Molecular Mechanism of Caspase-8-Dependent Interleukin-18 Activation in Pancreatic Cancer Cells Induced by 5-Fluorouracil and Nutrient Starvation.

Interleukin-18 (IL-18) is a pro-inflammatory cytokine, and higher IL-18 expression in pancreatic tumors is associated with poor prognosis. Although 5-fluorouracil (5-FU) has been reported to induce the release of bioactive (mature/cleaved) IL-18 from the pancreatic cancer cell line Capan-2, the underlying mechanism remains unclear. Here, we investigated IL-18 activation in pancreatic cancer cells after 5-FU treatment under low-nutrient conditions that mimic key features of the tumor microenvironment, using a monoclonal antibody we generated that specifically recognizes cleaved, active IL-18. We detected the release of active IL-18 from both Capan-2 and MIA PaCa-2 cells after 5-FU treatment. Analysis of separated attached and detached cell fractions showed that IL-18 cleavage occurred predominantly in detached cells. We also clarified that caspase-8-but not caspase-1/4-was activated in detached cells and was required for IL-18 and GSDMD cleavage that is a hallmark of pyroptosis. Surprisingly, detached cells from only nutrient starvation showed the same phenomenon, and 5-FU contributed to increased pyroptotic cells. On the other hand, the release of active IL-18 was not observed with gemcitabine. These findings suggest that a low-nutrient tumor microenvironment and 5-FU therapy can promote caspase-8-dependent pyroptotic cell death with IL-18 activation, potentially contributing to chronic inflammation in pancreatic tumors.