Concentration of spongiatriol needed to obtain 50% cytotoxicity (IC50) in four pancreatic cancer cell lines. Cells were incubated for 72 h in the presence of serial dilutions of spongiatriol. Proliferation was determined by following the reduction of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) into a formazan, normalized to solvent control and subjected to a non-linear regression analysis. Data is the average of three experiments ± standard deviation.