Delivery of antisense oligonucleotides to leukemia cells by RNA bacteriophage capsids

Virus-like particles derived from bacteriophage MS2 as antigen scaffolds and RNA protective shells

The versatile potential of bacteriophage MS2-derived virus-like particles (VLPs) in medical biotechnology has been extensively studied during the last 30 years. Since the first reports showing that MS2 VLPs can be produced at high yield and relatively easily engineered, numerous applications have been proposed. Particular effort has been spent in developing MS2 VLPs as protective capsules and delivery platforms for diverse molecules, such as chemical compounds, proteins and nucleic acids. Among these, two are particularly noteworthy: as scaffolds displaying heterologous epitopes for vaccine development and as capsids for encapsulation of foreign RNA. In this review, we summarize the progress in developing MS2 VLPs for these two areas.

A simple and high efficiency purification of His-tagged turnip yellow mosaic virus-like particle (TYMV-VLP) by nickel ion affinity precipitation

Virus-like particles (VLPs) is one of the most favourable subjects of study, especially in the field of nanobiotechnology and vaccine development because they possess good immunogenicity and self-adjuvant properties. Conventionally, VLPs can be tagged and purified using affinity chromatography or density gradient ultracentrifugation which is costly and time-consuming. Turnip yellow mosaic virus (TYMV) is a plant virus, where expression of the viral coat protein (TYMVc) in Escherichia coli (E. coli) has been shown to form VLP. In this study, we report a non-chromatographic method for VLP purification using C-terminally His-tagged TYMVc (TYMVcHis₆) as a protein model. Firstly, the TYMVcHis₆ was cloned and expressed in E. coli. Upon clarification of cell lysate, nickel (II) chloride [NiCl₂; 15µM or equivalent to 0.0000194% (w/v)] was added to precipitate TYMVcHis₆. Following centrifugation, the pellet was resuspended in buffer containing 1mM EDTA to chelate Ni²⁺, which is then removed via dialysis. A total of 50% of TYMVcHis₆ was successfully recovered with purity above 0.90. Later, the purified TYMVcHis₆ was analysed with sucrose density ultracentrifugation, dynamic light scattering (DLS), and transmission electron microscopy (TEM) to confirm VLP formation, which is comparable to TYMVcHis₆ purified using the standard immobilized metal affinity chromatography (IMAC) column. As the current method omitted the need for IMAC column and beads while significantly reducing the time needed for column washing, nickel affinity precipitation represents a novel method for the purification of VLPs displaying poly-histidine tags (His-tags).

Virus-like particle-based nanocarriers as an emerging platform for drug delivery

New nanocarrier technologies are emerging, and they have great potential for improving drug delivery, targeting efficiency, and bioavailability. Virus-like particles (VLPs) are natural nanoparticles from animal and plant viruses and bacteriophages. Hence, VLPs present several great advantages, such as morphological uniformity, biocompatibility, reduced toxicity, and easy functionalisation. VLPs can deliver many active ingredients to the target tissue and have great potential as a nanocarrier to overcome the limitations associated with other nanoparticles. This review will focus primarily on the construction and applications of VLPs, particularly as a novel nanocarrier to deliver active ingredients. Herein, the main methods for the construction, purification, and characterisation of VLPs, as well as various VLP-based materials used in delivery systems are summarised. The biological distribution of VLPs in drug delivery, phagocyte-mediated clearance, and toxicity are also discussed.

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.

Programmable polymorphism of a virus-like particle

Virus-like particles (VLPs) have significant potential as artificial vaccines and drug delivery systems. The ability to control their size has wide ranging utility but achieving such controlled polymorphism using a single protein subunit is challenging as it requires altering VLP geometry. Here we achieve size control of MS2 bacteriophage VLPs via insertion of amino acid sequences in an external loop to shift morphology to significantly larger forms. The resulting VLP size and geometry is controlled by altering the length and type of the insert. Cryo electron microscopy structures of the new VLPs, in combination with a kinetic model of their assembly, show that the abundance of wild type (T = 3), T = 4, D3 and D5 symmetrical VLPs can be biased in this way. We propose a mechanism whereby the insert leads to a change in the dynamic behavior of the capsid protein dimer, affecting the interconversion between the symmetric and asymmetric conformers and thus determining VLP size and morphology.

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.

