Interaction between a 54-kilodalton mammalian cell surface protein and cowpea mosaic virus

Research Progress on the Role of Intermediate Filament Vimentin in Atherosclerosis

The cytoskeleton is a biopolymer network composed of intermediate filaments, actin, and microtubules, which is the main mechanical structure of cells. Vimentin is an intermediate filament protein that regulates the mechanical and contractile properties of cells, thereby reflecting their mechanical properties. In recent years, the "nonmechanical function" of vimentin inside and outside of cells has attracted extensive attention. The content of vimentin in atherosclerotic plaques is increased, and the serum secretion of vimentin in patients with coronary heart disease is remarkably increased. In this review, the mechanistic and nonmechanistic roles of vimentin in atherosclerosis progression were summarized on the basis of current studies.

Single-Point Mutations in Qβ Virus-like Particles Change Binding to Cells

Virus-like particles (VLPs) constitute large, polyvalent platforms onto which a wide variety of functional units can be grafted. Their use in biological settings often depends on their specific binding to cells or receptors of interest; this can be compromised by excessive nonspecific association with other cells. We found that lysine residues mediate such nonspecific interactions, presumably by virtue of protonation and interaction with anionic membrane lipid headgroups and/or complementary residues of cell surface proteins and polysaccharides. Chemical acylation of surface-exposed amines of the Qβ VLP led to a significant reduction in the association of particles with mammalian cells. Single-point mutations of particular lysine residues to either glutamine, glutamic acid, tryptophan, or phenylalanine were mostly well-tolerated and formed intact capsids, but the introduction of double and triple mutants was far less forgiving. Introduction of glutamic acid at position 13 (K13E) led to a dramatic increase in cellular binding, whereas removal of the lysine at position 46 (K46Q) led to an equally striking reduction. Several plasma membrane components were found to specifically interact with the Qβ capsid irrespective of surface charge. These results suggest that specific cellular interactions are engaged or obviated by such mutations and provide us with more "benign" particles to which can be added binding functionality for targeted delivery applications.

The pharmacology of plant virus nanoparticles

The application of nanoparticles for medical purposes has made enormous strides in providing new solutions to health problems. The observation that plant virus-based nanoparticles (VNPs) can be repurposed and engineered as smart bio-vehicles for targeted drug delivery and imaging has launched extensive research for improving the therapeutic and diagnostic management of various diseases. There is evidence that VNPs are promising high value nanocarriers with potential for translational development. This is mainly due to their unique features, encompassing structural uniformity, ease of manufacture and functionalization by means of expression, chemical biology and self-assembly. While the development pipeline is moving rapidly, with many reports focusing on engineering and manufacturing aspects to tailor the properties and efficacy of VNPs, fewer studies have focused on gaining insights into the nanotoxicity of this novel platform nanotechnology. Herein, we discuss the pharmacology of VNPs as a function of formulation and route of administration. VNPs are reviewed in the context of their application as therapeutic adjuvants or nanocarrier excipients to initiate, enhance, attenuate or impede the formulation's toxicity. The summary of the data however also underlines the need for meticulous VNP structure-nanotoxicity studies to improve our understanding of their in vivo fates and pharmacological profiles to pave the way for translation of VNP-based formulations into the clinical setting.

The unique potency of Cowpea mosaic virus (CPMV) in situ cancer vaccine

The immunosuppressive tumor microenvironment enables cancer to resist immunotherapies. We have established that intratumoral administration of plant-derived Cowpea mosaic virus (CPMV) nanoparticles as an in situ vaccine overcomes the local immunosuppression and stimulates a potent anti-tumor response in several mouse cancer models and canine patients. CPMV does not infect mammalian cells but acts as a danger signal that leads to the recruitment and activation of innate and subsequently, adaptive immune cells. In the present study we addressed whether other icosahedral viruses or virus-like particles (VLPs) of plant, bacteriophage and mammalian origin can be similarly employed as intratumoral immunotherapy. Our results indicate that CPMV in situ vaccine outperforms Cowpea chlorotic mottle virus (CCMV), Physalis mosaic virus (PhMV), Sesbania mosaic virus (SeMV), bacteriophage Qβ VLPs, or Hepatitis B virus capsids (HBVc). Furthermore, ex vivo and in vitro assays reveal unique features of CPMV that makes it an inherently stronger immune stimulant.

