The histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA, vorinostat) is undergoing clinical trials as an antitumor drug and has received regulatory approval for cancer treatment. Here, we show that pre-treatment of human breast cancer cells with SAHA makes them susceptible to apoptosis induced by TRAIL (tumour necrosis factor-related apoptosis-inducing ligand). The apoptosis of breast tumour cells induced by TRAIL is blocked at the level of apical activation of caspase-8 and SAHA enhances the TRAIL-induced processing of procaspase-8. Consequently, a TRAIL associated pathway of apoptosis operated via mitochondria is activated in cells treated with SAHA. Interestingly, degradation of cellular FLICE-inhibitory proteins (cFLIPL and cFLIPS) by an ubiquitin/proteasome-dependent Itch/AIP4-independent mechanism is observed upon exposure to SAHA. Targeting cFLIPL directly with siRNA oligonucleotides also sensitizes human breast tumour cells to TRAIL-induced apoptosis. Furthermore, cFLIPL over-expression significantly inhibits the apoptosis elicited through the combined effects of SAHA and TRAIL. Together, these results indicate that SAHA sensitizes breast cancer cells to TRAIL-induced apoptosis by facilitating the activation of early events in the apoptotic TRAIL pathway. Therefore, the combination of TRAIL and SAHA may represent a therapeutic tool to combat breast tumours.

This work was supported by grants from Ministerio de Educación y Ciencia (SAF2006-00633 and SAF2009-07163), Red Temática de Investigación Cooperativa en Cáncer (RTICC: RD06/0020/0068) and Junta de Andalucía (CTS-211 and CVI-4497) to AL-R. RY was supported by contracts from Instituto de Salud Carlos III and Ministerio de Ciencia e Innovación.

Peer reviewed

Peer Reviewed