Chemically activatable viral capsid functionalized for cancer targeting

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

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

Biological evaluation of integrin α3β1-targeted 68Ga-labeled HEVNPs in HCT 116 colorectal tumor-bearing mice

Integrins are cell surface receptors involved in multiple functions vital for cellular proliferation. Various tumor cells overexpress αβ-integrins, making them ideal biomarkers for diagnostic imaging and tumor-targeted drug delivery. LXY30 is a peptide that can specifically recognize and interact with the integrin α₃β₁, a molecule overexpressed in breast, ovarian and colorectal cancer. Hepatitis E virus nanoparticles (HEVNPs) are virus-like particles that have been investigated as drug delivery agents for the targeted delivery of nucleic acids and small proteins. HEVNPs can be a theranostic platform for monitoring and evaluating tumor-targeted therapies if tagged with a suitable diagnostic marker. Herein, we describe the radiolabeling and biological evaluation of integrin α₃β₁-targeted HEVNPs. HEVNPs were conjugated with DOTA and radiolabeled with gallium-68 (t_1/2 = 67.7 min), a short-lived positron emitter used in positron emission tomography (PET). The synthesized [⁶⁸Ga]Ga-DOTA-HEVNPs were used to evaluate the efficacy of conjugated LXY30 peptide to improve HEVNPs binding and internalization to integrin α₃β₁ expressing human colorectal HCT 116 cells. In vivo tumor accumulation of [⁶⁸Ga]Ga-DOTA-HEVNP-LXY30 was evaluated in HCT 116 colorectal tumor-bearing mice. [⁶⁸Ga]Ga-DOTA-HEVNP-LXY30 and non-targeted [⁶⁸Ga]Ga-DOTA-HEVNP were radiolabeled with radiochemical yields (RCY) of 67.9 ± 3.3% and 73.7 ± 9.8%, respectively. [⁶⁸Ga]Ga-DOTA-HEVNP-LXY30 exhibited significantly higher internalization in HCT 116 cells than the non-targeted [⁶⁸Ga]Ga-DOTA-HEVNPs (21.0 ± 0.7% vs. 10.5 ± 0.3% at 3 h, ****P<0.0001). After intravenous administration to mice, accumulation of [⁶⁸Ga]Ga-DOTA-HEVNP-LXY30 to HCT 116 xenograft tumors was at its highest rate of 0.8 ± 0.4%ID/g at 60 min. [⁶⁸Ga]Ga-DOTA-HEVNP-LXY30 accumulated mainly in the liver and spleen (39.8 ± 13.0%%ID/g and 24.6 ± 24.1%ID/g, respectively). Despite the low targeting efficiency in vivo, we demonstrated that [⁶⁸Ga]Ga-DOTA-HEVNP is a promising diagnostic platform for quantitative analysis of HEVNP distribution in vivo. This nanosystem can be utilized in future studies assessing the success of further engineered HEVNP structures with optimized targeting efficiency in vivo.

Synthesis and ex vivo biodistribution of two 68Ga-labeled tetrazine tracers: Comparison of pharmacokinetics

Pretargeted PET imaging allows the use of radiotracers labeled with short-living PET radionuclides for tracing drugs with slow pharmacokinetics. Recently, especially methods based on bioorthogonal chemistry have been under intensive investigation for pretargeted PET imaging. The pharmacokinetics of the radiotracer is one of the factors that determine the success of the pretargeted strategy. Here, we report synthesis and biological evaluation of two ⁶⁸Ga-labeled tetrazine (Tz)-based radiotracers, [⁶⁸Ga]Ga-HBED-CC-PEG₄-Tz ([⁶⁸Ga]4) and [⁶⁸Ga]Ga-DOTA-PEG₄-Tz ([⁶⁸Ga]6), aiming for development of new tracer candidates for pretargeted PET imaging based on the inverse electron demand Diels-Alder (IEDDA) ligation between a tetrazine and a strained alkene, such as trans-cyclooctene (TCO). Excellent radiochemical yield (RCY) was obtained for [⁶⁸Ga]4 (RCY > 96%) and slightly lower for [⁶⁸Ga]6 (RCY > 88%). Radiolabeling of HBED-CC-Tz proved to be faster and more efficient under milder conditions compared to the DOTA analogue. The two tracers exhibited excellent radiolabel stability both in vitro and in vivo. Moreover, [⁶⁸Ga]4 was successfully used for radiolabeling two different TCO-functionalized nanoparticles in vitro: Hepatitis E virus nanoparticles (HEVNPs) and porous silicon nanoparticles (PSiNPs).

