Selective Intracellular Delivery of Ganglioside GM3-Binding Peptide through Caveolae/Raft-Mediated Endocytosis

Prevention of amyloid β fibril deposition on the synaptic membrane in the precuneus by ganglioside nanocluster-targeting inhibitors

Alzheimer's disease (AD), a progressive neurodegenerative condition, is one of the most common causes of dementia. Senile plaques, a hallmark of AD, are formed by the accumulation of amyloid β protein (Aβ), which starts to aggregate before the onset of the disease. Gangliosides, sialic acid-containing glycosphingolipids, play a key role in the formation of toxic Aβ aggregates. In membrane rafts, ganglioside-bound complexes (GAβ) act as nuclei for Aβ assembly, suggesting that GAβ is a promising target for AD therapy. The formation of GAβ-induced Aβ assemblies has been evaluated using reconstituted planar lipid membranes composed of synaptosomal plasma membrane (SPM) lipids extracted from human and mouse brains. Although the effects of gangliosides on Aβ accumulation in the precuneus have been established, effects on Aβ fibrils have not been determined. In this study, Aβ42 fibrils on reconstituted membranes composed of SPM lipids prepared from the precuneus cortex of human autopsied brains were evaluated by atomic force microscopy. In particular, Aβ42 accumulation, as well as the fibril number and size were higher for membranes with precuneus lipids than for membranes with calcarine cortex lipids. In addition, artificial peptide inhibitors targeting Aβ-sensitive ganglioside nanoclusters cleared Aβ assemblies on synaptic membranes in the brain, providing a novel therapeutic strategy for AD.

Cyclization of Peptides Enhances the Inhibitory Activity against Ganglioside-Induced Aβ Fibril Formation

Alzheimer's disease is a progressive neurodegenerative disease and is the most common cause of dementia. It has been reported that the assembly of amyloid β-protein (Aβ) on the cell membrane is induced by the interaction of the Aβ monomer with gangliosides such as GM1. The ganglioside-bound Aβ (GAβ) complex acts as a seed to promote the toxic assembly of the Aβ fibrils. In a previous study, we found that a GM1 cluster-binding peptide (GCBP) specifically recognizes Aβ-sensitive ganglioside nanoclusters and inhibits the assembly of Aβ on a GM1-containing lipid membrane. In this study, cysteine-substituted double mutants of GCBP were designed and cyclized by intramolecular disulfide bond formation. Affinity assays indicated that one of the cyclic peptides had a higher affinity to a GM1-containing membrane compared to that of GCBP. Furthermore, surface topography analysis indicated that this peptide recognizes GM1 nanoclusters on the lipid membrane. An evaluation of the inhibitory kinetics indicated that the cyclic peptide could inhibit the formation of Aβ fibrils with an IC50 value of 1.2 fM, which is 10,000-fold higher than that of GCBP. The cyclic peptide was also shown to have a clearance effect on Aβ fibrils deposited on the lipid membrane and suppressed the formation of toxic Aβ assemblies. Our results indicate that the cyclic peptide that binds to the Aβ-sensitive ganglioside nanocluster is a potential novel inhibitor of ganglioside-induced Aβ assembly.

Artificial Palmitoylation of Proteins Controls the Lipid Domain-Selective Anchoring on Biomembranes and the Raft-Dependent Cellular Internalization

