Cell-specific delivery of diverse cargos by bacteriophage MS2 virus-like particles

Active radar guides missile to its target: receptor-based targeted treatment of hepatocellular carcinoma by nanoparticulate systems

Patients with hepatocellular carcinoma (HCC) usually present at advanced stages and do not benefit from surgical resection, so drug therapy should deserve a prominent place in unresectable HCC treatment. But chemotherapy agents, such as doxorubicin, cisplatin, and paclitaxel, frequently encounter important problems such as low specificity and non-selective biodistribution. Recently, the development of nanotechnology led to significant breakthroughs to overcome these problems. Decorating the surfaces of nanoparticulate-based drug carriers with homing devices has demonstrated its potential in concentrating chemotherapy agents specifically to HCC cells. In this paper, we reviewed the current status of active targeting strategies for nanoparticulate systems based on various receptors such as asialoglycoprotein receptor, transferrin receptor, epidermal growth factor receptor, folate receptor, integrin, and CD44, which are abundantly expressed on the surfaces of hepatocytes or liver cancer cells. Furthermore, we pointed out their merits and defects and provided theoretical references for further research.

Functional nanostructures for effective delivery of small interfering RNA therapeutics

Small interfering RNA (siRNA) has proved to be a powerful tool for target-specific gene silencing via RNA interference (RNAi). Its ability to control targeted gene expression gives new hope to gene therapy as a treatment for cancers and genetic diseases. However, siRNA shows poor pharmacological properties, such as low serum stability, off-targeting, and innate immune responses, which present a significant challenge for clinical applications. In addition, siRNA cannot cross the cell membrane for RNAi activity because of its anionic property and stiff structure. Therefore, the development of a safe, stable, and efficient system for the delivery of siRNA therapeutics into the cytoplasm of targeted cells is crucial. Several nanoparticle platforms for siRNA delivery have been developed to overcome the major hurdles facing the therapeutic uses of siRNA. This review covers a broad spectrum of non-viral siRNA delivery systems developed for enhanced cellular uptake and targeted gene silencing in vitro and in vivo and discusses their characteristics and opportunities for clinical applications of therapeutic siRNA.

Hierarchical assembly of plasmonic nanostructures using virus capsid scaffolds on DNA origami templates

Building plasmonic nanostructures using biomolecules as scaffolds has shown great potential for attaining tunable light absorption and emission via precise spatial organization of optical species and antennae. Here we report bottom-up assembly of hierarchical plasmonic nanostructures using DNA origami templates and MS2 virus capsids. These serve as programmable scaffolds that provide molecular level control over the distribution of fluorophores and nanometer-scale control over their distance from a gold nanoparticle antenna. While previous research using DNA origami to assemble plasmonic nanostructures focused on determining the distance-dependent response of single fluorophores, here we address the challenge of constructing hybrid nanostructures that present an organized ensemble of fluorophores and then investigate the plasmonic response. By combining finite-difference time-domain numerical simulations with atomic force microscopy and correlated scanning confocal fluorescence microscopy, we find that the use of the scaffold keeps the majority of the fluorophores out of the quenching zone, leading to increased fluorescence intensity and mild levels of enhancement. The results show that the degree of enhancement can be controlled by exploiting capsid scaffolds of different sizes and tuning capsid-AuNP distances. These bioinspired plasmonic nanostructures provide a flexible design for manipulating photonic excitation and photoemission.

Viral nanoparticle-encapsidated enzyme and restructured DNA for cell delivery and gene expression

