Didox, a ribonucleotide reductase inhibitor, induces apoptosis and inhibits DNA repair in multiple myeloma cells

Br J Haematol. 2006 Oct;135(1):52-61. doi: 10.1111/j.1365-2141.2006.06261.x. Epub 2006 Aug 22.


Ribonucleotide reductase (RR) is the enzyme that catalyses the rate-limiting step in DNA synthesis, the production of deoxynucleotides. RR activity is markedly elevated in tumour tissue and is crucial for cell division. It is therefore an excellent target for cancer chemotherapy. This study examined the anti-myeloma activity of Didox (3,4-Dihydroxybenzohydroxamic acid), a novel RR inhibitor (RRI). Our data showed that Didox induced caspase-dependent multiple myeloma (MM) cell apoptosis. Didox, unlike other RRIs that mainly target the pyrimidine metabolism pathway, targets both purine and pyrimidine metabolism pathways in MM, as demonstrated by transcriptional profiling using the Affymetrix U133A 2.0 gene chip. Specifically, a >or=2-fold downregulation of genes in these anabolic pathways was shown as early as 12 h after exposure to Didox. Furthermore, apoptosis was accompanied by downregulation of bcl family proteins including bcl-2, bcl(xl), and XIAP. Importantly, RR M1 component transcript was also downregulated, associated with decreased protein expression. Genes involved in DNA repair mechanisms, specifically RAD 51 homologue, were also downregulated. As Didox acts on MM cells by inhibiting DNA synthesis and repair, combination studies with melphalan, an agent commonly used in MM, were performed. A strong in vitro synergism was shown, with combination indices of <0.7 as determined by the Chou-Talalay method. These studies therefore provide the preclinical rationale for evaluation of Didox, alone and in combination with DNA-damaging agents, to improve patient outcome in MM.

Publication types

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

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents, Alkylating / pharmacology
  • Apoptosis / drug effects*
  • Caspases / physiology
  • Cell Cycle / drug effects
  • Cell Survival / drug effects
  • DNA Repair / drug effects*
  • DNA Repair / genetics
  • Dose-Response Relationship, Drug
  • Down-Regulation / drug effects
  • Drug Evaluation, Preclinical
  • Drug Synergism
  • Enzyme Inhibitors / pharmacology
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Hydroxamic Acids / pharmacology*
  • Melphalan / pharmacology
  • Multiple Myeloma / genetics
  • Multiple Myeloma / metabolism
  • Multiple Myeloma / pathology*
  • Neoplasm Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Ribonucleotide Reductases / antagonists & inhibitors
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Antineoplastic Agents, Alkylating
  • Enzyme Inhibitors
  • Hydroxamic Acids
  • Neoplasm Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Ribonucleotide Reductases
  • Caspases
  • 3,4-dihydroxybenzohydroxamic acid
  • Melphalan