Immunoblot demonstrating the effect of quercetin on tumor necrosis factor–related apoptosis-inducing ligand (TRAIL)-induced proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), caspase-7/-8/-9, and Bid in U87-MG, A172, U251, LN229, and U373 cells. (A) U87-MG, (B) A172, (C) U251, (D) LN229, and (E) U373 cells were treated for 8 h with quercetin (200 μM) in the presence or absence of TRAIL (100 ng/ml). TR100, TRAIL 100 ng/ml; Q200, quercetin 200 μM; CF, cleaved fragment. Immunoblots are representative of at least three independent experiments.