Packaging specific exogenous active proteins and DNAs together within a single viral-nanocontainer is challenging. The bacteriophage T4 capsid (100 × 70 nm) is well suited for this purpose, because it can hold a single long DNA or multiple short pieces of DNA up to 170 kb packed together with more than 1,000 protein molecules. Any linear DNA can be packaged in vitro into purified procapsids. The capsid-targeting sequence (CTS) directs virtually any protein into the procapsid. Procapsids are assembled with specific CTS-directed exogenous proteins that are encapsidated before the DNA. The capsid also can display on its surface high-affinity eukaryotic cell-binding peptides or proteins that are in fusion with small outer capsid and head outer capsid surface-decoration proteins that can be added in vivo or in vitro. In this study, we demonstrate that the site-specific recombinase cyclic recombination (Cre) targeted into the procapsid is enzymatically active within the procapsid and recircularizes linear plasmid DNA containing two terminal loxP recognition sites when packaged in vitro. mCherry expression driven by a cytomegalovirus promoter in the capsid containing Cre-circularized DNA is enhanced over linear DNA, as shown in recipient eukaryotic cells. The efficient and specific packaging into capsids and the unpackaging of both DNA and protein with release of the enzymatically altered protein-DNA complexes from the nanoparticles into cells have potential in numerous downstream drug and gene therapeutic applications.

Encapsidated atom-transfer radical polymerization in Qβ virus-like nanoparticles

Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA.

Oncogene dependency and the potential of targeted RNAi-based anti-cancer therapy

Cancers arise through the progression of multiple genetic and epigenetic defects that lead to deregulation of numerous signalling networks. However, the last decade has seen the development of the concept of 'oncogene addiction', where tumours appear to depend on a single oncogene for survival. RNAi has provided an invaluable tool in the identification of these oncogenes and oncogene-dependent cancers, and also presents great potential as a novel therapeutic strategy against them. Although RNAi therapeutics have demonstrated effective killing of oncogene-dependent cancers in vitro, their efficacy in vivo is severely limited by effective delivery systems. Several virus-based RNAi delivery strategies have been explored, but problems arose associated with high immunogenicity, random genome integration and non-specific targeting. This has directed efforts towards non-viral formulations, including delivery systems based on virus-like particles, liposomes and cationic polymers, which can circumvent some of these problems by immunomasking and the use of specific tumour-targeting ligands. This review outlines the prevalence of oncogene-dependent cancers, evaluates the potential of RNAi-based therapeutics and assesses the relative strengths and weaknesses of different approaches to targeted RNAi delivery.

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.

Matrix metalloproteinase 2-responsive micelle for siRNA delivery

Systemic delivery of small interfering RNA (siRNA) into cancer cells remains the major obstacle to siRNA drug development. An ideal siRNA delivery vehicle for systemic administration should have long circulation time in blood, accumulate at tumor site, and sufficiently internalize into cancer cells for high-efficiency of gene silence. Herein, we report a core-shell Micelleplex delivery system that made from block copolymer bearing poly(ethylene glycol) (PEG), matrix metalloproteinase 2 (MMP-2)-degradable peptide PLG*LAG, cationic cell penetrating peptide polyarginine r9 and poly(ε-caprolactone) (PCL) for siRNA delivery. We show clear evidences in vitro and in vivo to prove that the micelle carrying siRNA can circulate enough time in blood, enrich accumulation at tumor sites, shed the PEG layer when triggered by tumor overexpressing MMP-2, and then the exposing cell penetrating peptide r9 enhanced cellular uptake of siRNA. Accordingly, this design strategy enhances the inhibition of breast tumor growth following systemic injection of this system carrying siRNA against Polo-like kinase 1, which demonstrating this Micelleplex can be a potential delivery system for systemic siRNA delivery in cancer therapy.

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.

Multivalent viral capsids with internal cargo for fibrin imaging

Thrombosis is the cause of many cardiovascular syndromes and is a significant contributor to life-threatening diseases, such as myocardial infarction and stroke. Thrombus targeted imaging agents have the capability to provide molecular information about pathological clots, potentially improving detection, risk stratification, and therapy of thrombosis-related diseases. Nanocarriers are a promising platform for the development of molecular imaging agents as they can be modified to have external targeting ligands and internal functional cargo. In this work, we report the synthesis and use of chemically functionalized bacteriophage MS2 capsids as biomolecule-based nanoparticles for fibrin imaging. The capsids were modified using an oxidative coupling reaction, conjugating ∼90 copies of a fibrin targeting peptide to the exterior of each protein shell. The ability of the multivalent, targeted capsids to bind fibrin was first demonstrated by determining the impact on thrombin-mediated clot formation. The modified capsids out-performed the free peptides and were shown to inhibit clot formation at effective concentrations over ten-fold lower than the monomeric peptide alone. The installation of near-infrared fluorophores on the interior surface of the capsids enabled optical detection of binding to fibrin clots. The targeted capsids bound to fibrin, exhibiting higher signal-to-background than control, non-targeted MS2-based nanoagents. The in vitro assessment of the capsids suggests that fibrin-targeted MS2 capsids could be used as delivery agents to thrombi for diagnostic or therapeutic applications.

