Virus-Like Particles (Vlps) from Synthesis to Targeted Drug Delivery, Vaccine Approaches, and Gene Therapy.

Nanotechnology has thepotential to make significant alterations in the treatment of diseases such ascancer through targeted drug delivery nanoparticles. Virus-like particles(VLPs) are composed of the capsid proteins that do not carry the viral genomeand are also noninfectious. VLPs are self-assembling competent proteinstructures with identical or highly related structures to their correspondingnative viruses. VLPs that have precise 3D nanostructures exhibit a notablediversity in shapes and structures. They can be produced in large quantitiesthrough biological amplification and growth. External protein inserts can bedisplayed through genetic methods or chemical modifications. FunctionalizedVLPs when used as delivery systems have the ability to target with specificityand can attract macrophages for the destruction of cancer cells. The capabilityto target tumors for the delivery of therapeutic agents is an important goal ofthe design approaches of VLPs. Against the current problems in cancertherapies, delivery systems using VLPs are an arising and promising field withthe potential to exhibit solutions. Cancer therapies require specific targetingof the diagnostic element or the drug to tumor cells without binding to oraffecting healthy cells and tissues. Specialization of the VLPs provides anopportunity for using them as site-specific drug delivery systems in cancertherapy while reducing the systemic toxicity and the overall damage to healthycells. With fewer side effects, immunotherapy is also a promising alternativefor cancer treatment by primarily activating the host’s immune system. Cancer vaccinesare aimed at inducing an immune response in the host, thereby generating adefensive mechanism against tumor cells. VLPs can be used as a vaccine withoutthe requirement of any adjuvant due to their naturally optimized particle sizeand their repetitive structural order. Therefore, the aim of this review is toprovide basic information about VLPs and describe previous research on VLPsused as drug and vaccine delivery systems and their applications in differenttypes of cancer.

BackgroundHuman metapneumovirus (HMPV) is now a major cause of lower respiratory infection in children. Although primary isolation of HMPV has been achieved in several different cell lines, the low level of virus replication and the subsequent recovery of low levels of infectious HMPV have hampered biochemical studies on the virus. These experimental methodologies usually require higher levels of biological material that can be achieved following HMPV infection. In this study we demonstrate that expression of the HMPV F, G and M proteins in mammalian cells leads to HMPV virus-like particles (VLP) formation. This experimental strategy will serve as a model system to allow the process of HMPV virus assembly to be examined.MethodsThe HMPV F, G and M proteins were expressed in mammalian cell lines. Protein cross-linking studies, sucrose gradient centrifugation and in situ imaging was used to examine interactions between the virus proteins. VLP formation was examined using sucrose density gradient centrifugation and electron microscopy analysis.ResultsAnalysis of cells co-expressing the F, G and M proteins demonstrated that these proteins interacted. Furthermore, in cells co-expression the three HMPV proteins the formation VLPs was observed. Image analysis revealed the VLPs had a similar morphology to the filamentous virus morphology that we observed on HMPV-infected cells. The capacity of each protein to initiate VLP formation was examined using a VLP formation assay. Individual expression of each virus protein showed that the G protein was able to form VLPs in the absence of the other virus proteins. Furthermore, co-expression of the G protein with either the M or F proteins facilitated their incorporation into the VLP fraction.ConclusionCo-expression of the F, G and M proteins leads to the formation of VLPs, and that incorporation of the F and M proteins into VLPs is facilitated by their interaction with the G protein. Our data suggests that the G protein plays a central role in VLP formation, and further suggests that the G protein may also play a role in the recruitment of the F and M proteins to sites of virus particle formation during HMPV infection.

