Analysis of median-effect and combination index (CI) in CLL cells incubated with 2-ME and arsenic trioxide.

Freshly isolated CLL cells were incubated with various concentrations of 2-ME and ATO for 72 hours. The drug effect on cell viability under various drug combination conditions was determined by MTT assay as described in “Materials and methods.” The median effect (A) and CI values (B) were calculated using a computer program by Chou and Hayball.51 In panel A ● indicates 2-ME; ▪, ATO; and ▾, 2-ME+0.5 μg/mL ATO. Dashed line at CI = 1.0 indicates an additive effect. If a CI value is below this line, it indicates synergistic activity, whereas CI values above this line suggest an antagonist effect.