title: SAHA overcomes FLIP-mediated inhibition of SMAC mimetic-induced apoptosis in mesothelioma.
abstract: Malignant pleural mesothelioma (MPM) is a highly pro-inflammatory malignancy that is rapidly fatal and increasing in incidence. Cytokine signaling within the pro-inflammatory tumor microenvironment makes a critical contribution to the development of MPM and its resistance to conventional chemotherapy approaches. SMAC mimetic compounds (SMCs) are a promising class of anticancer drug that are dependent on tumor necrosis factor alpha (TNFα) signaling for their activity. As circulating TNFα expression is significantly elevated in MPM patients, we examined the sensitivity of MPM cell line models to SMCs. Surprisingly, all MPM cell lines assessed were highly resistant to SMCs either alone or when incubated in the presence of clinically relevant levels of TNFα. Further analyses revealed that MPM cells were sensitized to SMC-induced apoptosis by siRNA-mediated downregulation of the caspase 8 inhibitor FLIP, an antiapoptotic protein overexpressed in several cancer types including MPM. We have previously reported that FLIP expression is potently downregulated in MPM cells in response to the histone deacetylase inhibitor (HDACi) Vorinostat (SAHA). In this study, we demonstrate that SAHA sensitizes MPM cells to SMCs in a manner dependent on its ability to downregulate FLIP. Although treatment with SMC in the presence of TNFα promoted interaction between caspase 8 and the necrosis-promoting RIPK1, the cell death induced by combined treatment with SAHA and SMC was apoptotic and mediated by caspase 8. These results indicate that FLIP is a major inhibitor of SMC-mediated apoptosis in MPM, but that this inhibition can be overcome by the HDACi SAHA.
authors.affiliation: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: N
authors.initials: N
authors.lastname: Crawford
authors.forename: I
authors.initials: I
authors.lastname: Stasik
authors.forename: C
authors.initials: C
authors.lastname: Holohan
authors.forename: J
authors.initials: J
authors.lastname: Majkut
authors.forename: M
authors.initials: M
authors.lastname: McGrath
authors.forename: P G
authors.initials: PG
authors.lastname: Johnston
authors.forename: G
authors.initials: G
authors.lastname: Chessari
authors.forename: G A
authors.initials: GA
authors.lastname: Ward
authors.forename: D J
authors.initials: DJ
authors.lastname: Waugh
authors.forename: D A
authors.initials: DA
authors.lastname: Fennell
authors.forename: D B
authors.initials: DB
authors.lastname: Longley
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004789:Enzyme Activation; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D008654:Mesothelioma; D018716:Molecular Mimicry; D010997:Pleural Neoplasms; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000378:metabolism; D000077337:Vorinostat
chemical_list: D000970:Antineoplastic Agents; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D051034:Inhibitor of Apoptosis Proteins; D000077337:Vorinostat; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; D053148:Caspase 3; D053181:Caspase 8; D002945:Cisplatin