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    Development of an Effective Functional Lipid Anchor for Membranes (FLAME) for the Bioorthogonal Modification of the Lipid Bilayer of Mesenchymal Stromal Cells
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    Abstract:
    The glycosylation of cellular membranes is crucial for the survival and communication of cells. As our target is the engineering of the glycocalyx, we designed a functionalized lipid anchor for the introduction into cellular membranes called Functional Lipid Anchor for MEmbranes (FLAME). Since cholesterol incorporates very effectively into membranes, we developed a twice cholesterol-substituted anchor in a total synthesis by applying protecting group chemistry. We labeled the compound with a fluorescent dye, which allows cell visualization. FLAME was successfully incorporated in the membranes of living human mesenchymal stromal cells (hMSC), acting as a temporary, nontoxic marker. The availability of an azido function─a bioorthogonal reacting group within the compound─enables the convenient coupling of alkyne-functionalized molecules, such as fluorophores or saccharides. After the incorporation of FLAME into the plasma membrane of living hMSC, we were able to successfully couple our molecule with an alkyne-tagged fluorophore via click reaction. This suggests that FLAME is useful for the modification of the membrane surface. Coupling FLAME with a galactosamine derivative yielded FLAME–GalNAc, which was incorporated into U2OS cells as well as in giant unilamellar vesicles (GUVs) and cell-derived giant plasma membrane vesicles (GPMVs). With this, we have shown that FLAME–GalNAc is a useful tool for studying the partitioning in the liquid-ordered (Lo) and the liquid-disordered (Ld) phases. The molecular tool can also be used to analyze the diffusion behavior in the model and the cell membranes by fluorescence correlation spectroscopy (FCS).
    Keywords:
    Bioorthogonal Chemistry
    POPC
    Fluorescence Correlation Spectroscopy
    Biocompatible and degradable injectable materials prepared via bioorthogonal reactions are highly promising for biomedical applications because they can be formed in situ and administered in a minimally invasive way. In this work, a PEG-based injectable hydrogel was fabricated via a copper-free, strain-promoted azide-alkyne cycloaddition (SPAAC) click chemistry. Azide and cyclooctyne moieties on the PEG backbones underwent a rapid click reaction to trigger the formation of the hydrogel within several minutes. Resulting from the introduction of ester groups into the cross-linked network, the hydrogel presented pH-dependent hydrolysis and biological fast degradability. Good biocompatibility of the hydrogel was verified by in vitro cytotoxicity assay and in vivo studies. The hydrogel formed in situ after subcutaneously injecting the gel precursors into Kungming (KM) mice. The implanted hydrogel caused a mild inflammatory response in vivo, and the surrounding tissues fully recovered a week after the injection. The injectable and fast-degradable hydrogel fabricated by the bioorthogonal click reaction may be useful as biomaterials such as embolic agents for interventional therapy.
    Bioorthogonal Chemistry
    Biocompatibility
    Alkyne
    Biomaterial
    Citations (61)
    Abstract We report the discovery of a new bioorthogonal click‐and‐release reaction involving iminosydnones and strained alkynes. This transformation leads to two products resulting from the ligation and fragmentation of iminosydnones under physiological conditions. Optimized iminosydnones were successfully used to design innovative cleavable linkers for protein modification, thus opening up new areas in the fields of drug release and target‐fishing applications. This click‐and‐release technology offers the possibility of exchanging tags on proteins for functionalized cyclooctynes under mild and bioorthogonal conditions.
    Bioorthogonal Chemistry
    Bioconjugation
    Citations (38)
    Click chemistry has become a ubiquitous chemical tool with applications in nearly all areas of modern chemistry, including drug discovery, bioconjugation, and nanoscience. Radiochemistry is no exception, as the canonical Cu(I)-catalyzed azide-alkyne cycloaddition, strain-promoted azide-alkyne cycloaddition, inverse electron demand Diels-Alder reaction, and other types of bioorthogonal click ligations have had a significant impact on the synthesis and development of radiopharmaceuticals. This review will focus on recent applications of click chemistry ligations in the preparation of imaging agents for SPECT and PET, including small molecules, peptides, and proteins labeled with radionuclides such as 18F, 64Cu, 111In, and 99mTc.
