Chemoresistance may involve the anti-apoptotic transcriptional regulator, nuclear factor-κB (NF-κB). The purpose of this study was to determine whether chemotherapy induces NF-κB activation in a human colon cancer cell line (SW48) and whether NF-κB is constitutively activated in colorectal cancer.

SW48 cells were incubated with gemcitabine hydrochloride (Gemzar) in the presence and absence of the 26s proteasome inhibitor, MG132, and NF-κB binding (electrophoretic mobility shift assay), DNA synthesis (tritiated thymidine uptake), cell viability (3-[4,5-dimethylthiazol-2-yl]-diphenyl-tetrazolium bromide assay), and apoptosis (caspase-3 activity) were measured at 24 hours. NF-κB binding (electrophoretic mobility shift assay) was also assayed in 10 colorectal cancer tumors.

SW48 cells demonstrated constitutive NF-κB binding that was enhanced by gemcitabine hydrochloride in a dose-dependent manner. MG132 inhibited NF-κB binding and enhanced gemcitabine hydrochloride's inhibition of DNA synthesis (gemcitabine hydrochloride = 73% ± 1.4% vs gemcitabine hydrochloride + MG132 = 6% ± 0.4%, P < .05), cell killing (gemcitabine hydrochloride = 87% ± 2.0 vs gemcitabine hydrochloride + MG132 = 25% ± 1.3%, P < .05), and caspase-3 activity (gemcitabine hydrochloride = 870 ± 17.4 vs gemcitabine hydrochloride + MG132 = 1075 ± 20.4, P < .05). NF-κB binding was increased in 8 of 10 colorectal cancer tumors compared with adjacent normal mucosa.

Gemcitabine hydrochloride enhances NF-κB binding in a colorectal cancer cell line, whereas inhibition of NF-κB enhances gemcitabine hydrochloride's antitumor activity. NF-κB is also activated in human colorectal cancer. NF-κB may identify chemoresistant tumors, whereas inhibition of NF-κB may be a novel, biologically based therapy. (Surgery 2001;130:363-9).