Affinity of plant viral nanoparticle potato virus X (PVX) towards malignant B cells enables cancer drug delivery

Non-Hodgkin's B cell lymphomas (NHL) include a diverse set of neoplasms that constitute ∼90% of all lymphomas and the largest subset of blood cancers. While chemotherapy is the first line of treatment, the efficacy of contemporary chemotherapies is hampered by dose-limiting toxicities. Partly due to suboptimal dosing, ∼40% of patients exhibit relapsed or refractory disease. Therefore more efficacious drug delivery systems are urgently needed to improve survival of NHL patients. In this study we demonstrate a new drug delivery platform for NHL based on the plant virus Potato virus X (PVX). We observed a binding affinity of PVX towards malignant B cells. In a metastatic mouse model of NHL, we show that systemically administered PVX home to tissues harboring malignant B cells. When loaded with the chemotherapy monomethyl auristatin (MMAE), the PVX nanocarrier enables effective delivery of MMAE to human B lymphoma cells in a NHL mouse model leading to inhibition of lymphoma growth in vivo and improved survival. Thus, PVX nanoparticle is a promising drug delivery platform for B cell malignancies.

Brome mosaic virus-like particles as siRNA nanocarriers for biomedical purposes

There is an increasing interest in the use of plant viruses as vehicles for anti-cancer therapy. In particular, the plant virus brome mosaic virus (BMV) and cowpea chlorotic mottle virus (CCMV) are novel potential nanocarriers for different therapies in nanomedicine. In this work, BMV and CCMV were loaded with a fluorophore and assayed on breast tumor cells. The viruses BMV and CCMV were internalized into breast tumor cells. Both viruses, BMV and CCMV, did not show cytotoxic effects on tumor cells in vitro. However, only BMV did not activate macrophages in vitro. This suggests that BMV is less immunogenic and may be a potential carrier for therapy delivery in tumor cells. Furthermore, BMV virus-like particles (VLPs) were efficiently loaded with small interfering RNA (siRNA) without packaging signal. The gene silencing was demonstrated by VLPs loaded with siGFP and tested on breast tumor cells that constitutively express the green fluorescent protein (GPF). After VLP-siGFP treatment, GFP expression was efficiently inhibited corroborating the cargo release inside tumor cells and the gene silencing. In addition, BMV VLP carring siAkt1 inhibited the tumor growth in mice. These results show the attractive potential of plant virus VLPs to deliver molecular therapy to tumor cells with low immunogenic response.

Cowpea mosaic virus nanoparticles for cancer imaging and therapy

Nanoparticle platforms are particularly attractive for theranostic applications due to their capacity for multifunctionality and multivalency. Some of the most promising nano-scale scaffold systems have been co-opted from nature including plant viruses such as cowpea mosaic virus (CPMV). The use of plant viruses like CPMV as viral nanoparticles is advantageous for many reasons; they are non-infectious and nontoxic to humans and safe for use in intravital imaging and drug delivery. The CPMV capsid icosahedral shape allows for enhanced multifunctional group display and the ability to carry specific cargoes. The native tropism of CPMV for cell-surface displayed vimentin and the enhanced permeability and retention effect allow them to preferentially extravasate from tumor neovasculature and efficiently penetrate tumors. Furthermore, CPMVs can be engineered via several straightforward chemistries to display targeting and imaging moieties on external, addressable residues and they can be loaded internally with therapeutic drug cargoes. These qualities make them highly effective as biocompatible platforms for tumor targeting, intravital imaging and cancer therapy.

Delivery of mitoxantrone using a plant virus-based nanoparticle for the treatment of glioblastomas

Mitoxatrone (MTO), an antineoplastic chemotherapeutic, has potent activity against the most common and agressive type of primary brain tumor, glioblastoma multiforme (GBM). However, its poor penetration through the blood brain barrier, and cardiotoxic side effects from systemic delivery limit its effectiveness for clinical treatment. To address these limitations, we utilize a plant virus-based nanoparticle, cowpea mosaic virus (CPMV), to deliver MTO to treat GBM. In this work, we loaded MTO into the interior cavity of CPMV (CPMV-MTO) through diffusion through its pores. We report the uptake of CPMV-MTO in glioma cells and demonstrate its cytotoxic effects in vitro as a solo therapy, and in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). These results reveal the potential for this plant virus-based nanoparticle platform for the treatment of GBM.

