Self-assembled Tat nanofibers as effective drug carrier and transporter

Peptide-drug conjugates as effective prodrug strategies for targeted delivery

Peptide-drug conjugates (PDCs) represent an important class of therapeutic agents that combine one or more drug molecules with a short peptide through a biodegradable linker. This prodrug strategy uniquely and specifically exploits the biological activities and self-assembling potential of small-molecule peptides to improve the treatment efficacy of medicinal compounds. We review here the recent progress in the design and synthesis of peptide-drug conjugates in the context of targeted drug delivery and cancer chemotherapy. We analyze carefully the key design features in choosing the peptide sequence and linker chemistry for the drug of interest, as well as the strategies to optimize the conjugate design. We highlight the recent progress in the design and synthesis of self-assembling peptide-drug amphiphiles to construct supramolecular nanomedicine and nanofiber hydrogels for both systemic and topical delivery of active pharmaceutical ingredients.

Mesoporous carbon nanoshells for high hydrophobic drug loading, multimodal optical imaging, controlled drug release, and synergistic therapy

Loading and controlled release of sufficient hydrophobic drugs to tumor cells has been the bottleneck in chemotherapy for decades. Herein we report the development of a fluorescent and mesoporous carbon nanoshell (FMP-CNS) that exhibits a loading capacity for the hydrophobic drug paclitaxel (PTX) as high as ∼80 wt% and releases the drug in a controllable fashion under NIR irradiation (825 nm) at an intensity of 1.5 W cm^-2. The high drug loading is primarily attributed to its mesoporous structure and to the supramolecular π-stacking between FMP-CNSs and PTX molecules. The FMP-CNS also exhibits wavelength-tunable and upconverted fluorescence properties and thus can serve as an optical marker for confocal, two-photon, and near infrared (NIR) fluorescence imaging. Furthermore, our in vitro results indicate that FMP-CNSs demonstrate high therapeutic efficacy through the synergistic effect of combined chemo-photothermal treatment. In vivo studies demonstrate marked suppression of tumor growth in mice bearing rat C6 glioblastoma after administration with a single intratumoral injection of PTX-loaded FMP-CNS.

Drug delivery by supramolecular design

Principles rooted in supramolecular chemistry have empowered new and highly functional therapeutics and drug delivery devices. This general approach offers elegant tools rooted in molecular and materials engineered to address the many challenges faced in treating disease.

Glutathione-responsive paclitaxel dimer nanovesicles with high drug content

Paclitaxel dimers containing mono thioether linkers can self-assemble into hollow nanovesicles that exhibit comparable cytotoxicity to Taxol.

Elucidating the stability of bolaamphiphilic polypeptide nanosheets using atomistic molecular dynamics

Atomistic molecular dynamics was employed to characterize bolaamphiphilic polypeptides nanosheets.

Self-assembled peptide nanomaterials for biomedical applications: promises and pitfalls

Over the last several decades, a great number of advances have been made in the area of self-assembled supramolecules for regenerative medicine. Such advances have involved the design, preparation, and characterization of brand new self-assembled peptide nanomaterials for a variety of applications. Among all biomolecules considered for self-assembly applications, peptides have attracted a great deal of attention as building blocks for bottom-up fabrication, due to their versatility, ease of manufacturing, low costs, tunable structures, and versatile properties. Herein, some of the more exciting new designs of self-assembled peptides and their associated unique features are reviewed and several promising applications of how self-assembled peptides are advancing drug delivery, tissue engineering, antibacterial therapy, and biosensor device applications are highlighted.

Preloading of Hydrophobic Anticancer Drug into Multifunctional Nanocarrier for Multimodal Imaging, NIR-Responsive Drug Release, and Synergistic Therapy

Applications of hydrophobic drug-based nanocarriers (NCs) remain largely limited because of their low loading capacity. Here, development of a multifunctional hybrid NC made of a magnetic Fe3O4 core and a mesoporous silica shell embedded with carbon dots (CDs) and paclitaxel (PTX), and covered by another layer of silica is reported. The NC is prepared via a one-pot process under mild condition. The PTX loading method introduced in this study simplifies drug loading process and demonstrates a high loading capacity due to mesoporous silica dual-shell structure, supramolecular π-stacking between conjugated rings of PTX molecules, and aromatic rings of the CDs in the hybrid NC. The CDs serve as both confocal and two-photon fluorescence imaging probes, while the Fe3O4 core serves as a magnetic resonance imaging contrast agent. Significantly, NC releases PTX in response to near infrared irradiation as a result of local heating of the embedded CDs and the heating of CDs also provides an additional therapeutic effect by thermally killing cancer cells in tumor in addition to the chemotherapeutic effect of released PTX. Both in vitro and in vivo results show that NC demonstrates high therapeutic efficacy through a synergistic effect from the combined chemo-photothermal treatments.

