Abstract 4630: Characterizing oncogene addiction in alveolar rhabdomyosarcoma reveals novel strategies for combination therapy

Rhabdomyosarcoma is the most common soft tissue sarcoma in children. The aggressive alveolar subtype (aRMS) is characterized by chromosomal translocations, most often a t(2;13) resulting in the expression of the oncogenic fusion protein PAX3-FOXO1 which is critical for tumorigenesis and cell survival. Our aim here was to identify a pharmacological combination therapy approach interfering with PAX3-FOXO1 biology at different levels. Since loss of the fusion protein results in cell death, we first aimed to pharmacologically enhance this effect. To this end, we screened aRMS tumor cells with a library of 208 drugs while simultaneously silencing PAX3-FOXO1 by shRNA. This identified the BH3-mimetic ABT-263 to sensitize aRMS cells to cell death after PAX3-FOXO1 depletion. To further characterize the cell death mechanisms we used combined shRNA and CRISPR approaches to perform a BH3 protein profiling. In accordance with identification of ABT-263 we demonstrate that aRMS cells undergo intrinsic apoptosis in a NOXA-dependent manner upon depletion of PAX3-FOXO1. In a parallel approach, and to identify drugs altering PAX3-FOXO1 protein stability, we screened the same drug library directly measuring fusion protein levels as read-out. This revealed that inhibition of Aurora kinase A negatively affects PAX3-FOXO1 protein levels. Finally, using both aRMS cell lines and patient-derived xenografts we demonstrate that combination treatment of Aurora kinase A inhibitors together with ABT-263 synergistically induces cell death and greatly slows tumor growth in vitro and in vivo. Taken together, these data show a novel functional interaction of Aurora kinase A and PAX3-FOXO1 and suggest new opportunities for targeted combination treatment of aRMS. Citation Format: Johannes Ommer, Marco Wachtel, Beat W. Schaefer. Characterizing oncogene addiction in alveolar rhabdomyosarcoma reveals novel strategies for combination therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4630.