Bacteriophages as Solid Tumor Theragnostic Agents

Cancer, especially the solid tumor sub-set, poses considerable challenges to modern medicine owing to the unique physiological characteristics and substantial variations in each tumor's microenvironmental niche fingerprints. Though there are many treatment methods available to treat solid tumors, still a considerable loss of life happens, due to the limitation of treatment options and the outcomes of ineffective treatments. Cancer cells evolve with chemo- or radiation-treatment strategies and later show adaptive behavior, leading to failed treatment. These challenges demand tailored and individually apt personalized treatment methods. Bacteriophages (or phages) and phage-based theragnostic vectors are gaining attention in the field of modern cancer medicine, beyond their bactericidal ability. With the invention of the latest techniques to fine-tune phages, such as in the field of genetic engineering, synthetic assembly methods, phage display, and chemical modifications, noteworthy progress in phage vector research for safe cancer application has been realized, including use in pre-clinical studies. Herein, we discuss the distinct fingerprints of solid tumor physiology and the potential for bacteriophage vectors to exploit specific tumor features for improvised tumor theragnostic applications.

Genetically Encoding Ultrastable Virus-like Particles Encapsulating Functional DNA Nanostructures in Living Bacteria

DNA nanotechnology is leading the field of in vitro molecular-scale device engineering, accumulating to a dazzling array of applications. However, while DNA nanostructures' function is robust under in vitro settings, their implementation in real-world conditions requires overcoming their rapid degradation and subsequent loss of function. Viruses are sophisticated supramolecular assemblies, able to protect their nucleic acid content in inhospitable biological environments. Inspired by this natural ability, we engineered in vitro and in vivo technologies, enabling the encapsulation and protection of functional DNA nanostructures inside MS2 bacteriophage virus-like particles (VLPs). We demonstrate the ssDNA-VLPs nanocomposites' (NCs) abilities to encapsulate single-stranded-DNA (ssDNA) in a variety of sizes (200-1500 nucleotides (nt)), sequences, and structures while retaining their functionality. Moreover, by exposing these NCs to hostile biological conditions, such as human blood serum, we exhibit that the VLPs serve as an excellent protective shell. These engineered NCs pose critical properties that are yet unattainable by current fabrication methods.

Inhibitory Effect of Lentivirus-Mediated Gag-Caspase-8 on the Growth of HER-2-Overexpressing Primary Human Breast Cancer Cells

Background: Apoptosis plays an essential role in the development and treatment of tumors, and caspase-8 (CASP8) plays an important role in the enzyme cascade reaction that leads to apoptosis. Human epidermal growth factor receptor 2 (HER-2)-overexpressing breast cancer is highly aggressive and has a high recurrence rate and poor prognosis. This study investigated whether lentivirus-mediated Gag-CASP8 can effectively deliver activated CASP8 into primary human breast cancer cells overexpressing HER-2 to induce apoptosis and explore the underlying mechanism. Materials and Methods: HER-2-overexpressing primary human breast cancer cells were infected with lentivirus-like particles carrying Gag-CASP8. Results: After a 48-h infection of primary human breast cancer cells with HER-2 by lentivirus-mediated Gag-CASP8, significant differences were observed in the survival rate, migration ability, S-phase number of cells, apoptosis rate, and intracellular activated CASP8 and caspase-3 levels in tumor cells compared with those in the control group (p < 0.05). Conclusions: Lentivirus-mediated Gag-CASP8 can deliver activated CASP8 into HER-2-overexpressing primary human breast cancer cells and induce apoptosis by activating caspase-3, a downstream apoptotic executive molecule. By blocking the S-phase to inhibit cell proliferation and migration, lentivirus-mediated Gag-CASP8 provides a reference for tumor gene therapy.

Bacteriophage Capsid Modification by Genetic and Chemical Methods

Bacteriophages are viruses whose ubiquity in nature and remarkable specificity to their host bacteria enable an impressive and growing field of tunable biotechnologies in agriculture and public health. Bacteriophage capsids, which house and protect their nucleic acids, have been modified with a range of functionalities (e.g., fluorophores, nanoparticles, antigens, drugs) to suit their final application. Functional groups naturally present on bacteriophage capsids can be used for electrostatic adsorption or bioconjugation, but their impermanence and poor specificity can lead to inconsistencies in coverage and function. To overcome these limitations, researchers have explored both genetic and chemical modifications to enable strong, specific bonds between phage capsids and their target conjugates. Genetic modification methods involve introducing genes for alternative amino acids, peptides, or protein sequences into either the bacteriophage genomes or capsid genes on host plasmids to facilitate recombinant phage generation. Chemical modification methods rely on reacting functional groups present on the capsid with activated conjugates under the appropriate solution pH and salt conditions. This review surveys the current state-of-the-art in both genetic and chemical bacteriophage capsid modification methodologies, identifies major strengths and weaknesses of methods, and discusses areas of research needed to propel bacteriophage technology in development of biosensors, vaccines, therapeutics, and nanocarriers.

