylenimine (PEI); the use of the 1800-Da PEI avoids the cytotoxicity problems associated with higher molecular-mass PEI.
Lipopeptides are composed of a human
protamine-derived
peptide that has been incubated with a reaction of O-(N-succinimidyl)-N,N,N',N',-tetramethyluronium tetrafluoroborate with
lithocholic acid in the presence of excess diisopropylethylamine. The therapeutic gene used as an example in this protocol encodes the murine
interleukin 12 (IL-12) subunits p35 and p40, each under the transcriptional control of a separate cytomegalovirus (CMV) promoter; the reporter plasmid contains the
luciferase gene driven by a CMV promoter. The target cells are C-26 colon
carcinoma cells.