Protein palmitoylation, a post-translational modification, is universally observed in eukaryotic cells. The localization of palmitoylated proteins to highly dynamic, sphingolipid- and cholesterol-rich microdomains (called lipid rafts) on the plasma membrane has been shown to play an important role in signal transduction in cells. However, this complex biological system is not yet completely understood. Here, we used a combined approach where an artificial lipidated protein was applied to biomimetic model membranes and plasma membranes in cells to illuminate chemical and physiological properties of the rafts. Using cell-sized giant unilamellar vesicles, we demonstrated the selective partitioning of enhanced green fluorescent protein modified with a C-terminal palmitoyl moiety (EGFP-Pal) into the liquid-ordered phase consisting of saturated phospholipids and cholesterol. Using Jurkat T cells treated with an immunostimulant (concanavalin A), we observed the vesicular transport of EGFP-Pal. Further cellular studies with the treatment of methyl β-cyclodextrin revealed the cholesterol-dependent internalization of EGFP-Pal, which can be explained by a raft-dependent, caveolae-mediated endocytic pathway. The present synthetic approach using artificial and natural membrane systems can be further extended to explore the potential utility of artificially lipidated proteins at biological and artificial interfaces.

Ganglioside Nanocluster-Targeting Peptidyl Inhibitor Prevents Amyloid β Fibril Formation on the Neuronal Membrane

Neurotoxicity caused by peptide and protein aggregates is associated with the onset of neurodegenerative diseases. Accumulation of the amyloid β protein (Aβ) induced by neuronal ganglioside-enriched nanodomains (nanoclusters) in the presynaptic neuronal membrane, resulting in toxic oligomeric and fibrous forms, is implicated in the onset of Alzheimer's disease (AD). In the current study, we found that the ganglioside cluster-binding peptide (GCBP), a pentadecapeptide VWRLLAPPFSNRLLP that binds to ganglioside-enriched nanoclusters, inhibits the formation of Aβ assemblies with an IC₅₀ of 12 pM and also removes Aβ fibrils deposited on the lipid membrane. Thus, in addition to inhibiting Aβ assembly formation, GCBP effectively clears toxic Aβ assemblies as well, thereby suppressing neuronal cellular damage and death induced by such assemblies. These results indicate that ganglioside cluster-binding molecules may act as novel Aβ-targeting drugs with a unique mechanism of action that may be utilized to ameliorate AD.

α/β-Peptides as Nanomolar Triggers of Lipid Raft-Mediated Endocytosis through GM1 Ganglioside Recognition

Cell delivery of therapeutic macromolecules and nanoparticles is a critical drug development challenge. Translocation through lipid raft-mediated endocytic mechanisms is being sought, as it can avoid rapid lysosomal degradation. Here, we present a set of short α/β-peptide tags with high affinity to the lipid raft-associated ganglioside GM1. These sequences induce effective internalization of the attached immunoglobulin cargo. The structural requirements of the GM1-peptide interaction are presented, and the importance of the membrane components are shown. The results contribute to the development of a receptor-based cell delivery platform.

Differential Internalization of Thrombin-Derived Host Defense Peptides into Monocytes and Macrophages

Proteolytic cleavage of thrombin generates C-terminal host defense peptides exerting multiple immunomodulatory effects in response to bacterial stimuli. Previously, we reported that thrombin-derived C-terminal peptides (TCPs) are internalized in monocytes and macrophages in a time- and temperature-dependent manner. In this study, we investigated which endocytosis pathways are responsible for the internalization of TCPs. Using confocal microscopy and flow cytometry, we show that both clathrin-dependent and clathrin-independent pathways are involved in the internalization of the prototypic TCP GKY25 in RAW264.7 and human monocyte-derived M1 macrophages, whereas the uptake of GKY25 in monocytic THP-1 cells is mainly dynamin-dependent. Internalized GKY25 was transported to endosomes and finally lysosomes, where it remained detectable for up to 10 h. Comparison of GKY25 uptake with that of the natural occurring TCPs HVF18 and FYT21 indicates that the pathway of TCP endocytosis is not only cell type-dependent but also depends on the length and composition of the peptide as well as the presence of LPS and bacteria. Finally, using neutron reflectometry, we show that the observed differences between HVF18 and the other 2 TCPs may be explained partially by differences in membrane insertion. Taken together, we show that TCPs are differentially internalized into monocytes and macrophages.

