Abstract 1572: FZD6 and RYK, non-canonical Wnt receptors in pancreatic cancer progression
Authors: Stevens Payton D. , Sall Emily , Zhong Alex , Hostetter Galen , Madaj Zachary , Thalappillil Jennifer , Dobin Alexander , Park Youngkyu , Tuveson David A. , Williams Bart O. 
Published: June 2022

Abstract
Pancreatic ductal adenocarcinoma (PDAC) has a grim prognosis with 5-year patient survival of less than 10%. Development of effective therapeutics has been hampered by the PDAC tumor microenvironment (TME), which contains dense desmoplastic stroma that likely impedes the ability of therapies to reach the tumor cells. We have found that aggressive, “basal-like” human PDAC tumors have high expression of proteins involved in planar-cell-polarity (PCP), a type of non-canonical Wnt signaling. We show that the increased expression of the PCP genes, including the putative non-canonical Wnt ligand, Wnt5a, the Frizzled 6 (FZD6) Wnt receptor, and RYK co-receptor negatively impact patient prognosis. Using a panel of FZD6 knock-down pancreatic cell lines, we show that loss of FZD6 increases expression of the epithelial marker, E-cadherin, and decreases cellular motility in Transwell assays. We also find that loss of Fzd6 dramatically inhibits tumor progression in two mouse models of PDAC, with a pronounced change to the TME; including the cancer-associated fibroblasts (CAFs) and immune cells. Blinded histologic pathology review of tumor and immune cell infiltrates, by H&E and alphaSMA staining, suggests that the CAF cell population is altered. We propose this is the cause of the looser stroma surrounding the tumors after Fzd6 loss, which also results in an increased abundance of CD4 and CD8 positive T cells surrounding and within the tumors. Additionally, immunohistochemical staining for other PCP proteins within the pancreatic tumors lacking Fzd6 suggests that Fzd6 loss reduces PCP-component protein levels. We hypothesize that the loss of Fzd6 reduces tumor cell EMT and PCP signaling, while the loose stroma allows more immune cells that further slow tumor growth and progression. We have also examined the expression of PCP proteins in a novel orthotopic xenotransplantation model of PDAC, intraductally grafted organoids (IGO). IGO is a powerful tool to study PDAC as the intraductal tumors that develop recapitulate patient to patient heterogeneity while displaying features of either classical or basal-like PDAC subtypes. FZD6 and RYK are both more highly expressed in the IGO basal-like tumors than the classical type. Introduction of fast-growing, basal-like human tumors into the murine pancreas also resulted in a TME that produces more Wnt5a, when compared to the stroma surrounding tumors formed by injecting the classical subtype. Taken together, we believe we have identified a Wnt5a/Fzd6 driven PCP-like signaling pathway that makes tumors more mesenchymal-like, and results in PDAC tumor progression and worse patient prognosis.
Citation Format: Payton D. Stevens, Emily Sall, Alex Zhong, Galen Hostetter, Zachary Madaj, Jennifer Thalappillil, Alexander Dobin, Youngkyu Park, David A. Tuveson, Bart O. Williams. FZD6 and RYK, non-canonical Wnt receptors in pancreatic cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1572.