1058 INSIGHTS ON PATHWAYS OF THIAZOLIDINEDIONES -PROMOTED APOPTOSIS IN “TUMOR NECROSIS FACTOR-RELATED APOPTOSIS INDUCING LIGAND”-RESISTANT MALIGNANT UROTHELIAL CELLS
INTRODUCTION AND OBJECTIVES
thiazolidinediones (TZD), including rosiglitazone, troglitazone, are insulin-sensitizing drugs and high-affinity ligands for the Peroxisome Proliferator-Activated Receptor γ (PPARγ). Apart from their antidiabetic activity, these molecules possess antitumor properties. We investigated their potential apoptotic effects on bladder cancer cells and studied whether they could sensitize “Tumor necrosis factor related apoptosis inducing ligand” (TRAIL)-resistant malignant urothelial cells to TRAIL-induced apoptosis.
METHODS
T24 bladder cancer cells, derived from an undifferentiated grade III carcinoma, were stimulated 24h with increasing concentrations of TZD. DNA fragmentation and cell cycle analysis were determined by flow cytometry. Extrinsic and intrinsic apoptotic pathways as well as caspases cascade were studied by western-blotting analyses. The level of TRAIL in conditioned media was evaluated by ELISA.
RESULTS
rosiglitazone induced G0/G1 phase cell cycle arrest without leading to cell death.Only troglitazone triggered apoptosis via both extrinsic and intrinsing pathways. Interestingly, rosiglitazone let TRAIL-refractory high grade T24 cells to respond to TRAIL. Thiazolidinediones acted through PPARγ activation-independent mechanisms. The underlying mechanisms involved for the first time in cancer cells the up-regulation of soluble and/or membrane-bound TRAIL. This was associated with increased cell surface death receptor 5 expression and ”cellular Fas/FasL-associated death domain protein-like inhibitory protein‘(c-FLIP) and survivin down-regulation, mediated in part through proteasome-dependent degradation in troglitazone-promoted cell death.
CONCLUSIONS
The combination of rosiglitazone and TRAIL could be clinically relevant as chemopreventive or therapeutic agents for the treatment of TRAIL-resistant high grade urothelial cancers.