Abstract PR-009: Targeting the sterol regulatory element-binding protein pathway in pancreatic ductal adenocarcinoma
Authors: Stephanie Myers, Meredith McGuire, Wei Shao, Chine Liu, Theodore Ewachiw, Zeshaan Rasheed, William Matsui, Toni Sepalla, Richard Burkhart, Peter Espenshade
Journal: Cancer Research (2021)

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is a very aggressive tumor with limited diagnostic and therapeutic options. Due to its proliferative nature and thick, desmoplastic stroma, PDAC tumor cells are challenged with meeting a high demand for lipids in a hypoxic, lipid-poor environment. Cancer cells respond to lipid conditions through sterol regulatory element-binding proteins (SREBPs). SREBPs are master transcriptional regulators of lipid homeostasis and require SREBP cleavage activating protein (SCAP) during signaling. While the SREBP pathway has been implicated in several cancers, its role in PDAC has not been examined. In this study, we assess the requirement of this pathway using both in vitro and in vivo model systems. Furthermore, we target the SREBP pathway using a novel combination therapy of two FDA-approved compounds: dipyridamole and statins. Methods: We acquired four patient-derived pancreatic adenocarcinoma cell lines containing mutations in both Kras and p53 and knocked out SCAP in each cell line followed by gene-based rescue. Functional growth assays were performed in both lipid-poor and lipid-rich media conditions. Subcutaneous and pancreatic orthotopic xenografts were performed in nude mice using these same cell lines. A previously established mouse line, LSL-KrasG12D/+; LSL-Trp53R172H/+; Pdx-1 Cre (KPC) on a C57Bl/6 background, was utilized as a PDAC model. KPC mice lacking Scap in one or both alleles (Sfl/+ or Sfl/fl) were generated. Cohort survival and histologic analysis were performed for all mice, and results plotted on a Kaplan-Meier survival curve. In each patient cell line, the following drugs were applied individually and in combination: Dipyridamole (DP), tetramethyl-DP (TMDP), Fluvastatin, and Simvastatin. Cell viability post-treatment was assessed, and synergy calculated for each combination using SynergyFinder. Results: In lipid-poor conditions, SCAP knockout cells showed significantly reduced growth when compared to wild type or SCAP rescued cells. In tumor xenograft models, SCAP knockout cells exhibited reduced tumor growth and tumor volume when compared to wild-type cells. In the genetically engineered mouse models, KPC mice exhibited a median survival time of 289 days, while KPCSfl/+ mice show a significantly increased median survival time of 425 days. Additionally, KPCSfl/fl mice did not develop invasive PDAC. Cells treated individually with DP, TMDP and both statins exhibit lipid-dependent growth defects in all cell lines tested. In combination, DP with either statin as well as TMDP with either statin demonstrate synergy in lipid-poor conditions. Conclusions: Our results demonstrate that loss of SCAP in PDAC tumor cells alters the growth capability both in vitro and using mouse xenograft models. Additionally, heterozygous loss of Scap in the KPC mouse model significantly increased survival. Finally, dipyridamole works in synergy with statins to alter growth of PDAC tumor cells. These findings suggest that targeting the SREBP pathway has significant therapeutic potential in PDAC. Citation Format: Stephanie Myers, Meredith McGuire, Wei Shao, Chine Liu, Theodore Ewachiw, Zeshaan Rasheed, William Matsui, Toni Sepalla, Richard Burkhart, Peter Espenshade. Targeting the sterol regulatory element-binding protein pathway in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PR-009.