Cell-selective bioorthogonal labeling

Bioorthogonal SERS-bioluminescence dual-modal imaging for real-time tracking of triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) represents an aggressive subtype of breast cancer, characterized by early metastasis and a poor prognosis. Traditional imaging modalities often lack the sensitivity and molecular specificity required for the early detection of metastatic lesions. In this study, we developed a dual-modal imaging strategy that integrates surface-enhanced Raman scattering (SERS) and bioluminescence imaging probes, utilizing bioorthogonal labeling to track TNBC organ metastasis. The SERS probes were encapsulated with azide-labeled macrophage membranes to extend circulation time and enhance targeting efficiency. Additionally, bioorthogonal metabolic glycolengineering was employed to modify luciferase-labeled tumor cells (4T1-Luc) with bicyclo[6.1.0]nonyne (BCN) groups, facilitating precise binding between the probes and 4T1-Luc cells through click chemistry reactions. This dual-modal imaging approach enabled real-time monitoring of small metastatic lesions with high sensitivity, providing a non-invasive and accurate method for assessing tumor metastasis and therapeutic response in vivo. Our findings indicate that the dual-modal imaging technique, combining SERS and bioluminescence with bioorthogonal labeling, holds significant potential for advanced applications in oncology. STATEMENT OF SIGNIFICANCE: This study devised a surface-enhanced Raman scattering (SERS) and bioluminescence dual-modal imaging strategy integrated with a bioorthogonal label to address the challenge of tracking the metastasis of aggressive triple-negative breast cancer (TNBC). In contrast to conventional methods, this approach facilitated real-time, whole-body monitoring of tumor dissemination through bioluminescence. Simultaneously, it achieved the detection of micro-metastases in organs using SERS, thereby exceeding the sensitivity limitations of existing imaging techniques. Clinical validation with human samples further demonstrated its potential for non-invasive therapeutic assessment and early intervention. By bridging preclinical innovation and clinical requirements, this research offered a transformative tool for precision oncology. It is expected to attract the interest of researchers in the fields of biomedicine, nanotechnology, and cancer therapeutics.

Evaluation of Pyrones in Bioorthogonal Reactions: Correlation between Structure, Reactivity, and Bioorthogonality

Alpha-pyrones have been used for applications ranging from total synthesis to antibiotics. However, their application as dienes in bioorthogonal reactions has not been extensively explored. In previous work, we demonstrated the promising application of ester-functionalized pyrones in bioorthogonal protein labeling. Here, we constructed a library of substituted pyrones to evaluate their potential in bioorthogonal reactions by exploring the relationships among structure, reactivity, and bioorthogonality. We found that most pyrone derivatives with electron-withdrawing groups exhibited reactivity toward endo-bicyclo[6.1.0]nonyne (BCN), producing tricyclic and tetracyclic products in good yields. As expected, pyrones with more and stronger electron-withdrawing substituents showed faster reaction kinetics with BCN. Bicyclic pyrone derivatives showed substantially decreased reactivity, most likely resulting from increased steric effects. Counterintuitively, we found that substitutions at pyrone positions 4 and 5 affected the reactivity more than those at positions 3 and 6. To provide insights into both the expected and counterintuitive reactivities of the pyrone library members, we performed a quantum chemical analysis. Additionally, we evaluated each pyrone's reactivity with L-cysteine and found no correlation between pyrone reactivity with BCN and cysteine-based bioorthogonality. Finally, we evaluated the reactivity of pyrones toward a collection of popular dienophiles used in bioorthogonal reactions.

