Effect of gemcitabine on viability and proliferation of four human pancreatic cancer cell lines. A. Cells were treated with the indicated concentrations of gemcitabine for 72 h. Proportions of viable cells measured by the WST-1 assay are shown in arbitrary units as a difference in absorbance measured at 450 nm and 690 nm (reference) wavelengths, respectively. B. Cell proliferation was determined by BrdU incorporation into genomic DNA. The results are expressed in percentage relative to the corresponding untreated controls. In both assays, three separate experiments were performed and data from one representative experiment [mean +/- standard deviation (STD) of four replicates] are shown. C. Phase contrast microscopy photographs of cells left untreated or incubated with 50 nM gemcitabine for 72 h. Pictures were originally captured at 400× magnification.