Objective To investigate the physicochemical properties and immunogenicity of virus like particles(VLPs) in two different conformations assembled from the essential capsid protein VP1 of GⅡ.4 norovirus (NoV) in Hansenula polymorpha. Methods NoV GⅡ.4 VLPs in two different conformations were prepared from high-density fermentation of recombinant engineered strains and VLPs purification. Physicochemical properties of the two forms of VLPs were identified by Western blot, size-exclusion high performance liquid chromatography (SEC-HPLC), dynamic light scattering(DLS) and transmission electron microscopy. Serum VLPs binding activities and blocking activities against VLPs binding to histo-blood group antigen(HBGA-VLPs) were evaluated after immunization of BALB/c mice with the two forms of VLPs. Results VLPs of two different diameters with high homogeneity were obtained after purification. DLS results showed that particle sizes of two VLPs were 53.98 nm and 45.18 nm, respectively. The two VLPs were similar in binding abilities to HBGA receptors. Serum VLPs binding activities and blocking activities against HBGA-VLPs were found higher in NoV-VLP-L than NoV-VLP-S, but the difference was not statistically significant (P>0.05). Conclusion VLPs in two different conformations were obtained by expressing NoV GⅡ.4 VP1 proteins in Hansenula polymorpha. Though they were similar in physicochemical properties and immunogenicity, the NoV-VLP-L might be potential antigen candidates for the development of recombinant human norovirus vaccine. Key words: Norovirus; Virus-like particles; Histo-blood group antigen; Receptor binding assay

Delivery of a foreign epitope by sharing amino acid residues with the carrier matrix

Objectives: Non-viral methods of gene transfer have been preferred in gene therapy approaches for several reasons, particularly for their safety, simplicity and convenience in introducing heterologous DNA into cells. Polyomavirus virus-like particles (VLPs) represent a promising carrier for encapsidation of foreign nucleic acids for gene therapy. For the development of such gene delivery systems as well as for providing reagents for improving virus diagnostics, an efficient yeast expression system for the generation of different polyomavirus VLPs was established. Methods: A galactose-inducible Saccharomyces cerevisiae yeast expression system was used. Formation of empty VLPs was confirmed by cesium chloride ultracentrifugation, agarose gel electrophoresis and electron microscopy. Cross-reactivity of the major capsid proteins (VP1) of different polyomaviruses was analyzed by Western blot using rabbit and mice sera raised against the VP1 proteins. Results: VP1 of polyomaviruses from humans (JC polyomavirus and serotypes AS and SB of BK polyomavirus), rhesus monkeys (simian virus 40), hamsters (hamster polyomavirus), mice (murine polyomavirus) and birds (budgerigar fledgling disease virus) were expressed at high levels in yeast. Empty VLPs formed by all yeast-expressed VP1 proteins were dissociated into pentamers and reassociated into VLPs by defined ion and pH conditions. Different patterns of cross-reactivity of the VP1 proteins with heterologous mice and rabbit sera were observed. Conclusion: The developed heterologous yeast expression system is suitable for high-level production of polyomavirus VLPs. Yeast-derived VLPs are generally free of toxins, host cell DNA and proteins. These VLPs might be useful for the generation of new diagnostical tools, gene delivery systems and antiviral vaccines.

Virus-like particles (VLPs), due to their nanoscale dimensions, presence of interior cavities, self-organization abilities and responsiveness to environmental changes, are of interest in the field of nanotechnology. Nevertheless, comprehensive knowledge of VLP self-assembly principles is incomplete. VLP formation is governed by two types of interactions: protein–cargo and protein–protein. These interactions can be modulated by the physicochemical properties of the surroundings. Here, we used brome mosaic virus (BMV) capsid protein produced in an E. coli expression system to study the impact of ionic strength, pH and encapsulated cargo on the assembly of VLPs and their features. We showed that empty VLP assembly strongly depends on pH whereas ionic strength of the buffer plays secondary but significant role. Comparison of VLPs containing tRNA and polystyrene sulfonic acid (PSS) revealed that the structured tRNA profoundly increases VLPs stability. We also designed and produced mutated BMV capsid proteins that formed VLPs showing altered diameters and stability compared to VLPs composed of unmodified proteins. We also observed that VLPs containing unstructured polyelectrolyte (PSS) adopt compact but not necessarily more stable structures. Thus, our methodology of VLP production allows for obtaining different VLP variants and their adjustment to the incorporated cargo.