Designing hydrogels for controlled drug delivery

Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.

Self-assembled peptide nanostructures for functional materials

Nature is an important inspirational source for scientists, and presents complex and elegant examples of adaptive and intelligent systems created by self-assembly. Significant effort has been devoted to understanding these sophisticated systems. The self-assembly process enables us to create supramolecular nanostructures with high order and complexity, and peptide-based self-assembling building blocks can serve as suitable platforms to construct nanostructures showing diverse features and applications. In this review, peptide-based supramolecular assemblies will be discussed in terms of their synthesis, design, characterization and application. Peptide nanostructures are categorized based on their chemical and physical properties and will be examined by rationalizing the influence of peptide design on the resulting morphology and the methods employed to characterize these high order complex systems. Moreover, the application of self-assembled peptide nanomaterials as functional materials in information technologies and environmental sciences will be reviewed by providing examples from recently published high-impact studies.

Controlled self-organization of cyanostilbene: emission tuning and photo-responsiveness

Cyanostilbene modified with dimethylaniline (CMD) could self-assemble into vesicles and fibrous morphologies depending on the solvophobic properties. Furthermore, morphology of well-defined nanostructures could be changed with enhanced emission triggered by the photo-isomerization of cyanostilbene. The present system has potential for building luminescent color conversion materials.

MMP-9 triggered self-assembly of doxorubicin nanofiber depots halts tumor growth

A central challenge in cancer care is to ensure that therapeutic compounds reach their targets. One approach is to use enzyme-responsive biomaterials, which reconfigure in response to endogenous enzymes that are overexpressed in diseased tissues, as potential site-specific anti-tumoral therapies. Here we report peptide micelles that upon MMP-9 catalyzed hydrolysis reconfigure to form fibrillar nanostructures. These structures slowly release a doxorubicin payload at the site of action. Using both in vitro and in vivo models, we demonstrate that the fibrillar depots are formed at the sites of MMP-9 overexpression giving rise to enhanced efficacy of doxorubicin, resulting in inhibition of tumor growth in an animal model.

Targeted conjugation of breast anticancer drug tamoxifen and its metabolites with synthetic polymers

Conjugation of antitumor drug tamoxifen and its metabolites, 4-hydroxytamxifen and ednoxifen with synthetic polymers poly(ethylene glycol) (PEG), methoxypoly (ethylene glycol) polyamidoamine (mPEG-PAMAM-G3) and polyamidoamine (PAMAM-G4) dendrimers was studied in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize the drug binding process to synthetic polymers. Structural analysis showed that drug-polymer binding occurs via both H-bonding and hydrophobic contacts. The order of binding is PAMAM-G4>mPEG-PAMAM-G3>PEG-6000 with 4-hydroxttamoxifen forming more stable conjugate than tamoxifen and endoxifen. Transmission electron microscopy showed significant changes in carrier morphology with major changes in the shape of the polymer aggregate as drug encapsulation occurred. Modeling also showed that drug is located in the surface and in the internal cavities of PAMAM with the free binding energy of -3.79 for tamoxifen, -3.70 for 4-hydroxytamoxifen and -3.69kcal/mol for endoxifen, indicating of spontaneous drug-polymer interaction at room temperature.

Destruction of vasculogenic mimicry channels by targeting epirubicin plus celecoxib liposomes in treatment of brain glioma

