Bio-orthogonal Supramolecular Latching inside Live Animals and Its Application for in Vivo Cancer Imaging

Supramolecular Guest Exchange in Cucurbit[7]uril for Bioorthogonal Fluorogenic Imaging across the Visible Spectrum

Fluorogenic probes that unmask fluorescence signals in response to bioorthogonal reactions are a powerful new addition to biological imaging. They can significantly reduce background fluorescence and minimize nonspecific signals, potentially enabling real-time, high-contrast imaging without the need to wash out excess fluorophores. While diverse classes of highly refined synthetic fluorophores are now readily available, integrating them into a bioorthogonal fluorogenic scheme still requires extensive design efforts and customized structural alterations to optimize quenching mechanisms for each specific fluorophore scaffold. Herein, we present a highly generalizable strategy that can produce an efficient bioorthogonal fluorogenic response from essentially any readily available fluorophore without further structural alterations. We designed this strategy based on the macrocyclic cucurbit[7]uril (CB7) host, where a fluorogenic response is achieved by programming a guest exchange reaction within the macrocyclic cavity. We employed this strategy to rapidly create fluorogenic probes across the visible spectrum from diverse fluorophore scaffolds, which enabled no-wash imaging in live cells and tissues with minimal background signal. Finally, we demonstrated that this strategy can be combined with metabolic labeling for fluorogenic detection of metabolically tagged mycobacteria under no-wash conditions and paired with covalently clickable probes for high-contrast super-resolution and multiplexed imaging in cells and tissues.

OrthoID: profiling dynamic proteomes through time and space using mutually orthogonal chemical tools

Identifying proteins at organelle contact sites, such as mitochondria-associated endoplasmic reticulum membranes (MAM), is essential for understanding vital cellular processes, yet challenging due to their dynamic nature. Here we report "OrthoID", a proteomic method utilizing engineered enzymes, TurboID and APEX2, for the biotinylation (Bt) and adamantylation (Ad) of proteins close to the mitochondria and endoplasmic reticulum (ER), respectively, in conjunction with high-affinity binding pairs, streptavidin-biotin (SA-Bt) and cucurbit[7]uril-adamantane (CB[7]-Ad), for selective orthogonal enrichment of Bt- and Ad-labeled proteins. This approach effectively identifies protein candidates associated with the ER-mitochondria contact, including LRC59, whose roles at the contact site were-to the best of our knowledge-previously unknown, and tracks multiple protein sets undergoing structural and locational changes at MAM during mitophagy. These findings demonstrate that OrthoID could be a powerful proteomics tool for the identification and analysis of spatiotemporal proteins at organelle contact sites and revealing their dynamic behaviors in vital cellular processes.

Overcoming barriers with non-covalent interactions: supramolecular recognition of adamantyl cucurbit[n]uril assemblies for medical applications

Adamantane, a staple in medicinal chemistry, recently became a cornerstone of a supramolecular host-guest drug delivery system, ADA/CB[n]. Owing to a good fit between the adamantane cage and the host cavity of the cucurbit[n]uril macrocycle, formed strong inclusion complexes find applications in drug delivery and controlled drug release. Note that the cucurbit[n]uril host is not solely a delivery vehicle of the ADA/CB[n] system but rather influences the bioactivity and bioavailability of drug molecules and can tune drug properties. Namely, as host-guest interactions are capable of changing the intrinsic properties of the guest molecule, inclusion complexes can become more soluble, bioavailable and more resistant to metabolic conditions compared to individual non-complexed molecules. Such synergistic effects have implications for practical bioapplicability of this complex system and provide a new viewpoint to therapy, beyond the traditional single drug molecule approach. By achieving a balance between guest encapsulation and release, the ADA/CB[n] system has also found use beyond just drug delivery, in fields like bioanalytics, sensing assays, bioimaging, etc. Thus, chemosensing in physiological conditions, indicator displacement assays, in vivo diagnostics and hybrid nanostructures are just some recent examples of the ADA/CB[n] applicability, be it for displacements purposes or as cargo vehicles.

Challenges and Opportunities of Functionalized Cucurbiturils for Biomedical Applications

Cucurbit[n]uril (CB[n]) macrocycles (especially CB[5] to CB[8]) have shown exceptional attributes since their discovery in 2000. Their stability, water solubility, responsiveness to several stimuli, and remarkable binding properties have enabled a growing number of biological applications. Yet, soon after their discovery, the challenge of their functionalization was set. Nevertheless, after more than two decades, a myriad of CB[n] derivatives has been described, many of them used in cells or in vivo for advanced applications. This perspective summarizes key advances of this burgeoning field and points to the next opportunities and remaining challenges to fully express the potential of these fascinating macrocycles in biology and biomedical sciences.

