ALDH1A3 and cholangiocarcinoma: To investigate the endogenous levels of ALDH1A3 in normal cells and tumor cells, we evaluated the protein expression level of ALDH1A3 in MMNK1, which is an immortalized human normal bile duct cell line, and in several cholangiocarcinoma cell lines—KKU-M055, KKU-100, and KKU-M213 (Figure 1A).