A biodistribution study of two differently shaped plant virus nanoparticles reveals new peculiar traits

Self-assembling plant virus nanoparticles (pVNPs) have started to be explored as nanometre-sized objects for biomedical applications, such as vaccine or drug delivery and imaging. Plant VNPs may be ideal tools in terms of biocompatibility and biodegradability endowed with a wide diversity of symmetries and dimensions, easy chemical/biological engineering, and rapid production in plants. Recently, we defined that icosahedral Tomato bushy stunt virus (TBSV) and filamentous Potato virus X (PVX) are neither toxic nor teratogenic. We report here the results of an interdisciplinary study aimed to define for the first time the biodistribution of unlabelled, unpegylated, underivatized TBSV and PVX by proved detecting antibodies. These data add new insights on the in vivo behaviour of these nano-objects and demonstrate that the pVNPs under scrutiny are each intrinsically endowed with peculiar properties foreshadowing different applications in molecular medicine.

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.

Utilizing Viral Nanoparticle/Dendron Hybrid Conjugates in Photodynamic Therapy for Dual Delivery to Macrophages and Cancer Cells

Photodynamic therapy (PDT) is a promising avenue for greater treatment efficacy of highly resistant and aggressive melanoma. Through photosensitizer attachment to nanoparticles, specificity of delivery can be conferred to further reduce potential side effects. While the main focus of PDT is the destruction of cancer cells, additional targeting of tumor-associated macrophages also present in the tumor microenvironment could further enhance treatment by eliminating their role in processes such as invasion, metastasis, and immunosuppression. In this study, we investigated PDT of macrophages and tumor cells through delivery using the natural noninfectious nanoparticle cowpea mosaic virus (CPMV), which has been shown to have specificity for the immunosuppressive subpopulation of macrophages and also targets cancer cells. We further explored conjugation of CPMV/dendron hybrids in order to improve the drug loading capacity of the nanocarrier. Overall, we demonstrated effective elimination of both macrophage and tumor cells at low micromolar concentrations of the photosensitizer when delivered with the CPMV bioconjugate, thereby potentially improving melanoma treatment.

Anti-atherogenic effect of trivalent chromium-loaded CPMV nanoparticles in human aortic smooth muscle cells under hyperglycemic conditions in vitro

Atherosclerosis, a major macrovascular complication associated with diabetes, poses a tremendous burden on national health care expenditure. Despite extensive efforts, cost-effective remedies are unknown. Therapies for atherosclerosis are challenged by a lack of targeted drug delivery approaches. Toward this goal, we turn to a biology-derived drug delivery system utilizing nanoparticles formed by the plant virus, Cowpea mosaic virus (CPMV). The aim herein is to investigate the anti-atherogenic potential of the beneficial mineral nutrient, trivalent chromium, loaded CPMV nanoparticles in human aortic smooth muscle cells (HASMC) under hyperglycemic conditions. A non-covalent loading protocol is established yielding CrCl3-loaded CPMV (CPMV-Cr) carrying 2000 drug molecules per particle. Using immunofluorescence microscopy, we show that CPMV-Cr is readily taken up by HASMC in vitro. In glucose (25 mM)-stimulated cells, 100 nM CPMV-Cr inhibits HASMC proliferation concomitant to attenuated proliferating cell nuclear antigen (PCNA, proliferation marker) expression. This is accompanied by attenuation in high glucose-induced phospho-p38 and pAkt expression. Moreover, CPMV-Cr inhibits the expression of pro-inflammatory cytokines, transforming growth factor-β (TGF-β) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), in glucose-stimulated HASMCs. Finally glucose-stimulated lipid uptake is remarkably abrogated by CPMV-Cr, revealed by Oil Red O staining. Together, these data provide key cellular evidence for an atheroprotective effect of CPMV-Cr in vascular smooth muscle cells (VSMC) under hyperglycemic conditions that may promote novel therapeutic ventures for diabetic atherosclerosis.

