Chemotherapy pro-drug activation by biocatalytic virus-like nanoparticles containing cytochrome P450

Advancements in Functional Nanomaterials Inspired by Viral Particles

Virus-like particles (VLPs) are nanostructures composed of one or more structural proteins, exhibiting stable and symmetrical structures. Their precise compositions and dimensions provide versatile opportunities for modifications, enhancing their functionality. Consequently, VLP-based nanomaterials have gained widespread adoption across diverse domains. This review focuses on three key aspects: the mechanisms of viral capsid protein self-assembly into VLPs, design methods for constructing multifunctional VLPs, and strategies for synthesizing multidimensional nanomaterials using VLPs. It provides a comprehensive overview of the advancements in virus-inspired functional nanomaterials, encompassing VLP assembly, functionalization, and the synthesis of multidimensional nanomaterials. Additionally, this review explores future directions, opportunities, and challenges in the field of VLP-based nanomaterials, aiming to shed light on potential advancements and prospects in this exciting area of research.

Plant Virus-Like Particles for RNA Delivery

Plant viruses such as brome mosaic virus and cowpea chlorotic mottle virus are effectively purified through PEG precipitation and sucrose cushion ultracentrifugation. Increasing ionic strength and an alkaline pH cause the viruses to swell and disassemble into coat protein subunits. The coat proteins can be reassembled into stable virus-like particles (VLPs) that carry anionic molecules at low ionic strength and through two-step dialysis from neutral pH to acidic buffer. VLPs have been extensively studied due to their ability to protect and deliver cargo, particularly RNA, while avoiding degradation under physiological conditions. Furthermore, chemical functionalization of the surface of VLPs allows for the targeted drug delivery. VLPs derived from plants have demonstrated great potential in nanomedicine by offering a versatile platform for drug delivery, imaging, and therapeutic applications.

Overcoming biological barriers by virus-like drug particles for drug delivery

Virus-like particles (VLPs) have natural structural antigens similar to those found in viruses, making them valuable in vaccine immunization. Furthermore, VLPs have demonstrated significant potential in drug delivery, and emerged as promising vectors for transporting chemical drug, genetic drug, peptide/protein, and even nanoparticle drug. With virus-like permeability and strong retention, they can effectively target specific organs, tissues or cells, facilitating efficient intracellular drug release. Further modifications allow VLPs to transfer across various physiological barriers, thus acting the purpose of efficient drug delivery and accurate therapy. This article provides an overview of VLPs, covering their structural classifications, deliverable drugs, potential physiological barriers in drug delivery, strategies for overcoming these barriers, and future prospects.

Virus-like particles nanoreactors: from catalysis towards bio-applications

Virus-like particles (VLPs) are self-assembled supramolecular structures found in nature, often used for compartmentalization. Exploiting their inherent properties, including precise nanoscale structures, monodispersity, and high stability, these architectures have been widely used as nanocarriers to protect or enrich catalysts, facilitating catalytic reactions and avoiding interference from the bulk solutions. In this review, we summarize the current progress of virus-like particles (VLPs)-based nanoreactors. First, we briefly introduce the physicochemical properties of the most commonly used virus particles to understand their roles in catalytic reactions beyond the confined space. Next, we summarize the self-assembly of nanoreactors forming higher-order hierarchical structures, highlighting the emerging field of nanoreactors as artificial organelles and their potential biomedical applications. Finally, we discuss the current findings and future perspectives of VLPs-based nanoreactors.

Viral protein-based nanoparticles (part 2): Pharmaceutical applications

Viral protein nanoparticles (ViP NPs) such as virus-like particles and virosomes are structures halfway between viruses and synthetic nanoparticles. The biological nature of ViP NPs endows them with the biocompatibility, biodegradability, and functional properties that many synthetic nanoparticles lack. At the same time, the absence of a viral genome avoids the safety concerns of viruses. Such characteristics of ViP NPs offer a myriad of opportunities for theirapplication at several points across disease development: from prophylaxis to diagnosis and treatment. ViP NPs present remarkable immunostimulant properties, and thus the vaccination field has benefited the most from these platforms capable of overcoming the limitations of both traditional and subunit vaccines. This was reflected in the marketing authorization of several VLP- and virosome-based vaccines. Besides, ViP NPs inherit the ability of viruses to deliver their cargo to target cells. Because of that, ViP NPs are promising candidates as vectors for drug and gene delivery, and for diagnostic applications. In this review, we analyze the pharmaceutical applications of ViP NPs, describing the products that are commercially available or under clinical evaluation, but also the advances that scientists are making toward the implementation of ViP NPs in other areas of major pharmaceutical interest.

