Transferrin-Modified Liposomes Equipped with a pH-Sensitive Fusogenic Peptide:  An Artificial Viral-like Delivery System

Abstract

Liposomes are one of the most promising systems for selective cellular targeting via introduction of specific ligands for cell-surface receptors. After being taken up by the cells, these liposomes usually follow intracellular pathways of receptor-mediated endocytosis. Control of intracellular trafficking is required for optimized drug delivery. In this study, we elucidated the intracellular fate of transferrin-modified liposomes and succeeded in altering it by introducing the pH-sensitive fusogenic peptide, GALA (WEAALAEALAEALAEHLAEALAEALEALAA). Transferrins that are chemically attached to a liposomal surface (Tf-L) were internalized via receptor-mediated endocytosis more slowly than unmodified transferrins. In contrast to the recyclable nature of transferrin, liposome-attached transferrins together with encapsulated rhodamines were retained in vesicular compartments. When GALA was introduced into liposomal membranes using a cholesteryl moiety for anchoring (Chol-GALA), rhodamines were efficiently released and diffused into the cytosol. The addition of GALA to the Tf-L-containing medium or the encapsulation of GALA in Tf-L did not induce similar effects. These results clearly indicate that GALA must be present on the surface of liposomes to exert its function. In vitro energy transfer and dynamic light scattering experiments suggested that the endosomal escape of the encapsulates in Tf-L equipped with Chol-GALA can be attributed to pH-dependent membrane fusion. With GALA present on the surface, intracellular trafficking of liposomes after receptor-mediated endocytosis could be successfully controlled.

Cytosolic Delivery of Liposomally Targeted Proteins Induced by Photochemical Internalization

“…Coencapsulation of a fusogenic peptide derived from the influenza virus hemagglutinin resulted in efficient cytosolic delivery of liposomal diphtheria toxin A-chain as reported by Mastrobattista et al (9). Kakuda et al demonstrated that the insertion of cholesterol derivatized GALA-peptide into the liposomal bilayer also stimulated release of liposomal contents into the cytosol (10).…”

Octaarginine-modified multifunctional envelope-type nanoparticles for gene delivery

“…Similar observations were made previously regarding the impact of the topology of the fusogenic peptide GALA on endosomal escape. 7 Thus, the topology and content of a lipid envelope significantly influence both particle uptake and the function of devices embedded in the envelope. Although the diameters of MENDs1-3 were somewhat different (Supplementary Table 1 online), it is suggested that this difference has no significant effect on the uptake pathway of the particles.…”

“…4,5 A variety of approaches have been used to overcome these barriers including ligandmediated targeting of cell surface receptors, pH-sensitive fusogenic peptides that improve cytosolic delivery and nuclear localization signals (NLSs) to enhance nuclear uptake. [6][7][8][9] Many of the currently available non-viral vectors have some functional devices that enhance their overall efficiency; however, they are still much less efficient than most viral vectors, 10 which evolved towards, maximum efficiency through the process of natural selection. Simple mixing of DNA with multiple devices does not guarantee that each device is functional and effective in reducing barriers to efficient gene delivery.…”

Intracellular trafficking of nonviral vectors

“…134 GALA enhanced cytosolic release of a fluid phase marker cointernalized with Tf-targeted liposomes compared to complexes lacking GALA. 135 While these particular studies did not examine DNA delivery by these complexes, they demonstrate that modified GALA, synthesized to attach to the surface of liposomes, undergoes pH-dependent conformational changes consistent with a-helix formation, and induces membrane fusion.…”