Synergistic in-vitro effects of combining an antiglycolytic, 3-bromopyruvate, and a bromodomain-4 inhibitor on U937 myeloid leukemia cells

Anticancer Drugs. 2018 Jun;29(5):429-439. doi: 10.1097/CAD.0000000000000613.

Abstract

This project investigated the in-vitro effects of a glycolytic inhibitor, 3-bromopyruvate (3-BrP), in combination with and a new in silico-designed inhibitor of the bromodomain-4 (BRD-4) protein, ITH-47, on the U937 acute myeloid leukemia cell line. 3-BrP is an agent that targets the altered metabolism of cancer cells by interfering with glucose metabolism in the glycolytic pathway. ITH-47 is an acetyl-lysine inhibitor that displaces bromdomain 4 proteins from chromatin by competitively binding to the acetyl-lysine recognition pocket of this bromodomain and extraterminal (BET) BRD protein, thereby preventing transcription of cancer-associated genes and further cell growth. Cell growth studies determined the IC50 after 48 h exposure for 3-BrP and ITH-47 to be 6 and 2 μmol/l, respectively. When combined, 2.4 and 1 μmol/l of 3-BrP and ITH-47, respectively, inhibited 50% of the cell population, yielding a synergistic combination index of 0.9. Subsequent mechanistic studies showed that the IC50 concentrations of ITH-47 and 3-BrP and the combination increased observable apoptotic bodies and cell shrinkage in U937 cells treated for 48 h. Cell cycle analysis showed an increase in the sub-G1 fraction in all treated cells, suggesting that cell death was increased in the treated samples. Annexin-V-FITC apoptosis analysis showed a statistically significant increase in the number of cells in early and late apoptosis, indicating that cell death occurred through apoptosis and not necrosis. Only U937 cells exposed to ITH-47 showed a decrease in mitochondrial membrane potential compared with the vehicle control. Reactive oxygen species production was decreased in all treated samples. ITH-47-exposed cells showed a decrease in c-Myc, Bcl-2, and p53 gene expressions. 3-BrP-treated cells showed an increase in c-myc and p53 gene expressions. The combination of ITH-47 and 3-BrP lead to downregulation of c-myc and Bcl-2 genes. ITH-47 exposure conditions yielded a marked decrease in c-myc protein levels as well as a decrease in Ser70 phosphorylated Bcl-2. Analysis of 3-BrP and the combination of ITH-47 and 3-BrP test conditions indicated an increase in p53 protein levels. This novel study is the first to investigate the in-vitro synergistic therapeutic effect of ITH-47 and 3-BrP. The current study contributes toward unraveling the in-vitro molecular mechanisms and signal transduction associated with a novel combination of BRD inhibitors and antiglycolytic agents, providing a basis for further research on these combinations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • Apoptosis / drug effects
  • Azepines / administration & dosage
  • Azepines / pharmacology*
  • Cell Cycle Proteins
  • Cell Proliferation / drug effects
  • Drug Synergism
  • Gene Expression Regulation, Neoplastic / drug effects
  • Glycolysis / drug effects
  • Humans
  • Membrane Potential, Mitochondrial / drug effects
  • Molecular Docking Simulation
  • Nuclear Proteins / antagonists & inhibitors*
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / metabolism
  • Phosphorylation / drug effects
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Proto-Oncogene Proteins c-myc / genetics
  • Proto-Oncogene Proteins c-myc / metabolism
  • Pyruvates / administration & dosage
  • Pyruvates / pharmacology*
  • Serine / metabolism
  • Transcription Factors / antagonists & inhibitors*
  • Transcription Factors / chemistry
  • Transcription Factors / metabolism
  • Triazoles / administration & dosage
  • Triazoles / pharmacology*
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • U937 Cells

Substances

  • (+)-JQ1 compound
  • Azepines
  • BRD4 protein, human
  • Cell Cycle Proteins
  • MYC protein, human
  • Nuclear Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Proto-Oncogene Proteins c-myc
  • Pyruvates
  • TP53 protein, human
  • Transcription Factors
  • Triazoles
  • Tumor Suppressor Protein p53
  • Serine
  • bromopyruvate