A Novel Formulation of Asparaginase Encapsulated into Virus-like Particles of Brome Mosaic Virus: In Vitro and In Vivo Evidence

The interest in plant-derived virus-like particles (pVLPs) for the design of a new generation of nanocarriers is based on their lack of infection for humans, their immunostimulatory properties to fight cancer cells, and their capability to contain and release cargo molecules. Asparaginase (ASNase) is an FDA-approved drug to treat acute lymphoblastic leukemia (LLA); however, it exhibits high immunogenicity which often leads to discontinuation of treatment. In previous work, we encapsulated ASNase into bacteriophage P22-based VLPs through genetic-directed design to form the ASNase-P22 nanobioreactors. In this work, a commercial ASNase was encapsulated into brome mosaic virus-like particles (BMV-VLPs) to form stable ASNase-BMV nanobioreactors. According to our results, we observed that ASNase-BMV nanobioreactors had similar cytotoxicity against MOLT-4 and Reh cells as the commercial drug. In vivo assays showed a higher specific anti-ASNase IgG response in BALB/c mice immunized with ASNase encapsulated into BMV-VLPs compared with those immunized with free ASNase. Nevertheless, we also detected a high and specific IgG response against BMV capsids on both ASNase-filled capsids (ASNase-BMV) and empty BMV capsids. Despite the fact that our in vivo studies showed that the BMV-VLPs stimulate the immune response either empty or with cargo proteins, the specific cytotoxicity against leukemic cells allows us to propose ASNase-BMV as a potential novel formulation for LLA treatment where in vitro and in vivo evidence of functionality is provided.

Viral protein nanoparticles (Part 1): Pharmaceutical characteristics

Viral protein nanoparticles fill the gap between viruses and synthetic nanoparticles. Combining advantageous properties of both systems, they have revolutionized pharmaceutical research. Virus-like particles are characterized by a structure identical to viruses but lacking genetic material. Another type of viral protein nanoparticles, virosomes, are similar to liposomes but include viral spike proteins. Both systems are effective and safe vaccine candidates capable of overcoming the disadvantages of both traditional and subunit vaccines. Besides, their particulate structure, biocompatibility, and biodegradability make them good candidates as vectors for drug and gene delivery, and for diagnostic applications. In this review, we analyze viral protein nanoparticles from a pharmaceutical perspective and examine current research focused on their development process, from production to administration. Advances in synthesis, modification and formulation of viral protein nanoparticles are critical so that large-scale production of viral protein nanoparticle products becomes viable and affordable, which ultimately will increase their market penetration in the future. We will discuss their expression systems, modification strategies, formulation, biopharmaceutical properties, and biocompatibility.

Manufacturing of non-viral protein nanocages for biotechnological and biomedical applications

Protein nanocages are highly ordered nanometer scale architectures, which are typically formed by homo- or hetero-self-assembly of multiple monomers into symmetric structures of different size and shape. The intrinsic characteristics of protein nanocages make them very attractive and promising as a biological nanomaterial. These include, among others, a high surface/volume ratio, multi-functionality, ease to modify or manipulate genetically or chemically, high stability, mono-dispersity, and biocompatibility. Since the beginning of the investigation into protein nanocages, several applications were conceived in a variety of areas such as drug delivery, vaccine development, bioimaging, biomineralization, nanomaterial synthesis and biocatalysis. The ability to generate large amounts of pure and well-folded protein assemblies is one of the keys to transform nanocages into clinically valuable products and move biomedical applications forward. This calls for the development of more efficient biomanufacturing processes and for the setting up of analytical techniques adequate for the quality control and characterization of the biological function and structure of nanocages. This review concisely covers and overviews the progress made since the emergence of protein nanocages as a new, next-generation class of biologics. A brief outline of non-viral protein nanocages is followed by a presentation of their main applications in the areas of bioengineering, biotechnology, and biomedicine. Afterwards, we focus on a description of the current processes used in the manufacturing of protein nanocages with particular emphasis on the most relevant aspects of production and purification. The state-of-the-art on current characterization techniques is then described and future alternative or complementary approaches in development are also discussed. Finally, a critical analysis of the limitations and drawbacks of the current manufacturing strategies is presented, alongside with the identification of the major challenges and bottlenecks.

Immobilized nanoparticles-mediated enzyme therapy; promising way into clinical development

Enzyme (Enz)-mediated therapy indicated a remarkable effect in the treatment of many human cancers and diseases with an insight into clinical phases. Because of insufficient immobilization (Imb) approach and ineffective carrier, Enz therapeutic exhibits low biological efficacy and bio-physicochemical stability. Although efforts have been made to remove the limitations mentioned in clinical trials, efficient Imb-destabilization and modification of nanoparticles (NPs) remain challenging. NP internalization through insufficient membrane permeability, precise endosomal escape, and endonuclease protection following release are the primary development approaches. In recent years, innovative manipulation of the material for Enz immobilization (EI) fabrication and NP preparation has enabled nanomaterial platforms to improve Enz therapeutic outcomes and provide low-diverse clinical applications. In this review article, we examine recent advances in EI approaches and emerging views and explore the impact of Enz-mediated NPs on clinical therapeutic outcomes with at least diverse effects.

