Maleimide-functionalized lipids that anchor polypeptides to lipid bilayers and membranes

Effects of a N-Maleimide-derivatized Phosphatidylethanolamine on the Architecture and Properties of Lipid Bilayers

N-maleimide-derivatized phospholipids are often used to facilitate protein anchoring to membranes. In autophagy studies, this is applied to the covalent binding of Atg8, an autophagy protein, to a phosphatidylethanolamine (PE) in the nascent autophagosome. However, the question remains on how closely the N-maleimide PE derivative (PE-mal) mimicks the native PE in the bilayer. In the present paper, spectroscopic and calorimetric techniques have been applied to vesicles containing either PE or PE-mal (together with other phospholipids) to compare the properties of the native and derivatized forms of PE. According to differential scanning calorimetry, and to infrared spectroscopy, the presence of PE-mal did not perturb the fatty acyl chains in the bilayer. Fluorescence spectroscopy and microscopy showed that PE-mal did not alter the bilayer permeability either. However, fluorescence emission polarization of the Laurdan and DPH probes indicated an increased order, or decreased fluidity, in the bilayers containing PE-mal. In addition, the infrared spectral data from the phospholipid phosphate region revealed a PE-mal-induced conformational change in the polar heads, accompanied by increased hydration. Globally considered, the results suggest that PE-mal would be a reasonable substitute for PE in model membranes containing reconstituted proteins.

Nanomedicine platform for targeting activated neutrophils and neutrophil-platelet complexes using an α1-antitrypsin-derived peptide motif

Targeted drug delivery to disease-associated activated neutrophils can provide novel therapeutic opportunities while avoiding systemic effects on immune functions. We created a nanomedicine platform that uniquely utilizes an α1-antitrypsin-derived peptide to confer binding specificity to neutrophil elastase on activated neutrophils. Surface decoration with this peptide enabled specific anchorage of nanoparticles to activated neutrophils and platelet-neutrophil aggregates, in vitro and in vivo. Nanoparticle delivery of a model drug, hydroxychloroquine, demonstrated significant reduction of neutrophil activities in vitro and a therapeutic effect on murine venous thrombosis in vivo. This innovative approach of cell-specific and activation-state-specific targeting can be applied to several neutrophil-driven pathologies.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

Intravenous administration of synthetic platelets (SynthoPlate) in a mouse liver injury model of uncontrolled hemorrhage improves hemostasis

BACKGROUND

Clinical resuscitative treatment of traumatic hemorrhage involves transfusion of RBC, platelets and plasma in controlled ratios. However, use of such blood components, especially platelets, present many challenges including availability, portability, contamination risks, and short shelf-life, which limit the use of platelet transfusions outside of large trauma centers such as remote civilian hospitals and austere prehospital settings. This has prompted significant research in platelet substitutes that may resolve the above issues while providing platelet-mimetic hemostatic action. In this framework, we have developed a synthetic platelet surrogate, SynthoPlate, by integrative decoration of platelet function mimetic peptides on a biocompatible lipid nanovesicle platform. We have previously demonstrated hemostatic capability of SynthoPlate in correcting tail-bleeding time in thrombocytopenic mice. Building on this, we hypothesized that SynthoPlate transfusion would decrease bleeding in a murine model of acute hemorrhagic shock.

METHODS

A validated model of uncontrolled intraperitoneal hemorrhage, via liver laceration was used to induce hemorrhagic shock in mice. SynthoPlate, control (unmodified) particles, and normal saline were administered as pretreatment and recue infusions to mice undergoing liver laceration and evaluated for hemostatic benefit by determining differences in blood loss and monitoring real-time hemodynamic data.

