Phosphatase‐Triggered Fusogenic Liposomes for Cytoplasmic Delivery of Cell‐Impermeable Compounds

Abstract

Viruses have evolved into what engineers view as sophisticated nanomachines containing fusion machinery responsible for membrane destabilization and cellular infection. [1][2][3] Activation of the fusion proteins exposes fusogenic peptide sequences that bridge the viral and cellular membranes to induce membrane fusion. Enzymetriggerable liposomes that can mimic viral-like activation might be useful delivery vehicles for proteins and genetic material. [4][5][6] However for liposomes to stably display fusogenic peptides on their surface, one must overcome the challenge of incorporating the peptide on the bilayer surface while preventing peptide insertion into the membrane, an event that would compromise bilayer integrity. 7 In this report, we gained control over the membrane destabilizing activities of fusion peptides by strategically placing phosphate groups within the peptide sequence. We then engineered phosphatase-triggerable lipid-based particles, termed PTP, by displaying phosphopeptides on the surface of liposomes. Phosphatases can remove the phosphate groups of the peptides, which then activate membrane fusion between the liposome and another membrane. In the cells, this results in cytosolic delivery of the liposome encapsulated cell-impermeable compounds.Phosphatases are enzymes responsible for catalyzing the hydrolysis of phosphate esters and can work on a variety of phosphorylated proteins, peptides, nucleotides, alkaloids, phospholipids, and lipopolysaccharides. [8][9][10][11][12][13] Interestingly, phosphatases are overexpressed in a number of inflammatory and chronic disorders [14][15][16] , especially in tumor microenvironments. 17,18 The broad range of phosphatases in the body and their selective over-expression in diseased tissue make them an attractive enzymatic trigger for engineered carriers. 13,19 As a result phosphatases have been used for decades as a trigger mechanism for the activation of pro-drugs whose water solubility is increased by the attachment of a phosphate. 20, 21 ** This work was supported by the National Institute of Health (R01GM003008) and the Cystic Fibrosis Foundation (R613CR11). JP Michael Motion is a recipient of the NIGMS predoctoral fellowship, supported by the NIGMS-IMSD grant (R25-GM56847). Juliane Nguyen is supported by the Deutsche Forschungsgemeinschaft Fellowship (DFG). We thank Dr. Justin Chan and Dr. David Pham for their assistance with peptide synthesis, and Sebastian Peck and Jessica Wong from the Biological Imaging Development Center at UCSF for their assistance in confocal microscopy. * Fax: (+1) 415-476-0688, szoka@cgl.ucsf.edu. We selected the well characterized HIV gp41 N-terminus fusion peptide 7 , 22-24 as a template for designing triggerable fusogenic phosphopeptides. Phosphate groups were placed in nonconserved positions at the N and C termini 25-27 of a 22 residue peptide in order to disrupt membrane insertion and increase sequence polarity and trigger control. Phosphorylated fusion peptides exhibited significant trigger control over the membrane des...

The fluorination effect of fluoroamphiphiles in cytosolic protein delivery

“…The covalent conjugation of PTD to cargo proteins might be involved with reduced bioactivity and safety concerns. Besides, many other delivery systems have been developed based on liposomes 14 , 15 , peptides 16 , polymers 17 , 18 , and inorganic nanoparticles 19 , 20 . These approaches still possess some limitations such as the need of protein modification, complicated synthesis, and limited transduction efficacy.…”

Dipole Orientation Matters: Longer-Circulating Choline Phosphate than Phosphocholine Liposomes for Enhanced Tumor Targeting

“…30 The structure of a dioleoyl-sn-glycero-3phosphocholine (DOPC) lipid is shown in Figure 1A, and its headgroup-flipped CP lipid with an ethyl cap (DOCPe) is shown in Figure 1B. 31 CP lipids have been used for drug delivery 32 and for preparing supported lipid bilayers. 33,34 Herein, we report a quite surprising and useful finding: the choline phosphate liposomes (named CPe) are more resistant to cellular uptake with an even longer blood circulation time than PC liposomes (Figure 1E).…”

Headgroup-Inversed Liposomes: Biointerfaces, Supported Bilayers and Applications

“…In that case, the role of DOCP was mainly to provide negative charges to the liposome. 36 In sharp contrast to the resisted cellular uptake of DOCPe liposomes, the CPm polymers were reported to have strong cell adhesion, which promoted cellular uptake. Using the CPm block copolymers shown in Figure 2C 29 and Figure 2E, Yu and co-workers demonstrated the delivery of doxorubicin (DOX) loaded in their micelles, while similar micelles with a PC headgroup had very poor cellular uptake.…”