Abstract 4011: Wnt/β-catenin transcriptional activation promotes tumorigenesis and predicts survival in pancreatic cancer.

Mutations in key regulators of Wnt/β-catenin signaling lead to its aberrant hyperactivation and promote oncogenesis in several cancer types. While Wnt/β-catenin signaling is variably increased in pancreatic adenocarcinoma (PDAC), there is a near absence of activating mutations in its key regulatory genes in PDAC tumors. As the precise role of Wnt/β-catenin signaling in pancreatic tumorigenesis is unclear, we sought to clarify the mechanisms by which it is altered and determine its specific consequences on gene transcription and phenotype in PDAC. Using a luciferase-based Wnt/β-catenin reporter platform to determine relative levels of Wnt/β-catenin transcriptional activation, we found pathway activation was highly variable across 22 PDAC cell lines, including distinct subsets with either low or much high levels of baseline reporter activity. Supervised analysis of microarray data was performed on these defined subsets to generate a pancreatic-specific gene expression signature able to discriminate levels of Wnt/β-catenin transcriptional activation in PDAC. This analysis identified a set of 208 genes (median FDR 3.4%) representing a robust candidate list of mediators or downstream transcriptional targets. Several genes were validated as bona fide downstream transcriptional targets of Wnt/β-catenin in PDAC cell lines by observing expected changes in their expression following genetic and pharmacologic manipulations that activate or inhibit Wnt signaling. WNT7B, FZD5 and TCF7L2 were among genes commonly overexpressed in Wnt high lines, representing potential positive mediators of Wnt/β-catenin signaling in PDAC. Likewise, NLK and CSNK1E were among genes overexpressed in Wnt low lines, representing potentially important negative regulators of the pathway in PDAC. When primary patient tumors were dichotomized based on a pancreas-specific Wnt/β-catenin transcriptional signature, PDAC tumors with higher Wnt/β-catenin transcriptional activation had worse disease-specific survival (median survival time 20.3 versus 43.9 months, log rank P=0.03), suggesting a possible direct link between Wnt/β-catenin transcriptional activation and aggressive tumor behavior. Furthermore, genetic and pharmacologic inhibition of Wnt/β-catenin signaling in PDAC cell lines significantly reduced non-adherent growth and tumorsphere formation in vitro. Inhibition of Wnt/β-catenin signaling also increased survival and reduce metastatic burden in an in vivo orthotopic xenograft model using PDAC cell lines. This study has defined a pancreatic cancer-specific Wnt/β-catenin transcriptional signature able to predict more aggressive clinical behavior and with potential utility for stratifying patients most likely to benefit from Wnt-targeted therapy. Citation Format: Michael Arensman, Anna R. Lay, Rima M. Kulikauskas, Andy J. Chien, David W. Dawson. Wnt/β-catenin transcriptional activation promotes tumorigenesis and predicts survival in pancreatic cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4011. doi:10.1158/1538-7445.AM2013-4011