Abstract LB-3: All-trans retinoic acid (ATRA) downregulates ALK in neuroblastoma cell lines and induces apoptotic cell death in neuroblastoma cell lines with activated ALK

Abstract

Abstract Neuroblastoma is the most common extracranial solid tumors in children and high-risk patients with such tumors have a poor prognosis despite recent advances with multimodal therapies. Retinoic acids have been clinically used for some cancers including neuroblastoma although the mechanism of their antitumor effect remains to be fully elucidated. It was recently reported that gene amplification and gain-of-function mutation of ALK were found in tumors from some neuroblastoma patients; and RNAi or small molecule inhibitors of ALK induced apoptotic cell death in neuroblastoma cell lines with these genetic alterations of ALK. In this study, we found that all-trans retinoic acid (ATRA) downregulated ALK expression in neuroblastoma cell lines; and the suppression of ALK by ATRA accompanied apoptotic cell death in neuroblastoma cell lines with activated ALK. We used four neuroblastoma cell lines: NB-39-nu cells with gene amplification of ALK, SH-SY5Y cells with gain-of-function mutation of ALK as well as TNB-1 and GOTO cells without such genetic alterations. Western blotting analysis demonstrated that the levels of ALK protein were remarkably reduced in all cell lines treated with ATRA at the concentration of 1 μM or 10 μM for 72 h. Analysis by quantitative real-time RT-PCR for mRNA expression levels in ATRA-treated NB-39-nu cells revealed that the ALK mRNA quantitative levels of the cells reduced at 24 h after such treatment. Apoptosis assays demonstrated obvious apoptosis in NB-39-nu and SH-SY5Y cells whereas it was not evident in TNB-1 and GOTO cells. Cleaved caspase-3 was also detected in NB-39-nu and SH-SY5Y cells 72 h after treatment with ATRA, but not in TNB-1 and GOTO cells. In addition, we observed cell growth inhibition that was accompanied with apoptosis in NB-39-nu and SH-SY5Y cells treated with ATRA. These results suggest that ALK downregulation by ATRA might lead to apoptotic cell death in neuroblastoma cells with activated ALK. This finding further suggests that ALK downregulation by retinoic acids could contribute to their therapeutic effect in a subset of neuroblastoma patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-3.