New cationized LDL-DNA complexes: their targeted delivery to fibroblasts in culture

Low density lipoproteins (LDL) have been cationized using the water-soluble carbodiimide, N-ethyl-N'-(3-trimethylpropylammonium) carbodiimide iodide at a reagent: lipoprotein mole ratio of 10 000:1. This was shown to increase the innate DNA-binding capacity of LDL 10-fold. [125I]-labeled carbodiimide-modified LDL ([125I])-labeled ECDI-LDL) appeared to recognize the LDL receptor on normal human skin fibroblasts, although some nonspecific binding also was detected. To demonstrate the large ionic component in the lipoprotein-DNA interactions, epsilon -NH2 amino groups on the apolipoprotein B-100 (apoB-100) component of LDL were acetylated with acetic anhydride. A nitrocellulose filter-binding assay revealed that acetylated LDL bound approximately 25% of the [3H]-labeled pBR322 plasmid DNA bound by native LDL under the same conditions. ECDI-LDL-[3H]-labeled plasmid DNA complexes were considerably more stable to NaCl challenge than complexes formed between [3H]-labeled plasmid DNA and native LDL. Thus, the half dissociation of ECDI-LDL containing complexes was achieved at 0.28 M NaCl, whereas for LDL-plasmid DNA complexes this was reached at 0.18 M NaCl. Displacement studies with native LDL studies showed that ECDI-LDL-[3H]-labeled plasmid DNA complexes retained the ability to recognize the LDL receptor on normal skin fibroblasts. Finally, ECDI-LDL complexes with pSV2CAT expression plasmid were shown to transfect CV-1 fibroblasts, a cell line known to specifically recognize apoB-liposome conjugates.