Acid-Triggered Release from Sterically Stabilized Fusogenic Liposomes via a Hydrolytic DePEGylation Strategy

Abstract

A novel acid-labile poly(ethylene glycol) (PEG)-conjugated lipid, (R)-1,2-di-O-(1′Z,9′Z-octadecadienyl)glyceryl-3-(ω-methoxy-poly(ethylene glycolate, MW5000) (BVEP), a neutral PEG-derivatized analogue of diplasmenylcholine, has been used at low molar ratios to disperse the nonlamellar, fusogenic lipid 1,2dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) as unilamellar liposomes. It was anticipated that acidcatalyzed hydrolysis of the vinyl ether linkages would destabilize BVEP/DOPE liposomes by removal of the water-soluble, sterically stabilizing PEG layer, thereby promoting contents release and membranemembrane fusion. This paper describes the hydrolysis rates, contents release rates, and fusion kinetics of BVEP-stabilized DOPE liposomes at 1:99, 3:97, and 5:95 molar ratios of BVEP/DOPE. Calcein leakage kinetics indicate that 3:97 BVEP/DOPE liposomes offer the best stability at pH 7.4 while retaining favorable leakage properties at pH 4.5 (t50%release ≈ 4 h). N-Rhodamine phosphatidylethanolamine/N-nitrobenzoxadiazole phosphatidylethanolamine lipid mixing assays show that membrane fusion occurs on a much slower time scale than leakage in these systems, with ∼12% lipid mixing occurring over a 24 h time period at pH 2.0. No appreciable membrane fusion occurred in these liposomes at either pH 7.4 or 4.5 when monitored for up to 3 days. 31 P NMR spectra at pH 7.4 contain a single isotropic line shape, consistent with the presence of large liposomes. The 31 P NMR line shape did not change significantly even after long exposure times at pH 4.0; however, Mn 2+ addition experiments with acid-treated samples produced linebroadened spectra, indicating that all the phosphorus sites were continuous with the bulk water phase. Time-dependent cryogenic transmission electron microscopy experiments indicate that extensive liposome collapse to give small dense aggregates occurs over a 1-4 h period when 3:97 BVEP/DOPE liposomes are acidified to pH 4.5. Taken together, these results suggest that acid-catalyzed hydrolysis of BVEP/DOPE liposomes does result in dePEGylative triggering; however, the primary outcome of this cleavage process is contents leakage and liposome collapse to give <100 nm particles that are presumed to be inverted hexagonal phase structures, with membrane lipid mixing occurring on a kinetically slower time scale. † Dedicated to the memory of David F. O'Brien, deceased July 2002.

Diversifying the Solid State and Lyotropic Phase Behavior of Nonionic Urea-Based Surfactants

“…1,2 Amphiphiles such as dioleoylphosphatidylethanolamime (DOPE) that adopt the H II phase at physiological temperatures have been employed in "fusogenic" lipid-based drug delivery systems. [3][4][5] Also, the 3D inverse bicontinuous cubic phases (Q II ) of glyceryl monooleate (GMO) and phytantriol (3,7,11,15-tetramethyl-1,2,3-hexadecanetriol) have been studied, as their high internal surface area and stability against dilution are of interest for pharmaceutical and cosmetic applications. [6][7][8][9][10][11][12][13][14] The non-lamellar 2D and 3D phase structures have been well described in the literature [15][16][17][18][19][20] and will be only briefly overviewed here.…”

Physical and Chemical Strategies for Therapeutic Delivery by Using Polymeric Nanoparticles

“…If the particles are required to be taken up by cells, PEGylation can be a factor that decreases their uptake (Ehrenberg et al, 2009;Mainardes et al, 2009). To overcome this hurdle, several groups have designed particles to have the PEG chain removed when it reaches the target area (Boomer et al, 2003;Romberg et al, 2008;Hatakeyama et al, 2009). These advanced particles have long circulation times to reach the target tissue where they shed the PEG chains, thus exposing charged particles that promote cellular uptake.…”

Selective injection and laser manipulation of nanotool inside a specific cell using Optical pH regulation and optical tweezers

“…DOPE was used for fusion to cell membrane. DOPE expresses the fusion-capability in weak acidic condition (< pH6) [15]. DOPE fuses the cell membrane protein such as clathrin in this condition.…”