Sulfadiazine/hydroxypropyl-β-cyclodextrin host–guest system: Characterization, phase-solubility and molecular modeling

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.

Cyclodextrin Derivative Enhances the Ophthalmic Delivery of Poorly Soluble Azithromycin

Azithromycin (AZM), a macrolide antibiotic used for the treatment of chlamydial conjunctivitis, is less effective for the treatment of this disease due to its poor bioavailability (38%). Various alternatives have been developed for improving the physicochemical properties (i.e., solubility) of the AZM without much success. To overcome the problems associated with AZM, an inclusion complex employing a modified cyclodextrin, i.e., sulfobutylether-β-cyclodextrin (SBE-β-CD), was prepared and characterized by phase solubility studies and PXRD techniques. The results portrayed the formation of an inclusion complex of AZM with SBE-β-CD in 1:2 molar stoichiometric ratios. This inclusion complex was later incorporated into a polymer matrix to prepare an in situ gel. Various combinations of Carbopol 934P and hydroxypropyl methylcellulose (HPMC K4M) polymers were used and evaluated by rheological and in vitro drug release studies. The optimized formulation (F4) containing Carbopol 934P (0.2% w/v) and HPMC K4M (0.2% w/v) was evaluated for clarity, pH, gelling capacity, drug content, rheological properties, in vitro drug release pattern, ocular irritation test, and antimicrobial efficacy. Finally, owing to the improved antimicrobial efficacy and increased residence time, the AZM:SBE-β-CD in situ gel was found to be a promising formulation for the efficient treatment of bacterial ocular disease.

Improving the solubility of vorinostat using cyclodextrin inclusion complexes: The physicochemical characteristics, corneal permeability and ocular pharmacokinetics of the drug after topical application

Vorinostat (suberoylanilide hydroxamic acid, SAHA), an FDA-approved drug for cutaneous T cell lymphoma, has antiangiogenic and anti-inflammatory activity and thus has therapeutic potential for inflammatory corneal neovascularization (CNV). However, its practical administration is limited due to its poor aqueous solubility and permeability. This study aimed to enhance the corneal permeability of SAHA by promoting its inclusion into a complex with hydroxypropyl-β-CD (HPβCD) for topical application. In phase-solubility studies, the solubility of SAHA with HPβCD and sulfobutyl ether-β-CD (SEβCD) was assessed at different temperatures, and complexation efficiencies (K) were calculated. The inclusion complexes (ICs) were prepared and characterized by differential scanning calorimetry (DSC), infrared spectrometry (IR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) after freeze-drying. The phase-solubility study showed that the complexation efficiencies of SAHA were higher in HPβCD solutions (297.35 M^-1, 115.28 M^-1 and 122.75 M^-1) than in SEβCD solutions (169.75 M^-1, 91.33 M^-1 and 96.49 M^-1) at 4 °C, 25 °C and 37 °C. HPβCD was selected for SAHA-IC preparation, and characterization revealed IC formation. SAHA existed in an amorphous state in the ICs. The ex vivo corneal permeability of SAHA was also evaluated and found to be greater when formulated as an HPβCD solution than as a suspension. Irritation assays in rabbit eyes showed that the SAHA-IC solution was not irritating after topical application. The ocular pharmacokinetics of SAHA in New Zealand White rabbits were assessed following topical administration (0.2%), and a 0.2% SAHA suspension was used as the control. Compared to its formulation as a suspension, the formulation of SAHA as an HPβCD solution increased its corneal bioavailability by more than 3-fold and its conjunctival bioavailability by more than 2-fold. Thus, IC formation was effective at improving the ocular bioavailability of SAHA. This study provides an important alternative approach for developing liquid pharmaceutical formulations of SAHA for topical ocular applications.

Boosting the mechanical strength and solubility-enhancement properties of hydroxypropyl-β-cyclodextrin nanofibrous films

2-hydroxypropyl-β-cyclodextrin (HPβCD) nanofiber films have high surface-to-volume ratio and show high dissolution rate of hydrophobic drugs. However, the solubility-enhancement effect of HPβCD films may not be enough to include an effective dose in a sublingually administrable film. Moreover, unmodified HPβCD films are very brittle and difficultly transported and/or handled. So, the addition of polyethylene glycol (PEG) as a plasticizer was suggested to improve their ultimate tensile strength (UTS) and solubilization of hydrophobic drugs. Accordingly, six nanofiber films were developed and characterized, using three molecular weights of PEG (400, 1500 and 6000 Da) with two concentrations each (1:100 and 2:100 PEG:HPβCD), in addition to the unmodified HPβCD nanofibrous film. The results revealed that adding 1:100 of PEG 400 increases the UTS (∼2-fold) and the average fiber diameter (AFD) (∼3-fold). Moreover, the addition of PEG 400 significantly increased the solubility of two hydrophobic model drugs; coumarin (up to 7.7-fold of the original solubility) and 2-nitroimidazole (up to 1.6-fold of the original solubility). However, with higher PEG concentration/molecular weight, both AFD and UTS of the films decreased. On the other hand, it was noted that the solubility of the two model drugs decreased upon using 1500-Da PEG, and then increased with 6000-Da PEG.

