title: Combination of azathioprine and UVA irradiation is a major source of cellular 8-oxo-7,8-dihydro-2'-deoxyguanosine.
abstract: Thiopurine antimetabolites, such as azathioprine (Aza) and 6-thioguanine (6-TG), are widely used in the treatment of cancer, inflammatory conditions and organ transplantation patients. Recent work has shown that cells treated with 6-TG and UVA generate ROS, with implied oxidatively generated modification of DNA. In a study of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in renal transplant patients, we provided the first in vivo evidence linking Aza and oxidatively damaged DNA. Using the hOGG1 comet assay, we herein demonstrate high levels of 8-oxodG and alkali-labile sites (ALS) in cells treated with biologically relevant doses of 6-TG, or Aza, plus UVA. This damage was induced dose-dependently. Surprisingly, given the involvement of 6-TG incorporation into DNA in its therapeutic effect, significant amounts of 8-oxodG and ALS were induced in quiescent cells, although less than in proliferating cells. We speculate that some activity of hOGG1 towards unirradiated, 6-TG treated cells, implies possible recognition of 6-TG or derivatives thereof. This is the first report to conclusively demonstrate oxidatively damaged DNA in cells treated with thiopurines and UVA. These data indicate that Aza-derived oxidative stress will occur in the skin of patients on Aza, following even low level UVA exposure. This is a probable contributor to the increased risk of non-melanoma skin cancer in these patients. However, as oxidative stress is unlikely to be involved in the therapeutic effects of Aza, intercepting ROS production in the skin could be a viable route by which this side effect may be minimised.
authors.affiliation: Radiation and Oxidative Stress Group, Department of Cancer Studies and Molecular Medicine, University of Leicester, Leicester LE2 7LX, UK. msc5@le.ac.uk
authors.forename: Marcus S
authors.initials: MS
authors.lastname: Cooke
authors.forename: Tiago L
authors.initials: TL
authors.lastname: Duarte
authors.forename: Deborah
authors.initials: D
authors.lastname: Cooper
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Sridevi
authors.initials: S
authors.lastname: Nandagopal
authors.forename: Mark D
authors.initials: MD
authors.lastname: Evans
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D001379:Azathioprine / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D020552:Comet Assay; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D045647:DNA Glycosylases / Q000378:metabolism; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013866:Thioguanine / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: D000964:Antimetabolites, Antineoplastic; D017382:Reactive Oxygen Species; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human; D013866:Thioguanine; D003849:Deoxyguanosine; D001379:Azathioprine