Characterization of the inclusion mode of beta-cyclodextrin sulfate and its effect on the chlorpromazine-induced hemolysis of rabbit erythrocytes

Cyclodextrin complexation studies as the first step for repurposing of chlorpromazine

The antipsychotic drug chlorpromazine (CPZ) has potential for the treatment of acute myeloid leukemia, if central nervous system side-effects resulting from its passage through the blood-brain barrier can be prevented. A robust drug delivery system for repurposed CPZ would be drug-in-cyclodextrin-in-liposome that would redirect the drug away from the brain while avoiding premature release in the circulation. As a first step, CPZ complexation with cyclodextrin (CD) has been studied. The stoichiometry, binding constant, enthalpy, and entropy of complex formation between CPZ and a panel of CDs was investigated by isothermal titration calorimetry (ITC). All the tested CDs were able to include CPZ, in the form of 1:1, 1:2 or a mixture of 1:1 and 1:2 complexes. In particular, a substituted γ-CD, sugammadex (the octasodium salt of octakis(6-deoxy-6-S-(2-carboxyethyl)-6-thio)cyclomaltooctaose), formed exclusively 1:2 complexes with an extremely high association constant of 6.37 × 10⁹ M^-2. Complexes were further characterized by heat capacity changes, one- and two-dimensional (ROESY) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations. Finally, protection of CPZ against photodegradation by CDs was assessed. This was accelerated rather than reduced by complexation with CD. Altogether these results provide a molecular basis for the use of CD in delayed release formulations for CPZ.

Carbohydrate-Based Host-Guest Complexation of Hydrophobic Antibiotics for the Enhancement of Antibacterial Activity

Host-guest complexation with various hydrophobic drugs has been used to enhance the solubility, permeability, and stability of guest drugs. Physical changes in hydrophobic drugs by complexation have been related to corresponding increases in the bioavailability of these drugs. Carbohydrates, including various derivatives of cyclodextrins, cyclosophoraoses, and some linear oligosaccharides, are generally used as host complexation agents in drug delivery systems. Many antibiotics with low bioavailability have some limitations to their clinical use due to their intrinsically poor aqueous solubility. Bioavailability enhancement is therefore an important step to achieve the desired concentration of antibiotics in the treatment of bacterial infections. Antibiotics encapsulated in a complexation-based drug delivery system will display improved antibacterial activity making it possible to reduce dosages and overcome the serious global problem of antibiotic resistance. Here, we review the present research trends in carbohydrate-based host-guest complexation of various hydrophobic antibiotics as an efficient delivery system to improve solubility, permeability, stability, and controlled release.

Design and evaluation of cyclodextrin-based drug formulation

The pharmaceutically useful cyclodextrins (CyDs) are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in design and evaluation of CyD-based drug formulation, focusing on their ability to enhance the drug absorption across biological barriers, the ability to control the rate and time profiles of drug release, and the ability to deliver a drug to a targeted site.

[Pharmaceutical application of cyclodextrins as multi-functional drug carriers]

Owing to the increasingly globalized nature of the cyclodextrin (CyD)-related science and technology, development of the CyD-based pharmaceutical formulation is rapidly progressing. The pharmaceutically useful CyDs are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in drug delivery and pharmaceutical formulation, focusing on the following evidences. 1) The hydrophilic CyDs enhance the rate and extent of bioavailability of poorly water-soluble drugs. 2) The amorphous CyDs such as 2-hydroxypropyl-beta-CyD are useful for inhibition of polymorphic transition and crystallization rates of drugs during storage. 3) The delayed release formulation can be obtained by the use of enteric type CyDs such as O-carboxymethyl-O-ethyl-beta-CyD. 4) The hydrophobic CyDs are useful for modification of the release site and/or time profile of water-soluble drugs with prolonged therapeutic effects. 5) The branched CyDs are particularly effective in inhibiting the adsorption to hydrophobic surface of containers and aggregation of polypeptide and protein drugs. 6) The combined use of different CyDs and/or pharmaceutical additives can serve as more functional drug carriers, improving efficacy and reducing side effects. 7) The CyD/drug conjugates may provide a versatile means for the constructions of not only colonic delivery system but also site-specific drug release system, including gene delivery. On the basis of the above-mentioned knowledge, the advantages and limitations of CyDs in the design of advanced dosage forms will be discussed.

