PEGylated DNA/transferrin-PEI complexes: reduced interaction with blood components, extended circulation in blood and potential for systemic gene delivery

We investigated the in vitro and in vivo properties of DNA/transferrin-poly ethylenimine (800 kDa) complexes before and after covalent coupling of poly (ethylene glycol) (PEG). Upon incubation with plasma, the positively charge d non-PEGylated DNA complexes form aggregates. Plasma proteins such as IgM, fibrinogen, fibronectin and complement C3 were found to bind to non-PEGyla ted DNA complexes. At DNA concentrations relevant for in vivo gene delivery a strong aggregation of erythrocytes was also observed PEGylation of the c omplexes strongly reduces plasma protein binding and erythrocyte aggregatio n. Furthermore, PEGylated complex size was stabilized and had a reduced sur face charge. Prolonged circulation in the blood of the PEGylated complexes was also observed when injected intravenously. In tumor bearing mice, appli cation of non-PEGylated complexes through the tail vein resulted in reporte r gene expression in fail and lung, but severe toxicity was observed in som e mice. in contrast, PEGylated complexes mediated reporter gene transfer to the tumor without significant toxicity.