DC-CHOL LIPID SYSTEM IN GENE-TRANSFER

Lipidic systems including cationic liposomes offer many potential adva ntages for delivering functional DNA to cells in intact animals. DC-Ch ol:DOPE, a cationic liposome formulation developed in this laboratory, is highly efficient for delivering nucleic acids into various cell ty pes in vitro as well as in vivo. Mixing DNA with cationic liposomes pr oduce condensed DNA along with tubular structures and aggregated lipos omes. Interaction with cell membrane, followed by endocytosis and disr uption of endosomes, appears to be the main mechanism of cytoplasmic d elivery of DNA by DNA/cationic liposome complex. In an attempt to over come the low efficiency of nuclear entry of cytoplasmic DNA, a limitin g step for the overall expression level of the transgene, a cytoplasmi c expression system was developed. A plasmid containing the reporter g ene, chloramphenicol acetyltransferase (CAT), driven by the bacterioph age T7 promoter, following co-delivery with T7 RNA polymerase by DC-Ch ol cationic liposomes into cells, gives a rapid, but transient CAT gen e expression. However, strong and sustained gene expression could be a chieved by co-delivery of a T7 RNA polymerase enzyme regenerating syst em such as a T7 autogene. An independent study found that a single i.p . injection of cisplatin could sensitize lipofection of tumors in situ . A combined and sequential protocol was therefore proposed for cancer gene therapy.