Fluorescence intercalator displacement assay for screening G4 ligands towards a variety of G-quadruplex structures

Biochimie. 2011 Aug;93(8):1288-96. doi: 10.1016/j.biochi.2011.05.011. Epub 2011 May 27.


The potential formation of G-quadruplexes in many regions of the genome makes them an attractive target for drug design. A large number of small molecules synthesized in recent years display an ability to selectively target and stabilize G-quadruplexes. To screen for G4 ligands, we modified a G4-FID (G-quadruplex Fluorescent Intercalator Displacement) assay. This test is based on the displacement of an "on/off" fluorescence probe, Thiazole Orange (TO), from quadruplex or duplex DNA matrices by increasing amounts of a putative ligand. Selectivity measurements can easily be achieved by comparing the ability of the ligand to displace TO from various quadruplex and duplex structures. G4-FID requires neither modified oligonucleotides nor specific equipment and is an isothermal experiment. This test was adapted for high throughput screening onto 96-well plates allowing the comparison of more than twenty different structures. Fifteen different known G4 ligands belonging to different families were tested. Most compounds showed a good G4 vs duplex selectivity but exhibited little, if any, specificity for one quadruplex sequence over the others. The quest for the "perfect" specific G4 ligand is not over yet!

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzothiazoles / chemistry
  • Circular Dichroism
  • Drug Evaluation, Preclinical / methods
  • Fluorescence
  • Fluorescent Dyes / chemistry
  • G-Quadruplexes*
  • High-Throughput Screening Assays
  • Intercalating Agents / chemistry*
  • Ligands
  • Quinolines / chemistry


  • Benzothiazoles
  • Fluorescent Dyes
  • Intercalating Agents
  • Ligands
  • Quinolines
  • thiazole orange