Pancreatic cancer cells breach endothelial barriers through protrusion-driven invasion or endothelial retraction

Extravasation, the exit of circulating cancer cells from blood vessels, is a critical yet poorly understood step in metastatic dissemination. Here we show that pancreatic ductal adenocarcinoma (PDAC) cells can breach endothelial barriers through two mechanistically distinct modes of extravasation. MIA PaCa-2 cells breach endothelial junctions via filopodia-like protrusions, enabling access to and spread across the basal extracellular matrix (ECM). By contrast, AsPC-1 cells remain rounded atop the endothelium and cross the barrier by triggering rapid retraction of neighbouring endothelial cells. These distinct extravasation modes were also observed in zebrafish larvae. In the mouse lung, AsPC-1 cells arrest, survive, induce endothelial detachment from the basal lamina, and extravasate through this retraction mechanism before metastatic outgrowth. Mechanistically, AsPC-1-secreted factors are sufficient to destabilise endothelial monolayers, and AsPC-1 cells also induce endothelial apoptosis; however, blocking apoptosis does not prevent barrier disruption. By contrast, treatment with saracatinib, a Src-family kinase inhibitor, protects endothelial barriers, limits early vascular disruption in the lung, and delays metastatic outgrowth. Together, these findings reveal that PDAC cells can extravasate via mechanistically distinct routes, suggesting that effective anti-metastatic strategies may need to target multiple modes of endothelial barrier breach rather than a single pathway.