Fig. 5. Inhibition of DC electrical-field-induced growth stimulation of multicellular tumor spheroids by suramin and the anion channel antagonist niflumic acid (A), and effects of anion channel blockers on tumor spheroid growth induced by exogenous ATP (B). (A) Multicellular tumor spheroids were treated with a single electrical field pulse (750 Vm^-1, 60 seconds) in the absence (control) or presence of either suramin (300 µM) or the anion channel inhibitor niflumic acid (200 µM). Subsequently they were immersed in cell culture medium in the absence of the compounds and cultivated for a further 6 days. Tumor spheroid volumes were determined immediately after electrical field treatment and after 6 days. (B) Tumor spheroids were treated with niflumic acid (200 µM), tamoxifen (50 µM) or NPPB (50 µM). After 30 minutes of incubation 10 µM ATP was added and tumor spheroids were incubated for a further 30 minutes. Subsequently, tumor spheroids were washed and tumor spheroid growth was evaluated after 24 hours. Tumor spheroid growth is presented as relative volume increase V/V₀ where V₀ is the spheroid volume at the beginning of the experiment and V is the spheroid volume at the end of the experiment.

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