PROJECT SUMMARY The prognosis for the aggressive histologies in uterine cancer patients is low. This is likely due to lack of identification of pathways specific to uterine serous cancer or high-grade endometrioid tumors specifically. Our data suggest that the AXL pathway is highly expressed in uterine serous (USC) and grade 3 endometrioid endometrial cancer (G3 EEC) is associated with worse survival. We have recently shown that high-affinity, highly-selective inhibitor of AXL, AVB-500 (now known as batiraxcept), can improve response to paclitaxel in USC and G3 EEC. Additionally, there is developing data that AXL expression is correlated with the highly glycolytic phenotype, and this correlation with glycolysis may allow us to determine which tumors can respond better to AXL inhibition. Furthermore, published data supports that AXL regulates VEGF-A, and our preclinical data supports that inhibition of AXL can improve response to the anti-angiogenic agent, bevacizumab. Our central hypothesis is that inhibiting GAS6/AXL with AVB-500 will improve response to standard of care treatment. We will expand to test this hypothesis in three specific aims. Aim 1: Determine the safety and tolerability of combining batiraxcept with standard-of-care paclitaxel in patients with recurrent, aggressive endometrial cancer histologies (USC and G3 EEC). Exploratory Aim 2: Identify tissue and blood markers that correlate with response to treatment. Aim 3: Determine the mechanisms by which batiraxcept improves response to the standard-of-care anti- angiogenic bevacizumab. Impact: The clinical trial data from Aim 1 will form the foundation of a future Phase II trial of batiraxcept plus paclitaxel in USC and G3 EEC patients. The data from Exploratory Aim 2 may allow us to develop a metabolic biomarker that can predict sensitivity to this drug combination and/or provide insight into the metabolic processes involved in tumors that do not respond to this drug combination. The data from Aim 3 will provide key mechanistic data to support a future clinical trial combining batiraxcept with bevacizumab. In the long term, this work will allow us to optimize and personalize treatment for patients with aggressive uterine cancer types. Our team is well-positioned to test our central hypothesis in clinical and experimental studies.