Enveloped virus labeling via both intrinsic biosynthesis and metabolic incorporation of phospholipids in host cells

Surface functionalization of virus-like particles via bioorthogonal click reactions for enhanced cell-specific targeting

Surface functionalization of nano drug carriers allows for precise delivery of therapeutic molecules to the target site. This technique involves attaching targeting molecules to the nanoparticle surface, facilitating selective interaction. In this study, we engineered virus-like particles (VLPs) to enhance their targeting capabilities. Azide groups incorporated on the lipid membranes of VLPs enabled bioorthogonal click reactions for conjugation with cycloalkyne-bearing molecules, providing efficient conjugation with high specificity. HIV-1 Gag VLPs were chosen due to their envelope, which allows host membrane component incorporation, and the Gag protein, which serves as a recognition motif for human T cells. This combination, along with antibody-mediated targeting, addresses the limitations of intracellular delivery to T cells, which typically exhibit low uptake of exogenous materials. The selective uptake of azide VLPs by CD3-positive T cells was evaluated in a co-culture system. Even without antibody conjugation, VLP uptake was enhanced in T cells, indicating their intrinsic targeting potential. Antibody conjugation further amplified this effect, demonstrating the synergistic benefits of the combined targeting approach. Our study shows that recombinant production of azide functionalized VLPs results in engineered nanoparticles that can be easily modified using bioorthogonal click reactions, providing high specificity and versatility for conjugation with various molecules, making it applicable to a wide range of biological products.

Organelle-selective click labeling coupled with flow cytometry allows pooled CRISPR screening of genes involved in phosphatidylcholine metabolism

Cellular lipid synthesis and transport are governed by intricate protein networks. Although genetic screening should contribute to deciphering the regulatory networks of lipid metabolism, technical challenges remain-especially for high-throughput readouts of lipid phenotypes. Here, we coupled organelle-selective click labeling of phosphatidylcholine (PC) with flow cytometry-based CRISPR screening technologies to convert organellar PC phenotypes into a simple fluorescence readout for genome-wide screening. This technique, named O-ClickFC, was successfully applied in genome-scale CRISPR-knockout screens to identify previously reported genes associated with PC synthesis (PCYT1A, ACACA), vesicular membrane trafficking (SEC23B, RAB5C), and non-vesicular transport (PITPNB, STARD7). Moreover, we revealed previously uncharacterized roles of FLVCR1 as a choline uptake facilitator, CHEK1 as a post-translational regulator of the PC-synthetic pathway, and CDC50A as responsible for the translocation of PC to the outside of the plasma membrane bilayer. These findings demonstrate the versatility of O-ClickFC as an unprecedented platform for genetic dissection of cellular lipid metabolism.

Modified Bacteriophage for Tumor Detection and Targeted Therapy

Malignant tumor is one of the leading causes of death in human beings. In recent years, bacteriophages (phages), a natural bacterial virus, have been genetically engineered for use as a probe for the detection of antigens that are highly expressed in tumor cells and as an anti-tumor reagent. Furthermore, phages can also be chemically modified and assembled with a variety of nanoparticles to form a new organic/inorganic composite, thus extending the application of phages in biological detection and tumor therapeutic. This review summarizes the studies on genetically engineered and chemically modified phages in the diagnosis and targeting therapy of tumors in recent years. We discuss the advantages and limitations of modified phages in practical applications and propose suitable application scenarios based on these modified phages.

Recent advances in developing active targeting and multi-functional drug delivery systems via bioorthogonal chemistry

Bioorthogonal chemistry reactions occur in physiological conditions without interfering with normal physiological processes. Through metabolic engineering, bioorthogonal groups can be tagged onto cell membranes, which selectively attach to cargos with paired groups via bioorthogonal reactions. Due to its simplicity, high efficiency, and specificity, bioorthogonal chemistry has demonstrated great application potential in drug delivery. On the one hand, bioorthogonal reactions improve therapeutic agent delivery to target sites, overcoming off-target distribution. On the other hand, nanoparticles and biomolecules can be linked to cell membranes by bioorthogonal reactions, providing approaches to developing multi-functional drug delivery systems (DDSs). In this review, we first describe the principle of labeling cells or pathogenic microorganisms with bioorthogonal groups. We then highlight recent breakthroughs in developing active targeting DDSs to tumors, immune systems, or bacteria by bioorthogonal chemistry, as well as applications of bioorthogonal chemistry in developing functional bio-inspired DDSs (biomimetic DDSs, cell-based DDSs, bacteria-based and phage-based DDSs) and hydrogels. Finally, we discuss the difficulties and prospective direction of bioorthogonal chemistry in drug delivery. We expect this review will help us understand the latest advances in the development of active targeting and multi-functional DDSs using bioorthogonal chemistry and inspire innovative applications of bioorthogonal chemistry in developing smart DDSs for disease treatment.