The efficacy of chemotherapy for brain glioma is restricted by the blood–brain barrier (BBB), and surgery or radiotherapy cannot eliminate the glioma cells because of their unique location. Residual brain glioma cells can form vasculogenic mimicry (VM) channels that can cause a recurrence of brain glioma. In the present study, targeting liposomes incorporating epirubicin and celecoxib were prepared and used for the treatment of brain glioma, along with the destruction of their VM channels. Evaluations were performed on the human brain glioma U87MG cells in vitro and on intracranial brain glioma-bearing nude mice. Targeting epirubicin plus celecoxib liposomes in the circulatory blood system were able to be transported across the BBB, and accumulated in the brain glioma region. Then, the liposomes were internalized by brain glioma cells and killed glioma cells by direct cytotoxic injury and the induction of apoptosis. The induction of apoptosis was related to the activation of caspase-8- and -3-signaling pathways, the activation of the proapoptotic protein Bax, and the suppression of the antiapoptotic protein Mcl-1. The destruction of brain glioma VM channels was related to the downregulation of VM channel-forming indictors, which consisted of MMP-2, MMP-9, FAK, VE-Cad, and VEGF. The results demonstrated that the targeting epirubicin plus celecoxib liposomes were able to effectively destroy the glioma VM channels and exhibited significant efficacy in the treatment of intracranial glioma-bearing nude mice. Therefore, targeting epirubicin plus celecoxib liposomes could be a potential nanostructured formulation to treat gliomas and destroy their VM channels.

pH-Responsive Wormlike Micelles with Sequential Metastasis Targeting Inhibit Lung Metastasis of Breast Cancer

Cancer metastasis is the main cause for the high mortality in breast cancer patients. Herein, we first report succinobucol-loaded pH-responsive wormlike micelles (PWMs) with sequential targeting capability to inhibit lung metastasis of breast cancer. PWMs can in a first step be delivered specifically to the sites of metastases in the lungs and then enable the intracellular pH-stimulus responsive drug release in cancer cells to improve the anti-metastatic effect. PWMs are identified as nanofibrillar assemblies with a diameter of 19.9 ± 1.9 nm and a length within the 50-200 nm range, and exhibited pH-sensitive drug release behavior in response to acidic intracellular environments. Moreover, PWMs can obviously inhibit the migration and invasion abilities of metastatic 4T1 breast cancer cells, and reduce the expression of the metastasis-associated vascular cell adhesion molecule-1 (VCAM-1) at 400 ng mL(-1) of succinobucol. In particular, PWMs can induce a higher specific accumulation in lung and be specifically delivered to the sites of metastases in lung, thereby leading to an 86.6% inhibition on lung metastasis of breast cancer. Therefore, the use of sequentially targeting PWMs can become an encouraging strategy for specific targeting and effective treatment of cancer metastasis.

Advancement in integrin facilitated drug delivery

The research of integrin-targeted anticancer agents has recorded important advancements in ingenious design of delivery systems, based either on the prodrug approach, or on nanoparticle carriers, but for now, none of these has reached a clinical stage of development. Past work in this area has been extensively reviewed by us and others. Thus, the purpose and scope of the present review is to survey the advancement reported in the last 3years, with focus on innovative delivery systems that appear to afford openings for future developments. These systems exploit the labelling with conventional and novel integrin ligands for targeting the interface of cancer cells and of endothelial cells involved in cancer angiogenesis, with the proteins of the extracellular matrix, in the circulation, in tissues, and in tumour stroma, as the site of progression and metastatic evolution of the disease. Furthermore, these systems implement the expertise in the development of nanomedicines to the purpose of achieving preferential biodistribution and uptake in cancer tissues, internalisation in cancer cells, and release of the transported drugs at intracellular sites. The assessment of the value of controlling these factors, and their combination, for future developments requires support of biological testing in appropriate mechanistic models, but also imperatively demand confirmation in therapeutically relevant in vivo models for biodistribution, efficacy, and lack of off-target effects. Thus, among many studies, we have tried to point out the results supported by relevant in vivo studies, and we have emphasised in specific sections those addressing the medical needs of drug delivery to brain tumours, as well as the delivery of oligonucleotides modulating gene-dependent pathological mechanism. The latter could constitute the basis of a promising third branch in the therapeutic armamentarium against cancer, in addition to antibody-based agents and to cytotoxic agents.

Supramolecular biomaterials

Polymers, ceramics and metals have historically dominated the application of materials in medicine. Yet rationally designed materials that exploit specific, directional, tunable and reversible non-covalent interactions offer unprecedented advantages: they enable modular and generalizable platforms with tunable mechanical, chemical and biological properties. Indeed, the reversible nature of supramolecular interactions gives rise to biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signalling. In this Review, we discuss the properties of several supramolecular biomaterials, as well as their applications in drug delivery, tissue engineering, regenerative medicine and immunology. We envision that supramolecular biomaterials will contribute to the development of new therapies that combine highly functional materials with unmatched patient- and application-specific tailoring of both material and biological properties.

