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Photo-oxidation of 6-thioguanine by UVA: the formation of addition products with low molecular weight thiol compounds

Ren, Xiaolin; Xu, Yao-Zhong and Karren, Peter (2010). Photo-oxidation of 6-thioguanine by UVA: the formation of addition products with low molecular weight thiol compounds. Photochemistry and Photobiology, 86(5) pp. 1038–1045.

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The thiopurine, 6-thioguanine (6-TG) is present in the DNA of patients treated with the immunosuppressant and anticancer drugs azathioprine or mercaptopurine. The skin of these patients is selectively sensitive to UVA radiation—which comprises >90% of the UV light in incident sunlight—and they suffer high rates of skin cancer. UVA irradiation of DNA 6-TG produces DNA lesions that may contribute to the development of cancer. Antioxidants can protect 6-TG against UVA but 6-TG oxidation products may undergo further reactions. We characterize some of these reactions and show that addition products are formed between UVA-irradiated 6-TG and N-acetylcysteine and other low molecular weight thiol compounds including b-mercaptoethanol, cysteine and the cysteine-containing tripeptide glutathione (GSH). GSH is also adducted to 6-TG-containing oligodeoxynucleotides in an oxygen- and UVA-dependent nucleophilic displacement reaction that involves an intermediate oxidized 6-TG, guanine sulfonate (GSO3). These photochemical reactions of 6-TG, particularly the formation of a covalent oligodeoxynucleotide–GSH complex, suggest that crosslinking of proteins or low molecular weight thiol compounds to DNA may be a previously unrecognized hazard in sunlight-exposed cells of thiopurine-treated patients.

Item Type: Journal Article
Copyright Holders: 2010 The Authors
ISSN: 0031-8655
Keywords: 6-thioguanine; DNA; UVA; photochemistry
Academic Unit/Department: Science > Life, Health and Chemical Sciences
Interdisciplinary Research Centre: Biomedical Research Network (BRN)
Item ID: 22986
Depositing User: Yao Xu
Date Deposited: 16 Sep 2010 09:04
Last Modified: 15 Jan 2016 14:54
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