Optimization of cationic lipid/DNA complexes for systemic gene transfer totumor lesions

Intravenous (i.v.) administration of cationic lipid N-[(1-(2-3-dioleyloxy)p ropyl)]-N-N-N-trimethylammonium chloride (DOTMA)-based transfection complex es in mice with subcutaneous squamous cell tumors yielded plasmid delivery and expression in tumor lesions. The efficiency of gene transfer in tumors was significantly lower than in the lung. This was consistent with low plas mid levels associated with the tumor, suggesting that plasmid delivery to t he tumor site was a limiting factor. Lowering the lipid/DNA charge ratio fr om 5:1 to 0.8:1 (+/-) did not change DNA levels in tumor but significantly reduced DNA levels in lung. However, expression levels were significantly r educed in both tissues at lower lipid/DNA charge ratios. Complexes prepared from small unilamellar liposomes gave significantly lower expression level s in the lungs but similar expression levels in tumors when compared to com plexes prepared from larger unilamellar liposomes, The small liposome compl exes were better tolerated than large liposome complexes. Varying the catio nic lipid to colipid (cholesterol or DOPE) molar ratio from 4:1 to 1:1 sign ificantly reduced expression levels in both tumor and lung. Cationic lipid substitution, using a cholesterol cationic lipid, diethyldiamino-carbamyl-c holesterol instead of DOTMA, produced reduced expression in all other tissu es except tumor. Incorporation of PEG into preformed transfection complexes reduced DNA delivery to lung, increased circulation half-life. and enhance d DNA delivery to tumor. In a lung metastatic mouse tumor model, where the accessibility of the i.v. administered transfection complexes to tumor lesi ons should be less challenging, DOTMA:CHOL complexes (4:1 lipid to colipid molar ratio, 3:1 +/- lipid to plasmid charge ratio) were preferentially loc alized in tumor lesions. These data demonstrate that systemic gene transfer to distal tumor sites by lipid DNA complexes may be limited by low plasmid delivery. Modifying the chemical surface properties of transfection comple xes enhanced both DNA delivery and expression in tumor and is one approach that may overcome limitations.