Complexation of clofazimine by macrocyclic cucurbit[7]uril reduced its cardiotoxicity without affecting the antimycobacterial efficacy

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.

Evolution of pediatric pharmaceutical forms for treatment of Hansen's disease (leprosy)

INTRODUCTION

Leprosy is a neglected, infectious, granulomatous and chronic disease caused by the pathological agent Mycobacterium leprae. The course of the disease is more aggressive in patients under 15 years of age, but the current treatment offered worldwide consists of solid forms, by the combination of antibiotics such as rifampicin, clofazimine and dapsone. This represents results in lack of adherence in pediatric patients and drug therapy failure, although numerous formulations and technologies have already been developed.

AREA COVERED

This study aims to analyze the technological evolution of the pharmaceutical treatment of leprosy, aimed at children. A review of patents around the world was conducted to look for technical and clinical aspects of formulations and devices.

EXPERT OPINION

Innovative formulations for pediatric patients were classified according to the routes of administration as oral, inhalable, injectable and transdermal. The formulations were organized as alternatives for pediatric therapy, taking into account the physicochemical aspects of drugs and the physiological aspects of pediatric patients. Among the difficulties for the patented formulations to reach the market, of special note is the low stability of the physicochemical characteristics of the drugs. Optimization of formulations would favor the pediatric treatment of leprosy, aiming at therapeutic success.

An innovative extraction strategy for herbal medicine by adopting p-sulphonatocalix[6]/[8]arenes

INTRODUCTION

Alkaloids exist in various herbal medicine widely and exhibit diverse biological and pharmacological activities. p-Sulphonatocalix[6]arenes (SC6A) and p-sulphonatocalix[8]arenes (SC8A) are water-soluble supramolecular macrocycles and are applied to the extraction of alkaloids from herbal products.

OBJECTIVE

In this study, an innovative method of SC6A/SC8A assisted extraction of the alkaloids from herbs was established.

METHODS

SC6A and SC8A were designed to extract 27 alkaloids from seven herbal medicines. Based on the significant solubilisation and extraction effect, Stephaniae Tetrandrae Radix (Fangji, FJ) was selected to obtain the optimal extraction process by adopting single factor test and orthogonal experiment. Then, the alkaloids and SC6A/SC8A were separated by one-step alkalisation and SCnA were reused. The host-guest complexes between alkaloids and SCnA were determined by competitive fluorescence titration, differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (¹ H-NMR) analysis.

RESULTS

The optimum condition for SC6A assisted extraction was 5:1:80 (g/g/mL) for herbs/SC6A/solution ratio, 355-250 μm particle size and ultrasonicate 0.5 h, whilst 10:1:40 (g/g/mL) for herbs/SC8A/solution ratio, 355-250 μm particle size and ultrasonicate 0.5 h for SC8A assisted extraction. The total yield of alkaloids (fangchinoline and tetrandrine) from FJ was increased by 4.87 times and 5.97 times with SC6A and SC8A. Moreover, a good reusability of SC6A/SC8A was achieved by alkalisation dissociation. Host-guest complexes were determined by competitive fluorescence titration at a molar ratio of 1:1 between most alkaloids (25/27, except evodiamine and rutaecarpine) and SC6A/SC8A. The complex structure was proved by DSC, FTIR and ¹ H-NMR analysis.

CONCLUSION

The study provided an effective eco-friendly and energy-saving extraction method of alkaloids from herbal medicine.

Host-Assisted Aggregation-Induced Emission of a Tetraphenylethylene Derivative and Its Responses toward External Stimuli

Aggregation-induced emission (AIE) of fluorogenic dyes offers many opportunities as smart materials, fluorescence sensing of analytes, bioimaging, molecular electronics, and many others. AIE dyes (called AIEgens) produce emission through aggregation, which are more advantageous than conventional emission of monomeric fluorophores, as the latter is unduly susceptible toward various quenching processes. Here, we report AIE enhancement of a polyanionic sulfonato-tetraphenylethylene (SuTPE) derivative, achieved through supramolecularly assisted dye aggregation, as SuTPE interacts with a multicationic amino-β-cyclodextrin (AβCD) host. Aggregation of the dye is induced mainly because of strong electrostatic interaction of SuTPE with AβCD, causing a significant extent of charge neutralization for the polyanionic dyes, helping their assemblage at the multicationic host portal. Job's plot studies suggest preferential formation of 2:1 dye-to-host stoichiometric complexes in the present system. Ionic-strength-dependent studies nicely support the involvement of electrostatic interaction in the present system through salt-induced disintegration of the SuTPE-AβCD complexes. The AIE enhancement for the SuTPE-AβCD system is very sensitive to the external stimuli, such as pH and temperature, suggesting its prospects in various stimuli-responsive applications. Furthermore, the SuTPE-AβCD system can suitably quantify an important bioanalyte, ATP, following a competitive binding strategy, suggesting its potential application as a supramolecular biosensor.

