PROJECT SUMMARY Endometrial cancer (EC) is the fourth most common cancer in women. While EC occurs most commonly in older women, the mortality rate and incidence is exponentially increasing in women under 40 years of age. EC is estimated to increase by 1–2% yearly and more than half of EC cases are attributable to obesity, which is recognized as an independent risk factor. Approximately 80% of EC belong to the endometrioid EC (EEC) (type I) and the remaining 20% is comprised of serous EC (SEC), clear cell EC (CEC), mixed EC, and uterine carcinosarcoma (UCS) (type II). Surgery is widely used to treat EC; however, patients with advanced EC often experience disease relapse. Despite receiving adjunctive therapy, these patients are at high risk of recurrence of cancer and death. There is an unmet need for the development of new targeted therapies that complement existing EC-directed therapies for advanced type I (grade 2, 3) and type II EC. The global gene expression analysis of the cancer databases revealed a negative correlation between EC survival and Leukemia inhibitory factor (LIF) and its receptor, LIFR expression. Further, obesity conditions function as potent inducers of the LIF/LIFR signaling. Together, these findings strongly suggest that LIF/LIFR signaling in EC may be clinically actionable, and targeting LIF/LIFR axis with a small molecule inhibitor may block EC progression. We recently developed a small molecule inhibitor of LIFR, EC359 and preliminary studies show that EC359 reduces the growth of EC cells with high potency and promotes apoptosis. The preclinical xenograft studies showed that EC359 is highly efficacious in reducing EC xenograft tumor growth and block EC progression driven by obesity. The objective of this proposal is to establish the mechanisms by which LIF/LIFR signaling contributes to EC progression and to test the efficacy of the LIFR inhibitor EC359 in treating EC. Our overarching hypothesis is that LIF/LIFR signaling promotes EC progression, and that the LIFR inhibitor EC359 functions as an effective targeted therapy to block EC progression. In Aim1, we will establish the mechanisms of how LIF/LIFR signaling contributes to EC progression, define the significance of LIF/LIFR axis using global genomic approaches, test the efficacy of EC359 in reducing stemness and chemoresistance of EC cells, investigate the mechanisms by which obesity promote LIF/LIFR signaling in EC. In Aim2, we will test the utility of blocking the LIF/LIFR axis with EC359 using multiple primary and established EC model cells and test the utility of EC359 on EC progression as a monotherapy or combination with chemotherapy using xenografts, patient-derived explants (PDE), organoids (PDO) and patient-derived xenograft (PDX) models. We will also test the utility of EC359 in reducing obesity-driven EC. This proposal is clinically significant because it will establish translatability, mechanisms of a first-in-class LIFR inhibitor, EC359, and enable a rat...