Enzymatic activatable self-assembled peptide nanowire for targeted therapy and fluorescence imaging of tumors

An activatable theranostic approach based on self-assembled peptide nanostructures with surface-displayed activatable cytotoxic agents for targeted cancer therapy was developed.

The HA-incorporated nanostructure of a peptide–drug amphiphile for targeted anticancer drug delivery

We demonstrate targeted anticancer drug delivery using transformable nanostructures of the complex of hyaluronic acid (HA) and KCK–CPT, a prodrug amphiphile composed of camptothecin (CPT) and tripeptide (KCK).

One-component nanomedicine

One-component nanomedicine (OCN) represents an emerging class of therapeutic nanostructures that contain only one type of chemical substance. This one-component feature allows for fine-tuning and optimization of the drug loading and physicochemical properties of nanomedicine in a precise manner through molecular engineering of the underlying building blocks. Using a precipitation procedure or effective molecular assembly strategies, molecularly crafted therapeutic agents (e.g. polymer-drug conjugates, small molecule prodrugs, or drug amphiphiles) could involuntarily aggregate, or self-assemble into nanoscale objects of well-defined sizes and shapes. Unlike traditional carrier-based nanomedicines that are inherently multicomponent systems, an OCN does not require the use of additional carriers and could itself possess desired physicochemical features for preferential accumulation at target sites. We review here recent progress in the molecular design, conjugation methods, and fabrication strategies of OCN, and analyze the opportunities that this emerging platform could open for the new and improved treatment of devastating diseases such as cancer.

Tumor-Specific Formation of Enzyme-Instructed Supramolecular Self-Assemblies as Cancer Theranostics

Despite the effort of developing various nanodelivery systems, most of them suffer from undesired high uptakes by the reticuloendothelial system, such as liver and spleen. Herein we develop an endogenous phosphatase-triggered coassembly strategy to form tumor-specific indocyanine green (ICG)-doped nanofibers (5) for cancer theranostics. Based on coordinated intermolecular interactions, 5 significantly altered near-infrared absorbance of ICG, which improves the critical photoacoustic and photothermal properties. The phosphatase-instructed coassembly process, as well as its theranostic capability, was successfully conducted at different levels ranging from in vitro, living cell, tissue mimic, to in vivo. Specifically, the tumor uptake of ICG was markedly increased to 15.05 ± 3.78%ID/g, which was 25-fold higher than that of free ICG (0.59 ± 0.24%ID/g) at 4 h after intravenous injection. The resulting ultrahigh T/N ratios (>15) clearly differentiated tumors from the surrounding normal tissue. Complete tumor elimination with high therapeutic accuracy has been successfully achieved upon laser irradiation (0.8 W/cm(2), 5 min) within 24-48 h postinjection. As the first example, in vivo formation of tumor-specific ICG-doped nanofiber for PTT theranostics owns the immense potential for clinical translation of personalized nanomedicine with targeted drug delivery as well as for cancer theranostics.

Strategies to stabilize cell penetrating peptides for in vivo applications

In the era of biomedicines and engineered carrier systems, cell penetrating peptides (CPPs) have been established as a promising tool for therapeutic application. Likewise, other therapeutic peptides, successful in vivo application of CPPs will strongly depend on peptide stability, the bottleneck for this type of biodegradable molecules. In this review, the authors describe the current knowledge of the in vivo degradation for known CPPs and the different strategies available to provide a higher resistance to metabolic degradation while preserving cell penetration efficiency. Peptide stability can be improved by different means, either modifying the structure to make it unrecognizable to proteases, or preventing access of proteolytic enzymes by applying conformation restriction or shielding strategies.

Acid-responsive PEGylated doxorubicin prodrug nanoparticles for neuropilin-1 receptor-mediated targeted drug delivery