Exploitation of viral properties for intracellular delivery

Nanotechnology is an expanding area of study with potentially pivotal applications in a discipline as medicine where new biomedical active molecules or strategies are continuously developing. One of the principal drawbacks for the application of new therapies is the difficulty to cross membranes that represent the main physiological barrier in our body and in all living cells. Membranes are selectively permeable and allow the selective internalization of substances; generally, they form a highly impermeable barrier to most polar and charged molecules, and represent an obstacle for drug delivery, limiting absorption to specific routes and mechanisms. Viruses provide attracting suggestions for the development of targeted drug carriers as they have evolved naturally to deliver their genomes to host cells with high fidelity.

A detailed understanding of virus structure and their mechanisms of entry into mammalian cells will facilitate the development and analysis of virus‐based materials for medical applications. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

Production and applications of engineered viral capsids

As biological agents, viruses come in an astounding range of sizes, with varied shapes and surface morphologies. The structures of viral capsids are generally assemblies of hundreds of copies of one or a few proteins which can be harnessed for use in a wide variety of applications in biotechnology, nanotechnology, and medicine. Despite their complexity, many capsid types form as homogenous populations of precise geometrical assemblies. This is important in both medicine, where well-defined therapeutics are critical for drug performance and federal approval, and nanotechnology, where precise placement affects the properties of the desired material. Here we review the production of viruses and virus-like particles with methods for selecting and manipulating the size, surface chemistry, assembly state, and interior cargo of capsid. We then discuss many of the applications used in research today and the potential commercial and therapeutic products from engineered viral capsids.

Bioengineered bacterial outer membrane vesicles as cell-specific drug-delivery vehicles for cancer therapy

Advances in genetic engineering tools have contributed to the development of strategies for utilizing biologically derived vesicles as nanomedicines for achieving cell-specific drug delivery. Here, we describe bioengineered bacterial outer membrane vesicles (OMVs) with low immunogenicity that can target and kill cancer cells in a cell-specific manner by delivering small interfering RNA (siRNA) targeting kinesin spindle protein (KSP). A mutant Escherichia coli strain that exhibits reduced endotoxicity toward human cells was engineered to generate OMVs displaying a human epidermal growth factor receptor 2 (HER2)-specific affibody in the membrane as a targeting ligand. Systemic injection of siRNA-packaged OMVs caused targeted gene silencing and induced highly significant tumor growth regression in an animal model. Importantly, the modified OMVs were well tolerated and showed no evidence of nonspecific side effects. We propose that bioengineered OMVs have great potential as cell-specific drug-delivery vehicles for treating various cancers.

Bioengineering virus-like particles as vaccines

Virus-like particle (VLP) technology seeks to harness the optimally tuned immunostimulatory properties of natural viruses while omitting the infectious trait. VLPs that assemble from a single protein have been shown to be safe and highly efficacious in humans, and highly profitable. VLPs emerging from basic research possess varying levels of complexity and comprise single or multiple proteins, with or without a lipid membrane. Complex VLP assembly is traditionally orchestrated within cells using black-box approaches, which are appropriate when knowledge and control over assembly are limited. Recovery challenges including those of adherent and intracellular contaminants must then be addressed. Recent commercial VLPs variously incorporate steps that include VLP in vitro assembly to address these problems robustly, but at the expense of process complexity. Increasing research activity and translation opportunity necessitate bioengineering advances and new bioprocessing modalities for efficient and cost-effective production of VLPs. Emerging approaches are necessarily multi-scale and multi-disciplinary, encompassing diverse fields from computational design of molecules to new macro-scale purification materials. In this review, we highlight historical and emerging VLP vaccine approaches. We overview approaches that seek to specifically engineer a desirable immune response through modular VLP design, and those that seek to improve bioprocess efficiency through inhibition of intracellular assembly to allow optimal use of existing purification technologies prior to cell-free VLP assembly. Greater understanding of VLP assembly and increased interdisciplinary activity will see enormous progress in VLP technology over the coming decade, driven by clear translational opportunity.

