Cavity Closure of 2-Hydroxypropyl-β-Cyclodextrin: Replica Exchange Molecular Dynamics Simulations

Solving the puzzle of 2-hydroxypropyl β-cyclodextrin: Detailed assignment of the substituent distribution by NMR spectroscopy

2-Hydroxypropyl-β-cyclodextrin (HPBCD) is one of the most important cyclodextrin derivatives, finding extensive applications in the pharmaceutical sector. Beyond its role as an excipient, HPBCD achieved orphan drug status in 2015 for Niemann-Pick type C disease treatment, prompting research into its therapeutic potential for various disorders. However, the acceptance of HPBCD as an active pharmaceutical ingredient may be impeded by its complex nature. Indeed, HPBCD is not a single entity with a well-defined structure, instead, it is a complex mixture of isomers varying in substituent positions and the degree of hydroxypropylation, posing several challenges for unambiguous characterization. Pharmacopoeias' methods only address the average hydroxypropylation extent, lacking a rapid approach to characterize the substituent positions on the CD scaffold. Recognizing that the distribution of substituents significantly influences the complexation ability and overall activity of the derivative, primarily by altering cavity dimensions, we present a straightforward and non-destructive method based on liquid state NMR spectroscopy to analyze the positions of the hydroxypropyl sidechains. This method relies on a single set of routine experiments to establish quantitative assignment and it provides a simple yet effective tool to disclose the substitution pattern of this complex material, utilizing easily accessible (400 MHz NMR) instrumentation.

Impact of 2-hydroxypropyl-β-cyclodextrin inclusion complex formation on dopamine receptor-ligand interaction - A case study

The octanol-water distribution coefficient (logP), used as a measure of lipophilicity, plays a major role in the drug design and discovery processes. While average logP values remain unchanged in approved oral drugs since 1983, current medicinal chemistry trends towards increasingly lipophilic compounds that require adapted analytical workflows and drug delivery systems. Solubility enhancers like cyclodextrins (CDs), especially 2-hydroxypropyl-β-CD (2-HP-β-CD), have been studied in vitro and in vivo investigating their ADMET (adsorption, distribution, metabolism, excretion and toxicity)-related properties. However, data is scarce regarding the applicability of CD inclusion complexes (ICs) in vitro compared to pure compounds. In this study, dopamine receptor (DR) ligands were used as a case study, utilizing a combined in silico/in vitro workflow. Media-dependent solubility and IC stoichiometry were investigated using HPLC. NMR was used to observe IC formation-caused chemical shift deviations while in silico approaches utilizing basin hopping global minimization were used to propose putative IC binding modes. A cell-based in vitro homogeneous time-resolved fluorescence (HTRF) assay was used to quantify ligand binding affinity at the DR subtype 2 (D2R). While all ligands showed increased solubility using 2-HP-β-CD, they differed regarding IC stoichiometry and receptor binding affinity. This case study shows that IC-formation was ligand-dependent and sometimes altering in vitro binding. Therefore, IC complex formation can't be recommended as a general means of improving compound solubility for in vitro studies as they may alter ligand binding.

Evaluating solubility, stability, and inclusion complexation of oxyresveratrol with various β-cyclodextrin derivatives using advanced computational techniques and experimental validation

Oxyresveratrol (OXY), a natural stilbenoid in mulberry fruits, is known for its diverse pharmacological properties. However, its clinical use is hindered by low water solubility and limited bioavailability. In the present study, the inclusion complexes of OXY with β-cyclodextrin (βCD) and its three analogs, dimethyl-β-cyclodextrin (DMβCD), hydroxypropyl-β-cyclodextrin (HPβCD) and sulfobutylether-β-cyclodextrin (SBEβCD), were investigated using in silico and in vitro studies. Molecular docking revealed two binding orientations of OXY, namely, 4',6'-dihydroxyphenyl (A-form) and 5,7-benzenediol ring (B-form). Molecular Dynamics simulations suggested the formation of inclusion complexes with βCDs through two distinct orientations, with OXY/SBEβCD exhibiting maximum atom contacts and the lowest solvent-exposed area in the hydrophobic cavity. These results corresponded well with the highest binding affinity observed in OXY/SBEβCD when assessed using the MM/GBSA method. Beyond traditional simulation methods, Ligand-binding Parallel Cascade Selection Molecular Dynamics method was employed to investigate how the drug enters and accommodates within the hydrophobic cavity. The in silico results aligned with stability constants: SBEβCD (2060 M-1), HPβCD (1860 M-1), DMβCD (1700 M-1), and βCD (1420 M-1). All complexes exhibited a 1:1 binding mode (AL type), with SBEβCD enhancing OXY solubility (25-fold). SEM micrographs, DSC thermograms, FT-IR and 1H NMR spectra confirm the inclusion complex formation, revealing novel surface morphologies, distinctive thermal behaviors, and new peaks. Notably, the inhibitory impact on the proliferation of breast cancer cell lines, MCF-7, exhibited by inclusion complexes particularly OXY/DMβCD, OXY/HPβCD, and OXY/SBEβCD were markedly superior compared to that of OXY alone.

