The combination of epigenetic drugs SAHA and HCI-2509 synergistically inhibits EWS-FLI1 and tumor growth in Ewing sarcoma

// Daniel Jose Garcia-Dominguez 1, * , Lourdes Hontecillas-Prieto 1, * , Pablo Rodriguez-Nunez 1 , Guillem Pascual-Pasto 2 , Monica Vila-Ubach 2 , Rosa Garcia-Mejias 1 , Maria Jose Robles 1, 3 , Oscar M. Tirado 4 , Jaume Mora 2 , Angel M. Carcaboso 2 and Enrique de Alava 1, 3 1 Institute of Biomedicine of Seville (IBiS), Hospital Universitario Virgen del Rocio/CSIC/Universidad de Sevilla/CIBERONC, Seville, Spain 2 Developmental Tumour Biology Laboratory, Hospital Sant Joan de Deu, Barcelona, Spain 3 Pathology Unit, Hospital Universitario Virgen del Rocio/CSIC/Universidad de Sevilla/CIBERONC, Seville, Spain 4 Sarcoma Research Group, Laboratori d’Oncologia Molecular, Institut d’Investigacio Biomedica de Bellvitge (IDIBELL)/CIBERONC, L’Hospitalet de Llobregat, Barcelona, Spain * These authors contributed equally to this work Correspondence to: Daniel Jose Garcia-Dominguez, email: dgarcia-ibis@us.es Lourdes Hontecillas-Prieto, email: lhontecillas-ibis@us.es Enrique de Alava, email: enrique.alava.sspa@juntadeandalucia.es Keywords: Ewing sarcoma; EWSR1; epigenetic drug; synergism effect; PDX Received: March 24, 2018      Accepted: July 12, 2018      Published: July 31, 2018 ABSTRACT Purpose: Epigenetic regulation is crucial in mammalian development and maintenance of tissue-cell specific functions. Perturbation of epigenetic balance may lead to alterations in gene expression, resulting in cellular transformation and malignancy. Previous studies in Ewing sarcoma (ES) have shown that the Nucleosome Remodeling Deacetylase (NuRD) complex binds directly to EWS-FLI1 oncoprotein and modulates its transcriptional activity. The role of EWS-FLI1 as a driver of proliferation and transformation in ES is widely known, but the effect of epigenetic drugs on fusion activity remains poorly described. The present study evaluated the combination effects of the histone deacetylases inhibitor suberoylanilide hydroxamic acid (SAHA) and Lysine-specific demethylase1 inhibitor (HCI-2509) on different biological functions in ES and in comparison to monotherapy treatments. Results: The study of proliferation and cell viability showed a synergistic effect in most ES cell lines analyzed. An enhanced effect was also observed in the induction of apoptosis, together with accumulation of cells in G1 phase and a blockage of the migratory capacity of ES cell lines. Treatment, either in monotherapy or in combination, caused a significant decrease of EWS-FLI1 mRNA and protein levels and this effect is mediated in part by fusion gene promoter regulation. The anti-tumor effect of this combination was confirmed in patient-derived xenograft mouse models, in which only the combination treatment led to a statistically significant decrease in tumor volume. Conclusions: The combination of SAHA and HCI-2509 is proposed as a novel treatment strategy for ES patients to inhibit the essential driver of this sarcoma and tumor growth.