Assessment of the Biocompatibility of Cucurbiturils in Blood Cells

Currently, cucurbiturils are being actively researched all over the world. Research is focused on the ways of improving the solubility and selectivity of cucurbiturils, increasing the stability of the complexes with other particles in various media and enhancing their ability to bind and release various substances. The most significant area of our research is the assessment of safety, studying the biological properties and synergistic effects of cucurbiturils during complexation with drugs. In this article, the hemocompatibility of erythrocytes and leukocytes with cucurbiturils was investigated. We demonstrated that cucurbiturils have no cytotoxic effect, even at high concentrations (1 mM) and do not affect the viability of PBMCs. However, cucurbiturils can increase the level of the early apoptosis of lymphocytes and cucurbit[7]uril enhances hemolysis in biologically relevant media. Despite this, cucurbiturils are fairly safe organic molecules in concentrations up to 0.3 mM. Thus, we believe that it will become possible to use polymer nanostructures as drug delivery systems in clinical practice, since cucurbiturils can be modified to improve pharmacological properties.

Cucurbituril Ameliorates Liver Damage Induced by Microcystis aeruginosa in a Mouse Model

Microcystis aeruginosa is a cyanobacterium that produces a variety of cyclic heptapeptide toxins in freshwater. The protective effects of the macromolecular container cucurbit[7]uril (CB7) were evaluated using mouse models of cyanotoxin-induced liver damage. Biochemical analysis of liver function was performed to gauge the extent of liver damage after exposure to cyanobacterial crude extract [CCE; LD₅₀ = 35 mg/kg body weight; intraperitoneal (i.p.)] in the absence or presence of CB7 (35 mg/kg body weight, i.p.). CCE injection resulted in liver enlargement, potentiated the activities of alanine aminotransferase (ALT) and glutathione S-transferase (GST), increased lipid peroxidation (LPO), and reduced protein phosphatase 1 (PP1) activity. CCE-induced liver enlargement, ALT and GST activities, and LPO were significantly reduced when CB7 was coadministered. Moreover, the CCE-induced decline of PP1 activity was also ameliorated in the presence of CB7. Treatment with CB7 alone did not affect liver function, which exhibited a dose tolerance of 100 mg/kg body wt. Overall, our results illustrated that the addition of CB7 significantly reduced CCE-induced hepatotoxicity (P < 0.05).

Stuffed pumpkins: mechanochemical synthesis of host-guest complexes with cucurbit[7]uril

Solvent-free mechanochemical synthesis (ball-milling) was used to prepare inclusion complexes with cucurbit[7]uril and four model guest molecules (adamantane, adamantyl-1-amine hydrochloride, toluidine hydrochloride, and p-phenylenediamine dihydrochloride). Successful formation of individual inclusions was independently confirmed by one- and two-dimensional solid-state NMR techniques and differential scanning calorimetry. Mechanochemical synthesis represents an alternative path towards new types of cucurbit[n]uril/guest inclusion complexes that are not accessible due to limited solubility of the individual components.

Submission for Special Issue: The Role of Platelet Activation in the Pathophysiology of HIV, Tuberculosis, and Pneumococcal Disease. Bedaquiline Suppresses ADP-Mediated Activation of Human Platelets In Vitro via Interference With Phosphatidylinositol 3-Kinase

Although bedaquiline has advanced the treatment of multidrug-resistant tuberculosis (TB), concerns remain about the cardiotoxic potential of this agent, albeit by unexplored mechanisms. Accordingly, we have investigated augmentation of the reactivity of human platelets in vitro as a potential mechanism of bedaquiline-mediated cardiotoxicity. Platelet-rich plasma (PRP) or isolated cells prepared from the blood of healthy, adult humans were treated with bedaquiline (0.625–10 µg/ml), followed by activation with adenosine 5’-diphosphate (ADP), thrombin or the thromboxane A₂ receptor agonist (U46619). Expression of platelet CD62P (P-selectin), platelet aggregation, Ca²⁺ fluxes and phosphorylation of Akt1 were measured using flow cytometry, spectrophotometry, fluorescence spectrometry, and by ELISA procedures, respectively. Exposure to bedaquiline caused dose-related inhibition of ADP-activated, but not thrombin- or U46619-activated, expression of CD62P by platelets, achieving statistical significance at a threshold concentration of 5 µg/ml and was paralleled by inhibition of aggregation and Ca²⁺ mobilization. These ADP-selective inhibitory effects of bedaquiline on platelet activation were mimicked by wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3-K), implicating PI3-K as being a common target of both agents, a contention that was confirmed by the observed inhibitory effects of bedaquiline on the phosphorylation of Akt1 following activation of platelets with ADP. These apparent inhibitory effects of bedaquiline on the activity of PI3-K may result from the secondary cationic amphiphilic properties of this agent. If operative in vivo, these anti-platelet effects of bedaquiline may contribute to ameliorating the risk of TB-associated cardiovascular disease, but this remains to be explored in the clinical setting.