Enhancing solubility and stability of piperine using β-cyclodextrin derivatives: computational and experimental investigations

Piperine (PP), a natural alkaloid found in black pepper, possesses significant bioactivities. However, its use in pharmaceutical applications is hindered by low water solubility and susceptibility to UV light degradation. To overcome these challenges, we investigated the potential of β-cyclodextrin (βCD) and its derivatives with dimethyl (DMβCD), hydroxy-propyl (HPβCD) and sulfobutyl-ether (SBEβCD) substitutions to enhance the solubility and stability of PP. This study employed computational and experimental approaches to examine the complexation between PP and βCDs. The results revealed the formation of two types of inclusion complexes: the P-form and M-form involving the insertion of piperidine moiety and the methylene-di-oxy-phenyl moiety, respectively. These complexes primarily rely on van der Waals interactions. Among the three derivatives, the PP/SBEβCD complex exhibited the highest stability followed by HPβCD, as attributed to maximum atom contacts and minimal solvent accessibility. Solubility studies confirmed the formation of inclusion complexes in a 1:1 ratio. Notably, the stability constant of the inclusion complex was approximately two-fold higher with SBEβCD and HPβCD compared to βCD. The DSC thermograms provided confirmation of the formation of the inclusion complex between the host and guest. These findings highlight the potential of βCD derivatives to effectively encapsulate PP, improving its solubility and presenting new opportunities for its pharmaceutical applications.Communicated by Ramaswamy H. Sarma.

Molecular dynamics simulation techniques and their application to aroma compounds/cyclodextrin inclusion complexes: A review

Homeostatic technologies play a crucial role in maintaining the quality and extending the service life of aroma compounds (ACs). Commercial cyclodextrins (CDs) are commonly used to form inclusion complexes (ICs) with ACs to enhance their solubility, stability, and morphology. The selection of suitable CDs and ACs is of paramount importance in this process. Molecular dynamics (MD) simulations provide an in-depth understanding of the interactions between ACs and CDs, aiding researchers in optimising the properties and effects of ICs. This review offers a systematic discussion of the application of MD simulations in ACs/CDs ICs, covering the establishment of the simulation process, parameter selection, model evaluation, and various application cases, along with their advantages and disadvantages. Additionally, this review summarises the major achievements and challenges of this method while identifying areas that require further exploration. These findings may contribute to a comprehensive understanding of the formation and stabilization mechanisms of ACs/CDs ICs and offer guidance for the selection and computational characterisation of CDs in the AC steady state.

Theoretical study of structures and charge distributions of 2-, 3- and 6-hydroxypropyl-β-cyclodextrin with different degrees of substitution

Hydroxypropyl-β-cyclodextrin (HPβCD) is a derivative of cyclodextrin extensively used in the pharmaceutical industry, since it improves the solubility of drugs, and widens their oral bioavailability and safety profile. Theoretical studies about HPβCD configurations are important so as to simulate by molecular mechanics and dynamics, the complex formation and enantiomeric separations of these cyclodextrins with other molecules. Twelve structures and charge distributions of 2-, 3- and 6-hydroxypropyl-β-cyclodextrin (2-, 3-, 6-HPβCD) with different degrees of substitution were obtained using ab initio methods. The atomic positions of glucose units, dihedral angles of hydroxypropyl groups (HPs), radius of gyration, and H-bonds formed were analysed in the structures. The 3-HPβCD configurations showed the greatest variations in their atomic positions, their HPs groups being slightly rotated towards the interior of the rim of cyclodextrin and hence narrowing its opening. The structures of 2-HPβCD are the least influenced by the degree of substitution and include fewer H-bonds. Different values for the partial atomic charges for each glucose unit in a molecule were obtained, as well as for all HPβCD configurations. This result, consequence of the ab initio methods used, is a new contribution that can be important to simulate processes in which small energy differences decisively influence the results. The electric potential due to the charge distribution of HPβCDs was calculated inside and outside the cavity. It was found that the changes at each position were mainly due to atomic configurations, since the differences in partial atomic charges are one or two orders of magnitude smaller than in atomic positions.Communicated by Ramaswamy H. Sarma.

Enhancing solubility and stability of sorafenib through cyclodextrin-based inclusion complexation: in silico and in vitro studies

