RNA bacteriophage capsid-mediated drug delivery and epitope presentation

Artificial viruses: A nanotechnology based approach

OBJECTIVES

The main objective of this work was to review and summarise the detailed literature available on viral nanoparticle and the strategies utilised for their manufacture along with their applications as therapeutic agents.

DATA ACQUISITION

The reported literature related to development and application of virus nanoparticles have been collected from electronic data bases like ScienceDirect, google scholar, PubMed by using key words like "viral nanoparticles", "targeted drug delivery" and "vaccines" and related combinations.

RESULT

From the detailed literature survey, virus nanoparticles were identified as carriers for the targeted delivery. Due to the presence of nanostructures in virus nanoparticles, these protect the drugs from the degradation in the gastrointestinal tract and in case of the delivery of gene medicine, they carry the nucleic acids to the target/susceptible host cells. Thus, artificial viruses are utilised for targeted delivery to specific organ in biomedical and biotechnological areas.

CONCLUSION

Thus, virus nanoparticles can be considered as viable option as drug/gene carrier in various healthcare sectors especially drug delivery and vaccine and can be explored further in future for the development of better drug delivery techniques.

MS2 Virus-like Particles as a Versatile Peptide Presentation Platform: Insights into the Deterministic Abilities for Accommodating Heterologous Peptide Lengths

Virus-like particles (VLPs) are nanostructures with the potential to present heterologous peptides at high density, thereby triggering heightened immunogenicity. RNA bacteriophage MS2 VLPs are a compelling delivery platform among them. However, a notable hurdle arises from the immune response toward MS2 coat protein, swiftly eliminating subsequent vaccinations via the same vector. Although larger inserts effectively mask carrier epitopes, current research predominantly focuses on displaying short conserved peptides (<30 aa). A systematic evaluation regarding the deterministic ability of MS2 VLPs as a platform for presenting heterologous peptides remains a gap. In light of this, we employed the "single-chain dimer" paradigm to scrutinize the tolerance of MS2 VLPs for peptide/protein insertions. The results unveiled functional MS2 VLP assembly solely for inserts smaller than 91 aa. Particularly noteworthy is the largest insertion achieved on the MS2 VLPs to date: the RNA helicase A (RHA) dsRNA-binding domains (dsRBD1). Attempts to introduce additional linkers or empty coat subunits fail to augment the expression level or assembly of the MS2 VLPs displaying dsRBD1, affirming 91 aa as the upper threshold for exogenous protein presentation. By illuminating the precise confines of MS2 VLPs in accommodating distinct peptide lengths, our study informs the selection of appropriate peptide and protein dimensions. This revelation not only underscores the scope of MS2 VLPs but also establishes a pivotal reference point, facilitating the strategic manipulation of MS2 VLPs to design next-generation epitope/antibody-based therapeutics.

Surface decorated reporter-tagged chikungunya virus-like particles for clinical diagnostics and identification of virus entry inhibitors

The ever-evolving and versatile VLP technology is becoming an increasingly popular area of science. This study presents surface decorated reporter-tagged VLPs of CHIKV, an enveloped RNA virus of the genus alphavirus and its applications. Western blot, IFA and live-cell imaging confirm the expression of reporter-tagged CHIK-VLPs from transfected HEK293Ts. CryoEM micrographs reveal particle diameter as ∼67nm and 56-70 nm, respectively, for NLuc CHIK-VLPs and mCherry CHIK-VLPs. Our study demonstrates that by exploiting NLuc CHIK-VLPs as a detector probe, robust ratiometric luminescence signal in CHIKV-positive sera compared to healthy controls can be achieved swiftly. Moreover, the potential activity of the Suramin drug as a CHIKV entry inhibitor has been validated through the reporter-tagged CHIK-VLPs. The results reported in this study open new avenues in the eVLPs domain and offer potential for large-scale screening of clinical samples and antiviral agents targeting entry of CHIKV and other alphaviruses.

The diversity of protein-protein interaction interfaces within T=3 icosahedral viral capsids

Some non-enveloped virus capsids assemble from multiple copies of a single type of coat-protein (CP). The comparative energetics of the diverse CP-CP interfaces present in such capsids likely govern virus assembly-disassembly mechanisms. The T = 3 icosahedral capsids comprise 180 CP copies arranged about two-, three-, five- and six-fold axes of (quasi-)rotation symmetry. Structurally diverse CPs can assemble into T = 3 capsids. Specifically, the Leviviridae CPs are structurally distinct from the Bromoviridae, Tombusviridae and Tymoviridae CPs which fold into the classic “jelly-roll” fold. However, capsids from across the four families are known to disassemble into dimers. To understand whether the overall symmetry of the capsid or the structural details of the CP determine virus assembly-disassembly mechanisms, we analyze the different CP-CP interfaces that occur in the four virus families. Previous work studied protein homodimer interfaces using interface size (relative to the monomer) and hydrophobicity. Here, we analyze all CP-CP interfaces using these two parameters and find that the dimerization interface (present between two CPs congruent through a two-fold axis of rotation) has a larger relative size in the Leviviridae than in the other viruses. The relative sizes of the other Leviviridae interfaces and all the jelly-roll interfaces are similar. However, the dimerization interfaces across families have slightly higher hydrophobicity, potentially making them stronger than other interfaces. Finally, although the CP-monomers of the jelly-roll viruses are structurally similar, differences in their dimerization interfaces leads to varied dimer flexibility. Overall, differences in CP-structures may induce different modes of swelling and assembly-disassembly in the T = 3 viruses.

