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.

Evaluation of the Immunosafety of Cucurbit[n]uril In Vivo

Cucurbiturils are a family of macrocyclic oligomers capable of forming host-guest complexes with various molecules. Due to noncovalent binding to drug molecules and low toxicity, cucurbiturils has been extensively investigated as potential carriers for drug delivery. However, the immune system's interactions with different drug carriers, including cucurbiturils, are still under investigation. In this study, we focused on cucurbiturils' immunosafety and immunomodulation properties in vivo. We measured blood counts and lymphocyte subpopulations in blood, spleen, and bone marrow, and assessed the in vivo toxicity to spleen and bone marrow cells after intraperitoneal administration to BALB/c mice. When assessing the effect of cucurbit[6]uril on blood parameters after three intraperitoneal injections within a week in laboratory animals, a decrease in white blood cells was found in mice after injections of cucurbit[6]util, but the observed decrease in the number of white blood cells was within the normal range. At the same time, cucurbit[7]uril and cucurbit[8]uril did not affect the leukocyte counts of mice after three injections. Changes in the number of platelets, erythrocytes, and monocytes, as well as in several other indicators, such as hematocrit or erythrocyte volumetric dispersion, were not detected. We show that cucurbiturils do not have immunotoxicity in vivo, with the exception of a cytotoxic effect on spleen cells after сucurbit[7]uril administration at a high dosage. We also evaluated the effect of cucurbiturils on cellular and humoral immune responses. We founded that cucurbiturils in high concentrations affect the immune system in vivo, and the action of various cucurbiturils differs in different homologues, which is apparently associated with different interactions in the internal environment of the body.

Water-soluble terphen[3]arene macrocycle: a versatile reversal agent of neuromuscular blockers

Herein we report the design and synthesis of a terphen[n]arene derivative functionalised with sulfate acid ester groups. This water-soluble terphen[3]arene host effectively encapsulates a multitude of neuromuscular blocking agents (NMBAs) with high affinity, showing great potential as a NMBAs reversal agent in pharmaceutical research.

Pillar[6]MaxQ: A Potent Supramolecular Host for In Vivo Sequestration of Methamphetamine and Fentanyl

Pillar[6]MaxQ (P6AS) functions as an in vivo sequestration agent for methamphetamine and fentanyl. We use 1H NMR, isothermal titration calorimetry, and molecular modelling to deduce the geometry and strength of the P6AS•drug complexes. P6AS forms tight complexes with fentanyl (Kd=9.8 nM), PCP (17.1 nM), MDMA (25.5 nM), mephedrone (52.4 nM), and methamphetamine (101 nM). P6AS has good in vitro biocompatibility according to MTS metabolic, Adenylate Kinase cell death, and hERG ion channel inhibition assays, and the Ames fluctuation test. The no observed adverse effect level for P6AS is 45 mg/kg. The hyperlocomotion of mice treated with methamphetamine (0.5 mg/kg) can be ameliorated by treatment with P6AS (35.7 mg/kg) 5-minutes later, whereas the hyperlocomotion of mice treated with fentanyl (0.1 mg/kg) can be controlled by treatment with P6AS (5 mg/kg) up to 15-minutes later. P6AS has significant potential for development as a broad spectrum in vivo sequestration agent.

Anthracene Walled Acyclic CB[n] Receptors: In Vitro and In Vivo Binding Properties Toward Drugs of Abuse

We report studies of the interaction of six acyclic CB[n]-type receptors toward a panel of drugs of abuse by a combination of isothermal titration calorimetry and 1H NMR spectroscopy.  Anthracene walled acyclic CB[n] host (M3) displays highest binding affinity toward methamphetamine (Kd = 15 nM) and fentanyl (Kd = 4 nM).  Host M3 is well tolerated by Hep G2 and HEK 293 cells up to 100 mM according to MTS metabolic and adenylate kinase release assays.  An in vivomaximum tolerated dose study with Swiss Webster mice showed no adverse effects at the highest dose studied (44.7 mg kg-1). Host M3 is not mutagenic based on the Ames fluctuation test and does not inhibit the hERG ion channel.  In vivoefficacy studies showed that pretreatment of mice with M3 significantly reduces the hyperlocomotion after treatment with methamphetamine, but M3 does not function similarly when administered 30 seconds after methamphetamine.

