Coupling of Metal Containing Homing Devices to Liposomes via a Maleimide Linker: Use of TCEP to Stabilize Thiol-groups without Scavenging Metals

Surface Functionalised Parenteral Nanoemulsions for Active and Homotypic Targeting to Melanoma

Despite recent progressions in cancer genomic and immunotherapies, advanced melanoma still represents a life threat, pushing to optimise new targeted nanotechnology approaches for specific drug delivery to the tumour. To this aim, owing to their biocompatibility and favourable technological features, injectable lipid nanoemulsions were functionalised with proteins owing to two alternative approaches: transferrin was chemically grafted for active targeting, while cancer cell membrane fragments wrapping was used for homotypic targeting. In both cases, protein functionalisation was successfully achieved. Targeting efficiency was preliminarily evaluated using flow cytometry internalisation studies in two-dimensional cellular models, after fluorescence labelling of formulations with 6-coumarin. The uptake of cell-membrane-fragment-wrapped nanoemulsions was higher compared to uncoated nanoemulsions. Instead, the effect of transferrin grafting was less evident in serum-enriched medium, since such ligand probably undergoes competition with the endogenous protein. Moreover, a more pronounced internalisation was achieved when a pegylated heterodimer was employed for conjugation (p < 0.05).

Novel controlled and targeted releasing hydrogen sulfide system exerts combinational cerebral and myocardial protection after cardiac arrest

BACKGROUND

Cardiac arrest (CA) is a leading cause of death worldwide. Even after successful cardiopulmonary resuscitation (CPR), the majorities of survivals are companied with permanent myocardial and cerebral injury. Hydrogen sulfide (H2S) has been recognized as a novel gasotransmitter exerting multiple organ protection; however, the lacks of ideal H2S donors which can controlled release H2S to targeted organs such as heart and brain limits its application.

RESULTS

This work utilized mesoporous iron oxide nanoparticle (MION) as the carriers of diallyl trisulfide (DATS), with polyethylene glycol (PEG) and lactoferrin (LF) modified to MIONs to acquire the prolonged circulation time and brain-targeting effects, and a novel targeted H2S releasing system was constructed (DATS@MION-PEG-LF), which exhibited excellent biocompatibility, controlled-releasing H2S pattern, heart and brain targeting features, and the ability to be non-invasive traced by magnetic resonance imaging. DATS@MION-PEG-LF presented potent protective effects against cerebral and cardiac ischemic injury after CA in both in vitro hypoxia/reoxygenation models and in vivo CA/CPR models, which mainly involves anti-apoptosis, anti-inflammatory and anti-oxidant mechanisms. Accordingly, the cardiac and cerebral functions were obviously improved after CA/CPR, with potentially improved survival.

CONCLUSIONS

The present work provides a unique platform for targeted controlled release of H2S based on MIONs, and offers a new method for combinational myocardial and cerebral protection from ischemic injury, bringing considerable benefits for CA patients.

CB1-Antibody Modified Liposomes for Targeted Modulation of Epileptiform Activities Synchronously Detected by Microelectrode Arrays

Temporal lobe epilepsy (TLE) is a focal, recurrent, and refractory neurological disorder. Therefore, precisely targeted treatments for TLE are greatly needed. We designed anti-CB1 liposomes that can bind to CB1 receptors in the hippocampus to deliver photocaged compounds (ruthenium bipyridine triphenylphosphine γ-aminobutyric acid, RuBi-GABA) in the TLE rats. A 16-channel silicon microelectrode array (MEA) was implanted for simultaneously monitoring electrophysiological signals of neurons. The results showed that anti-CB1 liposomes were larger in size and remained in the hippocampus longer than unmodified liposomes. Following the blue light stimulation, the neural firing rates and the local field potentials of hippocampal neurons were significantly reduced. It is indicated that RuBi-GABA was enriched near hippocampal neurons due to anti-CB1 liposome delivery and photolyzed by optical stimulation, resulting dissociation of GABA to exert inhibitory actions. Furthermore, K-means cluster analysis revealed that the firing rates of interneurons were decreased to a greater extent than those of pyramidal neurons, which may have been a result of the uneven diffusion of RuBi-GABA due to liposomes binding to CB1. In this study, we developed a novel, targeted method to regulate neural electrophysiology in the hippocampus of the TLE rat using antibody-modified nanoliposomes, implantable MEA, and photocaged compounds. This method effectively suppressed hippocampal activities during seizure ictus with high spatiotemporal resolution, which is a crucial exploration of targeted therapy for epilepsy.