Toolbox of Clickable Benzylguanines for Labeling of HoxB8-Derived Macrophages via SNAP-Tag and Bioorthogonal Chemistry

Inflammation is a dynamic process which importantly involves migration of immune cells. Understanding the onset, acute phase and resolution of inflammation is greatly facilitated by their in vivo imaging. However, immune cells are sensitive, difficult to genetically manipulate and prone to changes in response to contact, hindering the application of well-established cell labeling methods. We generated the first reported SNAP-tag expressing conditionally immortalized early hematopoietic progenitor cells (ER-HoxB8) and synthesized benzylguanine (BG) analogs with bioorthogonal groups for SNAP-tag mediated cell surface labeling. Comparative investigation of SNAP-tag positive HeLa cells, ER-HoxB8 progenitor cells and ER-HoxB8-derived macrophages as well as neutrophiles revealed remarkable differences in labeling depending on the bioorthogonal group and fluorescent reporter used. HeLa cells and ER-HoxB8 progenitor cells were efficiently labeled with BG analogs bearing an azide and a dioxolan-fused trans-cyclooctene (dTCO). When we differentiated ER-HoxB8 cells into macrophages, labeling was less bright due to lower SNAP-tag expression and only the tetrazine ligation of dTCO proved suitable for cell-type specific labeling. These results show that exploring different reactions and bioorthogonal groups is important to address the challenge of labeling differentiated immune cells. Combining the SNAP-tag with click chemistry provides a modular approach for cell-specific labeling and the combination of SNAP-tag and dTCO presents an improved system for labeling ER-HoxB8-derived macrophages.

Bioorthogonally activated probes for precise fluorescence imaging

Over the past two decades, bioorthogonal chemistry has undergone a remarkable development, challenging traditional assumptions in biology and medicine. Recent advancements in the design of probes tailored for bioorthogonal applications have met the increasing demand for precise imaging, facilitating the exploration of complex biological systems. These state-of-the-art probes enable highly sensitive, low background, in situ imaging of biological species and events within live organisms, achieving resolutions comparable to the size of the biomolecule under investigation. This review provides a comprehensive examination of various categories of bioorthogonally activated in situ fluorescent labels. It highlights the intricate design and benefits of bioorthogonal chemistry for precise in situ imaging, while also discussing future prospects in this rapidly evolving field.

A Nitroreductase-Activatable Metabolic Reporter for Covalent Labeling of Pathological Hypoxic Cells in Tumorigenesis

Aberrant hypoxic stress will initiate a cascade of pathological consequence observed prominently in tumorigenesis. Understanding of hypoxia's role in tumorigenesis is highly essential for developing effective therapeutics, which necessitates reliable tools to specifically distinguish hypoxic tumor cells (or tissues) and correlate their dynamics with the status of disease in complex living settings for precise theranostics. So far, disparate hypoxia-responsive probe molecules and prodrugs were designed via chemical or enzymatic reactions, yet their capability in real-time reporting pathogenesis development is often compromised due to unrestricted diffusion and less selectivity towards the environmental responsiveness. Herein we present an oxygen-insensitive nitroreductase (NTR)-activatable glycan metabolic reporter (pNB-ManNAz) capable of covalently labeling hypoxic tumor cells and tissues. Under pathophysiological hypoxic environments, the caged non-metabolizable precursor pNB-ManNAz exhibited unique responsiveness to cellular NTR, culminating in structural self-immolation and the resultant ManNAz could incorporate onto cell surface glycoproteins, thereby facilitating fluorescence labeling via bioorthogonal chemistry. This NTR-responsive metabolic reporter demonstrated broad applicability for multicellular hypoxia labeling, particularly in the dynamic monitoring of orthotopic tumorigenesis and targeted tumor phototherapy in vivo. We anticipate that this approach holds promise for investigating hypoxia-related pathological progression, offering valuable insights for accurate diagnosis and treatment.

