Abstract B65: Investigating the role of nuclear FGF2 signaling in pancreatic cancer.

Abstract

Background: It is now appreciated that, in pancreatic cancer, transformed cells interact with stromal cells, extracellular matrix proteins, and neighboring normal epithelial cells to exploit feedback mechanisms and facilitate tumor progression. The mechanisms driving these events are under intense investigation. We are focusing on the fibroblast growth factor family member FGF2 as a key driver in these events. Classically FGF2 mediates its biological effects by binding to a high-affinity cell surface receptor (FGFR) that spans the cell membrane. However, multiple forms of FGF2 exist with HMW forms localizing preferentially to the nucleus. In human glial cells, the accumulation of FGF2 and its receptor, FGFR1 in the nucleus is associated with mitotic activation and hypertrophy (Moffett et al. 1996; Stachowiak et al. 1996; Joy et al. 1997; Stachowiak, M. K. et al. 1997) and may be responsible for driving expression of genes associated with cell growth (Nakanishi et al. 1992). Studies have shown that overexpression of FGF2 in pancreatic cancer correlates with poor patient survival and nuclear FGF2 has been observed in pancreatic cancer patient tissue but not in normal patient samples (Yamanka et al 1993). A number of mechanisms have been proposed for the nuclear accumulation of FGFR1 and its ligand; however, the role of intracrine FGF2 signaling in tumor invasion remains poorly understood. Methods: Patient tissue microarrays were stained with FGF2 and FGFR1 antibodies to correlate cellular localization of FGF2 and FGFR1 in pancreatic cancer tissue. Twelve pancreatic cancer cell lines, a pancreatic stellate cell line (PSC) as well normal ductal epithelial cell lines were used for Western blot and immunocytochemistry analysis. FGF2 was silenced using siRNA in MiaPaCa2, COLO357 cancer cell lines as well and PSC to assess the effect in cell behavior following abolishment of nuclear FGF2. Furthermore, a small molecule inhibitor of FGFR signaling (PD173074) was used in 2-D and 3-D cultures to assess the effects of blocking FGF2 signaling on cell behavior and invasion. Results: FGF2 localized to the nucleus in the 30% of stromal fibroblasts found in pancreatic cancer tissue. Furthermore, in vitro, FGFR1 and FGF2 co-localized to the nucleus in 30% of PSCs but not in cancer cell or normal ductal epithelial cell lines. PSCs -secrete both HMW and LMW FGF2 isoforms. Silencing FGF2 using siRNA resulted in a significant reduction in nuclear FGFR1 and cell growth in PSCs but no effect was seen in cancer cell lines MIA PaCa2 or COLO357. Furthermore, inhibiting FGFR signaling in PSCs but not cancer cell lines, using 2μM PD173074, resulted in significant reduction in nuclear FGFR1 and FGF2 which correlated with a G1 cell cycle block and reduction in cell proliferation. Using PD173074 in organotypic 3-D models of pancreatic cancer resulted in a reduction in cancer cell and PSC cell invasion. Conclusion: In vivo, stroma is now appreciated as a major driver in promoting the aggressiveness of PDAC and makes up 80% the tumor volume (Li and Abbruzzese 2009). Furthermore, studies have shown that the presence of PSCs in orthotopic models of PDAC increases distant spread of the tumor (Vonlaufen et al. 2008). These studies show for the first time that nuclear FGFR1 and FGF2 may play a role in driving pancreatic stellate cell proliferation. Abolishment of FGFR mediated PSC proliferation may lead to disruption of the tumor microenvironment and prevent pancreatic cancer cell invasion. Though further studies are required to confirm these findings, these preliminary experiments suggest that possible novel therapeutic approach to target the stroma in PDAC. Citation Format: Stacey Coleman, Hemant Kocher, Richard Grose. Investigating the role of nuclear FGF2 signaling in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr B65.