Development of virus-like particles for diagnostic and prophylactic biomedical applications

As ordered nanoscale architectures, viruses and virus-like particles (VLPs) remain unsurpassed by synthetic strategies to produce uniform and symmetric nanoparticles. Maintaining or mimicking the symmetry of pathogenic viruses, VLPs offer a ready platform for facilitating recognition, uptake, and processing by the immune system. An emerging understanding of how viruses interact with the immune system offers a means of precisely designing nanoparticles for biomedical use, both with respect to the structure of the particle as well as their ability to stimulate the immune system. Here we discuss recent advances by our group toward two parallel and complementary applications of VLPs, derived primarily from plants, bacteriophage, and nonviral sources, in biomedicine: diagnostic imaging and rational vaccine design. First we discuss advances in increasing VLP payloads of gadolinium magnetic resonance imaging (MRI) contrast agent as well as controlling the characteristics of individual gadolinium containing molecules to increase efficacy. In order to better understand the in vivo potential of VLP constructs, we then discuss the interface of protein-cages and the immune system beginning with the nonspecific innate immune system stimulation and continuing into the use of nonpathogenic VLPs as scaffolds for specific antigen presentation and control of the immune response.

Interface of physics and biology: engineering virus-based nanoparticles for biophotonics

Virus-based nanoparticles (VNPs) have been used for a wide range of applications, spanning basic materials science and translational medicine. Their propensity to self-assemble into precise structures that offer a three-dimensional scaffold for functionalization has led to their use as optical contrast agents and related biophotonics applications. A number of fluorescently labeled platforms have been developed and their utility in optical imaging demonstrated, yet their optical properties have not been investigated in detail. In this study, two VNPs of varying architectures were compared side-by-side to determine the impact of dye density, dye localization, conjugation chemistry, and microenvironment on the optical properties of the probes. Dyes were attached to icosahedral cowpea mosaic virus (CPMV) and rod-shaped tobacco mosaic virus (TMV) through a range of chemistries to target particular side chains displayed at specific locations around the virus. The fluorescence intensity and lifetime of the particles were determined, first using photochemical experiments on the benchtop, and second in imaging experiments using tissue culture experiments. The virus-based optical probes were found to be extraordinarily robust under ultrashort, pulsed laser light conditions with a significant amount of excitation energy, maintaining structural and chemical stability. The most effective fluorescence output was achieved through dye placement at optimized densities coupled to the exterior surface avoiding conjugated ring systems. Lifetime measurements indicate that fluorescence output depends not only on spacing the fluorophores, but also on dimer stacking and configurational changes leading to radiationless relaxation—and these processes are related to the conjugation chemistry and nanoparticle shape. For biological applications, the particles were also examined in tissue culture, from which it was found that the optical properties differed from those found on the benchtop due to effects from cellular processes and uptake kinetics. Data indicate that fluorescent cargos are released in the endolysosomal compartment of the cell targeted by the virus-based optical probes. These studies provide insight into the optical properties and fates of fluorescent proteinaceous imaging probes. The cellular release of cargo has implications not only for virus-based optical probes, but also for drug delivery and release systems.

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

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

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

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

Differential uptake of chemically modified cowpea mosaic virus nanoparticles in macrophage subpopulations present in inflammatory and tumor microenvironments