Genetically Engineered Hepatitis C Virus-like Particles (HCV-LPs) Tagged with SP94 Peptide to Acquire Selectivity to Liver Cancer Cells via Grp78

Targeted cancer therapy is a challenging area that includes multiple chemical and biological vehicles. Virus-like particles (VLPs) combine safety and efficacy in their roles as potential vaccines and drug delivery vehicles. In this study, we propose a novel drug delivery system based on HCV-LPs engineered with SP94 and RGD peptides mediated by a specific molecular chaperone (Grp78) associated with cancer drug resistance. The PCR primers were designed for engineering two constructs, SP94-EGFP-CORE-HIS and RGD-EGFP-CORE-HIS, by sequential PCR reactions. The two fragments were cloned into pFastBac Dual under the polyhedrin promoter and then used to produce two recombinant baculoviruses (AcSP94 and AcRGD). The VLP's expression was optimized by recombinant virus infection with different MOIs, ranging from 1 to 20 MOI. Recombinant VLP2 were purified by Ni-NTA and their sizes and shapes were confirmed with TEM. They were incubated with different types of cells prior to examination using the fluorescence microscope to test the binding specificity. The effect of the overexpression of the Grp78 on the binding affinity of the engineered VLPs was tested in HepG2 and HeLa cells. The protocol optimization revealed that MOI 10 produced the highest fluorescence intensities after 72 h for the two recombinant proteins (SP94-core and RGD-core). Moreover, the binding assay tested on different types of mammalian cells (HeLa, HEK-293T, and HepG2 cells) showed green fluorescence on the periphery of all tested cell lines when using the RGD-core protein; while, the SP94-core protein showed green fluorescence only with the liver cancer cells, HepG2 and HuH7. Overexpression of Grp78 in HepG2 and HeLa cells enhanced the binding efficiency of the engineered VLPs. We confirmed that the SP94 peptide can be specifically used to target liver cancer cells, while the RGD peptide is sufficiently functional for most types of cancer cells. The overexpression of the Grp78 improved the binding capacity of both SP94 and RGD peptides. It is worth noting that the SP94 peptide can function properly as a recombinant peptide, and not only as a chemically conjugated peptide, as heretofore commonly used.

Development of 68Ga-Labeled Hepatitis E Virus Nanoparticles for Targeted Drug Delivery and Diagnostics with PET

Targeted delivery of diagnostics and therapeutics offers essential advantages over nontargeted systemic delivery. These include the reduction of toxicity, the ability to reach sites beyond biological barriers, and the delivery of higher cargo concentrations to diseased sites. Virus-like particles (VLPs) can efficiently be used for targeted delivery purposes. VLPs are derived from the coat proteins of viral capsids. They are self-assembled, biodegradable, and homogeneously distributed. In this study, hepatitis E virus (HEV) VLP derivatives, hepatitis E virus nanoparticles (HEVNPs), were radiolabeled with gallium-68, and consequently, the biodistribution of the labeled [⁶⁸Ga]Ga-DOTA-HEVNPs was studied in mice. The results indicated that [⁶⁸Ga]Ga-DOTA-HEVNPs can be considered as promising theranostic nanocarriers, especially for hepatocyte-targeting therapies.

Boosting antitumor response with PSMA-targeted immunomodulatory VLPs, harboring costimulatory TNFSF ligands and GM-CSF cytokine

Therapeutic strategies based on immunomodulation have improved cancer therapy. Most approaches target co-stimulatory pathways or the inhibition of immunosuppressive mechanisms, to enhance immune response and overcome the immune tolerance of tumors. Here, we propose a novel platform to deliver targeted immunomodulatory signaling, enhancing antitumor response. The platform is based on virus-like particles derived from lentiviral capsids. These particles may be engineered to harbor multifunctional ligands on the surface that drive tropism to the tumor site and deliver immunomodulatory signaling, boosting the antitumor response. We generated virus-like particles harboring a PSMA-ligand, TNFSF co-stimulatory ligands 4-1BBL or OX40L, and a membrane-anchored GM-CSF cytokine. The virus-like particles are driven to PSMA-expressing tumors and deliver immunomodulatory signaling from the TNFSF surface ligands and the anchored GM-CSF, inducing T cell proliferation, inhibition of regulatory T cells, and potentiating elimination of tumor cells. The PSMA-targeted particles harboring immunomodulators enhanced antitumor activity in immunocompetent challenged mice and may be explored as a potential tool for cancer immunotherapy.

