Figure 9.

Evidence for synergism of the genotoxic drug doxorubicin in combination with 9 or 10 in human U-87MG glioma cells. (A) Analysis of cell viability by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in U-87MG cells treated with doxorubicin (Doxo) and 9 and 10 alone or in combination (an inhibitor concentration ratio of 1:20) for 24 h, compared with the negative control 1. The results are reported as (viability of drug-treated cells/viability of control cells) × 100 and represent the mean ± SD of the two independent experiments performed in triplicate. (B) Interaction between doxorubicin (Doxo) and 1, 9, and 10 (drug concentration ratio 1:20) evaluated on the basis of the combination index (CI), which is plotted against fractional growth inhibition. The results represent the mean of two independent experiments performed in triplicate. CI values < 0.9 (below the black line), 0.9–1.1 (around the black line), and >1.1 (above the black line) represent synergism, additivity, and antagonism effect, respectively. (C) Table showing the dose effects relationship of cell inhibition parameters and the CI value of 9 and 10 compared with 1.