There remains a tremendous need to develop targeted therapeutics that can both image and localize the toxic effects of chemotherapeutics and antagonists on diseased tissue while reducing adverse systemic effects. These needs have fostered the development of a nanotechnology-based approach that can combine targeting and toxicity potential. In this study, CPMV nanoparticles were chemically modified with the dye Alexa Flour 488 and were also tandemly modified with PEG1000 followed by AF488; and the derivatized nanoparticles were subsequently added to macrophages stimulated with either LPS (M1) or IL-4 (M2). Previously published studies have shown that M1/M2 macrophages are both present in an inflammatory microenvironment (such as a tumor microenvironment and atherosclerosis) and play opposing yet balancing roles; M2 macrophages have a delayed and progressive onset in the tumor microenvironment (concomitant with an immunosuppression of M1 macrophages). In this study, we show higher uptake of CPMV-AF488 and CPMV-PEG-AF488 by M2 macrophages compared to M1 macrophages. M1 macrophages showed no uptake of CPMV-PEG-AF488. More specifically, M2 macrophages are known to be up-regulated in early atherosclerosis plaque. Indeed, previous work showed that M2 macrophages in plaque also correlate with CPMV internalization. These studies emphasize the potential effectiveness of CPMV as a tailored vehicle for targeting tumor macrophages involved in cancer metastasis or vascular inflammation and further highlight the potential of CPMV in targeted therapeutics against other diseases.

Endocytic uptake pathways utilized by CPMV nanoparticles

Cowpea mosaic virus (CPMV) has been used as a nanoparticle platform for biomedical applications including vaccine development, in vivo vascular imaging, and tissue-targeted delivery. A better understanding of the mechanisms of CPMV targeting and cell internalization would enable enhanced targeting and more effective delivery. Previous studies showed that, following binding and internalization by mammalian cells, CPMV localizes in a perinuclear late-endosome compartment where it remains for as long as several days. To further investigate endocytic trafficking of CPMV within the cell, we used multiple approaches including pharmacologic inhibition of pathways and colocalization with endocytic vesicle compartments. CPMV internalization was clathrin-independent and utilized a combination of caveolar endocytosis and macropinocytosis pathways for entry. CPMV particles colocalized with Rab5(+) early endosomes to traffic ultimately to a lysosomal compartment. These studies facilitate the further development of effective intracellular drug-delivery strategies using CPMV.

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.

Interaction of cowpea mosaic virus nanoparticles with surface vimentin and inflammatory cells in atherosclerotic lesions

AIMS

Detection of atherosclerosis has generally been limited to the late stages of development, after cardiovascular symptoms present or a clinical event occurs. One possibility for early detection is the use of functionalized nanoparticles. The aim of this study was the early imaging of atherosclerosis using nanoparticles with a natural affinity for inflammatory cells in the lesion.

MATERIALS & METHODS

We investigated uptake of cowpea mosaic virus by macrophages and foam cells in vitro and correlated this with vimentin expression. We also examined the ability of cowpea mosaic virus to interact with atherosclerotic lesions in a murine model of atherosclerosis.

RESULTS & CONCLUSION

We found that uptake of cowpea mosaic virus is increased in areas of atherosclerotic lesion. This correlated with increased surface vimentin in the lesion compared with nonlesion vasculature. In conclusion, cowpea mosaic virus and its vimentin-binding region holds potential for use as a targeting ligand for early atherosclerotic lesions, and as a probe for detecting upregulation of surface vimentin during inflammation.

Intravital imaging of human prostate cancer using viral nanoparticles targeted to gastrin-releasing Peptide receptors

Multivalent nanoparticles have several key advantages in terms of solubility, binding avidity, and uptake, making them particularly well suited to molecular imaging applications. Herein is reported the stepwise synthesis and characterization of NIR viral nanoparticles targeted to gastrin-releasing peptide receptors that are over-expressed in human prostate cancers. The pan-bombesin analogue, [β-Ala11, Phe13, Nle14]bombesin-(7-14), is conjugated to cowpea mosaic virus particles functionalized with an NIR dye (Alexa Fluor 647) and polyethylene glycol (PEG) using the copper(I)-catalyzed azide-alkyne cycloaddition reaction. Targeting and uptake in human PC-3 prostate cells is demonstrated in vitro. Tumor homing is observed using human prostate tumor xenografts on the chicken chorioallantoic membrane model using intravital imaging. Further development of this viral nanoparticle platform may open the door to potential clinical noninvasive molecular imaging strategies.

