Suberoylanilide hydroxamic acid sensitizes human oral cancer cells to TRAIL-induced apoptosis through increase DR5 expression

Suberoylanilide hydroxamic acid has been shown to selectively induce tumor apoptosis in cell cultures and animal models in several types of cancers and is about as a promising new class of chemotherapeutic agents. In addition, suberoylanilide hydroxamic acid showed synergistic anticancer activity with radiation, cisplatin, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in some cancers. Here, we report suberoylanilide hydroxamic acid also induced apoptosis in human oral cancer cells. Western blotting showed suberoylanilide hydroxamic acid increased Fas, Fas ligand, DR4, and DR5 protein expression and activated caspase-8 and caspase-9. The apoptosis was almost completely inhibited by caspase-8 inhibitor Z-IETD-FMK and attenuated by caspase-9 inhibitor Z-LEHD-FMK. Human recombinant DR5/Fc chimera protein but not Fas/Fc or DR4/Fc significantly inhibited apoptosis induced by suberoylanilide hydroxamic acid. These results suggest that suberoylanilide hydroxamic acid induces apoptosis mainly through activation of DR5/TRAIL death pathway. Furthermore, subtoxic concentrations of suberoylanilide hydroxamic acid sensitize two TRAIL resistant human oral cancer cells, SAS and Ca9-22, to exogenous recombinant TRAIL-induced apoptosis in a p53-independent manner. Combined treatment of suberoylanilide hydroxamic acid and TRAIL may be used as a new promising therapy for oral cancer. [Mol Cancer Ther 2009;8(9):2718-25]