Recent advances in supramolecular antidotes

Poisons always have fascinated humankind. Initially considered as deleterious or hazardous substances, the modern era has witnessed the controlled utilization of dangerous poisons in medicine and cosmetics. Simultaneously, antidotes have become crucial as reversal agents to counteract the effects of a poison, and they are also used today to positively cancel the benefits of a poison after use. Currently, the majority of poisons are composed of small molecules. This review focuses on recent developments to reverse or prevent toxic effects of poisons by encapsulation in host molecules. Cyclodextrins, cucurbiturils, acyclic cucurbituril derivatives, calixarenes, and pillararenes, have been reported to largely impact the effects of toxic compounds, thus extending the current paradigm of small molecule antidotes by adding a new family of macrocyclic compounds to the current arsenal of antidotes. Along this line of research, endogenous "harmful" species are also sequestered by one or more of these supramolecular host molecules, expanding the potential of supramolecular antidotes to diverse therapeutic areas.

Combining Two Antitubercular Drugs, Clofazimine and 4-Aminosalicylic Acid, in Order to Improve Clofazimine Aqueous Solubility and 4-Aminosalicylic Acid Thermal Stability

Four forms of a salt combining two antitubercular drugs, clofazimine and 4-aminosalicylic acid, are reported and the crystal structure of two of these forms are described. TG/DSC analysis of all four forms demonstrate an increase in the temperature at which degradation (upon decarboxylation) occurs in comparison to pure 4-aminosalicylic acid. Water solubility evaluation indicates a significant increase of the amount of clofazimine detected in water (10.26 ± 0.52 μg/mL for form I, 12.27 ± 0.32 μg/mL for form II, 7.15 ± 0.43 μg/mL for form III and 8.50 ± 1.24 μg/mL for form IV) in comparison to pure clofazimine (0.20 ± 0.03 μg/mL).

Highly Selective Binding and Inhibition of Pyr-His-Pro-NH2 (TRH) Function using a Polypyridinyl Macrocyclic Receptor with an Amphiphilic Cavity

Macrocycle, cyclo[4] [(1,3-(4,6)-dimethylbezene)[4](2,6-(3,5)-dimethylpyridine (B4P4), shows highly selective binding affinity with protirelin (Pyr-His-Pro-NH₂ ; TRH) among the tested 26 drug or drug adductive substrates. The stable complexation in a 1:1 manner was fully characterized in solution, gas phase, and solid state study. Furthermore, B4P4 acts as an efficient TRH inhibitor even at [macrocycle]:[drug] <1:300, both in membrane transport and cellar incubation. The current work provides an unprecedented strategy for macrocycles to be efficiently used in drug target therapy.

Evaluation of the Immunosafety of Cucurbit[n]uril on Peripheral Blood Mononuclear Cells In Vitro

Cucurbiturils (CB[n]s) are nanoscale macrocyclic compounds capable of encapsulating a molecule or part of a molecule by forming host–guest complexes. Integration of drugs with CB[n] is used for the following purposes: controlling clearance; protection of the drug from biodegradation; targeted delivery to specific organs, tissues, or cells; reduction of toxicity; and improving solubility. One of the major problems encountered in the application of new drug delivery systems is lack of knowledge of their biological properties. CB[n], unlike many other often toxic nanoparticles, has extremely low toxicity, even at high doses. However, many aspects of the biological actions of these nanoscale cavitands remain unclear, including the immunotropic properties. In this study, we investigated the immunotoxicity and immunomodulation properties of CB[n]. It was found that CB[7] and CB[6] did not decrease the viability of mononuclear cells at all tested concentrations from 0.1–1 mM. Overall, the results indicated an immunomodulatory effect of different concentrations of CB[n]. In the case of a longer cultivation time, CB[n] had an immunostimulating effect, which was indicated by an enhancement of the proliferative activity of cells and increased expression of HLA-DR on lymphocytes.