Recombinant turnip yellow mosaic virus coat protein as a potential nanocarrier

AIMS

To display a short peptide (GSRSHHHHHH) at the C-terminal end of turnip yellow mosaic virus coat protein (TYMVc) and to study its assembly into virus-like particles (TYMVcHis₆ VLPs).

METHODS AND RESULTS

In this study, recombinant TYMVcHis₆ expressed in Escherichia coli self-assembled into VLPs of approximately 30-32 nm. SDS-PAGE and Western blot analysis of protein fractions from the immobilized metal affinity chromatography (IMAC) showed that TYMVcHis₆ VLPs interacted strongly with nickel ligands in IMAC column, suggesting that the fusion peptide is protruding out from the surface of VLPs. These VLPs are highly stable over a wide pH range from 3·0 to 11·0 at different temperatures. At pH 11·0, specifically, the VLPs remained intact up to 75°C. Additionally, the disassembly and reassembly of TYMVcHis₆ VLPs were studied in vitro. Dynamic light scattering and transmission electron microscopy analysis revealed that TYMVcHis₆ VLPs were dissociated by 7 mol l^-1 urea and 2 mol l^-1 guanidine hydrochloride (GdnHCl) without impairing their reassembly property.

CONCLUSIONS

A 10-residue peptide was successfully displayed on the surface of TYMVcHis₆ VLPs. This chimera demonstrated high stability under extreme thermal conditions with varying pH and was able to dissociate and reassociate into VLPs by chemical denaturants.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first C-terminally modified TYMVc produced in E.  coli. The C-terminal tail which is exposed on the surface can be exploited as a useful site to display multiple copies of functional ligands. The ability of the chimeric VLPs to self-assemble after undergo chemical denaturation indicates its potential role to serve as a nanocarrier for use in targeted drug delivery.

The Role of Virus-Like Particles in Medical Biotechnology

Virus-like particles (VLPs) are protein-based, nanoscale, self-assembling, cage architectures, which have relevant applications in biomedicine. They can be used for the development of vaccines, imaging approaches, drug and gene therapy delivery systems, and in vitro diagnostic methods. Today, three relevant viruses are targeted using VLP-based recombinant vaccines. VLP-based drug delivery, nanoreactors for therapy, and imaging systems are approaches under development with promising outcomes. Several VLP-based vaccines are under clinical evaluation. Herein, an updated view on the VLP-based biomedical applications is provided; advanced methods for the production, functionalization, and drug loading of VLPs are described, and perspectives for the field are identified.

Plant Viruses and Bacteriophage-Based Reagents for Diagnosis and Therapy

Viral nanotechnology exploits the prefabricated nanostructures of viruses, which are already abundant in nature. With well-defined molecular architectures, viral nanocarriers offer unprecedented opportunities for precise structural and functional manipulation using genetic engineering and/or bio-orthogonal chemistries. In this manner, they can be loaded with diverse molecular payloads for targeted delivery. Mammalian viruses are already established in the clinic for gene therapy and immunotherapy, and inactivated viruses or virus-like particles have long been used as vaccines. More recently, plant viruses and bacteriophages have been developed as nanocarriers for diagnostic imaging, vaccine and drug delivery, and combined diagnosis/therapy (theranostics). The first wave of these novel virus-based tools has completed clinical development and is poised to make an impact on clinical practice.

SARS-CoV-2 vaccine research and development: Conventional vaccines and biomimetic nanotechnology strategies

The development of a massively producible vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus, is essential for stopping the current coronavirus disease (COVID-19) pandemic. A vaccine must stimulate effective antibody and T cell responses in vivo to induce long-term protection. Scientific researchers have been developing vaccine candidates for the severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) since the outbreaks of these diseases. The prevalence of new biotechnologies such as genetic engineering has shed light on the generation of vaccines against novel viruses. In this review, we present the status of the development of coronavirus vaccines, focusing particularly on the biomimetic nanoparticle technology platform, which is likely to have a major role in future developments of personalized medicine.