Protein Cages: From Fundamentals to Advanced Applications

Proteins that self-assemble into polyhedral shell-like structures are useful molecular containers both in nature and in the laboratory. Here we review efforts to repurpose diverse protein cages, including viral capsids, ferritins, bacterial microcompartments, and designed capsules, as vaccines, drug delivery vehicles, targeted imaging agents, nanoreactors, templates for controlled materials synthesis, building blocks for higher-order architectures, and more. A deep understanding of the principles underlying the construction, function, and evolution of natural systems has been key to tailoring selective cargo encapsulation and interactions with both biological systems and synthetic materials through protein engineering and directed evolution. The ability to adapt and design increasingly sophisticated capsid structures and functions stands to benefit the fields of catalysis, materials science, and medicine.

Transport of Molecular Cargo by Interaction with Virus-Like Particle RNA

Virus-like particles (VLPs) derived from Leviviridae virions contain substantial amounts of cellular and plasmid-derived RNA. This encapsidated polynucleotide serves as a reservoir for the efficient binding of the intercalating dye thiazole orange (TO). Polyethylene glycol (PEG) molecules and oligopeptides of varying length, end-functionalized with TO, were loaded into VLPs up to approximately 50 % of the mass of the capsid protein (hundreds to thousands of cargo molecules per particle, depending on size). The kinetics of TO-PEG binding included a significant entropic cost for the reptation of long chains through the capsid pores. Cargo molecules were released over periods of 20-120 hours following simple reversible first-order kinetics in most cases. These observations define a simple general method for the noncovalent packaging, and subsequent release, of functional molecules inside nucleoprotein nanocages in a manner independent of modifications to the capsid protein.

Bioengineering of virus-like particles as dynamic nanocarriers for in vivo delivery and targeting to solid tumours

Virus-like particles (VLPs) are known as self-assembled, non-replicative and non-infectious protein particles, which imitate the formation and structure of original wild type viruses, however, lack the viral genome and/or their fragments. The capacity of VLPs to encompass small molecules like nucleic acids and others has made them as novel vessels of nanocarriers for drug delivery applications. In addition, VLPs surface have the capacity to achieve variation of the surface display via several modification strategies including genetic modification, chemical modification, and non-covalent modification. Among the VLPs nanocarriers, Hepatitis B virus core (HBc) particles have been the most encouraging candidate. HBc particles are hollow nanoparticles in the range of 30-34 nm in diameter and 7 nm thick envelopes, consisting of 180 or 240 copies of identical polypeptide monomer. They also employ a distinctive position among the VLPs carriers due to the high-level synthesis, which serves as a strong protective capsid shell and efficient self-assembly properties. This review highlights on the bioengineering of HBc particles as dynamic nanocarriers for in vivo delivery and specific targeting to solid tumours.

Understanding the Folding Mediated Assembly of the Bacteriophage MS2 Coat Protein Dimers

The capsids of RNA viruses such as MS2 are great models for studying protein self-assembly because they are made almost entirely of multiple copies of a single coat protein (CP). Although CP is the minimal repeating unit of the capsid, previous studies have shown that CP exists as a homodimer (CP2) even in an acid-disassembled system, indicating that CP2 is an obligate dimer. Here, we investigate the molecular basis of this obligate dimerization using coarse-grained structure-based models and molecular dynamics simulations. We find that, unlike monomeric proteins of similar size, CP populates a single partially folded ensemble whose "foldedness" is sensitive to denaturing conditions. In contrast, CP2 folds similarly to single-domain proteins populating only the folded and the unfolded ensembles, separated by a prominent folding free energy barrier. Several intramonomer contacts form early, but the CP2 folding barrier is crossed only when the intermonomer contacts are made. A dissection of the structure of CP2 through mutant folding simulations shows that the folding barrier arises both from the topology of CP and the interface contacts of CP2. Together, our results show that CP2 is an obligate dimer because of kinetic stability, that is, dimerization induces a folding barrier and that makes it difficult for proteins in the dimer minimum to partially unfold and access the monomeric state without completely unfolding. We discuss the advantages of this obligate dimerization in the context of dimer design and virus stability.

Recent Progress on the Versatility of Virus-Like Particles

Virus-like particles (VLPs) are multimeric nanostructures composed of one or more structural proteins of a virus in the absence of genetic material. Having similar morphology to natural viruses but lacking any pathogenicity or infectivity, VLPs have gradually become a safe substitute for inactivated or attenuated vaccines. VLPs can achieve tissue-specific targeting and complete and effective cell penetration. With highly ordered epitope repeats, VLPs have excellent immunogenicity and can induce strong cellular and humoral immune responses. In addition, as a type of nanocarrier, VLPs can be used to display antigenic epitopes or deliver small molecules. VLPs have thus become powerful tools for vaccinology and biomedical research. This review highlights the versatility of VLPs in antigen presentation, drug delivery, and vaccine technology.

Plant/Bacterial Virus-Based Drug Discovery, Drug Delivery, and Therapeutics

Viruses have recently emerged as promising nanomaterials for biotechnological applications. One of the most important applications of viruses is phage display, which has already been employed to identify a broad range of potential therapeutic peptides and antibodies, as well as other biotechnologically relevant polypeptides (including protease inhibitors, minimizing proteins, and cell/organ targeting peptides). Additionally, their high stability, easily modifiable surface, and enormous diversity in shape and size, distinguish viruses from synthetic nanocarriers used for drug delivery. Indeed, several plant and bacterial viruses (e.g., phages) have been investigated and applied as drug carriers. The ability to remove the genetic material within the capsids of some plant viruses and phages produces empty viral-like particles that are replication-deficient and can be loaded with therapeutic agents. This review summarizes the current applications of plant viruses and phages in drug discovery and as drug delivery systems and includes a discussion of the present status of virus-based materials in clinical research, alongside the observed challenges and opportunities.

