Abstract LB-142: Regulation of MYCN stability by reactive oxygen species in neuroblastoma

Abstract

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Amplification of the MYCN proto-oncogene is associated with older age, rapid tumor progression, and the worst outcome of this disease. As MYCN amplification leads to its over-expression, high-level expression of MYCN is thought to cause an aggressive behavior of MYCN amplified tumors. In fact, the forced reduction of MYCN protein expression by siRNA results in growth suppression and apoptosis of NB cells with MYCN amplification. We have identified several compounds that can rapidly destabilize the MYCN protein (within a few hours), in NB cells and cause growth suppression. The compounds include FCCP, OSU-03012, and Salinomycin. Our recent data suggest that a common effect of the above compounds appears to be the inhibition of mitochondrial functions. Moreover, ascorbic acid, an anti-oxidant, abolishes the effect of these compounds on MYCN protein stability. It is known that inhibition of mitochondrial oxidative phosphorylation increases the production of reactive oxygen species (ROS), which include superoxide (O2-), hydroxyl radical (•OH), and hydrogen peroxide (H2O2). Anti-oxidants are also known to quench ROS. Preliminary data showed that ROS was detected when the IMR5 NB cells were treated with OSU-03012 for three hours. In addition, we have found that forced over-expression of pVHL, an E3 ubiquitin ligase, in NB cell lines results in reduction of MYCN protein levels. We are currently testing whether ROS regulates MYCN stability by hydroxylation of proline residues on MYCN, and whether pVHL recognizes the ROS-modified MYCN, which is then subjected to rapid proteasome-dependent degradation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-142. doi:10.1158/1538-7445.AM2011-LB-142

Destabilization of MYC/MYCN by the mitochondrial inhibitors, metaiodobenzylguanidine, metformin and phenformin

“…We previously demonstrated that FCCP, a known mitochondrial inhibitor, destabilized MYC and MYCN in NB cells and induced a growth suppressive effect ( 7 ). In this study, to investigate whether MIBG, which is also a mitochondrial inhibitor, exhibits a similar effect on MYC/MYCN in NB cells, we examined MYC/MYCN expression in NB cell lines treated with MIBG (10 and 20 μM) for 4 days.…”

“…These observations suggest that MYCN and/or MYC expression are among the major determining factors of NB aggressiveness. Previously, we also found that mitochondrial inhibitors, such as carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), can destabilize MYC/MYCN and suppress the growth of NB cells ( 7 ), suggesting the potential use of mitochondrial inhibitors in the treatment of NB.…”