Host-Guest Interactions between Oxaliplatin and Cucurbit[7]uril/Cucurbit[7]uril Derivatives under Pseudo-Physiological Conditions

Computational assessment of the use of graphene-based nanosheets as PtII chemotherapeutics delivery systems

Graphene is the newest form of elemental carbon and it is becoming rapidly a potential candidate in the framework of nano-bio research. Many reports confirm the successful use of graphene-based materials as carriers of anticancer drugs having relatively high loading capacities compared with other nanocarriers. Here, the outcomes of a systematic study of the adsorption behavior of FDA approved PtII drugs cisplatin, oxaliplatin, and carboplatin on surface models of pristine, holey, and nitrogen-doped holey graphene are reported. DFT investigations in water solvent have been carried out considering several initial orientations of the drugs with respect to the surfaces. Adsorption free energies, calculated including basis set superposition error (BSSE) corrections, result to be significantly negative for many of the drug@carrier adducts indicating that tested layers could be used as potential carriers for the delivery of anticancer PtII drugs. The reduced density gradient (RDG) analysis allows to show that many kinds of non-covalent interactions, including canonical H-bond, are responsible for the stabilization of the formed adducts.

Expanding the Hydrophobic Cavity Surface of Azocalix[4]arene to Enable Biotin/Avidin Affinity with Controlled Release

The development of artificial receptors that combine ultrahigh-affinity binding and controllable release for active guests holds significant importance in biomedical applications. On one hand, a complex with an exceedingly high binding affinity can resist unwanted dissociation induced by dilution effect and complex interferents within physiological environments. On the other hand, stimulus-responsive release of the guest is essential for precisely activating its function. In this context, we expanded hydrophobic cavity surface of a hypoxia-responsive azocalix[4]arene, affording Naph-SAC4A. This modification significantly enhanced its aqueous binding affinity to 1013 M-1, akin to the naturally occurring strongest recognition pair, biotin/(strept-)avidin. Consequently, Naph-SAC4A emerges as the first artificial receptor to simultaneously integrate ultrahigh recognition affinity and actively controllable release. The markedly enhanced affinity not only improved Naph-SAC4A's sensitivity in detecting rocuronium bromide in serum, but also refined the precision of hypoxia-responsive doxorubicin delivery at the cellular level, demonstrating its immense potential for diverse practical applications.

Cucurbit[7]uril-mediated Histidine Dimerization: Exploring the Structure and Binding Mechanism

Cucurbit[7,8]urils are known to form inclusion complexes with hydrophobic amino acids such as Trp, Tyr, Phe, and Met, as well as peptides containing these residues at the N-terminus. Despite their widespread use in protein purification, the affinity of histidine (His) for cucurbit[7,8]urils has not been extensively explored. In this study, X-ray diffraction experiments were conducted to investigate the binding of two histidine moieties to the cucurbit[7]uril (CB7) cavity, resulting in a network of π-π and hydrogen bonds. This assembly was found to induce a His pKa shift of ΔpKa=-4. Histidine weakly bound to CB7 or CB8; however, isothermal titration calorimetry revealed micromolar equilibrium dissociation constant values for CB7 and CB8 when bound to dipeptides containing His at the C-terminus. Conversely, dipeptides with His at the N-terminus exhibited millimolar values. Additionally, the His-Gly-Gly tripeptide formed a 2 : 1 complex with CB7. These findings suggest the potential use of histidine and histidine-containing tags in conjunction with CB7 for various biological applications.

