Structure-activity relationships of several anisidine and dibenzanthracene isomers in the w/w+ somatic assay of Drosophila melanogaster

Several structurally related anisidine and dibenzanthracene isomers were evaluated for genotoxic effects in the somatic w/w+ assay of Drosophila melanogaster employing insecticide-susceptible (IS) and insecticide-resistant (IR) tester strains. In addition, and in order to find whether or not at the genetic level a regulatory effect is found, crosses between ISxIR strains and IRxIS strains were done. Chemicals tested were the aromatic amines (AAs) ortho-anisidine (o-AN), meta-anisidine (m-AN), and para-anisidine (p-AN) and the polycyclic aromatic hydrocarbons (PAHs) 1,2;3,4-dibenzanthracene (1,2;3,4-DBA) and 1,2;5,6-dibenzanthracene (1,2;5,6-DBA). As positive control N-nitrosodimethylamine (DMN) was used. Our results show that the genotoxic activity of DMN was higher in the IR than in the IS strain. There seems to be a tendency for slightly lower values as measured by clone induction in crosses between ISxIR and IRxIS. o-AN was positive in the IS strain and in crosses between ISxIR and IRxIS but negative in the IR strain. m-AN, p-AN and 1,2;3,4-DBA proved to be not recombinogenic in all strains and crosses while 1,2;5,6-DBA was positive at the highest concentration tested in all the crosses assayed. These findings show that the recombinogenic activity of the anisidine isomers depends on the position of the chemical group relative to one another and that the position of the benzene ring seems to be structurally relevant for genotoxicity of DBA isomers. With respect to IR and IS strains it remains to be determined to what extent the spectrum of metabolizing capacity really differs between the strains of the test assay. Thus more information is needed about the regulation and expression of the cytochrome-P450 genes and action at the molecular level taking place in the eye imaginal disc as well as between insecticide susceptible and resistant strains after exposure to genotoxic chemicals.