Optical nano-constructs composed of genome-depleted brome mosaic virus doped with a near infrared chromophore for potential biomedical applications

We have engineered an optical nanoconstruct composed of genome-depleted brome mosaic virus doped with indocyanine green (ICG), an FDA-approved near-infrared (NIR) chromophore. Constructs are highly monodispersed with standard deviation of ±3.8 nm from a mean diameter of 24.3 nm. They are physically stable and exhibit a high degree of optical stability at physiological temperature (37 °C). Using human bronchial epithelial cells, we demonstrate the effectiveness of the constructs for intracellular optical imaging in vitro, with greater than 90% cell viability after 3 h of incubation. These constructs may serve as a potentially nontoxic and multifunctional nanoplatform for site-specific deep-tissue optical imaging, and therapy of disease.

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

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

PEGylated viral nanoparticles for biomedicine: the impact of PEG chain length on VNP cell interactions in vitro and ex vivo

PEGylation is an effective strategy for reducing biospecific interactions for pharmaceuticals. The plant virus Cowpea mosaic virus (CPMV) has been studied for potential nanobiomedical applications by virtue of its natural interactions with mammalian endothelial cells. To investigate the degree of PEGylation required to retarget CPMV-based formulations to other destinations, two CPMV-PEG formulations, CPMV-PEG1000 (P1) and CPMV-PEG2000 (P2) were tested. Modeling suggested that the PEG chains were displayed as flattened mushrooms on the particle with an estimated surface grafting area of 0.53% for P1 and 0.83% for P2. Only the P2 formulation effectively shielded the particles from interacting with cells or tissues, suggesting that either key interacting regions on the particle surface were blocked or that a sufficient hydration shell had been generated to inhibit cellular interactions. The large CPMV surface area available after PEGylation allows further attachment of imaging and therapeutic molecules to the particle to generate multifunctionality.

Supramolecular protein cage composite MR contrast agents with extremely efficient relaxivity properties

A DTPA-Gd containing polymer was grown in the interior of a heat shock protein cage resulting in T(1) particle relaxivities of 4200 mM(-1) sec(-1) for the 12 nm particle. Relaxivity parameters were determined, and this analysis suggests that the rotational correlation time has been optimized while the water exchange lifetime is longer than optimal. This synthetic approach holds much promise for the development of next generation contrast agents and this report will aid in their design.

Interaction of Cowpea mosaic virus (CPMV) nanoparticles with antigen presenting cells in vitro and in vivo

Background

Plant viruses such as Cowpea mosaic virus (CPMV) are increasingly being developed for applications in nanobiotechnology including vaccine development because of their potential for producing large quantities of antigenic material in plant hosts. In order to improve efficacy of viral nanoparticles in these types of roles, an investigation of the individual cell types that interact with the particles is critical. In particular, it is important to understand the interactions of a potential vaccine with antigen presenting cells (APCs) of the immune system. CPMV was previously shown to interact with vimentin displayed on cell surfaces to mediate cell entry, but the expression of surface vimentin on APCs has not been characterized.

Methodology

The binding and internalization of CPMV by several populations of APCs was investigated both in vitro and in vivo by flow cytometry and fluorescence confocal microscopy. The association of the particles with mouse gastrointestinal epithelium and Peyer's patches was also examined by confocal microscopy. The expression of surface vimentin on APCs was also measured.

Conclusions

We found that CPMV is bound and internalized by subsets of several populations of APCs both in vitro and in vivo following intravenous, intraperitoneal, and oral administration, and also by cells isolated from the Peyer's patch following gastrointestinal delivery. Surface vimentin was also expressed on APC populations that could internalize CPMV. These experiments demonstrate that APCs capture CPMV particles in vivo, and that further tuning the interaction with surface vimentin may facilitate increased uptake by APCs and priming of antibody responses. These studies also indicate that CPMV particles likely access the systemic circulation following oral delivery via the Peyer's patch.

