Inhibiting JNK activation abrogates arsenic trioxide-induced apoptosis in NB4 cells. (A) NB4 cells were treated with 10 μM As₂O₃ alone or in combination with 1 μM dicumarol for 16 hours. An immune complex kinase assay was performed to ensure inhibition of JNK1 at this dose of dicumarol. (B) NB4 cells were either left untreated () or were treated for 3 days with 0.5 μM As₂O₃ (left panel) or 0.01 μg/mL doxorubicin (right panel) alone (▪) or in combination with 1 μM dicumarol (^*), which was replenished daily. Growth inhibition was assessed by counting trypan blue-excluding cells, which always made up more than 97% of the total cells examined. Each data point shown represents an average of 3 independent replicates, and standard deviation error bars are shown.