Nanoconstruction on Living Cell Surfaces with Cucurbit[7]uril-Based Supramolecular Polymer Chemistry: Toward Cell-Based Delivery of Bio-Orthogonal Catalytic Systems

Employing living cells as carriers to transport transition metal-based catalysts for target-specific bio-orthogonal catalysis represents a cutting-edge approach in advancing precision biomedical applications. One of the initial hurdles in this endeavor involves effectively attaching the catalysts to the carrier cells while preserving the cells' innate ability to interact with biological systems and maintaining the unaltered catalytic activity. In this study, we have developed an innovative layer-by-layer method that leverages a noncovalent interaction between cucurbit[7]uril and adamantane as the primary driving force for crafting polymeric nanostructures on the surfaces of these carrier cells. The strong binding affinity between the host-guest pair ensures the creation of a durable polymer coating on the cell surfaces. Meanwhile, the layer-by-layer process offers high adaptability, facilitating the efficient loading of bio-orthogonal catalysts onto cell surfaces. Importantly, the polymeric coating shows no discernible impact on the cells' physiological characteristics, including their tropism, migration, and differentiation, while preserving the effectiveness of the bio-orthogonal catalysts.

Supramolecular platinum complexes for cancer therapy

The rise of supramolecular chemistry offers new tools to design therapeutics and delivery platforms for biomedical applications. This review aims to highlight the recent developments that harness host-guest interactions and self-assembly to design novel supramolecular Pt complexes as anticancer agents and drug delivery systems. These complexes range from small host-guest structures to large metallosupramolecules and nanoparticles. These supramolecular complexes integrate the biological properties of Pt compounds and novel supramolecular structures, which inspires new designs of anticancer approaches that overcome problems in conventional Pt drugs. Based on the differences in Pt cores and supramolecular structures, this review focuses on five different types of supramolecular Pt complexes, and they include host-guest complexes of the FDA-approved Pt(II) drugs, supramolecular complexes of nonclassical Pt(II) metallodrugs, supramolecular complexes of fatty acid-like Pt(IV) prodrugs, self-assembled nanotherapeutics of Pt(IV) prodrugs, and self-assembled Pt-based metallosupramolecules.

Cucurbituril Enhanced Electrochemiluminescence of Gold Nanoclusters via Host-Guest Recognition for Sensitive D-Dimer Sensing

Gold nanoclusters (AuNCs) are promising electrochemiluminescence (ECL) signal probes for their outstanding biocompatibility, unusual molecule-like structures, and versatile optical and electrochemical properties. Nevertheless, their relatively low ECL efficiency and poor stability in aqueous solutions hindered their application in the ECL sensing field. Herein, a facile host-guest recognition strategy was proposed to enhance the ECL efficiency and stability of Au NCs by rigidifying the surface of ligand-stabilized AuNCs via supramolecular self-assembly between cucurbiturils[7] (CB[7]) and l-phenylalanine (l-Phe). Meanwhile, mercaptopropionic acid (MPA) was introduced as a ligand in order to cooperatively enhance the performance of the AuNCs and facilitate the link between AuNCs and bioactive substances. The prepared CB[7]/l-Phe/MPA-AuNCs had a higher ECL emission efficiency, achieving about 2-fold stronger ECL intensity than that of l-Phe/MPA-AuNCs. In addition, after non-covalent modification with CB[7], the finite stability of the papered AuNCs was significantly improved. The prepared CB[7]/l-Phe/MPA-AuNCs showed excellent D-dimer sensing results, exhibiting a linear range from 50.00 fg/mL to 100.0 ng/mL and a detection limit of 29.20 fg/mL (S/N = 3). Our work demonstrated that the host-guest self-assembly strategy provided a universal approach for strengthening the ECL efficiency and stability of nanostructures on an ultra-small scale.

Co-encapsulation of Egg-White-Derived Peptides (EWDP) and Curcumin within the Polysaccharide-Based Amphiphilic Nanoparticles for Promising Oral Bioavailability Enhancement: Role of EWDP

The comprehensive utilization of food-derived nutraceuticals with different polarities has been extremely restricted by their poor bioavailability and coexistence in a single system. This study aimed to fabricate a self-assembly of amphiphilic nanoparticles (NPs) for the hydrophilic EWDP and hydrophobic curcumin based on the carboxymethyl chitosan (CMCS) shell and γ-cyclodextrin (γ-CD) core. Notably, EWDP could cooperate with CMCS to yield superior colloidal properties with an excellent curcumin aqueous solubility and co-encapsulation capacity (>10%) for the NPs (pH 2.0-7.0). This phenomenon was mainly ascribed to the additional hydrogen-bonding network and hydrophobic interaction introduced by EWDP. Besides, the overall antioxidant activity, bioaccessibility, gastrointestinal stability, and Caco-2 cell absorption properties were significantly improved in the presence of EWDP (>20% increase). Therefore, EWDP could function as both a potential affinity agent and a nutrition enhancer to expand the co-delivery applications for diverse nutraceuticals with promising oral bioavailability enhancement in food and pharmaceutical areas.

