Azathioprine and UVA light generate mutagenic oxidative DNA damage.
Oxidative stress and mutagenic DNA lesions formed by reactive oxygen species (ROS) are linked to human malignancy. Clinical treatments inducing chronic oxidative stress may therefore carry a risk of therapy-related cancer. We suggest that immunosuppression by azathioprine (Aza) may be one such treatment. Aza causes the accumulation of 6-thioguanine (6-TG) in patients' DNA. Here we demonstrate that biologically relevant doses of ultraviolet A (UVA) generate ROS in cultured cells with 6-TG-substituted DNA and that 6-TG and UVA are synergistically mutagenic. A replication-blocking DNA 6-TG photoproduct, guanine sulfonate, was bypassed by error-prone, Y-family DNA polymerases in vitro. A preliminary analysis revealed that in five of five cases, Aza treatment was associated with a selective UVA photosensitivity. These findings may partly explain the prevalence of skin cancer in long-term survivors of organ transplantation.
O'Donovan
Peter
P
Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK.
Perrett
Conal M
CM
Zhang
Xiaohong
X
Montaner
Beatriz
B
Xu
Yao-Zhong
YZ
Harwood
Catherine A
CA
McGregor
Jane M
JM
Walker
Susan L
SL
Hanaoka
Fumio
F
Karran
Peter
P
D000228:Adenine Phosphoribosyltransferase / Q000235:genetics; D001379:Azathioprine / Q000494:pharmacology* / Q000627:therapeutic use; D002460:Cell Line; D045744:Cell Line, Tumor; D004247:DNA / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D016296:Mutagenesis; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010787:Photosensitivity Disorders; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012867:Skin / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D013866:Thioguanine / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D014466:Ultraviolet Rays
D017382:Reactive Oxygen Species; D004247:DNA; D000228:Adenine Phosphoribosyltransferase; D004259:DNA-Directed DNA Polymerase; D013866:Thioguanine; D001379:Azathioprine