Effect of cyclodextrin charge on complexation of neutral and charged substrates: comparison of (SBE)7M-beta-CD to HP-beta-CD

PURPOSE

To understand the role of charge in substrate/cyclodextrin complexation by comparing the binding of neutral and charged substrates to a neutral cyclodextrin, such as hydroxypropyl beta-CD (HP-beta-CD) with 3.5 degrees of substitution, and an anionically charged cyclodextrin, such as sulfobutyl ether beta-CD ((SBE)7M-beta-CD) with 6.8 degrees of substitution.

METHOD

HP-beta-CD and (SBE)7M-beta-CD were evaluated in their ability to form inclusion complexes with neutral compounds, as well as to cationic and anionic substrates in their charged and uncharged forms. The complexation constants (Kc) were determined via a UV spectrophotometric technique, by monitoring the change in substrate absorbance upon incremental addition of a concentrated cyclodextrin solution. The role of electrostatic interaction was probed by observing Kc as a function of solution ionic strength.

RESULTS

Neutral molecules displayed a stronger interaction with (SBE)7M-beta-CD compared to HP-beta-CD. In those cases where the guest possessed a charge (positive or negative), HP-beta-CD/substrate complexes exhibited a decrease in complexation strength (2 to 31 times lower) compared to the neutral forms of the same substrate. The same was true (but to a larger extent, 41 times lower) for negatively charged molecules binding to (SBE)7M-beta-CD due to charge-charge repulsion. However, positively charged molecules interacting with the negatively charged (SBE)7M-beta-CD displayed a similar binding capability as their neutral counterpart, due to charge-charge attraction. Further evaluation through manipulation of solution ionic strength revealed strong electrostatic interactions between substrate and cyclodextrin charges. In addition, the studies suggested that on average two sulfonates out of seven may be involved in forming ionic attraction or repulsion effects with the positive charges on prazosin and papaverine, or negative charges of ionized naproxen and warfarin.

CONCLUSIONS

Presence of charge on the cyclodextrin structure provides an additional site of interaction compared to neutral cyclodextrins, which may be modified using solution ionic strength.

Effect of the complexation with cyclodextrins on the in vitro antiviral activity of ganciclovir against human cytomegalovirus

The toxicity of the molecules currently used in the treatment of human cytomegalovirus (HCMV) in immunocompromised hosts often causes interruption of the therapy. Cyclodextrins (Cds), oligosaccharides possessing a hydrophobic cavity, have the property of forming inclusion complexes with a great number of molecules, improving their bioavailability and their biological properties. In this study, we have tested the ability of three native Cds to improve the antiviral effect of ganciclovir (GCV) on two HCMV strains: AD169, a reference susceptible strain, and RC11, a GCV resistant strain. The efficacy of the GCV, expressed in IC50 values, showed no improvement in the presence of alpha-Cd, while the use of beta- and gamma-Cd improved by 6- and 4-fold, respectively, its antiviral activity tested on AD169 strain. The influence of beta- or gamma-Cd on GCV efficiency evaluated on RC11 strain showed a decrease of the IC50. Parallel NMR studies were undertaken in order to characterize formation of [GCV:Cd] complexes. The results showed that complexation between alpha- or gamma-Cd and GCV did not occur. In contrast, spectra proved that beta-Cd formed an inclusion complex with GCV. This complex was characterized in UV-Visible spectrophotometry and the influence of the beta-Cd on the GCV penetration in cells was measured. The use of Cds as carriers of antiviral drugs would be a good alternative to traditional treatment, because it may allow the administration of lower doses and so continuous treatment by reducing the toxic effects of drugs.