Liposome-ligand conjugates: a review on the current state of art

Early researchers focussed on developing stimuli-responsive liposomes in order to manipulate drug release at the site of action or under certain conditions. In recent times, a great deal of efforts has been made to modify the surface of liposomes with ligands for the purpose of achieving targeted drug delivery. Due to the morphology of liposomes, their surfaces can be engineered by attaching molecules such as oligosaccharides, peptides, antibodies, antigens and oligonucleotides to the bilayer structure. Over the years, a number of techniques including the use of covalent and non-covalent linkages have been utilised in designing ligand-liposome conjugates. In this review, various strategies for the functionalisation of liposomes as well as the different types of ligand-liposome conjugates have been discussed. Finally, the pros and cons of conjugation in liposomes are concisely summarised.

Methotrexate-Loaded Solid Lipid Nanoparticles: Protein Functionalization to Improve Brain Biodistribution

Glioblastoma is the most common and invasive primary tumor of the central nervous system and normally has a negative prognosis. Biodistribution in healthy animal models is an important preliminary study aimed at investigating the efficacy of chemotherapy, as it is mainly addressed towards residual cells after surgery in a region with an intact blood⁻brain barrier. Nanoparticles have emerged as versatile vectors that can overcome the blood⁻brain barrier. In this experimental work, solid lipid nanoparticles, prepared using fatty acid coacervation, have been loaded with an active lipophilic ester of cytotoxic drug methotrexate, and functionalized with either transferrin or insulin, two proteins whose receptors are abundantly expressed on the blood⁻brain barrier. Functionalization has been achieved by grafting a maleimide moiety onto the nanoparticle's surface and exploiting its reactivity towards thiolated proteins. The nanoparticles have been tested in vitro on a blood⁻brain barrier cellular model and in vivo for biodistribution in Wistar rats. Drug metabolites, in particular 7-hydroxymethotrexate, have also been investigated in the animal model. The data obtained indicate that the functionalization of the nanoparticles improved their ability to overcome the blood⁻brain barrier when a PEG spacer between the proteins and the nanoparticle's surface was used. This is probably because this method provided improved ligand⁻receptor interactions and selectivity for the target tissue.

Adequate Reducing Conditions Enable Conjugation of Oxidized Peptides to Polymers by One-Pot Thiol Click Chemistry

Thiol(-click) chemistry has been extensively investigated to conjugate (bio)molecules to polymers. Handling of cysteine-containing molecules may however be cumbersome, especially in the case of fast-oxidizing coiled-coil-forming peptides. In the present study, we investigated the practicality of a one-pot process to concomitantly reduce and conjugate an oxidized peptide to a polymer. Three thiol-based conjugation chemistries (vinyl sulfone (VS), maleimide, and pyridyldithiol) were assayed along with three reducing agents (tris(2-carboxyethyl)phosphine (TCEP), dithiothreitol, and β-mercaptoethanol). Seven out of the nine possible combinations significantly enhanced the conjugation yield, provided that an adequate concentration of reductant was used. Among them, the coincubation of an oxidized peptide with TCEP and a VS-modified polymer displayed the highest level of conjugation. Our results also provide insights into two topics that currently lack consensus: TCEP is stable in 10 mM phosphate buffered saline and it reacts with thiol-alkylating agents at submillimolar concentrations, and thus should be carefully used in order to avoid interference with thiol-based conjugation reactions.

Linear gold(I) complex with tris-(2-carboxyethyl)phosphine (TCEP): Selective antitumor activity and inertness toward sulfur proteins

