Abstract A058: UNC5B functions as a metastatic dependency in pancreatic ductal adenocarcinoma through SRC–ZEB1-driven invasion and epithelial-to-mesenchymal transition

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest malignancies, with metastatic dissemination representing the principal cause of patient mortality. Despite its clinical significance, the molecular mechanisms governing metastatic competence in PDAC remain incompletely understood. Epithelial-to-mesenchymal transition (EMT), invasion, migration, and anoikis resistance are critical biological processes that facilitate metastatic progression. Emerging evidence suggests that developmental axon-guidance pathways are reactivated during tumor evolution; however, their functional contribution to PDAC metastasis remains poorly defined. Here, we identify the axon-guidance receptor UNC5B as a central regulator of metastatic competence in PDAC. Using genetically engineered KPC-derived PDAC models and orthotopic mouse models, we demonstrate that genetic ablation of UNC5B profoundly suppresses metastatic dissemination in vivo. Across more than 21 tumor-bearing mice, UNC5B-deficient tumors remained confined to the pancreas, exhibited no detectable invasion into adjacent tissues or regional lymph nodes, and retained a more epithelial phenotype characterized by increased E-cadherin and pan-cytokeratin (AE1/AE3) expression. Loss of UNC5B was further associated with increased intratumoral necrosis and significantly reduced proliferative activity, as assessed by Ki67 staining. These in vivo findings were supported by studies in multiple human PDAC cell lines, where UNC5B depletion markedly impaired invasion and suppressed EMT programs, as determined by MAK EMT and PAMG transcriptional scoring systems. Mechanistically, UNC5B promoted metastatic progression through activation of the SRC–ZEB1 signaling axis. UNC5B selectively regulated the EMT transcription factor ZEB1, whereas expression of other canonical EMT regulators, including TWIST1, SNAIL1, and SLUG, remained largely unaffected. Pharmacologic or genetic inhibition of SRC reduced ZEB1 expression and significantly suppressed EMT and invasive behavior in PDAC cells. Conversely, ZEB1 silencing diminished EMT and invasion without altering SRC expression, supporting a model in which SRC functions upstream of ZEB1 within the UNC5B signaling network. Consistent with its functional role, UNC5B expression was significantly elevated in human PDAC specimens compared with normal pancreatic tissues. To further interrogate the mechanistic contribution of UNC5B at the protein level, we developed a degron-based protein degradation strategy that acutely depleted UNC5B and resulted in suppression of EMT programs, reduced invasive capacity, and modulation of oncogenic signaling pathways. Collectively, these findings establish UNC5B as a critical regulator of metastatic competence in PDAC and identify the UNC5B–SRC–ZEB1 axis as a previously unrecognized driver of metastatic progression. Our study provides strong preclinical evidence supporting UNC5B as an emerging molecular hub governing EMT, invasion, and metastatic dissemination in pancreatic cancer.