Intravenous (i.v.) administration of cationic
lipid N-[( 1-(2-3-dioleyloxy)propyl)]-N-N-N-trimethylammonium
chloride (
DOTMA)-based transfection complexes 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 plasmid levels associated with the
tumor, suggesting that plasmid delivery to the
tumor site was a limiting factor. Lowering the
lipid/
DNA charge ratio from 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 reduced in both tissues at lower
lipid/
DNA charge ratios. Complexes prepared from small
unilamellar liposomes gave significantly lower expression levels in the lungs but similar expression levels in
tumors when compared to complexes prepared from larger
unilamellar liposomes. The small
liposome complexes were better tolerated than large
liposome complexes. Varying the cationic
lipid to colipid (
cholesterol or DOPE) molar ratio from 4: 1 to 1: 1 significantly reduced expression levels in both
tumor and lung. Cationic
lipid substitution, using a
cholesterol cationic
lipid, diethyldiamino-carbamyl-
cholesterol instead of
DOTMA, produced reduced expression in all other tissues except
tumor. Incorporation of PEG into preformed transfection complexes reduced
DNA delivery to lung, increased circulation half-life, and enhanced
DNA delivery to
tumor. In a lung metastatic mouse
tumor model, where the accessibility of the i.v. administered transfection complexes to
tumor lesions should be less challenging,
DOTMA: CHOL complexes (4: 1
lipid to colipid molar ratio, 3: 1 +/-
lipid to plasmid charge ratio) were preferentially localized 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 complexes enhanced both
DNA delivery and expression in
tumor and is one approach that may overcome limitations.