Antigen/Adjuvant-Displaying Enveloped Viral Replica as a Self-Adjuvanting Anti-Breast-Cancer Vaccine Candidate

We report a promising cancer vaccine candidate comprising antigen/adjuvant-displaying enveloped viral replica as a novel vaccine platform. The artificial viral capsid, which consists of a self-assembled β-annulus peptide conjugated with an HER2-derived antigenic CH401 peptide, was enveloped within a lipid bilayer containing the lipidic adjuvant α-GalCer. The use of an artificial viral capsid as a scaffold enabled precise control of its size to ∼100 nm, which is generally considered to be optimal for delivery to lymph nodes. The encapsulation of the anionically charged capsid by a cationic lipid bilayer dramatically improved its stability and converted its surface charge to cationic, enhancing its uptake by dendritic cells. The developed CH401/α-GalCer-displaying enveloped viral replica exhibited remarkable antibody-production activity. This study represents a pioneering example of precise vaccine design through bottom-up construction and opens new avenues for the development of effective vaccines.

Application of Peptides in Construction of Nonviral Vectors for Gene Delivery

Gene therapy, which aims to cure diseases by knocking out, editing, correcting or compensating abnormal genes, provides new strategies for the treatment of tumors, genetic diseases and other diseases that are closely related to human gene abnormalities. In order to deliver genes efficiently to abnormal sites in vivo to achieve therapeutic effects, a variety of gene vectors have been designed. Among them, peptide-based vectors show superior advantages because of their ease of design, perfect biocompatibility and safety. Rationally designed peptides can carry nucleic acids into cells to perform therapeutic effects by overcoming a series of biological barriers including cellular uptake, endosomal escape, nuclear entrance and so on. Moreover, peptides can also be incorporated into other delivery systems as functional segments. In this review, we referred to the biological barriers for gene delivery in vivo and discussed several kinds of peptide-based nonviral gene vectors developed for overcoming these barriers. These vectors can deliver different types of genetic materials into targeted cells/tissues individually or in combination by having specific structure-function relationships. Based on the general review of peptide-based gene delivery systems, the current challenges and future perspectives in development of peptidic nonviral vectors for clinical applications were also put forward, with the aim of providing guidance towards the rational design and development of such systems.

Anticancer Activity of Reconstituted Ribonuclease S-Decorated Artificial Viral Capsid

Ribonuclease S (RNase S) is an enzyme that exhibits anticancer activity by degrading RNAs within cancer cells; however, the cellular uptake efficiency is low due to its small molecular size. Here we generated RNase S‐decorated artificial viral capsids with a size of 70–170 nm by self‐assembly of the β‐annulus‐S‐peptide followed by reconstitution with S‐protein at neutral pH. The RNase S‐decorated artificial viral capsids are efficiently taken up by HepG2 cells and exhibit higher RNA degradation activity in cells compared with RNase S alone. Cell viability assays revealed that RNase S‐decorated capsids have high anticancer activity comparable to that of standard anticancer drugs.

Fluorescence Correlation Spectroscopy Analysis of Effect of Molecular Crowding on Self-Assembly of β-Annulus Peptide into Artificial Viral Capsid

Recent progress in the de novo design of self-assembling peptides has enabled the construction of peptide-based viral capsids. Previously, we demonstrated that 24-mer β-annulus peptides from tomato bushy stunt virus spontaneously self-assemble into an artificial viral capsid. Here we propose to use the artificial viral capsid through the self-assembly of β-annulus peptide as a simple model to analyze the effect of molecular crowding environment on the formation process of viral capsid. Artificial viral capsids formed by co-assembly of fluorescent-labelled and unmodified β-annulus peptides in dilute aqueous solutions and under molecular crowding conditions were analyzed using fluorescence correlation spectroscopy (FCS). The apparent particle size and the dissociation constant (K_d) of the assemblies decreased with increasing concentration of the molecular crowding agent, i.e., polyethylene glycol (PEG). This is the first successful in situ analysis of self-assembling process of artificial viral capsid under molecular crowding conditions.

A Photoresponsive Artificial Viral Capsid Self-Assembled from an Azobenzene-Containing β-Annulus Peptide

Photoinduced structural changes in peptides can dynamically control the formation and dissociation of supramolecular peptide materials. However, the existence of photoresponsive viral capsids in nature remains unknown. In this study, we constructed an artificial viral capsid possessing a photochromic azobenzene moiety on the peptide backbone. An azobenzene-containing β-annulus peptide derived from the tomato bushy stunt virus was prepared through solid-phase synthesis using Fmoc-3-[(3-aminomethyl)-phenylazo]phenylacetic acid. The azobenzene-containing β-annulus (β-Annulus-Azo) peptide showed a reversible trans/cis isomerization property. The β-annulus-azo peptide self-assembled at 25 μM into capsids with the diameters of 30–50 nm before UV irradiation (trans-form rich), whereas micrometer-sized aggregates were formed after UV irradiation (cis-form rich). The artificial viral capsid possessing azobenzene facilitated the encapsulation of fluorescent-labeled dextrans and their photoinduced release from the capsid.

