Molecular mechanisms of tamoxifen-induced apoptosis in cholangiocarcinoma

B38 Cholangiocarcinoma is a highly fatal tumor of biliary epithelium with very limited therapeutic options. So far no chemotherapy regimen has been found to be effective in advanced stage cholangiocarcinoma. We have found that tamoxifen (TMX) induced apoptosis in cholangiocarcinoma cells, probably via its calmodulin (CaM) antagonist effects. In the present studies, we determined the role of TMX as a potential therapy and the molecular mechanisms responsible for TMX-induced apoptosis in cholangiocarcinoma.
 Cholangiocarcinoma tumorigenesis in a mouse xenograft model was inhibited by intratumoral injection of TMX (tumor volumes: control=696.9±123.1mm 3 and TMX=217.8±49.3mm 3 , n=7, p=0.004). Immunohistochemical analyses of the tumors identified the expression of phosphorylated-AKT (pAKT) in all non-treated tumors (pAKT-positive tumor cells=27.1±11.1%) but not in adjacent stromal cells. All sections from the TMX-treated tumors were negative for pAKT staining. TMX (10µM) induced a 1.9-fold increased apoptosis in cells isolated from mouse tumor xenografts (n=5, p 2+ -dependent direct binding of CaM and FLIP, which was increased upon Fas-stimulation. TMX inhibited Fas-induced increase in CaM-FLIP binding, suggesting that TMX may interfere with stabilization of FLIP by inhibiting CaM-FLIP binding after Fas stimulation to enhance sensitivity of cholangiocarcinoma cells to apoptosis.
 In summary, we demonstrated that TMX regulates AKT and FLIP activation to induce apoptosis of cholangiocarcinoma cells and may represent an effective therapy for cholangiocarcinoma.