Supramolecular Nano-Encapsulation of Anabasine Reduced Its Developmental Toxicity in Zebrafish

Anabasine (ANA), a major piperidine alkaloid originally isolated from wild tobacco trees (Nicotiana glauca), has been known to induce serious developmental toxicities such as skeletal deformities in livestock and humans. In this study, we thoroughly investigated the supramolecular nano-encapsulations of ANA by an artificial nanocontainer, cucurbit[7] uril (CB[7]), and examined the influences of the nano-encapsulation on ANA's inherent developmental toxicities on a zebrafish model. We have shown that CB[7] formed 1:1 host-guest inclusion complexes with ANA via a relatively high binding strength [K_a of (7.45 ± 0.31) × 10⁴ M⁻¹] in an aqueous solution, via UV-vis and ¹H nuclear magnetic resonance spectroscopic titrations, as well as isothermal titration calorimetry titration. As a consequence, CB[7] significantly attenuated the developmental toxicity of ANA on zebrafish in vivo. In contrast, for a comparative purpose, β-CD didn't exert any influence on the toxicity of ANA due to its weak binding with ANA, which was not even measurable via either spectroscopic methods or ITC titration. This is the first head-to-head comparison of this pair of nanocontainers, CB[7] and β-CD, on their potential roles in influencing the toxicity of guest molecules and the results suggested that CB[7] could become a more promising functional excipient for reducing the inherent toxicities of active pharmaceutical ingredients, particularly alkaloids that may form relatively strong host-guest binding species with the host.

Supramolecular prodrugs based on host–guest interactions

The concept, detailed progress, advantages and opportunities of supramolecular drugs via host–guest chemistry are summarized.

A LSER-based model to predict the solubilizing effect of drugs by inclusion with cucurbit[7]uril

A LSER model was built for predicting the solubility of inclusion complexes.

Locked and Loaded: Ruthenium(II)-Capped Cucurbit[n]uril-Based Rotaxanes with Antimetastatic Properties

We report here the first coupling of Ru(II) units with cucurbit[6/7]uril-based pseudorotaxane ligands meant for biological application. The resulting ruthenium-capped rotaxanes were fully characterized, and a structure of one supramolecular system was determined by X-ray diffraction. Because the biological properties of Ru-based metallodrugs are tightly linked to the ligand-exchange processes, the effect of salt concentration on the hydrolysis of chlorides from the Ru(II) center was monitored by using ¹H NMR spectroscopy. The biological activity of Ru(II)-based rotaxanes was evaluated for three selected mammalian breast cell lines, HBL-100, MCF-7, and MDA-MB-231. The antimetastatic activity of the assembled cationic Ru(II)-rotaxane systems, evaluated in migration assays against MCF-7 and MDA-MB-231 cell lines, is notably enhanced compared to that of RAPTA-C, a reference that was used. The indicated synergistic effect of combining Ru(II) with a pseudorotaxane unit opens a new direction in searching for anticancer supramolecular metallodrugs.

Overcoming clofazimine intrinsic toxicity: statistical modelling and characterization of solid lipid nanoparticles

The aim of this work was to develop solid lipid nanoparticles (SLNs) loaded with clofazimine (CLZ) (SLNs-CLZ) to overcome its intrinsic toxicity and low water solubility, for oral drug delivery. A Box-Behnken design was constructed to unravel the relations between the independent variables in the selected responses. The optimized SLNs-CLZ exhibited the following properties: particle size ca 230 nm, zeta potential of -34.28 mV, association efficiency of 72% and drug loading of 2.4%, which are suitable for oral delivery. Further characterization included Fourier transformed infrared spectroscopy that confirmed the presence of the drug and the absence of chemical interactions. By differential scanning calorimetry was verified the amorphous state of CLZ. The storage stability studies ensured the stability of the systems over a period of 12 weeks at 4°C. In vitro cytotoxicity studies evidenced no effect of both drug-loaded and unloaded SLNs on MKN-28 gastric cells and on intestinal cells, namely Caco-2 and HT29-MTX cells up to 25 µg ml^-1 in CLZ. Free CLZ solutions exhibited IC₅₀ values of 16 and 20 µg ml^-1 for Caco-2 and HT29-MTX cells, respectively. It can be concluded that the optimized system, designed considering important variables for the formulation of poorly soluble drugs, represents a promising platform for oral CLZ delivery.