P22-Based Nanovaccines against Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is an important causative agent of diarrhea in humans that causes outbreaks worldwide. Efforts have been made to mitigate the morbidity and mortality caused by these microorganisms; however, the global incidence is still high, causing hundreds of deaths per year. Several vaccine candidates have been evaluated that demonstrate some stability and therapeutic potential but have limited overarching effect. Virus-like particles have been used successfully as nanocontainers for the targeted delivery of drugs, proteins, or nucleic acids. In this study, phage P22 nanocontainers were used as a carrier for the highly antigenic T3SS structural protein EscC that is conserved between EHEC and other enteropathogenic bacteria. We were able to stably incorporate the EscC protein into P22 nanocontainers. The EscC-P22 particles were used to intranasally inoculate mice, which generated specific antibodies against EscC. These antibodies increased the phagocytic activity of murine macrophages infected with EHEC in vitro and reduced bacterial adherence to Caco-2 epithelial cells in vitro, illustrating their functionality. The EscC-P22-based particles are a potential nanovaccine candidate for immunization against EHEC O157:H7 infections. IMPORTANCE This study describes the initial attempt to use P22 viral-like particles as nanocontainers expressing enterohemorrhagic Escherichia coli (EHEC) proteins that are immunogenic and could be used as effective vaccines against EHEC infections.

Efficient Purification of Cowpea Chlorotic Mottle Virus by a Novel Peptide Aptamer

The cowpea chlorotic mottle virus (CCMV) is a plant virus explored as a nanotechnological platform. The robust self-assembly mechanism of its capsid protein allows for drug encapsulation and targeted delivery. Additionally, the capsid nanoparticle can be used as a programmable platform to display different molecular moieties. In view of future applications, efficient production and purification of plant viruses are key steps. In established protocols, the need for ultracentrifugation is a significant limitation due to cost, difficult scalability, and safety issues. In addition, the purity of the final virus isolate often remains unclear. Here, an advanced protocol for the purification of the CCMV from infected plant tissue was developed, focusing on efficiency, economy, and final purity. The protocol involves precipitation with PEG 8000, followed by affinity extraction using a novel peptide aptamer. The efficiency of the protocol was validated using size exclusion chromatography, MALDI-TOF mass spectrometry, reversed-phase HPLC, and sandwich immunoassay. Furthermore, it was demonstrated that the final eluate of the affinity column is of exceptional purity (98.4%) determined by HPLC and detection at 220 nm. The scale-up of our proposed method seems to be straightforward, which opens the way to the large-scale production of such nanomaterials. This highly improved protocol may facilitate the use and implementation of plant viruses as nanotechnological platforms for in vitro and in vivo applications.

Virus-like nanoparticles as enzyme carriers for Enzyme Replacement Therapy (ERT)

Enzyme replacement therapy (ERT) has been used to treat a few of the many existing diseases which are originated from the lack of, or low enzymatic activity. Exogenous enzymes are administered to contend with the enzymatic activity deficiency. Enzymatic nanoreactors based on the enzyme encapsulation inside of virus-like particles (VLPs) appear as an interesting alternative for ERT. VLPs are excellent delivery vehicles for therapeutic enzymes as they are biodegradable, uniformly organized, and porous nanostructures that transport and could protect the biocatalyst from the external environment without much affecting the bioactivity. Consequently, significant efforts have been made in the production processes of virus-based enzymatic nanoreactors and their functionalization, which are critically reviewed. The use of virus-based enzymatic nanoreactors for the treatment of lysosomal storage diseases such as Gaucher, Fabry, and Pompe diseases, as well as potential therapies for galactosemia, and Hurler and Hunter syndromes are discussed.

The Plant Viruses and Molecular Farming: How Beneficial They Might Be for Human and Animal Health?

Plant viruses have traditionally been studied as pathogens in the context of understanding the molecular and cellular mechanisms of a particular disease affecting crops. In recent years, viruses have emerged as a new alternative for producing biological nanomaterials and chimeric vaccines. Plant viruses were also used to generate highly efficient expression vectors, revolutionizing plant molecular farming (PMF). Several biological products, including recombinant vaccines, monoclonal antibodies, diagnostic reagents, and other pharmaceutical products produced in plants, have passed their clinical trials and are in their market implementation stage. PMF offers opportunities for fast, adaptive, and low-cost technology to meet ever-growing and critical global health needs. In this review, we summarized the advancements in the virus-like particles-based (VLPs-based) nanotechnologies and the role they played in the production of advanced vaccines, drugs, diagnostic bio-nanomaterials, and other bioactive cargos. We also highlighted various applications and advantages plant-produced vaccines have and their relevance for treating human and animal illnesses. Furthermore, we summarized the plant-based biologics that have passed through clinical trials, the unique challenges they faced, and the challenges they will face to qualify, become available, and succeed on the market.

