The H4 histamine receptor agonist, clobenpropit, suppresses human cholangiocarcinoma progression by disruption of epithelial mesenchymal transition and tumor metastasis

Cholangiocarcinoma (CCA) is a biliary cancer arising from damaged bile ducts. Epithelial-mesenchymal transition (EMT) occurs as epithelial cells begin to resemble mesenchymal cells leading to increased invasion potential as the extracellular matrix (ECM) degrades. Histamine exerts its effects by way of four receptors (H1-H4 HRs). Clobenpropit, a potent H4HR agonist, inhibits mammary adenocarcinoma growth. We have shown that (1) cholangiocytes and CCA cells express H1-H4 HRs and (2) the H3HR decreases CCA proliferation. We evaluated the effects of clobenpropit on CCA proliferation, invasion, EMT phenotypes, and ECM degradation. In vitro, we used CCA cell lines to study proliferation, signaling pathways, and the morphological invasive potential. Gene and protein expression of the hepatobiliary epithelial markers CK-7, CK-8, and CK-19, the focal contact protein paxillin, and the mesenchymal markers fibronectin, s100A4, and vimentin were evaluated. Cell invasion across an ECM layer was quantitated and matrix metalloproteinase-1, -2, -3, -9, and -11 gene and protein expression was examined. Evaluation of the specific role of H4HR was performed by genetic knockdown of the H3HR and overexpression of H4HR. Proliferation was evaluated by proliferating cellular nuclear antigen immunoblotting. In vivo, xenograft tumors were treated with either vehicle or clobenpropit for 39 days. Tumor volume was recorded every other day. Clobenpropit significantly decreased CCA proliferation by way of a Ca ²⁺-dependent pathway and altered morphological development and invasion. Loss of H3HR expression or overexpression of H4HR significantly decreased CCA proliferation. In vivo, clobenpropit inhibited xenograft tumor growth compared with controls. Conclusion: Modulation of H4HR by clobenpropit disrupts EMT processes, ECM breakdown, and invasion potential and decreases tumor growth. Interruption of tumorigenesis and invasion by histamine may add to therapeutic advances for CCAs.