title: Novel SMAC-mimetics synergistically stimulate melanoma cell death in combination with TRAIL and Bortezomib.
abstract: BACKGROUND
  XIAP (X-linked inhibitor of apoptosis protein) is an anti-apoptotic protein exerting its activity by binding and suppressing caspases. As XIAP is overexpressed in several tumours, in which it apparently contributes to chemoresistance, and because its activity in vivo is antagonised by second mitochondria-derived activator of caspase (SMAC)/direct inhibitor of apoptosis-binding protein with low pI, small molecules mimicking SMAC (so called SMAC-mimetics) can potentially overcome tumour resistance by promoting apoptosis.
  
  
  METHODS
  Three homodimeric compounds were synthesised tethering a monomeric SMAC-mimetic with different linkers and their affinity binding for the baculoviral inhibitor repeats domains of XIAP measured by fluorescent polarisation assay. The apoptotic activity of these molecules, alone or in combination with tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and/or Bortezomib, was tested in melanoma cell lines by MTT viability assays and western blot analysis of activated caspases.
  
  
  RESULTS
  We show that in melanoma cell lines, which are typically resistant to chemotherapeutic agents, XIAP knock-down sensitises cells to TRAIL treatment in vitro, also favouring the accumulation of cleaved caspase-8. We also describe a new series of 4-substituted azabicyclo[5.3.0]alkane monomeric and dimeric SMAC-mimetics that target various members of the IAP family and powerfully synergise at submicromolar concentrations with TRAIL in inducing cell death. Finally, we show that the simultaneous administration of newly developed SMAC-mimetics with Bortezomib potently triggers apoptosis in a melanoma cell line resistant to the combined effect of SMAC-mimetics and TRAIL.
  
  
  CONCLUSIONS
  Hence, the newly developed SMAC-mimetics effectively synergise with TRAIL and Bortezomib in inducing cell death. These findings warrant further preclinical studies in vivo to verify the anticancer effectiveness of the combination of these agents.
authors.affiliation: Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale Tumori, Via G Venezian 1, 20133 Milano, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Lecis
authors.forename: C
authors.initials: C
authors.lastname: Drago
authors.forename: L
authors.initials: L
authors.lastname: Manzoni
authors.forename: P
authors.initials: P
authors.lastname: Seneci
authors.forename: C
authors.initials: C
authors.lastname: Scolastico
authors.forename: E
authors.initials: E
authors.lastname: Mastrangelo
authors.forename: M
authors.initials: M
authors.lastname: Bolognesi
authors.forename: A
authors.initials: A
authors.lastname: Anichini
authors.forename: H
authors.initials: H
authors.lastname: Kashkar
authors.forename: H
authors.initials: H
authors.lastname: Walczak
authors.forename: D
authors.initials: D
authors.lastname: Delia
mesh_terms: D051017:Apoptosis Regulatory Proteins; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D053181:Caspase 8 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004347:Drug Interactions; D004357:Drug Synergism; D055785:Gene Knockdown Techniques; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D008545:Melanoma / Q000188:drug therapy*; D024101:Mitochondrial Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D011719:Pyrazines / Q000494:pharmacology*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000008:administration & dosage / Q000494:pharmacology*; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D001897:Boronic Acids; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D011719:Pyrazines; D053221:TNF-Related Apoptosis-Inducing Ligand; D051636:X-Linked Inhibitor of Apoptosis Protein; D000069286:Bortezomib; D053181:Caspase 8
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