Clofarabine targets the large subunit (α) of human ribonucleotide reductase in live cells by assembly into persistent hexamers

Chem Biol. 2012 Jul 27;19(7):799-805. doi: 10.1016/j.chembiol.2012.05.015.


Clofarabine (ClF) is a drug used in the treatment of leukemia. One of its primary targets is human ribonucleotide reductase (hRNR), a dual-subunit, (α(2))(m)(β(2))(n), regulatory enzyme indispensable in de novo dNTP synthesis. We report that, in live mammalian cells, ClF targets hRNR by converting its α-subunit into kinetically stable hexamers. We established mammalian expression platforms that enabled isolation of functional α and characterization of its altered oligomeric associations in response to ClF treatment. Size exclusion chromatography and electron microscopy documented persistence of in-cell-assembled-α(6). Our data validate hRNR as an important target of ClF, provide evidence that in vivo α's quaternary structure can be perturbed by a nonnatural ligand, and suggest small-molecule-promoted, persistent hexamerization as a strategy to modulate hRNR activity. These studies lay foundations for documentation of RNR oligomeric state within a cell.

Publication types

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

MeSH terms

  • Adenine Nucleotides / pharmacology*
  • Arabinonucleosides / pharmacology*
  • Cell Survival
  • Clofarabine
  • Humans
  • Kinetics
  • Liver / cytology*
  • Liver / drug effects*
  • Liver / enzymology
  • Molecular Structure
  • Protein Conformation / drug effects
  • Protein Multimerization / drug effects*
  • Protein Subunits / antagonists & inhibitors*
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Ribonucleotide Reductases / antagonists & inhibitors*
  • Ribonucleotide Reductases / chemistry*
  • Ribonucleotide Reductases / metabolism


  • Adenine Nucleotides
  • Arabinonucleosides
  • Protein Subunits
  • Clofarabine
  • Ribonucleotide Reductases