Sorafenib (SOR) is an oral multikinase inhibitor that effectively hampers the growth and spread of cancer cells by targeting angiogenesis and proliferation. However, SOR tablets (Nexavar) have limited oral bioavailability, ranging from 38% to 49%, due to their low water solubility. To address this issue, cyclodextrins (CDs), widely used to enhance the solubility and stability of lipophilic drugs by encapsulating them within their molecular structure, were considered in this study. We focused on β-cyclodextrin (βCD) and its derivatives, including hydroxypropyl-β-cyclodextrin (HPβCD), dimethyl-β-cyclodextrin (DMβCD), sulfobutylether-β-cyclodextrin (SBEβCD), and compared them with γ-cyclodextrin (γCD) for generating inclusion complexes with SOR. The 200 ns molecular dynamics simulations revealed that SOR could form inclusion complexes with all CDs in two possible orientations: pyridine group insertion (P-form) and chlorobenzotrifluoride group insertion (C-form), primarily driven by van der Waals interactions. Among the four βCD derivatives studied, SOR exhibited the highest number of atom contacts with SBEβCD and demonstrated the lowest solvent accessibility within the hydrophobic cavity of SBEβCD. These findings correlated with the highest binding affinity of SOR/SBEβCD complex determined by SIE, MM/GBSA, and MM/PBSA methods. Experimental results further supported our computational predictions, in which SBEβCD exhibited a stability constant of 940 M-1 at 25 °C, surpassing βCD's stability constant of 210 M-1. Taken together, our results suggest that the modified CDs, particularly SBEβCD, hold promising potential as an efficient molecular encapsulating agent for SOR, offering improved solubility and stability for this lipophilic drug.

Effect of temperature on the structure and drug-release behaviour of inclusion complex of β-cyclodextrin with cyclophosphamide: a molecular dynamics study

Cyclodextrins (CDs) are suitable drug carriers because of their doughnut-shaped cavities with hydrophilic outer and hydrophobic inner surfaces. Temperature-responsive CD-based drug carriers are expected to be one of the most promising candidates for drug delivery systems. In this study, we performed molecular dynamics simulations of the inclusion complex of β-CD with cyclophosphamide (CP) at temperatures from 300 K to 400 K to investigate the temperature dependency of the release behaviour of CP and structural changes of β-CD in an aqueous solution. We analysed the distance between the centres of mass of β-CD and CP and the radius of gyration of β-CD. The CP molecule was released from the β-CD cavity at 400 K, whereas two different inclusion complexes, partially and completely, were observed at T < 400 K. β-CD encapsulating a CP molecule had a more spherical shape and rigidity than β-CD without a CP, and the rigidity of their inclusion complex decreased with increasing temperature. Our findings provide fundamental insights into the behaviours of the β-CD/CP complex and drug release at the molecular level and can facilitate the development of new temperature-responsive drug delivery systems with CD nanocarriers triggered by localised temperature increases using focused ultrasound.

Aurisin A Complexed with 2,6-Di-O-methyl-β-cyclodextrin Enhances Aqueous Solubility, Thermal Stability, and Antiproliferative Activity against Lung Cancer Cells

Aurisin A (AA), an aristolane dimer sesquiterpene isolated from the luminescent mushroom Neonothopanus nambi, exhibits various biological and pharmacological effects. However, its poor solubility limits its use for further medicinal applications. This study aimed to improve the water solubility of AA via complexation with β-cyclodextrin (βCD) and its derivatives (2,6-di-O-methyl-βCD (DMβCD) and 2-hydroxypropyl-βCD (HPβCD). A phase solubility analysis demonstrated that the solubility of AA linearly enhanced with increasing concentrations of βCDs (ranked in the order of AA/DMβCD > AA/HPβCD > AA/βCD). Notably, βCDs, especially DMβCD, increased the thermal stability of the inclusion complexes. The thermodynamic study indicated that the complexation between AA and βCD(s) was a spontaneous endothermic reaction, and AA/DMβCD possesses the highest binding strength. The complex formation between AA and DMβCD was confirmed by means of FT-IR, DSC, and SEM. Molecular dynamics simulations revealed that the stability and compactness of the AA/DMβCD complex were higher than those of the DMβCD alone. The encapsulation of AA led to increased intramolecular H-bond formations on the wider rim of DMβCD, enhancing the complex stability. The antiproliferative activity of AA against A549 and H1975 lung cancer cells was significantly improved by complexation with DMβCD. Altogether, the satisfactory water solubility, high thermal stability, and enhanced antitumor potential of the AA/DMβCD inclusion complex would be useful for its application as healthcare products or herbal medicines.

Computational Insights Into the Influence of Substitution Groups on the Inclusion Complexation of β-Cyclodextrin

Cyclodextrins (CDs) and their derivatives have good prospects in soil remediation application due to their ability to enhance the stability and solubility of low water-soluble compounds by inclusion performance. To investigate the effect of different structural properties of cyclodextrin and its derivatives on the inclusion complexation, molecular dynamic (MD) simulations were performed on the inclusion complexes formed by three kinds of CDs with polycyclic aromatic hydrocarbons (PAHs). Based on neutral β-CD, the other two CDs were modified by introducing substitutional groups, including 2-hydroxypropyl and sulfonated butyl (SBE) functional groups in the ring structure, called HP-CD and SBE-CD. MD results show that PAH can merely enter into the cavity of SBE–β-CD from its wide rim. The substitutional groups significantly affect the structure of CDs, which may also cause the flipping of the glucose units. However, the substitutional groups can also enlarge the volume of the hydrophobic cavity, resulting in a tight combination with the guest molecules.