Investigating the Role of Fibulin 3 in Pancreatic Tumorigenesis - Project Summary/Abstract Pancreatic ductal adenocarcinoma (PDA) is a highly lethal malignancy with a five-year survival rate of less than 13%, making it one of the deadliest cancers. Notably, 95% of PDA cases exhibit KRAS mutations, contributing to highly dysregulated cell signaling networks. Despite extensive research into the interplay of various oncogenic pathways in pancreatic tumorigenesis, targeted therapies against these signaling networks have displayed modest efficacy, with most patients rapidly developing therapeutic resistance. Recent studies highlight the significance of the carbohydrate antigen 19-9 (CA19-9) as a functional biomarker linked to disease progression and resistance. However, understanding the detailed functions of CA19-9-modified proteins in PDA has been limited due to the lack of mouse models that can synthesize CA19-9. Recent development of unique mouse and 3D organoid culture models demonstrated that induction of CA19-9 led to an aggressive PDA phenotype through increased tumor proliferation and microenvironment (TME) remodeling. CA19-9 modification of Fibulin 3 (FBLN3), a secreted glycoprotein, stimulates pancreatitis through hyperactivation of EGFR. However, the precise functional role of FBLN3 in tumor development remains unclear, creating a substantial gap in understanding of PDA biology. In Aim 1, the tumor cell-intrinsic roles of FBLN3 in pancreatic tumorigenesis will be investigated. PDA organoid models will be used to determine how FBLN3 impacts CA19-9-accelerated PDA growth. Preliminary data suggest that the loss of FBLN3 in CA19-9pos, KRAS-mutant pancreatic ductal organoids significantly suppress EGFR and STAT3 activation. To build on this, the impact of glycosylation modification of FBLN3 on EGFR-dependent tumor growth will be delineated. Additionally, the mechanisms by which FBLN3 activates STAT3, potentially via EGFR or NF-kB signaling, and its contribution to PDA progression will be determined. To validate these findings in vivo, gene-edited CA19-9pos PDA organoids will be orthotopically transplanted into syngeneic mice to uncover how FBLN3-mediated EGFR and STAT3 signaling promote tumor proliferation. In Aim 2, the cancer cell-extrinsic roles of FBLN3 in TME remodeling will be investigated. Efemp1 (FBLN3) is expressed in cancer-associated fibroblasts (CAFs). Also, loss of FBLN3 in PDA organoids reduced production of IL1α and TGFβ as well as decreased CAF subtype differentiation in vitro. Therefore, both the direct and indirect roles of FBLN3 on CAF subtype proliferation and differentiation will be defined. To investigate the function of FBLN3 expressed by CAFs in vivo, gene-edited CA19-9pos PDA organoids will be orthotopically transplanted in Efemp1 (FBLN3) KO mice and define the changes to TME reprogramming. This proposal aims to identify the functional role of FBLN3 in pancreatic cancer progression and provide novel insights into PDA biology and paracrine mechanisms, suggesting FBLN3 as a potential therapeutic target for PDA to improve patient outcomes.
