title: Oral azathioprine leads to higher incorporation of 6-thioguanine in DNA of skin than liver: the protective role of the Keap1/Nrf2/ARE pathway.
abstract: Azathioprine is a widely used anti-inflammatory, immunosuppressive, and anticancer agent. However, chronic treatment with this drug is associated with a profoundly increased risk (in certain cases by more than 100-fold) of developing squamous cell carcinoma of the skin. Incorporation of its ultimate metabolite, thio-dGTP, in DNA results in partial substitution of guanine with 6-thioguanine which, combined with exposure to UVA radiation, creates a source of synergistic mutagenic damage to DNA. We now report that oral treatment with azathioprine leads to a much greater incorporation of 6-thioguanine in DNA of mouse skin than liver. These higher levels of 6-thioguanine, together with the fact that the skin is constantly exposed to UV radiation from the sun, may be responsible, at least in part, for the increased susceptibility of this organ to tumor development. Genetic upregulation of the Keap1/Nrf2/ARE pathway, a major cellular regulator of the expression of a network of cytoprotective genes, reduces the incorporation of 6-thioguanine in DNA of both skin and liver following treatment with azathioprine. Similarly, pharmacologic activation of the pathway by the potent inducer sulforaphane results in lower 6-thioguanine incorporation in DNA and protects 6-thioguanine-treated cells against oxidative stress following exposure to UVA radiation. Protection is accompanied by increased levels of glutathione and induction of multidrug resistance-associated protein 4, an organic anion efflux pump that also exports nucleoside monophosphate analogues. Our findings suggest that activation of the Keap1/Nrf2/ARE pathway could reduce the risk for skin cancer in patients receiving long-term azathioprine therapy.
authors.affiliation: Biomedical Research Institute, University of Dundee, Scotland, United Kingdom.
authors.forename: Sukirti
authors.initials: S
authors.lastname: Kalra
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Elena V
authors.initials: EV
authors.lastname: Knatko
authors.forename: Stewart
authors.initials: S
authors.lastname: Finlayson
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Albena T
authors.initials: AT
authors.lastname: Dinkova-Kostova
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000284:Administration, Oral; D000818:Animals; D001379:Azathioprine / Q000008:administration & dosage / Q000494:pharmacology*; D002478:Cells, Cultured; D019610:Cytoprotection / Q000187:drug effects*; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D008099:Liver / Q000187:drug effects* / Q000473:pathology / Q000528:radiation effects; D008114:Liver Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology; D008285:Major Histocompatibility Complex; D051379:Mice; D008810:Mice, Inbred C57BL; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D018384:Oxidative Stress; D011506:Proteins / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000528:radiation effects; D012867:Skin / Q000187:drug effects* / Q000473:pathology / Q000528:radiation effects; D013866:Thioguanine / Q000378:metabolism*; D014466:Ultraviolet Rays; D033921:Vesicular Transport Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D011506:Proteins; D017382:Reactive Oxygen Species; D033921:Vesicular Transport Proteins; C485462:Vps52 protein, mouse; D004247:DNA; D013866:Thioguanine; D001379:Azathioprine