Purpose: While many cancers are showing remarkable responses to targeted therapies, pediatric sarcomas, including Ewing sarcoma, remain recalcitrant. To broaden the therapeutic landscape, we explored the in vitro response of Ewing sarcoma cell lines against a large collection of investigational and approved drugs to identify candidate combinations. Experimental Design: Drugs displaying activity as single agents were evaluated in combinatorial (matrix) format to identify highly active, synergistic drug combinations, and combinations were subsequently validated in multiple cell lines using various agents from each class. Comprehensive metabolomic and proteomic profiling was performed to better understand the mechanism underlying the synergy. Xenograft experiments were performed to determine efficacy and in vivo mechanism. Results: Several promising candidates emerged, including the combination of small molecule poly ADP-ribose polymerase (PARP) and nicotinamide phosphoribosyltransferase (NAMPT) inhibitors, a rational combination as NAMPT inhibitors block the rate-limiting enzyme in the production of NAD+, a necessary substrate of PARP. Mechanistic drivers of the synergistic cell killing phenotype of these combined drugs included depletion of NMN and NAD+, diminished PAR activity, increased DNA damage, and apoptosis. Combination PARP and NAMPT inhibitors in vivo resulted in tumor regression, delayed disease progression and increased survival. Conclusions: These studies highlight the potential of these drugs as a possible therapeutic option in Ewing sarcoma.
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