RESULTS

Pretreatment SynthoPlate transfusion resulted in significant reduction of blood loss following hemorrhage, compared with control particles or normal saline treatment (0.86 ± 0.16 g control particles [CP] vs. 0.84 ± 0.13 g normal saline [NS] vs. 0.68 ± 0.09 g SynthoPlate, p < 0.005). SynthoPlate transfused mice demonstrated improved hemodynamics taking significantly longer to develop post-injury hypotension (168.3 ± 106.6 seconds CP vs. 137 ± 58 seconds NS vs. 546.7 ± 329.8 seconds SynthoPlate, p < 0.05). SynthoPlate infusion following liver laceration, that is, rescue transfusion, also resulted in a significant decrease in blood loss (0.89 ± 0.17 g CP vs. 0.92 ± 0.19 g NS vs. 0.69 ± 0.18 g SynthoPlate, p < 0.05).

CONCLUSION

Transfusion of SynthoPlate particles reduces blood loss in a murine model of liver injury, and SynthoPlates may represent a viable transfusion product for the mitigation of blood loss in acute, severe hemorrhagic shock.

Fabricating an intelligent cell-like nano-prodrug via hierarchical self-assembly based on the DNA skeleton for suppressing lung metastasis of breast cancer

A new intelligent cell-like nanostructure is designed for suppressing lung metastasis of breast cancer.

Development of lipopolyplexes for gene delivery: A comparison of the effects of differing modes of targeting peptide display on the structure and transfection activities of lipopolyplexes

The design, synthesis and formulation of non-viral gene delivery vectors is an area of renewed research interest. Amongst the most efficient non-viral gene delivery systems are lipopolyplexes, in which cationic peptides are co-formulated with plasmid DNA and lipids. One advantage of lipopolyplex vectors is that they have the potential to be targeted to specific cell types by attaching peptide targeting ligands on the surface, thus increasing both the transfection efficiency and selectivity for disease targets such as cancer cells. In this paper, we have investigated two different modes of displaying cell-specific peptide targeting ligands at the surface of lipopolyplexes. Lipopolyplexes formulated with bimodal peptides, with both receptor binding and DNA condensing sequences, were compared with lipopolyplexes with the peptide targeting ligand directly conjugated to one of the lipids. Three EGFR targeting peptide sequences were studied, together with a range of lipid formulations and maleimide lipid structures. The biophysical properties of the lipopolyplexes and their transfection efficiencies in a basal-like breast cancer cell line were investigated using plasmid DNA bearing genes for the expression of firefly luciferase and green fluorescent protein. Fluorescence quenching experiments were also used to probe the macromolecular organisation of the peptide and pDNA components of the lipopolyplexes. We demonstrated that both approaches to lipopolyplex targeting give reasonable transfection efficiencies, and the transfection efficiency of each lipopolyplex formulation is highly dependent on the sequence of the targeting peptide. To achieve maximum therapeutic efficiency, different peptide targeting sequences and lipopolyplex architectures should be investigated for each target cell type.

Intravenous synthetic platelet (SynthoPlate) nanoconstructs reduce bleeding and improve 'golden hour' survival in a porcine model of traumatic arterial hemorrhage

Traumatic non-compressible hemorrhage is a leading cause of civilian and military mortality and its treatment requires massive transfusion of blood components, especially platelets. However, in austere civilian and battlefield locations, access to platelets is highly challenging due to limited supply and portability, high risk of bacterial contamination and short shelf-life. To resolve this, we have developed an I.V.-administrable 'synthetic platelet' nanoconstruct (SynthoPlate), that can mimic and amplify body's natural hemostatic mechanisms specifically at the bleeding site while maintaining systemic safety. Previously we have reported the detailed biochemical and hemostatic characterization of SynthoPlate in a non-trauma tail-bleeding model in mice. Building on this, here we sought to evaluate the hemostatic ability of SynthoPlate in emergency administration within the 'golden hour' following traumatic hemorrhagic injury in the femoral artery, in a pig model. We first characterized the storage stability and post-sterilization biofunctionality of SynthoPlate in vitro. The nanoconstructs were then I.V.-administered to pigs and their systemic safety and biodistribution were characterized. Subsequently we demonstrated that, following femoral artery injury, bolus administration of SynthoPlate could reduce blood loss, stabilize blood pressure and significantly improve survival. Our results indicate substantial promise of SynthoPlate as a viable platelet surrogate for emergency management of traumatic bleeding.

