Selective inhibition of ion transport mechanisms regulating intracellular pH reduces proliferation and induces apoptosis in cholangiocarcinoma cells

Background. Cells within the acidic extracellular environment of solid tumours maintain their intracellular pH through the activity of the Na+/H+ exchanger and the Na+ dependent Cl-/HCO3- exchanger. The inhibition of these mechanisms could therefore inhibit cancer cell growth. Aim. We evaluated the effect of two selective inhibitors of these transporters (cariporide and S3705) on proliferation and apoptosis of human cholangiocarcinoma cells (HUH-28 and Mz-ChA-1 cells) as a function of external pH (7.4 and 6.8). Methods/results. HUH-28 cells incubated for 24 h at external pH 7.4 or 6.8 without inhibitors maintained intracellular pH at physiological level, whereas incubation with cariporide and/or S3705 caused the intracellular pH of cells to drop. Incubation of HUH-28 cells with cariporide and/or S3705 was able to reduce proliferation, evaluated by a colorimetric ELISA method, and to induce apoptosis, evaluated by measuring caspase-3 activity and Annexin-V staining, and these effects were more evident at external pH 6.8. S3705 but not cariporide was able to inhibit serum-induced phosphorylation of ERK1/2, AKT and BAD, intracellular molecules involved in cancer cell proliferation and survival. Similar results were obtained in Mz-ChA-1 cells. Conclusions. (1) Inhibition of intracellular pH regulatory mechanisms by cariporide and S3705 reduces proliferation and induces apoptosis in cholangiocarcinoma cells; and (2) these drugs might have potential therapeutic value against cholangiocarcinoma. (C) 2006 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.