Small-molecule probes from bench to bedside: advancing molecular analysis of drug-target interactions toward precision medicine

Over the past decade, remarkable advances have been witnessed in the development of small-molecule probes. These molecular tools have been widely applied for interrogating proteins, pathways and drug-target interactions in preclinical research. While novel structures and designs are commonly explored in probe development, the clinical translation of small-molecule probes remains limited, primarily due to safety and regulatory considerations. Recent synergistic developments - interfacing novel chemical probes with complementary analytical technologies - have introduced and expedited diverse biomedical opportunities to molecularly characterize targeted drug interactions directly in the human body or through accessible clinical specimens (e.g., blood and ascites fluid). These integrated developments thus offer unprecedented opportunities for drug development, disease diagnostics and treatment monitoring. In this review, we discuss recent advances in the structure and design of small-molecule probes with novel functionalities and the integrated development with imaging, proteomics and other emerging technologies. We further highlight recent applications of integrated small-molecule technologies for the molecular analysis of drug-target interactions, including translational applications and emerging opportunities for whole-body imaging, tissue-based measurement and blood-based analysis.

Preparation and In Vitro Validation of a Cucurbit[7]uril-Peptide Conjugate Targeting the LDL Receptor

Here we report the coupling of a cyclic peptide (VH4127) targeting the low density lipoprotein (LDL) receptor (LDLR) noncompetitively to cucurbit[7]uril (CB[7]) to develop a new kind of drug delivery system (DDS), namely, CB[7]-VH4127, with maintained binding affinity to the LDLR. To evaluate the uptake potential of this bismacrocyclic compound, another conjugate was prepared comprising a high-affinity group for CB[7] (adamantyl(Ada)-amine) coupled to the fluorescent tracker Alexa680 (A680). The resulting A680-Ada·CB[7]-VH4127 supramolecular complex demonstrated conserved LDLR-binding potential and improved LDLR-mediated endocytosis and intracellular accumulation potential in LDLR-expressing cells. The combination of two technologies, namely, monofunctionalized CB[7] and the VH4127 LDLR-targeting peptide, opens new avenues in terms of targeting and intracellular delivery to LDLR-expressing tissues or tumors. The versatile transport capacity of CB[7], known to bind a large spectrum of bioactive or functional compounds, makes this new DDS suitable for a wide range of therapeutic or imaging applications.

A Combination of Bio-Orthogonal Supramolecular Clicking and Proximity Chemical Tagging as a Supramolecular Tool for Discovery of Putative Proteins Associated with Laminopathic Disease

Protein mutations alter protein-protein interactions that can lead to a number of illnesses. Mutations in lamin A (LMNA) have been reported to cause laminopathies. However, the proteins associated with the LMNA mutation have mostly remained unexplored. Herein, a new chemical tool for proximal proteomics is reported, developed by a combination of proximity chemical tagging and a bio-orthogonal supramolecular latching based on cucurbit[7]uril (CB[7])-based host-guest interactions. As this host-guest interaction acts as a noncovalent clickable motif that can be unclicked on-demand, this new chemical tool is exploited for reliable detection of the proximal proteins of LMNA and its mutant that causes laminopathic dilated cardiomyopathy (DCM). Most importantly, a comparison study reveals, for the first time, mutant-dependent alteration in LMNA proteomic environments, which allows to identify putative laminopathic DCM-linked proteins including FOXJ3 and CELF2. This study demonstrates the feasibility of this chemical tool for reliable proximal proteomics, and its immense potential as a new research platform for discovering biomarkers associated with protein mutation-linked diseases.

Multivalent Cucurbituril Dendrons for Cell Membrane Engineering with Supramolecular Receptors

The affinity possible from certain supramolecular motifs rivals that for some of the best-recognized interactions in biology. Cucurbit[7]uril (CB[7]) macrocycles, for example, are capable of achieving affinities in their binding to certain guests that rival that of biotin-avidin. Supramolecular host-guest recognition between CB[7] and certain guests has been demonstrated to spatially localize guest-linked agents to desired sites in vivo, offering opportunities to better exploit this affinity axis for applications in biomedicine. Herein, architectures of CB[7] are prepared from a polyamidoamine (PAMAM) dendrimer scaffold, installing a PEG-linked cholesterol anchor on the opposite end of the dendron to facilitate cell membrane integration. Cells are then modified with this dendritic CB[7] construct in vitro, demonstrating the ability to deliver a model guest-linked agent to the cell membrane. This approach to realize synthetic supramolecular "membrane receptors" may be leveraged in the future for in situ imaging or modulation of cell-based therapies or to facilitate a synthetic supramolecular recognition axis on the cell membrane.