Heterogeneous Ganglioside-Enriched Nanoclusters with Different Densities in Membrane Rafts Detected by a Peptidyl Molecular Probe

The specific features of the lateral distribution of gangliosides play key roles in cell-cell communications and the onset of various diseases related to the plasma membrane. We herein demonstrated that an artificial peptide identified from a phage-displayed library is available as a molecular probe for specific ganglioside nanoclustering sites in caveolae/membrane rafts on the cell surface. Atomic force microscopy studies indicated that the peptide specifically binds to the highly enriched monosialoganglioside GM1 nanodomains of reconstituted lipid bilayers composed of GM1, sphingomyelin, cholesterol, and unsaturated phospholipids. The ganglioside-containing area recognized by the peptide on the surface of PC12 cells was part of the area recognized by the cholera toxin B subunit, which has high affinity for GM1. Furthermore, the peptide bound to the cell surface after a treatment with methyl-β-cyclodextrin (MβCD), which disrupts membrane rafts by removing cholesterol. The present results indicate that there are heterogeneous ganglioside clusters with different ganglioside densities in caveolae/membrane rafts, and the peptidyl probe selectively recognizes the high-density ganglioside nanodomain that resists the MβCD treatment. This peptidyl probe will be useful for obtaining information on the lipid organization of the cell membrane and will help clarify the mechanisms by which the lateral distribution of gangliosides affects biological functions and the onset of diseases.

Size-Controlled Preparation and Behavior Study of Phospholipid-Calcium Carbonate Hybrid Nanoparticles

Background

Calcium carbonate (CC) nanoparticles have broad biomedical utilizations, owing to their multiple intrinsic merits. However, bare CC nanoparticles do not allow for the development of multifunctional devices suitable for advanced drug delivery in cancer therapy.

Methods

Phospholipid-modified phospholipid–CC hybrid nanoparticles were prepared in our study using a combination of vapor-diffusion and solvent-diffusion methods to offer optimized pharmaceutical capabilities.

Results

Considering that particle size is a critical parameter that plays an important role in both in vitro and in vivo behaviors of nanoparticles, we here for the first time a present detailed protocol for the size-controlled preparation of hybrid nanoparticles, as well as analysis of the in vitro/in vivo behaviors of differently sized hybrid nanoparticles.

Conclusion

Our results might significantly advance the application of this promising material in more varied fields.

Routing Nanomolar Protein Cargoes to Lipid Raft-Mediated/Caveolar Endocytosis through a Ganglioside GM1-Specific Recognition Tag

There is a pressing need to develop ways to deliver therapeutic macromolecules to their intracellular targets. Certain viral and bacterial proteins are readily internalized in functional form through lipid raft-mediated/caveolar endocytosis, but mimicking this process with protein cargoes at therapeutically relevant concentrations is a great challenge. Targeting ganglioside GM1 in the caveolar pits triggers endocytosis. A pentapeptide sequence WYKYW is presented, which specifically captures the glycan moiety of GM1 (K D = 24 nm). The WYKYW-tag facilitates the GM1-dependent endocytosis of proteins in which the cargo-loaded caveosomes do not fuse with lysosomes. A structurally intact immunoglobulin G complex (580 kDa) is successfully delivered into live HeLa cells at extracellular concentrations ranging from 20 to 160 nm, and escape of the cargo proteins to the cytosol is observed. The short peptidic WYKYW-tag is an advantageous endocytosis routing sequence for lipid raft-mediated/caveolar cell delivery of therapeutic macromolecules, especially for cancer cells that overexpress GM1.