Protein-based nanoplatform for detection of tumorigenic polyps in the colon via noninvasive mucosal routes

The use of nanoparticulate systems to diagnose and treat tumors has gained momentum with the rapid development of nanomedicine. Many nanotheranostics fail due to insufficient bioavailability and low accumulation at the tumor site, resulting in undesirable side effects. We describe the use of an engineered hepatitis E viral nanoparticle (HEVNP) with enhanced bioavailability, tissue retention and mucosal penetration capacities. HEVNP is a modular nanocapsule that can encapsulate heterologous nucleotides, proteins and inorganic metals, such as ferrite oxide nanoparticles. Additionally, the exterior protruding arms of HEVNP is composed of loops that are used for chemical coupling of targeting and therapeutic peptides. We propose the use of HEVNP to target colorectal cancer (i.e., polyps) with imaging-guided delivery using colonoscopy.

A Multiscale Model for the Self-Assembly of Coat Proteins in Bacteriophage MS2

The self-assembly of viral capsids is an essential step to the formation of infectious viruses. Elucidating the kinetic mechanisms of how a capsid or virus-like particle assembles could advance our knowledge about the viral lifecycle, as well as the general principles in self-assembly of biomaterials. However, current understanding of capsid assembly remains incomplete for many viruses due to the fact that the transient intermediates along the assembling pathways are experimentally difficult to be detected. In this paper, we constructed a new multiscale computational framework to simulate the self-assembly of virus-like particles. We applied our method to the coat proteins of bacteriophage MS2 as a specific model system. This virus-like particle of bacteriophage MS2 has a unique feature that its 90 sequence-identical dimers can be classified into two structurally various groups: one is the symmetric CC dimer, and the other is the asymmetric AB dimer. The homotypic interactions between AB dimers result in a 5-fold symmetric contact, while the heterotypic interactions between AB and CC dimers result in 6-fold symmetric contact. We found that the assembly can be described as a physical process of phase transition that is regulated by various factors such as concentration and specific stoichiometry between AB and CC dimers. Our simulations also demonstrate that heterotypic and homotypic interfaces play distinctive roles in modulating the assembling kinetics. The interaction between AB and CC dimers is much more dynamic than that between two AB dimers. We therefore suggest that the alternate growth of viral capsid through the heterotypic dimer interactions dominates the assembling pathways. This is, to the best of our knowledge, the first multiscale model to simulate the assembling process of coat proteins in bacteriophage MS2. The generality of this approach opens the door to its further applications in assembly of other viral capsids, virus-like particles, and novel drug delivery systems.

Liver-specific Gene Delivery Using Engineered Virus-Like Particles of Hepatitis E Virus

Virus-like particles (VLPs) possess great potential for organ-specific transport of therapeutic agents due to their central cavity surrounded by viral capsid proteins and similar tropism to their original viruses. The N-terminal truncated second open reading frame (Nt-ORF2) of the hepatotropic hepatitis E virus (HEV) forms VLPs via self-assembly. In the present study, we investigated whether HEV-LPs could deliver foreign genes specifically to the liver. HEV-LPs were obtained from Nt-ORF2 expression in Huh7 cells that were transduced with recombinant baculoviruses and purified by continuous density gradient centrifugation. The purified HEV-LPs efficiently penetrated liver-derived cell lines and the liver tissues. To evaluate HEV-LPs as gene delivery tools, we encapsulated foreign plasmids in HEV-LPs with disassembly/reassembly systems. Green fluorescence was detected at higher frequency in liver-derived Huh7 cells treated with HEV-LPs bearing GFP-encoding plasmids than in control cells. Additionally, HEV-LPs bearing Bax-encoding plasmids induced apoptotic signatures in Huh7 cells. In conclusion, HEV-LPs produced in mammalian cells can encapsulate foreign genes in their central cavity and specifically transport these genes to liver-derived cells, where they are expressed. The present study could contribute to advances in liver-targeted gene therapy.

