Background: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor family, selectively induces apoptosis in various cancer cells; however, certain cancers can evade TRAIL-mediated apoptosis. FLICE-like inhibitory protein (FLIP), an inhibitor of caspase-8, (also known as FLICE) is regulated by the transcription factor nuclear factor-kappaB (NF-kappaB) and can contribute to TRAIL resistance. The purpose of our study was to determine whether inhibition of NF-kappaB can enhance TRAIL-mediated pancreatic cancer cell death and decrease FLIP levels.
Methods: The human pancreatic cancer cell lines MIA PaCa-2 and L3.6 were treated with TRAIL, NEMO-binding domain (NBD) peptide (a novel selective NF-kappaB inhibitor), or a combination of both. Cell viability and apoptosis were measured. Gel mobility shift assays were performed to assess NF-kappaB binding activity. Western blots were performed to assess FLIP levels after treatment with NBD or infection with an adenovirus encoding mutated IkappaBalpha.
Results: The aggressive L3.6 cell line was resistant to TRAIL treatment, whereas MIA PaCa-2 cells were sensitive to TRAIL. The combination of TRAIL and NBD significantly decreased cell viability and increased apoptosis in L3.6 cells. Cellular levels of FLIP were decreased by inhibition of NF-kappaB (either by NBD treatment or mutant IkappaBalpha infection).
Conclusions: Our findings demonstrate resistance of the aggressive L3.6 pancreatic cell line to TRAIL treatment alone; inhibition of NF-kappaB by NBD increased TRAIL-mediated cell death and decreased FLIP protein levels. Novel agents that selectively target the NF-kappaB pathway may be useful adjuvant therapies for chemoresistant pancreatic cancers.