Abstract 1682: Epithelial-mesenchymal heterogeneity of high-grade serous ovarian carcinoma samples correlates with let-7 levels and predicts tumor growth and metastasis

Objective: Patient-derived samples present an advantage over current cell line models of high grade serous ovarian cancer (HGSOC), which are flawed in terms of being reliable and phenotypically faithful models of in vivo HGSOC. To improve upon cell line models of HGSOC, we characterized a panel of patient-derived cells to determine their epithelial and mesenchymal characteristics, invasiveness, proliferation, stemness, and in vivo growth. Experimental procedures: Patient-derived xenograft (PDX) models of HGSOC were analyzed in vitro for phenotypic (RNA, let-7 miRNA, and protein expression, flow cytometry) and functional aspects including growth in spheroids, wound healing assays, invasion assays and in vivo (orthotopic PDX) growth characteristics. Results: Samples fell along the spectrum from epithelial to mesenchymal, and all had hybrid characteristics. Those toward the more epithelial end of the spectrum were most active in self-renewal assays, and grew most robustly in orthotopic xenograft models. Chemoresistance correlated both with the mesenchymal state and with BRCA2 wild type status. Loss of microRNA let-7 (lethal-7) is an important component of the cancer stem cell phenotype, and we observed an inverse association between let-7 expression and the epithelial state. We observed lower levels of let-7, more efficient spheroid and tumor formation, and increased sensitivity to platinum-based chemotherapy in cells with the most epithelial phenotype. Conclusions: Surprisingly, in these HGSOC cells, stemness could be dissociated from invasiveness: epithelial cells (those with least let-7 expression) were less migratory, but more tumorigenic, than the mesenchymal cells with higher let-7 expression. We conclude that epithelial/mesenchymal state and let-7 expression are valuable predictors of HGSOC proliferation, in vitro self-renewal, and tumor burden in vivo. Citation Format: Juli Unternaehrer, Evgeny Chirshev, Nozomi Hojo, Antonella Bertucci, Linda Sanderman, Anthony Nguyen, Hanmin Wang, Tise Suzuki, Emmanuel Brito, Shannalee Martine, Christine Castañón, Saied Mirshahidi, Marcelo Vazquez, Kerby C. Oberg, Yevgeniya J. Ioffe. Epithelial-mesenchymal heterogeneity of high-grade serous ovarian carcinoma samples correlates with let-7 levels and predicts tumor growth and metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1682.