Physical, chemical, and synthetic virology: Reprogramming viruses as controllable nanodevices

The fields of physical, chemical, and synthetic virology work in partnership to reprogram viruses as controllable nanodevices. Physical virology provides the fundamental biophysical understanding of how virus capsids assemble, disassemble, display metastability, and assume various configurations. Chemical virology considers the virus capsid as a chemically addressable structure, providing chemical pathways to modify the capsid exterior, interior, and subunit interfaces. Synthetic virology takes an engineering approach, modifying the virus capsid through rational, combinatorial, and bioinformatics-driven design strategies. Advances in these three subfields of virology aim to develop virus-based materials and tools that can be applied to solve critical problems in biomedicine and biotechnology, including applications in gene therapy and drug delivery, diagnostics, and immunotherapy. Examples discussed include mammalian viruses, such as adeno-associated virus (AAV), plant viruses, such as cowpea mosaic virus (CPMV), and bacterial viruses, such as Qβ bacteriophage. Importantly, research efforts in physical, chemical, and synthetic virology have further unraveled the design principles foundational to the form and function of viruses. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Surface Functionalization of Hepatitis E Virus Nanoparticles Using Chemical Conjugation Methods

Virus-like particles (VLPs) have been used as nanocarriers to display foreign epitopes and/or deliver small molecules in the detection and treatment of various diseases. This application relies on genetic modification, self-assembly, and cysteine conjugation to fulfill the tumor-targeting application of recombinant VLPs. Compared with genetic modification alone, chemical conjugation of foreign peptides to VLPs offers a significant advantage because it allows a variety of entities, such as synthetic peptides or oligosaccharides, to be conjugated to the surface of VLPs in a modulated and flexible manner without alteration of the VLP assembly. Here, we demonstrate how to use the hepatitis E virus nanoparticle (HEVNP), a modularized theranostic capsule, as a multifunctional delivery carrier. Functions of HEVNPs include tissue-targeting, imaging, and therapeutic delivery. Based on the well-established structural research of HEVNP, the structurally independent and surface-exposed residues were selected for cysteine replacement as conjugation sites for maleimide-linked chemical groups via thiol-selective linkages. One particular cysteine-modified HEVNP (a Cys replacement of the asparagine at 573 aa (HEVNP-573C)) was conjugated to a breast cancer cell-specific ligand, LXY30 and labeled with near-infrared (NIR) fluorescence dye (Cy5.5), rendering the tumor-targeted HEVNPs as effective diagnostic capsules (LXY30-HEVNP-Cy5.5). Similar engineering strategies can be employed with other macromolecular complexes with well-known atomic structures to explore potential applications in theranostic delivery.

Tissue targeted nanocapsids for oral insulin delivery via drink

For the past eight decades, subcutaneous injection has been the main route used for supplementing the suboptimal insulin secretion for administering insulin as a treatment for diabetes mellitus. Although this method is effective, subcutaneous injections are painful, inconvenient and carry a high risk of infections leading to poor patient compliance. The insulin-encapsulated hepatitis E virus nanoparticle, composed of the noninfectious hepatitis E viral capsid, is expected to deliver insulin from the GI tract to the liver after ingestion. Hepatitis E virus nanoparticle could be the answer to the long search of effective and efficient means to administer insulin orally and the most preferred route of drug delivery with highest patient compliance.

Brain- and brain tumor-penetrating disulfiram nanoparticles: Sequence of cytotoxic events and efficacy in human glioma cell lines and intracranial xenografts

There is great interest in repurposing disulfiram (DSF), a rapidly metabolizing nontoxic drug, for brain cancers and other cancers. To overcome the instability and low therapeutic efficacy, we engineered passively-targeted DSF-nanoparticles (DSFNPs) using biodegradable monomethoxy (polyethylene glycol) d,l-lactic-co-glycolic acid (mPEG-PLGA) matrix. The physicochemical properties, cellular uptake and the blood brain-barrier permeability of DSFNPs were investigated. The DSFNPs were highly stable with a size of ∼70 nm with a >90% entrapment. Injection of the nanoparticles labeled with HITC, a near-infrared dye into normal mice and tumor-bearing nude mice followed by in vivo imaging showed a selective accumulation of the formulation within the brain and subcutaneous tumors for >24 h, indicating an increased plasma half-life and entry of DSF into desired sites. The DSFNPs induced a potent and preferential killing of many brain tumor cell lines in cytotoxicity assays. Confocal microscopy showed a quick internalization of the nanoparticles in tumor cells followed by initial accumulation in lysosomes and subsequently in mitochondria. DSFNPs induced high levels of ROS and led to a marked loss of mitochondrial membrane potential. Activation of the MAP-kinase pathway leading to a nuclear translocation of apoptosis-inducing factor and altered expression of apoptotic and anti-apoptotic proteins were also observed. DSFNPs induced a powerful and significant regression of intracranial medulloblastoma xenografts compared to the marginal efficacy of unencapsulated DSF. Together, we show that passively targeted DSFNPs can affect multiple targets, trigger potent anticancer effects, and can offer a sustained drug supply for brain cancer treatment through an enhanced permeability retention (EPR).