Protein cargo encapsulation by virus‐like particles: Strategies and applications

Viruses and the recombinant protein cages assembled from their structural proteins, known as virus-like particles (VLPs), have gained wide interest as tools in biotechnology and nanotechnology. Detailed structural information and their amenability to genetic and chemical modification make them attractive systems for further engineering. This review describes the range of non-enveloped viruses that have been co-opted for heterologous protein cargo encapsulation and the strategies that have been developed to drive encapsulation. Spherical capsids of a range of sizes have been used as platforms for protein cargo encapsulation. Various approaches, based on native and non-native interactions between the cargo proteins and inner surface of VLP capsids, have been devised to drive encapsulation. Here, we outline the evolution of these approaches, discussing their benefits and limitations. Like the viruses from which they are derived, VLPs are of interest in both biomedical and materials applications. The encapsulation of protein cargo inside VLPs leads to numerous uses in both fundamental and applied biocatalysis and biomedicine, some of which are discussed herein. The applied science of protein-encapsulating VLPs is emerging as a research field with great potential. Developments in loading control, higher order assembly, and capsid optimization are poised to realize this potential in the near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Targeted Enzymatic VLP-Nanoreactors with β-Glucocerebrosidase Activity as Potential Enzyme Replacement Therapy for Gaucher's Disease

Gaucher disease is a genetic disorder and the most common lysosomal disease caused by the deficiency of enzyme β-glucocerebrosidase (GCase). Although enzyme replacement therapy (ERT) is successfully applied using mannose-exposed conjugated glucocerebrosidase, the lower stability of the enzyme in blood demands periodic intravenous administration that adds to the high cost of treatment. In this work, the enzyme β-glucocerebrosidase was encapsulated inside virus-like nanoparticles (VLPs) from brome mosaic virus (BMV), and their surface was functionalized with mannose groups for targeting to macrophages. The VLP nanoreactors showed significant GCase catalytic activity. Moreover, the Michaelis-Menten constants for the free GCase enzyme (KM =0.29 mM) and the functionalized nanoreactors (KM =0.32 mM) were similar even after chemical modification. Importantly, the stability of enzymes under physiological conditions (pH 7.4, 37 °C) was enhanced by ≈11-fold after encapsulation; this is beneficial for obtaining a higher blood circulation half-life, which may decrease the cost of therapy by reducing the requirement of multiple intravenous injections. Finally, the mannose receptor targeted enzymatic nanoreactors showed enhanced internalization into macrophage cells. Thus, the catalytic activity and cell targeting suggest the potential of these nanoreactors in ERT of Gaucher's disease.

A comprehensive review and meta-analysis of recent advances in biotechnology for plant virus research and significant accomplishments in human health and the pharmaceutical industry

Secondary metabolites made by plants and used through their metabolic routes are today's most reliable and cost-effective way to make pharmaceuticals and improve health. The concept of genetic engineering is used for molecular pharming. As more people use plants as sources of nanotechnology systems, they are adding to this. These systems are made up of viruses-like particles (VLPs) and virus nanoparticles (VNPs). Due to their superior ability to be used as plant virus expression vectors, plant viruses are becoming more popular in pharmaceuticals. This has opened the door for them to be used in research, such as the production of medicinal peptides, antibodies, and other heterologous protein complexes. This is because biotechnological approaches have been linked with new bioinformatics tools. Because of the rise of high-throughput sequencing (HTS) and next-generation sequencing (NGS) techniques, it has become easier to use metagenomic studies to look for plant virus genomes that could be used in pharmaceutical research. A look at how bioinformatics can be used in pharmaceutical research is also covered in this article. It also talks about plant viruses and how new biotechnological tools and procedures have made progress in the field.

VLP-Based COVID-19 Vaccines: An Adaptable Technology against the Threat of New Variants

Virus-like particles (VLPs) are a versatile, safe, and highly immunogenic vaccine platform. Recently, there are developmental vaccines targeting SARS-CoV-2, the causative agent of COVID-19. The COVID-19 pandemic affected humanity worldwide, bringing out incomputable human and financial losses. The race for better, more efficacious vaccines is happening almost simultaneously as the virus increasingly produces variants of concern (VOCs). The VOCs Alpha, Beta, Gamma, and Delta share common mutations mainly in the spike receptor-binding domain (RBD), demonstrating convergent evolution, associated with increased transmissibility and immune evasion. Thus, the identification and understanding of these mutations is crucial for the production of new, optimized vaccines. The use of a very flexible vaccine platform in COVID-19 vaccine development is an important feature that cannot be ignored. Incorporating the spike protein and its variations into VLP vaccines is a desirable strategy as the morphology and size of VLPs allows for better presentation of several different antigens. Furthermore, VLPs elicit robust humoral and cellular immune responses, which are safe, and have been studied not only against SARS-CoV-2 but against other coronaviruses as well. Here, we describe the recent advances and improvements in vaccine development using VLP technology.

Bioengineering bacterial encapsulin nanocompartments as targeted drug delivery system

The development of Drug Delivery Systems (DDS) has led to increasingly efficient therapies for the treatment and detection of various diseases. DDS use a range of nanoscale delivery platforms produced from polymeric of inorganic materials, such as micelles, and metal and polymeric nanoparticles, but their variant chemical composition make alterations to their size, shape, or structures inherently complex. Genetically encoded protein nanocages are highly promising DDS candidates because of their modular composition, ease of recombinant production in a range of hosts, control over assembly and loading of cargo molecules and biodegradability. One example of naturally occurring nanocompartments are encapsulins, recently discovered bacterial organelles that have been shown to be reprogrammable as nanobioreactors and vaccine candidates. Here we report the design and application of a targeted DDS platform based on the Thermotoga maritima encapsulin reprogrammed to display an antibody mimic protein called Designed Ankyrin repeat protein (DARPin) on the outer surface and to encapsulate a cytotoxic payload. The DARPin9.29 chosen in this study specifically binds to human epidermal growth factor receptor 2 (HER2) on breast cancer cells, as demonstrated in an in vitro cell culture model. The encapsulin-based DDS is assembled in one step in vivo by co-expressing the encapsulin-DARPin9.29 fusion protein with an engineered flavin-binding protein mini-singlet oxygen generator (MiniSOG), from a single plasmid in Escherichia coli. Purified encapsulin-DARPin_miniSOG nanocompartments bind specifically to HER2 positive breast cancer cells and trigger apoptosis, indicating that the system is functional and specific. The DDS is modular and has the potential to form the basis of a multi-receptor targeted system by utilising the DARPin screening libraries, allowing use of new DARPins of known specificities, and through the proven flexibility of the encapsulin cargo loading mechanism, allowing selection of cargo proteins of choice.