Endothelial targeting of cowpea mosaic virus (CPMV) via surface vimentin

Cowpea mosaic virus (CPMV) is a plant comovirus in the picornavirus superfamily, and is used for a wide variety of biomedical and material science applications. Although its replication is restricted to plants, CPMV binds to and enters mammalian cells, including endothelial cells and particularly tumor neovascular endothelium in vivo. This natural capacity has lead to the use of CPMV as a sensor for intravital imaging of vascular development. Binding of CPMV to endothelial cells occurs via interaction with a 54 kD cell-surface protein, but this protein has not previously been identified. Here we identify the CPMV binding protein as a cell-surface form of the intermediate filament vimentin. The CPMV-vimentin interaction was established using proteomic screens and confirmed by direct interaction of CPMV with purified vimentin, as well as inhibition in a vimentin-knockout cell line. Vimentin and CPMV were also co-localized in vascular endothelium of mouse and rat in vivo. Together these studies indicate that surface vimentin mediates binding and may lead to internalization of CPMV in vivo, establishing surface vimentin as an important vascular endothelial ligand for nanoparticle targeting to tumors. These results also establish vimentin as a ligand for picornaviruses in both the plant and animal kingdoms of life. Since bacterial pathogens and several other classes of viruses also bind to surface vimentin, these studies suggest a common role for surface vimentin in pathogen transmission.

Viral nanoparticles associate with regions of inflammation and blood brain barrier disruption during CNS infection

Targeted treatment of inflammatory diseases of the central nervous system (CNS) remains problematic due to the complex pathogenesis of these disorders and difficulty in drug delivery. The plant virus, cowpea mosaic virus (CPMV), has recently been explored as a nanoparticle delivery system for therapeutics targeting a number of diseases including cancer and neurodegeneration. To understand the biodistribution of CPMV in the CNS, we examined CPMV uptake during infection of mice with neurotropic mouse hepatitis virus (MHV). CPMV localized mainly to the CNS endothelium in areas that contained an intact blood brain barrier. However, in inflammatory lesions containing macrophage/microglial cell infiltration and IgG, CPMV could be detected in the brain parenchyma. Furthermore, CPMV showed rapid internalization in an in vitro model of the BBB. These results suggest that CPMV particles could be used as a vehicle to deliver therapeutics to the damaged CNS during neurodegenerative and infectious diseases of the CNS.

Chemical addressability of ultraviolet-inactivated viral nanoparticles (VNPs)

Background

Cowpea Mosaic Virus (CPMV) is increasingly being used as a nanoparticle platform for multivalent display of molecules via chemical bioconjugation to the capsid surface. A growing variety of applications have employed the CPMV multivalent display technology including nanoblock chemistry, in vivo imaging, and materials science. CPMV nanoparticles can be inexpensively produced from experimentally infected cowpea plants at high yields and are extremely stable. Although CPMV has not been shown to replicate in mammalian cells, uptake in mammalian cells does occur in vitro and in vivo. Thus, inactivation of the virus RNA genome is important for biosafety considerations, however the surface characteristics and chemical reactivity of the particles must be maintained in order to preserve chemical and structural functionality.

Methodology/Principal Findings

Short wave (254 nm) UV irradiation was used to crosslink the RNA genome within intact particles. Lower doses of UV previously reported to inactivate CPMV infectivity inhibited symptoms on inoculated leaves but did not prohibit systemic virus spread in plants, whereas higher doses caused aggregation of the particles and an increase in chemical reactivity further indicating broken particles. Intermediate doses of 2.0–2.5 J/cm² were shown to maintain particle structure and chemical reactivity, and cellular binding properties were similar to CPMV-WT.

Conclusions

These studies demonstrate that it is possible to inactivate CPMV infectivity while maintaining particle structure and function, thus paving the way for further development of CPMV nanoparticles for in vivo applications.

Layer-by-layer assembly of viral capsid for cell adhesion

Cowpea mosaic virus (CPMV)-based thin films are biologically active for cell culture. Using layer-by-layer assembly of CPMV and poly(diallyldimethylammonium chloride), quantitatively scalable biomolecular surfaces were constructed, which were well characterized using quartz crystal microbalance, UV-vis and atomic force microscopy. The surface coverage of CPMV nanoparticles depended on the adsorption time and pH of the virus solution, with a greater amount of CPMV adsorption occurring near its isoelectric point. It was found that the adhesion and proliferation of NIH-3T3 fibroblasts can be controlled by the coverage of viral particles using this multilayer technique.

