Abstract. Cimetidine is a histamine type-2 (H 2 ) receptor antagonist that has been demonstrated to have antitumor effects on various types of malignancy. However, its effect on cholangiocarcinoma (CCA), a chemotherapy-resistant bile duct tumor, has yet to be investigated. In the present study, the antitumor activity of cimetidine in vitro and in vivo was evaluated. A methylthiotetrazole assay revealed that the proliferation of certain CCA cell lines was inhibited by cimetidine, which induced the caspase-dependent apoptosis of CCA cells via suppression of the protein kinase B signaling pathway. Suppression of Akt phosphorylation, caspase-3, -8 and -9 activation, phosphotidylserine exposure determined by Annexin V binding assay and the presence of a sub-G1 population were demonstrated by western blotting and flow cytometry analysis. In a CCA xenograft mouse model cimetidine inhibited the growth of CCA cells without observable adverse effects. These results suggest that cimetidine has the potential to be an effective antitumor agent for the treatment of CCA.
IntroductionCholangiocarcinoma (CCA) is a highly lethal type of cancer that arises from the bile duct epithelium (1). Although CCA is a rare form of cancer, the global incidence of CCA is increasing, particularly that of the intrahepatic subtype (2). However, the highest incidence of CCA has been reported in the northeast of Thailand where the carcinogenic liver fluke Opisthorchis viverrini is considered a causative agent (3). The early diagnosis of CCA is challenging as patients with CCA typically have non-specific symptoms, and CCA tumor markers are yet to be developed (4). The majority of patients with CCA present with a late-stage disease that is frequently inoperable, and the outcomes of conventional chemotherapy or radiotherapy are unsatisfactory (5). Therefore, a unique approach to developing novel targeting therapies is required to reduce CCA-associated mortality.Cimetidine is an antagonist of histamine type-2 (H 2 ) receptors and is indicated for patients with gastro-esophageal reflux diseases, peptic ulcers or hypersecretory conditions (6,7). The effect of cimetidine on the survival of patients has been reported in various types of cancer, including gastric cancer (8), colorectal cancer (6,9,10), renal cell carcinoma (11), malignant melanoma (12) and glioblastoma (13). Numerous molecular mechanisms underlying the anticancer activities of cimetidine have been revealed, including the inhibition of cell proliferation by blocking the cell growth-promoting effect of histamine (14), the inhibition of tumor angiogenesis (15), the stimulation host immune responses (16) and the suppression of cell adhesion (17). However, the effects of cimetidine in CCA have yet to be demonstrated.In the present study, the anti-CCA activity of cimetidine was examined and the antiproliferative and apoptosis-inducing effects of cimetidine were determined. This was revealed to be partially due to the suppression of protein kinase B (Akt) phosphorylation. A CCA transplant xenogra...