Virus-like particles: the future of microbial factories and cell-free systems as platforms for vaccine development

Vaccines based on virus-like particles have proved their success in human health. More than 25 years after the approval of the first vaccine based on this technology, the substantial efforts to expand the range of applications and target diseases are beginning to bear fruit. The incursion of high-throughput screening technologies, combined with new developments in protein engineering and chemical coupling, have accelerated the development of systems capable of producing macrostructures useful for vaccinology, gene delivery, immunotherapy and bionanotechnology. This review summarizes the most recent developments in microbial cell factories and cell-free systems for virus-like particle production and discusses the future impact of this technology in human and animal health.

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.

A plant derived multifunctional tool for nanobiotechnology based on Tomato bushy stunt virus

Structure, size, physicochemical properties and production strategies make many plant viruses ideal protein based nanoscaffolds, nanocontainers and nano-building blocks expected to deliver a multitude of applications in different fields such as biomedicine, pharmaceutical chemistry, separation science, catalytic chemistry, crop pest control and biomaterials science. Functionalization of viral nanoparticles through modification by design of their external and internal surfaces is essential to fully exploit the potentiality of these objects. In the present paper we describe the development of a plant derived multifunctional tool for nanobiotechnology based on Tomato bushy stunt virus. We demonstrate the ability of this system to remarkably sustain genetic modifications and in vitro chemical derivatizations of its outer surface, which resulted in the successful display of large chimeric peptides fusions and small chemical molecules, respectively. Moreover, we have defined physicochemical conditions for viral swelling and reversible viral pore gating that we have successfully employed for foreign molecules loading and retention in the inner cavity of this plant virus nanoparticles system. Finally, a production and purification strategy from Nicotiana benthamiana plants has been addressed and optimized.

Theranostic magnetic nanoparticles for efficient capture and in situ chemotherapy of circulating tumor cells

Cancer is considered to be the leading factor which threatens human lives nowadays, and 90% of cancer-related deaths are attributed to the metastasis of cancer. Thus an effective and simultaneous separation and therapeutic method for circulating tumor cells is crucial for improving the diagnosis, prognosis, and treatment of cancer. Here, we report the design of theranostic magnetic nanoparticles conjugated with the targeting peptide SP94 and the anticancer drug doxorubicin (DOX) (symbolized as Fe₃O₄-DOX/SP94) for the targeted isolation of the human hepatocellular carcinoma cell line (HepG2), followed by the in situ chemotherapy of cancer cells upon capture. It was found that the capture efficiencies of 400 μg Fe₃O₄-DOX/SP94 for HepG2 cells and human embryonic kidney transformed 293 cells (293T) were around 75% and 5% respectively after 15 min incubation. Furthermore, it is worth mentioning that DOX was covalently conjugated via pH-sensitive hydrazone bonds, and the in vitro release studies demonstrated that DOX was released much faster at pH 5.0 than at pH 7.4. According to the in vitro cytotoxicity assays, significantly reduced cell viability was observed in HepG2 cells when the concentration of Fe₃O₄-DOX/SP94 nanoparticles was 300 μg mL^-1. Such a rapid and facile approach has considerable potential for the targeted capture as well as effective chemotherapy of circulating tumor cells, in an attempt to improve the curative effects against metastatic diseases.