Supramolecular therapeutics to treat the side effects induced by a depolarizing neuromuscular blocking agent

Succinylcholine (Sch) is the only depolarizing neuromuscular blocking agent widely used for rapid sequence induction in emergency rooms. Unfortunately, a variety of (sometimes lethal) adverse effects, such as hyperkalemia and cardiac arrest, are associated with its use, and currently there are no specific antidotes to reverse Sch or to treat these side-effects. Methods: The binding behaviors of Sch and several synthetic receptors, including cucurbit[7]uril, sulfo-calix[4]arene and water-soluble carboxylatopillar[6]arene (WP[6]), were first investigated. With a mouse model, a leathal dose of Sch was selected for evaluation of the antidotal effects of these synthetic receptors on Sch induced mortality. The antidotal effects of a selected synthetic receptor, WP[6], on Sch induced cardiac arrhythmias, hyperkalemia, rhabdomyolysis and paralysis were subsequently evaluated with rat and mouse models. The reversal mechanism was also investigated at a cellular level. Results: All of these macrocyclic molecules exhibited relatively high binding affinities with Sch in vitro. In a Sch-overdosed mouse model, immediate injection of these synthetic receptors right after Sch administration increased the overall survival rate, with WP[6] standing out with the most effective antidotal effects. In addition, administration of WP[6] also reversed the paralysis induced by Sch in a mouse model. Moreover, infusion of WP[6] to Sch-overdosed rats reduced the incidence of cardiac arrhythmia, inhibited the otherwise abnormally high serum potassium levels, and relieved the muscular damage. At the cellular level, WP[6] reversed the Sch induced depolarization and reduced the efflux of intracellular potassium. Conclusion: Synthetic receptors, particularly WP[6], exhibited high binding affinities towards Sch, and presented a significant potential as supramolecular therapeutics to treat the various side effects of Sch by specifically sequestering Sch in vivo.

A Synthetic Receptor as a Specific Antidote for Paraquat Poisoning

Accidental or suicidal ingestion of the world's most widely used herbicide, paraquat (PQ), may result in rapid multi-organ failure with a 60% fatality rate due to the absence of an effective detoxification solution. Effective, specific antidotes to PQ poisoning have been highly desired.

Methods: The binding constant of PQ and a synthetic receptor, cucurbit[7]uril (CB[7]), was first determined in various pH environments. The antidotal effects of CB[7] on PQ toxicity were firstly evaluated with in-vitro cell lines. With in-vivo mice models, the pharmacokinetics and the biodistribution of PQ in major organs were determined to evaluate the influence of CB[7] on the oral bioavailability of PQ. Major organs' injuries and overall survival rates of the mice were systemically examined to evaluate the therapeutic efficacy of CB[7] on PQ poisoning.

Results: We demonstrate that CB[7] may complex PQ strongly under various conditions and significantly reduce its toxicity in vitro and in vivo. Oral administration of PQ in the presence of CB[7] in a mouse model significantly decreased PQ levels in the plasma and major organs and alleviated major organs' injuries, when compared to those of mice administered with PQ alone. Further studies indicated that oral administration of CB[7] within 2 h post PQ ingestion significantly increased the survival rates and extended the survival time of the mice, in contrast to the ineffective treatment by activated charcoal, which is commonly recommended for PQ decontamination.

Conclusion: CB[7] may be used as a specific oral antidote for PQ poisoning by strongly binding with PQ and inhibiting its absorption in the gastrointestinal tracts.

Change of the kinetics of inclusion in cucurbit[7]uril upon hydrogenation and methylation of palmatine

The negative activation entropy of tetrahydropalmatine inclusion makes the entry into cucurbit[7]uril significantly slower than in the case of dehydrocorydaline.

Clofazimine, but Not Isoniazid or Rifampicin, Augments Platelet Activation in vitro

Although the inclusion of the cationic amphiphilic, anti-mycobacterial agent, clofazimine, in the chemotherapeutic regimens of patients with multidrug-resistant tuberculosis (TB) has contributed to improved outcomes, concerns remain about the cardiotoxic potential of this agent. Accordingly, the current study was undertaken with the primary objective of investigating the effects of clofazimine, on the reactivity of human platelets in vitro, a seemingly unexplored, mechanism of cardiotoxicity. Platelet-rich plasma (PRP) prepared from the blood of healthy, adult humans was treated with clofazimine (0.625–10 mg/L), or the primary anti-TB agents, isoniazid and rifampicin (at final concentrations of 5 and 10 mg/L), followed by addition of either adenosine 5′-diphosphate (ADP) or thrombin and measurement of platelet activation according to the magnitude of expression of CD62P (P-selectin), as well as the CD62P-mediated formation of heterotypic neutrophil:platelet (NP) aggregates, using flow cytometry. Clofazimine, but neither isoniazid nor rifampicin, caused dose-related potentiation of both ADP- and thrombin-activated expression of CD62P by platelets, achieving statistical significance at threshold concentrations of 0.625 and 2.5 mg/L, respectively, as well as significant formation of N:P aggregates. These stimulatory effects of clofazimine on platelet activation were partly attenuated by pre-treatment of PRP with the membrane-stabilizing agent, α-tocopherol, possibly consistent with a membrane-disruptive mechanism. In conclusion, clofazimine, at concentrations within the therapeutic range, augments platelet activation in vitro, probably by a mechanism linked to membrane destabilization. If operative in vivo, these pro-thrombotic activities of clofazimine may predispose for development of microvascular occlusion, exacerbating an already existing high risk for development of TB-associated cardiovascular disease.

