Differential TRAIL responsiveness of human prostate adenocarcinoma PC3 and colorectal carcinoma KM12 cells and their respective highly metastatic PC3-MM2 and KM12L4A sublines. PC3 and PC3-MM2 cells (A) or KM12 and KM12L4A cells (B) were treated with the indicated doses of TRAIL for 6 or 8 h, respectively, and the percentage of apoptotic cells in each cell population was determined using Annexin V staining and flow cytometry (left). In addition, PC3 and PC3-MM2 cells or KM12 and KM12L4A cells were treated with the indicated doses of TRAIL for 96 h, and cell survival (%) was determined using the MTT assay (right). Each value represents the mean ± SE of triplicate determinants. *p < 0.05, **p < 0.01, ***p < 0.001.