Recent Updates on Supramolecular-Based Drug Delivery - Macrocycles and Supramolecular Gels

Supramolecules-based drug delivery has attracted significant recent research attention as it could enhance drug solubility, retention time, targeting, and stimuli responsiveness. Among the different supramolecules and assemblies, the macrocycles and the supramolecular hydrogels are the two important categories investigated to a greater extent. Here, we provide the most recent advancements in these categories. Under macrocycles, reports on drug delivery by cyclodextrins, cucurbiturils, calixarenes/pillararenes, crown ethers and porphyrins are detailed. The second category discusses the supramolecular hydrogels of macrocycles/polymers and low molecular weight gelators. The updated information provided could be helpful to advance R & D in this vital area.

Host-guest interaction of cucurbit[8]uril with oroxin A and its effect on the properties of oroxin A

In this study, we investigated the host-guest interactions between oroxin A (OA) and cucurbit[8]uril (Q[8]) using 1H NMR, MS, UV-vis and IR spectroscopy. The results showed that OA and Q[8] formed an inclusion compound (OA@Q[8]) with a molar ratio of 1:1 and a binding constant of 1.299 × 107 L·mol-1. In addition, the effect of Q[8] on the properties of OA was investigated through comparative experiments. The solubility of OA in water increased 22.47-fold when the concentration of Q[8] was 1 × 10-4 mol·L-1. Q[8] hardly affected the antioxidant capacity of OA, while the cumulative release of OA in gastric juice increased 2.3-fold after forming the inclusion compound with Q[8].

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

Compared with conventional drug delivery systems (DDSs), DDSs based on host-guest interactions possess unique advantages, such as high selectivity, tunable binding ability, and controllable release of drugs. It is important to study the host-guest interactions between the carrier and drug under physiological conditions for constructing DDSs. In this work, we have studied the host-guest interaction between cucurbit[7]uril (CB[7]) and oxaliplatin (OxPt), a clinical antitumor drug, in the cell culture medium. The results show that amino acids such as phenylalanine in the 1640 culture medium can partially occupy the cavity of CB[7], which leads to the decrease of enthalpy changes of the host-guest interaction between OxPt and CB[7]. In addition, inorganic salts such as NaCl in the medium reduce the enthalpy change and increase the entropy change of the binding because of the preorganization of the portal of CB[7] and sodium cation. As a result, the binding constant of CB[7] with OxPt in the 1640 culture medium is 1/20 of that in pure water. When CB[7] is modified at the terminal of star-type PEG to construct the star-PEGylated CB[7], it is shown that the molecular weight and topological structure of the PEG polymer backbone exhibit little effect on the host-guest interactions between CB[7] and OxPt. This study enriches the host-guest chemistry of cucurbiturils and may provide guidance for constructing novel DDSs based on host-guest interactions with high loading and releasing efficiency.

Applications of Cucurbiturils in Medicinal Chemistry and Chemical Biology

The supramolecular chemistry of cucurbit[n]urils (CBn) has been rapidly developing to encompass diverse medicinal applications, including drug formulation and delivery, controlled drug release, and sensing for bioanalytical purposes. This is made possible by their unique recognition properties and very low cytotoxicity. In this review, we summarize the host-guest complexation of biologically important molecules with CBn, and highlight their implementation in medicinal chemistry and chemical biology.

Photocaged Competitor Guests: A General Approach Toward Light-Activated Cargo Release From Cucurbiturils

A general approach toward the light-induced guest release from cucurbit[7]uril by means of a photoactivatable competitor was devised. An o-nitrobenzyl-caged competitor is photolyzed to generate a competitive guest that can displace cargo from the host macrocycle solely based on considerations of chemical equilibrium. With this method the release of terpene guests from inclusion complexes with cucurbit[7]uril was demonstrated. The binding of the herein investigated terpenes, all being lead fragrant components in essential oils, has been characterized for the first time. They feature binding constants of up to 10⁸  L mol^-1 and a high differential binding selectivity (spanning four orders of magnitude for the binding constants for the particular set of terpenes). By fine-tuning the photoactivatable competitor guest, selective and also sequential release of the terpenes was achieved.

