Both rat cholangiocarcinoma cell lines exhibited a prominent band for p185 ErbB2. ErbB2 protein expressed in the BDEneu and C611B cell lines, respectively, was also previously shown

by us to be constitutively phosphorylated at Tyr1248, the major autophosphorylation site in the carboxy-terminal domain of ErbB2 linked to neoplastic transformation. Compared with the rat cholangiocarcinoma cell lines, the human HuCCT1 and TFK1 cholangiocarcinoma cell lines expressed p185 ErbB2 at more moderate levels. However, p170 ErbB1 was observed to be more dominantly expressed in the HuCCT1 and BDEneu cell lines, and at distinctly lower levels in the C611B and TFK1 cell lines (Fig. 1). Results of our fluorescence in situ hybridization analysis of c-erbB2 gene amplification in a cohort of selected archival surgical cases Ixazomib of formalin-fixed, paraffin-embedded human cholangiocarcinomas find more previously reported by us to exhibit strong immunoreactivity for ErbB2 localized to the plasma membrane of the neoplastic cholangiocytes8 are shown in Supporting Fig. 1 and Supporting Table 1. Amplification

of c-erbB2 was detected in 2 of 15 of the analyzed human cholangiocarcinoma cases strongly immunoreactive for plasma membrane ErbB2 phosphorylated at Tyr1248, and was not detected in the human HuCCT1 and TFK1 human cholangiocarcinoma cell lines used in this study. Likewise, we previously reported that the c-neu gene was not amplified in rat C611B cholangiocarcinoma cells overexpressing activated ErbB2.7 Figure 2 depicts the concentration-dependent effects after 72 hours of incubation of single-agent daily treatments with the ErbB1-specific TK inhibitor tryphostin AG1517, and the ErbB2-specific TK inhibitor tryphostin AG879, on suppressing the in vitro cell growth of the two rat and two human cholangiocarcinoma cell lines, respectively, when cultured on plastic substratum. A degree of concordance could be ascertained between ErbB TK inhibitor specificity, expressed levels of ErbB1 or ErB2 receptor protein (Fig. 1), and percent of resultant

cell growth inhibition (Fig. 2). The cholangiocarcinoma cell lines (BDEneu and HuCCT1) expressing the higher levels of ErbB1 protein were more sensitive to the in vitro growth inhibitory effect Thymidine kinase of AG1517 than those cell lines (C611B and TFK1) showing lower levels of ErbB1 protein expression. Conversely, AG879 elicited greater concentration-dependent cell growth inhibition in those cholangiocarcinoma cell lines (C611B and BDEneu) that exhibit more prominent levels of ErbB2 protein expression than in those (TFK1 and HuCCT1) with lower levels. BDEneu cells, expressing prominent bands for p185 ErbB2, as well as for p170 ErbB1, exhibited the highest sensitivity to AG1517. C611B cells, which expressed a prominent protein band for p185 ErbB2 (wild-type) and a weak band for p170 ErbB1, were least sensitive to the in vitro growth inhibitory effect of AG1517.