Purpose. The amount and intracellular distribution of DNA fragments (491 -bp) was characterized after transfection in vitro with a commercially available cationic lipid. Localization of fragment to the nucleus, its subcellular distribution, and integrity within the cells was determined for various times after transfection.

Methods. Cystic fibrosis (CF) airway epithelial cells were transfected with ³²P and FITC labeled single-stranded (ss) or double-stranded (ds) DNA fragments complexed with Lipofectamine^® at various charge ratios.

Results. A 5/1 (+/−) charge ratio was found to be the optimal ratio for transfection of both ss-and dsDNA. After a 5 h exposure, 7.51 ± 0.89% of the radioactivity was associated with the nuclear fraction whereas only 1.07 ± 0.23%, was found in the nuclear fraction when dsDNA was used. The nuclear radioactivity detected after a 24 h exposure was only 1/3 of that after 5 h. Analysis of fragment stability in the cytosolic and nuclear fractions showed the presence of intact fragment in each subcellular compartment. No intranuclear/intracellular fragment could be detected in control experiments with naked DNA.

Conclusions. The results from these experiments indicate that small fragments of DNA can be efficiently and rapidly transferred intact to the cell nucleus using cationic lipids and that ssDNA fragments are more effective than dsDNA fragments for nuclear delivery.