Thermodynamics of binding of neutral molecules to sulfobutyl ether beta-cyclodextrins (SBE-beta-CDs): the effect of total degree of substitution

PURPOSE

To understand the role of degree of substitution on binding of molecules to beta-Cyclodextrins (beta-CDs) with varying degrees of sulfobutyl ether (SBE) substitution.

METHODS

Using UV spectroscopy, complexation constants of molecules to SBE-beta-CDs were estimated as a function of temperature, allowing for calculation of thermodynamic parameters, including the enthalpy and entropy of binding.

RESULTS

Binding constants of various molecules to SBE-beta-CDs did not show a uniform trend to total degree of SBE substitution. However, a distinct pattern was observed with the enthalpy and entropy of complexation. The results showed the complexation of substrates to SBE-beta-CDs to be more entropy-favored as the number of SBE groups increased. This favorable entropy of interaction was compensated by a less favorable enthalpy of interaction.

CONCLUSIONS

Enthalpy and entropy of complexation provided additional insight into the role that the alkylsulfonate groups may play in the complexation of molecules with SBE-beta-CDs.

Comparative effects of (SBE)7m-beta-CD and HP-beta-CD on the stability of two anti-neoplastic agents, melphalan and carmustine

The purpose of this study was to evaluate and compare the potential use of two parenterally safe beta-cyclodextrins derivatives, (SBE)7m-beta-CD and HP-beta-CD, as solubilizers and stabilizers for melphalan and carmustine, two very unstable antineoplastic agents. Phase solubility and chemical stability of the compounds in the presence of the cyclodextrins were studied. UV, fluorescence, and several NMR techniques were used to probe the potential causes for the differences observed. The phase solubility method was found to provide only qualitative data on the binding of melphalan to the cyclodextrins since rapid degradation and the presence of products of degradation complicated the interpretation of the results. Qualitatively, however, the solubilizing potential was similar for the two cyclodextrins. The chemical stability studies indicate that both of the drugs had similar binding constants for both cyclodextrins; however, the intrinsic reactivities in the complexes were significantly lower with (SBE)7m-beta-CD than for HP-beta-CD. The main cause for this distinct difference appeared to correlate with differences in the site of binding and the polarity of the binding site.

Solubility and mass and nuclear magnetic resonance spectroscopic studies on interaction of cyclosporin A with dimethyl-alpha- and -beta-cyclodextrins in aqueous solution

The interaction of cyclosporin A (CsA) with dimethyl-alpha- and -beta-cyclodextrins (DM-alpha-CyD and DM-beta-CyD) was investigated by the solubility method, electrospray ionization mass spectrometry (ESI-MS) and 1H-nuclear magnetic resonance spectroscopy (1H NMR). The extremely low solubility (1.9 x 10(-5) M at 25 degreesC) of CsA in water was significantly improved by the complexation with DM-CyDs: for example, the solubility increased 87-fold in the presence of 5.0 x 10(-2) M DM-beta-CyD. The phase solubility diagram of CsA/DM-CyD systems showed an Ap type and the stability constants (1060 M-1 and 1050 M-1, respectively) of the 1:1 CsA/DM-alpha-CyD and CsA/DM-beta-CyD complexes were much higher than those of the 1:2 complexes (15 M-1 and 21 M-1, respectively). In ESI-MS spectra of the CsA/DM-beta-CyD system, a new signal emerged at 1268 which corresponds to the 1:1 adduct of the di-ionized guest molecule with the host molecule. This signal intensity was significantly decreased by the addition of chlorpromazine (CPZ) which has a large stability constant (8800 M-1) of the DM-beta-CyD complex, whereas the signal corresponding to the CPZ/DM-beta-CyD complex was little affected by the addition of CsA, indicating a competitive inclusion of CPZ and CsA within the host cavity. CsA gave many new peaks in the 1H NMR spectrum when the solvent was changed from chloroform to methanol/water, suggesting conformational diversity of CsA in polar solvents. Inspection of 1H-chemical shift changes and the two-dimensional rotating frame nuclear Overhauser effect (ROESY) spectra of the CsA/DM-CyD system suggested that the side chains of amino acids in CsA molecule take part in the inclusion within DM-CyDs, although there is seemingly no preference of particular amino acid residues. All the data obtained here suggested that CsA forms inclusion complexes with DM-alpha- and -beta-CyDs in an aqueous medium and side chains of CsA are mainly involved in the inclusion.

