Inhibition of inducible NF-κB activity reduces chemoresistance to 5-fluorouracil in human stomach cancer cell line

5-fluorouracil (5-FU) is used for the treatment of stomach and colon cancer, but many tumors are resistant to this chemotherapeutic agent. 5-FU induces apoptosis of several cancer cell lines, while some chemotherapeutic agents are known to activate the transcriptional factor NF-κB, which strongly suppresses apoptosis in vitro. In the present study, we investigated the relationship between activation of NF-κB and chemoresistance to 5-FU in human stomach cancer cell lines, NUGC3 (5-FU sensitive) and NUGC3/5FU/L (5-FU resistant). Treatment with 5-FU for 9-12 h caused activation of inducible NF-κB in NUGC3/5FU/L cells but not in NUGC3 cells. 5-FU also resulted in an increase in the number of TUNEL-positive cells and enhanced caspase-3 activity 3- to 5-fold in NUGC3 cells but not NUGC3/5FU/L cells. Moreover we also demonstrated that the inhibition of inducible NF-κB activation by using a NF-κB decoy could induce apoptosis and reduce chemoresistance against 5-FU. Our results suggest that 5-FU chemoresistance can be overcome by inhibition of inducible NF-κB activation, and that the use of the NF-κB decoy combined with 5-FU treatment is a new molecular and gene therapeutic strategy aimed at treatment of human stomach cancers resistant to 5-FU.