pH-Triggered Transition from Micellar Aggregation to a Host-Guest Complex Accompanied by a Color Change

A pH-triggered transition from micellar aggregation to a host-guest complex was achieved based on the supramolecular interactions between calixpyridinium and pyrroloquinoline quinone disodium salt (PQQ-2Na) accompanied by a color change. Our design has the following three advantages: (1) a regular spherical micellar assembly is fabricated by the supramolecular interactions between calixpyridinium and PQQ-2Na at pH 6 in an aqueous solution, (2) increasing the pH can lead to a transition from micellar aggregation to a host-guest complex due to the deprotonation of calixpyridinium, and at the same time (3) increasing the pH can lead to a color change owing to the deprotonation of calixpyridinium and the complexation of deprotonated calixpyridinium with PQQ-2Na. Benefitting from the low toxicity of calixpyridinium and PQQ-2Na, this pH-induced transition from micellar aggregation to a host-guest complex was further studied as a controllable-release model.

Supramolecular co-encapsulation of a photosensitizer and chemotherapeutic drug in cucurbit[8]uril for potential chemophototherapy

Supramolecular strategies as well as combinatorial approaches have been proposed to improve cancer therapeutics. In this work, we investigated the encapsulation of the photosensitizer acridine orange (AO) and the chemotherapeutic drug oxaliplatin (OxPt) in cucurbit[8]uril (CB[8]), and tested their effect both separate and combined on tumoral cells cultivated in vitro. Binding constants and enthalpies of reaction for the AO@CB[8], (AO)₂@CB[8] and OxPt@CB[8] complexes were determined by isothermal titration calorimetry. In the case of AO, a negative cooperativity for the binding of the second AO molecule was found, in agreement with previous fluorescence titration data. We show herein that the AO@CB[8] complex was effectively incorporated within the cells and showed important phototoxicity, while the OxPt@CB[8] complex was cytotoxic only at long incubation times (24 h). Pre-treatment of the cells with the OxPt@CB[8] complex for 24 h inhibited any photodynamic action by the later treatment with the AO@CB[8] complex. However, when both complexes were co-incubated for 90 min, the combined cytotoxicity/phototoxicity was superior to any of the treatments individually. A cooperative effect was identified that added up to an extra 30% cytotoxicity/phototoxicity. The results point to an interesting system where a photosensitizer and chemotherapeutic drug are co-encapsulated in a macrocycle to develop chemophototherapy applications.

Engineering living cells with cucurbit[7]uril-based supramolecular polymer chemistry: from cell surface engineering to manipulation of subcellular organelles

Supramolecular polymer chemistry, which closely integrates noncovalent interactions with polymeric structures, is a promising toolbox for living cell engineering. Here, we report our recent progress in exploring the applications of cucurbit[7]uril (CB[7])-based supramolecular polymer chemistry for engineering living cells. First, a modular polymer-analogous approach was established to prepare multifunctional polymers that contain CB[7]-based supramolecular recognition motifs. The supramolecular polymeric systems were successfully applied to cell surface engineering and subcellular organelle manipulation. By anchoring polymers on the cell membranes, cell–cell interactions were established by CB[7]-based host–guest recognition, which further facilitated heterogeneous cell fusion. In addition to cell surface engineering, placing the multifunctional polymers on specific subcellular organelles, including the mitochondria and endoplasmic reticulum, has led to enhanced physical contact between subcellular organelles. It is highly anticipated that the CB[7]-based supramolecular polymer chemistry will provide a new strategy for living cell engineering to advance the development of cell-based therapeutic materials.

