ACTIVATION OF THE COMPLEMENT-SYSTEM BY SYNTHETIC DNA COMPLEXES - A POTENTIAL BARRIER FOR INTRAVENOUS GENE DELIVERY

We have examined the complement-activating properties of synthetic cat ionic molecules and their complexes with DNA. Commonly used gene deliv ery vehicles include complexes of DNA with polylysine of various chain lengths, transferrin-polylysine, a fifth-generation poly(amidoamine) (PAMAM) dendrimer, poly(ethyleneimine), and several cationic lipids (D OTAP, DC-Chol/DOPE, DOGS/DOPE, and DOTMA/DOPE). These agents activate the complement system to varying extents. Strong complement activatio n is seen with long-chain polylysines, the dendrimer, poly(ethyleneimi ne), and DOGS (half-maximal at about 3 mu M amine content in the assay used). Compared to these compounds, the other cationic lipids (in lip osome formulations) are weak activators of the complement system (half -maximal approximate to 50-100 mu M positive charge in assay). Complem ent activation by polylysine is strongly dependent on the chain length . Short-chain oligolysines are comparable to cationic lipids in their activation of complement. Incubation of these compounds with DNA to fo rm complexes reduces complement activation in virtually all cases. The degree of complement activation by DNA complexes is strongly dependen t on the ratio of polycation and DNA (expressed as the charge ratio) f or polylysine, dendrimer, poly(ethyleneimine), and DOGS. To a lesser d egree, charge ratio also influences complement activation by monovalen t cationic lipid-DNA, complexes. For polylysine-DNA complexes, complem ent activation can be considerably reduced by modifying the surface of preformed DNA complexes with polyethyleneglycol (half-maximal approxi mate to 20 mu M amine content). The data suggests that, by appropriate formulation of DNA complexes, complement activation can be minimized or even avoided. These findings should facilitate the search for DNA c omplex formulations appropriate for reproducible intravenous gene deli very.