The role of surface functionalization of colloidal alumina particles on their controlled interactions with viruses

Materials that interact in a controlled manner with viruses attract increasing interest in biotechnology, medicine, and environmental technology. Here, we show that virus-material interactions can be guided by intrinsic material surface chemistries, introduced by tailored surface functionalizations. For this purpose, colloidal alumina particles are surface functionalized with amino, carboxyl, phosphate, chloropropyl, and sulfonate groups in different surface concentrations and characterized in terms of elemental composition, electrokinetic, hydrophobic properties, and morphology. The interaction of the functionalized particles with hepatitis A virus and phages MS2 and PhiX174 is assessed by virus titer reduction after incubation with particles, activity of viruses conjugated to particles, and imaged by electron microscopy. Type and surface density of particle functional groups control the virus titer reduction between 0 and 99.999% (5 log values). For instance, high sulfonate surface concentrations (4.7 groups/nm(2)) inhibit attractive virus-material interactions and lead to complete virus recovery. Low sulfonate surface concentrations (1.2 groups/nm(2)), native alumina, and chloropropyl-functionalized particles induce strong virus-particle adsorption. The virus conformation and capsid amino acid composition further influence the virus-material interaction. Fundamental interrelations between material properties, virus properties, and the complex virus-material interaction are discussed and a versatile pool of surface functionalization strategies controlling virus-material interactions is presented.

Reengineering viruses and virus-like particles through chemical functionalization strategies

Increasing demands from nanotechnology require increasingly more rigorous methods to control nanoparticle traits such as assembly, size, morphology, monodispersity, stability, and reactivity. Viruses are a compelling starting point for engineering nanoparticles, as eons of natural biological evolution have instilled diverse and desirable traits. The next step is to reengineer these viruses into something functional and useful. These reengineered particles, or virus-based nanoparticles (VNPs), are the foundation for many promising new technologies in drug delivery, targeted delivery, vaccines, imaging, and biocatalysis. To achieve these end goals, VNPs must often be manipulated genetically and post-translationally. We review prevailing strategies of genetic and noncovalent functionalization and focus on the covalent modifications using natural and unnatural amino acid residues.

Controlled integration of gold nanoparticles and organic fluorophores using synthetically modified MS2 viral capsids

The placement of fluorophores in close proximity to metal nanoparticle surfaces is proposed to enhance several photophysical properties of the dyes, potentially leading to improved quantum yields and decreased photobleaching. It is difficult in practice, however, to establish and maintain the nanoscale distances that are required to maximize these effects. The type of metal, size, and shape of the nanoparticle, the physical distance separating the metal nanoparticle from the organic dye, and the spectral properties of the fluorophore itself are all proposed to influence the quantum yield and lifetime. This results in a complex behavior that can lead to either enhanced or quenched fluorescence in different contexts. In this report, we describe a well-defined system that can be used to explore these effects, while physically preventing the fluorophores from contacting the nanoparticle surfaces. The basis of this system is the spherical protein capsid of bacteriophage MS2, which was used to house gold particles within its interior volume. The exterior surface of each capsid was then modified with Alexa Fluor 488 (AF 488) labeled DNA strands. By placing AF 488 dyes at distances of 3, 12, and 24 bp from the surface of capsids containing 10 nm gold nanoparticles, fluorescence intensity enhancements of 2.2, 1.2, and 1.0 were observed, respectively. A corresponding decrease in fluorescence lifetime was observed for each distance. Because of its well-defined and modular nature, this architecture allows the rapid exploration of the many variables involved in metal-controlled fluorescence, leading to a better understanding of this phenomenon.

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.

CPMV-DOX delivers

The plant virus, Cowpea mosaic virus (CPMV), is developed as a carrier of the chemotherapeutic drug doxorubicin (DOX). CPMV-DOX conjugate, in which eighty DOX molecules are covalently bound to external surface carboxylates of the viral nanoparticle (VNP), shows greater cytotoxicity than free DOX toward HeLa cells when administered at low dosage. At higher concentrations, CPMV-DOX cytotoxicity is time-delayed. The CPMV conjugate is targeted to the endolysosomal compartment of the cells, in which the proteinaceous drug carrier is degraded and the drug released. This study is the first demonstrating the utility of CPMV as a drug delivery vehicle.

