Twelve Thai medicinal plants as the ingredients of a Southern Thai traditional formula for cancer treatment were selected to test cytotoxicity activity against two types of human cancer cell lines ; large cell lung carcinoma (CORL-23) and prostate cancer cell lines (PC3) and one type of normal human cell line, fibroblast cells (10FS). SRB assay was used to test cytotoxic activity against all the cell types. Two of the extracts (water and ethanolic extracts) procedures used were similar to those practised by Thai traditional doctors. One concentration (50 µg/ml) of two different extracts was tested first against cell lines and the active plant extracts were diluted and tested for calculating IC50. The ethanolic extracts of six plants (Bridelia ovata, Curcuma zedoaria, Derris scandens, Dioscorea membranacea, Nardostachys jatamansi and Rhinacanthus nasutus) showed cytotoxic activity (IC50< 30 µg/ml) against lung and prostate cancer cell lines. Dioscorea membranacea roots showed the highest cytotoxic activity against lung cancer cell lines ( IC50= 4.6 µg/ml) but it exhibited low cytotoxic activity against prostate cancer cell lines (IC50= 17.55 µg/ml) and less cytotoxic activity against normal cell lines (IC50= 66.05 µg/ml). Curcuma zedoaria showed cytotoxic activity against COR L-23 and PC3 but less cytotoxic activity against 10FS (IC50 = 6.05, 17.84 and 55.50 µg/ml respectively) Rhinacanthus nasutus root extract showed the highest cytotoxic activity against PC3 ( IC50 = 2.01 µg/ml) and this extract also showed high activity against COR L-23 and 10FS (IC50=5.05 and 10.95 µg/ml respectively). The water extract of all plants exhibited no activity against all types of human cells. Two ethanolic plant extracts (Dioscorea membranacea and Curcuma zedoaria) which showed specific activity against lung cancer cell lines and less cytotoxic activity against normal cells should be further investigated for active compounds against lung cancer cell.
