Arsenic trioxide inhibits neuroblastoma growth in vivo and promotes apoptotic cell death in vitro

Recent clinical studies have shown that inorganic arsenic trioxide (As2O3) at low concentrations induces complete remission with minimal toxicity in p atients with refractory acute promyelocytic leukemia (APL), Preclinical stu dies suggest that As2O3 induces apoptosis and possibly differentiation in A PL cells. Like APL cells, neuroblastoma (NB) cells are thought to be arrest ed at an early stage of differentiation, and cells of highly malignant tumo rs fail to undergo spontaneous maturation. Both APL and NE cells can respon d with differentiation to retinoic acid (RA) treatment in vitro and probabl y also in vivo. For that reason we investigated the effect of As2O3 alone a nd in combination with RA on NE cell lines. In vitro, the number of viable NE cells was reduced at As2O3 concentrations around 1 muM after 72 h exposu re. The IC50 in six different cell lines treated for 3 days was in the 1.5 to 5 muM concentration interval, the most sensitive being SK-N-BE(2) cells derived from a chemotherapy resistant tumor. The combined treatment with RA (1 and 3 muM) showed no consistent additional effect with regard to induce d cell death. The effect of As2O3 on NB cell number involved As2O3-induced apoptotic pathways (decreased expression of Bcl-2 and stimulation of caspas e-3 activity) with no clear evidence of induced differentiation. The in viv o effect of As2O3 on NB growth was also investigated in nude mice bearing t umors of xenografted NE cells. Although tumor growth was reduced by As2O3 t reatment, complete remission was not achieved at the concentrations tested. We suggest that As2O3, in combination with existing treatment modalities, might be a treatment approach for high risk NB patients. (C) 2000 Academic Press.