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Evaluation of Test Results
Once the criteria for a valid assay were met, the results were evaluated. Test substance was considered to be positive if it induced a significant increase in mnPCE frequency (p£0.05) at any dose level or sampling time compared to the concurrent vehicle control. The test substance was considered to be negative if no significant increase in mnPCE frequency was observed (p > 0.05) compared to the concurrent vehicle control. Other criteria may have been used in reaching a conclusion about the study results (e.g., magnitude of any increase, dose-dependency, comparison to historical control values, biological significance, etc.). In such cases, the Study Director used sound scientific judgment and clearly reported and described any such considerations.
Definitive Micronucleus Assay
No mortality occurred during the course of the definitive assay. All rats appeared normal throughout the observation period. Clinical signs are presented inTable 1.
Bone Marrow Analysis
No appreciable reductions in the PCEs/EC ratio in the test substance group compared to the vehicle control group were observed indicating the test did not induce cytotoxicity.
No statistically significant increase in the incidence of mnPCEs in the test-substance treated group was observed relative to the negative control group (p > 0.05, Kastenbaum-Bowman tables). The positive control induced a statistically significant increase in the incidence of mnPCEs (p < 0.05, Kastenbaum-Bowman tables). The number of mnPCEs in the vehicle control groups did not exceed the historical control range.
The incidence of mnPCEs per 10,000 PCEs scored (2000 PCEs/animal) and the proportion of polychromatic erythrocytes per total erythrocytes are summarized and presented for each treatment group by sacrifice time inTable 2. Individual animal data is presented inTable 3.
Based upon this, all criteria for a valid test were met as specified in the protocol. The Common Technical Document (CTD) Summary Table is included inAppendix IV.
A well conducted guideline study to examine in vivo mutagenesis (chromosome aberration) of EXP1200078 at the MTD (2000 mg/kg) did not result in any mutagenic response. The test substance, EXP1200078,was evaluated for its clastogenic activity and/or disruption of the mitotic apparatus by detecting micronuclei in polychromatic erythrocyte (PCE) cells in rat bone marrow.
No adverse effects were found at the dose of 2000 mg/kg in this in vivo genetic toxicity assay.
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