In Vitro Delivery of Cell Impermeable Phallotoxin Using Cationic Liposomes Composed of Lipids Bearing Lysine Headgroup

Bioactive peptides, which act as biologically active regulators, often require intracellular delivery systems to access their therapeutic targets in the cytosolic space maintaining their bioactivity. Here, we report on the delivery of a polar cell impermeable bioactive peptide, phalloidin, into living HeLa cells with cationic liposomes prepared from lysine-based lipids. Liposome/Alexa Fluor 594 phalloidin complexes were characterized regarding their size and zeta potential, which were 85 ± 38 nm and +24.5 ± 4.21 mV, respectively. The delivery of Alexa Fluor 594 phalloidin into live HeLa cells with K3C14 liposomes was evaluated using a fluorescence activated cell sorter and confocal laser scanning microscopy. The highest Alexa Fluor 594 phalloidin delivery efficiency was 92% when using 200 μg of the cationic lipid/1 × 10⁵ cells seeded at 37 °C. The cellular uptake mechanism for the cationic liposome/Alexa Fluor 594 phalloidin complexes was investigated using various endocytosis inhibitors. We confirmed the complexes were mainly taken up through caveolae-mediated endocytosis. Incubation with bafilomycin A1, which inhibits the acidification of lysosomes, revealed that Alexa Fluor 594 phalloidin did not pass through the lysosomal pathway. Rather, Alexa Fluor 594 phalloidin was released from early endosomes or caveosomes to the cytosol to exhibit its bioactive effects including the multinucleation of HeLa cells.