Mutagenic and cytotoxic properties of 6-thioguanine, S6-methylthioguanine and guanine-S6-sulfonic acid. The Journal of biological chemistry [J Biol Chem] Journal article | | Title | Mutagenic and cytotoxic properties of 6-thioguanine, S6-methylthioguanine and guanine-S6-sulfonic acid. | | Author(s) | Yuan B, Wang Y | | Institution | Department of Chemistry-027, University of California, Riverside, Riverside, CA 92521-0403. | | Source | J Biol Chem 2008 Jun 30. | | Abstract | Thiopurine drugs, including 6-thioguanine ((S)G), 6-mercaptopurine and azathioprine, are widely employed anticancer agents and immunosuppressants. The formation of (S)G nucleotides from the thiopurine prodrugs and their subsequent incorporation into nucleic acids are important for the drugs to exert their cytotoxic effects. (S)G in DNA can be methylated by S-adenosyl-L-methionine to give S(6)-methylthioguanine (S(6)mG) and oxidized by UVA light to render guanine-S(6)-sulfonic acid ((SO3H)G). Here, we constructed single-stranded M13 shuttle vectors carrying a (S)G, S(6)mG, or (SO3H)G at a unique site and allowed the vectors to propagate in wild-type and bypass polymerase-deficient Escherichia coli (E. coli) cells. Analysis of the replication products, by using the competitive replication and adduct bypass (CRAB) and a slightly modified restriction enzyme digestion and post-labeling (REAP) assays, revealed that, while none of the three thionucleosides blocked considerably DNA replication in all transfected E. coli cells, both S(6)mG and (SO3H)G were highly mutagenic, which resulted in G-to-A mutation at frequencies of 94% and 77%, respectively, in wild-type E. coli cells. Deficiency in bypass polymerases does not result in alteration of mutation frequencies of these two lesions. In contrast to what was found from previous steady-state kinetic analysis, our data demonstrated that 6-thioguanine is mutagenic, with G-to-A transition occurring at a frequency of ~10%. The mutagenic properties of 6-thioguanine and its derivatives revealed in present study offered important knowledge about the biological implications of these thionucleosides. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 18591241 |
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