Visualization of Zika Virus Infection via a Light-Initiated Bio-Orthogonal Cycloaddition Labeling Strategy

Zika virus (ZIKV) is a re-emerging flavivirus that leads to devastating consequences for fetal development. It is crucial to visualize the pathogenicity activities of ZIKV ranging from infection pathways to immunity processes, but the accurate labeling of ZIKV remains challenging due to the lack of a reliable labeling technique. We introduce the photo-activated bio-orthogonal cycloaddition to construct a fluorogenic probe for the labeling and visualizing of ZIKV. Via a simple UV photoirradiation, the fluorogenic probes could be effectively labeled on the ZIKV. We demonstrated that it can be used for investigating the interaction between ZIKV and diverse cells and avoiding the autofluorescence phenomenon in traditional immunofluorescence assay. Thus, this bioorthogonal-enabled labeling strategy can serve as a promising approach to monitor and understand the interaction between the ZIKV and host cells.

Metabolic labeling of glycerophospholipids via clickable analogs derivatized at the lipid headgroup

Metabolic labeling, in which substrate analogs containing diminutive tags can infiltrate biosynthetic pathways and generate labeled products in cells, has led to dramatic advancements in the means by which complex biomolecules can be detected and biological processes can be elucidated. Within this realm, metabolic labeling of lipid products, particularly in a manner that is headgroup-specific, brings about a number of technical challenges including the complexity of lipid metabolic pathways as well as the simplicity of biosynthetic precursors to headgroup functionality. As such, only a handful of strategies for metabolic labeling of lipids have thus far been reported. However, these approaches provide enticing examples of how strategic modifications to substrate structures, particularly by introducing clickable moieties, can enable the hijacking of lipid biosynthesis. Furthermore, early work in this field has led to an explosion in diverse applications by which these techniques have been exploited to answer key biological questions or detect and track various lipid-containing biological entities. In this article, we review these efforts and emphasize recent advancements in the development and application of lipid metabolic labeling strategies.

Bioorthogonal Metabolic Labeling Utilizing Protein Biosynthesis for Dynamic Visualization of Nonenveloped Enterovirus 71 Infection

Bioorthogonal metabolic labeling through the endogenous cellular metabolic pathways (e.g., phospholipid and sugar) is a promising approach for effectively labeling live viruses. However, it remains a big challenge to label nonenveloped viruses due to lack of host-derived envelopes. Herein, a novel bioorthogonal labeling strategy is developed utilizing protein synthesis pathway to label and trace nonenveloped viruses. The results show that l-azidohomoalanine (Aha), an azido derivative of methionine, is more effective than azido sugars to introduce azido motifs into viral capsid proteins by substituting methionine residues during viral protein biosynthesis and assembly. The azide-modified EV71 (N₃-EV71) particles are then effectively labeled with dibenzocyclooctyl (DBCO)-functionalized fluorescence probes through an in situ bioorthogonal reaction with well-preserved viral infectivity. Dual-labeled imaging clearly clarifies that EV71 virions primarily bind to scavenger receptors and are internalized through clathrin-mediated endocytosis. The viral particles are then transported into early and late endosomes where viral RNA is released in a low-pH dependent manner at about 70 min postinfection. These results first reveal viral trafficking and uncoating mechanisms, which may shed light on the pathogenesis of EV71 infection and contribute to antiviral drug discovery.

