title: Forward-mutation tests on the antitumor agent ICR-170 in Neurospora crassa demonstrate that it induces gene/point mutations in the ad-3 region and an exceptionally high frequency of multiple-locus ad-3 mutations with closely linked sites of recessive lethal damage.
abstract: The mutagenicity of the antitumor agent ICR-170 (2-methoxy-6-chloro-9-[(ethyl-2-chloroethyl)amino propylamino] acridine dihydrochloride) in the adenine-3 (ad-3) region was studied with a two-component heterokaryon (H-12) of Neurospora crassa. The objective was to characterize the genetic damage produced by this acridine nitrogen mustard derivative to determine in a lower eukaryotic organism the basis for its potent activity against ascites tumors in mice. As in higher eukaryotes, specific-locus mutations in the ad-3 region of strain H-12 result from gene/point mutations, multiple-locus mutations, and multilocus deletion mutations at the closely linked ad-3A and ad-3B loci. Six different treatments of conidial suspensions of H-12 with ICR-170 were used to obtain dose-response curves for inactivation of conidia as well as the overall induction of ad-3 forward mutations using a direct method based on pigment accumulation rather than a requirement for adenine. These experiments demonstrated that: (1) the slope of the dose-response curve for ICR-170-induced specific-locus mutations in the ad-3 region was 1.97 +/- 0.02, and (2) ICR-170 is a potent mutagen (maximum forward-mutation frequency between 1000 and 10,000 ad-3 mutations per 10(6) survivors) for the induction of specific-locus mutations in the ad-3 region. Both biochemical and classical genetic tests were used to characterize the ICR-170-induced ad-3 mutations from each of the six treatments to distinguish the different genotypic classes and subclasses. The overall data base demonstrates that ICR-170-induced ad-3 mutations result exclusively from gene/point mutations at the ad-3A and ad-3B loci and not multilocus deletion mutations. In addition, the frequency of multiple-locus ad-3 mutations resulting from gene/point mutations at the ad-3A and ad-3B loci with a separate site of recessive lethal damage elsewhere in the genome increases as a function of dose. However, an exceptionally high frequency of multiple-locus ad-3 mutations consisting of gene/point mutations at the ad-3A and ad-3B loci with a separate site of closely linked recessive lethal damage was found at all doses. Comparison of the dose-response curves for the major classes and subclasses of ICR-170-induced ad-3 mutations demonstrates that the gene/point ad-3 mutations and multiple-locus ad-3 mutations with a separate site of recessive lethal damage elsewhere in the genome have different induction kinetics.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Center for Life Sciences and Toxicology, Research Triangle Institute, Research Triangle Park, NC 27709-2194.
authors.forename: F J
authors.initials: FJ
authors.lastname: de Serres
authors.forename: H V
authors.initials: HV
authors.lastname: Malling
mesh_terms: D000225:Adenine; D000483:Alleles; D000609:Aminoacridines; D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D005804:Genes, Lethal; D005808:Genes, Recessive; D005816:Genetic Complementation Test; D007700:Kinetics; D051379:Mice; D009152:Mutagenicity Tests; D009153:Mutagens / Q000633:toxicity*; D009492:Neurospora crassa / Q000187:drug effects* / Q000235:genetics; D009588:Nitrogen Mustard Compounds / Q000633:toxicity*
chemical_list: D000609:Aminoacridines; D000970:Antineoplastic Agents; D009153:Mutagens; D009588:Nitrogen Mustard Compounds; C091910:acridine mustard; D000225:Adenine