Diethylene glycol functionalized self-assembling peptide nanofibers and their hydrophobic drug delivery potential

Peptides as carriers of active ingredients: A review

Bioactive compounds are highly valuable in the fields of food and medicine, but their application is limited due to easy deterioration after oral or skin administration. In recent years, the use of peptides as delivery systems for bioactive compounds has been intensively researched because of their special physicochemical characteristics. Peptides can be assembled using various preparation methods and can form several composite materials such as hydrogels, micelles, emulsions and particles. The composite material properties are determined by peptides, bioactive compounds and the construction methods employed. Herein, this paper provides a comprehensive review of the peptides used for active ingredients delivery, fabrication methods for creating delivery systems, structures, targeting characteristics, functional activities and mechanism of delivery systems, as well as their absorption and metabolism, which provided theoretical basis and reference for further research and development of functional composites.

Fabrication of Supramolecular Antibacterial Nanofibers with Membrane-Disruptive Mechanism

By studying the principles of self-assembly and combining the structural parameters required for the asymmetric distribution of antimicrobial peptides (AMPs), we newly designed and screened the high-activity and low-toxicity AMP F2I-LL. This peptide can form a supramolecular hydrogel with a nanofiber microstructure in a simulated physiological environment (phosphate buffered saline), which exhibits broad-spectrum antibacterial activity. Compared with monomeric peptides, the introduction of a self-assembly strategy not only improved the bactericidal titer but also enhanced the serum stability of AMPs. Mechanistic studies showed that the positive charge enriched on the surface of the nanofiber was conducive to its rapid binding to the negatively charged part of the outer membrane of bacteria and further entered the inner membrane, increasing its permeability and ultimately leading to cell membrane rupture and death. This work provides insights into the design of nanopeptides with broad-spectrum antibacterial activity and provides new results for the development of biomedicine.

Protein and peptide delivery to lungs by using advanced targeted drug delivery

The challenges and difficulties associated with conventional drug delivery systems have led to the emergence of novel, advanced targeted drug delivery systems. Therapeutic drug delivery of proteins and peptides to the lungs is complicated owing to the large size and polar characteristics of the latter. Nevertheless, the pulmonary route has attracted great interest today among formulation scientists, as it has evolved into one of the important targeted drug delivery platforms for the delivery of peptides, and related compounds effectively to the lungs, primarily for the management and treatment of chronic lung diseases. In this review, we have discussed and summarized the current scenario and recent developments in targeted delivery of proteins and peptide-based drugs to the lungs. Moreover, we have also highlighted the advantages of pulmonary drug delivery over conventional drug delivery approaches for peptide-based drugs, in terms of efficacy, retention time and other important pharmacokinetic parameters. The review also highlights the future perspectives and the impact of targeted drug delivery on peptide-based drugs in the coming decade.

Advances in self-assembled injectable hydrogels for cancer therapy

Non-specific toxicity of chemotherapeutics and evolution of malignant tumors against them are major challenges for existing cancer chemotherapeutic regimens. Engineering of nanomaterials has attempted to minimize the toxicity of anticancer drugs, but systemic delivery of these nanomaterials still imposes many hurdles in their clinical use like burst release of chemotherapeutics and toxicity and immunogenicity associated with excipients of nanomaterials. However, there has been a surge in the development of natural and synthetic nanomaterials to deliver anticancer agents to the diseased (tumor) site as it can minimize the systemic circulation of anticancer drugs and reduce the toxicity-related challenges. Therefore, localized drug delivery is considered as the most effective way to deliver therapeutics but is further challenged by poor biodegradability, high immunogenicity, poor drug entrapment efficacy and inability to maintain sustained release of anticancer agents at the tumor site. This review maps out recent advancements in engineering of low molecular weight hydrogels derived from amino acid, fatty acyl, steroidal lipid and drug conjugated amphiphilic scaffolds. We have summarized the efforts for the development of molecular hydrogels in terms of biocompatibility, therapeutic potential and challenges associated with existing molecular hydrogels for cancer therapy.

Self-assembling Peptides in Current Nanomedicine: Versatile Nanomaterials for Drug Delivery

BACKGROUND

The development of modern nanomedicine greatly depends on the involvement of novel materials as drug delivery system. In order to maximize the therapeutic effects of drugs and minimize their side effects, a number of natural or synthetic materials have been widely investigated for drug delivery. Among these materials, biomimetic self-assembling peptides (SAPs) have received more attention in recent years. Considering the rapidly growing number of SAPs designed for drug delivery, a summary of how SAPs-based drug delivery systems were designed, would be beneficial.

METHOD

We outlined research works on different SAPs that have been investigated as carriers for different drugs, focusing on the design of SAPs nanomaterials and how they were used for drug delivery in different strategies.

