Chemopreventive Activity of Naphthoquinones from Alkanna tinctoria (L.) Tausch in Human Colorectal Cancer Cells

Abstract

Botanically derived natural products have recently become an attractive source of new chemotherapeutic agents. To explore active anti-colorectal cancer compounds, we performed phytochemical studies on Alkanna tinctoria and isolated eight quinone compounds. Using spectroscopical and physicochemical methods including high-resolution mass spectrometry and NMR spectra, compounds 1, 2, 3, 5 and 6 were identified as alkannin, acetylalkannin, angelylalkannin, dimethylacryl alkannin and arnebifuranone, respectively. Novel compounds 4, 7, and 8 are named as 5-methoxyangenylalkannin, alkanfuranol and alkandiol, respectively, and structurally elucidated based on extensive spectroscopic evidence. The anti-proliferative effects of these eight compounds on HCT-116 and SW-480 human colorectal cancer cells were determined by the MTS method. Cell cycle and apoptosis were determined using flow cytometry. Enzymatic activities of caspases were determined by colorimetric assay, and interactions of compound 4 and caspase 9 were explored by docking analysis. Among the eight compounds, alkannin (1), angelylalkannin (3), and 5-methoxyangenylalkannin (4) showed strong anti-proliferative effects, while compound 4 showed the most potent effects. Compound 4 arrested cancer cells in the S and G2/M phases, and significantly induced cell apoptosis. The apoptotic effects of compound 4 were supported by caspase assay and docking analysis.