Application of Plant Viruses in Biotechnology, Medicine, and Human Health

Plant-based nanotechnology programs using virus-like particles (VLPs) and virus nanoparticles (VNPs) are emerging platforms that are increasingly used for a variety of applications in biotechnology and medicine. Tobacco mosaic virus (TMV) and potato virus X (PVX), by virtue of having high aspect ratios, make ideal platforms for drug delivery. TMV and PVX both possess rod-shaped structures and single-stranded RNA genomes encapsidated by their respective capsid proteins and have shown great promise as drug delivery systems. Cowpea mosaic virus (CPMV) has an icosahedral structure, and thus brings unique benefits as a nanoparticle. The uses of these three plant viruses as either nanostructures or expression vectors for high value pharmaceutical proteins such as vaccines and antibodies are discussed extensively in the following review. In addition, the potential uses of geminiviruses in medical biotechnology are explored. The uses of these expression vectors in plant biotechnology applications are also discussed. Finally, in this review, we project future prospects for plant viruses in the fields of medicine, human health, prophylaxis, and therapy of human diseases.

Innovative Applications of Plant Viruses in Drug Targeting and Molecular Imaging- A Review

BACKGROUND

Nature had already engineered various types of nanoparticles (NPs), especially viruses, which can deliver their cargo to the host/targeted cells. The ability to selectively target specific cells offers a significant advantage over the conventional approach. Numerous organic NPs, including native protein cages, virus-like particles, polymeric saccharides, and liposomes, have been used for the preparation of nanoparticles. Such nanomaterials have demonstrated better performance as well as improved biocompatibility, devoid of side effects, and stable without any deterioration.

OBJECTIVE

This review discusses current clinical and scientific research on naturally occurring nanomaterials. It also illustrates and updates the tailor-made approaches for selective delivery and targeted medications that require a high-affinity interconnection to the targeted cells.

METHODS

A comprehensive search was performed using keywords for viral nanoparticles, viral particles for drug delivery, viral nanoparticles for molecular imaging, theranostics applications of viral nanoparticles and plant viruses in nanomedicine. We searched on Google Scholar, PubMed, Springer, Medline, and Elsevier from 2000 till date and by the bibliographic review of all identified articles.

RESULTS

The findings demonstrated that structures dependent on nanomaterials might have potential applications in diagnostics, cell marking, comparing agents (computed tomography and magnetic resonance imaging), and antimicrobial drugs, as well as drug delivery structures. However, measures should be taken in order to prevent or mitigate, in pharmaceutical or medical applications, the toxic impact or incompatibility of nanoparticle-based structures with biological systems.

CONCLUSION

The review provided an overview of the latest advances in nanotechnology, outlining the difficulties and the advantages of in vivo and in vitro structures that are focused on a specific subset of the natural nanomaterials.

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.

Virus as nanocarrier for drug delivery redefining medical therapeutics - A status report

Over the last two decades, drug delivery systems have evolved at a tremendous rate. Synthetic nanoparticles have played an important role in the design of vaccine and their delivery as many of them have shown improved safety and efficacy over conventional formulations. Nanocarriers formulated by natural, biological building blocks have become an important tool in the field biomedicine. A successful nanocarrier must have certain properties like evading the host immune system, target specificity, cellular entry, escape from endosomes, and ability to release material into the cytoplasm. Some or all of these functions can be performed by viruses making them a suitable candidate for naturally occurring nanocarriers. Moreover, viruses can be made non-infectious and non-replicative without compromising their ability to penetrate cells thus making them useful for a vast spectrum of applications. Currently, various carrier molecules are under different stages of development to become bio-nano capsules. This review covers the advances made in the field of viruses as potential nanocarriers and discusses the related technologies and strategies to target specific cells by using virus inspired nanocarriers. In future, these virus-based nano-formulations will be able to provide solutions towards pressing and emerging infectious diseases.

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.