Flexible organic frameworks sequester neuromuscular blocking agents in vitro and reverse neuromuscular block invivo

Supramolecular sequestration and reversal of neuromuscular block (NMB) have great clinical applications. Water-soluble flexible organic frameworks (FOFs) cross-linked by disulfide bonds are designed and prepared. Different linker lengths are introduced to FOFs to give them varied pore sizes. FOFs are anionic nanoscale polymers and capable of encapsulating cationic neuromuscular blocking agents (NMBAs), including rocuronium (Roc), vecuronium (Vec), pancuronium (Panc) and cisatracurium (Cis). A host–guest study confirms that FOFs bind NMBAs in water. The multivalency interaction between FOFs and NMBAs is able to sequester NMBAs, and prevent them from escaping. These FOFs are non-toxic and biocompatible. Animal studies show that FOFs are effective for the reversal of NMB induced by Roc, Vec and Cis, which shorten the time to a train-of-four ratio of 0.9 by 2.6, 3.8 and 5.7-fold compared to a placebo, respectively.

Water-soluble flexible organic frameworks are prepared and used to sequester neuromuscular blocking agents, and reverse their neuromuscular block in vivo.

Host–guest complexation of APP+ with cucurbit[7]uril. Theoretical and experimental studies on the supramolecular inhibition of its cytotoxicity on SERT

The supramolecular binding behavior of APP+ and CB[7] in aqueous solution was studied by different techniques. APP+ showed cytotoxicity towards HEK293 cells expressing hSERT. This cytotoxicity was inhibited by the treatment of the cells with CB[7].

In Vitro and In Vivo Sequestration of Methamphetamine by a Sulfated Acyclic CB[n]-Type Receptor

We report the synthesis of two new acyclic sulfated acyclic CB[n]-type receptors (TriM0 and Me4 TetM0) and investigations of their binding properties toward a panel of drugs of abuse (1-13) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry. TetM0 is the most potent receptor with Ka ≥106  M-1 toward methamphetamine, fentanyl, MDMA and mephedrone. TetM0 is not cytotoxic toward HepG2 and HEK 293 cells below 100 μM according to MTS metabolic and adenylate kinase release assays and is well tolerated in vivo when dosed at 46 mg kg-1 . TetM0 does not inhibit the hERG ion channel and is not mutagenic based on the Ames fluctuation test. Finally, in vivo efficacy studies show that the hyperlocomotion of mice treated with methamphetamine can be greatly reduced by treatment with TetM0 up to 5 minutes later. TetM0 has potential as a broad spectrum in vivo sequestrant for drugs of abuse.

A Supramolecular Antidote to Macromolecular Toxins Prepared through Coassembly of Macrocyclic Amphiphiles

Poisoning is a leading cause of admission to medical emergency departments and intensive care units. Supramolecular detoxification, which involves injecting supramolecular receptors that bind with toxins to suppress their biological activity, is an emerging strategy for poisoning treatment; it has few requirements and a broad application scope. However, it is still a formidable challenge to design supramolecular therapeutic materials as an antidote to macromolecular toxins, because the large size, flexible conformation, and presence of multiple and diverse binding sites of biomacromolecules hinder their recognition. Herein, a supramolecular antidote to macromolecular toxins is developed through the coassembly of macrocyclic amphiphiles, relying on heteromultivalent recognition between the coassembled components and toxic macromolecules. The coassembly of amphiphilic cyclodextrin and calixarene strongly and selectively captures melittin, a toxin studied herein; this imparts various therapeutic effects such as inhibiting the interactions of melittin with cell membranes, alleviating melittin cytotoxicity and hemolytic toxicity, reducing the mortality rate of melittin-poisoned mice, and mitigating damage to major organs. The use of the proposed antidote overcomes the limitation of supramolecular detoxification applicability to only small-molecular toxins. The antidote can also detoxify other macromolecular toxins as long as selective and strong binding is achieved because of the coassembling tunability.

