MM cells are sensitive to As₂O₃ at clinically relevant concentrations.

(A) 8226/Dox40 and 8226/S cells were cultured in the absence (control, ■) or the presence of etoposide (10 μg/mL, ░) or doxorubicin (200 nM, ▪) for 48 hours. Viability was assessed as described in “Materials and methods.” Data are presented as the mean ± SD of at least 3 experiments. *Means for the treatment groups were significantly lower than for the control group (P < .0001). (B) Cells were incubated in the presence or absence of the indicated concentration of As₂O₃(1-100 μM) for 48 hours. Viability was assessed as described in “Materials and methods.” Data are presented as the mean ± SD of 5 experiments with 8226/S (▪) and 8226/Dox40 (♦) cells and of 3 experiments with U266 cells (●). (C) Cells were treated with (▨) or without IL-6 (■, 100 ng/mL) for 1 hour. Cultures were then incubated in the presence or absence of As₂O₃ (2 μM) for 48 hours. Viability was assessed as described in “Materials and methods.” Data are presented as the mean ± SD of at least 3 experiments per treatment group. *Means for As-treated (░) and As+IL-6–treated (▪) cells were significantly lower than for control cells (P < .003).