Cytotoxic effects of compounds from Iris tectorum on human cancer cell lines

In the course of searching for novel cytotoxic compounds which can be used in chemotherapy, several Traditional Chinese Medicines (TCM) have been screened by bioassay-guided fractionation and isolation. An extract of rhizomes of Iris tectorum Maxim., a TCM used to treat cancer, exhibited highest potency and led to the isolation of two flavonoids, 7-O-methylaromadendrin and tectorigenin, and four iridal-type triterpenes, iritectols A and B, isoiridogermanal and iridobelamal A. The cytotoxicities of the isolated compounds against four human cancer cell lines were evaluated by the SRB assay. Iritectol B, isoiridogermanal and iridobelamal A showed similar cytotoxicity with IG50 around 11 μM and 23 μM against MCF-7 and C32 cell lines, respectively. Cell cycle-specific inhibition and apoptosis induced by the isolated compounds were determined using flow cytometry with two sets of co-labelling systems: annexin V-FITC/propidium iodide and fluorescein diacetate/propidium iodide. Iritectol B demonstrated dose-dependent apoptotic effect against COR-L23 cells with an apoptotic rate of 33% at 100 μM. Tectorigenin (an analogue of genistein) showed cell cycle specific inhibition and arrested cells at G2/M phase up to 400 μM, but did not demonstrate apoptotic effect against COR-L23 cells up to 1 mM. The overall activities of isolated compounds observed in the present study support the traditional use of Iris tectorum Maxim. in the treatment of cancer.