title: Targeting aberrant PI3K/Akt activation by PI103 restores sensitivity to TRAIL-induced apoptosis in neuroblastoma.
abstract: OBJECTIVE
  Because we recently identified Akt activation as a novel poor prognostic indicator in neuroblastoma, we investigated whether phosphoinositide 3'-kinase (PI3K) inhibition sensitizes neuroblastoma cells for TRAIL-induced apoptosis.
  
  
  METHODS
  The effect of pharmacological or genetic inhibition of PI3K or mTOR was analyzed on apoptosis induction, clonogenic survival, and activation of apoptosis signaling pathways in vitro and in a neuroblastoma in vivo model. The functional relevance of individual Bcl-2 family proteins was examined by knockdown or overexpression experiments.
  
  
  RESULTS
  The PI3K inhibitor PI103 cooperates with TRAIL to synergistically induce apoptosis (combination index < 0.1), to suppress clonogenic survival, and to reduce tumor growth in a neuroblastoma in vivo model. Similarly, genetic silencing of PI3K significantly increases TRAIL-mediated apoptosis, whereas genetic or pharmacological blockage of mTOR fails to potentiate TRAIL-induced apoptosis. Combined treatment with PI103 and TRAIL enhances cleavage of Bid and the insertion of tBid into mitochondrial membranes, and reduces phosphorylation of Bim(EL). Additionally, PI103 decreases expression of Mcl-1, XIAP, and cFLIP, thereby promoting Bax/Bak activation, mitochondrial perturbations, and caspase-dependent apoptosis. Knockdown of Bid or Noxa or overexpression of Bcl-2 rescues cells from PI103- and TRAIL-induced apoptosis, whereas Mcl-1 silencing potentiates apoptosis. Bcl-2 overexpression also inhibits cleavage of caspase-3, caspase-8, and Bid pointing to a mitochondria-driven feedback amplification loop.
  
  
  CONCLUSIONS
  PI103 primes neuroblastoma cells for TRAIL-induced apoptosis by shifting the balance toward proapoptotic Bcl-2 family members and increased mitochondrial apoptosis. Thus, PI3K inhibitors represent a novel promising approach to enhance the efficacy of TRAIL-based treatment protocols in neuroblastoma.
authors.affiliation: University Children's Hospital, Ulm and Institute for Experimental Cancer Research in Pediatrics, Goethe-University, Frankfurt, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Opel
authors.forename: Ivonne
authors.initials: I
authors.lastname: Naumann
authors.forename: Maxi
authors.initials: M
authors.lastname: Schneider
authors.forename: Daniela
authors.initials: D
authors.lastname: Bertele
authors.forename: Klaus-Michael
authors.initials: KM
authors.lastname: Debatin
authors.forename: Simone
authors.initials: S
authors.lastname: Fulda
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects*; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000473:pathology; D002642:Chick Embryo; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004357:Drug Synergism; D004789:Enzyme Activation / Q000235:genetics; D005663:Furans / Q000008:administration & dosage* / Q000494:pharmacology; D006801:Humans; D051379:Mice; D058990:Molecular Targeted Therapy; D009154:Mutation / Q000502:physiology; D009447:Neuroblastoma / Q000188:drug therapy* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011725:Pyridines / Q000008:administration & dosage* / Q000494:pharmacology; D011743:Pyrimidines / Q000008:administration & dosage* / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000008:administration & dosage* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D005663:Furans; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D011725:Pyridines; D011743:Pyrimidines; D053221:TNF-Related Apoptosis-Inducing Ligand; C522973:PI103