Encapsulation of Trimethine Cyanine in Cucurbit[8]uril: Solution versus Solid‐State Inclusion Behavior

Inclusion of polymethine cyanine dyes in the cavity of macrocyclic receptors is an effective strategy to alter their absorption and emission behavior in aqueous solution. In this paper, the effect of the host‐guest interaction between cucurbit[8]uril (CB[8]) and a model trimethine indocyanine (Cy3) on dye spectral properties and aggregation in water is investigated. Solution studies, performed by a combination of spectroscopic and calorimetric techniques, indicate that the addition of CB[8] disrupts Cy3 aggregates, leading to the formation of a 1 : 1 host‐guest complex with an association constant of 1.5×10⁶ M⁻¹. At concentrations suitable for NMR experiments, the slow formation of a supramolecular polymer was observed, followed by precipitation. Single crystals X‐ray structure elucidation confirmed the formation of a polymer with 1 : 1 stoichiometry in the solid state.

Bioorthogonal Assembly Based on Metallophilic Interactions for Selective Imaging and PDT Treatment of Cancer Cells

Precise control of the luminescence and singlet oxygen generation is important for selective photo-theranostics applications. In this work, bioorthogonal assembly based on d10···d10 metallophilic interactions was first proposed for selective...

Supramolecular capture of highly polar amidosquaraine dye in water with nanomolar affinity and large turn-on fluorescence

A supramolecular dye-capture system comprising anionic amidosquaraine guest and macrocyclic tetralactam host exhibits nanomolar affinity and "turn on" visible fluorescence. Utility is demonstrated with a new fluorescent assay for liposome leakage induced by the biomedically important enzyme phospholipase A₂.

Visualization of lipophagy using a supramolecular FRET pair

A rationally designed supramolecular FRET pair consisting of cyanine3-cucurbit[7]uril (Cy3-CB[7]) and boron-dipyrromethene 630/650-adamantylammonium (BDP-AdA) can be used to visualize organelle-specific autophagy events. The intracellular accumulations of Cy3-CB[7] in lysosomes and BDP-AdA in lipid droplets (LDs) and the formation of an intracellular host-guest complex between Cy3-CB[7] and BDP-AdA resulting in FRET signals allow us to visualize the fusion of LDs with lysosomes, namely, lipophagy. This study demonstrates the potential of supramolecular imaging based on bio-orthogonal host-guest interactions in the investigation of selective autophagy events.

Targeted Delivery and Site-Specific Activation of β-Cyclodextrin-Conjugated Photosensitizers for Photodynamic Therapy through a Supramolecular Bio-orthogonal Approach

Targeted delivery of photosensitizers using hydrophilic and tumor-directing carriers and site-specific activation of their photocytotoxicity are two common strategies to enhance the specificity of anticancer photodynamic therapy. We report herein a novel supramolecular bio-orthogonal approach to integrate these two functions. A β-cyclodextrin-substituted aza-boron-dipyrromethene-based photosensitizer was first complexed with a ferrocene-substituted black-hole quencher to inhibit its photosensitizing ability. Upon encountering the adamantane moieties that had been delivered to target cancer cells through specific binding of the conjugated peptide to the overexpressed epidermal growth factor receptor, the ferrocene-based guest species were displaced due to the stronger binding interactions between β-cyclodextrin and adamantane, thereby restoring the photodynamic activity of the photosensitizer. Hence, this two-step process enabled targeted delivery and site-specific activation of the photosensitizer, as demonstrated through a series of experiments in aqueous media, in a range of cancer cell lines and in tumor-bearing nude mice.

Supramolecular Tropism Driven Aggregation of Nanoparticles In Situ for Tumor-Specific Bioimaging and Photothermal Therapy

Inorganic nanomedicine has attracted increasing attentions in biomedical sciences due to their excellent biocompatibility and tunable, versatile functionality. However, the relatively poor accumulation and retention of these nanomedicines in targeted tissues have often hindered their clinical translation. Herein, highly efficient, targeted delivery, and in situ aggregation of ferrocene (Fc)-capped Au nanoparticles (NPs) are reported to cucurbit[7]uril (CB[7])-capped Fe₃ O₄ NPs (as an artificial target) that are magnetically deposited into the tumor, driven by strong, multipoint CB[7]-Fc host-guest interactions (here defined as "supramolecular tropism" for the first time), leading to high tumor accumulation and retention of these NPs. The in vitro and in vivo studies demonstrate the precisely controlled, specific accumulation, and retention of Au NPs in the tumor cells and tissue via supramolecular tropism and in situ aggregation, which afford locally enhanced CT imaging of cancer and enable tumor-specific photothermal therapy attributed to the plasmonic coupling effects between adjacent Au NPs within the supramolecular aggregations. This work provides a novel concept of supramolecular tropism, which may drive targeted delivery and enable specific accumulation, retention, and activation of nanomedicine for improved bioimaging and therapy of cancer.