In Vitro and In Vivo Sequestration of Phencyclidine by Me4 Cucurbit[8]uril*

We report investigations of the use of cucurbit[8]uril (CB[8]) macrocycles as an antidote to counteract the in vivo biological effects of phencyclidine. We investigate the binding of CB[8] and its derivative Me4 CB[8] toward ten drugs of abuse (3-9, 12-14) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry in phosphate buffered water. We find that the cavity of CB[8] and Me4 CB[8] are able to encapsulate the 1-amino-1-aryl-cyclohexane ring system of phencyclidine (PCP) and ketamine as well as the morphinan skeleton of morphine and hydromorphone with Kd values ≤50 nm. In vitro cytotoxicity (MTS metabolic and adenylate kinase cell death assays in HEK293 and HEPG2 cells) and in vivo maximum tolerated dose studies (Swiss Webster mice) which were performed for Me4 CB[8] indicated good tolerability. The tightest host⋅guest pair (Me4 CB[8]⋅PCP; Kd =2 nm) was advanced to in vivo efficacy studies. The results of open field tests demonstrate that pretreatment of mice with Me4 CB[8] prevents subsequent hyperlocomotion induction by PCP and also that treatment of animals previously dosed with PCP with Me4 CB[8] significantly reduces the locomotion levels.

Supramolecular Modulation of Antibacterial Activity of Ambroxol by Cucurbit[7]uril

Supramolecular encapsulation by cucurbit[7]uril (CB[7]) was recently demonstrated to provide a simple and efficient method for antibacterial activity regulation of antibiotics. In this work, CB[7] was shown to form binary host-guest complex with ambroxol hydrochloride (ABX), a clinical mucokinetic and expectorant drug, which was reported to exhibit certain antibacterial activity. ¹ H NMR titration and isothermal titration calorimetry experiment results suggested that the 4-hydroxyl cyclohexylamine group of ABX was included inside the CB[7] cavity, with a binding constant K_a of (6.69±0.11)×10⁵  M^-1 in phosphate buffered saline (PBS) solution, thermodynamically driven by both enthalpy change (ΔH=-12.2 kJ/mol) and entropy change (TΔS=21.1 kJ/mol). More importantly, ABX's inhibitory activity (MIC₅₀ ) against bacillary strains towards Pseudomonas aeruginosa and Escherichia coli strains was decreased from (5.11±0.31)×10^-6  M^-1 and (2.63±0.34)×10^-5  M^-1 to zero upon encapsulation by CB[7], and was subsequently recovered to almost its original activity when a competitive guest, amantadine hydrochloride, for disassembling CB[7]-ABX complex, was added, suggesting that the antibacterial activity of ABX could be readily "turned off/on" upon its complexation and decomplexation with CB[7].

Reversing cytotoxicity of uric acid by supramolecular encapsulation with acyclic cucurbit[n]uril

Supramolecular encapsulation removes harmful substances from organisms has evolved into a new strategy. In this article, we prepared three supramolecular complexes of acyclic cucurbit[n]urils (ACBs) with uric acid (UA), and studied the inclusion behaviors of ACBs and UA by fluorescence spectroscopy, UV-vis spectroscopy and nuclear magnetic resonance. Furthermore, we characterized the effect of the complexes of UA with ACBs on the expression of inflammatory biomarkers in human hepatoma HepG2 cell lines through C-reactive protein (CRP) western blot. The results showed UA molecules can be recognized by three ACBs with different binding constants, and ACBs successfully blocked the inflammatory stimulation of uric acid on HepG2 cell lines and inhibited the expression of the major inflammatory factor CRP by formations of complexes between UA and ACBs. This article proves that ACBs can efficiently reversing cytotoxicity of UA, which provides a new method to treating hyperuricemia disease.