Chemical and biological properties of a supramolecular complex of tuftsin and cucurbit[7]uril

Cucurbit[7]uril (CB7) is an uncharged and water-soluble macrocyclic host. CB7 binds to doubly protonated tuftsin, which is the tetrapeptide Thr-Lys-Pro-Arg, with moderate affinity (K_a=2.1×10³M^-1). In this study, the host-guest complexation was confirmed by fluorescence titration. This affinity would allow for easy release of the peptide under physiological conditions. According to density functional theory calculations, the structural binding motif involves hydrogen bonding. The most energetically stable form had the Arg side chain inside the CB7 cavity. The effects of the tuftsin-CB7 complex on the proliferation and cytokine activity of immune cells were studied. The complex had broader spectrum immunomodulation than free peptides, and caused statistically significant (p<0,05) changes in cytokine production (tumor necrosis factor-α, interleukin-2, interferon-γ, and interleukin-10) by mononuclear cells. By contrast, the free peptide only activated tumor necrosis factor-α production.

Five-Component Self-Assembly of Cucurbituril-Based Hetero-pseudorotaxanes

[5]Pseudorotaxanes can be obtained by self-sorting using heteroditopic guests and various cucurbituril homologues as hosts. The assembly and chemically induced disassembly of the pseudorotaxanes can be monitored by measuring the fluorescence of the anthracene guest in solution. Mass spectral evidence for the supramolecular assemblies is obtained in the gas phase. The disassembly in the gas phase can be achieved by collision-induced dissociation leading to the corresponding [2]- and [3]pseudorotaxanes.

Kinetics of the reversible inclusion of flavopereirine in cucurbit[7]uril

The temperature dependence of the formation and dissociation kinetics of the flavopereirine–cucurbit[7]uril complex is revealed.

Encapsulation of Thiotepa and Altretamine as neurotoxic anticancer drugs in Cucurbit[n]uril (n=7, 8) nanocapsules: A DFT study

The encapsulation of Altretamine (ALT) and Thiotepa (THI) as neurotoxic anticancer drugs in Cucurbit[[Formula: see text]]uril (CB[[Formula: see text]]) family of macrocycles ([Formula: see text],8) have been investigated and their potential in drug delivery, ability to provide physical and chemical stability, improving water solubility and decreasing the side effects have been studied using density functional theory (DFT) approach with B3LYP and the dispersion corrected functional WB97XD methods by employing the 3-21G* basis set. All the calculations were evaluated for gas phase and water as a pharmaceutical and biological solvent according to the polarizable continuum model (PCM). The non-covalent inter-molecular interactions between the host and guest parts were visualized using reduced density gradient analysis. The molecular characteristics for drugs, CB[[Formula: see text]] and their complexes calculated and the global and local descriptors were employed to study the chemical stability of the host–guest complexes. The results show that the encapsulation of THI and ALT for both CB[7] and CB[8] energetically favorable and this can decrease the central nervous system (CNS) neurotoxicity, and increase the stability of THI in electrophilic and nucleophilic. Beside the CNS neurotoxicity reduction and increasing the stability in electrophilic and nucleophilic attacks, the solubility in water for ALT was improved.

Interactions of cucurbit[6,7]urils with human serum albumin and their effects on zaltoprofen transportation

Interference of CB[6,7]s on a HSA–zaltoprofen binding system was studied for conducting the applications of CB[6,7]s.

Phototriggered release of amine from a cucurbituril macrocycle

Amines are released from a cucurbituril macrocycle by photoinduced pH jump and modulation of the competitiveness of a fluorescent guest.

Recognition-mediated cucurbit[7]uril-heptamolybdate hybrid material: a facile supramolecular strategy for99mTc separation

Employing a novel cucurbit[7]uril (CB7)-heptamolybdate hybrid material developed as a solid generator bed, we demonstrate an efficient and facile supramolecular strategy to separate the^99mTc nuclide from⁹⁹Mo solution for its use in theranostic applications.

Solvent control in the formation of supramolecular host–guest complexes of isoniazid with p-sulfonatocalix[4]arene

The position of the anti-tuberculosis drug isoniazid inside (endo) or outside (exo) to the macrocyclic cavity of p-sulfonatocalix[4]arene can be regulated by the appropriate choice of the solvent system.

Developmental and organ-specific toxicity of cucurbit[7]uril: in vivo study on zebrafish models

The macrocyclic Cucurbit[7]uril was evaluated for its in vivo toxicity profile, including developmental toxicity and organ-specific toxicities using zebrafish models.

In vivo reversal of general anesthesia by cucurbit[7]uril with zebrafish models

We demonstrate for the first time that cucurbit[7]uril effectively reversed general anesthesia induced by tricaine in zebrafish models.