Camouflaged, activatable and therapeutic tandem bionanoreactors for breast cancer theranosis

The one-pot cascade reaction of naturally occurring enzymes is exciting for highly selective complex reaction and biodegradable approaches. Tamoxifen is the main drug against breast cancer for decades and induces an anticancerous effect upon metabolic activation by cytochrome P450 (CYP450). Herein, bi-enzymatic nanoreactors (NRs) are developed as a multimodality platform for smart action against breast tumors. CYP_BM3 of Bacillus magaterium (CYP) is co-confined with glucose oxidase (GOx) where GOx produces H₂O₂ in the presence of glucose that elicits the CYP-mediated transformation of tamoxifen. The scintillating and mesoporous LaF₃:Tb as nanocarrier showed advantages like a wide range of pore size and positive surface charge for efficient loading of enzyme couple, while the smallest pores were available for substrate/product diffusion. The obtained NRs were camouflaged with human serum albumin (HSA) to overcome premature enzyme leaching and provide active stealth properties. The nanocomposite was characterized for physicochemical properties and glucose-mediated sequential catalysis. The in vitro studies demonstrated the cell internalization of NRs in both ER+ and triple-negative breast cancer cell lines and showed significant cytotoxicity. The developed NRs not only improve the outcomes of endocrine therapy in ER+ cells but also synergistically act with oxidation therapy for enhanced therapeutic effect. Importantly, inhibition of triple-negative cells was also achieved. Thus, the development of the new multimodal nanomedicine of the present work should afford new tools towards the theranosis of breast cancer with minimized adverse effects.

Insight into N-terminal localization and dynamics of engineered virus-like particles

Virus-like particles composed of the cowpea chlorotic mottle virus (CCMV) capsid protein (CP) have been extensively studied as carrier systems in nanoscience. One well-established method to improve their stability under physiological conditions is to fuse a stimulus-responsive elastin-like polypeptide (ELP) to the N-terminus of the CPs. Even though the N-terminus should in principle be localized in the inner cavity of the protein cage, studies on the native CCMV revealed its accessibility on the particle surface. We verified that such phenomenon also applies to ELP-CCMVs, by exploiting the covalent functionalization of the CP N-terminal domain via a sortase A-mediated reaction. Western-blot analysis and Förster resonance energy transfer (FRET) experiments furthermore revealed this to be caused by both the external display of the N-termini and the interchange of CPs among preformed capsids. Our findings demonstrate the tunability of ELP-CCMV stability and dynamics and their potential effect on the exploitation of such protein cages as a drug delivery system.

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.

Plant viral nanoparticles for packaging and in vivo delivery of bioactive cargos

Nanoparticles have unique capabilities and considerable promise for many different biological uses. One capability is delivering bioactive cargos to specific cells, tissues, or organisms. Depending on the task, there are multiple variables to consider including nanoparticle selection, targeting strategies, and incorporating cargo so it can be delivered in a biologically active form. One nanoparticle option, genetically controlled plant viral nanoparticles (PVNPs), is highly uniform within a given virus but quite variable between viruses with a broad range of useful properties. PVNPs are flexible and versatile tools for incorporating and delivering a wide range of small or large molecule cargos. Furthermore, PVNPs can be modified to create nanostructures that can solve problems in medical, environmental, and basic research. This review discusses the currently available techniques for delivering bioactive cargos with PVNPs and potential cargos that can be delivered with these strategies. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Viral nanoparticles for drug delivery, imaging, immunotherapy, and theranostic applications

Viral nanoparticles (VNPs) encompass a diverse array of naturally occurring nanomaterials derived from plant viruses, bacteriophages, and mammalian viruses. The application and development of VNPs and their genome-free versions, the virus-like particles (VLPs), for nanomedicine is a rapidly growing. VLPs can encapsulate a wide range of active ingredients as well as be genetically or chemically conjugated to targeting ligands to achieve tissue specificity. VLPs are manufactured through scalable fermentation or molecular farming, and the materials are biocompatible and biodegradable. These properties have led to a wide range of applications, including cancer therapies, immunotherapies, vaccines, antimicrobial therapies, cardiovascular therapies, gene therapies, as well as imaging and theranostics. The use of VLPs as drug delivery agents is evolving, and sufficient research must continuously be undertaken to translate these therapies to the clinic. This review highlights some of the novel research efforts currently underway in the VNP drug delivery field in achieving this greater goal.

Encapsidation of Different Plasmonic Gold Nanoparticles by the CCMV CP

Different types of gold nanoparticles have been synthesized that show great potential in medical applications such as medical imaging, bio-analytical sensing and photothermal cancer therapy. However, their stability, polydispersity and biocompatibility are major issues of concern. For example, the synthesis of gold nanorods, obtained through the elongated micelle process, produce them with a high positive surface charge that is cytotoxic, while gold nanoshells are unstable and break down in a few weeks due to the Ostwald ripening process. In this work, we report the self-assembly of the capsid protein (CP) of cowpea chlorotic mottle virus (CCMV) around spherical gold nanoparticles, gold nanorods and gold nanoshells to form virus-like particles (VLPs). All gold nanoparticles were synthesized or treated to give them a negative surface charge, so they can interact with the positive N-terminus of the CP leading to the formation of the VLPs. To induce the protein self-assembly around the negative gold nanoparticles, we use different pH and ionic strength conditions determined from a CP phase diagram. The encapsidation with the viral CP will provide the nanoparticles better biocompatibility, stability, monodispersity and a new biological substrate on which can be introduced ligands toward specific cells, broadening the possibilities for medical applications.

