SLC22A1 and cholangiocarcinoma: For instance, upregulation of the human equilibrative nucleoside transporter 1 (hENT1) in CCA cells is associated with a better response to gemcitabine in patients with resected CCA58 and aBTC,59 and impaired expression of the organic cation transporter 1 (OCT1) is thought to mediate the poor response to cisplatin and the multikinase inhibitor sorafenib.60,61 By contrast, ATP-binding cassette proteins, such as MDR1, MRP1 and MRP3, which are highly expressed in CCA, are able to export a wide variety of antitumour drugs out of cells, thereby limiting their effect.