Structural Requirement of Casein Peptides for Transcytosis through the Caco-2 Cell Monolayer: Hydrophobicity and Charge Property Affect the Transport Pathway and Efficiency

Casein is a rich source of bioactive peptides with complete amino acid composition. In this study, the casein peptides identified in our previous study with different hydrophobicities and charge properties were employed to investigate the transport efficiency via the transcytosis pathway across Caco-2 cell monolayers. Results revealed that the apparent permeability coefficient (P_app) values of transcytosis exhibited a linear correlation with a pI of positively charged peptides during bidirectional transport. A similar law was found as for the peptides with different hydrophobicities. The transcytosis route of Pep-II to Pep-VII appears to be the clathrin- and caveolin-independent transcytosis pathway as well as caveolae-mediated transcytosis pathway, showing a linear correlation with P_app values, respectively. Additionally, no direct correlation was shown between the hydrophobicity of peptides and clathrin-mediated transcytosis. Our results help to increase the bioaccessibility of peptide drugs across intestinal mucosa by developing strategies to alter the physicochemical properties without changing bioactivity.

Oligoarginine-Bearing Tandem Repeat Penetration-Accelerating Sequence Delivers Protein to Cytosol via Caveolae-Mediated Endocytosis

To facilitate the cytosolic delivery of larger molecules such as proteins, we developed a new cell-penetrating peptide sequence, named Pas2r12, consisting of a repeated Pas sequence (FFLIG-FFLIG) and d-dodeca-arginine (r12). This peptide significantly enhanced the cellular uptake and cytosolic release of enhanced green fluorescent protein and immunoglobulin G as cargos. We found that simply mixing Pas2r12 with cargos could generate cytosolic introducible forms. The cytosolic delivery of cargos by Pas2r12 was found to be an energy-requiring process, to rely on actin polymerization, and to be suppressed by caveolae-mediated endocytosis inhibitors (genistein and methyl-β-cyclodextrin) and small interfering RNA against caveolin-1. These results suggest that Pas2r12 enhances membrane penetration of cargos without the need for cross-linking and that caveolae-mediated endocytosis may be the route by which cytosolic delivery is enhanced.

Using an RNA aptamer probe for super-resolution imaging of native EGFR

Aptamers, referred to as "chemical antibodies", are short single-stranded oligonucleotides that bind to targets with high affinity and specificity. Compared with antibodies, aptamers can be designed, developed and modified easily. Since their discovery, aptamers have been widely used in in vitro diagnostics and molecular imaging. However, they are relatively less studied and applied in advanced microscopy. Here we used an RNA aptamer in dSTORM imaging and obtained a high-quality image of EGFR nanoscale clusters on live cell membranes. The results showed that the cluster number and size with aptamer labeling were almost the same as those with labeling with the natural ligand EGF, but the morphology of the clusters was smaller and more regular than that with cetuximab labeling. Meanwhile, dual-color imaging demonstrated sufficient fluorophore labeling, highly specific recognition and greatly accurate clustering information provided by aptamers. Furthermore, the aptamer labeling method indicated that active EGFR formed larger clusters containing more molecules than resting EGFR, which was hidden under the antibody labeling. Our work suggested that aptamers can be used as versatile probes in super-resolution imaging with small steric hindrance, opening a new avenue for detailed and precise morphological analysis of membrane proteins.

A Tf-modified tripterine-loaded coix seed oil microemulsion enhances anti-cervical cancer treatment

Purpose

A transferrin-modified microemulsion carrying coix seed oil and tripterine (Tf-CT-MEs) was developed for improved tumor-specific accumulation and penetration to enhance cervical cancer treatment.

Materials and methods

Tripterine-loaded coix seed oil microemulsion (CT-MEs) was prepared through one-step emulsion method. The morphology, size, and zeta potential of CT-MEs and Tf-CT-MEs were examined by transmission electron microscopy and dynamic light scattering. The cellular uptake and mechanisms of HeLa cells were investigated by flow cytometry. Intratumor penetration was investigated using a HeLa three-dimensional (3D) tumor spheroid as the model. The cytotoxicity of the CT-MEs and Tf-CT-MEs against HeLa cells were evaluated by the MTT assay. Additionally, the apoptotic rate of CT-MEs and Tf-CT-MEs inducing apoptosis in HeLa cells was evaluated.

