title: The mutagenic spectrum of acridine-linked aniline nitrogen mustards in AS52 cells: implications of DNA targeting with high selectivity for adenine or guanine bases.
abstract: The mutational spectra generated in AS52 cells at the gpt gene locus by aniline mustards were studied by the isolation of resistant clones and sequencing of the altered gene. A set of four aniline mustards (both mono- and bifunctional) linked to a DNA-affinic 9-aminoacridine (9-AA) carrier was used, together with the untargeted mustards chlorambucil (CHL) and its half-mustard, and the DNA binding carrier, 9-AA. Both 9-AA and CHL were weak cytotoxins, with the DNA-targeted mustards being markedly (10-40-fold) more dose potent, and the bifunctional ones somewhat more toxic than the monofunctional ones. 9-AA produced a different spectrum of mutations to the spontaneous background, with more minor addition events and less base pair substitutions, and showing for the first time that frameshift events so characteristic of 9-AA in bacteria or bacteriophage also occur in mammalian cells. The mutational spectra of the DNA-targeted mustards were quite different both from this and from the lesions caused by the untargeted mustards, which cause largely transition mutations at AT sites (despite a clear preference for formation of N(7)-guanine adducts). There were very few transition mutations, suggesting that the initial O(6)-alkylguanine/O(4)-alkylthymine lesions considered to give rise to these are relatively rare. There was also a lower incidence of complete deletions, usually attributed to DNA cross-links. For the short chain length targeted mustards, which form initial stable adducts largely (95%) at guanine N(7) sites, base pair substitution mutations, predominantly transversions, involved AT and GC base pairs equally. In contrast, the longer chain length targeted mustards, which form >90% of initial adducts at adenine N(1) sites, generated also formed transversion mutations, but these overwhelmingly (24/27) involved AT base pairs.
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, 1000, Auckland, New Zealand. l.ferguson@auckland.az.nz
authors.forename: L R
authors.initials: LR
authors.lastname: Ferguson
authors.forename: P M
authors.initials: PM
authors.lastname: Turner
authors.forename: W A
authors.initials: WA
authors.lastname: Denny
mesh_terms: D000585:Aminacrine / Q000633:toxicity; D019943:Amino Acid Substitution; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002699:Chlorambucil / Q000633:toxicity*; D006224:Cricetinae; D003412:Cricetulus; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial / Q000187:drug effects; D009152:Mutagenicity Tests; D009153:Mutagens / Q000633:toxicity*; D010430:Pentosyltransferases; D011506:Proteins; D011994:Recombinant Proteins / Q000235:genetics; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D009153:Mutagens; D011506:Proteins; D011994:Recombinant Proteins; D002699:Chlorambucil; C113412:chlorambucil half mustard; D000585:Aminacrine; D010430:Pentosyltransferases; C071962:Gpt protein, E coli