Abstract #5510: Molecular mechanism of tamoxifen therapy for cholangiocarcinoma

AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO Cholangiocarcinoma is a highly lethal tumor with limited therapeutic options. We have reported that tamoxifen (TMX), as a calmodulin (CaM) antagonist, induces apoptosis in cholangiocarcinoma cells. Here, we have determined the effects of TMX on tumorigenesis and the molecular mechanisms of TMX-induced apoptosis. A nude mouse xenograft model was used to characterize cholangiocarcinoma tumorigenesis with SK-ChA-1 cells. Intra-peritoneal or intra-tumoral injection of TMX did not affect mouse survival, but decreased cholangiocarcinoma tumorigenesis by 39% and 82% compared to PBS-injected control groups (n=10 mice in each group). Phosphorylated AKT (pAKT) was demonstrated in all non-treated tumors, but was absent in all TMX-treated tumors. In cholangiocarcinoma xenograft cells, TMX consistently inhibited pAKT and the expression of FLICE-like inhibitory protein (FLIP). TMX activated caspase-8 and -10, and their respective inhibitors partially blocked TMX-induced apoptosis in cholangiocarcinoma cells. Lentiviruse-mediated overexpression of FLIP in cholangiocarcinoma cells inhibited TMX-induced apoptosis and enhanced tumorigenesis of cholangiocarcinoma cells in nude mice. The role of FLIP on cell survival and TMX-induced apoptosis was confirmed with two additional cholangiocarcinoma cell lines, MZ-ChA-1 and HuCCT-1. Deletion of the CaM binding domain on FLIP restored the sensitivity of cholangiocarcinoma cells to TMX and inhibited tumorigenesis, suggesting CaM/FLIP binding is critical for FLIP-mediated cell survival. In summary, TMX inhibits cholangiocarcinoma tumorigenesis in nude mice. TMX-induced apoptosis is partially dependent on caspases, and associated with inhibition of pAKT and expression of FLIP. CaM-FLIP binding appears to be important in FLIP mediated resistance to TMX. These studies support that TMX may be used as therapy for cholangiocarcinoma and possibly other malignancies, in which the CaM targets, AKT and FLIP play important roles in tumor pathogenesis. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 5510.