Encapsulation and modulation of protolytic equilibrium of β-carboline-based norharmane drug by cucurbit[7]uril and micellar environments for enhanced cellular uptake

The effect of supramolecular nanocavity on photophysical and acid-dissociation properties of Norharmane (NHM), a physiologically important, anxiety control and memory-enhancing β-carboline-based drug, has been investigated using steady-state absorption and fluorescence spectroscopy. Self-assembled organization derived from surfactants and rigid water-soluble macrocyclic host Cucurbit[7]uril (CB7) have been selected for this investigation. The confined-space offered by the supramolecular assemblies modulates the pK_a value of NHM (up to 3 units) as it can exist in two protolytic forms at near neutral pH. Therefore, the pH-dependent binding properties, modulation of pK_a value and its consequences on the photophysical, chemical and solubility properties are investigated in detail. This investigation shows a large shift in the protolytic equilibrium which in turn causes ca. 15 times solubility-enhancement at near neutral pH. Moreover, the effect of enhanced solubility has been further investigated by the augmentation in the cellular uptake of NHM entrapped inside CB7. Thus, the modulation of the acid-base properties and solubility of β-carboline-based drugs will have immense potential for their formulation, cellular uptake and bioavailability.

A systematic evaluation of the biocompatibility of cucurbit[7]uril in mice

As one of the most water-soluble members in the macrocyclic cucurbit[n]uril (CB[n]) family, CB[7] has attracted increasing attention in pharmaceutical and biomedical fields. Despite extensive studies regarding the potential use of CB[7] for biomedical applications, its full safety and toxicity profile in a clinically relevant model is still lacking. Herein we report the full biocompatibility profile of CB[7], administered orally, peritoneally or intravenously in mice, respectively. Body-weight changes showed no significant differences among various groups of mice after they were administered with CB[7] at a single dose of 5 g/kg orally, 500 mg/kg peritoneally and 150 mg/kg intravenously, respectively. Hematology tests, as well as hepatic and renal function biochemical markers tests, of the blood collected from these mice sacrificed 21 days after CB[7] administration all exhibited normal ranges of values that were comparable with those of the control group. Moreover, histopathological analysis on the sections of major organs (including the heart, liver, spleen, lungs and kidneys) and gastrointestinal tissues revealed no detectable injuries and inflammatory cells infiltration. Taken together, these results suggest an excellent biocompatibility profile of CB[7] in mice, which provide important foundations for further investigations and even clinical applications of CB[7] in biomedical areas.

Supramolecular alleviation of cardiotoxicity of a small-molecule kinase inhibitor

Small-molecule kinase inhibitors (SMKIs) have been widely used in the treatment of a variety of cancers due to their clinically demonstrated efficacy. However, the use of some SMKIs, such as sorafenib (SO), has been plagued by their cardiotoxicity that has been frequently observed in treated patients. Herein we report that the encapsulation of SO by a synthetic receptor cucurbit[7]uril (CB[7]) alleviated the inherent cardiotoxicity of SO, as demonstrated in an in vivo zebrafish model. Moreover, the anti-cancer activity of SO was well preserved, upon its encapsulation by CB[7], as demonstrated by both in vitro and in vivo cancer/angiogenesis models. This discovery may provide new insights into a novel supramolecular formulation of SMKIs for the management of their side-effects.

