Requirement of Nuclear Factor kB for Smac Mimetic-Mediated Sensitization of Pancreatic Carcinoma Cells for Gemcitabine-Induced Apoptosis

Defects in apoptosis contribute to treatment resistance and poor outcome of pancreatic cancer, calling for novel therapeutic strategies. Here, we provide the first evidence that nuclear factor (NF)kappa B is required for Smac mimetic-mediated sensitization of pancreatic carcinoma cells for gemcitabine-induced apoptosis. The Smac mimetic BV6 cooperates with gemcitabine to reduce cell viability and to induce apoptosis. In addition, BV6 significantly enhances the cytotoxicity of several anticancer drugs against pancreatic carcinoma cells, including doxorubicin, cisplatin, and 5-fluorouracil. Molecular studies reveal that BV6 stimulates NF-kappa B activation, which is further increased in the presence of gemcitabine. Importantly, inhibition of NF-kappa B by overexpression of the dominant- negative I kappa B alpha superrepressor significantly decreases BV6- and gemcitabine-induced apoptosis, demonstrating that NF-kappa B exerts a proapoptotic function in this model of apoptosis. In support of this notion, inhibition of tumor necrosis factor alpha (TNF alpha) by the TNF alpha blocking antibody Enbrel reduces BV6- and gemcitabine-induced activation of caspase 8 and 3, loss of mitochondrial membrane potential, and apoptosis. By demonstrating that BV6 and gemcitabine trigger a NF-kappa B-dependent, TNF alpha-mediated loop to activate apoptosis signaling pathways and caspase-dependent apoptotic cell death, our findings have important implications for the development of Smac mimetic-based combination protocols in the treatment of pancreatic cancer.