Cholangiocarcinoma is a highly malignant
tumor with limited therapeutic options. We have previously reported that
tamoxifen (TMX) induces apoptosis of
cholangiocarcinoma cells and reduces
cholangiocarcinoma tumorigenesis in mice. In the present studies, we determined the effect of combination
therapy of TMX and
gemcitabine (GMT), another chemotherapeutical
reagent for many
cancers, on
cholangiocarcinoma tumorigenesis and investigated the responsible mechanisms. GMT inhibited cell growth and induced apoptosis of
cholangiocarcinoma cells in a concentration-dependent manner. TMX enhanced GMT-induced apoptosis of
cholangiocarcinoma cells. Consistently, GMT (15 mg/kg) inhibited
cholangiocarcinoma tumorigenesis in nude mice by 50%. TMX (15 mg/kg) enhanced the inhibitory effect of GMT on
tumorigenesis by 33%. The inhibition of
tumor growth correlated with enhanced apoptosis in
tumor tissues. To elucidate the mechanisms underlying the additive effects of TMX on GMT-induced apoptosis, we determined the activation of
caspases in
cholangiocarcinoma cells exposed to GMT, TMX, or both. Activation of
caspases 9 and 3, as well as
cytochrome c release to the cytosol, was demonstrated in cells exposed to both
reagents. In contrast, TMX activated
caspase 2, whereas GMT had no effect. Inhibition of
caspase 2 activation decreased TMX-, but not GMT-, induced activation of
caspase 3 and apoptosis of
cholangiocarcinoma cells. Similarly, activation of
caspase 2 was found in
tumors from TMX-treated mice, but not GMT-treated mice. Therefore, the enhanced effect of TMX on GMT-induced
cholangiocarcinoma cell death is partially mediated by activation of
caspase 2. TMX and GMT both induce apoptosis and inhibit
cholangiocarcinoma tumorigenesis, which may be attributed to the activation of distinct apoptosis signals by TMX and GMT. Our studies provide in vivo evidence and molecular insight to support the use of TMX and GMT in combination as an effective
therapy for
cholangiocarcinoma.