Melting Behavior of Zipper-Structured Lipopeptides in Lipid Bilayer

In situ formation of a near-infrared controlled dual-antibacterial platform

An in situ formed antibacterial platform was designed for near-infrared controlled pharmacotherapy and photothermal therapy of drug-resistant bacteria.

pH/Redox-Controlled Interaction between Lipid Membranes and Peptide Derivatives with a "Helmet"

How to reduce the cytotoxicity of antitumor peptides to normal cells remains an ongoing challenge. Here, we designed a pH/redox-responsive supramolecular structure (Pep-V⊂P-PEG) composed of a peptide modified with viologen (Pep-V) and polyethylene glycol bearing pillar[5]arene (P-PEG) as a "helmet". By shielding the hydrophobic moiety of the peptide derivative with pillar[5]arene via host-guest interactions, its disruption on normal cells can be effectively reduced. At acidic pH, the supramolecular structure can selectively adsorb onto negatively charged lipid membranes because of electrostatic interactions. Owing to redox responsiveness of the viologen group, Pep-V could be separated from P-PEG after the addition of reductants and inserted into lipid bilayers, which leads to membrane disruption. Cargo leakage of liposome models was investigated to understand Pep-V⊂P-PEG-induced liposomal membrane disruption under different pH values and redox conditions. Results showed that Pep-V⊂P-PEG caused almost no cargo leakage from (1,2-dipalmitoyl-sn-glycerol-3-phosphocholine) liposomes at pH 7.4 but significant leakage from negatively charged (1,2-dipalmitoyl-sn-glycerol-3-phospho-(1-rac-glyerol)) liposomes at pH 5.0 under a reducing environment. Pep-V⊂P-PEG displayed low destructive effects on mimic normal cells and significant disruption to mimic tumor cells when exposed to a reducing environment that is expected to be a potential antitumor agent.

Disruption of Tumor Cells Using a pH-Activated and Thermosensitive Antitumor Lipopeptide Containing a Leucine Zipper Structure

Antitumor peptides may potentially alleviate the problem of chemoresistance but do not yet target tumor cells and would be cytotoxic to normal cells. Here, we designed a pH-activated and thermosensitive lipopeptide (C6-Pep) containing a leucine zipper and an alkyl chain and assessed the ability of C6-Pep to kill cancer cells. Pep, the same sequence without the N-terminal hexanoic acid moiety, was generated as a less hydrophobic control. First, lipopeptide adsorption into lipid monolayers was studied using Langmuir-Blodgett and polarization modulation infrared reflection adsorption spectroscopy. Under weakly acid conditions, electrostatic interactions between C6-Pep and negatively charged phospholipids increased the adsorption/insertion of C6-Pep (vs Pep) into lipid monolayers. Cargo leakage from liposomes was assayed to model lipopeptide-induced lipid membrane disruption. The ability of C6-Pep to disrupt liposomes depended on the peptide molecular structure/hydrophobicity, solution pH, and temperature-induced uncoiling of the zipper structure; the greatest cargo leakage from the liposome with negative charge was observed for C6-Pep at pH 5.5 under mildly hyperthermic conditions (45 °C). In vitro, C6-Pep was significantly more cytotoxic toward HeLa cells at pH 5.5 under hyperthermic conditions than at pH 7.4 and/or 37 °C. Overall, this study demonstrates that amphipathic C6-Pep can insert into cell membranes in the low-pH tumor microenvironment, whereas the application of heat promotes the uncoiling of the zipper structure, leading to the disruption of tumor cell membranes and cell death. pH-activated and thermosensitive C6-Pep represents a promising tool to kill cancer cells via a strategy that does not invoke chemoresistance and may have low side effects.

Modulation of phase transition of thermosensitive liposomes with leucine zipper-structured lipopeptides

Targeted therapy for cancer requires thermosensitive components in drug carriers for controlled drug release against viral cells. The conformational transition characteristic of leucine zipper-structured lipopeptides is utilized in our lab to modulate the phase transition temperature of liposomes, thus achieving temperature-responsive control. In this study, we computationally examined the conformational transition behaviors of leucine zipper-structured lipopeptides that were modified at the N-terminus by distinct functional groups. The conformational transition temperatures of these lipopeptides were determined by structural analysis of the implicit-solvent replica exchange molecular dynamics simulation trajectories using the dihedral angle principal component analysis and the dictionary of protein secondary structure method. Our calculations revealed that the computed transition temperatures of the lipopeptides are in good agreement with the experimental measurements. The effect of hydrogen bonds on the conformational stability of the lipopeptide dimers was examined in conventional explicit-solvent molecular dynamics simulations. A quantitative correlation of the degree of structural dissociation of the dimers and their binding strength is well described by an exponential fit of the binding free energies to the conformation transition temperatures of the lipopeptides.