SAHA/TRAIL combination induces detachment and anoikis of MDA-MB231and MCF-7 breast cancer cells

SAHA, an inhibitor of histone deacetylase activity, has been shown to sensitize tumor cells to apoptosisinduced by TRAIL, a member of TNF-family. In this paper we investigated the effect of SAHA/TRAILcombination in two breast cancer cell lines, the ERa positive MCF-7 and the ERa negative MDA-MB231.Treatment of MDA-MB231 and MCF-7 cells with SAHA in combination with TRAIL caused detachment ofcells followed by anoikis, a form of apoptosis which occurs after cell detachment, while treatment withSAHA or TRAIL alone did not produce these effects. The effects were more evident in MDA-MB231 cells,which were chosen for ascertaining the mechanism of SAHA/TRAIL action. Our results show that SAHAdecreased the level of c-FLIP, thus favouring the interaction of TRAIL with the specific death receptorsDR4 and DR5 and the consequent activation of caspase-8. These effects increased when the cells weretreated with SAHA/TRAIL combination. Because z-IEDT-fmk, an inhibitor of caspase-8, prevented boththe cleavage of the focal adhesion-kinase FAK and cell detachment, we suggest that activation of caspase-8 can be responsible for both the decrement of FAK and the consequent cell detachment. In addition,treatment with SAHA/TRAIL combination caused dissipation of DJm, activation of caspase-3 anddecrement of both phospho-EGFR and phospho-ERK1/2, a kinase which is involved in the phosphorylationof BimEL. Therefore, co-treatment also induced decrement of phospho-BimEL and a concomitantincrease in the dephosphorylated form of BimEL, which plays an important role in the induction ofanoikis.Our findings suggest the potential application of SAHA in combination with TRAIL in clinical trials forbreast cancer.