We have recently shown that several pancreatic carcinoma cell lines are resistant to topoisomerase IIalpha inhibitors due to elevated basal nuclear factor kappaB (NF-kappaB) activity, and blockade of this activity by various means strongly increased chemosensitivity. In search of possible mechanisms leading to exaggerated NF-kappaB activity, we identified interleukin (IL)-1beta as a key mediator of this activation in two of the chemoresistant cell lines (A818-4 and PancTu-1). These cells express and secrete high levels of IL-1beta, as demonstrated by reverse transcription-PCR, immunocytochemistry, and ELISA. Culture supernatants from both cell lines induced NF-kappaB activity in chemosensitive PT45-P1 pancreatic carcinoma cells and significantly attenuated etoposide-induced apoptosis in a NF-kappaB-dependent fashion, similar to that seen in PT45-P1 cells treated with recombinant IL-1beta. Treatment of these cells with IL-1beta also changed the DNA damage characteristics toward those observed in A818-4 and PancTu-1 cells. NF-kappaB activation and the gain of chemoresistance in PT45-P1 cells on treatment with supernatants from both chemoresistant cell lines was abolished in the presence of a blocking anti-IL-1 receptor (I) antibody. Furthermore, this antibody decreased the resistance of A818-4 and PancTu-1 cells to etoposide treatment along with reduced NF-kappaB activity. Blockade of NF-kappaB activation by MG132, sulfasalazine, or an IkappaBalpha superrepressor disrupted the IL-1beta-mediated amplification loop and the accompanying chemoresistance. Our data provide insights into an autocrine mechanism involving IL-1beta by which pancreatic carcinoma cells develop chemoresistance that could serve as a molecular target in anticancer therapy.