CDK4 and cholangiocarcinoma: To investigate acquired vulnerability in CCA cells that proliferate despite CDK4/6 inhibition, we developed the CDK4/6 inhibitor-resistant CCA cell lines KKU-055R and KKU-213BR from parental KKU-055 (KKU-055wt) and KKU-213B (KKU-213Bwt) cells by culturing the parental cells with the CDK4/6 inhibitor palbociclib using a step-wise dosing protocol (Figure 1A).