Figure 3
Combination index (CI) as a function of affected fraction (Fa) in BCR–ABL-positive BV173 (A) and EM-3 (B) cells. Fa values of e.g. 0.25, 0.5 or 0.75 correspond to 25, 50 or 75% growth inhibition. CI values were calculated for distinct Fa values (e.g. Fa 0.1, 0.2, etc.) on the basis of experimentally determined Fa data such as shown in Table 1. By this method, CI values for different levels of growth inhibition and different drug combinations can easily be compared. The synergistic activity increases with higher levels of growth inhibition in all combinations (most apparently in the combination γ-irradiation + imatinib) suggesting optimal (maximal) activity of the pro-apoptotic treatment (γ-irradiation, busulfan, treosulfan) when imatinib is efficiently blocking BCR–ABL tyrosine kinase activity and the associated anti-apoptotic mechanisms. Solid lines, means; dotted lines, 1 s.d.-range.