Supramolecular hosts as in vivo sequestration agents for pharmaceuticals and toxins

Pharmaceutical agents, drugs of abuse, and toxic substances have a large impact, positive and negative, on modern society. Efforts to mitigate the side effects of pharmaceuticals and counteract the life threatening effects of drugs of abuse and toxins can occur either by pharmacodynamic (PD) approaches based on bioreceptor·drug antagonism or by pharmacokinetic (PK) approaches that seek to reduce the concentration of free drug. In this tutorial review, we present the use of supramolecular hosts (cyclodextrins, calixarenes, (acyclic) cucurbiturils, and pillararenes) as in vivo sequestration agents for neuromuscular blockers, drugs of abuse (methamphetamine and fentanyl), anesthetics, neurotoxins, the pesticide paraquat, and heparin anti-coagulants by the PK approach. The review presents the basic physical and molecular recognition features of the supramolecular hosts and some of the principles used in their selection and structural optimization for in vivo sequestration applications. The influence of host·guest complexation on other relevant in vivo properties of drugs (e.g. distribution, circulation time, excretion, redox properties) is also mentioned. The article concludes with a discussion of future directions.

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.

An Eco- and User-Friendly Herbicide

The increasing use of pesticides in agriculture and gardening has caused severe deterioration to both the ecosystem and the health of users (human beings), so there is an urgent need for eco- and user-friendly pesticides. Among a variety of herbicides, paraquat (PQ), frequently used as an effective herbicidal agent worldwide, is well-known for its serious toxicity that has killed, and harmed, thousands of people and countless wildlife such as fish. Herein, we present a facile supramolecular formulation of PQ@cucurbit[7]uril (PQ@CB[7]), prepared by simply mixing PQ with equivalent (molar) CB[7] in water. With addition of CB[7], PQ's cellular uptake was dramatically inhibited. The reactive oxygen species (ROS) generation and the associated apoptosis otherwise induced by PQ in cellular models were both reduced, resulting in increased cellular viability. In a wildtype zebrafish model that is a typical fragile wildlife species in the ecosystem, the supramolecular formulation exhibited significantly reduced hepatotoxicity and increased survival rate, in comparison with those of the fish exposed to free PQ. In a mouse model that is clinically relevant to human being, the administration of PQ@CB[7] significantly alleviated major organ injuries and unusual hematological parameters that were otherwise induced by free PQ, resulting in a significantly increased survival rate. Meanwhile, this formulation maintained effective herbicidal activity that was equivalent to that of free PQ. Taken together, this facile supramolecular PQ formulation is providing not only an extremely rare example of an eco- and user-friendly herbicide that has been desired for decades but also a practical solution for green agriculture.

Triazole functionalized acyclic cucurbit[n]uril-type receptors: host·guest recognition properties

We report the synthesis of three new triazole functionalized acyclic CB[n]-type receptors (2-4) by click chemistry. The compounds have good solubility in water (≥8 mM) and do not undergo strong self-association (Ks ≤ 903 M-1). We measured the binding constants of 2-4 toward guests 9-24 and compared the results to those obtained for the prototypical acyclic CB[n]-type receptor 1. The X-ray crystal structure of 4 is also described.

Supramolecular Interaction Between Cucurbit[8]uril and the Quinolone Antibiotic Ofloxacin

The host–guest inclusion complex of cucurbit[8]uril (Q[8]) and ofloxacin (OFLX) has been prepared and characterised by means of 1H NMR spectroscopy, MALDI-TOF mass spectrometry, isothermal titration calorimetry (ITC), fluorescence spectroscopy, and UV-vis absorption spectroscopy. The findings demonstrated that a host–guest inclusion complex could be formed through an encapsulation of the methylmorpholine and piperazine rings in OFLX. ITC results indicated that the formation of this inclusion complex (1:1 molar ratio) was primarily dependent on enthalpy and entropy changes. In addition, the release of OFLX from the inclusion complex was increased under acidic conditions.

