2.5 Transwell migration/invasion assay
The migration and invasion abilities of pancreatic cancer cells were determined by using Transwell Boyden Chambers with 8-μm pores (Corning Inc., Lowell, MA, USA). The upper Transwell chambers were uncoated for cell migration assay or pre-coated with 50 µL of Matrigel (1:4 mixed with PBS; BD Biosciences, San Jose, CA, USA) for cell invasion assay. The cells were precultured in serum-free medium for 12 h. Next, the cells were harvested and resuspended in serum-free medium containing serial concentrations of TA, and then plated on the upper chambers at an appropriate density. At the same time, complete medium containing 10% FBS was added to the lower chambers. After an incubation of 48 h, the tumor cells on the upper side of the filters were wiped off with cotton swabs. The tumor cells on the lower surface of the membrane were then fixed with 4% paraformaldehyde and stained with 0.1% crystal violet. The images of stained tumor cells were acquired using an inverted microscope (Olympus, Tokyo, Japan).