Supramolecular "Click Chemistry" for Targeting in the Body

The fields of precision imaging and drug delivery have revealed a number of tools to improve target specificity and increase efficacy in diagnosing and treating disease. Biological molecules, such as antibodies, continue to be the primary means of assuring active targeting of various payloads. However, molecular-scale recognition motifs have emerged in recent decades to achieve specificity through the design of interacting chemical motifs. In this regard, an assortment of bioorthogonal covalent conjugations offer possibilities for in situ complexation under physiological conditions. Herein, a related concept is discussed that leverages interactions from noncovalent or supramolecular motifs to facilitate in situ recognition and complex formation in the body. Classic supramolecular motifs based on host-guest complexation offer one such means of facilitating recognition. In addition, synthetic bioinspired motifs based on oligonucleotide hybridization and coiled-coil peptide bundles afford other routes to form complexes in situ. The architectures to include recognition of these various motifs for targeting enable both monovalent and multivalent presentation, seeking high affinity or engineered avidity to facilitate conjugation even under dilute conditions of the body. Accordingly, supramolecular "click chemistry" offers a complementary tool in the growing arsenal targeting improved healthcare efficacy.

Synthesis of an AIEgen functionalized cucurbit[7]uril for subcellular bioimaging and synergistic photodynamic therapy and supramolecular chemotherapy

Aggregation-induced emission (AIE) based fluorophores (AIEgens) have attracted increasing attention for biomedical applications due to their unique optical properties. Here we report an AIE photosensitizer functionalized CB[7], namely AIECB[7], which could spontaneously self-assemble into nanoaggregates in aqueous solutions. Interestingly, the carbonyl-lace of CB[7] may potentially act as a proton acceptor in an acidic environment to fine-tune the fluorescence and singlet oxygen generation of AIECB[7] nanoaggregates by regulating the inner stacking of AIEgens. Additionally, benefiting from the guest-binding properties of CB[7], oxaliplatin was included into AIECB[7] nanoaggregates for combined photodynamic therapy and supramolecular chemotherapy. To show the modular versatility of this supramolecular system, a hypoxia-activatable prodrug banoxantrone (AQ4N) was loaded into AIECB[7] nanoaggregates, which exhibited synergistic antitumor effects on a multicellular tumor spheroid model (MCTS). This work not only provides AIECB[7] for versatile theranostic applications, but also offers important new insights into the design and development of macrocycle-conjugated AIE materials for diverse biomedical applications.

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Cucucrbituril (CB) belongs to a family of macrocycles that are easily accessible. Their structural specificity provides excellent molecular recognition capabilities, with the ability to be readily chemically modified. Because of these properties, researchers have found CB to be a useful molecular carrier for delivering drug molecules and therapeutic biomolecules. Their significance lies in the fact that CB not only increases the solubility and stability of an encapsulated guest but also provides the possibility to achieve targeted delivery of the guest molecule. Therefore, the emergence of CB undoubtedly provides opportunities for the development of targeted drug delivery in an era where intelligent drugs have attracted considerable attention. It has also been found that CB can enhance fluorescent dyes, allowing the preparation of biosensors with enhanced sensitivity for use in clinical settings. In the present review, the acquisition, properties, and structural modifications of CB are first comprehensively described, and then the value of this macrocycle in applications within the medical field is discussed. In addition, we have also summarized patent applications of CB in this field over recent years, aiming to illustrate the current status of developments of this molecule. Finally, we discuss the challenges faced by CB in the medical field and future trends in its development.

Purification of protein therapeutics via high-affinity supramolecular host-guest interactions

Efficient purification is crucial to providing large quantities of recombinant therapeutic proteins, such as monoclonal antibodies and cytokines. However, affinity techniques for manufacturing protein therapeutics that use biomolecule-conjugated agarose beads that harness specific biomolecular interactions suffer from issues related to protein denaturation, contamination and the need to maintain biomolecule-specific conditions for efficient protein capture. Here, we report a versatile and scalable method for the purification of recombinant protein therapeutics. The method exploits the high-affinity and controllable host-guest interactions between cucurbit[7]uril (CB[7]) and selected guests such as adamantylammonium. We show that the Herceptin (the brand name of trastuzumab, a monoclonal antibody drug used to treat breast cancer) and the much smaller cytokine interferon α-2a can be purified by site-specifically tagging them with adamantylammonium using the enzyme sortase A, followed by high-affinity binding with CB[7]-conjugated agarose beads and the recovery of the protein using a guest with a stronger affinity for CB[7]. The thermal and chemical stability of CB[7] beads and their scalability, recyclability and low cost may also make them advantageous for the manufacturing of biosimilars.