Abstract 4854: Fibulin5 as a novel therapeutic target for pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a challenging disease with a five-year survival rate less than 5% due to late diagnosis, aggressive local and metastatic progression and high resistance to chemotherapy. Desmoplasia is thought to be a major contributor to chemoresistance in PDA. However, desmoplasia can also drive an elevation in oxidative stress. Fibronectin (FN) is a major constituent of the extracellular matrix of PDA that can mediate integrin-induced reactive oxygen species (ROS) production by stromal cells. Thus oxidation therapy is an attractive strategy that takes advantage of the elevated level of oxidative stress typically present in solid tumors, especially PDA. We demonstrated previously that the matricellular protein Fibulin5 (Fbln5) reduces FN-mediated integrin-induced ROS production by competing with FN for binding to α5β1 integrin. Fbln5 binds to integrin via an RGD domain but does not activate integrin-induced ROS. Thus Fbln5 functions as a rheostat to dampen integrin-mediated ROS production. Mutation of the RGD domain in Fbln5 to RGE abolishes the binding of Fbln5 with the integrin. Here, we generated KIC (Fbln5 +/+ , LSL-Kras G12D , Ink4a/Arf Lox/Lox , p48-Cre) and EE (Fbln5 RGE/RGE ) KIC mice to further explore the therapeutic potential of Fbln5 and underlying mechanisms. EEKIC mice survived longer and had smaller tumors than KIC littermates. Accordingly, ROS levels were higher in tumors from EEKIC mice. Importantly, survival and tumor burden could be returned to wild-type levels in EEKIC mice by systemic treatment with the antioxidant N-acetyl cysteine. ROS induction correlated with reduction in blood vessel density and endothelial cell proliferation in EEKIC tumors. Furthermore, gemcitabine was more effective in EEKIC mice. These data confirm the essential contribution of elevated ROS to disease burden in the EEKIC mice. To explore the oxidative pathways affected by the EE mutation in Fbln5, primary mouse embryonic fibroblasts (MEFs) and tumor-associated fibroblast (TAFs) were evaluated by qPCR gene array. The levels of multiple oxidative stress-induced genes were induced significantly in EE MEFs when plated on FN. These genes are being investigated for potential mechanistic contribution to the elevated ROS. To determine if Fbln5 is a target that can be exploited therapeutically, we developed a specific Fbln5-targeting peptoid (JM-454). Peptoids closely resemble peptides except that the side chains extend from the main chain nitrogen rather than the α-carbon. They are achiral, protease resistant, non-immunogenic and more cell/tissue permeable. JM-454 induces ROS both in MEFs plated on FN and orthotopic pancreatic tumors. The therapeutic efficacy of JM-454 will be examined later. Our studies show that a therapeutic antagonism of Fbln5 has the potential to be a first in class drug that harnesses the biology of ECM-integrin signaling to elevate oxidative stress in the tumor microenvironment. Citation Format: Miao Wang, Mary Topalovski, Jaya Matharage, Jason Toombs, Christopher Wright, Gomika Udugamasooriya, Rolf A. Brekken. Fibulin5 as a novel therapeutic target for pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4854. doi:10.1158/1538-7445.AM2014-4854