Crystal structures, DNA interaction of natural anthraquinone compounds and dual apoptotic mechanisms in oral cancer CAL-27 cells.

Natural anthraquinone compounds have demonstrated significant potential as anticancer agents due to their diverse biological activities. Herein, we determined the crystal structures of a series of natural anthraquinone compounds (chrysophanol, emodin, aloe emodin, and rhein) for the first time, and observed that these compounds form one-dimensional supramolecular chain structures and two-dimensional supramolecular structures through C-H…O, C-H…O or C-H…S hydrogen bonding interactions. Besides, we evaluated the anti-proliferative activity of these natural anthraquinone compounds on oral cancer CLA-27 cells. Among them, rhein exhibited significant anti-proliferative activity, superior to carboplatin, with an IC₅₀ value of 72.4 ± 3.7 μM against CAL-27 cells. The strong intercalation effect of rhein with DNA was verified by EB-DNA fluorescence spectroscopy, and the Stern-Volmer quenching constant (Kₛᵥ) for the rhein-DNA interaction was determined to be 5.67 × 104 L·mol-1. The flow cytometry results indicated that that rhein induced apoptosis in a dose-dependent manner, with apoptosis percentages of 15.4 ± 0.7%, 25.2 ± 2.3%, and 34.6 ± 1.8% at 25, 50, and 100 μM, respectively. Moreover, rhein not only activates the mitochondrial-mediated apoptosis signaling pathway (Bax/Bcl-2/cytochrome C/cleaved caspase-3) but also highly activates the expression level of the DNA damage protein γ-H2AX. This study provides new insights into the development of natural anthraquinone compounds as promising candidates for oral cancer therapies.