Roles of volume-sensitive Cl^- channel in cisplatin-induced apoptosis in human epidermoid cancer cells

The anti-cancer drug cisplatin induces apoptosis by damaging DNA. Since a stilbene-derivative blocker of Cl^-/HCO₃^- exchangers and Cl^- channels, SITS, is known to induce cisplatin resistance in a manner independent of intracellular pH and extracellular HCO₃^-, we investigated the relation between cisplatin-induced apoptosis and Cl^- channel activity in human adenocarcinoma KB cells. A stilbene derivative, DIDS, reduced cisplatin-induced caspase-3 activation and cell death, which were detected over 18 h after treatment with cisplatin. DIDS was also found to reduce sensitivity of KB cells to 5-day exposure to cisplatin. Whole-cell patch-clamp recordings showed that KB cells functionally express volume-sensitive outwardly rectifying (VSOR) Cl ^- channels which are activated by osmotic cell swelling and sensitive to DIDS. Pretreatment of the cells with cisplatin for 12 h augmented the magnitude of VSOR Cl^- current. Thus, it is concluded that cisplatin-induced cytotoxicity in KB cells is associated with augmented activity of a DIDS-sensitive VSOR Cl^- channel and that blockade of this channel is, at least in part, responsible for cisplatin resistance induced by a stilbene derivative.