Supramolecular polyelectrolyte complexes based on cyclodextrin-grafted chitosan and carrageenan for controlled drug release

In the present study, supramolecular polyelectrolyte complexes (SPEC) based on a cyclodextrin-grafted chitosan derivative and carrageenan were prepared and evaluated for controlled drug release. Samples were characterized by FTIR, SEM, and ζ-potential measurements, which confirmed the formation of the polymeric complex. The phenolphthalein test confirmed the presence and availability of inclusion sites from the attached βCD. Silver sulfadiazine was used as the model drug and the association with the SPEC was studied by FTIR and computational molecular modeling, using a semi-empirical method. DRS and TEM analyses have shown that Ag⁺ ions from the drug were reduced to form metallic silver nanostructures. In vitro tests have shown a clear bacterial activity toward Gram-positive bacteria Staphylococcus aureus and Enterococcus durans/hirae and Gram-negative bacteria Klebsiella pneumoniae and Escherichia coli. Finally, this work shows that βCD-chitosan/carrageenan supramolecular polyelectrolyte complexes hold an expressive potential to be applied as a polymer-based system for controlled drug release.

Nasal powders of thalidomide for local treatment of nose bleeding in persons affected by hereditary hemorrhagic telangiectasia

In this work nasal powder formulations of thalidomide were designed and studied to be used by persons affected by hereditary hemorrhagic telangiectasia as a complementary anti-epistaxis therapy, with the goal of sustaining the effect obtained with thalidomide oral treatment after its discontinuation for adverse effects. Three nasal powders were prepared using as carriers β-CD or its more hydrophilic derivatives such as hydropropyl-β-CD and sulphobutylether-β-CD and tested with respect to technological and biopharmaceutical features after emission with active and passive nasal powder devices. For all formulated powders, improved dissolution rate was found compared to that of the raw material, making thalidomide promptly available in the nasal environment at a concentration favouring an accumulation in the mucosa. The very limited transmucosal transport measured in vitro suggests a low likelihood of significant systemic absorption. The topical action on bleeding could benefit from the poor absorption and from the fact that about 2-3% of the thalidomide applied on the nasal mucosa was accumulated within the tissue, particularly with the β-CD nasal powder.

Enhanced oral bioavailability and anticancer efficacy of fisetin by encapsulating as inclusion complex with HPβCD in polymeric nanoparticles

Fisetin (FST), a potent anticancer phytoconstituent, exhibits poor aqueous solubility and hence poor bioavailability. The aim of the present study is to improve the oral bioavailability of FST by encapsulating into PLGA NPs (poly-lactide-co-glycolic acid nanoparticles) as a complex of HPβCD (hydroxyl propyl beta cyclodextrin) and to assess its anti-cancer activity against breast cancer cells. FST-HPβCD inclusion complex (FHIC) was prepared and the supramolecular complex formation was characterized by FTIR, DSC, PXRD and ¹H NMR. FHIC encapsulated PLGA nanoparticles (FHIC-PNP) were prepared and were studied for in vitro anticancer activity, cellular uptake, apoptosis and reactive oxygen species generation in MCF-7 human breast cancer cells. Comparative bioavailability of FST was determined after oral administration in C57BL6 mice as pure FST and FHIC-PNP. The results revealed that FHIC-PNP not only enhanced the anti-cancer activity and apoptosis of FST against MCF-7 cells but also improved its oral bioavailability, as demonstrated by increased peak plasma concentration and total drug absorbed.

Host–Guest Inclusion System of Luteolin with Polyamine-β-cyclodextrin: Preparation, Characterisation, Anti-oxidant and Anti-cancer Activity

The characterisation, inclusion complexation behaviours, and binding ability of inclusion complexes of luteolin (LU) with four polyamine-modified β-cyclodextrins (NH2-βCD, EN-βCD, DETA-βCD, TETA-βCD; where EN = ethylenediamine; DETA = diethylenediamine; TETA = triethylenetetramine) were investigated in both the solid and solution forms by photoluminescence spectroscopy, 1H and 2D NMR spectroscopy, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The results showed that the water solubility, and the anti-oxidant activity and anti-cancer activity of LU were significantly increased in the inclusion complex with polyamine-β-cyclodextrin. The LU/CDs complex will be useful for its application as herbal medicine or healthcare product.