Biomimetic DNA Nanotubes: Nanoscale Channel Design and Applications

Biomacromolecular nanotubes play important physiological roles in transmembrane ion/molecule channeling, intracellular transport, and inter-cellular communications. While genetically encoded protein nanotubes are prevalent in vivo, the in vitro construction of biomimetic DNA nanotubes has attracted intense interest with the rise of structural DNA nanotechnology. The abiotic use of DNA assembly provides a powerful bottom-up approach for the rational construction of complex materials with arbitrary size and shape at the nanoscale. More specifically, a typical DNA nanotube can be assembled either with parallel-aligned DNA duplexes or by closing DNA tile lattices. These artificial DNA nanotubes can be tailored and site-specifically modified to realize biomimetic functions including ionic or molecular channeling, bioreactors, drug delivery, and biomolecular sensing. In this Minireview, we aim to summarize recent advances in design strategies, including the characterization and applications of biomimetic DNA nanotubes.

Engineering hepatitis B virus core particles for targeting HER2 receptors in vitro and in vivo

Hepatitis B Virus core (HBc) particles have been studied for their potential as drug delivery vehicles for cancer therapy. HBc particles are hollow nano-particles of 30–34 nm diameter and 7 nm thick envelopes, consisting of 180–240 units of 21 kDa core monomers. They have the capacity to assemble/dis-assemble in a controlled manner allowing encapsulation of various drugs and other biomolecules. Moreover, other functional motifs, i.e. receptors, receptor binding sequences, peptides and proteins can be expressed. This study focuses on the development of genetically modified HBc particles to specifically recognise and target human epidermal growth factor receptor-2 (HER2)-expressing cancer cells, in vitro and in vivo, for future cancer therapy. The non-specific binding capacity of wild type HBc particles was reduced by genetic deletion of the sequence encoding arginine-rich domains. A specific HER2-targeting was achieved by expressing the Z_HER2 affibodies on the HBc particles surface. In vitro studies showed specific uptake of Z_HER2-ΔHBc particles in HER2 expressing cancer cells. In vivo studies confirmed positive uptake of Z_HER2-ΔHBc particles in HER2-expressing tumours, compared to non-targeted ΔHBc particles in intraperitoneal tumour-bearing mice models. The present results highlight the potential of these nanocarriers in targeting HER2-positive metastatic abdominal cancer following intra-peritoneal administration.

Biodistribution of Antibody-MS2 Viral Capsid Conjugates in Breast Cancer Models

A variety of nanoscale scaffolds, including virus-like particles (VLPs), are being developed for biomedical applications; however, little information is available about their in vivo behavior. Targeted nanoparticles are particularly valuable as diagnostic and therapeutic carriers because they can increase the signal-to-background ratio of imaging agents, improve the efficacy of drugs, and reduce adverse effects by concentrating the therapeutic molecule in the region of interest. The genome-free capsid of bacteriophage MS2 has several features that make it well-suited for use in delivery applications, such as facile production and modification, the ability to display multiple copies of targeting ligands, and the capacity to deliver large payloads. Anti-EGFR antibodies were conjugated to MS2 capsids to construct nanoparticles targeted toward receptors overexpressed on breast cancer cells. The MS2 agents showed good stability in physiological conditions up to 2 days and specific binding to the targeted receptors in in vitro experiments. Capsids radiolabeled with ⁶⁴Cu isotopes were injected into mice possessing tumor xenografts, and both positron emission tomography-computed tomography (PET/CT) and scintillation counting of the organs ex vivo were used to determine the localization of the agents. The capsids exhibit surprisingly long circulation times (10-15% ID/g in blood at 24 h) and moderate tumor uptake (2-5% ID/g). However, the targeting antibodies did not lead to increased uptake in vivo despite in vitro enhancements, suggesting that extravasation is a limiting factor for delivery to tumors by these particles.

Design of virus-based nanomaterials for medicine, biotechnology, and energy

This review provides an overview of recent developments in "chemical virology." Viruses, as materials, provide unique nanoscale scaffolds that have relevance in chemical biology and nanotechnology, with diverse areas of applications. Some fundamental advantages of viruses, compared to synthetically programmed materials, include the highly precise spatial arrangement of their subunits into a diverse array of shapes and sizes and many available avenues for easy and reproducible modification. Here, we will first survey the broad distribution of viruses and various methods for producing virus-based nanoparticles, as well as engineering principles used to impart new functionalities. We will then examine the broad range of applications and implications of virus-based materials, focusing on the medical, biotechnology, and energy sectors. We anticipate that this field will continue to evolve and grow, with exciting new possibilities stemming from advancements in the rational design of virus-based nanomaterials.

Different applications of virus-like particles in biology and medicine: Vaccination and delivery systems

Virus-like particles (VLPs) mimic the whole construct of virus particles devoid of viral genome as used in subunit vaccine design. VLPs can elicit efficient protective immunity as direct immunogens compared to soluble antigens co-administered with adjuvants in several booster injections. Up to now, several prokaryotic and eukaryotic systems such as insect, yeast, plant, and E. coli were used to express recombinant proteins, especially for VLP production. Recent studies are also generating VLPs in plants using different transient expression vectors for edible vaccines. VLPs and viral particles have been applied for different functions such as gene therapy, vaccination, nanotechnology, and diagnostics. Herein, we describe VLP production in different systems as well as its applications in biology and medicine.

