Abstract PR007: Patient derived organoids as a model to study estrogen mediated endometrial cancer

Abstract The purpose of our study was to develop a more optimal in vitro model to study the mechanisms of hormone action on endometrial cancer. Endometrial cancer (EC) represents a major health disparity with a 21% increase in mortality in African American women. The cause for this excess mortality is unknown. Endometrial cancer is commonly characterized by histological subtype into Endometrioid or Non-Endometrioid with estrogen being a driver for many endometroid type tumors. Most EC cell lines do not have high expression of estrogen receptor or do not respond to physiological levels of hormones in vitro; this lack of functional experimental models has hampered progress in the study of this disease. We have developed Patient Derived Organoids (PDOs) from 9 patient-derived xenografts (PDX) that are from both African American and Non-Hispanic Caucasian women with various stages and subtypes of EC, as a model to study EC. This model system captures the characteristics of different histological and molecular subtypes in vitro, as they maintain not only EC tumor cells but also cells from the adjacent tumor stroma. Our developed PDOs were derived from multiple molecular subtypes of EC that have different characteristics and genomic features, allowing us to observe differences in the basal properties of each tumor in vitro. The use of this organoid model system is advantageous for studying EC because growth characteristics are similar to an in vivo model, with the organoids preserving the genotype and phenotype of the native EC, allowing us to observe cellular interactions. We have observed inter-organoid variation of protein expression of β-catenin, E-cadherin, and vimentin, proteins playing a pivotal role in cellular contact, signaling, and epithelial-mesenchymal transition (EMT). Using qPCR and Western blot analysis we have observed high expression levels of estrogen receptor and progesterone receptor in endometrioid type PDOs to begin the exploration of hormonal signaling in this model. Treatment of these same PDOs with β-estradiol resulted in an increase in proliferation of the stromal cells. Single cell RNA sequencing was performed on two PDO’s that had the highest expression of progesterone and estrogen receptors. This analysis demonstrated cell population heterogeneity with multiple cell clusters forming with differential gene expression. From this analysis we can see that the cells recapitulate the gene expression from the tumor of origin, with cells containing the same genetic mutation as the original patient. These results make this model potentially good for studying hormone signaling cascades seen in EC patients that have not been previously observed in established EC cell lines. These studies will also aid in the opportunity to explore the function of differential cell types in the pathogenesis of this disease. Citation Format: Breanna M. W. Jeffcoat, Andrew B. Galdden, Russell R. Broaddus. Patient derived organoids as a model to study estrogen mediated endometrial cancer abstract. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30 (5Suppl): Abstract nr PR007.