CD95L Inhibition Impacts Gemcitabine-Mediated Effects and Non-Apoptotic Signaling of TNF-α and TRAIL in Pancreatic Tumor Cells

SIMPLE SUMMARY: Death receptors may induce cellular death upon ligand binding but also activate other pro-inflammatory mechanisms in cancer cells, which may increase malignancy. The transcription factor NFkB works as a central hub in this system and connects the signaling of three major death ligands: TNF, CD95L and TRAIL. In this study, we analyzed the impact of a recombinant inhibitor of CD95L on the respective tri-lateral cross-talk using highly malignant pancreatic cancer cells as a model and in context of the standard chemotherapeutic agent, gemcitabine. We show that the specific “uni-lateral” inhibitor also clearly impacts the two other cytokines and importantly reduces the pro-inflammatory status of pancreatic cancer cells as well as their stem cell phenotype. Consequently, the local recurrent tumor growth after surgery of the primary tumor was reduced. Further, the unwanted, pro-inflammatory side-effects of gemcitabine are inhibited. ABSTRACT: Despite the potential apoptotic functions, the CD95/CD95L system can stimulate survival as well as pro-inflammatory signaling, particularly through the activation of NFκB. This holds true for the TNF/TNFR and the TRAIL/TRAILR systems. Thus, signaling pathways of these three death ligands converge, yet the specific impact of the CD95/CD95L system in this crosstalk has not been well studied. In this study, we show that gemcitabine stimulates the expression of pro-inflammatory cytokines, such as IL6 and IL8, under the influence of the CD95/CD95L system and the pharmacological inhibitor, sCD95Fc, substantially reduced the expression in two PDAC cell lines, PancTuI-luc and A818-4. The stem cell phenotype was reduced when induced upon gemcitabine as well by sCD95Fc. Moreover, TNF-α as well as TRAIL up-regulate the expression of CD95 and CD95L in both cell lines. Conversely, we detected a significant inhibitory effect of sCD95Fc on the expression of both IL8 and IL6 induced upon TNF-α and TRAIL stimulation. In vivo, CD95L inhibition reduced xeno-transplanted recurrent PDAC growth. Thus, our findings indicate that inhibition of CD95 signaling altered the chemotherapeutic effects of gemcitabine, not only by suppressing the pro-inflammatory responses that arose from the CD95L-positive tumor cells but also from the TNF-α and TRAIL signaling in a bi-lateral crosstalk manner.