PhiXing-it, displaying foreign peptides on bacteriophage ΦX174

Although bacteriophage φX174 is easy to propagate and genetically tractable, it is use as a peptide display platform has not been explored. One region within the φX174 major spike protein G tolerated 13 of 16 assayed insertions, ranging from 10 to 75 amino acids. The recombinant proteins were functional and incorporated into infectious virions. In the folded protein, the peptides would be icosahedrally displayed within loops that extend from the protein׳s β-barrel core. The well-honed genetics of φX174 allowed permissive insertions to be quickly identified by the cellular phenotypes associated with cloned gene expression. The cloned genes were easily transferred from plasmids to phage genomes via recombination rescue. Direct ELISA validated several recombinant virions for epitope display. Some insertions conferred a temperature-sensitive (ts) protein folding defect, which was suppressed by global suppressors in protein G, located too far away from the insertion to directly alter peptide display.

Virus-Based Nanoparticles as Versatile Nanomachines

Nanoscale engineering is revolutionizing the way we prevent, detect, and treat diseases. Viruses have played a special role in these developments because they can function as prefabricated nanoscaffolds that have unique properties and are easily modified. The interiors of virus particles can encapsulate and protect sensitive compounds, while the exteriors can be altered to display large and small molecules in precisely defined arrays. These properties of viruses, along with their innate biocompatibility, have led to their development as actively targeted drug delivery systems that expand on and improve current pharmaceutical options. Viruses are naturally immunogenic, and antigens displayed on their surface have been used to create vaccines against pathogens and to break self-tolerance to initiate an immune response to dysfunctional proteins. Densely and specifically aligned imaging agents on viruses have allowed for high-resolution and noninvasive visualization tools to detect and treat diseases earlier than previously possible. These and future applications of viruses have created an exciting new field within the disciplines of both nanotechnology and medicine.

A novel delivery platform based on Bacteriophage MS2 virus-like particles

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Here we reviewed Bacteriophage MS2 virus-like particles, including introduction to their structure, their potential as a delivery platform, and their expected use in medicine and other fields.

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Bacteriophage MS2 virus-like particles represent the novel delivery platform.

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Bacteriophage MS2 virus-like particles possess promising application prospect.

Our objective here is to review the novel delivery platform based on Bacteriophage MS2 virus-like particles (VLPs), including introduction to their structure, their potential as a delivery platform, and their expected use in medicine and other fields. Bacteriophage MS2 VLPs are nanoparticles devoid of viral genetic material and can self-assemble from the coat protein into an icosahedral capsid. As a novel delivery platform, they possess numerous features that make them suitable and attractive for targeted delivery of RNAs or DNAs, epitope peptides, and drugs within the protein capsid. In short, as a novel delivery platform, MS2 VLPs are suitable for delivery of targeted agents and hold promise for use in diagnostics, vaccines, and therapeutic modalities.

Photonics and plasmonics go viral: self-assembly of hierarchical metamaterials

Sizing and shaping of mesoscale architectures with nanoscale features is a key opportunity to produce the next generation of higher-performing products and at the same time unveil completely new phenomena. This review article discusses recent advances in the design of novel photonic and plasmonic structures using a biology-inspired design. The proteinaceous capsids from viruses have long been discovered as platform technologies enabling unique applications in nanotechnology, materials, bioengineering, and medicine. In the context of materials applications, the highly organized structures formed by viral capsid proteins provide a 3D scaffold for the precise placement of plasmon and gain materials. Based on their highly symmetrical structures, virus-based nanoparticles have a high propensity to self-assemble into higher-order crystalline structures, yielding hierarchical hybrid materials. Recent advances in the field have led to the development of virus-based light harvesting systems, plasmonic structures for application in high-performance metamaterials, binary nanoparticle lattices, and liquid crystalline arrays for sensing or display technologies. There is still much that could be explored in this area, and we foresee that this is only the beginning of great technological advances in virus-based materials for plasmonics and photonics applications.

Synthetically Modified Viral Capsids as Versatile Carriers for Use in Antibody-Based Cell Targeting

The present study describes an efficient and reliable method for the preparation of MS2 viral capsids that are synthetically modified with antibodies using a rapid oxidative coupling strategy. The overall protocol delivers conjugates in high yields and recoveries, requires a minimal excess of antibody to achieve modification of more than 95% of capsids, and can be completed in a short period of time. Antibody-capsid conjugates targeting extracellular receptors on human breast cancer cell lines were prepared and characterized. Notably, conjugation to the capsid did not significantly perturb the binding of the antibodies, as indicated by binding affinities similar to those obtained for the parent antibodies. An array of conjugates was synthesized with various reporters on the interior surface of the capsids to be used in cell studies, including fluorescence-based flow cytometry, confocal microscopy, and mass cytometry. The results of these studies lay the foundation for further exploration of these constructs in the context of clinically relevant applications, including drug delivery and in vivo diagnostics.