Acyclic Cucurbit[n]uril Type Receptors: Secondary Versus Tertiary Amide Arms

Two acyclic CB[n]-type hosts (1 and 2) which possess four 2° or 3° amide arms are reported; 1 and 2 are slightly soluble in water and do not self-associate. Host 2 has four 3° amide arms that exist as a mixture of E- and Z-isomers. ¹H NMR was used to qualitatively investigate the binding properties of 1 and 2 which indicates they retain the essential binding features of macrocyclic CB[n] hosts (e.g. cavity binding of hydrophobic residues and portal binding of cationic groups). We measured the K_a values of 1 and 2 toward guests 6 - 12, methamphetamine, and fentanyl by ITC to evaluate their potential as in vivo sequestration agents. Neutral hosts 1 and 2 bind less tightly than tetraanionic hosts M1, ACB1, and ACB2. We attribute the lower K_a values to the absence of secondary ion-ion (ammonium•••sulfonate or ammonium•••carboxylate) electrostatic interactions for host•guest complexes of 1 and 2. The secondary amide functionality on 1 decreases affinity by formation of intramolecular NH•••O=C H-bonds. Tertiary amide host 2 binds even more weakly than 1 due to backfolding of the amide N-CH₃-groups of 2 into its own cavity. The x-ray crystal structure of 2 supports this conclusion.

Inhibition of drug-induced seizure development in both zebrafish and mouse models by a synthetic nanoreceptor

A synthetic nanoreceptor, cucurbit[7]uril (CB[7]), fully encapsulated pentylenetetrazol (PTZ), a seizure-inducing model drug. As a consequence of the encapsulation, the development of PTZ induced convulsion behaviors in both larval zebrafish and mouse models were dramatically alleviated, suggesting that CB[7] holds great neuroprotection potential against neurotoxic drugs for clinical applications.

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.

Acyclic Cucurbit[n]uril-type Receptors: Preparation, Molecular Recognition Properties and Biological Applications

This article traces the development of acyclic cucurbit[n]uril-type receptors with a focus on work from the Isaacs group. First, we describe the synthesis of methylene bridged glycoluril dimers capped with aromatic sidewalls which allowed us to probe the interconversion of the S- and C-shaped dimers which is a fundamental step in CB[n] formation. The C-shaped compounds were found to undergo discrete self-assembly (dimerization) in both water and organic solvents which lead us to investigate multicomponent self-sorting systems. We supressed the self-association of 8 by electrostatic repulsion in the putative dimer which allowed expression of its innate molecular recognition properties toward methylene blue and related planar cationic dyes. Longer glycoluril oligomers (trimer - hexamer, acyclic decamer) were prepared by starving the CB[n]-forming reaction of formaldehyde. The longer oligomers (e.g. 15 and 16) bind to alkylammonium ions in water ≈ 100-fold weaker than macrocyclic CB[n] highlighting the high preorganization of the acyclic but polycyclic framework. We prepared a wide variety of acyclic CB[n] compounds (wall variants, solubilizing group variants, linker variants) based on glycoluril trimer and tetramer. In particular, 26 and 27 have been shown to possess a wide variety of chemically and biologically interesting functions. For example, 26 was used to formulate the insoluble drug Albendazole and treat mice bearing SK-OV-3 xenograft tumors. Compound 27 binds tightly to the neuromuscular blocking agents rocuronium, vecuronium, and cisatracurium and acts as an in vivo reversal agent for these compounds in anesthetized rats. Container 27 was also found to modulate the hyperlocomotive effect of rats that had been treated with methamphetamine. Finally, 38 has been used as a cross reactive component of sensor arrays that are capable of classifying and quantifying cancer related nitroamines and a range of over the counter drugs. Overall, the work demonstrates that acyclic CB[n]-type compounds are nicely pre-organized and therefore retain the essential aspects of the recognition properties of macrocyclic CB[n] but allow for more straightforward tailoring of structure and solubility that enables a variety of chemically and biologically important applications.