Activation of Alpha-7 Nicotinic Acetylcholine Receptors (α7nAchR) Promotes the Protective Autophagy in LPS-Induced Acute Lung Injury (ALI) In Vitro and In Vivo

The release of inflammatory cytokines and chemokines and autophagy has been reported to be involved in the pathogenic mechanism of acute lung injury (ALI). Reportedly, alpha-7 nicotinic acetylcholine receptors (α7nAchR) might play a protective role in LPS-induced ALI. In the current research, we established LPS-induced ALI model in mice and α7nAchR agonist PNU-282987 improved LPS-induced injury. In MH-S cells, LPS stimulation inhibited, whereas α7nAchR agonist PNU-282987 enhanced the autophagy. α7nAchR agonist PNU-282987 protected MH-S cells from LPS-induced inflammation by reducing the concentrations of IL-6, TNF-α, and IL-1β. Finally, LPS stimulation dramatically inhibited MH-S cell viability but enhanced cell apoptosis, whereas PNU-282987 treatment exerted opposite effects; α7nAchR might regulate the cellular homeostasis via affecting the crosstalk between the autophagy and apoptosis in MH-S cells; in other words, α7nAChR agonist enhances MH-S cell autophagy and inhibits MH-S cell apoptosis. In conclusion, α7nAchR promote the protective autophagy in LPS-induced ALI model in mice and MH-S cells. The application of α7nAchR agonist is considered a potent target for LPS-induced ALI, which needs further clinical investigation.

Bacteriophage MS2 displays unreported capsid variability assembling T = 4 and mixed capsids

Bacteriophage MS2 is a positive-sense, single-stranded RNA virus encapsulated in an asymmetric T = 3 pseudo-icosahedral capsid. It infects Escherichia coli through the F-pilus, in which it binds through a maturation protein incorporated into its capsid. Cryogenic electron microscopy has previously shown that its genome is highly ordered within virions, and that it regulates the assembly process of the capsid. In this study, we have assembled recombinant MS2 capsids with non-genomic RNA containing the capsid incorporation sequence, and investigated the structures formed, revealing that T = 3, T = 4 and mixed capsids between these two triangulation numbers are generated, and resolving structures of T = 3 and T = 4 capsids to 4 Å and 6 Å respectively. We conclude that the basic MS2 capsid can form a mix of T = 3 and T = 4 structures, supporting a role for the ordered genome in favouring the formation of functional T = 3 virions.

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.

In Vitro Assembly of Virus-Derived Designer Shells Around Inorganic Nanoparticles

Nanoparticle-templated assembly of virus shells provides a promising approach to the production of hybrid nanomaterials and a potential avenue toward new mechanistic insights in virus phenomena originating in many-body effects, which cannot be understood from examining the properties of molecular subunits alone. This approach complements the successful molecular biology perspective traditionally used in virology, and promises a deeper understanding of viruses and virus-like particles through an expanded methodological toolbox. Here we present protocols for forming a virus coat protein shell around functionalized inorganic nanoparticles.

Functional RNAs: combined assembly and packaging in VLPs

We describe here a one pot RNA production, packaging and delivery system based on bacteriophage Qβ. We demonstrate a method for production of a novel RNAi scaffold, packaged within Qβ virus-like particles (VLPs). The RNAi scaffold is a general utility chimera that contains a functional RNA duplex with paired silencing and carrier sequences stabilized by a miR-30 stem-loop. The Qβ hairpin on the 5΄ end confers affinity for the Qβ coat protein (CP). Silencing sequences can include mature miRNAs and siRNAs, and can target essentially any desired mRNA. The VLP-RNAi assembles upon co-expression of CP and the RNAi scaffold in E. coli. The annealing of the scaffold to form functional RNAs is intramolecular and is therefore robust and concentration independent. We demonstrate dose- and time-dependent inhibition of GFP expression in human cells with VLP-RNAi. In addition, we target the 3΄UTR of oncogenic Ras mRNA and suppress Pan-Ras expression, which attenuates cell proliferation and promotes mortality of brain tumor cells. This combination of RNAi scaffold design with Qβ VLP packaging is demonstrated to be target-specific and efficient.

Nanocaged platforms: modification, drug delivery and nanotoxicity. Opening synthetic cages to release the tiger

Nanocages (NCs) have emerged as a new class of drug-carriers, with a wide range of possibilities in multi-modality medical treatments and theranostics. Nanocages can overcome such limitations as high toxicity caused by anti-cancer chemotherapy or by the nanocarrier itself, due to their unique characteristics. These properties consist of: (1) a high loading-capacity (spacious interior); (2) a porous structure (analogous to openings between the bars of the cage); (3) enabling smart release (a key to unlock the cage); and (4) a low likelihood of unfavorable immune responses (the outside of the cage is safe). In this review, we cover different classes of NC structures such as virus-like particles (VLPs), protein NCs, DNA NCs, supramolecular nanosystems, hybrid metal-organic NCs, gold NCs, carbon-based NCs and silica NCs. Moreover, NC-assisted drug delivery including modification methods, drug immobilization, active targeting, and stimulus-responsive release mechanisms are discussed, highlighting the advantages, disadvantages and challenges. Finally, translation of NCs into clinical applications, and an up-to-date assessment of the nanotoxicology considerations of NCs are presented.