Fluorescence enhancement and pKa shift of a rho kinase inhibitor by a synthetic receptor

Fasudil (FSD), a selective rho kinase (ROCK) inhibitor, was found to form 1 : 1 host-guest inclusion complexes with a synthetic macrocyclic receptor, cucurbit[7]uril (CB[7]), in aqueous solutions, as evidenced by ¹H NMR, photoluminescence and UV-visible spectroscopic titrations, isothermal titration calorimetry (ITC) titration, and electrospray ionization (ESI) mass spectrometry, as well as density functional theory (DFT) molecular modeling. Upon encapsulation, whereas the UV-vis absorbance of FSD experienced a moderate decrease and bathochromic shift, the fluorescence intensity of FSD at 354 nm was dramatically enhanced for up to 69-fold at neutral pH, which could potentially be applied in fluorescent tracking of the drug delivery and release. More interestingly, the binding affinity (K_a = (4.28 ± 0.21) × 10⁶ M^-1), of FSD-CB[7] complexes under acidic conditions (pH = 2.0), is approximately three orders of magnitude higher than that (2.2∼6.6 × 10³ M^-1) under neutral pH conditions (pH = 7.0). Accordingly, UV-visible spectroscopic titration of the free and complexed FSD under various pH conditions has demonstrated that the encapsulation of FSD by CB[7] shifted the pK_a of the isoquinoline-N upward from 3.05 to 5.96 (ΔpK_a of 2.91). The significantly higher binding affinity of the complexes under acidic conditions may be applied in developing the "enteric" formulation of FSD. Furthermore, our in vitro study of the bioactivity of FSD in the absence and presence of CB[7] on a neural cell line, SH-SY5Y, showed that the complexation preserved the drug's pro-neurite efficacy. Thus this discovery may lead to a fluorescence-trackable, orally administered enteric formulation of rho kinase inhibitors that are stable under gastric conditions, without compromising bioactivity of the drugs.

Probing the pharmacokinetics of cucurbit[7, 8 and 10]uril: and a dinuclear ruthenium antimicrobial complex encapsulated in cucurbit[10]uril

The relatively non-toxic family of cucurbit[n]uril, Q[n], have shown considerable potential in vitro as drug delivery agents, with only a few examples of pharmacokinetic (PK) studies for drug⊂Q[n]. Drug-free Q[n] PK studies are the next step in determining the pharmacological applicability in their drug delivery potential. The results for the first PK and bio-distribution of drug-free ¹⁴C-Q[7] are described for administration via intravenous (i.v.) and intraperitoneal (i.p.) dosing. A study of oral administration of drug-free ¹⁴C-Q[8] has also been undertaken to determine the time course for the gastrointestinal tract (GIT), absorption and subsequent bio-distribution. Q[10], a potential drug carrier for larger drugs, was evaluated for its effect on the PK profile of a dinuclear ruthenium complex (Rubb₁₂), a potential antimicrobial agent. The Rubb₁₂⊂Q[10] complex and free Rubb₁₂ were administered by i.v. to determine differences in Rubb₁₂ plasma concentrations and organ accumulation. Interestingly, the PK profiles and bio-distribution observed for Q[7] showed similarities to those of Rubb₁₂⊂Q[10]. Drug-free Q[7] has a relatively fast plasma clearance and a generally low organ accumulation except for the kidneys. Drug-free Q[8] showed a low absorption from the GIT into the blood stream but the small percentage absorbed reflected the organ accumulation of Q[7]. These results provide a better understanding of the probable PK profile and bio-distribution for a drug⊂Q[n] through the influence of the drug delivery vehicle and the positive clearance of drug-free Q[n] via the kidneys supports its potential value in future drug delivery applications.

Supramolecular Encapsulation and Bioactivity Modulation of a Halonium Ion by Cucurbit[ n]uril ( n = 7, 8)

This is the first time that cucurbit[7]uril and cucurbit[8]uril have been demonstrated to serve as synthetic receptors for a halonium guest species, diphenyleneiodonium, modulating its bioactivities and alleviating its cardiotoxicity, which further expands the onium family of guest molecules for the cucurbit[ n]uril family and provides new insights for halonium-cucurbit[ n]uril host-guest chemistry and its potential applications in pharmaceutical chemistry.

Alkaline earth cation-mediated photoluminescent complexes of thioflavin T with twisted cucurbit[14]uril

The introduction of alkaline earth metal cations into the tQ[14]–ThT interaction system leds to the precipitation of solid tQ[14]/ThT/AE²⁺ interaction products, which emitted strong blue fluorescence.

Supramolecular strategy for reducing the cardiotoxicity of bedaquiline without compromising its antimycobacterial efficacy

Bedaquiline (BDQ) is a newly approved anti-tuberculosis drug in treating multidrug-resistant tuberculosis. However, it has very poor aqueous solubility and several case reports have proposed that BDQ has potential risk of cardiotoxicity to patients. In this present study, we have explored into employing host-guest interactions between a synthetic receptor, cucurbit[7]uril (CB[7]), and BDQ aiming to improve the solubility and reduce the inherent cardiotoxicity of BDQ. HPLC-UV test on the solubility of BDQ in the absence and in the presence of increasing concentrations of CB[7] suggested a host-dependent guest-solubility enhancements. Cardiovascular studies using an in vivo zebrafish model demonstrated that the cardiotoxicity of BDQ was indeed alleviated upon its complexations by the synthetic receptor. Furthermore, our in vitro antibacterial studies suggested that CB[7] formulated BDQ preserved its antimycobacterial efficacy against Mycobacterium smegmatis. Therefore, CB[7] may become a suitable pharmaceutical excipient in formulating BDQ for improving its physiochemical properties (such as solubility), and for alleviating its side effects (such as cardiotoxicity), while the antimycobacterial efficacy of BDQ may be well maintained.