A Redox-Active Fluorescent pH Indicator for Detecting Plasmodium falciparum Strains with Reduced Responsiveness to Quinoline Antimalarial Drugs

Mutational changes in the Plasmodium falciparum chloroquine resistance transporter (PfCRT) have been associated with differential responses to a wide spectrum of biologically active compounds including current and former quinoline and quinoline-like antimalarial drugs. PfCRT confers altered drug responsiveness by acting as a transport system, expelling drugs from the parasite's digestive vacuole where these drugs exert, at least part of, their antiplasmodial activity. To preserve the efficacy of these invaluable drugs, novel functional tools are required for epidemiological surveys of parasite strains carrying mutant PfCRT variants and for drug development programs aimed at inhibiting or circumventing the action of PfCRT. Here we report the synthesis and characterization of a pH-sensitive fluorescent chloroquine analogue consisting of 7-chloro-N-{2-[(propan-2-yl)amino]ethyl}quinolin-4-amine functionalized with the fluorochrome 7-nitrobenzofurazan (NBD) (henceforth termed Fluo-CQ). In the parasite, Fluo-CQ accumulates in the digestive vacuole, giving rise to a strong fluorescence signal but only in parasites carrying the wild type PfCRT. In parasites carrying the mutant PfCRT, Fluo-CQ does not accumulate. The differential handling of the fluorescent probe, combined with live cell imaging, provides a diagnostic tool for quick detection of those P. falciparum strains that carry a PfCRT variant associated with altered responsiveness to quinoline and quinoline-like antimalarial drugs. In contrast to the accumulation studies, chloroquine (CQ)-resistant parasites were observed cross-resistant to Fluo-CQ when the chemical probe was tested in various CQ-sensitive and -resistant parasite strains. NBD derivatives were found to act as redox cyclers of two essential targets, using a coupled assay based on methemoglobin and the NADPH-dependent glutathione reductase (GRs) from P. falciparum. This redox activity is proposed to contribute to the dual action of Fluo-CQ on redox equilibrium and methemoglobin reduction via PfCRT-mediated drug efflux in the cytosol and then continuous redox-dependent shuttling between food vacuole and cytosol. Taking into account these physicochemical characteristics, a model was proposed to explain Fluo-CQ antimalarial effects involving the contribution of PfCRT-mediated transport, methemoglobin reduction, hematin binding, and NBD reduction activity catalyzed by PfGR in CQ-resistant versus CQ-sensitive parasites. Therefore, introduction of NBD fluorophore in drugs is not inert and should be taken into account in drug transport and imaging studies.

Smart tools and orthogonal click-like reactions onto small unilamellar vesicles

Click-based reactions were conducted at the surface of small unilamellar vesicles (SUVs) to provide onto-vesicle chemistry with efficient innovative ready-for-use tools. For that purpose, four amphiphilic molecules were designed to insert into bilayers while presenting a reactive functional head. In this manner, a dioleylglycero-ethoxy-ethoxy-ethoxy-ethanamine (DOG-PEG4-NH2) was chosen as a common platform while the reactive amine head was converted into several electrophilic functions. Thus, two dioleylglycerol-based cyclooctyne anchors were prepared: cyclooct-1-yn-3-glycolic acid-based anchor (DOG-COA) and 1-fluorocyclooct-2-ynecarboxylic acid-based anchor (DOG-FCOA). The last one differed from the first one in that a fluorine atom reinforces the electrophilic properties of the unsaturated bond. In addition, a third dioleylglycerol-based triphenylphosphine (DOG-PPh3) was synthesized for the first time. These three innovative amphiphilic anchors were designed to react with any azide-based biomolecule following copper-free Huisgen 1,4-cycloaddition and Staudinger ligation, respectively. A fourth anchor bearing a 3,4-dibromomaleimide ring (DOG-DBM) was also unprecedentedly synthesized, to be further substituted by two thiols. Model reactions conducted in solution with either model biotinyl azide or model biotinyl disulfide gave good to total conversions and excellent isolated yields. The four new anchors were inserted into SUVs whose formula is classically used in in vivo biology. Stability and surface overall electrostatic charge were in the expected range and constant over the study. Then, the functionalized liposomes were ligated to biotin-based reagents and the experimental conditions were finely tuned to optimize the conversion. The biotinyl liposomes were demonstrated functional and totally accessible in an affinity test based on biotin scaffold quantification. Finally, DOG-FCOA's reactivity was confronted to that of DOG-DBM in a 'one-pot' orthogonal reaction. (Biotin-S)2 and TAMRA-N3 (tetramethylcarboxyrhodamine azide) were successively conjugated to the liposome suspension in a successful manner. These data implement and reinforce the interest of bioorthogonal click-like reactions onto lipid nanoparticles.