Host–Guest Inclusion System of Scutellarin with Polyamine-β-Cyclodextrin: Preparation, Characterisation, and Anti-cancer Activity

The inclusion complexation behaviours of scutellarin (SCU) with four polyamine-modified β-cyclodextrins (NH2-βCD, EN-βCD, DETA-βCD, and TETA-βCD; EN = ethylenediamine; DETA = diethylenetriamine; TETA = triethylenetetramine) have been investigated in both solution and solid state by photoluminescence spectroscopy, 1H and two-dimensional NMR spectroscopy, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. The results showed that, with the increase in the number of amino groups, the hosts polyamine-modified β-cyclodextrins (NH2-βCD, EN-βCD, DETA-βCD, TETA-βCD) were able to solubilise SCU to higher levels than native β-CD (9.0 mg mL–1) up to 15.8, 20.4, 44.6, 50.7 mg mL–1 (calculated as SCU), respectively. Besides, the anti-tumour activity of SCU obviously increased after formation of the inclusion complexes. The SCU/CD complexes will be potentially useful for the design of a novel formulation of SCU for clinical treatment.

Synthesis, characterization, and in vitro evaluation of artesunate-β-cyclodextrin conjugates as novel anti-cancer prodrugs

A novel series of artesunate-β-cyclodextrin (ATS-β-CD) conjugates, in which artesunate (ATS) was coupled covalently to one of the primary hydroxyl groups of β-cyclodextrin (β-CD) through amino bond formation, were synthesized and characterized by (1)H NMR, HRMS, 2D NMR (ROESY), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results showed that the aqueous solubility of ATS-β-CD conjugates was 26-45 times better than that of free ATS. The cytotoxicity of the ATS-β-CD conjugates was evaluated on human colon cancer cell lines HCT116, LOVO, SW480, and HT-29, and the results indicated that ATS-2NβCD exhibited a very high cytotoxicity against HCT116, LOVO, and HT-29 with IC50 values of 0.58, 1.62, and 5.18μmol/L, respectively. In addition, the supposition of better cytotoxicity was further supported by the control experiment of fluorescent cyclodextrin.

Effects of β-cyclodextrin on the intestinal absorption of berberine hydrochloride, a P-glycoprotein substrate

The major objective of this work is to investigate the enhancing effect of β-cyclodextrin on the intestinal absorption of berberine hydrochloride, a P-glycoprotein (Pgp) substrate. The inclusion complexation behavior of BBH with β-CD was investigated by phase-solubility diagram, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray powder diffractometry, NMR spectroscopy, and molecular modeling studies. Results indicated that the 1,3-benzodioxole of BBH was included into the cavity of β-CD to form an inclusion complex which exhibited higher dissolution rate than BBH in vitro. The intestinal absorption of the inclusion complex in rats was significantly higher than the free drug due to its solubilizing effect and Pgp modulatory activity. The mechanisms of β-CD on Pgp modulation were demonstrated by modifying the Pgp ATPase activity, the Pgp mRNA level and the Pgp expression.

Lima M, Pitta MGR, Hernandes MZ, Santos-Magalhães NS. Enhanced antiproliferative activity of the new anticancer candidate LPSF/AC04 in cyclodextrin inclusion complexes encapsulated into liposomes

LPSF/AC04 (5Z)-[5-acridin-9-ylmethylene-3-(4-methyl-benzyl)-thiazolidine-2,4-dione] is an acridine-based derivative, part of a series of new anticancer agents synthesized for the purpose of developing more effective and less toxic anticancer drugs. However, the use of LPSF/AC04 is limited due to its low solubility in aqueous solutions. To overcome this problem, we investigated the interaction of LPSF/AC04 with hydroxypropyl-β-cyclodextrin (HP-β-CyD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CyD) in inclusion complexes and determine which of the complexes formed presents the most significant interactions. In this paper, we report the physical characterization of the LPSF/AC04-HP-CyD inclusion complexes by thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy absorption, Raman spectroscopy, (1)HNMR, scanning electron microscopy, and by molecular modeling approaches. In addition, we verified that HP-β-CyD complexation enhances the aqueous solubility of LPSF/AC04, and a significant increase in the antiproliferative activity of LPSF/AC04 against cell lines can be achieved by the encapsulation into liposomes. These findings showed that the nanoencapsulation of LPSF/AC04 and LPSF/AC04-HP-CyD inclusion complexes in liposomes leads to improved drug penetration into the cells and, as a result, an enhancement of cytotoxic activity. Further in vivo studies comparing free and encapsulated LPSF/AC04 will be undertaken to support this investigation.

