title: The novel Raf inhibitor Raf265 decreases Bcl-2 levels and confers TRAIL-sensitivity to neuroendocrine tumour cells.
abstract: The tumour-selective death receptor ligand tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent for the treatment of human cancer. However, many tumours have evolved mechanisms to resist TRAIL-induced apoptosis. A number of studies have demonstrated that aberrant PI(3)K-Akt-mTOR survival signalling may confer TRAIL resistance by altering the balance between pro- and anti-apoptotic proteins. Here, we show that neuroendocrine tumour (NET) cell lines of heterogeneous origin exhibit a range of TRAIL sensitivities and that TRAIL sensitivity correlates with the expression of FLIP(S), caspase-8, and Bcl-2. Neither single mTOR inhibition by everolimus nor dual mTOR/PI(3)K inhibition by NVP-BEZ235 was able to enhance TRAIL susceptibility in any of the tested cell lines. In contrast, dual PI(3)K-Akt-mTOR and Raf-MEK-Erk pathway inhibition by the IGF-1R inhibitor NVP-AEW541 effectively restored TRAIL sensitivity in NCI-H727 bronchus carcinoid cells. Furthermore, blocking Raf-MEK-Erk signalling by the novel Raf inhibitor Raf265 significantly enhanced TRAIL sensitivity in NCI-H727 and CM insulinoma cells. While having no effect on FLIP(S) or caspase-8 expression, Raf265 strongly decreased Bcl-2 levels in those cell lines susceptible to its TRAIL-sensitizing action. Taken together, our findings suggest that combinations of Raf-MEK-Erk pathway inhibitors and TRAIL might offer a novel therapeutic strategy in NET disease.
authors.affiliation: Department of Internal Medicine II, University-Hospital Munich-Grosshadern, University of Munich, Marchioninistr.15, 81377 Munich, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Zitzmann
authors.forename: Enrico
authors.initials: E
authors.lastname: de Toni
authors.forename: Janina
authors.initials: J
authors.lastname: von Rüden
authors.forename: Stephan
authors.initials: S
authors.lastname: Brand
authors.forename: Burkhard
authors.initials: B
authors.lastname: Göke
authors.forename: Rüdiger P
authors.initials: RP
authors.lastname: Laubender
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Auernhammer
mesh_terms: D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000068338:Everolimus; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D018358:Neuroendocrine Tumors / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D004791:Enzyme Inhibitors; D007093:Imidazoles; D000081082:Phosphoinositide-3 Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011725:Pyridines; D011804:Quinolines; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C559019:RAF265; D000068338:Everolimus; C546842:MTOR protein, human; D017526:Receptor, IGF Type 1; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D058570:TOR Serine-Threonine Kinases; D053181:Caspase 8; C531198:dactolisib; D020123:Sirolimus