Discovery of a series of dihydroquinoxalin-2(1H)-ones as selective BET inhibitors from a dual PLK1-BRD4 inhibitor

Eur J Med Chem. 2017 Sep 8;137:176-195. doi: 10.1016/j.ejmech.2017.05.049. Epub 2017 May 27.


Recent years have seen much effort to discover new chemotypes of BRD4 inhibitors. Interestingly, some kinase inhibitors have been demonstrated to be potent bromodomain inhibitors, especially the PLK1 inhibitor BI-2536 and the JAK2 inhibitor TG101209, which can bind to BRD4 with IC50 values of 0.025 μM and 0.13 μM, respectively. Although the concept of dual inhibition is intriguing, selective BRD4 inhibitors are preferred as they may diminish off-target effects and provide more flexibility in anticancer drug combination therapy. Inspired by BI-2536, we designed and prepared a series of dihydroquinoxalin-2(1H)-one derivatives as selective bromodomain inhibitors. We found compound 54 had slightly higher activity than (+)-JQ1 in the fluorescence anisotropy assay and potent antiproliferative cellular activity in the MM.1S cell line. We have successfully solved the cocrystal structure of 52 in complex with BRD4-BD1, providing a solid structural basis for the binding mode of compounds of this series. Compound 54 exhibited high selectivity over most non-BET subfamily members and did not show bioactivity towards the PLK1 kinase at 10 or 1 μM. From in vivo studies, compound 54 demonstrated a good PK profile, and the results from in vivo pharmacological studies clearly showed the efficacy of 54 in the mouse MM.1S xenograft model.

Keywords: BI-2536; BRD4 inhibitor; Dihydroquinoxalin-2(1H)-one; Kinase.

MeSH terms

  • Animals
  • Antineoplastic Agents / chemical synthesis
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacology*
  • Cell Cycle Proteins / antagonists & inhibitors*
  • Cell Cycle Proteins / metabolism
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Dose-Response Relationship, Drug
  • Drug Discovery*
  • Female
  • Humans
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Molecular Structure
  • Neoplasms, Experimental / drug therapy
  • Neoplasms, Experimental / pathology
  • Nuclear Proteins / antagonists & inhibitors*
  • Nuclear Proteins / metabolism
  • Protein Kinase Inhibitors / chemical synthesis
  • Protein Kinase Inhibitors / chemistry
  • Protein Kinase Inhibitors / pharmacology*
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / antagonists & inhibitors*
  • Proto-Oncogene Proteins / metabolism
  • Quinoxalines / chemical synthesis
  • Quinoxalines / chemistry
  • Quinoxalines / pharmacology*
  • Structure-Activity Relationship
  • Transcription Factors / antagonists & inhibitors*
  • Transcription Factors / metabolism
  • Xenograft Model Antitumor Assays


  • Antineoplastic Agents
  • BRD4 protein, human
  • Cell Cycle Proteins
  • Nuclear Proteins
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins
  • Quinoxalines
  • Transcription Factors
  • dihydroquinoxalinone
  • Protein-Serine-Threonine Kinases
  • polo-like kinase 1