Anti-cancer applications of titanocene-functionalised nanostructured systems: an insight into cell death mechanisms

A series of alkenyl-substituted titanocene compounds have been supported on the mesoporous silica-based material KIT-6. The corresponding functionalised materials were completely characterised by different techniques (solid-state multinuclear NMR spectroscopy, IR spectroscopy, N2 adsorption-desorption isotherms, X-ray fluorescence and diffraction, SEM and TEM) to observe the incorporation of the titanocene derivatives on the external surface of the material KIT-6. Both the titanocene compounds and the materials were tested in vitro against a wide variety of human cancer and normal cell lines. A very high cytotoxicity of the synthesised titanocene derivatives (IC50 values in the range of those described in the literature for the most active cytotoxic titanocene compounds), with selectivity towards cancer cell lines was observed. The cytotoxic activity of the materials is the highest reported to date for titanocene-functionalised materials. In addition, higher Ti uptake (from 4 to 23% of the initial amount of Ti) of the cells treated with materials was observed with respect to those treated with "free" titanocene derivatives (which gave Ti uptake values from 0.4 to 4.6% of the initial amount of Ti). Additional experiments with the titanocene derivatives and the functionalised materials revealed that changes to the morphological and functional dynamics of apoptosis occurred when the active titanocene species were incorporated into mesoporous materials. In addition, the materials could induce programmed cell death in tumour cell populations by impairing the damaged DNA repair mechanisms and by upregulation of intrinsic and extrinsic apoptotic signalling pathways.

A cisplatin slow-release hydrogel drug delivery system based on a formulation of the macrocycle cucurbit[7]uril, gelatin and polyvinyl alcohol

The anticancer drug cisplatin was encapsulated within the cucurbit[7]uril macrocycle to form the host-guest complex: cisplatin@CB[7]. This was then incorporated into gelatin and 0-4% w/v polyvinyl alcohol (PVA)-based hydrogels as slow release drug delivery vehicles. The hydrogels demonstrated predicable swelling and disintegration dependent on the PVA concentration. The hydrogel with the highest PVA content was slower to swell and release drug compared with lower concentrations of PVA. The effect of the hydrogel PVA concentration on in vitro cytotoxicity was examined using A2780/CP70 ovarian cancer cells. Over the 24h drug exposure time used, hydrogels containing 4% PVA showed a 20% decrease in viable cells compared to the control, whereas hydrogels containing 0% and 2% PVA induced an 80% and 45% inhibition of cell growth, respectively. There was no measurable difference in the in vitro cytotoxicity of free cisplatin and cisplatin@CB[7] containing hydrogels. Finally, the in vivo effectiveness of a 2%-PVA hydrogel implanted under the skin of nude mice bearing A2780/CP70 xenografts showed that low dose hydrogels containing cisplatin@CB[7] (30 μg equivalent of drug) was just as effective as an intraperitoneal high dose administration of free cisplatin (150 μg) at inhibiting tumour growth.

pH-sensitive amphiphilic copolymer brush Chol-g-P(HEMA-co-DEAEMA)-b-PPEGMA: synthesis and self-assembled micelles for controlled anti-cancer drug release

A novel pH-sensitive amphiphilic copolymer Chol-g-P(HEMA-co-DEAEMA)-b-PPEGMA and its micelles were developed as a promising anti-cancer drug carrier.

The delivery of triamterene by cucurbit[7]uril: synthesis, structures and pharmacokinetics study

In recent years, cucurbit[7]uril (CB[7]) has attracted great attention in drug delivery. Though the effect of CB[7] in enhancing the solubility of water insoluble drugs has been validated, the underlying mechanism remains poorly understood, particularly at a molecular level. This study is designed to evaluate a CB[7]-based pharmaceutical formulation to improve solubility and bioavailability of triamterene (a mild potassium-sparing diuretic). Two polymorphs of triamterene@CB[7] were obtained, and their crystal structures were determined by single crystal X-ray diffraction. The CB[7] molecule forms a stable host-guest complex with triamterene (Ka = 1.69 ± 0.34 × 10(4) M(-1)) in aqueous solution (pH = 1.0). The results of dissolution study demonstrate that the apparent solubility value of triamterene@CB[7] complex in 0.1 M HCl is 1.6 times as large as that of triamterene, while free triamterene was released from triamterene@CB[7] complex in phosphate buffer of pH 6.8. Pharmacokinetic studies in rats reveal that the AUC0-∞ value of triamterene@CB[7] complex increases 2.8-fold compared with that of free triamterene, and t1/2 is prolonged from 1.42 to 2.61 h (P < 0.05) after oral administration. The increased solubility and oral bioavailability are attributed to the formation of a hydrophilic capsule composed of two CB[7] molecules, in which two insoluble triamterene molecules are encapsulated. These results demonstrate that triamterene@CB[7] complex is a stable and effective pharmaceutical formulation.

