Characterization of lactoferrin as a targeting ligand for nonviral gene delivery to airway epithelial cells

In this study lactoferrin (Lf) was investigated as a targeting ligand for receptor-mediated gene delivery to human bronchial epithelial cells. A high number of lactoferrin receptors (LfRs) were detected on bronchial epithelial (BEAS-2B), but not on alveolar epithelial (A549) cells by fluorescence microscopy and FACS measurements, suggesting potential targeting selectivity for bronchial epithelial cells. Molecular conjugates with ratios of Lf to branched polyethylenimine 25 kDa (PEI) ranging from 4:1 to 1:40 (mol/mol) were synthesized and analyzed for complexation of plasmid DNA (pDNA), transfection efficiency, and cytotoxicity. Whereas particle size increased with the degree of Lf coupling from 45 to 225 nm, surface charge was not significantly influenced. Transfection studies on BEAS-2B cells revealed that Lf-PEI 1:20 exhibited the highest luciferase gene expression which was 5-fold higher at an N/P ratio (molar ratio of PEI nitrogen to pDNA phosphate) of 4 than PEI and could be inhibited by an excess of free Lf. With A549 cells, no significant enhancement in transfection efficiency between Lf-PEI/pDNA and PEI/pDNA complexes could be observed. Increasing the degree of Lf coupling to PEI resulted in reduced transfection efficiency in both alveolar and bronchial epithelial cells. Cell viability assays resulted in significantly lower cellular toxicity of Lf-PEI/pDNA compared with PEI/pDNA complexes. We suggest that Lf represents a potent targeting ligand for receptor-mediated gene delivery to bronchial epithelial cells and might be a promising candidate for lung gene transfer in vivo.