In silico and in vitro studies on inclusion complexation of anthraquinone derivatives with beta-cyclodextrin derivatives

Abstract

In this study, we investigated the cytotoxicity of 6 anthraquinones (ventilanone K, emodin, chrysophanol, aurantio-obtusin, 1-O-methyl-2-methyoxychrysophanol, and questin) toward A549 lung cancer cells and emodin (ED) exerted the most potent cytotoxicity with IC50 value of 34.27 ± 1.27 µM. The anti-cancer activity of ED has been well reported but its usage in practical applications has been restricted due to its poor solubility. To address this issue, we performed inclusion complexation of ED with βCD, hydroxypropyl-β-cyclodextrin (HPβCD), 2,6-di-O-methyl-β-cyclodextrin (DMβCD), and sulfobutylether-β-cyclodextrin (SBEβCD) theoretically using molecular dynamics simulations and experimentally using phase solubility study and cytotoxicity screening toward cholangiocarcinoma cell lines (KKU-213A and KKU-213B). The 500-ns MD simulations revealed that ED is able to form inclusion complexes with βCDs in two possible orientations: resorcinol ring insertion (R-form) and m-cresol ring insertion (C-form) mainly driven by van der Waals interaction. The ED in complex with SBEβCD (degree of substitution, DS-7) inclusion complex showed the highest number of atom contacts and the lowest solvent accessibility, in line with the ΔGbind results ranked in the order of ED/SBEβCD (-6.18 ± 1.15 kcal/mol) > ED/HPβCD (-3.81 ± 0.65 kcal/mol) > ED/βCD (0.11 ± 0.51 kcal/mol). Consequently, the inclusion complexes between ED and βCDs (βCD, HPβCD, SBEβCD and DMβCD), were experimentally studied. The phase solubility testing provides AL-type diagrams indicating the 1:1 stoichiometry between ED and βCDs. Altogether, the stability constants of studied complexes can be ranked in the order of ED/DMβCD (1500 M-1) > ED/HPβCD (1000 M-1) > ED/βCD (980 M-1) > SBEβCD with low degree of substitution (880 M-1) at 25оC and the highest water solubility was observed in ED/DMβCD complex with 113.86 ug/mL. Moreover, ED/DMβCD complex shows the most promising inhibition with the IC50 values of 52.78 ± 1.57 and 47.00± 0.58 µM toward KKU-213A and KKU-213B, respectively.