Cucurbit[7]uril-based supramolecular polymer chemistry, which closely integrates host–guest recognition with multifunctional polymeric structures, is a promising toolbox for living cell engineering.

Colorimetric determination of Listeria monocytogenes using aptamer and urease dual-labeled magnetic nanoparticles and cucurbit[7]uril-mediated supramolecular assembly of gold nanoparticle

A host-guest colorimetric strategy is described for the detection of Listeria monocytogenes (L. monocytogenes). The optical probes were self-assembled based on the supramolecular interactions between the carbonyl groups of cucurbit[7]uril portals and gold nanoparticles (CB[7]-AuNPs). Aptamer and urease modified magnetic nanoparticles were used to specifically recognize and binding to L. monocytogenes, simultaneously hydrolyzing urea to produce ammonium ion (NH₄⁺) that can reverse CB[7] induced AuNPs aggregation. In the presence of L. monocytogenes, the above-mentioned magnetic conjugates preferentially bind to the bacterial surface, which results in blocking the catalytic active sites, thus inhibiting the production of ammonium ions. The normalized absorbance ratio of A_{700 nm}/A_{525 nm} was proportional to the L. monocytogenes concentration ranging from 10 to 10⁶ cfu·mL^-1, and the visual determination can be done down to 10 cfu·mL^-1. For spiked food samples analyzed without pre-enrichment, recoveries of 98.4% to 99.3% were achieved could be verified and RSD were less than 10%. This work may offer a broad prospect for sensitive and specific determination  of pathogens.

An Activatable Host-Guest Conjugate as a Nanocarrier for Effective Drug Release through Self-Inclusion

There is a challenge in supramolecular chemotherapy for constructing a system equipped with both sufficient protection and high-efficiency release of drugs. To this end, a new strategy of an activatable host-guest conjugate with self-inclusion property is proposed. Based on the binding affinity gain of intramolecular host-guest self-inclusion, an activatable host-guest conjugate was designed, bearing cucurbit[7]uril as the host, an alkyl ammonium moiety as the guest, and the redox-responsive disulfide linkage. Oxaliplatin, a clinical antitumor drug, could be firmly encapsulated by the activatable host-guest conjugate to form the supramolecular drug with high stability. Moreover, oxaliplatin loaded in the activatable host-guest conjugate could be almost completely released by self-inclusion triggered by glutathione in a tumor microenvironment, thus exhibiting comparable antitumor bioactivity with naked oxaliplatin through in vitro cell experiments. It is highly anticipated that this line of research may open new horizons for programmable and on-demand supramolecular chemotherapy with high antitumor efficiency.

The Effect of Cucurbit[7]uril on the Antitumor and Immunomodulating Properties of Oxaliplatin and Carboplatin

Cucurbit[7]uril (CB[7]) is a molecular container that may form host–guest complexes with platinum(II) anticancer drugs and modulate their efficacy and safety. In this paper, we report our studies of the effect of CB[7]–oxaliplatin complex and the mixture of CB[7] and carboplatin (1:1) on viability and proliferation of a primary cell culture (peripheral blood mononuclear cells), two tumor cell lines (B16 and K562) and their activity in the animal model of melanoma. At the same time, we studied the impact of platinum (II) drugs with CB[7] on T cells and B cells in vitro. Although the stable CB[7]–carboplatin complex was not formed, the presence of cucurbit[7]uril affected the biological properties of carboplatin. In vivo, CB[7] increased the antitumor effect of carboplatin, but, at the same time, increased its acute toxicity. Compared to free oxaliplatin, its complex with CB[7] shows a greater cytotoxic effect on tumor cell lines B16 and K562, while in vivo, the effects of the free drug and encapsulated drug were comparable. However, in vivo studies also demonstrated that the encapsulation of oxaliplatin in CB[7] lowered the toxicity of the drug.

