Identification of inhibitors of Tartrate-resistant acid phosphatase (TRAP/ACP5) activity by small-molecule screening

Chem Biol Drug Des. 2018 Jul;92(1):1255-1271. doi: 10.1111/cbdd.13187. Epub 2018 Mar 30.


Tartrate-resistant acid phosphatase (TRAP/ACP5) occurs as two isoforms-TRAP 5a with low enzymatic activity due to a loop interacting with the active site and the more active TRAP isoform 5b generated upon proteolytic cleavage of this loop. TRAP has been implicated in several diseases, including cancer. Thus, this study set out to identify small-molecule inhibitors of TRAP activity. A microplate-based enzymatic assay for TRAP 5b was applied in a screen of 30,315 compounds, resulting in the identification of 90 primary hits. After removal of promiscuous compounds, unwanted groups, and false positives by orthogonal assays and three-concentration validation, the properties of 52 compounds were further investigated to better understand their mechanism of action. Full-concentration-response curves for these compounds were established under different enzyme concentrations and (pre)incubation times to remove compounds with inconsistent results and low potencies. Full-concentration-response curves were also performed for both isoforms, to examine isoform prevalence. Filtering led to six prioritized compounds, representing different clusters. One of these, CBK289001 or (6S)-6-[3-(2H-1,3-benzodioxol-5-yl)-1,2,4-oxadiazol-5-yl]-N-(propan-2-yl)-1H,4H,5H,6H,7H-imidazo[4,5-c]pyridine-5-carboxamide, demonstrated efficacy in a migration assay and IC50 values from 4 to 125 μm. Molecular docking studies and analog testing were performed around CBK289001 to provide openings for further improvement toward more potent blockers of TRAP activity.

Keywords: ACP5; TRAP; compound library screening; enzyme activity; small-molecule inhibitors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Catalytic Domain
  • Cell Line, Tumor
  • Cell Movement / drug effects
  • Enzyme Inhibitors / chemistry*
  • Enzyme Inhibitors / metabolism
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / metabolism
  • Molecular Docking Simulation
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / isolation & purification
  • Small Molecule Libraries / chemistry*
  • Small Molecule Libraries / metabolism
  • Small Molecule Libraries / pharmacology
  • Tartrate-Resistant Acid Phosphatase / antagonists & inhibitors*
  • Tartrate-Resistant Acid Phosphatase / genetics
  • Tartrate-Resistant Acid Phosphatase / metabolism


  • Enzyme Inhibitors
  • Isoenzymes
  • Recombinant Proteins
  • Small Molecule Libraries
  • Tartrate-Resistant Acid Phosphatase