Self-assembled prodrug nanoparticles have demonstrated great promise in cancer chemotherapy. In the present study, we developed a new kind of prodrug nanoparticles for targeted drug delivery. PEGylated doxorubicin conjugate with an acid-cleavable cis-aconityl spacer was prepared. Then it was functionalized with a tumor-penetrating peptide, Cys-Arg-Gly-Asp-Lys (CRGDK), providing the prodrug nanoparticles with the specific binding ability to neurophilin-1 receptor. In acid mediums, doxorubicin could be released from the prodrug nanoparticles with an accumulative release around 60% through the acid-triggered hydrolysis of cis-aconityl bond and nanoparticle disassembly. Whereas, drug release was slow under a neutral pH and the accumulative drug release was less than 16%. In the cell culture tests, our prodrug nanoparticles showed enhanced endocytosis and cytotoxicity in cancer cells including HepG2, MCF-7 and MDA-MB-231 cells, but lower cytotoxicity in human cardiomyocyte H2C9. In the animal experiments, the prodrug nanoparticles were intravenously injected into Balb/c nude mice bearing MDA-MB-231 tumors. Enhanced drug penetration and accumulation in tumors, accompanying with a rapid early tumor-binding behavior, was observed after intravenous injection of the peptide modified prodrug nanoparticles. These data suggests that the acid-sensitive and tumor-targeting PEGylated doxorubicin prodrug nanoparticle may be an efficient drug delivery system for cancer chemotherapy.

Intracellular Delivery of Molecular Cargo Using Cell-Penetrating Peptides and the Combination Strategies

Cell-penetrating peptides (CPPs) can cross cellular membranes in a non-toxic fashion, improving the intracellular delivery of various molecular cargos such as nanoparticles, small molecules and plasmid DNA. Because CPPs provide a safe, efficient, and non-invasive mode of transport for various cargos into cells, they have been developed as vectors for the delivery of genetic and biologic products in recent years. Most common CPPs are positively charged peptides. While delivering negatively charged molecules (e.g., nucleic acids) to target cells, the internalization efficiency of CPPs is reduced and inhibited because the cationic charges on the CPPs are neutralized through the covering of CPPs by cargos on the structure. Even under these circumstances, the CPPs can still be non-covalently complexed with the negatively charged molecules. To address this issue, combination strategies of CPPs with other typical carriers provide a promising and novel delivery system. This review summarizes the latest research work in using CPPs combined with molecular cargos including liposomes, polymers, cationic peptides, nanoparticles, adeno-associated virus (AAV) and calcium for the delivery of genetic products, especially for small interfering RNA (siRNA). This combination strategy remedies the reduced internalization efficiency caused by neutralization.

Shrapnel nanoparticles loading docetaxel inhibit metastasis and growth of breast cancer

Metastasis is one of the major obstacles for the successful therapy of breast cancer. To inhibit the metastasis and growth of breast cancer simultaneously, a new docetaxel (DTX) loaded shrapnel nano delivery system with the reduction- and enzyme-sensitive properties was designed and developed. Firstly, methoxy polyethylene glycol-peptide-vitamin E succinate (PPV), a matrix metalloproteinases (MMPs)-sensitive copolymer, was synthesized by conjugating mPEG and vitamin E succinate (VES) using an enzyme-sensitive peptide. Then, DTX loaded methoxy polyethylene glycol-s-s-vitamin E succinate (PSV) micelles (DPM) @ PPV-based liposomes (DPM@PL) were prepared by the incorporation of DPM into the PPV-based liposomes. DPM@PL showed a shrapnel structure with average particle size 113.3 ± 2.7 nm. The drug loading and encapsulation efficiency of DPM@PL were 1.93% and 99.02%, respectively. An obvious burst release (>90%) of drug was observed in the simulated tumor microenvironment with MMPs and reductive glutathione. The cellular uptake and cytotoxicity of DPM@PL in 4T1 cells were significantly enhanced after the pre-treatment of activated MMP-9. Compared with Taxotere(®), DPM@PL remarkably increased the distribution of DTX in lung and tumor of 4T1 tumor-bearing mice, and inhibited the in situ tumor growth and pulmonary metastasis formation effectively through the enhanced DTX-induced apoptosis and the reduced metastasis-promoting proteins expression. Compared with saline group, the inhibitory rates of DPM@PL against tumor volume and lung metastasis were about 81% and 92%, respectively, and it didn't produce the significant systemic toxicity. As a result, DPM@PL could be a promising nano delivery system for the successful therapy of breast cancer.

A supramolecular hydrogelator of curcumin

Here we report on the first supramolecular hydrogelator of curcumin and the evaluation of its inhibition capacity towards cancer cells and tumor growth.

Drug delivery with nanospherical supramolecular cell penetrating peptide-taxol conjugates containing a high drug loading

HYPOTHESIS

Supramolecular nanostructures via small molecule self-assembly hold great promise for controlled delivery of hydrophobic anticancer drugs. Particularly, taxol has recently been discovered to possess excellent self-assembly property, which may provide new opportunities to develop a new class of functional supramolecular nanomaterials for drug delivery application.