Cell-Membrane-Based Biomimetic Systems with Bioorthogonal Functionalities

During the past decade, there was a fast development of cell-based biomimetic systems, which are commonly derived from cell membranes, cell vesicles, or living cells. Such systems have unique and inherent bioinspired features originating from their parent biological systems. In particular, they are capable of (i) prolonging blood circulation time, (ii) avoiding immune response, (iii) targeting desired sites, (iv) providing antigens in cancer immunotherapy, and (v) loading and delivering therapeutic or imaging agents. Thus, these biomimetic systems are promising as prevention, detection, diagnosis, and therapeutic modalities. Though promising, these cell-based biomimetic systems are still far from wide application. One of the important reasons is the inevitable difficulty in their further efficient and precise functionalization. Bioorthogonal chemistry results in fast, specific, and high-yielding ligation under mild biological conditions without interactions with surrounding biomolecules or disturbance of the whole biosystem. Moreover, bioorthogonal chemical groups can be introduced into cells, especially into cell membranes, through cellular biosynthesis and metabolic incorporation. Hence, a specific and reliable approach for cell membrane functionalization based on bioorthogonal chemistry has been opportunely put forward and rapidly developed. In this Account, we summarize our recent research on the development of biomimetic systems by integrating bioorthogonal chemistry with biomimetic approaches. First, an exogenously supplied unnatural biosynthetic precursor (e.g., an amino acid or lipid) bearing a bioorthogonal group (e.g., azide or tetrazine) is fed to living cells and metabolically incorporated into targeted biomolecules via cellular biosynthesis regardless of the cell phenotype. After that, different functional molecules can be anchored to the cell membranes through bioorthogonal chemical reactions by using previously inserted "artificial chemical groups". Therefore, this safe, direct, and long-term engineering strategy endows the natural cell-based biomimetic systems with additional chemical or biological performances such as labeling, targeting, imaging, and therapeutic capabilities, providing a powerful tool for the construction of biomimetic systems. Interestingly, we have successfully fabricated various biomimetic systems and applied them in (1) living virus labeling, (2) targeting delivery and enrichment of drugs/imaging agents, and (3) disease theranostics. This Account may contribute to the further development of biomimetic systems and facilitate their biological and biomedical applications in the future. With this Account we also hope to attract more cooperative interests from different fields such as chemistry, materials science, biology, pharmacy, and medicine in promoting lab-to-clinic translation of cell-based biomimetic systems combined with these two cutting-edge techniques.

Single-Virus Tracking: From Imaging Methodologies to Virological Applications

Uncovering the mechanisms of virus infection and assembly is crucial for preventing the spread of viruses and treating viral disease. The technique of single-virus tracking (SVT), also known as single-virus tracing, allows one to follow individual viruses at different parts of their life cycle and thereby provides dynamic insights into fundamental processes of viruses occurring in live cells. SVT is typically based on fluorescence imaging and reveals insights into previously unreported infection mechanisms. In this review article, we provide the readers a broad overview of the SVT technique. We first summarize recent advances in SVT, from the choice of fluorescent labels and labeling strategies to imaging implementation and analytical methodologies. We then describe representative applications in detail to elucidate how SVT serves as a valuable tool in virological research. Finally, we present our perspectives regarding the future possibilities and challenges of SVT.

Two-step tumor-targeting therapy via integrating metabolic lipid-engineering with in situ click chemistry

A highly efficient two-step targeting strategy integrating metabolic lipid-engineering with in situ click chemistry is developed, thus significantly improved the tumor theranostic performance of the red blood cells ghosts based drug delivery.

Responsive Exosome Nano-bioconjugates for Synergistic Cancer Therapy

Exosomes hold great potential in therapeutic development. However, native exosomes usually induce insufficient effects in vivo and simply act as drug delivery vehicles. Herein, we synthesize responsive exosome nano-bioconjugates for cancer therapy. Azide-modified exosomes derived from M1 macrophages are conjugated with dibenzocyclooctyne-modified antibodies of CD47 and SIRPα (aCD47 and aSIRPα) through pH-sensitive linkers. After systemic administration, the nano-bioconjugates can actively target tumors through the specific recognition between aCD47 and CD47 on the tumor cell surface. In the acidic tumor microenvironment, the benzoic-imine bonds of the nano-bioconjugates are cleaved to release aSIRPα and aCD47 that can, respectively, block SIRPα on macrophages and CD47, leading to abolished "don't eat me" signaling and improved phagocytosis of macrophages. Meanwhile, the native M1 exosomes effectively reprogram the macrophages from pro-tumoral M2 to anti-tumoral M1.

