Isobolograms showing the interaction between 5-FU and LY294002 in AGS and SNU-719 cells. Synergistic analysis of the interaction between 5-FU and LY294002 in AGS and SNU-719 gastric cancer cells. The interaction between 5-FU and LY294002 given on the schedule 5-FU → LY294002 is shown with an isobologram technique. The experimental isoeffect points are the concentrations (expressed relative to the 5-FU and LY294002 IC50 concentrations) of the two agents which, when combined, reduced cell viability by 50%. The data points above the diagonal line of the additive effects in the isobole suggest antagonism; those below the diagonal line suggest synergism. The isobologram analysis was based only on data obtained directly from actual experiments.