FIG 2.

Combinations of HU with sampangine (SMP) show a highly synergistic cytotoxic effect in S. pombe. (A) The cell survival of wild-type S. pombe in the presence of increasing concentrations of HU or SMP alone or in various combinations of the two drugs (combos 1 to 4) was assessed by the 96-well plate assay as described in Materials and Methods. The A₆₀₀ values are shown to present cell survival. The combination index (CI) values shown on the right of the table were calculated by using the Chou-Talalay method (17). The values marked in bold indicate the drug combinations showing very strong synergism (CI values of <0.1). (B) Graphical representation of the cell-killing effects of HU, SMP, and the four combinations of HU and SMP. The cell survival rate was calculated using the A₆₀₀ values from panel A relative to the no-drug control and shown as percentages. (C) Combination index plot. Fa on the x axis is the cell growth inhibition value at various CI values. The horizontal line indicates the additive drug interaction (CI values are between 0.9 to 1.1). The CI values above and below the horizontal line represent antagonistic and synergistic drug effects, respectively.