Cucurbit[7]uril encapsulated cisplatin overcomes cisplatin resistance via a pharmacokinetic effect

The cucurbit[n]uril (CB[n]) family of macrocycles has been shown to have potential in drug delivery where they are able to provide physical and chemical stability to drugs, improve drug solubility, control drug release and mask the taste of drugs. Cisplatin is a small molecule platinum-based anticancer drug that has severe dose-limiting side-effects. Cisplatin forms a host-guest complex with cucurbit[7]uril (cisplatin@CB[7]) with the platinum atom and both chlorido ligands located inside the macrocycle, with binding stabilised by four hydrogen bonds (2.15-2.44 Å). Whilst CB[7] has no effect on the in vitro cytotoxicity of cisplatin in the human ovarian carcinoma cell line A2780 and its cisplatin-resistant sub-lines A2780/cp70 and MCP1, there is a significant effect on in vivo cytotoxicity using human tumour xenografts. Cisplatin@CB[7] is just as effective on A2780 tumours compared with free cisplatin, and in the cisplatin-resistant A2780/cp70 tumours cisplatin@CB[7] markedly slows tumour growth. The ability of cisplatin@CB[7] to overcome resistance in vivo appears to be a pharmacokinetic effect. Whilst the peak plasma level and tissue distribution are the same for cisplatin@CB[7] and free cisplatin, the total concentration of circulating cisplatin@CB[7] over a period of 24 hours is significantly higher than for free cisplatin when administered at the equivalent dose. The results provide the first example of overcoming drug resistance via a purely pharmacokinetic effect rather than drug design or better tumour targeting, and demonstrate that in vitro assays are no longer as important in screening advanced systems of drug delivery.

A photoinduced pH jump applied to drug release from cucurbit[7]uril

A proof-of-principle for the application of a photoinduced pH jump for delivery of the Hoechst 33258 drug by disassembly of its host-guest complex with cucurbit[7]uril is described.

Inclusion complex formation of sanguinarine alkaloid with cucurbit[7]uril: inhibition of nucleophilic attack and photooxidation

The inclusion of sanguinarine, a biologically active natural benzophenanthridine alkaloid, in cucurbit[7]uril (CB7) was studied by NMR and ground-state absorption spectroscopy, as well as steady-state and time-resolved fluorescence measurements in aqueous solution. The iminium form of sanguinarine (SA(+)) produces very stable 1 : 1 inclusion complex with CB7 (K = 1.0 × 10(6) M(-1)), whereas the equilibrium constant for the binding of the second CB7 is about 3 orders of magnitude smaller. Marked fluorescence quantum yield and fluorescence lifetime enhancements are found upon encapsulation of SA(+) due to the deceleration of the radiationless deactivation from the single-excited state, but the fluorescent properties of 1 : 1 and 1 : 2 complexes barely differ. The equilibrium between the iminium and alkanolamine forms is shifted 3.69 pK unit upon addition of CB7 as a consequence of the preferential encapsulation of the iminium form and the protection of the 6 position of sanguinarine against the nucleophilic attack by hydroxide anion. On the basis of thermodynamic cycle, about 225 M(-1) is estimated for the equilibrium constant of the complexation between the alkanolamine form of sanguinarine (SAOH) and CB7. The confinement in the CB7 macrocycle can be used to impede the nucleophilic addition of OH(-) to SA(+) and to hinder the photooxidation of SAOH.

Synthesis, processing and solid state excipient interactions of cucurbit[6]uril and its formulation into tablets for oral drug delivery

The synthesis, processing, and solid state excipient interactions of cucurbit[6]uril (CB[6]) and its formulation into oral tablets has been examined using a range of physical chemistry techniques. Rapid precipitation from HCl by the addition of water yields microcrystalline CB[6] with smaller and more consistent particle size (30-165 μm) compared with the sieved CB[6] (50-540 μm) produced from large crystals grown by slow evaporation from HCl. The microcrystalline particles also contain fewer water molecules in the crystal compared with the sieved particles: 10 and 16% respectively. Microcrystalline CB[6] can be formulated into tablets suitable for oral delivery with a CB[6] content of 1-50% w/w, with the other excipients including lactose, talc, Avicel, magnesium stearate and Ac-Di-Sol. In the solid state microcrystalline CB[6] does not interact significantly with the talc, Ac-Di-Sol or Avicel, but significant interactions are observed when mixed or ground with either magnesium stearate or lactose, resulting in the lowering of the melting points of both excipients. This work represents the first study of the physical processing and solid state chemistry of CB[n]s for pharmaceutical formulation and represents an important development step in the use of CB[n]s as drug delivery vehicles.