Abstract 2017: Phenotypic plasticity and class switching in ovarian cancer
Authors: Sharmila A. Bapat, Sagar Varankar, Swapnil Kamble
Journal: Cancer Research (2018)

Abstract The multifaceted evolution of cancer involves differential responses of tumor cell populations to intrinsic and extrinsic stimuli. Numerous reports have examined the role of epithelial-mesenchymal transition (EMT) in the progression of high-grade serous ovarian carcinoma (HGSC). An earlier study from our group successfully resolved molecular subclasses in HGSC wherein metastasis was mediated by cooperative cell migration in the epithelial subclass and EMT in the mesenchymal subclass. We now explore the transcriptional circuitry in expression datasets and cell lines regulating these states. This led to the identification that Tcf21 and Slug expression correlated with the epithelial and mesenchymal phenotypes, respectively, and inversely correlated with each other. Probing the differential altered localization and expression of TCF21 and Slug further resolved a spectrum of intermediary phenotypic states along the epithelial to mesenchymal spectrum, each of which is associated with the expression of specific markers. Further, functional assays reveal the inherent plasticity of each phenotype with migratory mechanisms emerging as a differential parameter. Rigidity and high degree of differentiation of the epithelial and mesenchymal state is evident from a lack of responsiveness to specific microenvironmental conditions. Importantly, such cellular plasticity induced shifts from a steady-state phenotype following modulation of the microenvironment only in the intermediate phenotypes to exhibit flexibility to transit towards either the two ends of the spectrum. Specifically, a tendency to acquire an epithelial phenotype on growth factor deprivation was noted. The effects of BMP7 and TGFβ to induce epithelial or mesenchymal phenotypes, respectively, were also noted exclusively within the intermediary states. The stress generated by chemotherapeutic agents like paclitaxel led to enrichment of and dominant effects of the epithelial state. We further queried if this plasticity is also a feature of HGSC tumors. Marker expression (Tcf21, E-cadherin, Parp1, Slug, Anxa2 and Hyaluronan) was scored based on their frequency, intensity and location in tumors to derive a definitive scoring system comprising biomarker and tumor class indices. Application of such scoring could effectively stratifiy 95 human HGSC cases comprising primary and metastatic tumors into epithelial and mesenchymal classes, and further resolve a third class likely to represent the intermediate states. A salient feature noted was that metastases and chemotherapy could lead to class switching. Our study thus provides a comprehensive view of the intrinsic and extrinsic molecular events governing cellular plasticity in HGSC. Citation Format: Sharmila A. Bapat, Sagar Varankar, Swapnil Kamble. Phenotypic plasticity and class switching in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2017.