Bacteriophages and phage-inspired nanocarriers for targeted delivery of therapeutic cargos

The main goal of drug delivery systems is to target therapeutic cargoes to desired cells and to ensure their efficient uptake. Recently a number of studies have focused on designing bio-inspired nanocarriers, such as bacteriophages, and synthetic carriers based on the bacteriophage structure. Bacteriophages are viruses that specifically recognize their bacterial hosts. They can replicate only inside their host cell and can act as natural gene carriers. Each type of phage has a particular shape, a different capacity for loading cargo, a specific production time, and their own mechanisms of supramolecular assembly, that have enabled them to act as tunable carriers. New phage-based technologies have led to the construction of different peptide libraries, and recognition abilities provided by novel targeting ligands. Phage hybridization with non-organic compounds introduces new properties to phages and could be a suitable strategy for construction of bio-inorganic carriers. In this review we try to cover the major phage species that have been used in drug and gene delivery systems, and the biological application of phages as novel targeting ligands and targeted therapeutics.

Bioengineered protein-based nanocage for drug delivery

Nature, in its wonders, presents and assembles the most intricate and delicate protein structures and this remarkable phenomenon occurs in all kingdom and phyla of life. Of these proteins, cage-like multimeric proteins provide spatial control to biological processes and also compartmentalizes compounds that may be toxic or unstable and avoids their contact with the environment. Protein-based nanocages are of particular interest because of their potential applicability as drug delivery carriers and their perfect and complex symmetry and ideal physical properties, which have stimulated researchers to engineer, modify or mimic these qualities. This article reviews various existing types of protein-based nanocages that are used for therapeutic purposes, and outlines their drug-loading mechanisms and bioengineering strategies via genetic and chemical functionalization. Through a critical evaluation of recent advances in protein nanocage-based drug delivery in vitro and in vivo, an outlook for de novo and in silico nanocage design, and also protein-based nanocage preclinical and future clinical applications will be presented.

Biomedical and Catalytic Opportunities of Virus-Like Particles in Nanotechnology

Within biology, molecules are arranged in hierarchical structures that coordinate and control the many processes that allow for complex organisms to exist. Proteins and other functional macromolecules are often studied outside their natural nanostructural context because it remains difficult to create controlled arrangements of proteins at this size scale. Viruses are elegantly simple nanosystems that exist at the interface of living organisms and nonliving biological machines. Studied and viewed primarily as pathogens to be combatted, viruses have emerged as models of structural efficiency at the nanoscale and have spurred the development of biomimetic nanoparticle systems. Virus-like particles (VLPs) are noninfectious protein cages derived from viruses or other cage-forming systems. VLPs provide incredibly regular scaffolds for building at the nanoscale. Composed of self-assembling protein subunits, VLPs provide both a model for studying materials' assembly at the nanoscale and useful building blocks for materials design. The robustness and degree of understanding of many VLP structures allow for the ready use of these systems as versatile nanoparticle platforms for the conjugation of active molecules or as scaffolds for the structural organization of chemical processes. Lastly the prevalence of viruses in all domains of life has led to unique activities of VLPs in biological systems most notably the immune system. Here we discuss recent efforts to apply VLPs in a wide variety of applications with the aim of highlighting how the common structural elements of VLPs have led to their emergence as paradigms for the understanding and design of biological nanomaterials.

The application of virus-like particles as vaccines and biological vehicles

Virus-like particles (VLPs) can be spontaneously self-assembled by viral structural proteins under appropriate conditions in vitro while excluding the genetic material and potential replication probability. In addition, VLPs possess several features including can be rapidly produced in large quantities through existing expression systems, highly resembling native viruses in terms of conformation and appearance, and displaying repeated cluster of epitopes. Their capsids can be modified via genetic insertion or chemical conjugation which facilitating the multivalent display of a homologous or heterogeneous epitope antigen. Therefore, VLPs are considered as a safe and effective candidate of prophylactic and therapeutic vaccines. VLPs, with a diameter of approximately 20 to 150 nm, also have the characteristics of nanometer materials, such as large surface area, surface-accessible amino acids with reactive moieties (e.g., lysine and glutamic acid residues), inerratic spatial structure, and good biocompatibility. Therefore, assembled VLPs have great potential as a delivery system for specifically carrying a variety of materials. This review summarized recent researches on VLP development as vaccines and biological vehicles, which demonstrated the advantages and potential of VLPs in disease control and prevention and diagnosis. Then, the prospect of VLP biology application in the future is discussed as well.

