Specific targeting of ovarian
carcinoma cells using pegylated
polyethylenimine (
PEG-PEI) conjugated to the
antigen binding
fragment (Fab') of the OV-TL16 antibody, which is directed to the OA3
surface antigen, was the objective of this study. OA3 is expressed by a majority of human ovarian
carcinoma cell lines. To demonstrate the ability of the
PEG-PEI-Fab' to efficiently complex
DNA, an
ethidium bromide exclusion assay was performed. Comparison with
PEG-PEI or PEI 25 kDa showed only minor differences in the ability to condense
DNA. Since conjugation of Fab' to
PEG-PEI might influence complex stability, this issue was addressed by incubating the complexes with increasing amounts of
heparin. This assay revealed stability similar to that of unmodified
PEG-PEI/
DNA or PEI 25 kDa/
DNA complexes. Complexes displayed a size of approximately 150 nm with a zeta potential close to neutral. The latter property is of particular interest for potential in vivo use, since a neutral surface charge reduces nonspecific interactions. Binding studies using flow cytometry and fluorescently labeled
DNA revealed a more than 6-fold higher degree of binding of
PEG-PEI-Fab'/
DNA complexes to
epitope-expressing cell lines compared to unmodified
PEG-PEI/
DNA complexes. In OA3-expressing OVCAR-3 cells,
luciferase reporter gene expression was elevated up to 80-fold compared to
PEG-PEI and was even higher than that of PEI 25 kDa. The advantage of this system is its specificity, which was demonstrated by competition experiments with free Fab' in the cell
culture media during transfection experiments and by using OA3-negative cells. In the latter case, only a low level of reporter gene expression could be achieved with
PEG-PEI-Fab'.