Microplate-based analysis of protein-membrane binding interactions via immobilization of whole liposomes containing a biotinylated anchor

Cellular membranes play key roles in the regulation of a range of important biological processes. However, the characterization of membrane involvement in these events is difficult to achieve due to the complexity of the membrane bilayer and the challenges associated with handling and analyzing these systems. As such, rapid and reliable approaches for characterizing membrane-based processes are necessary. To address this issue, we have first developed an azide-tagged modular lipid anchor scaffold (2) that can be conveniently derivatized via click chemistry to functionalize the membrane surface. This was used to access biotin- and fluorescein-lipid conjugates 1a and 1b, respectively. These compounds were then employed to perform and characterize the immobilization of liposomes containing biotin-anchor 1a onto streptavidin-coated microplates. Results from these studies indicated clean, biotin-dependent surface deposition. This strategy for liposome attachment was then applied to a microplate-based platform to detect the binding of receptor proteins to immobilized liposomes, specifically for the membrane binding of protein kinase Calpha (PKCalpha). The resulting data indicated direct detection of binding to the membrane-functionalized surface. The reported approaches provide efficient methods for the derivatization of the membrane surface, which is applicable to the study of membrane-based processes. Finally, the described microplate-based liposome binding assay allows for high-throughput analysis of important protein-membrane binding events.

In situ synthesis of lipopeptides as versatile receptors for the specific binding of nanoparticles and liposomes to solid-supported membranes

A detailed study of the in situ coupling of small peptides such as CGGH6 (H6) and CGWK8 (K8) to maleimide functionalized phospholipid bilayers is presented. Individually addressable microstructured membranes are employed to unequivocally probe the conjugation. The in situ coupling of peptides via a terminal cysteine moiety to maleimide functionalized phospholipids is shown to be a convenient and versatile way to selectively fabricate peptide-modified phospholipid bilayers serving as specific receptor platforms for functionalized vesicles and nanoparticles. Specific binding of functional vesicles to the peptide-modified bilayers is achieved by either histidine complexation with Ni-NTA-DOGS containing vesicles or electrostatic interaction between positively charged oligolysine bearing lipopeptides and negatively charged POPC/POPG vesicles. Peptide receptors are also found to be easily accessible from the aqueous phase and not buried within the membrane interior.

Aqueous-Soluble, Non-Reversible Lipid Conjugate of Salmon Calcitonin: Synthesis, Characterization and In Vivo Activity

PURPOSE

A novel, non-reversible, aqueous-based lipidization strategy with palmitic acid as a model lipid was evaluated for conjugation with salmon calcitonin (sCT).

MATERIALS AND METHODS

A water-soluble epsilon-maleimido lysine derivative of palmitic acid was synthesized from reaction of palmitic acid N-succinimidyl ester and epsilon-maleimido lysine. The latter was generated from reaction of alpha-Boc-lysine and methylpyrrolecarboxylate, with subsequent deprotection of the Boc group. The palmitic derivative was further conjugated with sCT via a thio-ether bond to produce Mal-sCT in aqueous solution. The identity and purity of Mal-sCT was confirmed by Electrospray Ionisation Mass spectrometry (ESI-MS) and HPLC.