Enzyme encapsulation by protein cages

Protein cages are hollow protein shells with a nanometric cavity that can be filled with useful materials. The encapsulating nature of the cages means that they are particularly attractive for loading with biological macromolecules, affording the guests protection in conditions where they may be degraded. Given the importance of proteins in both industrial and all cellular processes, encapsulation of functional protein cargoes, particularly enzymes, are of high interest both for in vivo diagnostic and therapeutic use as well as for ex vivo applications. Increasing knowledge of protein cage structures at high resolution along with recent advances in producing artificial protein cages means that they can now be designed with various attachment chemistries on their internal surfaces - a useful tool for cargo capture. Here we review the different available attachment strategies that have recently been successfully demonstrated for enzyme encapsulation in protein cages and consider their future potential.

Tuning the catalytic properties of P22 nanoreactors through compositional control

Enzymes are biomacromolecular protein catalysts that are widely used in a plethora of industrial-scale applications due to their high selectivity, efficiency and ability to work under mild conditions. Many industrial processes require the immobilization of enzymes to enhance their performance and stability. Encapsulation of enzymes in protein cages provides an excellent immobilization platform to create nanoreactors with enhanced enzymatic stability and desired catalytic activities. Here we show that the catalytic activity of nanoreactors, derived from the bacteriophage P22 viral capsids, can be finely-tuned by controlling the packaging stoichiometry and packing density of encapsulated enzymes. The packaging stoichiometry of the enzyme alcohol dehydrogenase (AdhD) was controlled by co-encapsulating it with wild-type scaffold protein (wtSP) at different stoichiometric ratios using an in vitro assembly approach and the packing density was controlled by selectively removing wtSP from the assembled nanoreactors. An inverse relationship was observed between the catalytic activity (k_cat) of AdhD enzyme and the concentration of co-encapsulated wtSP. Selective removal of the wtSP resulted in the similar activity of AdhD in all nanoreactors despite the difference in the volume occupied by enzymes inside nanoreactors, indicating that the AdhD enzymes do not experience self-crowding even under high molarity of confinement (M_conf) conditions. The approach demonstrated here not only allowed us to tailor the activity of encapsulated AdhD catalysts but also the overall functional output of nanoreactors (enzyme-VLP complex). The approach also allowed us to differentiate the effects of crowding and confinement on the functional properties of enzymes encapsulated in an enclosed system, which could pave the way for designing more efficient nanoreactors.

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.

VLPs Derived from the CCMV Plant Virus Can Directly Transfect and Deliver Heterologous Genes for Translation into Mammalian Cells

Virus-like particles (VLPs) are being used for therapeutic developments such as vaccines and drug nanocarriers. Among these, plant virus capsids are gaining interest for the formation of VLPs because they can be safely handled and are noncytotoxic. A paradigm in virology, however, is that plant viruses cannot transfect and deliver directly their genetic material or other cargos into mammalian cells. In this work, we prepared VLPs with the CCMV capsid and the mRNA-EGFP as a cargo and reporter gene. We show, for the first time, that these plant virus-based VLPs are capable of directly transfecting different eukaryotic cell lines, without the aid of any transfecting adjuvant, and delivering their nucleic acid for translation as observed by the presence of fluorescent protein. Our results show that the CCMV capsid is a good noncytotoxic container for genome delivery into mammalian cells.

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.

Packaging of Genomic RNA in Positive-Sense Single-Stranded RNA Viruses: A Complex Story

The packaging of genomic RNA in positive-sense single-stranded RNA viruses is a key part of the viral infectious cycle, yet this step is not fully understood. Unlike double-stranded DNA and RNA viruses, this process is coupled with nucleocapsid assembly. The specificity of RNA packaging depends on multiple factors: (i) one or more packaging signals, (ii) RNA replication, (iii) translation, (iv) viral factories, and (v) the physical properties of the RNA. The relative contribution of each of these factors to packaging specificity is different for every virus. In vitro and in vivo data show that there are different packaging mechanisms that control selective packaging of the genomic RNA during nucleocapsid assembly. The goals of this article are to explain some of the key experiments that support the contribution of these factors to packaging selectivity and to draw a general scenario that could help us move towards a better understanding of this step of the viral infectious cycle.

Structural nanotechnology: three-dimensional cryo-EM and its use in the development of nanoplatforms for in vitro catalysis

The organization of enzymes into different subcellular compartments is essential for correct cell function. Protein-based cages are a relatively recently discovered subclass of structurally dynamic cellular compartments that can be mimicked in the laboratory to encapsulate enzymes. These synthetic structures can then be used to improve our understanding of natural protein-based cages, or as nanoreactors in industrial catalysis, metabolic engineering, and medicine. Since the function of natural protein-based cages is related to their three-dimensional structure, it is important to determine this at the highest possible resolution if viable nanoreactors are to be engineered. Cryo-electron microscopy (cryo-EM) is ideal for undertaking such analyses within a feasible time frame and at near-native conditions. This review describes how three-dimensional cryo-EM is used in this field and discusses its advantages. An overview is also given of the nanoreactors produced so far, their structure, function, and applications.