Chemical modification of enveloped viruses for biomedical applications

The unique characteristics of enveloped viruses including nanometer size, consistent morphology, narrow size distribution, versatile functionality and biocompatibility have attracted attention from scientists to develop enveloped viruses for biomedical applications. The biomedical applications of the viral-based nanoparticles include vaccine development, imaging and targeted drug delivery. The modification of the structural elements of enveloped viruses is necessary for the desired functions. Here, we review the chemical approaches that have been utilized to develop bionanomaterials based on enveloped viruses for biomedical applications. We first provide an overview of the structures of enveloped viruses which are composed of nucleic acids, structural and functional proteins, glycan residues and lipid envelope. The methods for modification, including direct conjugation, metabolic incorporation of functional groups and peptide tag insertion, are described based on the biomolecular types of viral components. Layer-by-layer technology is also included in this review to illustrate the non-covalent modification of enveloped viruses. Then, we further elaborate the applications of chemically-modified enveloped viruses, virus-like particles and viral subcomponents in biomedical research.

A Spotlight on Viruses-Application of Click Chemistry to Visualize Virus-Cell Interactions

The replication of a virus within its host cell involves numerous interactions between viral and cellular factors, which have to be tightly controlled in space and time. The intricate interplay between viral exploitation of cellular pathways and the intrinsic host defense mechanisms is difficult to unravel by traditional bulk approaches. In recent years, novel fluorescence microscopy techniques and single virus tracking have transformed the investigation of dynamic virus-host interactions. A prerequisite for the application of these imaging-based methods is the attachment of a fluorescent label to the structure of interest. However, their small size, limited coding capacity and multifunctional proteins render viruses particularly challenging targets for fluorescent labeling approaches. Click chemistry in conjunction with genetic code expansion provides virologists with a novel toolbox for site-specific, minimally invasive labeling of virion components, whose potential has just recently begun to be exploited. Here, we summarize recent achievements, current developments and future challenges for the labeling of viral nucleic acids, proteins, glycoproteins or lipids using click chemistry in order to study dynamic processes in virus-cell interactions.

Engineering oncolytic vaccinia virus with functional peptides through mild and universal strategy

Oncolytic virotherapy is one of promising tumor therapy modalities. However, its therapeutic efficacy is still limited due to the immunogenicity and poor tumor-targeting capability. In this report, an engineered oncolytic vaccinia virus (OVV) was constructed by site-specifically introducing azide groups to the envelope of OVV during the in situ assembling process of virions. Subsequently, dibenzocyclooctynes (DBCO) derivate T7 peptide and DBCO derivate self-peptide were simultaneously conjugated to the azide-modified OVV (azide-OVV) via copper-free click chemistry. The infectivity of peptide-conjugated virus was well kept. Meanwhile, both of the targeting capacity to transferrin receptor (TfR)-overexpressed tumor cells and the in vivo blood circulation time increased. Therefore, the growth of TfR-positive tumor could be significantly inhibited after intravenously injecting the engineered OVV, while no noticeable side effects. This construction strategy can be popularized to other enveloped oncolytic virus (OV), thus a universal engineering platform can be provided for OV cancer therapy. Graphical Abstract An engineered oncolytic vaccinia virus (OVV) was constructed by bioconjugating DBCO derivate T7 peptide and DBCO derivate self-peptide with azide-modified OVV via copper-free click chemistry. As a result, the tumor inhibit effect was significantly enhanced attributed to the prolonged in vivo circulation time and improved targeting recognition capability.

In Vivo Tracking of Multiple Tumor Exosomes Labeled by Phospholipid-Based Bioorthogonal Conjugation

Exosomes are cell-secreted nanoscale membrane vesicles that play critical roles in many pathophysiological processes. The clinical value of exosomes is under intense investigation, yet current knowledge regarding their in vivo properties is very limited because of the lack of efficient labeling techniques. Here, we report a phospholipid-based bioorthogonal labeling strategy to endow exosomes with optical probes without influencing their native biological functions. We investigated the dynamic in vivo biodistribution and organotropic uptake of multiple tumor exosomes in a single mouse. The results indicate that the exosomes derived from different cell lines show specific organotropic uptake. This phospholipid-based labeling strategy opens a new window to directly visualize and monitor exosome trafficking in living systems and holds great promise for exploring exosome-involved biological events such as cancer metastasis.

