Arsenic trioxide-induced mitotic arrest and apoptosis in acute promyelocytic leukemia cells

Arsenic trioxide (As(2)O(3)), an effective drug for the treatment of acute promyelocytic leukemia (APL), can induce apoptosis and partial differentiation in APL cells in vitro and in vivo. However, As(2)O(3) also induces apoptosis in cancer cells other than APL with complex mechanisms, which seem to be cell type dependent. In this study, we report that APL cells (NB4 cell line) are arrested at early mitotic phase before the collapse of mitochondrial transmembrane potential (Deltavarphi(m)) and apoptosis after treatment with pharmacological concentrations (1.0-2.0 micro M) of As(2)O(3). We have also made the following new discoveries: (1) 0.5 micro M As(2)O(3) that fails to induce apoptosis has no effects on cell cycle distribution. (2) With inhibition of As(2)O(3)-induced Deltavarphi(m) collapse and apoptosis, dithiothreitol also effectively inhibits As(2)O(3)-induced mitotic arrest, suggesting that both As(2)O(3)-induced apoptosis and mitotic arrest involve proteins with thiol groups. (3) 1.5 mM caffeine that relieves cells from G(2)/M arrest also inhibits As(2)O(3)-induced Deltavarphi(m) collapse and apoptosis, (4) 1.0 micro M As(2)O(3) increases the expression of both cyclin B(1) and hCDC20 whereas it inhibits Tyr15 phosphorylation of p34(cdc2). In conclusion, our results strongly support that there is a tight link between As(2)O(3)-induced apoptosis and mitotic arrest, the latter being one of common mechanisms for As(2)O(3)-induced apoptosis in cancer cells.