Graphene oxide based fluorescence sensor for cucurbit[7]uril

Rhodamine B (RhB) anchored reduced graphene oxide (RhBGO) offers a very sensitive and selective sensing potential for cucurbit[7]uril (CB[7]).

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.

A novel compound DT-010 protects against doxorubicin-induced cardiotoxicity in zebrafish and H9c2 cells by inhibiting reactive oxygen species-mediated apoptotic and autophagic pathways

Doxorubicin (Dox) is an effective anti-cancer agent but limited by its cardiotoxicity, thus the search for pharmacological agents for enhancing anti-cancer activities and protecting against cardiotoxicity has been a subject of great interest. We have previously reported the synergistic anti-cancer effects of a novel compound DT-010. In the present study, we further investigated the cardioprotective effects of DT-010 in zebrafish embryos in vivo and the molecular underlying mechanisms in H9c2 cardiomyocytes in vitro. We showed that DT-010 prevented the Dox-induced morphological distortions in the zebrafish heart and the associated cardiac impairments, and especially improved ventricular functions. By using H9c2 cells model, we showed that DT-010 directly inhibited the generation of reactive oxygen species by Dox and protected cell death and cellular damage. We further observed that DT-010 protected against Dox-induced myocardiopathy via inhibiting downstream molecular pathways in response to oxidative stress, including reactive oxygen species-mediated MAPK signaling pathways ERK and JNK, and apoptotic pathways involving the activation of caspase 3, caspase 7, and PARP signaling. Recent studies also suggest the importance of alterations in cardiac autophagy in Dox cardiotoxicity. We further showed that DT-010 could inhibit the induction of autophagosomes formation by Dox via regulating the upstream Akt/AMPK/mTOR signaling. Since Dox-induced cardiotoxicity is multifactorial, our results suggest that multi-functional agent such as DT-010 might be an effective therapeutic agent for combating cardiotoxicity associated with chemotherapeutic agents such as Dox.

The in vitro zebrafish heart as a model to investigate the chronotropic effects of vapor anesthetics

In addition to their intended clinical actions, all general anesthetic agents in common use have detrimental intrasurgical and postsurgical side effects on organs and systems, including the heart. The major cardiac side effect of anesthesia is bradycardia, which increases the probability of insufficient systemic perfusion during surgery. These side effects also occur in all vertebrate species so far examined, but the underlying mechanisms are not clear. The zebrafish heart is a powerful model for studying cardiac electrophysiology, employing the same pacemaker system and neural control as do mammalian hearts. In this study, isolated zebrafish hearts were significantly bradycardic during exposure to the vapor anesthetics sevoflurane (SEVO), desflurane (DES), and isoflurane (ISO). Bradycardia induced by DES and ISO continued during pharmacological blockade of the intracardiac portion of the autonomic nervous system, but the chronotropic effect of SEVO was eliminated during blockade. Bradycardia evoked by vagosympathetic nerve stimulation was augmented during DES and ISO exposure; nerve stimulation during SEVO exposure had no effect. Together, these results support the hypothesis that the cardiac chronotropic effect of SEVO occurs via a neurally mediated mechanism, while DES and ISO act directly upon cardiac pacemaker cells via an as yet unknown mechanism.

