Recently, we demonstrated that the
cyclooxygenase-2 (COX-2) inhibitor
celecoxib acts to significantly suppress the growth of rat C611B
cholangiocarcinoma (ChC) cells in vitro. To establish a molecular mechanism for this growth suppression, we investigated the effects of
celecoxib on apoptotic signaling pathways in cultured rat C611B ChC cells.
Celecoxib and another
COX-2 inhibitor,
rofecoxib, at 5 microM were almost equally effective in inhibiting
prostaglandin E(2) (
PGE(2)) production by these cells, but at this low concentration, neither inhibitor suppressed growth or induced apoptosis.
Celecoxib at 50 microM induced prominent apoptosis in these cells, whereas
rofecoxib at 50 microM was without effect in either suppressing growth or inducing apoptosis.
Celecoxib (50 microM) did not alter Bcl-2, Bcl-x(L), or COX-2
protein levels, nor did it inhibit p42/44
mitogen-activated protein kinase (MAPK) phosphorylation; however, it significantly suppressed
serine/threonine kinase Akt/PKB (Akt) phosphorylation and
kinase activity in cultured C611B cells. This effect, in turn, directly correlated with Bax translocation to mitochondria,
cytochrome c release into cytosol, activation of
caspase-9 and
caspase-3, and cleavage of
poly (ADP-ribose) polymerase (PARP). Addition of 25 microM
PGE(2) to C611B cell cultures blocked the apoptotic actions of
celecoxib.
Rofecoxib (50 microM) was without effect in suppressing Akt phosphorylation and
caspase-3 activation. In vivo,
celecoxib partially suppressed tumorigenic growth of C611B ChC cells. In conclusion, our results indicate that
celecoxib preferentially acts in vitro to induce apoptosis in ChC cells through a mechanism involving Akt inactivation, Bax translocation, and
cytochrome c release. Our in vivo results further suggest
celecoxib might have potential therapeutic or chemopreventive value against ChC.