A Simple RNA-DNA Scaffold Templates the Assembly of Monofunctional Virus-Like Particles

Using the components of a particularly well-studied plant virus, cowpea chlorotic mottle virus (CCMV), we demonstrate the synthesis of virus-like particles (VLPs) with one end of the packaged RNA extending out of the capsid and into the surrounding solution. This construct breaks the otherwise perfect symmetry of the capsid and provides a straightforward route for monofunctionalizing VLPs using the principles of DNA nanotechnology. It also allows physical manipulation of the packaged RNA, a previously inaccessible part of the viral architecture. Our synthesis does not involve covalent chemistry of any kind; rather, we trigger capsid assembly on a scaffold of viral RNA that is hybridized at one end to a complementary DNA strand. Interaction of CCMV capsid protein with this RNA-DNA template leads to selective packaging of the RNA portion into a well-formed capsid but leaves the hybridized portion poking out of the capsid through a small hole. We show that the nucleic acid protruding from the capsid is capable of binding free DNA strands and DNA-functionalized colloidal particles. Separately, we show that the RNA-DNA scaffold can be used to nucleate virus formation on a DNA-functionalized surface. We believe this self-assembly strategy can be adapted to viruses other than CCMV.

Methods for Preparation of MS2 Phage-Like Particles and Their Utilization as Process Control Viruses in RT-PCR and qRT-PCR Detection of RNA Viruses From Food Matrices and Clinical Specimens

RNA viruses are pathogenic agents of many serious infectious diseases affecting humans and animals. The detection of pathogenic RNA viruses is based on modern molecular methods, of which the most widely used methods are the reverse transcription polymerase chain reaction (RT-PCR) and the real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). All steps of RT-PCR and qRT-PCR should be strictly controlled to ensure the validity of obtained results. False-negative results may be caused not only by inhibition of RT or/and PCR steps but also by failure of the nucleic acid extraction step, particularly in the case of viral RNA extraction. The control of nucleic acid extraction generally involves the utilization of a non-pathogenic virus (process control virus) of similar structural properties to those of the target virus. Although in clinical samples the use of such process control virus is only recommended, in other kinds of settings such as food matrices its use is necessary. Currently, several different process control viruses are used for these purposes. Process control viruses can also be constructed artificially using technology for production of MS2 phage-like particles, which have many advantages in comparison with other used controls and are especially suited for controlling the detection and quantification of certain types of RNA viruses. The technology for production of MS2 phage-like particles is theoretically well established, uses the knowledge gained from the study of the familiar bacteriophage MS2 and utilizes many different approaches for the construction of the various process control viruses. Nevertheless, the practical use of MS2 phage-like particles in routine diagnostics is relatively uncommon. The current situation with regard to the use of MS2 phage-like particles as process control viruses in detection of RNA viruses and different methods of their construction, purification and use are summarized and discussed in this review.

Functionalization of protein-based nanocages for drug delivery applications

Traditional drug delivery strategies involve drugs which are not targeted towards the desired tissue. This can lead to undesired side effects, as normal cells are affected by the drugs as well. Therefore, new systems are now being developed which combine targeting functionalities with encapsulation of drug cargo. Protein nanocages are highly promising drug delivery platforms due to their perfectly defined structures, biocompatibility, biodegradability and low toxicity. A variety of protein nanocages have been modified and functionalized for these types of applications. In this review, we aim to give an overview of different types of modifications of protein-based nanocontainers for drug delivery applications.

Infusion of imaging and therapeutic molecules into the plant virus-based carrier cowpea mosaic virus: cargo-loading and delivery

This work is focused on the development of a plant virus-based carrier system for cargo delivery, specifically 30nm-sized cowpea mosaic virus (CPMV). Whereas previous reports described the engineering of CPMV through genetic or chemical modification, we report a non-covalent infusion technique that facilitates efficient cargo loading. Infusion and retention of 130-155 fluorescent dye molecules per CPMV using DAPI (4',6-diamidino-2-phenylindole dihydrochloride), propidium iodide (3,8-diamino-5-[3-(diethylmethylammonio)propyl]-6-phenylphenanthridinium diiodide), and acridine orange (3,6-bis(dimethylamino)acridinium chloride), as well as 140 copies of therapeutic payload proflavine (PF, acridine-3,6-diamine hydrochloride), is reported. Loading is achieved through interaction of the cargo with the CPMV's encapsidated RNA molecules. The loading mechanism is specific; empty RNA-free eCPMV nanoparticles could not be loaded. Cargo-infused CPMV nanoparticles remain chemically active, and surface lysine residues were covalent modified with dyes leading to the development of dual-functional CPMV carrier systems. We demonstrate cargo-delivery to a panel of cancer cells (cervical, breast, and colon): CPMV nanoparticles enter cells via the surface marker vimentin, the nanoparticles target the endolysosome, where the carrier is degraded and the cargo is released allowing imaging and/or cell killing. In conclusion, we demonstrate cargo-infusion and delivery to cells; the methods discussed provide a useful means for functionalization of CPMV toward its application as drug and/or contrast agent delivery vehicle.

Messenger RNA vaccine based on recombinant MS2 virus-like particles against prostate cancer

Prostate cancer (PCa) is the most diagnosed cancer in the western male population with high mortality. Recently, alternative approaches based on immunotherapy including mRNA vaccines for PCa have shown therapeutic promise. However, for mRNA vaccine, several disadvantages such as the instability of mRNA, the high cost of gold particles, the limited production scale for mRNA-transfected dendritic cells in vitro, limit their development. Herein, recombinant bacteriophage MS2 virus-like particles (VLPs), which based on the interaction of a 19-nucleotide RNA aptamer and the coat protein of bacteriophage MS2, successfully addressed these questions, in which target mRNA was packaged by MS2 capsid. MS2 VLP-based mRNA vaccines were easily prepared by recombinant protein technology, nontoxic and RNase-resistant. We show the packaged mRNA was translated into protein as early as 12 hr after phagocytosed by macrophages. Moreover, MS2 VLP-based mRNA vaccines induced strong humoral and cellular immune responses, especially antigen-specific cytotoxic T-lymphocyte (CTL) and balanced Th1/Th2 responses without upregulation of CD4(+) regulatory T cells, and protected C57BL/6 mice against PCa completely. As a therapeutic vaccine, MS2 VLP-based mRNA vaccines delayed tumor growth. Our results provide proof of concept on the efficacy and safety of MS2 VLP-based mRNA vaccine, which provides a new delivery approach for mRNA vaccine and implies important clinical value for the prevention and therapy of PCa.