Engineering nanoscale protein compartments for synthetic organelles

Advances in metabolic engineering have given rise to the biological production of novel fuels and chemicals, but yields are often low without significant optimization. One generalizable solution is to create a specialized organelle for the sequestration of engineered metabolic pathways. Bacterial microcompartments are an excellent scaffold for such an organelle. These compartments consist of a porous protein shell that encapsulates enzymes. To repurpose these structures, researchers have begun to determine how the protein shell is assembled, how pores may be used to control small molecule transport across the protein shell, and how to target heterologous enzymes to the compartment interior. With these advances, it will soon be possible to use engineered forms of these protein shells to create designer organelles.

Osmolyte-mediated encapsulation of proteins inside MS2 viral capsids

The encapsulation of enzymes in nanometer-sized compartments has the potential to enhance and control enzymatic activity, both in vivo and in vitro. Despite this potential, there is little quantitative data on the effect of encapsulation in a well-defined compartment under varying conditions. To gain more insight into these effects, we have characterized two improved methods for the encapsulation of heterologous molecules inside bacteriophage MS2 viral capsids. First, attaching DNA oligomers to a molecule of interest and incubating it with MS2 coat protein dimers yielded reassembled capsids that packaged the tagged molecules. The addition of a protein-stabilizing osmolyte, trimethylamine-N-oxide, significantly increased the yields of reassembly. Second, we found that expressed proteins with genetically encoded negatively charged peptide tags could also induce capsid reassembly, resulting in high yields of reassembled capsids containing the protein. This second method was used to encapsulate alkaline phosphatase tagged with a 16 amino acid peptide. The purified encapsulated enzyme was found to have the same K(m) value and a slightly lower k(cat) value than the free enzyme, indicating that this method of encapsulation had a minimal effect on enzyme kinetics. This method provides a practical and potentially scalable way of studying the complex effects of encapsulating enzymes in protein-based compartments.

Tools from viruses: bacteriophage successes and beyond

Viruses are ubiquitous and can infect any of the three existing cellular lineages (Archaea, Bacteria and Eukarya). Despite the persisting negative public perception of these entities, scientists learnt how to domesticate some of them. The study of molecular mechanisms essential to the completion of viral cycles has greatly contributed to deciphering fundamental processes in biology. Nowadays, viruses have entered the biotechnological era and numerous applications have already been developed. Viral-derived tools are used to manipulate genetic information, detect, diagnose, control and cure infectious diseases, or even design new structural assemblies. With the recent advances in the field of metagenomics, an overwhelming amount of information on novel viruses has become available. As current tools have been historically developed from a limited number of viruses, the potential of discoveries from new archaeal, bacterial and eukaryotic viruses may be limited only by our understanding of the multiple facets of viral cycles.

Engineered mutations change the structure and stability of a virus-like particle

The single-coat protein (CP) of bacteriophage Qβ self-assembles into T = 3 icosahedral virus-like particles (VLPs), of interest for a wide range of applications. These VLPs are very stable, but identification of the specific molecular determinants of this stability is lacking. To investigate these determinants along with manipulations that confer more capabilities to our VLP material, we manipulated the CP primary structure to test the importance of various putative stabilizing interactions. Optimization of a procedure to incorporate fused CP subunits allowed for good control over the average number of covalent dimers in each VLP. We confirmed that the disulfide linkages are the most important stabilizing elements for the capsid and that acidic conditions significantly enhance the resistance of VLPs to thermal degradation. Interdimer interactions were found to be less important for VLP assembly than intradimer interactions. Finally, a single point mutation in the CP resulted in a population of smaller VLPs in three distinct structural forms.

Photodynamic activity of viral nanoparticles conjugated with C60

The development of viral nanoparticles (VNP) displaying multiple copies of the buckyball (C(60)) and their photodynamic activity is described. VNP-C(60) conjugates were assembled using click chemistry. Cell uptake and cell killing using white light therapy and a prostate cancer cell line is demonstrated.

