Abstract 609: Molecular subtyping of pancreatic adenocarcinoma identifies SV2 positive subpopulation in classical PDAC
Authors: Dias-Santos Daniela , Ligorio Matteo , Arora Kshitij , Thapar Vishal , MacKenzie Olivia C. , Sil Srinjoy , Desai Niyati , Deshpande Vikram , Rivera Miguel N. , Ferrone Cristina R. , Ting David T. 
Published: August 2015

Abstract
Pancreatic adenocarcinoma (PDAC) is a lethal disease with a rising incidence, expected to become the second cause of cancer death in the next 5 years. Despite advances in novel therapies for other malignancies, PDAC has remained a highly chemorefractory disease leading to inevitable disease recurrence in the vast majority of patients. The identification of the cellular mechanisms of chemoresistance unique to PDAC is of particular importance. Our prior work using single cell RNA-sequencing in pancreatic circulating tumor cells (CTCs) identified 878 genes enriched in CTCs compared to matched primary tumor cells. CTCs are thought to be enriched for cells with high metastatic potential, which we predict to have intrinsic chemoresistant behavior. We hypothesized that CTC enriched genes may identify a subpopulation of cells resistant to chemotherapy that could be used as a biomarker and novel therapeutic target. The neuroendocrine marker SV2 was found in both mouse and human pancreatic CTCs and was selected given its presence on cell membranes, providing a potential therapeutic target. We evaluated a panel of patient derived cell lines and identified an SV2 positive subpopulation comprising ∼1% of cells in 3 of 5 cell lines. Notably, only differentiated epithelioid PDAC cell lines contained an SV2 subpopulation, while this population is not present in poorly differentiated quasi-mesenchymal cell lines. We performed RNA-ISH for SV2 isoforms in an annotated PDAC tissue microarray demonstrating positive staining in 77% of samples (245/317). Interestingly, SV2 positivity was often focally positive in a subpopulation of cells at the basolateral region of ductal adenocarcinoma and was found in more differentiated morphology (69% well/moderate vs 31% poor/undifferentiated; p = 0.047). The presence of SV2 cells was associated with an improved disease free survival (HR: 0.49 p = 0.009) and overall survival (HR: 0.54 p = 0.018) even after correction in multivariate analysis.
Analysis in both cell lines and tissue revealed SV2 positive cells were also found to have higher levels of the ALDH1 stem cell marker (Pearson coefficient = 0.92 in tissue). Initial in vivo treatment of human orthotopic xenografts with gemcitabine, reveal an enrichment of SV2 positive cells pointing to their potential role as the recalcitrant cancer cells treated with cytotoxic chemotherapy population.
Together, this is consistent with prior work demonstrating classical epithelial PDAC has improved survival compared to quasi-mesenchymal tumors. However, almost all patients with classical epithelial PDAC will die from recurrent disease, and we have now shown SV2 as a potential marker that identifies the chemoresistant pancreatic cancer cells in this patient population. Ultimately, a more detailed characterization of the SV2 subpopulation in classical PDAC will help us develop novel targeted therapies to overcome chemoresistance.
Citation Format: Daniela Dias-Santos, Matteo Ligorio, Kshitij Arora, Vishal Thapar, Olivia C. MacKenzie, Srinjoy Sil, Niyati Desai, Vikram Deshpande, Miguel N. Rivera, Cristina R. Ferrone, David T. Ting. Molecular subtyping of pancreatic adenocarcinoma identifies SV2 positive subpopulation in classical PDAC. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 609. doi:10.1158/1538-7445.AM2015-609