Supramolecular Architectures of Nucleic Acid/Peptide Hybrids

Supramolecular architectures that are built artificially from biomolecules, such as nucleic acids or peptides, with structural hierarchical orders ranging from the molecular to nano-scales have attracted increased attention in molecular science research fields. The engineering of nanostructures with such biomolecule-based supramolecular architectures could offer an opportunity for the development of biocompatible supramolecular (nano)materials. In this review, we highlighted a variety of supramolecular architectures that were assembled from both nucleic acids and peptides through the non-covalent interactions between them or the covalently conjugated molecular hybrids between them.

Horseradish Peroxidase-Decorated Artificial Viral Capsid Constructed from β-Annulus Peptide via Interaction between His-Tag and Ni-NTA

Artificial construction of spherical protein assemblies has attracted considerable attention due to its potential use in nanocontainers, nanocarriers, and nanoreactors. In this work, we demonstrate a novel strategy to construct peptide nanocapsules (artificial viral capsids) decorated with enzymes via interactions between His-tag and Ni-NTA. A β-annulus peptide derived from the tomato bushy stunt virus was modified with Ni-NTA at the C-terminus, which is directed toward the exterior surface of the artificial viral capsid. The β-annulus peptide bearing Ni-NTA at the C-terminus self-assembled into capsids of about 50 nm in diameter. The Ni-NTA-displayed capsids were complexed with recombinant horseradish peroxidase (HRP) with a C-terminal His-tag which was expressed in Escherichia coli. The β-annulus peptide-HRP complex formed spherical assemblies whose sizes were 30–90 nm, with the ζ-potential revealing that the HRP was decorated on the outer surface of the capsid.

Encapsulation of mRNA into Artificial Viral Capsids via Hybridization of a β-Annulus-dT20 Conjugate and the Poly(A) Tail of mRNA

Messenger RNA (mRNA) drugs have attracted considerable attention as promising tools with many therapeutic applications. The efficient delivery of mRNA drugs using non-viral materials is currently being explored. We demonstrate a novel concept where mCherry mRNA bearing a poly(A) tail is encapsulated into capsids co-assembled from viral β-annulus peptides bearing a 20-mer oligothymine (dT20) at the N-terminus and unmodified peptides via hybridization of dT20 and poly(A). Dynamic light scattering measurements and transmission electron microscopy images of the mRNA-encapsulated capsids show the formation of spherical assemblies of approximately 50 nm. The encapsulated mRNA shows remarkable ribonuclease resistance. Further, modification by a cell-penetrating peptide (His16) on the capsid enables the intracellular expression of mCherry of encapsulated mRNA.

Enveloped artificial viral capsids self-assembled from anionic β-annulus peptide and cationic lipid bilayer

Anionic artificial viral capsids were self-assembled from β-annulus-EE peptide, then complexed with lipid-bilayer-containing cationic lipids via electrostatic interaction to form enveloped artificial viral capsids. The critical aggregation concentration of the enveloped artificial viral capsid was significantly lower than that of the uncomplexed artificial viral capsid, indicating that the lipid bilayer stabilised the capsid structure.

Construction of Ribonuclease-Decorated Artificial Virus-like Capsid by Peptide Self-assembly

Artificial virus-like capsids decorated with ribonuclease S (RNase S) on their exterior were constructed by the self-assembly of β-annulus-S-peptide and the interaction between S-peptide moiety and S-protein. The β-annulus-S-peptide was synthesized by native chemical ligation of β-annulus-SBz peptide with Cys-containing S-peptide that self-assembled into artificial virus-like capsids of approximately 47 nm in size. Reconstruction of RNase S on the artificial virus-like capsids afforded spherical assembly attached small spheres on the surface, which retained ribonuclease activity.

Artificial Viral Capsid Dressed Up with Human Serum Albumin

Capsid of tomato bushy stunt virus consists of an outer coat protein shell decorated on an internal skeleton comprising a β-annulus motif. We mimicked this capsid structure with our artificial viral capsid dressed up with protein. We synthesized the β-annulus peptide bearing a Cys at the C-terminal side and linked it with Cys34 of the human serum albumin (HSA) via a bismaleimide linker. The β-annulus peptide-HSA conjugate self-assembled into spherical structures of a 50-70 nm size range in the Tris-HCl buffer, with the ζ-potential of assemblies of such conjugate revealing that HSA proteins were displayed on the outer surface of the artificial viral capsid. Interestingly, the critical aggregation concentration (CAC) of the conjugate in the Tris-HCl buffer at 25 °C was approximately 0.01 μM, or 1/2500 lower than that of the unmodified β-annulus peptides, suggesting that the artificial viral capsids were stabilized via HSA modification. The present strategy of constructing protein nanocapsule by self-assembly of a β-annulus peptide-protein conjugate is simpler than that of previously reported protein nanocapsules.