2.4 Colony formation assay
The clonogenic growth of pancreatic cancer cells was evaluated by plate colony formation assay. The cells were plated into six-well plates at 300-500 cells per well (depending on the cell lines used). After incubation for 24 h, the cells were treated with various concentrations of TA. The plates were incubated at 37 °C in a humidified incubator containing 5% CO2 for 7 days. The colonies were washed twice with cold PBS and fixed with 4% paraformaldehyde, then stained with 0.1% crystal violet. The images of stained colonies were captured using a digital camera (Nikon, Tokyo, Japan).