EXPERIMENTS

A cell penetrating peptide (CPP)-taxol conjugate (Taxol-CPP) was designed and synthesized. The self-assembling property of Taxol-CPP was investigated and the resultant nanomaterials were well characterized. Subsequently, the cytotoxicity of the Taxol-CPP after self-assembly against HepG2 cancer cells was evaluated.

FINDINGS

It is found that the Taxol-CPP possesses a high drug loading of 26.4% in each molecule, which is able to self-assemble into supramolecular nanospheres. By taking advantages of the self-assembly ability of taxol, Taxol-CPP supramolecular nanospheres with a mean size of around 130 nm can be obtained, composed of only the functional peptide (CPP) and the drug (taxol). Furthermore, we have demonstrated that the Taxol-CPP nanospheres do not compromise the taxol's potency, which can also be utilized as the carriers for co-delivery of another anticancer drug (doxorubicin).

When cationic cell-penetrating peptides meet hydrocarbons to enhance in-cell cargo delivery

Cell-penetrating peptides (CPPs) are short sequences often rich in cationic residues with the remarkable ability to cross cell membranes. In the past 20 years, CPPs have gained wide interest and have found numerous applications in the delivery of bioactive cargoes to the cytosol and even the nucleus of living cells. The covalent or non-covalent addition of hydrocarbon moieties to cationic CPPs alters the hydrophobicity/hydrophilicity balance in their sequence. Such perturbation dramatically influences their interaction with the cell membrane, might induce self-assembling properties and modifies their intracellular trafficking. In particular, the introduction of lipophilic moieties changes the subcellular distribution of CPPs and might result in a dramatically increase of the internalization yield of the co-transported cargoes. Herein, we offer an overview of different aspects of the recent findings concerning the properties of CPPs covalently or non-covalently associated to hydrocarbons. We will focus on the impact of the hydrocarbon moieties on the delivery of various cargoes, either covalently or non-covalently bound to the modified CPPs. We will also provide some key elements to rationalize the influence of the hydrocarbons moieties on the cellular uptake. Furthermore, the recent in vitro and in vivo successful applications of acylated CPPs will be summarized to provide a broad view of the versatility of these modified CPPs as small-molecules and oligonucleotides vectors.

Nanospheres of doxorubicin as cross-linkers for a supramolecular hydrogelation

In this study, we synthesized a peptide of Nap-GFFYGRGD, which could self-assemble into supramolecular nanofibers. The peptide itself could only form nanofibers but not hydrogels due to the relative weak inter-fiber interactions. The resulting nanofibers were then utilized as the vehicles for anticancer drug doxorubicin. It was found that the nanofibers of Nap-GFFYGRGD could not encapsulate doxorubicin, whereas the drug formed nanospheres, which were located at the surface of the nanofibers. Due to the electrostatic interactions between the negatively charged nanofibers and the positively charged doxorubicin nanospheres, the doxorubicin nanospheres were able to serve as a cross-linker to increase the inter-fiber interactions, leading to the formation of stable three-dimentional fiber networks and hydrogels. The resulting doxorubicin-peptide hydrogels were capable of releasing the drug in a sustained manner, which also showed comparable cytotoxicity as compared to free doxorubicin against a variety of cancer cell lines including HeLa and MCF-7 cancer cells. Therefore, this successful example using drug as the peptide nanofiber cross-linkers provided a new strategy for fabricating supramolecular hydrogelation for controlled delivery of anticancer drugs.

Self-assembling surfactant-like peptide A6K as potential delivery system for hydrophobic drugs

Background

Finding a suitable delivery system to improve the water solubility of hydrophobic drugs is a critical challenge in the development of effective formulations. In this study, we used A₆K, a self-assembling surfactant-like peptide, as a carrier to encapsulate and deliver hydrophobic pyrene.

Methods

Pyrene was mixed with A₆K by magnetic stirring to form a suspension. Confocal laser scanning microscopy, transmission electron microscopy, dynamic light scattering, atomic force microscopy, fluorescence, and cell uptake measurements were carried out to study the features and stability of the nanostructures, the state and content of pyrene, as well as the pyrene release profile.

Results

The suspension formed contained pyrene monomers trapped in the hydrophobic cores of the micellar nanofibers formed by A₆K, as well as nanosized pyrene crystals wrapped up and stabilized by the nanofibers. The two different encapsulation methods greatly increased the concentration of pyrene in the suspension, and formation of pyrene crystals wrapped up by A₆K nanofibers might be the major contributor to this effect. Furthermore, the suspension system could readily release and transfer pyrene into living cells.

