Time course of fluorescent-labelled oligonucleotide accumulation in cells with the use of folate receptor-targeted cationic liposomes

Abstract

INTRODUCTION. The use of cationic liposomes is a promising approach to the delivery of therapeutic nucleic acids to target cells because liposomes can protect nucleic acids from degradation by extracellular nucleases. However, to ensure selective delivery to the site of action, this approach needs modification, including liposome surface functionalisation with targeting ligands.AIM. This study aimed to compare the time courses of the accumulation of a fluorescent-labelled oligonucleotide (FITC-ODN), which simulated a nucleic acid-based medicinal product, in cells with the use of folate receptor-targeted (F) and conventional (L) cationic liposomes.MATERIALS AND METHODS. F- and L-liposomes were prepared using the polycationic amphiphile 2X3, the zwitterionic helper lipid DOPE, and the folate lipoconjugate F12. Physicochemical characterisation of the liposomes was performed using dynamic light scattering and transmission electron microscopy. Liposome–FITC-ODN complexes were formed at various nitrogen to phosphate (N/P) charge ratios. Flow cytometry, fluorescence microscopy, and confocal microscopy methods were used to study the accumulation of liposome–FITC-ODN complexes in human cervical carcinoma (KB-3-1) and human embryonic kidney (HEK 293) cells.RESULTS. The prepared F- and L-liposomes were spherical particles with a diameter of 75–100 nm. The authors selected the optimal N/P ratio of 2/1 to obtain complexes of F- and L-liposomes with the FITC-ODN. This N/P ratio yielded homogeneous liposome–FITC-ODN complexes having a polydispersity index below 0.200 and a size of 112.4–125.1 nm. F-liposomes were 25% more efficient than L-liposomes in FITC-ODN delivery to KB-3-1 cells at 90, 120, and 240 minutes after transfection. In the first few minutes of cell transfection, fluorescence and confocal microscopy data on the distribution of liposome–FITC-ODN complexes showed that cationic liposome fluorescence signals colocalised with FITC-ODN signals. Later, FITC-ODN accumulation in the cytoplasm was observed.CONCLUSIONS. Cationic liposomes demonstrated efficient FITC-ODN delivery into the cytoplasm of cancer cells. F-liposomes enhanced the percentage of transfected cells and improved FITC-ODN delivery compared with L-liposomes. The results obtained can be used in the further development of targeted medicinal products based on therapeutic nucleic acids and liposomes.

Keywords

• therapeutic nucleic acids
• antisense oligonucleotide
• fluorescent-labelled oligonucleotide
• liposome
• folate
• targeted delivery
• folate receptor-targeted cationic liposomes
• accumulation time course
• cancer cells