Triggered Liposomal Release through a Synthetic Phosphatidylcholine Analogue Bearing a Photocleavable Moiety Embedded within the sn‐2 Acyl Chain

Abstract

Liposomes represent promising carriers for drug delivery applications. To maximize this potential, there has been significant interest in developing liposomal systems encapsulating molecular cargo that are highly stable until their contents are released remotely in a controlled manner. Herein, we describe the design, synthesis, and analysis of a photocleavable analogue of the ubiquitous lipid phosphoatidylcholine (PC) for the development of highly stable and controllable photodisruptable membranes. Our strategy was to develop a lipid that closely mimics the structure of PC to optimize favorable properties including biocompatibility and stability of subsequent liposomes when mixed with lipids possessing a broad range of physicochemical properties. Thus, NB-PC was designed, which contains a photocleavable 2-nitrobenzyl group embedded within the acyl chain at the sn-2 position. Following the synthesis of NB-PC, liposome disruption efficacy was evaluated through photolysis studies involving the detection of nile red release. Studies performed using a range of liposomes with different percentages of NB-PC, PC, phosphatidylethanolamine (PE), cholesterol, and polyethylene glycol-PE (PEG-PE) demonstrated minimal background release in controls, release efficacies that correlate directly with the amount of NB-PC incorporation, and that release is only minimally impacted by the inclusion of the lipids PE and cholesterol that possess disparate properties. These results demonstrate that the NB-PC system is a highly stable, flexible, and tunable system for photoinitiated release from liposomal systems.

Calcium‐Responsive Liposomes via a Synthetic Lipid Switch

“…As can be seen from the results shown in Figure A, we observed a gradual decrease in nile red fluorescence upon titration with calcium that was dependent on the percentage of 1 in liposomes. Results from control liposomes lacking 1 indicated a background fluorescence decrease of ≈10 %, which is in line with previous work . This was enhanced to ≈25 % decrease with liposomes containing 3 % of 1 , ≈50 % with 5 % of 1 , and ≈65 % with 10 % of 1 .…”

“…Following the synthesis, we set out to evaluate triggered release from liposomes incorporating 1 by conducting fluorescence release assays employing the dye, nile red. Nile red is a hydrophobic fluorophore that is solubilized by encapsulation within liposome bilayers, and therefore mimics the properties of commonly used non‐polar drugs . This leads to a standard fluorescence signal for the dye when solubilized by the liposomes.…”

Mechanisms of light‐induced liposome permeabilization

“…Bayer et al reported the synthesis of a new photocleavable phospholipid, namely NB‐PC . Stable NB‐PC liposomes were generated from the modification of the natural occurring phosphatidylcholine (PC) to include 2‐nitrobenzyl in the acyl chain at the sn ‐2 position.…”

“…(B) Nile red is released from the bilayer after NB‐PC photolysis. Figure used with permission from the publisher…”

A Clickable and Photocleavable Lipid Analogue for Cell Membrane Delivery and Release

“…38 Prior work involving the incorporation of photocleavable groups into lipids has focused on light-initiated release of molecules from liposomes. 39–45 In these cases, molecules such as drugs have been non-covalently encapsulated in the liposome and release was stimulated by decomposition or disruption of the membrane. However, noncovalent molecular encapsulation can suffer from background leakage, and thus it may be preferable to covalently attach target molecules to lipids prior to triggering the release through bond cleavage.…”