Structural characterization of site-modified nanocapsid with monodispersed gold clusters

Hepatitis E Virus-like particles self-assemble in to noninfectious nanocapsids that are resistant to proteolytic/acidic mucosal delivery conditions. Previously, the nanocapsid was engineered to specifically bind and enter breast cancer cells, where successful tumor targeting was demonstrated in animal models. In the present study, the nanocapsid surface was modified with a solvent-exposed cysteine to conjugate monolayer protected gold nanoclusters (AuNC). Unlike commercially available gold nanoparticles, AuNCs monodisperse in water and are composed of a discrete number of gold atoms, forming a crystalline gold core. Au₁₀₂ pMBA₄₄ (Au₁₀₂) was an ideal conjugate given its small 2.5 nm size and detectability in cryoEM. Au₁₀₂ was bound directly to nanocapsid surface cysteines via direct ligand exchange. In addition, Au₁₀₂ was functionalized with a maleimide linker (Au₁₀₂_C₆MI) for maleimide-thiol conjugation to nanocapsid cysteines. The AuNC-bound nanocapsid constructs were conjugated in various conditions. We found Au₁₀₂_C₆MI to bind nanocapsid more efficiently, while Au₁₀₂ remained more soluble over time. Nanocapsids conjugated to Au₁₀₂_C₆MI were imaged in cryoEM for single particle reconstruction to localize AuNC position on the nanocapsid surface. We resolved five unique high intensity volumes that formed a ring-shaped density at the 5-fold symmetry center. This finding was further supported by independent rigid modeling.

Surface modulatable nanocapsids for targeting and tracking toward nanotheranostic delivery

Nanoparticle diagnostics and therapeutics (nanotheranostics) have significantly advanced cancer detection and treatment. However, many nanotheranostics are ineffective due to defects in tumor localization and bioavailability. An engineered Hepatitis E Virus (HEV) nanocapsid is a proposed platform for targeted cancer-cell delivery. Self-assembling from HEV capsid subunits, nanocapsids retain the capacity to enter cells and resist proteolytic/acidic conditions, but lack infectious viral elements. The nanocapsid surface was modified for chemical activation to confer tumor-specific targeting and detection, immune-response manipulation and controlled theranostic delivery. Nanotheranostic molecules can be packaged in the hollow nanocapsid shell during in vitro assembly. Complementing the adapted stability and cell-entry characteristics of the HEV capsid, a modified nanocapsid serves as a tunable tumor-targeting platform for nanotheronostic delivery.

Taking a Stab at Cancer; Oncolytic Virus-Mediated Anti-Cancer Vaccination Strategies

Vaccines have classically been used for disease prevention. Modern clinical vaccines are continuously being developed for both traditional use as well as for new applications. Typically thought of in terms of infectious disease control, vaccination approaches can alternatively be adapted as a cancer therapy. Vaccines targeting cancer antigens can be used to induce anti-tumour immunity and have demonstrated therapeutic efficacy both pre-clinically and clinically. Various approaches now exist and further establish the tremendous potential and adaptability of anti-cancer vaccination. Classical strategies include ex vivo-loaded immune cells, RNA- or DNA-based vaccines and tumour cell lysates. Recent oncolytic virus development has resulted in a surge of novel viruses engineered to induce powerful tumour-specific immune responses. In addition to their use as cancer vaccines, oncolytic viruses have the added benefit of being directly cytolytic to cancer cells and thus promote antigen recognition within a highly immune-stimulating tumour microenvironment. While oncolytic viruses are perfectly equipped for efficient immunization, this complicates their use upon previous exposure. Indeed, the host's anti-viral counter-attacks often impair multiple-dosing regimens. In this review we will focus on the use of oncolytic viruses for anti-tumour vaccination. We will explore different strategies as well as ways to circumvent some of their limitations.