Abstract PR10: Inhibition of deacetylase SIRT1 offers a novel treatment option in metastatic Ewing sarcoma
Authors: Ban Jozef , Fourtouna Argyrou , Machado Isidro , Niedan Stephan , Snaar-Jagalska Ewa , Aryee Dave NT , Kauer Maximilian , Alberghini Marco , Flanagan Adrienne , Scotlandi Katia , Strauss Sandra J. , Lawlor Elisabeth R. , Llombart-Bosch Antonio , Kovar Heinrich 
Published: May 2015

Abstract
Metastasis is the major cause of disease-related death in Ewing sarcoma. Patients, who present with clinically overt disseminated disease at diagnosis and those who relapse early with distant metastases have a poor outcome despite multi-modal high-dose chemotherapy. Therefore, new treatment options are highly warranted. Ewing sarcoma pathogenesis is driven by the chimeric ETS oncogene EWS-FLI1. We here describe regulation of sirtuin SIRT1 by EWS-FLI1 and its role in metastasis.
SIRT1 belongs to a family of NAD+-dependent group III deacetylases that target histone and non-histone proteins in response to metabolic stress resulting in widespread gene expression changes through epigenetic and direct transcriptional mechanisms. Among SIRT1 target proteins is the tumor suppressor p53. SIRT1 overexpression prevents p53 acetylation, which is otherwise required for the induction of its transcriptional activity. Also, SIRT1 is involved in negative regulation of several signaling pathways including NOTCH that we had previously described as being inactivated in Ewing sarcoma by the EWS-FLI1 fusion oncogene. Studying the molecular basis of EWS-FLI1 mediated functional p53 perturbation in Ewing sarcoma, we here describe a feed-back regulatory loop in which the NOTCH effector HEY1, which is epigenetically repressed by SIRT1, in turn suppresses SIRT1 expression leading to histone H4K16 and H3K56 acetylation and to p53 activation, and consequently to Ewing sarcoma cell death in vitro. By immunohistochemistry, the study of almost 400 Ewing sarcoma patient samples revealed high SIRT1 expression in about one third of primary tumors and a highly significant association of SIRT1 positivity with Ewing sarcoma metastases. The analysis of 18 paired primary tumor/metastasis samples indicated that SIRT1 was more frequently observed in lung metastases (88%) than in bone marrow metastases (55%), and was already detectable in the corresponding primary tumors in more than 60% of cases. In vitro treatment of Ewing sarcoma cell lines with a pharmacological SIRT1/2 inhibitor resulted in cell death with IC50 values between 0.8 and 3.5 μmol that depended on SIRT1 expression level and p53 status. The greatest sensitivity was obtained with cells that express high SIRT1 and are wildtype for p53. Consistent with this in vitro result, SIRT1 inhibition prohibited tumor cell migration and proliferation in a zebrafish yolk sac xenotransplantation model of a SIRT1 positive, wildtype p53 Ewing sarcoma cell line, but not of a mutant p53 cell line with low SIRT1 expression. Together, these results suggest that SIRT1 expression, which is enabled by EWS-FLI1 mediated suppression of the NOTCH signaling pathway resulting in p53 inactivation, may be therapeutically targeted to fight metastasis using pharmacological sirtuin inhibitors.
Supported by EU-FP7 grant 259348 (“ASSET”) and by the Austrian Research Fund FWF, ERA-NET grant I1225-B19 (“PROVABES”).
This abstract is also presented as Poster A38.
Citation Format: Jozef Ban, Argyrou Fourtouna, Isidro Machado, Stephan Niedan, Ewa Snaar-Jagalska, Dave NT Aryee, Maximilian Kauer, Marco Alberghini, Adrienne Flanagan, Katia Scotlandi, Sandra J. Strauss, Elisabeth R. Lawlor, Antonio Llombart-Bosch, Heinrich Kovar. Inhibition of deacetylase SIRT1 offers a novel treatment option in metastatic Ewing sarcoma. [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 PR10.