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Stolte, Björn; Iniguez, Amanda Balboni; Dharia, Neekesh V.; Robichaud, Amanda L.; Conway, Amy Saur; Morgan, Ann M.; Alexe, Gabriela; Schauer, Nathan J.; Liu, Xiaoxi; Bird, Gregory H.; Tsherniak, Aviad; Vazquez, Francisca; Buhrlage, Sara J.; Walensky, Loren D.; Stegmaier, Kimberly (2018): Genome-scale CRISPR-Cas9 screen identifies druggable dependencies in TP53 wild-type Ewing sarcoma. In: Journal of Experimental Medicine, Vol. 215, No. 8: pp. 2137-2155
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Abstract

Ewing sarcoma is a pediatric cancer driven by EWS-ETS transcription factor fusion oncoproteins in an otherwise stable genomic background. The majority of tumors express wild-type TP53, and thus, therapies targeting the p53 pathway would benefit most patients. To discover targets specific for TP53 wild-type Ewing sarcoma, we used a genome-scale CRISPR-Cas9 screening approach and identified and validated MDM2, MDM4, USP7, and PPM1D as druggable dependencies. The stapled peptide inhibitor of MDM2 and MDM4, ATSP-7041, showed anti-tumor efficacy in vitro and in multiple mouse models. The USP7 inhibitor, P5091, and the Wip1/PPM1D inhibitor, GSK2830371, decreased the viability of Ewing sarcoma cells. The combination of ATSP-7041 with P5091, GSK2830371, and chemotherapeutic agents showed synergistic action on the p53 pathway. The effects of the inhibitors, including the specific USP7 inhibitor XL-188, were rescued by concurrent TP53 knockout, highlighting the essentiality of intact p53 for the observed cytotoxic activities.