Cyclodextrin Derivatives Conjugated with Aromatic Moieties as pH- responsive Drug Carriers for Anthracycline Olga Swiech, † Paula Dutkiewicz, † Karolina Wó jciuk, ‡ Kazimierz Chmurski, † Marcin Kruszewski, ‡,§ and Renata Bilewicz* ,† † Faculty of Chemistry, University of Warsaw, Pasteura 1, Warsaw, Poland ‡ Institute of Nuclear Chemistry and Technology, Dorodna 16, Warsaw, Poland § Institute of Rural Health, Jaczewskiego 2, Lublin, Poland ABSTRACT: 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 β-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-β-CD system revealed different possible interactions between Dox and β-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. ■ INTRODUCTION Anthracycline drugs have been used for nearly 40 years for the treatment of several malignancies, and hundreds of analogues of the first anthracycline antibiotics, doxorubicin (Dox) and daunorubicin, have been synthesized and evaluated. Clinical treatment with anthracycline chemotherapeutics is limited by severe adverse effects such as cardiotoxicity and myelosup- pression. 1-3 In this context, tumor drug targeting has proven to be a new, promising strategy to increase the local drug concentration and reduce unwanted side effects. The specific toxicity of anthracycline drugs is due to the reactive forms of oxygen, namely, superoxide anion radical, hydrogen peroxide, and very reactive hydroxyl radical, that are produced in the redox reactions of anthracyclines, such as the Fenton reaction, where antracyclines create complexes with free iron cations through the anthraquinone group. 4-6 This specific toxicity can be reduced by creating a complex between the anthracycline molecule and a cyclodextrin (CD). In addition, Dox is not stable in aqueous solution because of its photosensitivity. 7,8 However, the stability of Dox can be enhanced by complexing with CDs. The formation of complexes between Dox and both β- and γ-CDs has been confirmed by a variety of methods, including fluorescence, absorbance, circular dichroism, and NMR spectroscopy. 9 In the complex, the anthraquinone group of the drug is located inside the CD cavity, resulting in a significantly lower rate of degradation. 10 The limitation in the use of CD as a carrier of anthracycline drugs is the low stability constant of the complex compared with that of the drug-DNA complex. 11 Conjugation of CDs with appropriate moieties is proposed as a strategy toward complex-controlled target drug carriers. 12-14 Recently, we showed that the modification of CDs with appropriate aromatic groups can significantly increase their drug-inclusion ability. The stability constants of Dox complexes with CD derivatives that have a single pendant 4- methoxyphenyl-terminated arm are 2-3 orders of magnitude larger than those of the complex with native β-CD. Moreover, complex formation depends on the solvent. The formation of the inclusion complex takes place in the presence of water, whereas in aprotic solvents, the complex is not formed because Dox cannot compete with the side chain of CD for the place in the cavity. 15 Studies of the tumor cells show that the pH of the interstitial fluid surrounding the tumor is lower than the pH of normal Received: June 19, 2013 Revised: August 29, 2013 Published: September 30, 2013 Article pubs.acs.org/JPCB © 2013 American Chemical Society 13444 dx.doi.org/10.1021/jp4060632 | J. Phys. Chem. B 2013, 117, 13444-13450