RESULTS

Based on the principle rules of chemical complementarity and structural compatibility, SAPs such as ionic self-complementary peptide, peptide amphiphile and surfactant-like peptide could be designed. Determined by the features of peptide materials and the drugs to be delivered, different strategies such as hydrogel embedding, hydrophobic interaction, electrostatic interaction, covalent conjugation or the combination of them could be employed to fabricate SAPs-drug complex, which could achieve slow release, targeted or environment-responsive delivery of drugs. Furthermore, some SAPs could also be combined with other types of materials for drug delivery, or even act as drug by themselves.

CONCLUSION

Various types of SAPs have been designed and used for drug delivery following various strategies, suggesting that SAPs as a category of versatile nanomaterials have promising potential in the field of nanomedicine.

cAMP-modulated biomimetic ionic nanochannels based on a smart polymer

Dynamic gating behaviour of ionic nanochannel is precisely manipulated by cyclic 3′,5′-adenosine monophosphate (cAMP) by taking advantage of reversible conformational transition of the smart polymer chains in response to cAMP specific adsorption, which provides a new idea for developing smart nanochannels regulated by crucial signal-biomolecules.

Developing an Inositol-Phosphate-Actuated Nanochannel System by Mimicking Biological Calcium Ion Channels

In eukaryotic cells, ion channels, which ubiquitously present as polypeptides or proteins, usually regulate the ion transport across biological membranes by conformational switching of the channel proteins in response to the binding of diverse signaling molecules (e.g., inositol phosphate, abbreviated to InsP). To mimic the gating behaviors of natural Ca²⁺ channels manipulated by InsPs, a smart poly[(N-isopropylacrylamide-co-4-(3-acryloylthioureido) benzoic acid)_0.2] (denoted as PNI-co-ATBA_0.2) was integrated onto a porous anodic alumina (PAA) membrane, building an InsP-actuated nanochannel system. Driven by the intensive hydrogen bonding complexation of ATBA monomer with InsP, the copolymer chains displayed a remarkable and reversible conformational transition from a contracted state to a swollen one, accompanied with significant changes in surface morphology, wettability, and viscoelasticity. Benefiting from these features, dynamic gating behaviors of the nanochannels located on the copolymer-modified PAA membrane could be precisely manipulated by InsPs, reflected as a satisfactory linear relationship between real-time variation in transmembrane ionic current and the InsP concentration over a wide range from 1 nmol L^-1 to 10 μmol L^-1, as well as a clear discrimination among InsP₂, InsP₃, and InsP₆. This study indicates the great potential of biomolecule-responsive polymers in the fabrication of biomimetic ion nanochannels and other nanoscale biodevices.

Smart Nanotransformers with Unique Enzyme-Inducible Structural Changes and Drug Release Properties

We previously reported a high aspect ratio peptide nanofiber that could be effectively delivered to tumors with minimal nonspecific uptake by other organs. The peptidic nature offers the design flexibility of smart formulation with unique responsiveness. Two new formulations that behave congruously as nanotransformers (NTFs) are reported herein. NTF1 and NTF2 could biomechanically remodel upon enzyme activation to generate a degradable and an aggregable effect, respectively, within the lysosomal compartment. These NTFs were further evaluated as carriers of mertansine (DM1), a microtubule inhibitor. DM1-loaded NTF1 could be degraded by cathepsin B (CathB) to release the same active metabolite, as previously described in the lysosomal degradation of antibody-DM1 conjugate. In contrast, CathB only partially digested DM1-loaded NTF2 and induced aggregate formation to become a storage reservoir with slow payload release property. The DM1-loaded NTF1 exhibited a comparable cytotoxicity to the free drug and was more effective than the NTF2 formulation in eradicating triple negative breast cancer. Our data suggested that biological transformers with distinct enzyme-induced structural changes and payload release profiles could be designed for the intracellular delivery of cytotoxic and imaging agents.

PEGylated substrates of NSP4 protease: A tool to study protease specificity

Herein we present the synthesis of a novel type of peptidomimetics composed of repeating diaminopropionic acid residues modified with structurally diverse heterobifunctional polyethylene glycol chains (abbreviated as DAPEG). Based on the developed compounds, a library of fluorogenic substrates was synthesized. Further library deconvolution towards human neutrophil serine protease 4 (NSP4) yielded highly sensitive and selective internally quenched peptidomimetic substrates. In silico analysis of the obtained peptidomimetics revealed the presence of an interaction network with distant subsites located on the enzyme surface.

Surface Stiffness--a Parameter for Sensing the Chirality of Saccharides

Surface stiffness is considered a key parameter for designing high-performance implantable materials and artificial extracellular matrices because of its substantial effects on cell behavior. How to transform biomolecule recognition events, particularly chiral recognition, into stiffness change on material surfaces is biologically essential but very challenging for chemists. Here, we report a chirality-triggered stiffness transition on a smart polymer film, which consists of flexible polyethylenimine (PEI) main chains grafted with dipeptide units capable of discriminating chiral monosaccharides. The polymer film became substantially softer after interacting with L-ribose and became more rigid after interacting with D-ribose (the basic building block of DNA and RNA). This chiral effect provides a new method for determining the enantiomeric purity of an L/D-ribose mixture and facilitates the chiral separation of deoxyribose racemates as well as the separation of diverse mono-, di-, and oligosaccharides. These are three puzzle problems in carbohydrate chemistry. Furthermore, taking advantage of the significant differences in the surface stiffness, the proliferation of fibroblast cells on the polymeric surfaces can also be regulated by chiral biomolecules.

