Background. Chemoresistance may involve the anti-apoptotic transcriptional
regulator, nuclear factor-kappaB (NF-kappaB). The purpose of this study was
to determine whether chemotherapy induces NF-kappaB activation in a human
colon cancer cell line (SW48) and whether NF-kappaB is constitutively activ
ated in colorectal cancer.
Methods. SW48 cells were incubated with gemcitabine hydrochloride (Gemzar)
in the presence and absence of the 26s proteasome inhibitor, MG132, and NF-
kappaB binding (electrophoretic mobility shift assay), DNA synthesis (triti
ated thymidine uptake), cell viability (3-[4,5-dimetltylthiazol-2-yl]-diphe
nyltetrazolium bromide assay), and apoptosis (caspase-3 activity) were meas
ured at 24 hours. NF-kappaB binding (electrophoretic mobility shift assay)
was also assayed in 10 colorectal cancer tumors.
Results. SW48 cells demonstrated constitutive NF-kappaB binding that was en
hanced by gemcitabine hydrochloride in a dose-dependent manner MG132. inhib
ited NF-kappaB binding and enhanced gemcitabine hydrochloride inhibition of
DNA synthesis (gemcitabine hydrochloride = 73% +/- 1.4% vs gemcitabine hyd
rochloride + MG132 = 6% +/- 0.4%, P < .05), cell killing (gemcitabine hydro
chloride = 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-<kappa>
B binding was increased in 8 of 10 colorectal cancer tumors compared with a
djacent normal mucosa.
Conclusions. Gemcitabine hydrochloride enhances NF-kappaB binding in a colo
rectal cancer cell line, whereas inhibition of NF-kappaB enhances gemcitabi
ne hydrochloride's antitumor activity. NF-kappaB is also activated in human
colorectal cancer. NF-kappaB may identify chemoresistant tumors, whereas i
nhibition of NF-kappaB may be a novel, biologically based therapy.