Secondary metabolites from the underground parts of <i>Valeriana sisymbriifolia</i> Vahl. and their <i>in vitro</i> cytotoxic activities

Cytotoxic activity-guided isolation studies on the underground parts of Valeriana sisymbriifolia Vahl. led to the isolation of 12 secondary metabolites including two undescribed iridoids, sisymbriifolivaltrate and sisymbriifolioside, and two unreported sesquiterpene lactones, sisymbriifolins A and B. Chemical structures of the isolates were established by extensive 1D and 2D NMR analyses as well as HR-ESI-MS. The in vitro cytotoxic activities of the extract, sub-fractions and isolates on lung (A549), breast (MCF7), gastric (HGC27) and prostate (PC3) cancer cell lines were evaluated by MTS assay. Sisymbriifolivaltrate, didrovaltrate, valtrate, 7-homovaltrate and 1-alpha-acevaltrate exhibited promising cytotoxic activity on MCF7 cell line with IC50 values ranging from 2.5 to 12.3 mu M, while valtrate demonstrated the best cytotoxicity against A549 cells with the IC50 value of 7.5 mu M. Valtrate and 7-homovaltrate were found to exert noteworthy cytotoxicity towards HGC27 cell line (IC50 values: 2.3 and 3.7 mu M, respectively), whereas valtrate, 7-homovaltrate and 1-alpha-acevaltrate (IC50 values: 2.3-9.7 mu M) were found to be potent cytotoxic against PC3 cells. Among the tested compounds, particularly valepotriate-type iridoids were found to be the main cytotoxic principles of V. sisymbriifolia.