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.

Functional nanomaterials can optimize the efficacy of vaccines

Nanoscale materials can improve the efficacy of vaccines. Herein we review latest developments that use nanomaterials for vaccines. By highlighting the relationships between the nanoscale physicochemical characteristics and working mechanisms of nanomaterials, this paper shows the current status of the developments where researchers employ functional nanomaterials as vector and/or immunoregulators for vaccines. It also provides us some clues for improving the design and application of nanomaterials to optimize the efficacy of vaccines.

Self-assembling peptide of D-amino acids boosts selectivity and antitumor efficacy of 10-hydroxycamptothecin

D-peptides, which consist of D-amino acids and can resist the hydrolysis catalyzed by endogenous peptidases, are one of the promising candidates for construction of peptide materials with enhanced biostability in vivo. In this paper, we report on a self-assembling supramolecular nanostructure of D-amino acid-based peptide Nap-G(D)F(D)F(D)YGRGD (D-fiber, (D)F meant D-phenylalanine, (D)Y meant D-tyrosine), which were used as carriers for 10-hydroxycamptothecin (HCPT). Transmission electron microscopy observations demonstrated the filamentous morphology of the HCPT-loaded peptides (d-fiber-HCPT). The better selectivity and antitumor activity of D-fiber-HCPT than L-fiber-HCPT were found in the in vitro and in vivo antitumor studies. These results highlight that this model D-fiber system holds great promise as vehicles of hydrophobic drugs for cancer therapy.

Immuno- and hemocompatibility of amino acid pairing peptides for potential use in anticancer drug delivery

Amino acid pairing peptide-based nanoparticles were recently introduced as promising carriers for hydrophobic anticancer drugs. The AC8 peptide, n-FEFQFNFK-c, is based on the amino acid pairing (AAP) design with 8 amino acids and hence the designated name AAP8. The nanoparticles (NPs) AAP8 have modified either on the C-terminal or on both terminal, by conjugation with diethylene glycol (DEG) . Here, the in vitro biocompatibilities of the NPs and their modified versions were compared and the potential of these NPs as carriers for the hydrophobic anticancer drug pirarubicin was determined as well as the peptide-drug co-assembly complexes. The toxicity of the NPs, DEGylated NPs, and blended mixtures with pirarubicin, was tested against the human adenocarcinoma lung cancer cell line, A549. The amino-end DEGylated NP, (NP-I), had superior biocompatibility over the non-modified NPs or double DEGylated NPs (NP-II). NP-I had very low hemolytic activity (1%) while NP and NP-II had marginal (8%) and acceptable (5%) hemolytic activity, respectively. All three types of NPs did not activate the complement system via the classical and alternative pathways nor did they activate the anaphylotoxin C3a. However, NP-II and its drug complex effectively activate the complement terminal attack complex. The lectin pathway was not activated by NP-I and NP-II, but was to a small extent by the non-modified NPs, with no lectin activation when complexed with drug. These results indicate NP-I is the most promising peptide for use as a drug delivery system, highlighting the importance of proper modification in peptides for drug delivery systems.

Self/co-assembling peptide, EAR8-II, as a potential carrier for a hydrophobic anticancer drug pirarubicin (THP)--characterization and in-vitro delivery

A short ionic-complementary peptide, EAR8-II, was employed to encapsulate the hydrophobic anticancer drug pirarubicin (THP). EAR8-II was designed to inherit advantages from two previously introduced peptides, AAP8 and EAK16-II, in their self/co-assembly. This peptide is short, simple, and inexpensive to synthesize, while possessing a low critical assembly concentration (CAC). The choice of alanine (A) residues in the peptide sequence provides moderate hydrophobic interactions, causing a minimal degree of aggregation, compared with other more hydrophobic residues. EAR8-II is an ionic-complementary peptide, similar to EAK16-II, can self/co-assemble with hydrophobic compounds such as THP, and forms a stable fibular nanostructure in aqueous solution. Physiochemical properties and cellular activities of the EAR8-II and THP complexes were evaluated and show dependency on the peptide-to-drug ratio. The complex at the peptide-to-drug mass ratio of 5:1 provides a stable solution, uniform nanostructure, and highly effective anticancer activity against various cancer cell lines. This work forms the basis for detailed studies on EAR8-II and THP formulations in vitro and in vivo, for future development of peptide-based delivery systems for hydrophobic anticancer drugs.