Dicoumarol sensitizes renal cell carcinoma Caki cells to TRAIL-induced apoptosis through down-regulation of Bcl-2, Mcl-1 and c-FLIP in a NQO1-independent manner

In the study, we investigated the effect of dicoumarol, an anti-coagulant agent with the inhibitory activity of NAD(P)H quinone oxidoreductase 1 (NQO1), on TRAIL-induced apoptosis in renal cancer cell. Combined treatment with dicoumarol and TRAIL significantly induced apoptosis in various human renal carcinoma cells including Caki, ACHN, and A498, but not in normal human skin fibroblasts (HSF) and mouse kidney cells (TMCK-1). When we elucidated the relevance of NQO1 in dicoumarol plus TRAIL-mediated apoptosis, both ES936 (a NQO1 inhibitor) and knockdown of NQO1 with siRNA had no effect on TRAIL-mediated apoptosis, suggesting that the stimulating effect of dicoumarol on TRAIL-mediated apoptosis is independent of NQO1 activity. We found that dicoumarol transcriptionally down-regulated Bcl-2 expression via inhibition of NF-κB and CREB activity, whereas it down-regulated Mcl-1 and c-FLIP expression at the post-translational level. Overexpression of Bcl-2, Mcl-1, or c-FLIP overcame the dicoumarol plus TRAIL-induced apoptosis, indicating that down-regualtion of these anti-apoptotic proteins may critically contribute to the sensitizing effect of dicoumarol on TRAIL-mediated apoptosis.