Development of novel cationic liposomes for efficient gene transfer into peritoneal disseminated tumor

A novel series of cationic lipids has been found, by lit vivo screening, to be effective for gene transfer into peritoneal disseminated tumor. O,O' -D itetradecanoyl-N-(Lu-trimethylammonioa chloride (DC-6-14), having dimyristy l acid, has shown the highest transfection activity in vitro, provided that 10% fetal bovine serum is present. To enhance the transfection efficiency of DC-6-14, we added dioleoylphosphatidylethanolamine (DOPE) and/or cholest erol (Chol) as helper lipids in various ratios. Cationic liposomes containi ng DC-6-14, DOPE, and Chol in molar ratios of 1:0.75:0.75 and 1:1:0.8 maint ained efficient transfection activity under serum-containing conditions in HRA, mEIIL, and ES-2 cell lines in vitro, as determined by luciferase assay . With our novel liposomes, transfection efficiencies were higher in cells proliferating faster than in cells proliferating slower, depending on mitot ic activity as represented by labeling index. In the mEIIL peritoneal disse minated tumor model, cancer cells were specifically transfected with the la cZ gene. Gene transfer was observed by X-Gal staining not only in floating cancer cells in the ascites, but also in the peritoneal disseminated cancer tissue. The percentage of LacZ-positive cells was about 1%, which was sign ificantly higher than with commercially available Lipofectin (0.38%), Lipof ectACE (0.62%), or LipofectAMINE (0.23%). In the mEIIL peritoneal dissemina ted tumor-nude mouse model, herpes simplex thymidine kinase gene (HSV tie) transfer with our novel liposomes, followed by ganciclovir (GCV) treatment, resulted in significantly longer survival compared with control mice (p < 0.05, Cox-Mantel). These results suggest that these liposomes show promise as tools in gene therapy for patients with intraperitoneal disseminated can cer.