Antitumor activity of arsenic trioxide on retinoblastoma: cell differentiation and apoptosis depending on arsenic trioxide concentration.

PURPOSE. Arsenic trioxide (ATO) targets multiple pathways in malignant cells, resulting in the promotion of differentiation or in the induction of apoptosis. The antitumor activity of ATO on retinoblastoma was investigated. METHODS. Human retinoblastoma cells were incubated with various ATO concentrations. The antiproliferative effect of ATO was evaluated by 3-(4,5-dimethylthiazol-2-yl>2,5-diphenyltetrazolium bromide assay, and the effect of ATO on cell-cycle progression was validated by flow cytometry. At a low concentration, the ATO-induced differentiation of retinoblastoma cells was evaluated by neurofilament expression and extracellular signal-regulated kinase (ERK)1/2 activation, which was confirmed by the inhibition of ERK1/2. At a high concentration, ATO-induced H 2 O 2 production was investigated with the cell-permeable fluorescent dye 2'7'-dichlorofluorescein-diacetate, and the relationship of ATO-induced H 2 O 2 production with caspase-3-dependent apoptosis was validated by Western blot and 4'6-diamidino-2-phenolindole staining, which wwas confirmed by reactive oxygen species (ROS) inhibition. The effect of ATO on tumor formation was assessed with an orthotopic animal model of retinoblastoma. RESULTS. The antitumor activity of ATO in retinoblastoma was related to two main mechanisms, differentiation and apoptosis, which were determined by the level of ATO. At a low dose (≤1 μM), ATO induced the differentiation of retinoblastoma cells through ERK1/2 activation, whereas ROS generation by a high dose (≥2 μM) of ATO induced apoptosis in retinoblastoma cells. Moreover, ATO at low and high doses effectively inhibited tumor formation. CONCLUSIONS. These results suggest that ATO can be used as an effective alternative therapeutic for the treatment of retinoblastoma.