Clonogenic growth assays were performed in 6-well cell culture plates with 2,000 cells per well, as we previously described.41 (link), 43 (link) All wells were pre-coated with 0.5% agarose as the bottom layer whereas the top layer is consisted of 0.3% agarose and tumor cells. After 6–8 weeks, colonies were stained with crystal violet blue solution (Sigma) for 1 hr and counted under a microscope. Triplicate wells were used for each cell line and three independent experiments were performed.