Near-infrared light-activated membrane fusion for cancer cell therapeutic applications

The spatiotemporal stimulation of liposome-liposome or liposome-membrane fusion processes attracts growing interest as a means to mimic cell-cell interactions in nature and for using these processes for biomedical applications. We report the use of o -nitrobenzyl phosphate functionalized-cholesterol tethered nucleic acid-modified liposomes as functional photoresponsive units for inducing, by NIR-irradiation, spatiotemporal liposome-liposome or liposome-membrane fusion processes. The liposomes are loaded with upconversion nanoparticles (UCNPs) and their NIR irradiation ( λ = 980 nm) yields luminescence at λ = 365 nm, providing a localized light-source to deprotect the o -nitrobenzyl phosphate groups and resulting in the fragmentation of the nucleic acid structures. In one system, the NIR-triggered fusion of two liposomes, L 1 and L 2 , is exemplified. Liposome L 1 is loaded with UCNPs and Tb 3+ ions, and the liposome boundary is functionalized with a cholesterol-tethered, o -nitrobenzyl phosphate caged hairpin nucleic acid structure. Liposome L 2 is loaded with 2,6-pyridinedicarboxylic acid, DPA, and its boundary is modified with a cholesterol-tethered nucleic acid, complementary to a part of the caged hairpin, associated with L 1 . NIR-irradiation of the L 1 /L 2 mixture resulted in the photocleavage of the hairpin structure, associated with L 1 , and the resulting fragmented nucleic acid associated with L 1 hybridized with the nucleic acid linked to L 2 , leading to the fusion of the two liposomes. The fusion process was followed by dynamic light scattering, and by monitoring the fluorescence of the Tb 3+ -DPA complex generated upon the fusion of the liposomes and their exchange of contents (fusion efficiency 30%). In a second system, the fusion of the liposomes L 1 , loaded with UCNPs and doxorubicin (DOX), with HeLa cancer cells functionalized with nucleic acid tethers, complementary to the hairpin units associated with the boundary of L 1 , and linked to the MUC-1 receptor sites associated with the HeLa cells, through a MUC-1 aptamer unit is exemplified. The effect of DOX-loaded L 1 /HeLa cell fusion on the cytotoxicity towards HeLa cells is addressed. The NIR UCNP-stimulated cleavage of the o -nitrobenzyl phosphate caged hairpin units associated with L 1 leads to the fragmentation of the hairpin units and the resulting nucleic acid tethers hybridize with the nucleic acid-modified HeLa cells, resulting in the liposome-HeLa cell fusion and the release o