Highly potent activation of Nrf2 by topical tricyclic bis(cyano enone): implications for protection against UV radiation during thiopurine therapy

Cancer Prev Res (Phila). 2012 Jul;5(7):973-81. doi: 10.1158/1940-6207.CAPR-12-0041. Epub 2012 Jun 1.


Chronic treatment with azathioprine, a highly effective anti-inflammatory and immunosuppressive agent, profoundly increases the risk for development of unusually aggressive cutaneous squamous cell carcinoma. Its ultimate metabolite, 6-thioguanine (6-TG) nucleotide, is incorporated in DNA of skin cells, and upon exposure to UVA radiation, causes oxidative stress, followed by damage of DNA and associated proteins. The acetylenic tricyclic bis(cyano enone) TBE-31 is a strong inhibitor of inflammation and a potent inducer of the Keap1/Nrf2/ARE pathway, which orchestrates the expression of a large network of cytoprotective genes. We now report that long-term (five days per week for four weeks) topical daily applications of small (200 nmol) quantities of TBE-31 cause a robust systemic induction of the Keap1/Nrf2/ARE pathway and decreases the 6-TG incorporation in DNA of skin, blood, and liver of azathioprine-treated mice, indicating extraordinary bioavailability and efficacy. In addition, TBE-31, at nanomolar concentrations, protects cells with 6-TG in their genomic DNA against oxidative stress caused by UVA radiation through induction of the Keap1/Nrf2/ARE pathway. At the same 6-TG DNA levels, Keap1-knockout cells, in which the pathway is constitutively upregulated, are highly resistant to UVA radiation-induced oxidative stress. The protective effects of both the Keap1-knockout genotype and TBE-31 are completely lost in the absence of transcription factor Nrf2. Our findings suggest that compounds of this kind are excellent candidates for mechanism-based chemoprotective agents against conditions in which oxidative stress and inflammation underlie disease pathogenesis. Moreover, their potential skin patch incorporation for transdermal delivery is an exciting possibility.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / physiology
  • Administration, Topical
  • Animals
  • Cells, Cultured
  • Cytoprotection*
  • Cytoskeletal Proteins / physiology
  • Embryo, Mammalian / cytology
  • Embryo, Mammalian / drug effects
  • Embryo, Mammalian / radiation effects
  • Female
  • Fibroblasts / cytology
  • Fibroblasts / drug effects
  • Fibroblasts / radiation effects
  • Kelch-Like ECH-Associated Protein 1
  • Liver / cytology
  • Liver / drug effects*
  • Liver / radiation effects
  • Mice
  • Mice, Hairless
  • Mice, Inbred C57BL
  • Mice, Knockout
  • NF-E2-Related Factor 2 / physiology*
  • Oxidative Stress / drug effects*
  • Oxidative Stress / radiation effects
  • Phenanthrenes / administration & dosage*
  • Phenanthrenes / pharmacology
  • Reactive Oxygen Species / metabolism
  • Skin / cytology
  • Skin / drug effects*
  • Skin / radiation effects
  • Thioguanine / metabolism*
  • Ultraviolet Rays / adverse effects*


  • Adaptor Proteins, Signal Transducing
  • Cytoskeletal Proteins
  • Keap1 protein, mouse
  • Kelch-Like ECH-Associated Protein 1
  • NF-E2-Related Factor 2
  • Nfe2l2 protein, mouse
  • Phenanthrenes
  • Reactive Oxygen Species
  • TBE 31
  • Thioguanine