To further characterize the Drosophila-based prescreen to detect developmental toxicants, Mitomycin C (Ametycine, Mutamycin [MMC]; CAS No. 50-07-7), was studied. MMC, a documented animal teratogen, is an antibiotic used clinically as an antineoplastic agent. During metabolism multiple metabolites capable of alkylation and/or redox cycling may be formed. Initially, 7 MMC concentrations ranging from 5 - 500 microg/vial were evaluated. No flies were found to emerge at concentrations greater than 20 microg/vial. In the second experiment, 3 concentrations from the first experiment were replicated, and 4 new, lower concentrations were added, to better characterize any developmental toxicity and to determine if a threshold could be observed. Each experiment included a concurrent control. Drosophila were exposed throughout development (egg through third instar larva) in culture vials to medium containing MMC. A mated, untreated, Oregon-R wild-type female (Mid American Drosophila Stock Center, BGSU, Ohio) was added to each vial and allowed to oviposit for 20 hours, then removed. Emerging offspring were collected over 10 days, and examined microscopically (25x) for bent humeral bristles and wing blade notches; morphological defects shown to occur with an increased incidence in flies exposed to developmental toxicants. In each experiment, the incidence of the two defects at each concentration was compared to the controls using chi-square. In cases where replicate data were available at a given concentration, incidence data were also pooled and compared to the pooled controls. In the first experiment the incidence of bent humeral bristles was significantly increased at 10 ug/vial, 11/128 (p< 0.05); in the second experiment bristle defects were increased at 5 ug/vial, 10/277 (p< 0.01) and at 10 microg/vial, 18/260, 15 microg/vial 26/234, and 20 microg/vial 14/188 (all p< 0.001). No wing blade notches were observed. These results with MMC parallel the teratogenicity reported in mammals and provide additional support for increased utilization of this assay as a prescreen for the detection of developmental toxicants.
The Toxicologist. Society of Toxicology 40th Annual Meeting, March 25-29, 2001, San Francisco, California