Isolation and characterization of beta-cyclodextrin sulfates by preparative gradient polyacrylamide gel electrophoresis, capillary electrophoresis and electrospray ionization - mass spectrometry

A beta-cyclodextrin sulfate mixture has been fractionated using discontinuous gradient polyacrylamide gel electrophoresis. Semidry electrotransfer of the sample onto a positively charged nylon membrane and visualization of a portion of this membrane with Alcian blue stain showed multiple bands. The bands were cut from the remaining portion of the membrane and after washing with 8 M urea, the beta-cyclodextrin sulfate fractions were eluted with 2 M sodium chloride and dialyzed. Analysis of each fraction using high resolution analytical gradient polyacrylamide gel electrophoresis as well as capillary electrophoresis, using indirect detection, showed some of the fractions to be pure while others were mixtures. Each beta-cyclodextrin sulfate fraction was complexed with a basic synthetic peptide and analyzed by electrospray ionization mass spectrometry to define the mass of the components in each mixture and thereby to determine the purity of each sample.

Effect of alkyl chain length and degree of substitution on the complexation of sulfoalkyl ether beta-cyclodextrins with steroids

This study was designed to test how the sulfoalkyl ether (SAE) modification of beta-cyclodextrin (beta-CD) affects the binding capacity of testosterone and progesterone, thereby enhancing their solubility. The SAE-beta-CD derivatives contain either sulfopropyl ether (SPE) or sulfobutyl ether (SBE) groups on the 2-, 3-, and 6-hydroxyl positions of the dextrose moieties. SAE-beta-CDs are a mixture of positional and regional isomers containing from one to as many as 12 SAE groups per CD. The effect of chain length and the degree of substitution on complexation behavior was investigated by the phase-solubility method. The results were compared with those obtained with beta-CD, where possible, and with hydroxypropyl-beta-CD (HP-beta-CD). To determine the effect of degree of substitution (DS) on the binding, mixtures of SAE-beta-CDs with multiple substitution levels and varying average degrees of substitution were studied as well as mixtures of SAE-beta-CDs that contained the same degree of substitution. Mixtures that contained SAE-beta-CDs of the same degree of substitution were isolated from the multiple substitution level mixtures by ion-exchange chromatography and purified for investigation. Unlike the parent beta-CD, linear increases in the apparent solubilities of testosterone and progesterone were observed, and the binding potentials were comparable to those of beta-CD or better. The results demonstrate that the binding potentials of the SAE-beta-CD derivatives were dependent on the guest molecule, the degree of substitution, and the alkyl ether chain length. Our previous study showed the inhibition of complexation by direct sulfonation of the beta-CD. However, in the present work, interferences with the charged sulfonate groups were avoided by repositioning them away from the cavity. Increasing the degree of substitution assisted in complex formation; however, its effects were limited. Reduction of the alkyl chain length, as in the case of SPE-beta-CD compared with SBE-beta-CD, decreased the complexation potential. This decrease in complexation potential was further suppressed with an increase in the number of substituents placed on the CD torus. Generally, the binding potential of SAE-beta-CD derivatives increased with increasing alkyl chain length. However, placement of more than an optimum number of SAE groups on the CD torus resulted in inhibition of complexation.