Inclusion complexation of emodin with various β-cyclodextrin derivatives: Preparation, characterization, molecular docking, and anticancer activity

Encapsulation with β-cyclodextrin (βCD) has primarily been used to enhance the solubility of lipophilic guest molecules. Emodin (ED) stands out for its profound biological properties, especially anticancer activity. However, its usage in pharmaceutical applications has been hindered by its poor aqueous solubility. In the present work, we performed inclusion complexation of ED with βCD and its derivatives: hydroxypropyl-β-cyclodextrin (HPβCD), sulfobutylether-β-cyclodextrin with degree of substitution (DS) of 2 (SBE2βCD) and 6.0–7.1 (SBE7βCD) and 2,6-di-O-methyl-β-cyclodextrin (DMβCD), to identify the most promising drug carrier to enhance the water solubility and the anticancer activity of ED. The AL-type phase solubility diagram indicates 1:1 stoichiometry between ED and βCDs. The ED/DMβCD complex shows the highest stability (KC = 3800 M−1) and the highest water solubility (113.86 µg/mL) at 30 °C, followed by ED/SBE7βCD, ED/HPβCD, ED/SBE2βCD, and ED/βCD complexes. The SEM micrographs and DSC thermograms confirmed the inclusion complex formation between host and guest by attaining new surface morphological structures and thermal behaviors, respectively. Molecular docking suggests C-form insertion as the preferred binding mode of ED toward βCDs. Interestingly, the anti-proliferative effect on KKU-213A, KKU-213B, A549, and H1975 cancer cell lines of inclusion complexes, especially ED/DMβCD, ED/SBE7βCD, and ED/HPβCD, was significantly higher than that of ED alone.