CB7 as a drug vehicle and controlled release of drug through non ionic surfactant: Spectroscopic technique

A study of the comparative drug carrier properties of cucurbituril[7] (CB7) and β-cyclodextrin (β-CD) with a naphthalimide derivative, [2-(2-aminoethyl)-1H-benzo[deisoquinoline-1,3(2H)-dione] (NAP) and its release in aqueous solution using micellar environment, is the key research interest of this work. The profound changes in the different spectroscopic behavior have been attributed to the formation of a 1:1 inclusion complex for NAP:CB7 system. Several experimental outcomes clearly interpreted that CB7 has better drug carrier properties for NAP compared to β-CD. It has been also focused on the systematic release of NAP molecule from CB7 by using different ionic and non ionic surfactants. Before releasing the drug molecules from CB7 the interaction between NAP and the three different types of surfactants has also been investigated separately. The selectivity of drug carrier and releaser has been monitored, using different spectroscopic techniques like absorbance, fluorescence, fluorescence decay life time and ¹H NMR spectroscopy. Besides, a theoretical approach has been followed for a proper geometrical optimized structure of NAP molecule and molecular arrangement of NAP:CB7 inclusion complex. From Density Functional Theory (DFT) it has been seen that NAP molecule is oriented as a t-bone like structure in its optimized form.

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).

Cucurbit[7]uril Enables Multi-Stimuli-Responsive Release from the Self-Assembled Hydrophobic Phase of a Metal Organic Polyhedron

Mixed self-assembly of ligands 1, 2, 1,6-hexanediamine (HDA), and Pd(NO3)2 afforded Fujita-type metal organic polyhedron MOP1 (diameter ≈ 8.2 nm), which is covalently functionalized with an average of 18 cucurbit[7]uril (CB[7]) units, as evidenced by 1H NMR, diffusion-ordered spectroscopy NMR, and transmission electron microscopy measurements. By virtue of the host-guest properties of CB[7], the inner cavity of MOP can be rendered hydrophobic by using octadecyl HDA (3) as guest during the self-assembly process. The hydrophobic cavity was successfully utilized to trap the hydrophobic dye Nile Red (NR) and the anticancer drug doxorubicin (DOX). The stimuli-responsive release of encapsulated NR or DOX occurs (1) upon addition of a competitive binder (e.g., adamantane ammonium (ADA)) for CB[7], (2) by a dual pH-chemical stimulus involving the protonation state change of adamantane carboxylate at pH 5.8, and (3) by a dual pH-photochemical stimulus involving photoisomerization of trans-6 to cis-6 at pH 5.8. NR is released from NR@MOP2 within HeLa cancer cells. This body of work suggests that the covalent attachment of cucurbit[n]uril to metal organic polyhedra constitutes a promising vehicle for the development of both diagnostic and therapeutic nanoparticles.

Metal-Organic Polyhedron Capped with Cucurbit[8]uril Delivers Doxorubicin to Cancer Cells

Self-assembly of ligand 1 and Pd(NO3)2 delivers Fujita-type metal-organic polyhedron (MOP) 3 which bears 24 covalently attached methyl viologen units on its external surface, as evidenced by 1H NMR, diffusion-ordered spectroscopy NMR, electrospray mass spectrometry, transmission electron microscopy, and atomic force microscopy measurements. MOP 3 undergoes noncovalent complexation with cucurbit[n]urils to yield MOPs 4-6 with diameter ≈5-6 nm. MOP 5 can be fully loaded with doxorubicin (DOX) prodrug 2 via hetero-ternary complex formation to yield 7. The MOPs exhibit excellent stability toward neutral to slightly acidic pH in 10 mM sodium phosphate buffer, mitigating the concern of disassembly during circulation. The results of MTS assays show that MOP 7 is 10-fold more cytotoxic toward HeLa cells than equimolar quantities of DOX prodrug 2. The enhanced cytotoxicity can be traced to a combination of enhanced cellular uptake of 7 and DOX release as demonstrated by flow cytometry and confocal fluorescence microscopy. The confluence of properties imparted by the polycationic MOP architecture and plug-and-play CB[n] complexation provides a potent new platform for drug delivery application.

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.

