Multidrug-resistant neuroblastoma cells are responsive to arsenic trioxide at both normoxia and hypoxia

Abstract

Despite intensive treatment, the outcome of high-risk neuroblastoma patients is poor with acquired multidrug resistance as an important cause. Previously, our group has shown that arsenic trioxide (As₂O₃) kills multidrug-resistant neuroblastoma cells in vitro and in vivo at clinically tolerable doses. Regions of tissue hypoxia often arise in aggressive solid tumors, and hypoxic tumors exhibit augmented invasiveness and metastatic ability in several malignancies. Furthermore, hypoxia may impair the treatment efficiency; therefore, we have studied the cytotoxic effect of As₂O₃ on neuroblastoma cells grown under normoxic as well as hypoxic (1% oxygen) conditions. At both normoxia and hypoxia, 2 and 4 μmol/L As₂O₃ induced evident cell death in the drug-sensitive SH-SY5Y and IMR-32 cells as well as in the multidrug-resistant SK-N-BE(2)c (with a mutated p53) and SK-N-FI cells after 72 hours of exposure. In contrast, the conventional chemotherapeutic drug etoposide showed lowered efficiency in hypoxic IMR-32 cells. In accordance with our previously published results, although not to the same extent as in their normoxic counterparts, Bax is proteolytically cleaved also in neuroblastoma cells exposed to As₂O₃ at hypoxia. This suggests that similar molecular mechanisms are involved in As₂O₃-induced neuroblastoma cell death during hypoxia compared with normoxia. Together, our results support As₂O₃ as a potential candidate drug as a complement to conventional treatments for high-risk neuroblastoma patients and perhaps also for patients with other multidrug-resistant solid tumors.