title: Perifosine-mediated Akt inhibition in neuroendocrine tumor cells: role of specific Akt isoforms.
abstract: The majority of neuroendocrine tumors (NETs) of the gastroenteropancreatic system show aberrant Akt activity. Several inhibitors of the phosphoinositide 3-kinase (PI(3)K)-Akt-mTOR signaling pathway are currently being evaluated in clinical phase II and III studies for the treatment of NETs with promising results. However, the molecular mechanisms and particularly the role of different Akt isoforms in NET signaling are not fully understood. In this study, we examine the effect of Akt inhibition on NET cells of heterogeneous origin. We show that the Akt inhibitor perifosine effectively inhibits Akt phosphorylation and cell viability in human pancreatic (BON1), bronchus (NCI-H727), and midgut (GOT1) NET cells. Perifosine treatment suppressed the phosphorylation of Akt downstream targets such as GSK3α/β, MDM2, and p70S6K and induced apoptosis. To further investigate the role of individual Akt isoforms for NET cell function, we specifically blocked Akt1, Akt2, and Akt3 via siRNA transfection. In contrast to Akt2 knockdown, knockdown of Akt isoforms 1 and 3 decreased phosphorylation levels of GSK3α/β, MDM2, and p70S6K and suppressed NET cell viability and colony-forming capacity. The inhibitory effect of simultaneous downregulation of Akt1 and Akt3 on tumor cell viability was significantly stronger than that caused by downregulation of all Akt isoforms, suggesting a particular role for Akt1 and Akt3 in NET signaling. Akt3 siRNA-induced apoptosis while all three isoform-specific siRNAs impaired BON1 cell invasion. Together, our data demonstrate potent antitumor effects of the pan-Akt inhibitor perifosine on NET cells in vitro and suggest that selective targeting of Akt1 and/or Akt3 might improve the therapeutic potential of Akt inhibition in NET disease.
authors.affiliation: Department of Internal Medicine II, University-Hospital Munich-Grosshadern, Munich, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Zitzmann
authors.forename: George
authors.initials: G
authors.lastname: Vlotides
authors.forename: Stephan
authors.initials: S
authors.lastname: Brand
authors.forename: Harald
authors.initials: H
authors.lastname: Lahm
authors.forename: Gerald
authors.initials: G
authors.lastname: Spöttl
authors.forename: Burkhard
authors.initials: B
authors.lastname: Göke
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Auernhammer
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001984:Bronchial Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation; D006801:Humans; D007414:Intestinal Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D009361:Neoplasm Invasiveness; D018358:Neuroendocrine Tumors / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics
chemical_list: D020033:Protein Isoforms; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D010767:Phosphorylcholine; C105905:perifosine; D051057:Proto-Oncogene Proteins c-akt