Figure 2.

Normalized isobologram for CPT-11/SN-38 and DAC in HCT116 cells. CI for various combinations of DAC (3.9–31.25 nM) and either CPT-11 (125, 250 and 500 nM) or SN-38 (0.35, 0.5, 0.7 and 1.0 nM). Cells were treated with various concentrations of (A) CPT-11 and DAC, or (B) SN-38 and DAC. The combination effects can be summarized as follows: CI<1, dots located lower left; CI=1, dots on the hypotenuse; and CI>1, dots located upper right; these results indicate synergistic, additive, and antagonistic effects, respectively. DAC, 5-aza-2′-deoxycytidine; CPT-11, irinotecan; SN-38, 7-ethyl-10-hydroxycamptothecin; CI, combination index.