Changes in the intestinal absorption mechanism of icariin in the nanocavities of cyclodextrins

Icariin is a bioactive herbal ingredient isolated from Herba epimedii, which has been widely used for the treatment of osteoporosis and male sexual dysfunction in traditional Chinese medicine. The major objective of this work is to investigate the different enhancing effects of β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) on the intestinal absorption of icariin, and to identify the molecular mechanisms of this action. Host-guest-type interactions of icariin with cyclodextrins nanocavities were unambiguously demonstrated by the phase-solubility diagram, ultraviolet spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray powder diffractometry, and two dimensional proton nuclear magnetic resonance rotating-frame Overhauser effect spectroscopy. These results were further supported using molecular modeling studies. The rat single-pass intestinal perfusion model showed that the absorption of icariin was affected by P-glycoprotein (Pgp). The icariin/HP-β-CD inclusion complex provided greater enhancement in the intestinal absorption than the icariin/β-CD inclusion complex. Therefore, the enhancing effect was involved in a solubilizing effect and/or Pgp inhibitory effect. Finally, fluorescence anisotropy measurements and Pgp adenosine triphosphatase (ATPase) assay demonstrated that β-CD exhibited no effect on Pgp, while HP-β-CD showed inhibition by restraining the Pgp ATPase activity rather than changing the fluidity of cell membrane.

Enhancing effect of hydroxypropyl-β-cyclodextrin on the intestinal absorption process of genipin

The purpose of this work is to investigate the effect of the genipin/hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex on the intestinal absorption of genipin and identify its mechanism of action. The phase solubility profile was classified as A(L) type, indicating the formulation of a 1:1 stoichiometry inclusion complex. Fourier transform infrared spectroscopy, Differential scanning calorimetry, X-ray powder diffractometry, and (1)H nuclear magnetic resonance (NMR) and two-dimensional (2D) (1)H rotating-frame Overhauser enhancement (ROESY) NMR spectroscopies further confirmed the formulation of the inclusion complex with superior dissolution properties than the drug alone. The results of single-pass intestinal perfusion showed that the intestinal absorption of genipin was affected by P-glycoprotein (Pgp). The absorption rate and permeability value of the inclusion complex were significantly higher than the free drug, suggesting that its enhancing effect was involved in its solubilizing effect and Pgp inhibitory effect. The mechanisms of HP-β-CD on Pgp inhibition were demonstrated by restraining the Pgp ATPase activity rather than changing the fluidity of the cell membrane.

Structural and theoretical-experimental physicochemical study of trimethoprim/randomly methylated-β-cyclodextrin binary system

Here we report the structural characterization, physicochemical study and molecular modeling of the inclusion complex of trimethoprim in randomly methylated beta-cyclodextrin. The phase-solubility diagram obtained at pH 7.0 exhibited a linear behavior for the RAMEB concentrations studied suggesting a 1:1 stoichiometry and absence of aggregation in solution. From stoichiometric determination by the continuous variation method we confirmed a 1:1 stoichiometry. To make a detailed characterization of the inclusion mode, spectroscopic measurements by infrared and 1D and 2D (1)H NMR spectroscopy provided evidence that the inclusion mode is characterized by inclusion of the trimethoxyphenyl ring in the cavity; interactions with methyl groups located in the border of the cavity were also detected. The structure proposed was also confirmed by semiempirical molecular modeling.

Complexation of sulfonamides with beta-cyclodextrin studied by experimental and theoretical methods

The complex formation between three structurally related sulfonamides (sulfadiazine (SDZ), sulfamerazine (SMR), and sulfamethazine (SMT)) and beta-cyclodextrin (beta-CD) was studied, by exploring its structure affinity relationship. In all the cases, 1:1 stoichiometries were determined with different relative affinities found by phase solubility (SDZ:beta-CD > SMR:beta-CD > SMT:beta-CD) and nuclear magnetic resonance (NMR) (SMT:beta-CD > SMR:beta-CD > SDZ:beta-CD) studies. The spatial configurations determined by NMR were in agreement with those obtained by molecular modeling, showing that SDZ included its aniline ring into beta-CD, while SMR and SMT included the substituted pyrimidine ring. Energetic analyses demonstrated that hydrophobicity is the main driving force to complex formation.