Adjusting the Structure of ß-Cyclodextrin to Improve Complexation of Anthraquinone-Derived Drugs.

ß-Cyclodextrin (CD) derivatives containing an aromatic triazole ring were studied as potential carriers of the following drugs containing an anthraquinone moiety: anthraquinone-2-sulfonic acid (AQ2S); anthraquinone-2-carboxylic acid (AQ2CA); and a common anthracycline, daunorubicin (DNR). UV-Vis and voltammetry measurements were carried out to determine the solubilities and association constants of the complexes formed, and the results revealed the unique properties of the chosen CDs as effective pH-dependent drug complexing agents. The association constants of the drug complexes with the CDs containing a triazole and lipoic acid (ßCDLip) or galactosamine (ßCDGAL), were significantly larger than that of the native ßCD. The AQ2CA and AQ2S drugs were poorly soluble, and their solubilities increased as a result of complex formation with ßCDLip and ßCDGAL ligands. AQ2CA and AQ2S are negatively charged at pH 7.4. Therefore, they were less prone to form an inclusion complex with the hydrophobic CD cavity than at pH 3 (characteristic of gastric juices) when protonated. The ßCDTriazole and ßCDGAL ligands were found to form weaker inclusion complexes with the positively charged drug DNR at an acidic pH (pH 5.5) than in a neutral medium (pH 7.4) in which the drug dissociates to its neutral, uncharged form. This pH dependence is favorable for antitumor applications.

Impact of Medium pH on DOX Toxicity toward HeLa and A498 Cell Lines.

The influence of the pH of the multicomponent cell medium on the performance of doxorubicin (DOX), an anticancer drug, was studied on the examples of cervical (HeLa) and kidney (A498) cancer cell lines. The change of pH of the cell medium to more acidic led to a decrease of DOX toxicity on both cell lines due to the change of drug permeability across the cell membrane as a result of drug protonation. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) studies and lactate dehydrogenase (LDH) release tests have shown low toxicity of the drug, especially in the case of A498 cells, which are characterized by an extremely high glycolytic metabolism. The behavior was ascribed primarily to the increased proton concentration in the peripheral blood follicle in the presence of products of the acidic glycolytic metabolism. It is not observed in the measurements performed in commercially available media since they usually have a neutral pH. In earlier reports on kidney cancer, several mechanisms were discussed, including the metabolism of DOX to its less toxic derivative, doxorubicinol, overexpression of ATP binding cassette subfamily B member 1 (ABCB1) transporters, that remove DOX from the inside of cells; however, there was no focus on the simple but very important contribution of drug protonation described in the present study. Drug pH-dependent equilibria in the cell medium should be considered since changes in the drug form may be an additional reason for multidrug resistance.

Water-soluble galactosamine derivative of ß-cyclodextrin as protective ligand and targeted carrier for delivery of toxic anthracycline drug.

ß-cyclodextrin modified with an electron-rich aromatic triazole linker and targeting moiety (galactosamine) was synthesized and studied as a carrier for the anticancer drug, doxorubicin (DOX), with the aim of targeting the pathological cells, reducing the cardiotoxic side effects and increasing the binding of the drug to DNA. The ß-cyclodextrins modified with galactosamine (ßCDGAL) are non-toxic and highly soluble in aqueous medium compared to the native ßCD and ßCD modified only with aromatic moiety, such as triazole linker. Molecular modelling and NMR study gave a deeper insight into the ligand structure, providing an explanation for its increased solubility, and the drug-ligand interactions. The triazole linker strengthened the drug binding and introduced pH dependence of the complex stability constants for ßCDGAL derivative, as confirmed by the voltammetry measurements. Spectroscopic studies have shown that entrapment of the DOX in ßCDGAL cavity reduces the stability constant of the DOX:Fe(III) complex responsible for the production of cardiotoxic reactive oxygen species and additionally supports the binding of the drug to the double strand DNA. The MTT assay and confocal microscopy results showed that despite encapsulation of the drug in the cyclodextrin molecule, its cytotoxic effect on the liver cancer cell line (HepG2) is comparable to that of the free, non-protected drug.

Competition between self-inclusion and drug binding explains the pH dependence of the cyclodextrin drug carrier - molecular modelling and electrochemistry studies.

A non-toxic lipoic acid derivative of ß cyclodextrin (ßCDLip) with an electron-rich aromatic linker was studied as a carrier for the drug doxorubicin with the aim of decreasing the toxic side effects of this drug. The modified cyclodextrin strengthened the drug binding and differentiated the complex-forming ability with dependence on pH. The stability constants of the complexes were evaluated by voltammetry and spectrofluorometry. Molecular modelling provided deeper insight into the nature of the ligand structure itself and the drug-ligand interactions, showing the different contributions of the self-inclusion of the ligand substituent at different pH values. As a result, the modes of interaction of ßCDLip with the drug and factors affecting the stabilities of the complex under the pH conditions of healthy and tumour cells could be discovered and explained.

Cyclodextrin derivatives conjugated with aromatic moieties as pH-responsive drug carriers for anthracycline.

The modification of cyclodextrins (CDs) with side chains containing aromatic groups was found to lead to an increase of the stability of the complex with the anticancer drug doxorubicin (Dox). The formation constants evaluated by voltammetry were several orders of magnitude larger than that of the unmodified ß-CD ligand. For the CDs with aromatic moieties connected by linkers containing a triazole group, the formation constants of the complexes at pH 5.5 and 7.4 were very different. At lower pH, binding was much weaker as a result of protonation of the triazole moiety in the linker. The drug was then released from the complex. Molecular modeling of the Dox-ß-CD system revealed different possible interactions between Dox and ß-CD. The observed pH dependence of the complex formation constant can be exploited for drug delivery to the targeted cells. The toxicities of the synthesized complexes and each of the complex components were tested by the MTT assay on two cell lines, the human lung carcinoma and human cervical cancer cell lines.

Intermolecular interactions between doxorubicin and ß-cyclodextrin 4-methoxyphenol conjugates.

Newly synthesized derivatives of ß-cyclodextrin, mono(6-deoxy-6-(1-1,2,3-triazo-4-yl)-1-propane-3-O-(4-methoxyphenyl))ß-cyclodextrin (1) and mono(6-deoxy-6thio(1-propane-3-O-(4-methoxyphenyl))) ß-cyclodextrin (2) were designed to be receptors of the anticancer drug doxorubicin, which could potentially decrease the adverse effects of the drug during treatment. In both aqueous and aqueous dimethyl sulfoxide (DMSO) solutions, doxorubicin forms an inclusion complex with the new cyclodextrin derivatives with formation constants of K(s) = 2.3 × 10(4) and K(s) = 3.2 × 10(5) M(-1) for cyclodextrins 1 and 2, respectively. The stabilities of the complexes are 2-3 orders of magnitude greater than those with native ß-cyclodextrin, and the flexibility of the linker of the side group of the cyclodextrins contributes to this stability. In a hydrogen-bond-accepting solvent, such as pure DMSO, an association that includes hydrogen bonding and chloride ions is favored over the binding of doxorubicin in the cavity of the cyclodextrin derivative. This contrasts with an aqueous medium in which a strong inclusion complex is formed. Cyclic voltammetry, UV-vis, (1)H NMR, and molecular modeling studies of solutions in DMSO and of solutions in water/DMSO demonstrated that the two different modes of intermolecular interaction between doxorubicin and the cyclodextrin derivative depended on the solvent system being utilized.