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.

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.

A novel method to produce armored double-stranded DNA by encapsulation of MS2 viral capsids

With the rapid development of molecular diagnostic techniques, there is a growing need for quality controls and standards with favorable properties to monitor the entire detection process. In this study, we describe a novel method to produce armored hepatitis B virus (HBV) and human papillomavirus (HPV) DNA for use in nucleic acid tests, which was confirmed to be stable, homogeneous, noninfectious, nuclease resistant, and safe for shipping. We demonstrated that MS2 bacteriophage could successfully package double-stranded DNA of 1.3-, 3-, 3.5-, and 6.5-kb length into viral capsids with high reassembly efficiency. This is the first application of RNA bacteriophage MS2 as a platform to encapsulate double-stranded DNA, forming virus-like particles (VLPs) which were indistinguishable from native MS2 capsids in size and morphology. Moreover, by analyzing the interaction mechanism of pac site and the MS2 coat protein (CP), we found that in addition to the recognized initiation signal TR-RNA, TR-DNA can also trigger spontaneous reassembly of CP dimers, providing a more convenient and feasible method of assembly. In conclusion, this straightforward and reliable manufacturing approach makes armored DNA an ideal control and standard for use in clinical laboratory tests and diagnostics, possessing prospects for broad application, especially providing a new platform for the production of quality controls for DNA viruses.

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.

A microfluidic method to synthesize transferrin-lipid nanoparticles loaded with siRNA LOR-1284 for therapy of acute myeloid leukemia

The siRNA LOR-1284 targets the R2 subunit of ribonucleotide reductase (RRM2) and has shown promise in cancer therapy. In this study, transferrin (Tf) conjugated lipid nanoparticles (Tf-NP-LOR-1284) were synthesized by microfluidic hydrodynamic focusing (MHF) and evaluated for the targeted delivery of LOR-1284 siRNA into acute myeloid leukemia (AML) cells. The in vitro study showed that Tf-NP-LOR-1284 can protect LOR-1284 from serum nuclease degradation. Selective uptake of Tf-NP-LOR-1284 was observed in MV4-11 cells. In addition, qRT-PCR and Western blot results revealed that Tf-NP-LOR-1284 was more effective than the free LOR-1284 in reducing the R2 mRNA and protein levels. The Tf-NP-LOR-1284 showed prolonged circulation time and increased AUC after i.v. administration relative to the free LOR-1284. Furthermore, Tf-NP-LOR-1284 facilitated increased accumulation at the tumor site along with the decreased R2 mRNA and protein expression in a murine xenograft model. These results suggest that Tf-conjugated NPs prepared by MHF provide a suitable platform for efficient and specific therapeutic delivery of LOR-1284 into AML cells.

Caged protein nanoparticles for drug delivery

Caged protein nanoparticles possess many desirable features for drug delivery, such as ideal sizes for endocytosis, non-toxic biodegradability, and the ability to functionalize at three distinct interfaces (external, internal, and inter-subunit) using the tools of protein engineering. Researchers have harnessed these attributes by covalently and non-covalently loading therapeutic molecules through mechanisms that facilitate release within specific microenvironments. Effective delivery depends on several factors, including specific targeting, cell uptake, release kinetics, and systemic clearance. The innate ability of the immune system to recognize and respond to proteins has recently been exploited to deliver therapeutic compounds with these platforms for immunomodulation. The diversity of drugs, loading/release mechanisms, therapeutic targets, and therapeutic efficacy are discussed in this review.

Photosensitive fluorescent dye contributes to phototoxicity and inflammatory responses of dye-doped silica NPs in cells and mice

Dye-doped fluorescent silica nanoparticles provide highly intense and photostable fluorescence signals. However, some dopant dye molecules are photosensitive. A widely-used photosensitive fluorescent dopant, RuBpy, was chosen to systematically investigate the phototoxicity of the dye-doped silica nanoparticles (NPs). We investigated cell viability, DNA damage, and Reactive Oxygen Species (ROS) levels in alveolar macrophages using the dye-doped NPs with or without irradiation. Our results showed that the RuBpy-doped silica NPs could induce significant amount of ROS, DNA damage, apoptosis and impaired proliferation in MH-S cells. In vivo studies in mice showed that RuBpy-doped silica NPs induced significant inflammatory cytokine production and lowered expression in signaling proteins such as ERK1/2 and NF-κB as well as increased lung injury determined by myeloperoxidase and lipid peroxidation. Strikingly, we also found that both RuBpy alone and NPs induced systemic signaling activation in the kidney compared to the liver and lung where showed highly selective signaling patterns, which is more pronounced than RuBpy-doped silica NPs. Moreover, we discovered a critical biomarker (e.g., HMGB1) for silica NPs-induced stress and toxicity and demonstrated differentially-regulated response patterns in various organs. Our results indicate for the first time that the RuBpy-doped silica NPs may impose less inflammatory responses but stronger thermotherapeutic effects on target cells in animals than naked NPs in a time- and dose-dependent manner.

