Cucurbit[7]uril-based host-guest complexes for improving bioavailability and reducing side effects of piroxicam

Piroxicam (PX) is a nonsteroidal anti-inflammatory drug (NSAID) commonly associated with gastrointestinal (GI) injuries, including dyspepsia, heartburn, inflammation, bleeding, ulceration, and life-threatening perforation. The β-cyclodextrin (β-CD)-based PX formulation (PX@CD) has been shown to reduce gastric side effects by improving PX's solubility and dissolution rates. However, the solubility of PX can only be increased to a limited extent by β-CD, due to the low binding constant between PX and β-CD (∼100 M-1). As a result, adverse reactions such as epigastric pain and pyrosis are still commonly reported. Cucurbit[7]uril (CB[7]) is a synthetic macrocyclic host compound that binds strongly to various drugs. In this study, we demonstrated that CB[7] forms complexes with PX in the gastric acid environment with a binding constant approximately 70 times higher than that between β-CD and PX. The PX@CB[7] inclusion complexes exhibited rapid dissolution rates in the gastric environment. In addition, PX@CB[7] showed significantly higher oral bioavailability and maximum concentration (Cmax) compared to PX and PX@CD (1:2.5), resulting in improved anti-inflammatory effects in both mouse and rat models. Moreover, PX@CB[7] (1:2.5) had the least adhesion to the gastric mucosa and caused the mildest gastric side effects in rat models when compared to PX, PX@CD (1:2.5), and PX@CB[7] (1:1). Lastly, CB[7] demonstrated good oral biocompatibility in a subacute toxicity evaluation study. These findings indicate that CB[7] could be used as an excipient to improve treatment effectiveness and decrease adverse reactions in orally administered formulations with a favorable safety profile.

The cucurbit[7]uril effect on reference substances for NMR in deuterium oxide solution

The effect of macrocyclic molecule cucurubit[7]uril on the chemical shifts of internal reference substances for NMR studies in deuterium oxide solution and the cause were investigated.

Passive Diffusion vs Active pH-Dependent Encapsulation of Tyrosine Kinase Inhibitors Vandetanib and Lenvatinib into Folate-Targeted Ferritin Delivery System

Introduction

The present study reports on examination of the effects of encapsulating the tyrosine kinase inhibitors (TKIs) vandetanib and lenvatinib into a biomacromolecular ferritin-based delivery system.

Methods

The encapsulation of TKIs was performed via two strategies: i) using an active reversible pH-dependent reassembly of ferritin´s quaternary structure and ii) passive loading of hydrophobic TKIs through the hydrophobic channels at the junctions of ferritin subunits. After encapsulation, ferritins were surface-functionalized with folic acid promoting active-targeting capabilities.

Results

The physico-chemical and nanomechanical analyses revealed that despite the comparable encapsulation efficiencies of both protocols, the active loading affects stability and rigidity of ferritins, plausibly due to their imperfect reassembly. Biological experiments with hormone-responsive breast cancer cells (T47-D and MCF-7) confirmed the cytotoxicity of encapsulated and folate-targeted TKIs to folate-receptor positive cancer cells, but only limited cytotoxic effects to healthy breast epithelium. Importantly, the long-term cytotoxic experiments revealed that compared to the pH-dependent encapsulation, the passively-loaded TKIs exert markedly higher anticancer activity, most likely due to undesired influence of harsh acidic environment used for the pH-dependent encapsulation on the TKIs’ structural and functional properties.

Conclusion

Since the passive loading does not require a reassembly step for which acids are needed, the presented investigation serves as a solid basis for future studies focused on encapsulation of small hydrophobic molecules.

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

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

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.

Enhancing the solubility and bioactivity of anticancer drug tamoxifen by water-soluble pillar[6]arene-based host-guest complexation

A water-soluble pillar[6]arene functions as a solubilizing agent to enhance the solubility and bioactivity of poorly water-soluble anticancer drug tamoxifen by host-guest complexation between it and tamoxifen.

A pH-induced conformational switch in a tyrosine kinase inhibitor identified by electronic spectroscopy and quantum chemical calculations

Tyrosine kinase inhibitors (TKIs) are a major class of drug utilised in the clinic. During transit to their cognate kinases, TKIs will encounter different pH environments that could have a major influence on TKI structure. To address this, we report UV-Vis spectroscopic and computational studies of the TKI, AG1478, as a function of pH. The electronic absorption spectrum of AG1478 shifted by 10 nm (from 342 nm to 332 nm) from acid to neutral pH and split into two peaks (at 334 nm and 345 nm) in highly alkaline conditions. From these transitions, the pKa value was calculated as 5.58 ± 0.01. To compute structures and spectra, time-dependent density functional theory (TD-DFT) calculations were performed along with conductor-like polarizable continuum model (CPCM) to account for implicit solvent effect. On the basis of the theoretical spectra, we could assign the AG1478 experimental spectrum at acidic pH to a mixture of two twisted conformers (71% AG1478 protonated at quinazolyl nitrogen N(1) and 29% AG1478 protonated at quinazolyl nitrogen N(3)) and at neutral pH to the neutral planar conformer. The AG1478 absorption spectrum (pH 13.3) was fitted to a mixture of neutral (70%) and NH-deprotonated species (30%). These studies reveal a pH-induced conformational transition in a TKI.

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).

Cucurbiturils: from synthesis to high-affinity binding and catalysis

Major developments in the synthesis of cucurbiturils and applications related to their high-affinity binding and catalysis have recently taken place.