Down-regulation of RIP expression by 17-dimethylaminoethylamino-17-demethoxygeldanamycin promotes TRAIL-induced apoptosis in breast tumor cells.

The Hsp90 inhibitor 17DMAG (17-dimethylaminoethylamino-17-demethoxygeldanamycin) is undergoing clinical trials as an antitumor drug. We show here that treatment of human breast cancer cells with 17DMAG facilitates tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Down-regulation of receptor interacting protein (RIP1) is observed upon 17DMAG treatment concomitantly with inhibition of IkappaBalpha phosphorylation. Interestingly, RNAi-mediated knockdown of RIP1 expression is sufficient to sensitize human breast tumor cells to TRAIL-induced apoptosis through a NF-kappaB-independent, mitochondria-operated pathway. Our results indicate that RIP1 is important in maintaining resistance to TRAIL-induced apoptosis in breast tumor cells and highlight the potential therapeutic benefit of the combination of Hsp90 inhibitors and TRAIL against breast tumor cells. Copyright 2009 Elsevier Ireland Ltd. All rights reserved.