1-[5-(2,6-difluorophenyl)-4,5-dihydro-1,2-oxazol-3-yl]ethanone

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Mutagenic effects - bacterial: OECD 471; Ames study. Negative. Reliability = 1.

Clastogenic effects - mammalian: OECD 473; Chromosome aberrations in human peripheral blood lymphocytes. Positive. Reliability = 1.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (positive)

Genetic toxicity in vivo

Description of key information

Clastogenic effects - mammalian: OECD 474; in vivo mouse micronucleus study; Negative at doses up to 1350 (females) and 1800 (males) mg/kg. Reliability = 1.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

The test substance was evaluated for mutagenicity in the Bacterial Reverse Mutation Test using the plate incorporation method. Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537 and Escherichia coli strain WP2uvrA were tested in the absence and presence of an exogenous metabolic activation system (Aroclor-induced rat liver S9). The dose levels selected for the mutagenicity test were 333, 667, 1000, 3333, and 5000 μg per plate. No positive mutagenic responses were observed at any dose level or with any tester strain in either the absence or presence of S9 metabolic activation.
The test substance was evaluated for its ability to induce structural chromosome aberrations in vitro using human peripheral blood lymphocytes in the absence and presence of an exogenous metabolic activation system (Aroclor-induced rat liver S9). Based on the results of a preliminary test, a confirmatory chromosome aberration assay was conducted for the 4-hour S9-activated test condition only. The concentrations chosen for the 4-hour confirmatory assay, S9-activated test condition, were 250, 500, 700, 750, 775, 800, 825 and 850 μg/mL. A statistically significant increase (p < 0.05, Fisher’s exact test) in the percentage of structural aberrations was observed in a dose responsive trend (p < 0.05, Cochran-Armitage) at 800 and 825 μg/mL. The percentage of cells with numerical aberrations in the test substance-treated groups was not significantly increased above that of the vehicle control at any concentration (p ≥ 0.05, Fisher’s exact test). The test substance was found to induce structural aberrations in the in vitro mammalian chromosome aberration test in human peripheral blood lymphocytes in the S9-activated test system only. It was concluded that the test substance was positive in this in vitro test.
An oral micronucleus study was conducted in mice to determine whether the test material induces an increase in the frequency of micronucleated polychromatic erythrocytes in bone marrow. Groups of male and female mice were given doses of 0, 450, 900, 1350 (female only) and 1800 (male only) mg/kg body weight (bw) of the test substance. Bone marrow smears were prepared approximately 24 and 48 hours after dosing. In the main study, adverse clinical signs of toxicity were observed on test day 0 at all dose levels tested in male and female mice exposed to the test substance. No test substance related abnormalities were detected with any animals at either the 24 or 48 hour observation time point. No statistically significant increases in micronucleated PCE frequency were observed in any evaluated test substance-treated group of male or female animals at either timepoint. A statistically significant decrease in PCEs among 1000 erythrocytes was observed with male mice in the top dose group of 1800 mg/kg/bw, at the 48 hour time point, indicating that the test substance reached the target cells. No other reductions in PCE frequency were detected at any other time point or at any other dose level for male or female mice administered the test substance. The test substance did not induce biologically relevant increases in micronucleated polychromatic erythrocytes in animal bone marrow and was concluded to be negative in this in vivo study.

Justification for classification or non-classification

The test substance was positive in vitro in mammalian cells, but was negative in vitro in bacterial cells and when evaluated in vivo in laboratory animals. Based on an assessment of the robust genetic toxicity data for this substance, the substance does not need to be classified for mutagenicity according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.