Abstract A66: NF-kappa B is a potential therapeutic target in a subset of rhabdomyosarcomas
Authors: Albert Catherine M. , Loeb David M. , Paz-Priel Ido 
Published: May 2015

Abstract
Rhabdomyosarcoma (RMS) is a tumor that arises from skeletal muscle progenitor cells and is the most common soft tissue sarcoma of childhood. RMS cells are characterized by impaired myogenesis and do not undergo terminal differentiation. Nuclear factor-kappa B (NF-κB) is a family of transcription factors found in virtually all mammalian cells that is commonly associated with inflammation and has been implicated in numerous malignancies. NF-κB p65 containing dimers are the most prevalent active species of NF-κB. Increased NF-κB activity has been shown to disrupt myogenesis by suppressing the differentiation of myoblasts through a regulatory circuit involving microRNA miR-29. However, the role of NF-κB in RMS is largely unexplored. The purpose of this study is to investigate the role of NF-κB in RMS tumorigenesis and evaluate its potential as a therapeutic target in this disease.
NF-κB activity was surveyed in a panel of embryonal RMS (ERMS) and alveolar RMS (ARMS) cell lines. Four out of 8 RMS cell lines (2 ERMS and 2 ARMS) demonstrated increased NF-κB activation at baseline as assessed by increased levels of p65 and phosphorylated p65 on western blotting, nuclear localization of p65 on EMSA super shift, and increased NF-κB transcriptional activity on a luciferase reporter assay. RMS cell lines, including TTC442 (ERMS), also demonstrated dose-dependent cytotoxicity after treatment with Bortezomib, a proteasome inhibitor. BAY 16-1942, a specific inhibitor of IκB kinase-β (IKK-β), was ineffective as a single agent; however, doxorubicin-induced cytotoxicity was enhanced by up to 39% in TTC442 cells treated concurrently with this agent. RH30 (ARMS), TTC442 (ERMS), and RD (ERMS) cells were transfected with IκB-SR, a doxycycline-inducible super-repressor form of IκBα, and effects on proliferation and clonogenic activity were assessed. WST-1 assay of cellular proliferation revealed growth impairment of TTC442 cells expressing the IκB-SR mutant, with average values of only 63% and 60% of control cells after 72 and 96 hours in culture. In addition, TTC442 and RH30 cells expressing the IκB-SR mutant formed 35% and 29% fewer colonies, respectively, compared to control cells when plated in low concentration. No differences in proliferation or clonogenic capacity were observed in RD cells, a line that did not show consistent NF-κB activation in our initial survey.
These data indicate that NF-κB is activated in a subset of RMS cells and suggest that modulation of NF-κB activity may affect baseline tumor growth, sensitivity to chemotherapy, and clonogenic potential of these cells. These findings support the hypothesis that NF-κB is a promising new therapeutic target for RMS.
Citation Format: Catherine M. Albert, David M. Loeb, Ido Paz-Priel. NF-kappa B is a potential therapeutic target in a subset of rhabdomyosarcomas. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A66.