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Advanced-stage endometrial cancer patients typically receive a combination of platinum and paclitaxel chemotherapy. However, limited treatment options are available for those with recurrent disease, and there is a need to identify alternative treatment options for the advanced setting. Our goal was to evaluate the pre-clinical efficacy and mechanism of action of Oklahoma Nitrone 007 (OKN-007) alone and in combination with carboplatin and paclitaxel in endometrial cancer. The effect of OKN-007 on the metabolic viability of endometrial cancer cells in both two- and three-dimensional (2D and 3D) cultures, as well as on clonogenic growth, in vitro was assessed. We also evaluated OKN-007 in vivo using an intraperitoneal xenograft model and targeted gene expression profiling to determine the molecular mechanism and gene expression programs altered by OKN-007. Our results showed that endometrial cancer cells were generally sensitive to OKN-007 in both 2D and 3D cultures. OKN-007 displayed a reduction in 3D spheroid and clonogenic growth. Subsequent targeted gene expression profiling revealed that OKN-007 significantly downregulated the immunosuppressive and immunometabolic enzyme indolamine 2,3-dioxygenase 1 (IDO1) (-11.27-fold change) and modulated upstream inflammatory pathways that regulate IDO1 expression (interferon- (IFN-), Jak-STAT, TGF-β, and NF-kB), downstream IDO1 effector pathways (mTOR and aryl hydrocarbon receptor (AhR)) and altered T-cell co-signaling pathways. OKN-007 treatment reduced IDO1, SULF2, and TGF-β protein expression in vivo, and inhibited TGF-β, NF-kB, and AhR- receptor-mediated nuclear signaling in vitro. These findings indicate that OKN-007 surmounts pro-inflammatory, immunosuppressive, and pro-tumorigenic pathways and is a promising approach for the effective treat endometrial cancer. Women with advanced and recurrent endometrial cancer have limited therapeutic options. OKN-007, which has minimal toxicity and is currently being evaluated in early-phase clinical trials for the treatment of cancer, is a potential new strategy for the treatment of endometrial cancer.