Supramolecular Chemotherapy: Host-Guest Complexes of Heptaplatin-Cucurbit[7]uril toward Colorectal Normal and Tumor Cells

Supramolecular chemotherapy is a strategy that is currently used to improve the therapeutic efficacy of traditional chemotherapy while mitigating side effects. Heptaplatin, a platinum chemotherapeutic antitumor drug in colorectal tumors, is traditionally used in the clinic. However, its side effects and low efficiency in killing tumors remain unresolved. Herein, a facile supramolecular chemotherapy platform on account of the host-guest chemistry between cucurbit[7]uril and the commercially available heptaplatin was studied. At pH 7.4, heptaplatin showed a strong binding to the cucurbit[7]uril nanocarrier by ¹H NMR, whose K_a was (1.38 ± 0.06) × 10⁶ M^-1 by isothermal titration calorimetry (ITC). At pH 6.0 in a tumor microenvironment, overexpressed spermine can exchange competitively heptaplatin from heptaplatin-CB[7]. This supramolecular complex achieved higher antitumor activity on colorectal tumor cells and lower cytotoxicity than the drug alone on colorectal normal cells. Furthermore, the antitumor mechanisms of supramolecular complex were investigated by apoptosis, cell cycle, and spermine synthase. It was found that heptaplatin-CB[7] consumed more colorectal tumorous intracellular spermine by the spermine synthase assay (413.85 ± 0.004 pg/mL); hepataplatin-CB[7] caused early apoptosis (87.73%) of colorectal tumor cells; heptaplatin-CB[7] induced an inhibitory response in the G₁ phase of the tumor cell cycle. These findings demonstrated that heptaplatin-CB[7] had higher antitumor activity toward human colorectal tumor cells but lower cytotoxicity toward human colorectal normal cells. It is expected to promote the supramolecular chemotherapy and translational development of the nanocomplex into the clinical field.

Capture of Phenylalanine and Phenylalanine-Terminated Peptides Using a Supramolecular Macrocycle for Surface-Enhanced Raman Scattering Detection

The cucurbit[n]uril (CB[n]) family of macrocycles are known to bind a variety of small molecules with high affinity. These motifs thus have promise in an ever-growing list of trace detection methods. Surface-enhanced Raman scattering (SERS) detection schemes employing CB[n] motifs exhibit increased sensitivity due to selective concentration of the analyte at the nanoparticle surface, coupled with the ability of CB[n] to facilitate the formation of well-defined electromagnetic hot spots. Herein, we report a CB[7] SERS assay for quantification of phenylalanine (Phe) and further demonstrate its utility for detecting peptides with an N-terminal Phe. The CB[7]-guest interaction improves the sensitivity 5-25-fold over direct detection of Phe using citrate-capped silver nanoparticle aggregates, enabling use of a portable Raman system. We further illustrate detection of insulin via binding of CB[7] to the N-terminal Phe residue on its B-chain, suggesting a general strategy for detecting Phe-terminated peptides of clinically relevant biomolecules.

Injectable Cucurbit[8]uril-Based Supramolecular Gelatin Hydrogels for Cell Encapsulation

Recent efforts to develop hydrogel biomaterials have focused on better recapitulating the dynamic properties of the native extracellular matrix. In hydrogel biomaterials, binding thermodynamics and cross-link kinetics directly affect numerous bulk dynamic properties such as strength, stress relaxation, and material clearance. However, despite the broad range of bulk dynamic properties observed in biological tissues, present strategies to incorporate dynamic linkages in cell-encapsulating hydrogels rely on a relatively small number of dynamic covalent chemical reactions and host-guest interactions. To expand this toolkit, we report the preparation of supramolecular gelatin hydrogels with cucurbit[8]uril (CB[8])-based cross-links that form on demand via thiol-ene reactions between preassembled CB[8]·FGGC peptide ternary complexes and grafted norbornenes. Human fibroblast cells encapsulated within these optically transparent, shear thinning, injectable hydrogels remained highly viable and exhibited a well-spread morphology in culture. These CB[8]-based gelatin hydrogels are anticipated to be useful in applications ranging from bioprinting to cell and drug delivery.