Polyethylenimine/DNA complexes shielded by transferrin target gene expression to tumors after systemic application

Systemic application of positively charged polycation/DNA complexes has bee n shown to result in predominant gene expression in the lungs. Targeting ge ne expression to other sites, eg distant tumors, is hampered by nonspecific interactions largely due to the positive surface charge of transfection co mplexes. In the present study we show that the positive surface charge of P N (25kDa branched or 22kDa linear)/DNA complexes can be efficiently shielde d by covalently incorporating transferrin at sufficiently high densities in the complex, resulting in a dramatic decrease in nonspecific interactions, eg with erythrocytes, and decreased gene expression in the lung. Systemic application of transferrin-shielded PEI/DNA complexes into A/J mice bearing subcutaneously growing Neuro2a tumors via the tail vein resulted in prefer ential (100- to 500-fold higher) luciferase reporter gene expression in dis tant tumors as compared with the major organs including the lungs. Tumor ta rgeting is also demonstrated by DNA uptake and beta -galactosidase gene exp ression in tumor cells. Assessing DNA distribution following systemic appli cation significant amounts of DNA were found in the liver and tumor. Howeve r, in the liver, DNA was mainly taken up by Kupffer cells and degraded with out significant transgene expression. In the tumor, DNA was associated main ly with tumor cells and frequently found near structures which resemble pri mitive blood vessels.