Concepts and System Design for the Rate-Controlled Drug Delivery Fundamentals of Rate-Controlled Drug Delivery Oral Drug Delivery and Delivery Systems Mucosal Drug Delivery: Potential Routes for Noninvasive Systemic Administration Nasal Drug Delivery and Delivery Systems Ocular Drug Delivery and Delivery Systems Transdermal Drug Delivery and Delivery Systems Parenteral Drug Delivery and Delivery Systems Vaginal Drug Delivery and Delivery Systems Intrauterine Drug Delivery and Delivery Systems Systemic Delivery of Peptide-Based Pharmaceuticals Regulatory Considerations in Controlled Drug Delivery

Virus-like particles (VLPs) show considerable potential for a wide array of therapeutic applications, spanning from vaccines targeting infectious diseases to applications in cancer immunotherapy and drug delivery. In the context of hepatitis B core antigen (HBcAg) VLPs, a promising candidate for gene delivery approaches, the naturally occurring nucleic acid (NA) binding region is commonly utilized for effective binding of various types of therapeutic nucleic acids (NAther). During formation of the HBcAg VLPs, host cell-derived nucleic acids (NAhc) might be associated to the NA binding region, and are thus encapsulated into the VLPs. Following a VLP harvest, the NAhc need to be removed effectively before loading the VLP with NAther. Various techniques reported in literature for this NAhc removal, including enzymatic treatments, alkaline treatment, and lithium chloride precipitation, lack quantitative evidence of sufficient NAhc removal accompanied by a subsequent high VLP protein recovery. In this study, we present a novel heparin chromatography-based process for effective NAhc removal from HBcAg VLPs. Six HBcAg VLP constructs with varying lengths of the NA binding region and diverse NAhc loadings were subjected to evaluation. Process performance was thoroughly examined through NAhc removal and VLP protein recovery analyses. Hereby, reversed phase chromatography combined with UV/Vis spectroscopy, as well as silica spin column-based chromatography coupled with dye-based fluorescence assay were employed. Additionally, alternative process variants, comprising sulfate chromatography and additional nuclease treatments, were investigated. Comparative analyses were conducted with LiCl precipitation and alkaline treatment procedures to ascertain the efficacy of the newly developed chromatography-based methods. Results revealed the superior performance of the heparin chromatography procedure in achieving high NAhc removal and concurrent VLP protein recovery. Furthermore, nuanced relationships between NA binding region length and NAhc removal efficiency were elucidated. Hereby, the construct Cp157 surpassed the other constructs in the heparin process by demonstrating high NAhc removal and VLP protein recovery. Among the other process variants minimal performance variations were observed for the selected constructs Cp157 and Cp183. However, the heparin chromatography-based process consistently outperformed other methods, underscoring its superiority in NAhc removal and VLP protein recovery.

BackgroundA protective immune response against Hepatitis B infection can be obtained through the administration of a single viral polypeptide, the Hepatitis B surface antigen (HBsAg). Thus, the Hepatitis B vaccine is generated through the utilization of recombinant DNA technology, preferentially by using yeast-based expression systems. However, the polypeptide needs to assemble into spherical particles, so-called virus-like particles (VLPs), to elicit the required protective immune response. So far, no clear evidence has been presented showing whether HBsAg assembles in vivo inside the yeast cell into VLPs or later in vitro during down-stream processing and purification.ResultsHigh level production of HBsAg was carried out with recombinant Pichia pastoris using the methanol inducible AOX1 expression system. The recombinant vaccine was isolated in form of VLPs after several down-stream steps from detergent-treated cell lysates. Search for the intracellular localization of the antigen using electron microscopic studies in combination with immunogold labeling revealed the presence of HBsAg in an extended endoplasmic reticulum where it was found to assemble into defined multi-layered, lamellar structures. The distance between two layers was determined as ~6 nm indicating that these lamellas represent monolayers of well-ordered HBsAg subunits. We did not find any evidence for the presence of VLPs within the endoplasmic reticulum or other parts of the yeast cell.ConclusionsIt is concluded that high level production and intrinsic slow HBsAg VLP assembly kinetics are leading to retention and accumulation of the antigen in the endoplasmic reticulum where it assembles at least partly into defined lamellar structures. Further transport of HBsAg to the Golgi apparatus is impaired thus leading to secretory pathway disfunction and the formation of an extended endoplasmic reticulum which bulges into irregular cloud-shaped formations. As VLPs were not found within the cells it is concluded that the VLP assembly process must take place during down-stream processing after detergent-mediated disassembly of HBsAg lamellas and subsequent reassembly of HBsAg into spherical VLPs.