RESULTS

Yield of Mal-sCT was 83%. Dynamic light scattering and circular dichroism data suggested that Mal-sCT presented as a stable helical structure in aqueous solutions of varying polarity, with a propensity to aggregate at concentrations above 11 microM. Cellular uptake of Mal-sCT was twice that of sCT in the Caco-2 cell model, and the conjugate was more resistant to liver enzyme degradation. Mal-sCT exhibited comparable hypocalcemic activity to sCT when administered subcutaneously in the rat model at sCT equivalent dose of 0.114 mg/kg. Peroral Mal-sCT, however, produced variability in therapeutic outcome. While four out of six rats did not respond following intragastric gavage with Mal-sCT, two rats showed significantly suppressed plasma calcium levels (approximately 60% of baseline) for up to 10 h.

CONCLUSION

A novel non-reversible, water-soluble lipid conjugate of sCT was successfully synthesized that showed (1) different aggregation behavior and secondary structure, (2) improved enzymatic stability and cellular uptake, and (3) comparable hypocalcemic activity in vivo compared to sCT.

Gravimetric antigen detection utilizing antibody-modified lipid bilayers

Lipid bilayers containing 5% nitrilotriacetic acid (NTA) lipids supported on SiO2 have been used as a template for immobilization of oligohistidine-tagged single-chained antibody fragments (scFvs) directed against cholera toxin. It was demonstrated that histidine-tagged scFvs could be equally efficiently coupled to an NTA-Ni2+-containing lipid bilayer from a purified sample as from an expression supernatant, thereby providing a coupling method that eliminates time-consuming protein prepurification steps. Irrespective of whether the coupling was made from the unpurified or purified antibody preparation, the template proved to be efficient for antigen (cholera toxin) detection, verified using quartz crystal microbalance with dissipation monitoring. In addition, via a secondary amplification step using lipid vesicles containing GM1 (the natural membrane receptor for cholera toxin), the detection limit of cholera toxin was less than 750 pM. To further strengthen the coupling of scFvs to the lipid bilayer, scFvs containing two histidine tags, instead of just one tag, were also evaluated. The increased coupling strength provided via the bivalent anchoring significantly reduced scFv displacement in complex solutions containing large amounts of histidine-containing proteins, verified via cholera toxin detection in serum.

Synthesis, characterization, photophysical properties, and biological labeling studies of a series of luminescent rhenium(I) polypyridine maleimide complexes

We report the synthesis, characterization, and photophysical properties of a series of rhenium(I) polypyridine maleimide complexes [Re(N-N)(CO)(3)(py-3-mal)](CF(3)SO(3)) [N-N = 1,10-phenanthroline, phen (1), 2,9-dimethyl-1,10-phenanthroline, 2,9-Me(2)-phen (2), 3,4,7,8-tetramethyl-1,10-phenanthroline, 3,4,7,8-Me(4)-phen (3), 4,7-diphenyl-1,10-phenanthroline, 4,7-Ph(2)-phen (4), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, 2,9-Me(2)-4,7-Ph(2)-phen (5), 2,2'-biquinonine, biq (6); py-3-mal = N-(3-pyridyl)maleimide]. The X-ray crystal structure of complex 2 has been investigated. Upon excitation, the complexes exhibit intense and long-lived photoluminescence in fluid solutions at 298 K. The emission wavelengths range from 514 to 654 nm, and the emission lifetimes fall in the microsecond time scale. The luminescence is assigned to originate from a metal-to-ligand charge-transfer MLCT [dpi(Re) --> pi*(diimine)] triplet excited state. As the maleimide group can react with the sulfhydryl group to form a stable thioether moiety, these complexes have been used as thiol-specific luminescent labels for a thiolated oligonucleotide, glutathione, and bovine serum albumin and human serum albumin. The photoluminescence properties of the labeled biological species have also been investigated.