Abstract 126: Gemcitabine enhances therapeutic effect of tamoxifen on cholangiocarcinoma
Authors: Jing Gu , Turk Amy N. , Sun Yong , Pawar Pritish , Chen Yabing , McDonald Jay M. 
Published: February 2011

Gemcitabine enhances therapeutic effect of tamoxifen on cholangiocarcinoma

Gu Jing, Amy N Turk, Yong Sun, Pritish Pawar, Yabing Chen, Jay M McDonald

Cholangiocarcinoma is a highly malignant tumor with limited therapeutic options. We and others have reported that regulation of apoptosis of cancer cells is a promising avenue for cholangiocarcinoma therapy. Previous reports from our group have demonstrated that tamoxifen (TMX), as a calmodulin antagonist, induces apoptosis of cholangiocarcinoma cells via a mechanism related to Fas-death receptor mediated extrinsic apoptotic pathway (Clin Cancer Res, 2009: 15, 1288-96). The present studies determined whether gemcitabine (GMT), an inducer of intrinsic apoptotic signals, might enhancethe efficacy of tamoxifen therapy on cholangiocarcinoma.

Nude mice xenograft model was utilized for in vivo cholangiocarcinoma tumorigenesis, as we previously reported. Tamoxifen (15mg/kg) and gemcitabine (120mg/kg) were administrated by intraperitoneal injection. The effect of tamoxifen and gemcitabine on cholangiocarcinoma cell apoptosis in vitro was determined by annexin V staining and flow cytometry analysis and downstream signaling events assessed by Western blotting..

Consistent with our previous reports, we observed that tumorigenesis of cholangiocarcinoma in nude mice was inhibited by tamoxifen by 59%, compared with control group (tumor size, control=1014±295 mm3, and TMX=416±63mm3, n=6, p=0.01). Importantly, gemcitabine was found to further enhance the inhibitory effect of tamoxifen on cholangiocarcinoma tumorigenesis by 54% (tumor size, GMT+TMX=228±38 mm3, n=6, p&lt;0.0001). Mechanistic analyses demonstrated that gemcitabine enhanced the apoptotic effect of tamoxifen on cholangiocarcinoma cells (% apoptotic cells: Control=10.5±2.8, TMX=24.1±1.6 and TMX+GMT=44.7±1.8, n=3, p&lt;0.05), which was found to be dependent on the concentration of gemcitabine. Activation of caspase-3 was induced by both tamoxifen and gemcitabine. However, gemcitabine did not affect the phosphorylation of AKT, which was inhibited by tamoxifen. Furthermore, activation of caspase-9 was induced by gemcitabine, whereas tamoxifen-induced apoptosis was associated with activation of caspase 8 and 10. Therefore, gemcitabine and tamoxifen appeared to induce apoptosis of cholangiocarcinoma cells via activation of distinct signals of the apoptotic machinery.

In aggregation, we have demonstrated that gemcitabine enhanced the inhibitory effect of tamoxifen on cholangiocarcinoma tumorigenesis in nude mice. Gemcitabine and tamoxifen synergistically induce apoptosis of cholangiocarcinoma cells, which may be attributed to activation of distinct apoptosis signals by tamoxifen and gemcitabine. Our studies provide in vivo evidence and molecular insight to support the use of tamoxifen and gemcitabine in combination as an effective therapy for cholangiocarcinoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 126.