Curcumin potentiates the antitumor effects of 5-FU in treatment of esophageal squamous carcinoma cells through downregulating the activation of NF-κB signaling pathway <italic>in vitro</italic> and <italic>in vivo</italic>

Although constitutive activation of nuclear factor-kappaB (NF-κB) signaling pathway has been reported in multiple different human tumors, the role of NF-κB pathway in esophageal squamous cell carcinoma (ESCC) remains ill-defined. Abundant sources have provided interesting insights into the multiple mechanisms by which curcumin may mediate chemotherapy and chemopreventive effects on cancer. In this study, we first analyzed the status of NF-κB pathway in the two ESCC cell lines Eca109 and EC9706, and then further investigated whether curcumin alone or in combination with 5-fluorouracil (5-FU) could modulate NF-κB pathway in vitro and in vivo. The results showed that NF-κB signaling pathway was constitutively activated in the ESCC cell lines. Curcumin suppressed the activation of NF-κB via the inhibition of IκBα phosphorylation, and downregulated the expressions of Bcl-2 and CyclinD1 in ESCC cell lines. Curcumin combined with 5-FU led to the lower cell viability and higher apoptosis than 5-FU treated alone. In a human ESCC xenograft model, curcumin or 5-FU alone reduced the tumor volume, but their combination had the strongest anticancer effects. Besides, curcumin could also inhibit NF-κB signaling pathway through downregulation of the IκBα phosphorylation and induction of cell apoptosis in vivo. Overall, our results indicated that constitutively activated NF-κB signaling pathway exists in the two ESCC cells and the chemopreventive effects of curcumin were associated with downregulation of NF-κB signaling pathway and its downstream genes.