Engineered viral nanoparticles for flow cytometry and fluorescence microscopy applications

Viral nanoparticles (VNPs) are attractive platforms for use in the biotechnology and biomedical fields because of their biological nature. A wide variety of these particles, labeled with fluorescent reporters, have been characterized using flow cytometry and cellular imaging techniques. Fluorescence microscopy allows the direct observation of VNPs on the cell surface or inside the membrane as well as the cellular localization of the nanoparticles while flow cytometry allows the statistical quantification of nanoparticle uptake and targeting specificity. These techniques are essential when characterizing the properties of VNPs and provide information toward the use of VNPs for targeting, imaging, and/or cargo delivery.

Virus scaffolds as enzyme nano-carriers

The cooperative organization of enzymes by cells is a key feature for the efficiency of living systems. In the field of nanotechnologies, effort currently aims at mimicking this natural organization. Nanoscale resolution and high-registration alignment are necessary to control enzyme distribution in nano-containers or on the surface of solid supports. Virus capsid self-assembly is driven by precise supramolecular combinations of protein monomers, which have made them attractive building blocks to engineer enzyme nano-carriers (ENCs). We discuss some examples of what in our opinion constitute the latest advances in the use of plant viruses, bacteriophages and virus-like particles (VLPs) as nano-scaffolds for enzyme selection, enzyme confinement and patterning, phage therapy, raw material processing, and single molecule enzyme kinetics studies.

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.

Site-directed coordination chemistry with P22 virus-like particles

Protein cage nanoparticles (PCNs) are attractive platforms for developing functional nanomaterials using biomimetic approaches for functionalization and cargo encapsulation. Many strategies have been employed to direct the loading of molecular cargos inside a wide range of PCN architectures. Here we demonstrate the exploitation of a metal-ligand coordination bond with respect to the direct packing of guest molecules on the interior interface of a virus-like PCN derived from Salmonella typhimurium bacteriophage P22. The incorporation of these guest species was assessed using mass spectrometry, multiangle laser light scattering, and analytical ultracentrifugation. In addition to small-molecule encapsulation, this approach was also effective for the directed synthesis of a large macromolecular coordination polymer packed inside of the P22 capsid and initiated on the interior surface. A wide range of metals and ligands with different thermodynamic affinities and kinetic stabilities are potentially available for this approach, highlighting the potential for metal-ligand coordination chemistry to direct the site-specific incorporation of cargo molecules for a variety of applications.

Deletion of the Hoc and Soc capsid proteins affects the surface and cellular uptake properties of bacteriophage T4 derived nanoparticles

Recently the use of engineered viral scaffolds in biotechnology and medical applications has been increasing dramatically. T4 phage capsid derived nanoparticles (NPs) have potential advantages as sensors and in biotechnology. These applications require that the physical properties and cellular uptake of these NPs be understood. In this study we used a T4 deletion mutant to investigate the effects of removing both the Hoc and Soc proteins from the capsid surface on T4 tailless NPs. The surface charge, zeta potential, size, and cellular uptake efficiencies for both the T4 NP and T4ΔHocΔSoc NP mutant were measured and compared using dynamic light scattering and flow cytometry and significant differences were detected.

Biological activities of histidine-rich peptides; merging biotechnology and nanomedicine

Histidine-rich peptides are commonly used in recombinant protein production as purification tags, allowing the one-step affinity separation of the His-tagged proteins from the extracellular media or cell extracts. Genetic engineering makes feasible the post-purification His-tag removal by inserting, between the tag and the main protein body, a target site for trans-acting proteases or a self-proteolytic peptide with regulatable activities. However, for technical ease, His tags are often not removed and the fusion proteins eventually used in this form. In this commentary, we revise the powerful biological properties of histidine-rich peptides as endosomolytic agents and as architectonic tags in nanoparticle formation, for which they are exploited in drug delivery and other nanomedical applications. These activities, generally unknown to biotechnologists, can unwillingly modulate the functionality and biotechnological performance of recombinant proteins in which they remain trivially attached.