Plant Viruses in Plant Molecular Pharming: Toward the Use of Enveloped Viruses

Plant molecular pharming has emerged as a reliable platform for recombinant protein expression providing a safe and low-cost alternative to bacterial and mammalian cells-based systems. Simultaneously, plant viruses have evolved from pathogens to molecular tools for recombinant protein expression, chimaeric viral vaccine production, and lately, as nanoagents for drug delivery. This review summarizes the genesis of viral vectors and agroinfection, the development of non-enveloped viruses for various biotechnological applications, and the on-going research on enveloped plant viruses.

Bioengineering Strategies for Protein-Based Nanoparticles

In recent years, the practical application of protein-based nanoparticles (PNPs) has expanded rapidly into areas like drug delivery, vaccine development, and biocatalysis. PNPs possess unique features that make them attractive as potential platforms for a variety of nanobiotechnological applications. They self-assemble from multiple protein subunits into hollow monodisperse structures; they are highly stable, biocompatible, and biodegradable; and their external components and encapsulation properties can be readily manipulated by chemical or genetic strategies. Moreover, their complex and perfect symmetry have motivated researchers to mimic their properties in order to create de novo protein assemblies. This review focuses on recent advances in the bioengineering and bioconjugation of PNPs and the implementation of synthetic biology concepts to exploit and enhance PNP's intrinsic properties and to impart them with novel functionalities.

Recent Progress in Micro/Nanoreactors toward the Creation of Artificial Organelles

Artificial organelles created from a bottom up approach are a new type of engineered materials, which are not designed to be living but, instead, to mimic some specific functions inside cells. By doing so, artificial organelles are expected to become a powerful tool in biomedicine. They can act as nanoreactors to convert a prodrug into a drug inside the cells or as carriers encapsulating therapeutic enzymes to replace malfunctioning organelles in pathological conditions. For the design of artificial organelles, several requirements need to be fulfilled: a compartmentalized structure that can encapsulate the synthetic machinery to perform an enzymatic function, as well as a means to allow for communication between the interior of the artificial organelle and the external environment, so that substrates and products can diffuse in and out the carrier allowing for continuous enzymatic reactions. The most recent and exciting advances in architectures that fulfill the aforementioned requirements are featured in this review. Artificial organelles are classified depending on their constituting materials, being lipid and polymer-based systems the most prominent ones. Finally, special emphasis will be put on the intracellular response of these newly emerging systems.

Multifunctionalized biocatalytic P22 nanoreactor for combinatory treatment of ER+ breast cancer

Background

Tamoxifen is the standard endocrine therapy for breast cancers, which require metabolic activation by cytochrome P450 enzymes (CYP). However, the lower and variable concentrations of CYP activity at the tumor remain major bottlenecks for the efficient treatment, causing severe side-effects. Combination nanotherapy has gained much recent attention for cancer treatment as it reduces the drug-associated toxicity without affecting the therapeutic response.

Results

Here we show the modular design of P22 bacteriophage virus-like particles for nanoscale integration of virus-driven enzyme prodrug therapy and photodynamic therapy. These virus capsids carrying CYP activity at the core are decorated with photosensitizer and targeting moiety at the surface for effective combinatory treatment. The estradiol-functionalized nanoparticles are recognized and internalized into ER+ breast tumor cells increasing the intracellular CYP activity and showing the ability to produce reactive oxygen species (ROS) upon UV_365 nm irradiation. The generated ROS in synergy with enzymatic activity drastically enhanced the tamoxifen sensitivity in vitro, strongly inhibiting tumor cells.

Conclusions

This work clearly demonstrated that the targeted combinatory treatment using multifunctional biocatalytic P22 represents the effective nanotherapeutics for ER+ breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0345-2) contains supplementary material, which is available to authorized users.

Encapsulation and Controlled Release of Protein Guests by the Bacillus subtilis Lumazine Synthase Capsid

In Bacillus subtilis, the 60-subunit dodecahedral capsid formed by lumazine synthase (BsLS) acts as a container for trimeric riboflavin synthase (BsRS). To test whether the C-terminal sequence of BsRS is responsible for its encapsulation by BsLS, the green fluorescent protein (GFP) was fused to either the last 11 or the last 32 amino acids of BsRS, yielding variant GFP11 or GFP32, respectively. After purification, BsLS capsids that had been co-produced in bacteria with GFP11 and GFP32 are 15- and 6-fold more fluorescent, respectively, than BsLS co-produced with GFP lacking any BsRS fragment, indicating complex formation. Enzyme-linked immunosorbent assay experiments confirm that GFP11 is localized within the BsLS capsid. In addition, fusing the last 11 amino acids of BsRS to the C-terminus of the Abrin A chain also led to its encapsulation by BsLS at a level similar to that of GFP11. Together, these results demonstrate that the C-terminal tail of BsRS can act as an encapsulation tag capable of targeting other proteins to the BsLS capsid interior. As with the natural BsLS-BsRS complex, mild changes in pH and buffer identity trigger dissociation of the GFP11 guest, accompanied by a substantial expansion of the BsLS capsid. This system for protein encapsulation and release provides a novel tool for bionanotechnology.