Design rules for nanomedical engineering: from physical virology to the applications of virus-based materials in medicine

Physical virology seeks to define the principles of physics underlying viral infections, traditionally focusing on the fundamental processes governing virus assembly, maturation, and disassembly. A detailed understanding of virus structure and assembly has facilitated the development and analysis of virus-based materials for medical applications. In this Physical Virology review article, we discuss the recent developments in nanomedicine that help us to understand how physical properties affect the in vivo fate and clinical impact of (virus-based) nanoparticles. We summarize and discuss the design rules that need to be considered for the successful development and translation of virus-based nanomaterials from bench to bedside.

Nanoscale assemblies and their biomedical applications

Nanoscale assemblies are a unique class of materials, which can be synthesized from inorganic, polymeric or biological building blocks. The multitude of applications of this class of materials ranges from solar and electrical to uses in food, cosmetics and medicine. In this review, we initially highlight characteristic features of polymeric nanoscale assemblies as well as those built from biological units (lipids, nucleic acids and proteins). We give special consideration to protein nanoassemblies found in nature such as ferritin protein cages, bacterial microcompartments and vaults found in eukaryotic cells and designed protein nanoassemblies, such as peptide nanofibres and peptide nanotubes. Next, we focus on biomedical applications of these nanoscale assemblies, such as cell targeting, drug delivery, bioimaging and vaccine development. In the vaccine development section, we report in more detail the use of virus-like particles and self-assembling polypeptide nanoparticles as new vaccine delivery platforms.

A virus-like particle that elicits cross-reactive antibodies to the conserved stem of influenza virus hemagglutinin

The discovery of broadly neutralizing antibodies that recognize highly conserved epitopes in the membrane-proximal region of influenza virus hemagglutinin (HA) has revitalized efforts to develop a universal influenza virus vaccine. This effort will likely require novel immunogens that contain these epitopes but lack the variable and immunodominant epitopes located in the globular head of HA. As a first step toward developing such an immunogen, we investigated whether the 20-residue A-helix of the HA2 chain that forms the major component of the epitope of broadly neutralizing antibodies CR6261, F10, and others is sufficient by itself to elicit antibodies with similarly broad antiviral activity. Here, we report the multivalent display of the A-helix on icosahedral virus-like particles (VLPs) derived from the capsid of Flock House virus. Mice immunized with VLPs displaying 180 copies/particle of the A-helix produced antibodies that recognized trimeric HA and the elicited antibodies had binding characteristics similar to those of CR6261 and F10: they recognized multiple HA subtypes from group 1 but not from group 2. However, the anti-A-helix antibodies did not neutralize influenza virus. These results indicate that further engineering of the transplanted peptide is required and that display of additional regions of the epitope may be necessary to achieve protection.

Development of a microRNA delivery system based on bacteriophage MS2 virus-like particles

Recently, microRNA (miRNA)-mediated RNA interference has been developed as a useful tool in gene function analysis and gene therapy. A major obstacle in miRNA-mediated RNAi is cellular delivery, which requires an efficient and flexible delivery system. The self-assembly of the MS2 bacteriophage capsids has been used to develop virus-like particles (VLPs) for RNA and drug delivery. However, MS2 VLP-mediated miRNA delivery has not yet been reported. We therefore used an Escherichia coli expression system to produce the pre-miR 146a contained MS2 VLPs, and then conjugated these particles with HIV-1 Tat(47-57) peptide. The conjugated MS2 VLPs effectively transferred the packaged pre-miR146a RNA into various cells and tissues, with 0.92-14.76-fold higher expression of miR-146a in vitro and about two-fold higher expression in vivo, and subsequently suppressed its targeting gene. These findings suggest that MS2 VLPs can be used as a novel vehicle in miRNA delivery systems, and may have applications in gene therapy.

Quantifying reversibility in a phase-separating lattice gas: an analogy with self-assembly

We present dynamic measurements of a lattice gas during phase separation, which we use as an analogy for self-assembly of equilibrium ordered structures. We use two approaches to quantify the degree of reversibility of this process: First, we count events in which bonds are made and broken; second, we use correlation-response measurements and fluctuation-dissipation ratios to probe reversibility during different time intervals. We show how correlation and response functions can be related directly to microscopic (ir)reversibility and we discuss the time dependence and observable dependence of these measurements, including the role of fast and slow degrees of freedom during assembly.

Colorful virus-like particles: fluorescent protein packaging by the Qβ capsid

Qβ virus-like particles encapsulating multiple copies of fluorescent proteins were generated in high yields using a modular system enhanced by specific engineered RNA--protein interactions. The resulting particles were structurally indistinguishable from recombinant Qβ alone. The encapsidated proteins were nearly identical in photochemical properties to monomeric analogues, were more stable toward thermal degradation, and were protected from proteolytic cleavage. Residues on the outer capsid surface were chemically derivatized by acylation and azide--alkyne cycloaddition without affecting the fluorescence properties of the packaged proteins. A high-affinity carbohydrate-based ligand of the CD22 receptor was thereby attached, and specific cell labeling by the particles was successfully detected by flow cytometry and confocal laser microscopy.