    Bioorthogonal Chemistry
    Bioconjugation
    Alkyne
    Citations (115)
    Due to their high reaction rate and reliable selectivity, bioorthogonal click reactions have been extensively investigated in numerous research fields, such as nanotechnology, drug delivery, molecular imaging, and targeted therapy. Previous reviews on bioorthogonal click chemistry for radiochemistry mainly focus on 18F-labeling protocols employed to produce radiotracers and radiopharmaceuticals. In fact, besides fluorine-18, other radionuclides such as gallium-68, iodine-125, and technetium-99m are also used in the field of bioorthogonal click chemistry. Herein, to provide a more comprehensive perspective, we provide a summary of recent advances in radiotracers prepared using bioorthogonal click reactions, including small molecules, peptides, proteins, antibodies, and nucleic acids as well as nanoparticles based on these radionuclides. The combination of pretargeting with imaging modalities or nanoparticles, as well as the clinical translations study, are also discussed to illustrate the effects and potential of bioorthogonal click chemistry for radiopharmaceuticals.
    Bioorthogonal Chemistry
    Pretargeting
    The term "click chemistry" describes a class of organic transformations that were developed to make chemical synthesis simpler and easier, in essence allowing chemists to combine molecular subunits as if they were puzzle pieces. Over the last 25 years, the click chemistry toolbox has swelled from the canonical copper-catalyzed azide–alkyne cycloaddition to encompass an array of ligations, including bioorthogonal variants, such as the strain-promoted azide–alkyne cycloaddition and the inverse electron-demand Diels–Alder reaction. Without question, the rise of click chemistry has impacted all areas of chemical and biological science. Yet the unique traits of radiopharmaceutical chemistry have made it particularly fertile ground for this technology. In this update, we seek to provide a comprehensive guide to recent developments at the intersection of click chemistry and radiopharmaceutical chemistry and to illuminate several exciting trends in the field, including the use of emergent click transformations in radiosynthesis, the clinical translation of novel probes synthesized using click chemistry, and the advent of click-based in vivo pretargeting.
    Bioorthogonal Chemistry
    Chemical Biology
    Alkyne
    Dynamic Covalent Chemistry
    Abstract The term “click chemistry” defines a powerful set of chemical reactions that are rapid, selective, and high‐yielding. These reactions, some of which are less than 10 years old, have been applied in diverse areas, including drug discovery, materials science, and chemical biology. In chemical biology, click chemistry has been used in the selective labeling of biomolecules within living systems, allowing proteins, glycans, and other important biomolecules to be monitored in a physiologically relevant environment rather than in an in vitro setting. This demanding application requires not only the aforementioned characteristics of click chemistry but, additionally, that the reactions are bioorthogonal – that is, non‐interacting with biological functionality while proceeding under physiological conditions – and that the reagents are non‐toxic. Of the many extant click reactions, only a select few possess this unique combination of attributes, notably the Staudinger ligation of azides and triarylphosphines and [3+2] dipolar cycloadditions of azides with strained alkynes. This minireview describes the characteristics of bioorthogonal click reactions as well as recent applications toward labeling biomolecules in cells and living organisms.
    Bioorthogonal Chemistry
    Biomolecule
    Chemical Biology
    Citations (315)
    A series of naphthalimide-tetrazines were developed as bioorthogonal fluorogenic probes, which could produce significant fluorescence enhancement, notable aggregation-induced emission (AIE) characters and multicolor emissions after bioorthogonal reaction with strained dienophiles. Manipulating the π-bridge in the fluorophore skeleton allows fine-tuning of the emission wavelength and influences the AIE-active properties. With these probes, we succeeded in no-wash fluorogenic protein labeling and mitochondria-selective bioorthogonal imaging in live cells.
    Bioorthogonal Chemistry
    Tetrazine
    Citations (25)
    Abstract We report the discovery of a new bioorthogonal click‐and‐release reaction involving iminosydnones and strained alkynes. This transformation leads to two products resulting from the ligation and fragmentation of iminosydnones under physiological conditions. Optimized iminosydnones were successfully used to design innovative cleavable linkers for protein modification, thus opening up new areas in the fields of drug release and target‐fishing applications. This click‐and‐release technology offers the possibility of exchanging tags on proteins for functionalized cyclooctynes under mild and bioorthogonal conditions.
    Bioorthogonal Chemistry
    Bioconjugation
    Citations (105)
    Synthetic cell–cell adhesion with high stability and robustness is demonstrated by S. H. Yun and co-workers using a bioorthogonal click chemistry-based cell gluing method. On page 6458, they show how tetrazine (Tz) and trans-cyclooctene (TCO) conjugated to the cell surface form covalent bonds between cells within 10 min in aqueous conditions. Glued cells remain viable and stably attached in blood flow, showing the potential for biomedical applications.
    Bioorthogonal Chemistry
    Tetrazine
    Citations (1)