X-linked inhibitor of apoptosis protein (XIAP) downregulation sensitizes HCT116 cells to recombinant human tumor necrosis factor-related apoptosis-inducing ligand (rhTRAIL)-mediated apoptosis. (A) HCT116 cells were treated with rhTRAIL, sunitinib, and the combination for 24 h. IAPs, FLIP-L, and BCL-2 levels were measured by immunoblotting. (B,C) Knockdown of XIAP and FLIP sensitizes HCT116 cells to rhTRAIL-mediated apoptosis. XIAP and FLIP expression were silenced by shRNA. Cells were treated with 100 ng/mL rhTRAIL for 24 h and apoptosis was measured by propidium iodide fluorescence activated cell sorting (PI-FACS) analysis. Mean ± Standard Deviation (SD), n = 3. * Indicates a significant difference compared to shRNA Control cells, p < 0.05.