Zeta potential: a surface electrical characteristic to probe the interaction of nanoparticles with normal and cancer human breast epithelial cells

We demonstrate the use of surface Zeta potential measurements as a new tool to investigate the interactions of iron oxide nanoparticles and cowpea mosaic virus (CPMV) nanoparticles with human normal breast epithelial cells (MCF10A) and cancer breast epithelial cells (MCF7) respectively. A substantial understanding in the interaction of nanoparticles with normal and cancer cells in vitro will enable the capabilities of improving diagnostic and treatment methods in cancer research, such as imaging and targeted drug delivery. A theoretical Zeta potential model is first established to show the effects of binding process and internalization process during the nanoparticle uptake by cells and the possible trends of Zeta potential change is predicted for different cell endocytosis capacities. The corresponding changes of total surface charge of cells in the form of Zeta potential measurements were then reported after incubated respectively with iron oxide nanoparticles and CPMV nanoparticles. As observed, after MCF7 and MCF10A cells were incubated respectively with two types of nanoparticles, the significant differences in their surface charge change indicate the potential role of Zeta potential as a valuable biological signature in studying the cellular interaction of nanoparticles, as well as specific cell functionality.

Folic acid-mediated targeting of cowpea mosaic virus particles to tumor cells

Cowpea mosaic virus (CPMV) is a well-characterized nanoparticle that has been used for a variety of nanobiotechnology applications. CPMV interacts with several mammalian cell lines and tissues in vivo. To overcome natural CPMV targeting and redirect CPMV particles to cells of interest, we attached a folic acid-PEG conjugate by using the copper-catalyzed azide-alkyne cycloaddition reaction. PEGylation of CPMV completely eliminated background binding of the virus to tumor cells. The PEG-folate moiety allowed CPMV-specific recognition of tumor cells bearing the folate receptor. In addition, by testing CPMV formulations with different amounts of the PEG-FA moiety displayed on the surface, we show that higher-density loading of targeting ligands on CPMV may not be necessary for efficient targeting to tumor cells. These studies help to define the requirements for efficiently targeting nanoparticles and protein cages to tumors.

Plant viruses as biotemplates for materials and their use in nanotechnology

In recent years, plant virus capsids, the protein shells that form the surface of a typical plant virus particle, have emerged as useful biotemplates for material synthesis. All virus capsids are assembled from virus-coded protein subunits. Many plant viruses assemble capsids with precise 3D structures providing nanoscale architectures that are highly homogeneous and can be produced in large quantities. Capsids are amenable to both genetic and chemical modifications allowing new functions to be incorporated into their structure by design. The three capsid surfaces, the interior surface, the exterior surface, or the interface between coat protein subunits, can be independently functionalized to produce multifunctional biotemplates. In this review, we examine the recent advances in using plant virus capsids as biotemplates for nanomaterials and their potential for applications in nanotechnology, especially medicine.

Bio-distribution, toxicity and pathology of cowpea mosaic virus nanoparticles in vivo

Virus-based nanoparticles (VNPs) from a variety of sources are being developed for biomedical and nanotechnology applications that include tissue targeting and drug delivery. However, the fate of most of those particles in vivo has not been investigated. Cowpea mosaic virus (CPMV), a plant comovirus, has been found to be amenable to the attachment of a variety of molecules to its coat protein, as well as to modification of the coat protein sequence by genetic means. We report here the results of studies of the bio-distribution, toxicology, and pathology of CPMV in mice. Plasma clearance and tissue biodistribution were measured using CPMV particles derivatized with lanthanide metal complexes. CPMV particles were cleared rapidly from plasma, falling to undetectable levels within 20 min. By 30 min the majority of the injected VNPs were trapped in the liver and to a lesser extent the spleen with undetectable amounts in other tissues. At doses of 1 mg, 10 mg and 100 mg per kg body weight, no toxicity was noted and the mice appeared to be normal. Hematology was essentially normal, although with the highest dose examined, the mice were somewhat leukopenic with relative decreases in both neutrophils and lymphocytes. Histological examination of the spleen showed cellular infiltration, which upon flow cytometry analyses revealed elevated B lymphocytes on the first day following virus administration that subsequently subsided. Microscopic evaluation of various other tissues revealed a lack of apparent tissue degeneration or necrosis. Overall, CPMV appears to be a safe and non-toxic platform for in vivo biomedical applications.