Vernodalidimer L, a sesquiterpene lactone dimer from Vernonia extensa and anti-tumor effects of vernodalin, vernolepin, and vernolide on HepG2 liver cancer cells

Vernonia extensa, known as Phim Phai Lin in Thai, is distributed in most regions of Thailand. The plant has been used in Ayurveda and traditionally used to treat malaria and cancer, and possesses several sesquiterpene lactones. This study aimed to investigate and identify the active constituents by bioactivity-based analysis, as well as to evaluate the cytotoxic activity of V. extensa by MIT or XTT assays in ten cancer cell lines (Liver HepG2 and 5102; Bile duct HuCCA-1; Leukemia HL-60 and MOLT-3; Lung A549 and H69AR; Breast MDA-MB-231 and T47D; Cervical HeLa). Bioactivity-guided fractionation and semi-preparative HPLC purification were used to separate the bioactive constituents. Apoptosis-inducing activity and cell cycle inhibitory effect of selected active compounds were determined on HepG2 cells by flow cytometric analysis. Bioactivity-guided fractionation of the CH2Cl2 extract and chemical investigation of the cytotoxic fractions led to the isolation of a new sesquiterpenoid pseudo-dimer named vernodalidimer L, together with eight known sesquiterpenoids from the aerial part of V. extensa. The structures of the isolates were elucidated based on spectroscopic analysis, including 1D and 2D NMR and HRMS. Vernolide has potent broad-spectrum cytotoxicity with IC50 values in the range of 0.91-13.84 mu M, against all ten cancer cell lines. The annexin-V flow cytometric analysis showed that vernodalin, vernolepin, and vernolide induced apoptosis on HepG2 cells in a dose dependent manner and these effects correlated with G2/M phase cell cycle arrest. Our results indicated that vernodalin, vernolepin, and vernolide have potential to be used as lead compounds in the development of a therapeutic natural product for treatment of liver cancer.