Abstract 3489: Profound cytotoxicity of the histone deacetylase inhibitor SAHA (Suberoylanilide Hydroxamic Acid) and TRAIL (Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand) combination in malignant pleural mesothelioma
Authors: Santos Javier V. , Vara Alex , Thomas Craig , Wangpaichitr Medhi , You Min , Savaraj Niramol , Nguyen Dao M. 
Published: February 2011

Abstract
Background: The majority of solid malignancies including malignant pleural mesothelioma (MPM) are refractory to TRAIL-mediated cytotoxicity. SAHA has mild antitumor activity against MPM in a phase I clinical trial. This study is designed to evaluate the cytotoxicity of the SAHA+TRAIL combination on a panel of 10 MPM cells and two normal cells (primary fibroblasts and endothelial cells).
Material and methods: Cytotoxicity and apoptosis mediated by TRAIL (0 - 100 ng/ml), SAHA (0.5 - 5.0 microM) or concurrent SAHA+TRAIL combinations are evaluated by MTT assay and AnnexinV-FITC. NF-kB transcriptional activity is measured by luciferase-based reporter plasmid and lucinometer.
Results: MPM cells exhibit a wide range of intrinsic susceptibility to TRAIL (2/10 sensitive: IC50 &lt;50 ng/ml, 5/10 mildly sensitive: IC50: 150 to 2500 ng/ml, 3/10 resistant: IC50: infinity). Profound enhancement of cytotoxicity is observed following treatment with SAHA+TRAIL combinations in 7 MPM cells that exhibit some degrees of TRAIL sensitivity as indicated by 2-fold to &gt;100-fold reduction of TRAIL IC50's. TRAIL-refractory cells H2373, Gats and H2052 are resistant to SAHA+TRAIL combinations. Supra-additive induction of treatment-specific apoptosis is observed in representative Gard and H513 MPM cells treated with this combination (Gard: TRAIL(20ng/ml): 18±5%, SAHA (1 microM): 3±2%, SAHA+TRAIL: 68±5%; H513: TRAIL: 30±5%, SAHA: 2±2%; SAHA+TRAIL: 80±4%, n=3). Combination-induced cytotoxicity and apoptosis is equally abrogated by either selective caspase 8 or caspase 9 inhibitor and thus implicating the essential role of the mitochondria-driven death signaling cascade. SAHA-dependent strong activation of NF-kB is completely abrogated by TRAIL and this is paralleled with caspase 8-mediated cleavage of RIP (receptor-interacting protein) to form the NF-kB dominant negative cRIP fragment in combination-treated cells. Induction of mild TRAIL sensitivity by the SMAC-mimetic drug SM164 in TRAIL-resistant cells H2373 or Gats greatly sensitizes them to SAHA+TRAIL cytotoxic effects. Most importantly, SAHA+TRAIL combinations with or without SM164 are not toxic to normal cells.
Conclusion: SAHA+TRAIL combination induces profound cytotocidal effect in MPM cells that is dependent on intrinsic death signaling pathway, RIP processing and modulation of NF-kB transcriptional activity. Ongoing investigations are undertaken to further elucidate the molecular basis of this salutary drug combination effects and to develop molecular strategy aiming at promoting SAHA+TRAIL cytotoxicity in TRAIL-resistant MPM cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3489.