Fluorosomes: fluorescent virus-like nanoparticles that represent a convenient tool to visualize receptor-ligand interactions

Viruses are the smallest life forms and parasitize on many eukaryotic organisms, including humans. Consequently, the study of viruses and viral diseases has had an enormous impact on diverse fields of biology and medicine. Due to their often pathogenic properties, viruses have not only had a strong impact on the development of immune cells but also on shaping entire immune mechanisms in their hosts. In order to better characterize virus-specific surface receptors, pathways of virus entry and the mechanisms of virus assembly, diverse methods to visualize virus particles themselves have been developed in the past decades. Apart from characterization of virus-specific mechanisms, fluorescent virus particles also serve as valuable platforms to study receptor-ligand interactions. Along those lines the authors have developed non-infectious virus-like nanoparticles (VNP), which can be decorated with immune receptors of choice and used for probing receptor-ligand interactions, an especially interesting application in the field of basic but also applied immunology research. To be able to better trace receptor-decorated VNP the authors have developed technology to introduce fluorescent proteins into such particles and henceforth termed them fluorosomes (FS). Since VNP are assembled in a simple expression system relying on HEK-293 cells, gene-products of interest can be assembled in a simple and straightforward fashion—one of the reasons why the authors like to call fluorosomes ‘the poor-man's staining tool’. Within this review article an overview on virus particle assembly, chemical and recombinant methods of virus particle labeling and examples on how FS can be applied as sensors to monitor receptor-ligand interactions on leukocytes are given.

MS2 VLP-based delivery of microRNA-146a inhibits autoantibody production in lupus-prone mice

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the presence of pathogenic autoantibodies. Recent studies suggest that microRNAs (miRNAs) play an essential role in immunoregulation and may be involved in the pathogenesis of SLE. Therefore, it was of interest to investigate the potential therapeutic application of miRNAs in SLE, a concept that has not been thoroughly investigated thus far. Virus-like particles (VLPs) are a type of recombinant nanoparticle enveloped by certain proteins derived from the outer coat of a virus. Herein, we describe a novel miRNA-delivery approach via bacteriophage MS2 VLPs and investigate the therapeutic effects of miR-146a, a well-studied and SLE-related miRNA, in BXSB lupus-prone mice.

METHODS

VLPs containing miR-146a, and the control VLPs, were prepared using an Escherichia coli expression system and then administered to lupus-prone mice over a 12-day period. We performed an enzyme-linked immunosorbent assay to evaluate the anti-dsDNA antibody, autoantibody to nuclear antigen (ANA), total IgG and total IgM levels in serum. The expression of miR-146a was analyzed by qRT-PCR. SLE-related cytokines as well as some toll-like receptor signaling pathway molecules were also measured.

RESULTS

Treatment with MS2-miR146a VLP showed profound effects on lupus-prone BXSB mice, including an increased level of mature miR-146a, which led to a significant reduction in the expression of autoantibodies and total IgG. Remarkably, these mice also exhibited reduced levels of proinflammatory cytokines, including IFN-Interferon-α (IFN-α), Interleukin-1β (Il-1β) and Interleukin-6 (Il-6). Moreover, we showed that the toll-like receptor pathway was involved in this regulation.

CONCLUSION

Restoring the loss of miR-146a was effective in eliminating the production of autoantibodies and ameliorating SLE progression in lupus-prone mice. Thus, the induction of dysregulated miRNAs by an MS2 VLP-based delivery system may lead to novel therapies.

CCAAT/enhancer-binding protein γ is a critical regulator of IL-1β-induced IL-6 production in alveolar epithelial cells

CCAAT/enhancer binding protein γ (C/EBPγ) is a member of the C/EBP family of transcription factors, which lacks known activation domains. C/EBPγ was originally described as an inhibitor of C/EBP transactivation potential. However, previous study demonstrates that C/EBPγ augments the C/EBPβ stimulatory activity in lipopolysaccharide induction of IL-6 promoter in a B lymphoblast cell line. These data indicate a complexing functional role for C/EBPγ in regulating gene expression. Furthermore, the expression and function of C/EBPγ during inflammation are still largely unknown. In this study, we demonstrate that C/EBPγ activation was induced by IL-1β treatment in lung epithelial cells. Importantly, we demonstrate for the first time that C/EBPγ plays a critical role in regulating IL-1β-induced IL-6 expression in both mouse primary alveolar type II epithelial cells and a lung epithelial cell line, MLE12. We further provide the evidence that C/EBPγ inhibits IL-6 expression by inhibiting C/EBPβ but not NF-κB stimulatory activity in MLE12 cells. These findings suggest that C/EBPγ is a key transcription factor that regulates the IL-6 expression in alveolar epithelial cells, and may play an important regulatory role in lung inflammatory responses.

