Abstract A24: High expression of ErbB2 contributes to cholangiocarcinoma cell invasion and proliferation through AKT/p70S6K

Field: Biochemistry, Genetics and Molecular Biology (Life Sciences)

Abstract Cholangiocarcinoma (CCA), an adenocarcinoma of the biliary tract, is an incurable and highly lethal cancer. Its incidence has been increasing worldwide during to the past three decades and all cases have almost the same mortality rate. Due to the lack of a specific tumor marker and its silent symptom, this tumor is difficult to diagnose and the majority of patients present at the late stage (stage III or IV) of the disease progression. From 70% to 80% of CCA patients are inoperable and are generally treated by chemotherapy and radiation, which unfortunately have no significant impact for long-term survival. Thus, new diagnostic/prognosis markers and targeted therapies for CCA need to be investigated. Several lines of evidences have implicated the role of ErbB2 in aggressive forms of CCA. High expression of ErbB2 has been found in a variety of non-cancerous biliary proliferative diseases, such as in hepatolithiasis and primary sclerosing cholangitis, both of which are risk factors associated with CCA. Immunohistochemical data have demonstrated that 20% to 30% of tumor specimens from CCA patients show moderate to strong immunostaining for ErbB2 and most of them confer poor clinical outcomes (high metastasis and short survival rate). Moreover, about 30% of transgenic mice constitutively expressing wide type Neu develop gallbladder cancer and intrahepatic CCA within 8 months. Although many reports have indicated the involvement of ErbB2 in cholangiocarcinogenesis and CCA progression, the mechanism of aberrant ErbB2 expression in promoting CCA progression remains unclear. In this study, the role of ErbB2 in governing the malignant phenotype (invasion and proliferation) of CCA was investigated by suppressing ErbB2 function in three human CCA cell lines expressing different levels of ErbB2. Level of endogenous ErbB2 expression in three CCA cell lines, namely HuCCA-1, KKU-100 and KKU-M213, was determined by real time RT-PCR. Two ErbB2 inhibitory methods, a small molecule ErbB2 kinase inhibitor (AG825) and siRNA, were used to disrupt ErbB2 function in the cell lines. CCA cell invasion, motility and proliferation under ErbB2-disrupted conditions were detected using Transwell and MTT assays. In addition, ErbB2 downstream effectors were investigated by western blot analysis. Suppression of ErbB2 activity using a specific kinase inhibitor (AG825) reduced invasion, motility, and proliferation of all three CCA cell lines. The ability of this drug to inhibit neoplastic properties (invasion, motility and proliferation) increased concomitantly with the level of ErbB2 expression. Similarly, knockdown of ErbB2 level by siRNA inhibited cell invasion and proliferation of KKU-M213, a high ErbB2-expressing cell, better than those of the lower ErbB2-expressing cells, HuCCA-1 and KKU-100. Thus, both inhibitory methods indicated that there is more ErbB2-dependency for malignancy of high ErbB2-expressing cell, KKU-M213, than that of low ErbB2-expressing ones. In addition, interrupting ErbB2 activity decreased phosphorylation of AKT and p70S6K, but not ERK1/2, in the high ErbB2 expressing CCA cell line. Our data indicated that high ErbB2 expression enhances CCA invasion, motility and proliferation via AKT/p70S6K pathway, indicating the possibility of targeting these molecules for cancer therapy. Citation Information: Clin Cancer Res 2010;16(14 Suppl):A24.