One-Pot Two-Step Metabolic Labeling of Teichoic Acids and Direct Labeling of Peptidoglycan Reveals Tight Coordination of Both Polymers Inserted into Pneumococcus Cell Wall

A method for labeling teichoic acids in the human pathogen Streptococcus pneumoniae has been developed using a one-pot two-step metabolic labeling approach. The essential nutriment choline modified with an azido-group was incorporated and exposed at the cell surface more rapidly than it reacted with the strain promoted azide alkyne cycloaddition (SPAAC) partner also present in the medium. Once at the cell surface on teichoic acids, coupling of the azido group could then occur within 5 min by the bio-orthogonal click reaction with a DIBO-linked fluorophore. This fast and easy method allowed pulse-chase experiments and was combined with another fluorescent labeling approach to compare the insertion of teichoic acids with peptidoglycan synthesis with unprecedented temporal resolution. It has revealed that teichoic acid and peptidoglycan processes are largely concomitant, but teichoic acid insertion persists later at the division site.

Specific and spatial labeling of choline-containing teichoic acids in Streptococcus pneumoniae by click chemistry

Propargyl-choline was efficiently incorporated into teichoic acid (TA) polymers on the surface of Streptococcus pneumoniae. The introduction of a fluorophore by click chemistry enabled sufficient labeling of the pneumococcus, as well as its specific detection when mixed with other bacterial species. The labeling is localized at the septal site, suggesting a similar location of the TA and peptidoglycan (PG) synthetic machineries. This method is a unique opportunity to improve our understanding of the spatial location of pneumococcal TA biosynthesis.

SpyCatcher-SpyTag mediated in situ labelling of progeny baculovirus with quantum dots for tracking viral infection in living cells

A non-invasive labelling strategy is proposed to label baculovirus via genetic insertion of a SpyTag into the viral glycoprotein, followed by specific conjugation with the SpyCatcher protein on modified quantum dots (QDs) through an isopeptide bond. The labelling method is convenient and efficient and shows little attenuation of viral infectivity. Therefore, it is a biologically compatible technique for tracking viral infection.

Labeling and Single-Particle-Tracking-Based Entry Mechanism Study of Vaccinia Virus from the Tiantan Strain

Entry is the first and critical step of viral infection, while the entry mechanisms of many viruses are still unclear due to the lack of efficient technology. In this report, by taking advantage of the single-virion fluorescence tracking technique and simultaneous dual-labeling methods for viruses we developed, the entry pathway of vaccinia virus from tiantan strain (VACV-TT) was studied in real-time. By combining with the technologies of virology and cell biology, we found that VACV-TT moved toward the Vero cell body along the filopodia induced by the virions interaction, and then, they were internalized through macropinocytosis, which was an actin-, ATP-dependent but clathrin-, caveolin-independent endocytosis. These results are of significant importance for VACV-TT-based vaccine vectors and oncolytic virus study.

In Situ Bioorthogonal Metabolic Labeling for Fluorescence Imaging of Virus Infection In Vivo

Optical fluorescence imaging is an important strategy to explore the mechanism of virus-host interaction. However, current fluorescent tag labeling strategies often dampen viral infectivity. The present study explores an in situ fluorescent labeling strategy in order to preserve viral infectivity and precisely monitor viral infection in vivo. In contrast to pre-labeling strategy, mice are first intranasally infected with azide-modified H5N1 pseudotype virus (N₃ -H5N1p), followed by injection of dibenzocyclooctyl (DBCO)-functionalized fluorescence 6 h later. The results show that DBCO dye directly conjugated to N₃ -H5N1p in lung tissues through in vivo bioorthogonal chemistry with high specificity and efficacy. More remarkably, in situ labeling rather than conventional prelabeling strategy effectively preserves viral infectivity and immunogenicity both in vitro and in vivo. Hence, in situ bioorthogonal viral labeling is a promising and reliable strategy for imaging and tracking viral infection in vivo.

