Abstract IA-02: Pancreatic cancer heterogeneity and plasticity: The mix of seed and soil

A series of transcriptomic analyses of human pancreatic ductal adenocarcinoma (PDAC) have consistently demonstrated multiple cancer subtypes with different functional behavior in preclinical models and patient outcomes in clinical studies. The two major molecular subtypes described in PDAC are the classical epithelial (E) and the quasi-mesenchymal (QM) subtypes, otherwise known as the basal-like or squamous subtype. Although a model of E and QM subtypes to dichotomize PDAC tumor behavior affords the simplicity of use in biomarker and functional studies, there has been increasing evidence of epithelial mesenchymal transition (EMT) transcriptional plasticity of PDAC cells in model systems as well as evidence from single cell RNA-seq studies. This suggests that the E and QM states are on a continuum that can result in interconverting cell types. We have utilized single cell technologies, functional model systems, and human tumor analysis to characterize the landscape of PDAC heterogeneity and the factors involved with cellular plasticity between E and QM states. Initial single cell RNA-seq studies in PDAC mouse models revealed that partial EMT is enriched in circulating tumor cells (CTCs) compared to primary tumor cells (Ting DT et al. Cell Reports 2014). These CTCs were also highly enriched for extracellular matrix (ECM) gene expression that were shared with stromal fibroblasts in the primary tumor indicating that the “seeds” of metastasis produce their own “soil”. Functional studies in patient derived PDAC cell lines and cancer associated fibroblasts (CAFs) revealed EMT heterogeneity was partially driven by the relative amounts of stromal CAFs (Ligorio M*, Sil S* et al. Cell 2019). Using RNA in situ hybridization (RNA-ISH) in human primary PDAC tumors and high content digital image analysis, we classified individual tumor cells for EMT and proliferative (PRO) phenotypes that were linked with relative stromal content and characterize the significant inter- and intra-tumoral heterogeneity of these cell types within distinct tumor glands. In addition, analysis of PDAC tumorspheres revealed a significant induction of EMT changes in response to FOLFIRINOX, which was also found in patient tumors that were resected after neoadjuvant FOLFIRINOX (Porter RL et al. PNAS 2019). Finally, we have recently characterized human PDAC CTCs that has identified 4 different stem cell genes (WNT5A/KLF4, LGALS3, LIN28B) that are enriched in these metastatic precursors and cluster separately between patients (Franses JW*, Philipp J* et al. Nature Communications 2020). Each of these CTC phenotypes are all associated with EMT features suggestive of different pathways that can achieve similar metastatic behavior. Altogether, single cell heterogeneity of PDAC is functionally linked with tumor stromal interactions, response to chemotherapy, and the ability to seed distant metastases. Citation Format: David T. Ting. Pancreatic cancer heterogeneity and plasticity: The mix of seed and soil [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr IA-02.