Alleviating the hepatotoxicity of trazodone via supramolecular encapsulation

In order to develop a novel strategy to alleviate the inherent hepatotoxicity of antidepressant trazodone (TZ), Cucurbit[7]uril (CB[7]) was adopted as pharmaceutical excipients and was studied for its capability to reduce the hepatotoxicity of TZ via supramolecular encapsulation. CB[7] was found to form strong 1:1 host-guest complexes with TZ and its metabolite m-chlorophenyl piperazine (mCPP), with binding constants of 1.50 (±0.13) × 10⁶ M^-1 and 6.90 (±0.49) × 10⁵ M^-1, respectively. The supramolecular complexations were examined by ¹H NMR and UV-visible spectroscopic titrations, ESI-MS and ITC. In the presence of 0.5 mM CB[7], the IC₅₀ values of TZ and mCPP on a human normal liver cell line L02 were increased from 215.5 ± 3.3 μM to 544.1 ± 51.2 μM, and from 166.8 ± 3.8 μM to 241.7 ± 6.8 μM, respectively. Evaluation on a zebrafish model demonstrated that CB[7] (0.1 mM) significantly alleviated the TZ induced liver toxicity, as shown by the level of liver degeneration, liver size and yolk sac retention. Our study may provide a supramolecular strategy to alleviate the hepatotoxicity induced by TZ and its metabolite mCPP, and this strategy may be extendable to other drugs that have inherent hepatotoxicity or other adverse effects.

Concealing the taste of the Guinness World's most bitter substance by using a synthetic nanocontainer

Upon supramolecular encapsulation by using a synthetic nanocontainer (cucurbit[7]uril), the taste of the Guinness World's most bitter substance, denatonium benzoate, was dramatically concealed during a two-bottle preference drinking test in a mammalian model, demonstrating the significant potential of cucurbit[7]uril as a taste-masking nanocontainer for the first time.

Cucurbit[7]uril: an emerging candidate for pharmaceutical excipients

Cucurbit[7]uril (CB[7]), belonging to the cucurbit[n]uril family (CB[n], n = 5-8, 10, or 13-15), may form host-guest complexes with a variety of small molecules of biomedical interest. The physical and chemical properties of the complexed drugs are often improved as a result of this complexation, suggesting the potential application of CB[7] as a pharmaceutical excipient. This review has summarized the most recent research progress reported between 2011 and early 2017 regarding the biocompatibility of CB[7] and the influence of CB[7] on the stability, solubility, biouptake, and biological activities (including therapeutic efficacies and toxicities) of guest drug molecules. Through this systemic summary and analysis, we intend to stimulate further research efforts in this area and promote the use of CB[7] as an emerging pharmaceutical excipient to improve various properties of drug molecules (or active pharmaceutical ingredients).

The new supramolecular nano-aggregate curcumin-cucurbit[7]uril: synthesis, photophysical properties and biocompatibility evaluation

The supramolecular nano-aggregate CUR–CB[7] was efficiently prepared by mixing curcumin (CUR) and cucurbit[7]uril (CB[7]) in ethanol at room temperature.

Molecular Encapsulation of Histamine H₂-Receptor Antagonists by Cucurbit[7]Uril: An Experimental and Computational Study

The histamine H₂-receptor antagonists cimetidine, famotidine and nizatidine are individually encapsulated by macrocyclic cucurbit[7]uril (CB[7]), with binding affinities of 6.57 (±0.19) × 10³ M(-1), 1.30 (±0.27) × 10⁴ M(-1) and 1.05 (±0.33) × 10⁵ M(-1), respectively. These 1:1 host-guest inclusion complexes have been experimentally examined by ¹H-NMR, UV-visible spectroscopic titrations (including Job plots), electrospray ionization mass spectrometry (ESI-MS), and isothermal titration calorimetry (ITC), as well as theoretically by molecular dynamics (MD) computation. This study may provide important insights on the supramolecular formulation of H₂-receptor antagonist drugs for potentially enhanced stability and controlled release based on different binding strengths of these host-guest complexes.