Results

In the physicochemical characterization, coix seed oil and CT-MEs exhibited a small size (32.47±0.15 nm) and nearly neutral surface charge (−0.36±0.11 mV). After modification with transferrin, the particle size of Tf-CT-MEs slightly increased to 40.02±0.21 nm, but the zeta potential decreased remarkably to -13.63±1.31 mV. The IC₅₀ of Tf-CT-MEs against HeLa cells was 0.7260 µM, which was 2.58-fold lower than that of CT-MEs. In cellular studies, the intracellular fluorescence intensity of fluorescein isothiocyanate (FITC)-labeled Tf-CT-MEs (FITC/Tf-CT-MEs) was 2.28-fold higher than that of FITC-labeled CT-MEs (FITC/CT-MEs). The fluorescence signal of Tf-CT-MEs was observed at 350 µm below the surface of the 3D tumor spheroid. The apoptotic rate of cells treated with Tf-CT-MEs was 1.73- and 2.77-fold higher than that of cells treated with CT-MEs and tripterine, respectively, which was associated with mitochondrial-targeted delivery of tripterine. Moreover, Tf-CT-MEs was capable of significantly downregulating the cellular level of antiapoptotic proteins and arrested cell proliferation in the G₂/M phase.

Conclusion

Taken together, Tf-CT-MEs holds promising potential to be an efficient drug delivery system for combinational therapy of cervical cancer.

A multicomponent microemulsion using rational combination strategy improves lung cancer treatment through synergistic effects and deep tumor penetration

Previously, we have developed a multicomponent-based microemulsion composed of etoposide, coix seed oil, and ginsenoside Rh2 (ECG-MEs). In this study, our goal was to validate the feasibility of ECG-MEs in lung cancer treatment and explore the mechanism underling the enhanced antitumor efficacy. The optimal weight ratio of ginsenoside Rh2 (G-Rh2) in ECG-MEs was determined as 3% (wt%), that was capable of forming the microemulsion readily with small particle size and high drug encapsulation efficiency. In cellular studies, the intracellular fluorescence of human non-small cell lung cancer (A549) cells treated with fluorescein isothiocyanate-labeled ECG-MEs (FITC/ECG-MEs) was significantly higher than that of various controls, leading to the obviously synergistic anticancer activities in cytotoxicity and in vitro cell apoptosis induction. The anticancer efficacy in vivo results showed that ECG-MEs markedly inhibited the growth of A549 tumor xenografts, potently induced tumor cells apoptosis, and obviously prolonged the survival time of mice. Of note, the mechanisms of enhanced anticancer efficiency were connected with the small size-mediated deep tumor penetration and increase in serum concentration of T helper 1 (Th1) cytokines. In summary, ECG-MEs exerting the rational drug combination strategy offers a solid evidence for lung cancer treatment, and has a promising potential for clinical application.

Self-delivering prodrug-nanoassemblies fabricated by disulfide bond bridged oleate prodrug of docetaxel for breast cancer therapy

Breast cancer leads to high mortality of women in the world. Docetaxel (DTX) has been widely applied as one of the first-line chemotherapeutic drugs for breast cancer therapy. However, the clinical outcome of DTX is far from satisfaction due to its poor drug delivery efficiency. Herein, a novel disulfide bond bridged oleate prodrug of DTX was designed and synthesized to construct self-delivering prodrug-based nanosystem for improved anticancer efficacy of DTX. The uniquely engineered prodrug-nanoassemblies showed redox-responsive drug release, increased cellular uptake and comparable cytotoxicity against 4T1 breast cancer cells when compared with free DTX. In vivo, oleate prodrug-based nanoparticles (NPs) demonstrated significantly prolonged systemic circulation and increased accumulation in tumor site. As a result, prodrug NPs produced a notable antitumor activity in 4T1 breast cancer xenograft in BALB/c mice. This prodrug-based self-assembly and self-delivery strategy could be utilized to improve the delivery efficiency of DTX for breast cancer treatment.