Conclusion

A₆K could be further exploited as a promising delivery system for hydrophobic drugs.

Dual-tuning multidimensional superstructures based on a T-shaped molecule: vesicle, helix, membrane and nanofiber-constructed gel

Dual-tuning self-assembly of Fmoc–Gly (a T-shape molecule) supramolecular self assembly was firstly reported here.

Does lipophilicity affect the effectiveness of a transmembrane anion transporter? Insight from squaramido-functionalized bis(choloyl) conjugates

Lipophilicity was found to have little effect on the effectiveness of squaramido-functionalized bis(choloyl) conjugates.

Dual peptide conjugation strategy for improved cellular uptake and mitochondria targeting

Mitochondria are critical regulators of cellular function and survival. Delivery of therapeutic and diagnostic agents into mitochondria is a challenging task in modern pharmacology because the molecule to be delivered needs to first overcome the cell membrane barrier and then be able to actively target the intracellular organelle. Current strategy of conjugating either a cell penetrating peptide (CPP) or a subcellular targeting sequence to the molecule of interest only has limited success. We report here a dual peptide conjugation strategy to achieve effective delivery of a non-membrane-penetrating dye 5-carboxyfluorescein (5-FAM) into mitochondria through the incorporation of both a mitochondrial targeting sequence (MTS) and a CPP into one conjugated molecule. Notably, circular dichroism studies reveal that the combined use of α-helix and PPII-like secondary structures has an unexpected, synergistic contribution to the internalization of the conjugate. Our results suggest that although the use of positively charged MTS peptide allows for improved targeting of mitochondria, with MTS alone it showed poor cellular uptake. With further covalent linkage of the MTS-5-FAM conjugate to a CPP sequence (R8), the dually conjugated molecule was found to show both improved cellular uptake and effective mitochondria targeting. We believe these results offer important insight into the rational design of peptide conjugates for intracellular delivery.

Supramolecular nanofibers of triamcinolone acetonide for uveitis therapy

Supramolecular nanofibers of prodrugs hold advantages for drug release due to their high drug payload, sustained and constant drug release behavior, and stimuli responsiveness. In this study, we report on a supramolecular hydrogel mainly formed by a clinically used drug triamcinolone acetonide (TA). Such a hydrogel could only be prepared via an ester bond hydrolysis process from its prodrug of succinated triamcinolone acetonide (STA). The resulting hydrogel could constantly release TA in the in vitro release experiment. The TA hydrogel possessed an excellent transscleral penetration ability, as evaluated by the in vitro transscleral transport study. The developed TA hydrogel also exhibited a great ocular compatibility in rats, as indicated by the optical coherence tomography (OCT) images, HE observation, and glial fibrillary acidic protein (GFAP) and vimentin immuno-staining assays of the retinas. Our TA hydrogel showed a decreased efficacy to inhibit ocular inflammation in the rat's experiment autoimmune uveitis (EAU) model compared to the commercial TA suspension (Transton), but without causing complications such as high intraocular pressure and cataracts. These promising properties of the hydrogel indicated its great potential for the treatment of eye diseases.

Molecular dynamics study of surfactant-like peptide based nanostructures

Surfactant-like peptide (SLP) based nanostructures are investigated using all-atomistic molecular dynamics (MD) simulations. We report structure properties of nanostructures belonging to the ANK peptide group. In particular, the mathematical models for the two A3K membranes, A6K nanotube, and A9K nanorod were developed. Our MD simulation results are consistent with the experimental data, indicating that A3K membranes are stable in two different configurations: (1) SLPs are tilted relative to the normal membrane plane; (2) SLPs are interdigitated. The former configuration is energetically more stable. The cylindrical nanostructures feature a certain order of the A6K peptides. In turn, the A9K nanorod does not exhibit any long-range ordering. Both nanotube and nanorod structure contain large amounts of water inside. Consequently, these nanostructures behave similar to hydrogels. This property may be important in the context of biotechnology. Binding energy analysis-in terms of Coulomb and van der Waals contributions-unveils an increase as the peptide size increases. The electrostatic interaction constitutes 70-75% of the noncovalent attraction energy between SLPs. The nanotubular structures are notably stable, confirming that A6K peptides preferentially form nanotubes and A9K peptides preferentially form nanorods.

