title: Inhibition of mTOR's Catalytic Site by PKI-587 Is a Promising Therapeutic Option for Gastroenteropancreatic Neuroendocrine Tumor Disease.
abstract: BACKGROUND
  The characteristic clinical heterogeneity and mostly slow-growing behavior of gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) cause problems in finding appropriate treatments. Thus, the current therapy options are not satisfactory. PKI-587 is a highly potent, novel dual inhibitor of PI3K and mTORC1/C2.
  
  
  OBJECTIVE
  We assessed the effects of PKI-587 in different GEP-NEN tumor models, including the poorly differentiated cell line LCC-18, and compared them with those of the established mTORC1 inhibitor everolimus.
  
  
  METHODS
  We treated BON, QGP-1, KRJ-I, and LCC-18 cell lines with increasing concentrations of the inhibitor PKI-587, and compared the results with those of everolimus and DMSO. We assessed the impact of the treatments on viability (WST-1 assay), on apoptotic processes (caspase 3/7 assay, JC-1), and on cell cycle regulation (flow cytometry). We determined alterations in signaling mediators by phosphor-specific Western blot analysis and conducted multiplexed gene expression analysis (nCounter® technology).
  
  
  RESULTS
  In all cell lines, PKI-587 dose-dependently inhibited proliferation, whereas everolimus was less effective. Treatment with PKI-587 led to cell cycle arrest and induction of apoptosis and successfully suppressed activity of the direct mTORC1 target 4E-BP1, a crucial factor for tumor genesis only partially inhibited by everolimus. Gene expression analyses revealed relevant changes of RAS, MAPK, STAT, and PI3K pathway genes after treatment. Treatment-dependent and cell line-characteristic effects on AKT/Rb/E2F signaling regarding cell cycle control and apoptosis are extensively discussed in this paper.
  
  
  CONCLUSIONS
  PI3K/mTOR dual targeting is a promising new therapeutic approach in neuroendocrine tumor disease that should be evaluated in further clinical trials.
authors: Department of Gastroenterology, Infectious Diseases, Rheumatology CC13, Charité - Universitätsmedizin Berlin, Germany.
authors: Helma
authors: H
authors: Freitag
authors: Friederike
authors: F
authors: Christen
authors: Florentine
authors: F
authors: Lewens
authors: Irina
authors: I
authors: Grass
authors: Franziska
authors: F
authors: Briest
authors: Sara
authors: S
authors: Iwaszkiewicz
authors: Britta
authors: B
authors: Siegmund
authors: Patricia
authors: P
authors: Grabowski
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D020134:Catalytic Domain / Q000187:drug effects*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002470:Cell Survival; D058534:Class I Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000068338:Everolimus / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007414:Intestinal Neoplasms / Q000473:pathology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology*; D018358:Neuroendocrine Tumors / Q000473:pathology; D010190:Pancreatic Neoplasms / Q000473:pathology; D050791:STAT Transcription Factors / Q000378:metabolism; D013274:Stomach Neoplasms / Q000473:pathology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D014227:Triazines / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D009025:Morpholines; D050791:STAT Transcription Factors; D014227:Triazines; C549060:gedatolisib; D000068338:Everolimus; C546842:MTOR protein, human; D058534:Class I Phosphatidylinositol 3-Kinases; D058570:TOR Serine-Threonine Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020559:Monomeric GTP-Binding Proteins
keywords: 4E-BP1; Everolimus; Gastroenteropancreatic neuroendocrine tumors; Gedatolisib; LCC-18 cell line; PKI-587; Signaling; mTOR inhibition