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.

Autophagy plays an essential role in the clearance of Pseudomonas aeruginosa by alveolar macrophages

Intracellular bacteria have been shown to cause autophagy, which impacts infectious outcomes, whereas extracellular bacteria have not been reported to activate autophagy. Here, we demonstrate that Pseudomonas aeruginosa, a Gram-negative extracellular bacterium, activates autophagy with considerably increased LC3 punctation in both an alveolar macrophage cell line (MH-S) and primary alveolar macrophages. Using the LC3 Gly120 mutant, we successfully demonstrated a hallmark of autophagy, conjugation of LC3 to phosphatidylethanolamine (PE). The accumulation of typical autophagosomes with double membranes was identified morphologically by transmission electron microscopy (TEM). Furthermore, the increase of PE-conjugated LC3 was indeed induced by infection rather than inhibition of lysosome degradation. P. aeruginosa induced autophagy through the classical beclin-1-Atg7-Atg5 pathway as determined by specific siRNA analysis. Rapamycin and IFN-γ (autophagy inducers) augmented bacterial clearance, whereas beclin-1 and Atg5 knockdown reduced intracellular bacteria. Thus, P. aeruginosa-induced autophagy represents a host protective mechanism, providing new insight into the pathogenesis of this infection.

8-Oxoguanine-DNA glycosylase 1 deficiency modifies allergic airway inflammation by regulating STAT6 and IL-4 in cells and in mice

8-Oxoguanine-DNA glycosylase (OGG-1) is a base excision DNA repair enzyme; however, its function in modulating allergic diseases remains undefined. Using OGG-1 knockout (KO) mice, we show that this protein affects allergic airway inflammation after sensitization and challenge by ovalbumin(OVA). OGG-1 KO mice exhibited less inflammatory cell infiltration and reduced oxidative stress in the lungs after OVA challenge compared to WT mice. The KO phenotype included decreased IL-4, IL-6, IL-10, and IL-17 in lung tissues. In addition, OGG-1 KO mice showed decreased expression and phosphorylation of STAT6 as well as NF-κB. Down-regulation of OGG-1 by siRNA lowered ROS and IL-4 levels but increased IFN-γ production in cultured epithelial cells after exposure to house dust mite extracts. OGG-1 may affect the levels of oxidative stress and proinflammatory cytokines during asthmatic conditions. OGG-1 deficiency negatively regulates allergen-induced airway inflammatory response.

The transferrin receptor and the targeted delivery of therapeutic agents against cancer

BACKGROUND

Traditional cancer therapy can be successful in destroying tumors, but can also cause dangerous side effects. Therefore, many targeted therapies are in development. The transferrin receptor (TfR) functions in cellular iron uptake through its interaction with transferrin. This receptor is an attractive molecule for the targeted therapy of cancer since it is upregulated on the surface of many cancer types and is efficiently internalized. This receptor can be targeted in two ways: 1) for the delivery of therapeutic molecules into malignant cells or 2) to block the natural function of the receptor leading directly to cancer cell death.

SCOPE OF REVIEW

In the present article we discuss the strategies used to target the TfR for the delivery of therapeutic agents into cancer cells. We provide a summary of the vast types of anti-cancer drugs that have been delivered into cancer cells employing a variety of receptor binding molecules including Tf, anti-TfR antibodies, or TfR-binding peptides alone or in combination with carrier molecules including nanoparticles and viruses.

MAJOR CONCLUSIONS

Targeting the TfR has been shown to be effective in delivering many different therapeutic agents and causing cytotoxic effects in cancer cells in vitro and in vivo.

GENERAL SIGNIFICANCE

The extensive use of TfR for targeted therapy attests to the versatility of targeting this receptor for therapeutic purposes against malignant cells. More advances in this area are expected to further improve the therapeutic potential of targeting the TfR for cancer therapy leading to an increase in the number of clinical trials of molecules targeting this receptor. This article is part of a Special Issue entitled Transferrins: molecular mechanisms of iron transport and disorders.