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

Cucurbit[7]uril (CB[7]) has recently attracted increasing attention in pharmaceutical sciences due to its great potential in improving the physicochemical properties and bioactivity of drug molecules. Herein, we have investigated the influence of CB[7]'s complexation on the solubility, antimycobacterial activity, and cardiotoxicity of a model anti-tuberculosis drug, clofazimine (CFZ), that has poor water-solubility and inherent cardiotoxicity. In our study, CFZ was found to be complexed by CB[7], in a 1 : 1 binding mode with a relatively strong binding affinity (in the order of magnitude of 10(4)-10(5) M(-1)), as determined by the phase solubility method via HPLC-UV analysis and (1)H NMR titration, as well as UV-visible spectroscopic titration, and further confirmed by electrospray ionization mass spectrometry (ESI-MS). Upon complexation, the solubility of virtually insoluble CFZ was significantly increased, reaching a concentration of up to approximately 0.53-fold of the maximum solubility of CB[7]. The inherent cardiotoxicity of CFZ was dramatically reduced to almost nil in the presence of CB[7]. Importantly, on the other hand, such a supramolecular complexation of the drug did not compromise its therapeutic efficacy, as shown by the antimycobacterial activities examined against Mycobacterium smegmatis, demonstrating the significant potential of CB[7] as a functional pharmaceutical excipient.

Acyclic Cucurbit[n]uril-Type Molecular Containers: Influence of Linker Length on Their Function as Solubilizing Agents

Two acyclic cucurbit[n]uril (CB[n])-type molecular containers that differ in the length of the (CH2 )n linker (M2C2: n=2, M2C4: n=4) between their aromatic sidewalls and sulfonate solubilizing groups were prepared and studied. The inherent solubilities of M2C2 (68 mm) and M2C4 (196 mm) are higher than the analogue with a (CH2 )3 linker (M2, 14 mm) studied previously. (1) H NMR dilution experiments show that M2C2 and M2C4 do not self-associate in water, which enables their use as solubilizing excipients. We used phase solubility diagrams (PSDs) to compare the solubilizing capacities of M2, M2C2, M2C4, hydroxypropyl-β-cyclodextrin (HP-β-CD), and sulfobutylether-β-cyclodextrin (SBE-β-CD) toward 15 insoluble drugs. We found that M2C2 and M2C4-as gauged by the slope of their PSDs-are less potent solubilizing agents than M2. However, the higher inherent solubility of M2C2 allows higher concentrations of drug to be formulated using M2C2 than with M2 in several cases. The solubilizing ability of M2C2 and SBE-β-CD were similar in many cases, with Krel values averaging 23 and 12, respectively, relative to HP-β-CD. In vitro cytotoxicity and in vivo maximum tolerated dose studies document the biocompatibility of M2C2.

In Vitro selectivity of an acyclic cucurbit[n]uril molecular container towards neuromuscular blocking agents relative to commonly used drugs

An acyclic cucurbit[n]uril (CB[n]) based molecular container (2, a.k.a. Calabadion 2) binds to both amino-steroidal and benzylisoquinolinium type neuromuscular blocking agents (NMBAs) in vitro, and reverses the effect of these drugs in vivo displaying faster recovery times than placebo and the γ-cyclodextrin (CD) based and clinically used reversal agent Sugammadex. In this study we have assessed the potential for other drugs commonly used during and after surgery (e.g. antibiotics, antihistamines, and antiarrhythmics) to interfere with the ability of 2 to bind NMBAs rocuronium and cisatracurium in vitro. We measured the binding affinities (Ka, M(-1)) of twenty seven commonly used drugs towards 2 and simulated the equilibrium between 2, NMBA, and drug based on their standard clinical dosages to calculate the equilibrium concentration of 2·NMBA in the presence of the various drugs. We found that none of the 27 drugs studied possess the combination of a high enough binding affinity with 2 and a high enough standard dosage to be able to promote the competitive dissociation (a.k.a. displacement interactions) of the 2·NMBA complex with the formation of the 2·drug complex. Finally, we used the simulations to explore how the potential for displacement interactions is affected by a number of factors including the Ka of the 2·NMBA complex, the Ka of the AChR·NMBA complex, the Ka of the 2·drug complex, and the dosage of the drug.