The search for modulating ligand substitution reaction in gold complexes is essential to find new active metallo compounds for medical applications. In this work, a new linear and hydrosoluble gold^I complex with tris-(2-carboxyethylphosphine) (AuTCEP). The two phosphines coordinate linearly to the metal as solved by single crystal X-ray diffraction. Complete spectroscopic characterization is also reported. In vitro growth inhibition (GI₅₀) in a panel of nine tumorigenic and one non-tumorigenic cell lines demonstrated the complex is highly selective to ovarium adenocarcinoma (OVCAR-03) with GI₅₀ of 3.04 nmol mL^-1. Moreover, non-differential uptake of AuTCEP was observed between OVCAR-03 (tumor) and HaCaT (non-tumor) two cell lines. Biophysical evaluation with the sulfur-rich biomolecules showed the compound does not interact with two types of zinc fingers, bovine serum albumin, N-acetyl-l-cysteine and also l-histidine, revealing to be inert to ligand substitution reactions with these molecules. However, AuTCEP demonstrated to cleave plasmidial DNA, suggesting DNA as a possible target. No antibacterial activity was observed in the strains evaluated. Besides, it inhibits 15% of the activity of a mixture of serine-β-lactamase and metallo-β-lactamase from Bacillus cereus in the enzymatic activity assay, similarly to EDTA. These results suggest AuTCEP is selective to metallo-β-lactamase but the cell uptake is hindered, and the compound does not reach the periplasmic space of Gram-positive bacteria. The unique inert behavior of AuTCEP is interesting and represent the modulation of the reactivity through coordination chemistry to decrease the toxicity associated with Au^I complexes and its lack of specificity, generating very selective compounds with unexpected targets.

In Situ Quenching of Trialkylphosphine Reducing Agents Using Water-Soluble PEG-Azides Improves Maleimide Conjugation to Proteins

Trialkylphosphines tris(2-carboxy-ethyl)-phosphine and tris(3-hydroxypropyl)-phosphine are popular reagents for the reduction of cysteine residues in bioconjugation reactions using maleimides. However, it has been demonstrated that these phosphines are reactive toward maleimide, necessitating their removal before the addition of the Michael acceptor. Here, a method using water-soluble PEG-azides is reported for the quenching of trialkylphosphines in situ, which is demonstrated to improve the level of maleimide conjugation to proteins.

Characterization of Reactions between Water-Soluble Trialkylphosphines and Thiol Alkylating Reagents: Implications for Protein-Conjugation Reactions

Water-soluble trialkylphosphines such as tris(carboxyethyl)phosphine (TCEP) and trishydroxypropyl phosphine (THPP) are effective agents for reducing disulfide bonds in proteins and are increasingly becoming the reagents of choice for bioconjugation strategies that modify cysteine (thiol containing) amino acids. These reducing agents are often considered as being chemically compatible with Michael acceptors such as maleimides and, as such, are often not removed prior to performing protein conjugation reactions. Here, we demonstrate the rapid and irreversible reaction of both TCEP and THPP with derivatives of the commonly employed thiol alkylating groups, maleimide and vinyl sulfone. Mechanistic investigations revealed distinct differences between the reactions of TCEP and THPP with maleimide, leading to the production of either nonproductive ylenes or succidimidyl derivatives, respectively. Importantly, we also demonstrate the incorporation of nonproductive ylenes formed between maleimide and TCEP into the Pneumococcal capsular polysaccharide Pn6b following strategies employed toward the production of conjugate vaccines.

A thiol fluorescent probe reveals the intricate modulation of cysteine's reactivity by Cu(II)

In this study, Cu(II)-mediated differential alteration of cysteine (Cys) reactivity is reported by using a Cys-specific fluorescent probe. The probe could react with Cys to give out strong fluorescence. When Cys was preincubated with Cu(II), the fluorescence of the probe was decreased due to the inhibition of Cys's reactivity by Cu(II). Remarkably, experimental results reveal that the probe could detect Cu(II) at subnanomolar concentrations. In contrast, Cu(II) could only partially inhibit the reaction between Cys and Ellman's reagent (DTNB). Furthermore, selectivity experiments show that Cu(II) is a much more potent inhibitor for Cys compared to other metal ions. Cell imaging experiments also confirm the inhibitory effects of Cu(II) on Cys's reactivity in living cells. We envision that the probe could add a useful tool for sensitive and selective detection of Cu(II) for biomedical research.

Microwave-mediated reduction of disulfide bridges with supported (tris(2-carboxyethyl)phosphine) as resin-bound reducing agent

We report on the synthesis and use of a new supported reagent consisting in tris(2-carboxyethyl)phosphine (TCEP) immobilized on hydrophilic PEG based resin beads. Used in conjunction with a 5 min microwave (MW) irradiation, "supported TCEP" reduced disulfide bridges in free thiols in peptides having two or more cysteine residues. Separation of reaction products from reducing agent was easily performed by simple filtration.

Live cell surface labeling with fluorescent Ag nanocluster conjugates

DNA-encapsulated silver clusters are readily conjugated to proteins and serve as alternatives to organic dyes and semiconductor quantum dots. Stable and bright on the bulk and single molecule levels, Ag nanocluster fluorescence is readily observed when staining live cell surfaces. Being significantly brighter and more photostable than organics and much smaller than quantum dots with a single point of attachment, these nanomaterials offer promising new approaches for bulk and single molecule biolabeling.

