The bromodomain and extra-terminal inhibitor CPI203 enhances the antiproliferative effects of rapamycin on human neuroendocrine tumors

Cell Death Dis. 2014 Oct 9;5(10):e1450. doi: 10.1038/cddis.2014.396.

Abstract

Endogenous c-MYC (MYC) has been reported to be a potential pharmacological target to trigger ubiquitous tumor regression of pancreatic neuroendocrine tumors (PanNETs) and lung tumors. Recently inhibitors of bromodomain and extra-terminal (BET) family proteins have shown antitumor effects through the suppression of MYC in leukemia and lymphoma. In this paper, we investigated the antitumor activity of a BET protein bromodomain inhibitor (BETi) CPI203 as a single agent and in combination with rapamycin in human PanNETs. We found that exposure of human PanNET cell lines to CPI203 led to downregulation of MYC expression, G1 cell cycle arrest and nearly complete inhibition of cell proliferation. In addition, overexpression of MYC suppressed the growth inhibition caused by CPI203 and knockdown of MYC phenocopied the effects of CPI203 treatment. These findings indicate that suppression of MYC contributed to the antiproliferative effects of BETi inhibition in human PanNET cells. Importantly, CPI203 treatment enhanced the antitumor effects of rapamycin in PanNET cells grown in monolayer and in three-dimensional cell cultures, as well as in a human PanNET xenograft model in vivo. Furthermore, the combination treatment attenuated rapamycin-induced AKT activation, a major limitation of rapamycin therapy. Collectively, our data suggest that targeting MYC with a BETi may increase the therapeutic benefits of rapalogs in human PanNET patients. This provides a novel clinical strategy for PanNETs, and possibly for other tumors as well.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetamides / pharmacology*
  • Antineoplastic Agents / pharmacology
  • Apoptosis / drug effects
  • Azepines / pharmacology*
  • Cell Cycle Proteins
  • Cell Line, Tumor
  • Cell Proliferation / drug effects*
  • G1 Phase Cell Cycle Checkpoints / drug effects
  • Humans
  • Neuroendocrine Tumors / genetics
  • Neuroendocrine Tumors / metabolism
  • Neuroendocrine Tumors / physiopathology*
  • Nuclear Proteins / antagonists & inhibitors
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins c-myc / antagonists & inhibitors
  • Proto-Oncogene Proteins c-myc / genetics
  • Proto-Oncogene Proteins c-myc / metabolism
  • RNA-Binding Proteins / antagonists & inhibitors
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism
  • Sirolimus / pharmacology*
  • Transcription Factors / antagonists & inhibitors
  • Transcription Factors / genetics
  • Transcription Factors / metabolism

Substances

  • Acetamides
  • Antineoplastic Agents
  • Azepines
  • BRD2 protein, human
  • BRD3 protein, human
  • BRD4 protein, human
  • CPI203
  • Cell Cycle Proteins
  • Nuclear Proteins
  • Proto-Oncogene Proteins c-myc
  • RNA-Binding Proteins
  • Transcription Factors
  • Protein-Serine-Threonine Kinases
  • Sirolimus