Applications of viral nanoparticles in medicine

Several nanoparticle platforms are currently being developed for applications in medicine, including both synthetic materials and naturally occurring bionanomaterials such as viral nanoparticles (VNPs) and their genome-free counterparts, virus-like particles (VLPs). A broad range of genetic and chemical engineering methods have been established that allow VNP/VLP formulations to carry large payloads of imaging reagents or drugs. Furthermore, targeted VNPs and VLPs can be generated by including peptide ligands on the particle surface. In this article, we highlight state-of-the-art virus engineering principles and discuss recent advances that bring potential biomedical applications a step closer. Viral nanotechnology has now come of age and it will not be long before these formulations assume a prominent role in the clinic.

Transferrin-mediated targeting of bacteriophage HK97 nanoparticles into tumor cells

AIMS

Next-generation targeted nanodevices are currently under development for imaging and therapeutic applications. We engineered HK97 viral nanoparticles (VNPs) for tumor cell-specific targeting.

METHODS

A combination of genetic and chemical engineering methods were developed and applied to generate dual-labeled HK97 cysteine mutant particles displaying transferrin and fluorescent labels. The targeting properties of transferrin-conjugated VNPs were evaluated by in vitro experiments using different cancer cell lines.

RESULTS

We found that HK97-transferrin formulations were indeed targeted to cancer cells in vitro via the transferrin receptor. These studies highlight the utility and facilitate the further development of HK97-based VNPs.

Surface functionalization of virus-like particles by direct conjugation using azide-alkyne click chemistry

We present a cell-free protein synthesis (CFPS) platform and a one-step, direct conjugation scheme for producing virus-like particle (VLP) assemblies that display multiple ligands including proteins, nucleic acids, and other molecules. Using a global methionine replacement approach, we produced bacteriophage MS2 and bacteriophage Qβ VLPs with surface-exposed methionine analogues (azidohomoalanine and homopropargylglycine) containing azide and alkyne side chains. CFPS enabled the production of VLPs with yields of ~ 300 μg/mL and with 85% incorporation of methionine analogues without requiring a methionine auxotrophic production host. We then directly conjugated azide- and alkyne-containing proteins (including an antibody fragment and the granulocyte-macrophage colony stimulating factor, or GM-CSF), nucleic acids and poly(ethylene glycol) chains to the VLP surface using Cu(I) catalyzed click chemistry. The GM-CSF protein, after conjugation to VLPs, was shown to partially retain its ability to stimulate the proliferation of cells. Conjugation of GM-CSF to VLPs resulted in a 3-5-fold reduction in its bioactivity. The direct attachment scheme facilitated conjugation of three different ligands to the VLPs in a single step, and enabled control of the relative ratios and surface abundance of the attached species. This platform can be used for the production of novel VLP bioconjugates for use as drug delivery vehicles, diagnostics, and vaccines.

The art of engineering viral nanoparticles

Viral nanotechnology is an emerging and highly interdisciplinary field in which viral nanoparticles (VNPs) are applied in diverse areas such as electronics, energy and next-generation medical devices. VNPs have been developed as candidates for novel materials, and are often described as "programmable" because they can be modified and functionalized using a number of techniques. In this review, we discuss the concepts and methods that allow VNPs to be engineered, including (i) bioconjugation chemistries, (ii) encapsulation techniques, (iii) mineralization strategies, and (iv) film and hydrogel development. With all these techniques in hand, the potential applications of VNPs are limited only by the imagination.

Chemoselective modification of turnip yellow mosaic virus by Cu(I) catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction and its application in cell binding

Turnip yellow mosaic virus (TYMV) is an icosahedral plant virus with a diameter of 28-30 nm that can be isolated in gram quantities from turnip or Chinese cabbage inexpensively. In this study, TYMV combined with spatially addressable surface chemistries was selected as a prototype bionanoparticle for modulating patterns of cell adhesion, morphology, and proliferation. We exploited the chemical reactivity of TYMV using the mild conditions of Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction, the best example of "click" chemistry. Oligo-ethylene glycol (OEG) short chain, coumarintriazole, and RGD-containing peptide were grafted on the surface of TYMV via carbodiimide activation and CuAAC reaction. The bioconjugation to intact viral particles was confirmed by MS, TEM, FPLC, and SDS-PAGE with fluorescence visualization analysis. Therefore, this method is a generally useful means of incorporating various types of functionalities onto the TYMV surface. Further studies were done to learn the behavior of NIH-3T3 fibroblast cells on the modified or unmodified TYMV surfaces. OEG-modified TYMV surfaces retarded cell attachment and growth, while cell adhesion, spreading, and proliferation were dramatically enhanced on RGD-modified TYMV surfaces. Compared with RGD immobilized 3-aminopropyltriethoxysilane-coated glass surface, the cells are more ready to spread fully and proliferate on TYMV-RGD coated surface, which thus provides a more cell-friendly environment with nanometer-scale surface features. This illustrates the potential application of plant virus based materials in tissue engineering, drug delivery, and biosensing.