Stimuli-responsive prodrugs with self-immolative linker for improved cancer therapy

Self-immolative prodrugs have gained significant attention as an innovative approach for targeted cancer therapy. These prodrugs are engineered to release the active anticancer agents in response to specific triggers within the tumor microenvironment, thereby improving therapeutic precision while reducing systemic toxicity. This review focuses on the molecular architecture and design principles of self-immolative prodrugs, emphasizing the role of stimuli-responsive linkers and activation mechanisms that enable controlled drug release. Recent advancements in this field include the development of prodrugs that incorporate targeting moieties for enhanced site-specificity. Moreover, the review discusses the incorporation of targeting moieties to achieve site-specific drug delivery, thereby improving the selectivity of treatment. By summarizing key research from the past five years, this review highlights the potential of self-immolative prodrugs to revolutionize cancer treatment strategies and pave the way for their integration into clinical practice.

Redox-Activated Substrates for Enhancing Activatable Cyclopropene Bioorthogonal Reactions

Bioorthogonal chemistry has become a mainstay in chemical biology and is making inroads in the clinic with recent advances in protein targeting and drug release. Since the field's beginning, a major focus has been on designing bioorthogonal reagents with good selectivity, reactivity, and stability in complex biological environments. More recently, chemists have imbued reagents with new functionalities like click-and-release or light/enzyme-controllable reactivity. We have previously developed a controllable cyclopropene-based bioorthogonal ligation, which has excellent stability in physiological conditions and can be triggered to react with tetrazines by exposure to enzymes, biologically significant small molecules, or light spanning the visual spectrum. Here, to improve reactivity and gain a better understanding of this system, we screened diene reaction partners for the cyclopropene. We found that a cyclopropene-quinone pair is 26 times faster than reactions with 1,2,4,5-tetrazines. Additionally, we showed that the reaction of the cyclopropene-quinone pair can be activated by two orthogonal mechanisms: caging group removal on the cyclopropene and oxidation/reduction of the quinone. Finally, we demonstrated that this caged cyclopropene-quinone can be used as an imaging tool to label the membranes of fixed, cultured cells.

Stepwise virus assembly in the cell nucleus revealed by spatiotemporal click chemistry of DNA replication

Biomolecular assemblies are fundamental to life and viral disease. The spatiotemporal coordination of viral replication and assembly is largely unknown. Here, we developed a dual-color click chemistry procedure for imaging adenovirus DNA (vDNA) replication in the cell nucleus. Late- but not early-replicated vDNA was packaged into virions. Early-replicated vDNA segregated from the viral replication compartment (VRC). Single object tracking, superresolution microscopy, fluorescence recovery after photobleaching, and correlative light-electron microscopy revealed a stepwise assembly program involving vDNA and capsid intermediates. Depending on replication and the scaffolding protein 52K, late-replicated vDNA with rapidly exchanging green fluorescent protein-tagged capsid linchpin protein V and incomplete virions emerged from the VRC periphery. These nanogel-like puncta exhibited restricted movements and were located with the capsid proteins hexon, VI, and virions in the nuclear periphery, suggestive of sites for virion formation. Our findings identify VRC dynamics and assembly intermediates, essential for stepwise productive adenovirus morphogenesis.

Pyranthiones/Pyrones: "Click and Release" Donors for Subcellular Hydrogen Sulfide Delivery and Labeling

Hydrogen sulfide (H2 S), one of the most important gasotransmitters, plays a critical role in endogenous signaling pathways of many diseases. However, developing H2 S donors with both tunable release kinetics and high release efficiency for subcellular delivery has been challenging. Here, we describe a click and release reaction between pyrone/pyranthiones and bicyclononyne (BCN). This reaction features a release of CO2 /COS with second-order rate constants comparable to Strain-Promoted Azide-Alkyne Cycloaddition reactions (SPAACs). Interestingly, pyranthiones showed enhanced reaction rates compared to their pyrone counterparts. We investigated pyrone biorthogonality and demonstrated their utility in protein labeling applications. Moreover, we synthesized substituted pyranthiones with H2 S release kinetics that can address the range of physiologically relevant H2 S dynamics in cells and achieved quantitative H2 S release efficiency in vitro. Finally, we explored the potential of pyranthiones as H2 S/COS donors for mitochondrial-targeted H2 S delivery in living cells.