Modern Synthetic Avenues for the Preparation of Functional Fluorophores

Biomedical research relies on the fast and accurate profiling of specific biomolecules and cells in a non‐invasive manner. Functional fluorophores are powerful tools for such studies. As these sophisticated structures are often difficult to access through conventional synthetic strategies, new chemical processes have been developed in the past few years. In this Minireview, we describe the most recent advances in the design, preparation, and fine‐tuning of fluorophores by means of multicomponent reactions, C−H activation processes, cycloadditions, and biomolecule‐based chemical transformations.

A two-step strategy to radiolabel choline phospholipids with 99mTc in S180 cell membranes via strain-promoted cyclooctyne-azide cycloaddition reaction

As tumor markers, the radiolabeling of choline (Cho)-containing phospholipids in cellular membranes with ^99mTc is a challenge. The conventional strategy to combine the metallic radionuclide with Cho by large ligand damages the bioactivity of Cho, resulting in low tumor-to-nontumor ratios. Pretargeting strategy based on strain-promoted cyclooctyne-azide cycloaddition (SPAAC) reaction was applied to solve this general problem. Functional click synthons were synthesized as pretargeting components: azidoethyl-choline (AECho) serves as tumor marker and azadibenzocyclooctyne (ADIBO) conjugated to bis(2-pieolyl) amine (BPA) ligand (ADIBO-BPA) as ^99mTc(CO)₃-labeling and azido-binding group. Both in vitro cell experiment and in vivo biodistribution experiment indicate that it is versatile to radiolabel Cho in cellular membranes via this two-step pretargeting strategy. We believe that this pretargeting strategy can indeed enhance the target-specificity and also reduce background signals to optimize imaging quality.

Surface labeling of enveloped virus with polymeric imidazole ligand-capped quantum dots via the metabolic incorporation of phospholipids into host cells

We report a general method for the preparation of quantum dot-labeled viruses through a strain-promoted azide-alkyne cycloaddition (SPAAC) reaction. The quantum dot sample was functionalized with methacrylate-based polymeric imidazole ligands (MA-PILs) bearing dibenzocyclooctyne groups. Enveloped measles virus was labeled with azide groups through the metabolic incorporation of a choline analogue into the host cell membrane, and then linked with the modified QDs. The virus retained its infectious ability against host cells after the modification with MA-PIL capped QDs.

Labeling of Enveloped Virus via Metabolic Incorporation of Azido Sugars

Modification of an enveloped measles virus was achieved by metabolic incorporation of azido sugars in host cells through the protein glycosylation process. Based on this, the resulting measles virus particles could be modified with azido groups on the surface glycoproteins, which could be further labeled with fluorescence dyes using a strain-promoted azide-alkyne cycloaddition reaction. We envision this metabolic labeling approach to be applicable to a wide variety of enveloped viruses, allowing the facile conjugation and surface modification.

Real-time light scattering tracking of gold nanoparticles- bioconjugated respiratory syncytial virus infecting HEp-2 cells

Real-time tracking of virus invasion is crucial for understanding viral infection mechanism, which, however, needs simple and efficient labeling chemistry with improved signal-to-noise ratio. For that purpose, herein we investigated the invasion dynamics of respiratory syncytial virus (RSV) through dark-field microscopic imaging (iDFM) technique by using Au nanoparticles (AuNPs) as light scattering labels. RSV, a ubiquitous, non-segmented, pleiomorphic and negative-sense RNA virus, is an important human pathogen in infants, the elderly, and the immunocompromised. In order to label the enveloped virus of paramyxoviridae family, an efficient streptavidin (SA)-biotin binding chemistry was employed, wherein AuNPs and RSV particles modified with SA and biotin, respectively, allowing the AuNP-modified RSVs to maintain their virulence without affecting the native activities of RSV, making the long dynamic visualization successful for the RSV infections into human epidermis larynx carcinoma cells.

Progress on the labeling and single-particle tracking technologies of viruses

We review recent advances in virus labeling and the emerging fluorescence imaging technologies used in the imaging and tracking of viruses.