A study of the endocytosis mechanism and transendothelial activity of lung-targeted GALA-modified liposomes.

The GALA peptide (WEAALAEALAEALAEHLAEALAEALEALAA) was originally designed to induce the destabilization of endosomal membranes based on its ability to undergo a pH-dependent conformational change from a random coil to an α-helix. We recently found that liposomes modified with GALA peptide (GALA-LPs) extensively accumulate in lung endothelial cells (ECs) after intravenous injection. However, the uptake mechanism of GALA-LPs and their ability to reach alveolar epithelium was unclear. We report herein that GALA-LPs are internalized into ECs via a clathrin-mediated pathway. Surprisingly, GALA-LPs had the ability to pass lung ECs and reach other cells through transcytosis. GALA-LPs were taken up by >70% of lung ECs, while they also accumulated in ~30% of type I alveolar epithelium (ATI). GALA-modified gold nanoparticles were detected in ECs, in the basement membrane and in other cells such as ATI, type II alveolar epithelium (ATII) and alveolar macrophages. Consistent with this result, a significant gene knockdown was achieved in lung epithelium cells using GALA-LPs encapsulating anti-podoplanin siRNA. This indicates that GALA-LPs can be used as a carrier for delivering macromolecules to parenchymal as well as to endothelial cells in the lung. Although caveolae are commonly linked to the transendothelial transport of proteins and antibodies, our data indicate that clathrin-mediated endocytosis might also participate in the transcytosis process.

PEGylation of the GALA Peptide Enhances the Lung-Targeting Activity of Nanocarriers That Contain Encapsulated siRNA.

A α-helical GALA peptide (WEAALAEALAEALAEHLAEALAEALEALAA) has been found to possess dual functions: a pH-dependent inducer of endosomal escape, and a ligand that targets lung endothelium. In the present study, the flexibility of GALA was improved by modifying the edge with polyethylene glycol linker, to increase lung-targeting activity. We first investigated the uptake of the GALA-modified liposomes in which GALA was directly conjugated to the lipid (Cholesterol: GALA/Chol) or the phospholipid-PEG (GALA/PEG2000). The liposomes that were modified with GALA/PEG2000 (GALA/PEG2000-LPs) were taken up at a higher level by human lung endothelial cells (HMVEC-L), in comparison with particles that were modified with GALA/Chol (GALA/Chol-LPs). Small-interfering RNA-encapsulating liposomal-based nanocarriers (multifunctional envelope-type nano device: MEND) that were formulated with a vitamin E-scaffold SS-cleavable pH-activated lipid-like material, namely GALA/PEG2000-MENDssPalmE were also modified with GALA/PEG2000. Gene silencing activity in the lung endothelium was then evaluated against an endothelial marker; CD31. In comparison with the unmodified MENDssPalmE, GALA/PEG2000-MENDssPalmE exhibited a higher silencing activity in the lung. Optimization of GALA/PEG2000-MENDssPalmE resulted in silencing activity in the lung with an ED50 value of 0.21 mg/kg, while non-specific gene silencing in liver was marginal. Collectively, PEGylated GALA is a promising device for use in targeting the lung endothelium.

Transcytosis-Targeting Peptide: A Conductor of Liposomal Nanoparticles through the Endothelial Cell Barrier.

The ultimate goal in the area of drug-delivery systems is the development of a nanoparticle that can penetrate the endothelial cell monolayer for the targeting of tissue parenchyma. In the present study, we identify a transcytosis-targeting peptide (TTP) that permits polyethyleneglycol (PEG)-modified liposomes (PEG-LPs) to penetrate through monolayers of brain-derived endothelial cells. These endothelial cells were layered on a gelatin nanofiber sheet, a nanofiber meshwork that allows the evaluation of transcellular transport of nanosized particles (ca. 100 nm). Systematic modification of the sequences results in the identification of the consensus sequence of TTP as L(R/K)QZZZL, where Z denotes hydrophilic amino acids (R/K/S and partially D). The TTP-modified liposomes are bound on the heparin sulfate proteoglycan, and are then taken up via lipid raft-mediated endocytosis. Subsequent intracellular imaging of the particles reveals a unique intracellular sorting of TTP-modified PEG liposomes (TTP-PEG-LPs); namely the TTP-LPs are not localized with the lysosomes, whereas this co-localization is dominant in the unmodified PEG liposomes (PEG-LPs). The in vivo endothelial penetration of liposomes in adipose tissue is conferred by the dual modification of the particles with TTP and tissue-targeting ligands. This technology promises innovations in intravenously available delivery system to tissue parenchyma.

Advantages of ethanol dilution method for preparing GALA-modified liposomal siRNA carriers on the in vivo gene knockdown efficiency in pulmonary endothelium.

We previously reported that a multifunctional envelope-type nano device (MEND) modified with a GALA peptide (GALA/MEND) exerted dual functions; effective targeting the pulmonary endothelium and endosomal escape. The GALA/MEND containing encapsulated siRNA was originally prepared by the film coated hydration method (GALA/MENDHyd). However, an ethanol dilution method was found to be more appropriate for scaling up the preparation of this liposomal nanoparticle. In this study, we report on the preparation of a GALA/MEND based on the principal of the ethanol dilution (GALA/MENDEtOH). The gene knockdown efficiency of the MENDHyd and MENDEtOH without GALA-modification was equivalent regardless of the method used in the preparation. The GALA/MENDEtOH induced more efficient gene silencing in the pulmonary endothelium (ED50; approximately 0.17 mg siRNA/kg) compared to the GALA/MENDHyd. The GALA/MENDEtOH escaped from endosomes more rapidly than GALA/MENDHyd, while the pharmacokinetics and lung accumulation of GALA/MENDEtOH and GALA/MENDHyd were comparable after i.v. administration. Collectively, the ethanol dilution method improves the function of the GALA/MEND as a lung-targeting siRNA carrier.