Amino acid sequence in constitutionally isomeric tetrapeptide amphiphiles dictates architecture of one-dimensional nanostructures

The switching of two adjacent amino acids can lead to differences in how proteins fold thus affecting their function. This effect has not been extensively explored in synthetic peptides in the context of supramolecular self-assembly. Toward this end, we report here the use of isomeric peptide amphiphiles as molecular building blocks to create one-dimensional (1D) nanostructures. We show that four peptide amphiphile isomers, with identical composition but a different sequence of their four amino acids, can form drastically different types of 1D nanostructures under the same conditions. We found that molecules with a peptide sequence of alternating hydrophobic and hydrophilic amino acids such as VEVE and EVEV self-assemble into flat nanostructures that can be either helical or twisted. On the other hand, nonalternating isomers such as VVEE and EEVV result in the formation of cylindrical nanofibers. Furthermore, we also found that when the glutamic acid is adjacent to the alkyl tail the supramolecular assemblies appear to be internally flexible compared to those with valine as the first amino acid. These results clearly demonstrate the significance of peptide side chain interactions in determining the architectures of supramolecular assemblies.

A survey on "Trojan Horse" peptides: opportunities, issues and controlled entry to "Troy"

Cell-penetrating peptides (CPPs), often vividly termed as the "Trojan Horse" peptides, have attracted considerable interest for the intracellular delivery of a wide range of cargoes, such as small molecules, peptides, proteins, nucleic acids, contrast agents, nanocarriers and so on. Some preclinical and clinical developments of CPP conjugates demonstrate their promise as therapeutic agents for drug discovery. There is increasing evidence to suggest that CPPs have the potential to cross several bio-barriers (e.g., blood-brain barriers, intestinal mucosa, nasal mucosa and skin barriers). Despite revolutionary process in many aspects, there are a lot of basic issues unclear for these entities, such as internalization mechanisms, translocation efficiency, translocation kinetics, metabolic degradation, toxicity, side effect, distribution and non-specificity. Among them, non-specificity remains a major drawback for the in vivo application of CPPs in the targeted delivery of cargoes. So far, diverse organelle-specific CPPs or controlled delivery strategies have emerged and improved their specificity. In this review, we will look at the opportunities of CPPs in clinical development, bio-barriers penetration and nanocarriers delivery. Then, a series of basic problems of CPPs will be discussed. Finally, this paper will highlight the use of various controlled strategies in the organelle-specific delivery and targeted delivery of CPPs. The purpose of this review will be to emphasize most influential advance in this field and present a fundamental understanding for challenges and utilizations of CPPs. This will accelerate their translation as efficient vectors from the in vitro setting into the clinic arena, and retrieve the entry art to "Troy".

Cell penetrating peptides: efficient vectors for delivery of nanoparticles, nanocarriers, therapeutic and diagnostic molecules

Efficient delivery of therapeutic and diagnostic molecules to the cells and tissues is a difficult challenge. The cellular membrane is very effective in its role as a selectively permeable barrier. While it is essential for cell survival and function, also presents a major barrier for intracellular delivery of cargo such as therapeutic and diagnostic agents. In recent years, cell-penetrating peptides (CPPs), that are relatively short cationic and/or amphipathic peptides, received great attention as efficient cellular delivery vectors due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargo such as plasmid DNA (pDNA), small interfering RNA (siRNAs), drugs, and nanoparticulate pharmaceutical carriers. This review discusses the various uptake mechanisms of these peptides. Furthermore, we discuss recent advances in the use of CPP for the efficient delivery of nanoparticles, nanocarriers, DNA, siRNA, and anticancer drugs to the cells. In addition, we have been highlighting new results for improving endosomal escape of CPP-cargo molecules. Finally, pH-responsive and activable CPPs for tumor-targeting therapy have been described.

Self-assembling amphiphilic peptides

The self-assembly of several classes of amphiphilic peptides is reviewed, and selected applications are discussed. We discuss recent work on the self-assembly of lipopeptides, surfactant-like peptides and amyloid peptides derived from the amyloid-β peptide. The influence of environmental variables such as pH and temperature on aggregate nanostructure is discussed. Enzyme-induced remodelling due to peptide cleavage and nanostructure control through photocleavage or photo-cross-linking are also considered. Lastly, selected applications of amphiphilic peptides in biomedicine and materials science are outlined.