Quercetin enhances TRAIL-mediated apoptosis in colon cancer cells by inducing the accumulation of death receptors in lipid rafts

Cytokines such as tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) can induce apoptosis in colon cancer cells through engagement of death receptors. Nevertheless, evading apoptosis induced by anticancer drugs characterizes many types of cancers. This results in the need for combination therapy. In this study, we have investigated whether the flavonoid quercetin could sensitize human colon adenocarcinoma cell lines to TRAIL-induced apoptosis. We report that quercetin enhanced TRAIL-induced apoptosis by causing the redistribution of DR4 and DR5 into lipid rafts. Nystatin, a cholesterol-sequestering agent, prevented quercetin-induced clustering of death receptors and sensitization to TRAIL-induced apoptosis in colon adenocarcinoma cells. In addition, our experiments show that quercetin, in combination with TRAIL, triggered the mitochondrial-dependent death pathway, as shown by Bid cleavage and the release of cytochrome c to the cytosol. Together, our findings propose that quercetin, through its ability to redistribute death receptors at the cell surface, facilitates death-inducing signaling complex formation and activation of caspases in response to death receptor stimulation. Based on these results, this study provides a challenging approach to enhance the efficiency of TRAIL-based therapies. [Mol Cancer Ther 2007;6(9):2591–9]