Isolation, Characterization and Anticancer Activity of Secondary Metabolites from Verbascum speciosum.

Two iridoid glucosides aucubin (1) and ajugol (2), and two phenyl ethanoids, verbascoside (3) and poliumoside (4) were isolated from the methanol extract of the aerial parts of Verbascum speciosum and used to study about their anticancer activity for the first time. The structures of all compounds were elucidated using spectroscopic data (IR, 1D and 2D NMR, LC-MS TOF). In addition, the antiproliferative activities of aucubin (1) and verbascoside (3) were tested against A-549 (human lung cancer), HT-29 (human colon cancer), MDA-MB-453 (human breast cancer), and 3T3-L1 (mouse fibroblast) cell lines by XTT assay. According to the results, both compounds exhibited dose-dependent cytotoxic activity on all the cell lines, but 3 was more potent against all the cell lines with its lower IC50 values when compared to 1, and again 3 showed the strongest activity (IC50: 40.63 μg/ml) and highest selectivity index (SI:4.27) against A-549 cells. This is the first report of the isolation of 1 and 3 from the Verbascum speciosum plant and investigation of their cytotoxic effects against diverse cancer cell types.