Radioprotective effect of transferrin targeted citicoline liposomes

The high level of expression of transferrin receptors (Tf-R) on the surface of endothelial cells of the blood-brain-barrier (BBB) had been widely utilized to deliver drugs to the brain. The primary aim of this study was to use transferrin receptor mediated endocytosis as a pathway for the rational development of holo-transferrin coupled liposomes for drug targeting to the brain. Citicoline is a neuroprotective agent used clinically to treat for instance Parkinson disease, stroke, Alzheimer's disease and brain ischemia. Citicoline does not readily cross the BBB because of its strong polar nature. Hence, citicoline was used as a model drug. (Citicoline liposomes have been prepared using dipalmitoylphosphatidylcholine (DPPC) or distearoylphosphatidylcholine (DSPC) by dry lipid film hydration-extrusion method). The effect of the use of liposomes composed of DPPC or DSPC on their citicoline encapsulation efficiency and their stability in vitro were studied. Transferrin was coupled to liposomes by a technique which involves the prevention of scavenging diferric iron atoms of transferrin. The coupling efficiency of transferrin to the liposomes was studied. In vitro evaluation of transferrin-coupled liposomes was performed for their radioprotective effect in radiation treated cell cultures. In this study, OVCAR-3 cells were used as a model cell type over-expressing the Tf-R and human umbilical vein endothelial cells (HUVEC) as BBB endothelial cell model. The average diameter of DPPC and DSPC liposomes were 138 +/- 6.3 and 79.0 +/- 3.2 nm, respectively. The citicoline encapsulation capacity of DPPC and DSPC liposomes was 81.8 +/- 12.8 and 54.9 +/- 0.04 microg/micromol of phospholipid, respectively. Liposomes prepared from DSPC showed relatively better stability than DPPC liposomes at 37 degrees C and in the presence of serum. Hence, DSPC liposomes were used for transferrin coupling and an average of 46-55 molecules of transferrin were present per liposome. Free citicoline has shown radioprotective effect at higher doses tested. Interestingly, encapsulation of citicoline in pegylated liposomes significantly improved the radioprotective effect by 4-fold compared to free citicoline in OVCAR-3 but not in HUVEC. Further, citicoline encapsulation in transferrin-coupled liposomes has significantly improved the radioprotective effect by approximately 8-fold in OVCAR-3 and 2-fold in HUVEC cells with respect to the free drug. This is likely due to the entry of citicoline into cells via transferrin receptor mediated endocytosis. In conclusion, our results suggest that low concentrations of citicoline encapsulated in transferrin-coupled liposomes could offer therapeutic benefit in treating stroke compared to free citicoline.

Brisk production of nitric oxide and associated formation ofS-nitrosothiols in early hemorrhage

The results of previous inhibitor studies suggest that there is some increase in nitric oxide (NO) production from constitutive NO synthase in early hemorrhage (H), but the magnitude of NO production early after H has not been previously assessed. It is generally believed that only modest production rates are possible from the constitutively expressed NO synthases. To study this, anesthetized male Sprague-Dawley rats were subjected to 90 min of isobaric (40 mmHg) H. During this period of time, the dynamics of accumulation of NO intermediates in the arterial blood was assessed using electron paramagnetic resonance spectroscopy, chemiluminescence, fluorescence imaging, and mass spectrometry. Electron paramagnetic resonance-detectable NO adducts were also measured with spin traps in blood plasma and red blood cells. H led to an increase in the concentration of hemoglobin-NO from 0.9 ± 0.2 to 4.8 ± 0.7 μM. This accumulation was attenuated by a nonselective inhibitor of NO synthase, NG-nitro-l-argininemethyl ester (l-NAME), but not by NG-nitro-d-argininemethyl ester (d-NAME) or 1400W. Administration of l-NAME (but not 1400W or d-NAME) during H produced a short-term increase in mean arterial pressure (∼90%). In H, the level of N oxides in red blood cells increased sevenfold. S-nitrosylation of plasma proteins was revealed with “biotin switch” techniques. The results provide compelling evidence that there is brisk production of NO in early H. The results indicate that the initial compensatory response to H is more complicated than previously realized, and it involves an orchestrated balance between intense vasoconstrictor and vasodilatory components.