Inhibition of mTOR's Catalytic Site by PKI-587 Is a Promising Therapeutic Option for Gastroenteropancreatic Neuroendocrine Tumor Disease

Neuroendocrinology. 2017;105(1):90-104. doi: 10.1159/000448843. Epub 2016 Aug 12.

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.

Aim: 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.

Conclusion: PI3K/mTOR dual targeting is a promising new therapeutic approach in neuroendocrine tumor disease that should be evaluated in further clinical trials.

Keywords: 4E-BP1; Everolimus; Gastroenteropancreatic neuroendocrine tumors; Gedatolisib; LCC-18 cell line; PKI-587; Signaling; mTOR inhibition.

MeSH terms

  • Antineoplastic Agents / pharmacology
  • Apoptosis / drug effects
  • Catalytic Domain / drug effects*
  • Cell Cycle
  • Cell Line, Tumor
  • Cell Survival
  • Class I Phosphatidylinositol 3-Kinases / metabolism
  • Everolimus / pharmacology
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Intestinal Neoplasms / pathology
  • Membrane Potential, Mitochondrial / drug effects
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Monomeric GTP-Binding Proteins / metabolism
  • Morpholines / pharmacology*
  • Neuroendocrine Tumors / pathology
  • Pancreatic Neoplasms / pathology
  • STAT Transcription Factors / metabolism
  • Stomach Neoplasms / pathology
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • TOR Serine-Threonine Kinases / chemistry*
  • Triazines / pharmacology*

Substances

  • Antineoplastic Agents
  • Morpholines
  • STAT Transcription Factors
  • Triazines
  • gedatolisib
  • Everolimus
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Class I Phosphatidylinositol 3-Kinases
  • Mitogen-Activated Protein Kinase Kinases
  • Monomeric GTP-Binding Proteins

Supplementary concepts

  • Gastro-enteropancreatic neuroendocrine tumor