Viral nanoparticles and virus-like particles: platforms for contemporary vaccine design

Current vaccines that provide protection against infectious diseases have primarily relied on attenuated or inactivated pathogens. Virus‐like particles (VLPs), comprised of capsid proteins that can initiate an immune response but do not include the genetic material required for replication, promote immunogenicity and have been developed and approved as vaccines in some cases. In addition, many of these VLPs can be used as molecular platforms for genetic fusion or chemical attachment of heterologous antigenic epitopes. This approach has been shown to provide protective immunity against the foreign epitopes in many cases. A variety of VLPs and virus‐based nanoparticles are being developed for use as vaccines and epitope platforms. These particles have the potential to increase efficacy of current vaccines as well as treat diseases for which no effective vaccines are available. WIREs Nanomed Nanobiotechnol 2011 3 174–196 DOI: 10.1002/wnan.119

This article is categorized under: 1

Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease

Viral nanoparticles as platforms for next-generation therapeutics and imaging devices

Nanomaterials have been developed for potential applications in biomedicine, such as tissue-specific imaging and drug delivery. There are many different platforms under development, each with advantages and disadvantages, but viral nanoparticles (VNPs) are particularly attractive because they are naturally occurring nanomaterials, and as such they are both biocompatible and biodegradable. VNPs can be designed and engineered using both genetic and chemical protocols. The use of VNPs has evolved rapidly since their introduction 20 years ago, encompassing numerous chemistries and modification strategies that allow the functionalization of VNPs with imaging reagents, targeting ligands, and therapeutic molecules. This review discusses recent advances in the design of "smart" targeted VNPs for therapeutic and imaging applications.

FROM THE CLINICAL EDITOR

This review focuses on viral nanoparticles, which are considered attractive naturally occurring nanomaterials due to their inherent biocompatibility and biodegradability. These can be used as imaging reagents, targeting ligands and therapeutic molecules.

Tomatine adjuvantation of protective immunity to a major pre-erythrocytic vaccine candidate of malaria is mediated via CD8+ T cell release of IFN-gamma

The glycoalkaloid tomatine, derived from the wild tomato, can act as a powerful adjuvant to elicit an antigen-specific cell-mediated immune response to the circumsporozoite (CS) protein, a major pre-erythrocytic stage malaria vaccine candidate antigen. Using a defined MHC-class-I-restricted CS epitope in a Plasmodium berghei rodent model, antigen-specific cytotoxic T lymphocyte activity and IFN-γ secretion ex vivo were both significantly enhanced compared to responses detected from similarly stimulated splenocytes from naive and tomatine-saline-immunized mice. Further, through lymphocyte depletion it is demonstrated that antigen-specific IFN-γ is produced exclusively by the CD8⁺ T cell subset. We conclude that the processing of the P. berghei CS peptide as an exogenous antigen and its presentation via MHC class I molecules to CD8⁺ T cells leads to an immune response that is an in vitro correlate of protection against pre-erythrocytic malaria. Further characterization of tomatine as an adjuvant in malaria vaccine development is indicated.

Hydrazone ligation strategy to assemble multifunctional viral nanoparticles for cell imaging and tumor targeting

Multivalent nanoparticle platforms are attractive for biomedical applications because of their improved target specificity, sensitivity, and solubility. However, their controlled assembly remains a considerable challenge. An efficient hydrazone ligation chemistry was applied to the assembly of Cowpea mosaic virus (CPMV) nanoparticles with individually tunable levels of a VEGFR-1 ligand and a fluorescent PEGylated peptide. The nanoparticles recognized VEGFR-1 on endothelial cell lines and VEGFR1-expressing tumor xenografts in mice, validating targeted CPMV as a nanoparticle platform in vivo.

Virus-like particle vaccines and adjuvants: the HPV paradigm

Complex antigen structures currently represent the most-studied approach for prophylactic as well as therapeutic vaccines. Different types of complex vaccines, including virus-like particles and virosomes, have been developed depending on the nature of the viral pathogen they are trying to replicate (enveloped vs naked) or the modality to express antigenic epitopes (i.e., the binding of envelope protein on liposomic structures). The complex structure of these vaccines provides them with some adjuvanted properties, not uniformly present for all virus-like particle types. The further inclusion of specific adjuvants in vaccine preparations can modify the presentation modality of such particles to the immune system with a specific Th1 versus Th2 polarization efficacy. A paradigm of the relevance of these new adjuvants are the immunological results obtained with the inclusion of monophosphoryl lipid A adjuvant in the formulation of L1-based human papillomavirus-naked virus-like particles to reduce a Th1 cellular immunity impairment, peculiar for alum-derived adjuvants, along with the induction of highly enhanced humoral and memory B-cellular immunity.

Assembly of hybrid bacteriophage Qbeta virus-like particles

Bacteriophage Qbeta coat protein forms uniform virus-like particles when expressed recombinantly in a variety of organisms. We have inserted the IgG-binding Z domain at the carboxy terminus of the coat protein and coexpressed this chimeric subunit with native coat protein to create hybrid, IgG-binding virus-like particles. Extracellular osmolytes were found to have an effect on the efficiency of incorporation of fusion proteins into VLPs in Escherichia coli when a carbenicillin, but not a kanamycin, selection marker was used. The addition of sucrose to the growth medium decreased the incorporation efficiency; the osmoprotectant glycine betaine eliminated this effect. The decrease in efficiency was not observed when carbenicillin was omitted from the final expression culture. The addition of sodium chloride instead of sucrose gave rise to particles with a larger number of fusion proteins than the standard conditions. These results illustrate that cellular conditions should be taken into account even in apparently simple systems when natural or engineered protein nanoparticles are made.