The production of virus-like particles (VLPs) constitutes a relevant and safe model to study molecular determinants of virion egress. The minimal requirement for the assembly of VLPs for the coronavirus responsible for severe acute respiratory syndrome in humans (SARS-CoV) is still controversial. Recent studies have shown that SARS-CoV VLP formation depends on either M and E proteins or M and N proteins. Here we show that both E and N proteins must be coexpressed with M protein for the efficient production and release of VLPs by transfected Vero E6 cells. This suggests that the mechanism of SARS-CoV assembly differs from that of other studied coronaviruses, which only require M and E proteins for VLP formation. When coexpressed, the native envelope trimeric S glycoprotein is incorporated onto VLPs. Interestingly, when a fluorescent protein tag is added to the C-terminal end of N or S protein, but not M protein, the chimeric viral proteins can be assembled within VLPs and allow visualization of VLP production and trafficking in living cells by state-of-the-art imaging technologies. Fluorescent VLPs will be used further to investigate the role of cellular machineries during SARS-CoV egress.

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

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

Plant virus nanoparticles (VNPs) can be used to generate versatile, functionalized nanomaterials, but they contain replicative genomic DNA whose impact on the environment must be assessed carefully. In contrast, plant virus-like particles (VLPs) lack replicative genomic information and are therefore non-infectious. However, the production of VLPs in plants is associated with challenges such as low yields and a purification process that is difficult to scale up. To address these issues, we used cell-free lysates derived from Nicotiana tabacum BY-2 cells to produce tobacco mosaic virus (TMV)-like particles. The objective of this approach was to generate VLPs with and without encapsulated RNA. SDS-PAGE and Western blotting indicated the accumulation of abundant quantities of the viral coat protein, with yields of up to 3.56 ± 0.62 mg per ml of cell-free lysate confirmed by enzyme-linked immunosorbent assay before purification. The yield of purified TMV VLP is comparable to that obtained from plants due to the low assembly efficiency, with assembled VLPs yielding up to 0.70 ± 0.16 mg per ml of lysate. Notably, this yield is approximately 23 times higher than that obtained through microbial expression systems, obviating the need for the labor-intensive processes typically associated with plant-based methods. Transmission electron microscopy revealed that VLPs assembled in the lysate at pH 7, and remained stable at up to pH 8.5. Cell-free expression therefore offers a rapid, straightforward and cost-effective method for the production of plant VLPs at high yields, and establishes a foundation for the on-demand production of functionalized VLPs under controlled and reproducible conditions.

Currently virus-like particles (VLPs) are receiving much attention as platforms for next generation vaccines. However, chromatography-based methods for purifying VLPs remain challenging. Unlike traditional methods using density gradient for purifying VLPs, there have been few advances in explaining how assembled particles can be obtained by chromatography. Nervous necrosis virus (NNV) infects over 30 species of fish and leads to large economic losses in the farmed fish industry. Previously we developed a heparin chromatography-based method for purifying red-spotted grouper NNV (RGNNV) VLPs. However it is unclear how the assembled RGNNV VLPs are obtained by this method. It is known that assembly of NNV capsid proteins depends on calcium ions. In the present study, we found that the yield of purified RGNNV capsid protein in heparin chromatography was enhanced when calcium ions were present during binding. Also, it appears that the capsid protein of RGNNV undergoes partial disassembly and reassembly during sample preparation prior to heparin chromatography and the protein finally undergoes assembly during the chromatography. Therefore, our results indicated that heparin-binding affinity of RGNNV capsid protein is linked to its ability for VLP formation. The assembly of RGNNV capsid proteins recombinantly produced is a good model for explaining VLP formation during chromatography-based purification processes.

Characterization of virus-like particles assembled by co-expression of BmCPV capsid shell protein and large protrusion protein