title: DNA adduct of the mitomycin C metabolite 2,7-diaminomitosene is a nontoxic and nonmutagenic DNA lesion in vitro and in vivo.
abstract: Mitomycin C (MC) is a cytotoxic and mutagenic antitumor agent that alkylates and cross-links DNA. These effects are dependent on reductive bioactivation of MC. 2,7-Diaminomitosene (2,7-DAM) is the major metabolite of MC in tumor cells, generated by the reduction of MC. 2,7-DAM alkylates DNA in the cell in situ, forming an adduct at the N7 position of 2'-deoxyguanosine (2,7-DAM-dG-N7). To determine the biological effects of this adduct, we have synthesized an oligonucleotide containing a single 2,7-DAM-dG-N7 adduct and inserted it into an M13 bacteriophage genome. Replication of this construct in repair-competent Escherichia coli showed that the adduct was only weakly toxic and generated approximately 50% progeny as compared to control. No mutant was isolated after analysis of more than 4000 progeny phages from SOS-induced or uninduced host cells; therefore, we estimate that the mutation frequency of 2,7-DAM-dG-N7 was less than 2 x 10(-4) in E. coli. Subsequently, to determine if this adduct might be mutagenic in mammalian cells, it was incorporated into a single-stranded shuttle phagemid vector, pMS2, and replicated in simian kidney (COS-7) cells. Analysis of the progeny showed that mutational frequency of a site specific 2,7-DAM-dG-N7 was not higher than the spontaneous mutation frequency in simian kidney cells. In parallel experiments in cell free systems, template oligonucleotides containing a single 2,7-DAM-dG-N7 adduct directed selective incorporation of cytosine in the 5'-32P-labeled primer strands opposite the adducted guanine, catalyzed by Klenow (exo-) DNA polymerase. The adducted templates also supported full extension of primer strands by Klenow (exo-) and T7 (exo-) DNA polymerases and partial extension by DNA polymerase eta. The innocuous behavior of the 2,7-DAM-dG-N7 monoadduct in vivo and in vitro is in sharp contrast to that of the toxic MC-dG-N2 monoadduct reported earlier.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Utzat
authors.forename: Cristina C
authors.initials: CC
authors.lastname: Clement
authors.forename: Leilani A
authors.initials: LA
authors.lastname: Ramos
authors.forename: Arunangshu
authors.initials: A
authors.lastname: Das
authors.forename: Maria
authors.initials: M
authors.lastname: Tomasz
authors.forename: Ashis K
authors.initials: AK
authors.lastname: Basu
mesh_terms: D000818:Animals; D019556:COS Cells; D004247:DNA / Q000187:drug effects; D018736:DNA Adducts / Q000737:chemistry*; D004249:DNA Damage; D004926:Escherichia coli / Q000737:chemistry / Q000187:drug effects; D016685:Mitomycin / Q000737:chemistry*; D008937:Mitomycins / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D015394:Molecular Structure; D009152:Mutagenicity Tests; D009841:Oligonucleotides / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology
chemical_list: D018736:DNA Adducts; D008937:Mitomycins; D009841:Oligonucleotides; D016685:Mitomycin; C056707:2,7-diaminomitosene; D004247:DNA