Effect of ATP-depletion in doxorubicin-retention. INER-51 cells as monolayers or multicellular spheroids were pre-incubated (open symbols) or not (filled symbols) with 1 mM sodium-cyanide, 10 mM sodium-fluoride, 10 mM sodium azide before the addition of increased DXR concentrations. The intracellular DXR-fluorescence was evaluated by spectrofluormetry. Each point represents the mean of at least 3 experiments and the error bars are the standard error of the mean. The Student's t-test for paired data was performed to identify changes in DXR retention. The results were considered to be significant when p < 0.05. NS: no significant.