6-methyl-2-oxoperhydropyrimidin-4-ylurea

Endpoint summary

Additional information

Justification for read-across

No sufficient data are available on the genotoxic properties of 6-methyl-2-oxoperhydropyrimidin-4-ylurea (Crotodur, CAS 1129-42-6). In order to fulfil the standard information requirements set out in Annex VIII, 8.5, in accordance with Annex XI, 1.5, of Regulation (EC) No 1907/2006, read-across from a structurally related substance was conducted.

In accordance with Article 13 (1) of Regulation (EC) No 1907/2006, "information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met.” In particular for human toxicity, information shall be generated whenever possible by means other than vertebrate animal tests, which includes the use of information from structurally related substances (read-across).

Having regard to the general rules for grouping of substances and read-across approach laid down in Annex XI, Item 1.5, of Regulation (EC) No 1907/2006 whereby substances may be predicted as similar provided that their physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity.

 

Developmental Toxicity/Teratogenicity

CAS	1129-42-6 TARGET SUBSTANCE	6104-30-9
Chemical Name	6-methyl-2-oxoperhydropyrimidin-4-ylurea (Crotodur)	N,N”-(2-methylpropane-1,1-diyl) diurea (Isodur)
MW	172.1851 g/mol	174.2010 g/mol
Genetic Toxicity in vitro: gene mutation in bacteria	Experimental result: Negative	--
Genetic Toxicity in vitro: mutagenicity in mammalian cells	Experimental result: Negative	--
Genetic Toxicity in vivo	RA: CAS 6104-30-9	Experimental result: Negative

 

The above mentioned substances are considered to be similar on the basis of structural similarity resulting in similar properties and/or activities. The available endpoint information is used to predict the same endpoints for 6-methyl-2-oxoperhydropyrimidin-4-ylurea (Crotodur, CAS 1129-42-6).

A detailed analogue approach justification is provided in the technical dossier (see IUCLID Section 13).

 

Discussion

 

In vitro

- Gene mutation in bacteria

One study is available, in which 6-methyl-2-oxoperhydropyrimidin-4-ylurea (Crotodur, CAS 1129-42-6) was investigated for mutagenicity to bacteria in the Ames test, conducted according to the OECD test guideline 471, and in compliance with GLP (BSL, 2012e). The test material was diluted in A. dest. and applied to S. typhimurium strains TA 98, TA 100, TA 1535, TA 1537, and TA 102 up to the limit concentration of 5000 µg/plate both with and without metabolic activation system (S9 mix) for 48 h. The test was conducted in two independent experiments: Experiment 1 was the plate incorporation assay and Experiment 2 was the preincubation assay (60 min of preincubation period). No cytotoxic effect, expressed as a clearing or rather diminution of the background lawn or a reduction in the number of revertants down to a mutation factor of approximately ≤0.5 in relation to the solvent control, was observed in any tester strain, neither the pre-experiment for toxicity, nor in the main mutagenicity experiments up to the limit concentrations. No biologically relevant increases in the revertant colony numbers of any of the five tester strains were observed following treatment with the test item at any concentration level, neither in the presence nor absence of a metabolic activation system in any experiment. Appropriate solvent and negative controls were included into the test and gave the expected results. No test-specific confounding factors were reported, and the solvent control data are within the range of the historical control data. Thus, the test was considered to be reliable and the test item is concluded to not mutagenic to bacteria under the conditions of the test.

 

- Gene mutation in mammalian cells

One study is available, in which 6-methyl-2-oxoperhydropyrimidin-4-ylurea (Crotodur, CAS 1129-42-6) was investigated for mammalian mutagenicity according to the OECD TG 476, and in compliance with GLP (BSL, 2012f). Mouse lymphoma L5178Y cells were treated with the test item up to the limit concentration of 10.0 mM both in the presence and absence of a metabolic activation system for 4 h. Precipitation was observed at concentrations of 7.5 mM and higher with and without metabolic activation, and hence, the test item was tested as a suspension. 2 days after the end of the treatment, cells were plated for determination of the cloning efficiency and the mutation frequency in 96-well microtitre plates. The cloning efficiency was determined after 6 days of incubation based on the number of cultures with cell growth (positive) compared to those without cell growth (negative) compared to the total number of cells seeded. Cells cultured in selective medium containing TFT (trifluorothymidine) were incubated for 14 days and scored by dividing the number of TFT resistent colonies by the number of cells plated for selection, corrected by the plating efficiency of cells from the same culture grown in the absence of TFT. No growth inhibition was observed in the pre-test or in the main experiment with or without metabolic activation up to the limit concentration of 10.0 mM and no increase in induced mutant frequency (IMF) was observed in the presence or absence of a metabolic activation system. Appropriate negative and positive controls were included into the test and gave the expected results, and the negative control data are within the range of the historical control data. Thus, the test was considered to be reliable and the test item is concluded to not mutagenic to mammalian cells under the conditions of the test.

 

In vivo

No studies are available on the induction of genetic toxicity of 6-methyl-2-oxoperhydropyrimidin-4-ylurea (Crotodur, CAS 1129-42-6) in vivo, but there is one reliable study from the structurally related substance N,N”-(2-methylpropane-1,1-diyl) diurea (Isodur, CAS 6104-30-9) available, which is used for read-across based on the analogue approach.

In the available study (RCC, 1999) the structural analogue substance CAS 6104-30-9 was evaluated for genotoxicity to mammals in the in vivo mouse micronucleus assay in a study conducted according to the OECD TG 474, and in compliance with GLP. Within 24 h the test item was administered in two applications by gavage to male NMRI mice at doses of 500, 10000, and 2000 mg/kg bw. The dose selection was based on a previous acute toxicity conducted with 3 males and 3 females at doses of 1000, 1500, and 2000 mg/kg bw. Samples from bone marrow cells were taken 24 h after the last test material gavage. Appropriate vehicle and positive controls were included into the study and gave the expected results. No statistically significant increase in micronuclei induction was observed in any dose group. No increase in the ratio of polychromatic erythrocytes (PCE) to normochromatic erthrocytes (NCE) was noted at any dose level, which would indicate cytotoxicity. However, clinical signs of toxicity were observed, indicating systemic availability of the test article. Based on these results, the test material can be considered to be not clastogenic to mammals under the conditions of this test.

Justification for selection of genetic toxicity endpoint
Hazard assessment is conducted by means of read-across from a structural analogue. No study was selected, since all available in vitro and in vivo genetic toxicity studies were negative. All available studies are adequate and reliable based on the identified similarities in structure and intrinsic properties between source and target substance and overall quality assessment (refer to the endpoint discussion for further details).

Short description of key information:
In vitro:
Gene mutation (Bacterial reverse mutation assay / Ames test): S. typhimurium TA 98, TA 100, TA 1535, TA 1537, and TA 102: negative with and without metabolic activation (OECD 471)
Gene mutation (Mouse Lymphoma Assay): Mouse Lymphoma L5178Y Cells: negative with and without metabolic activation (OECD 476)
In vivo:
Micronucleus Test (OECD 474, RA from CAS 6104-30-9): negative

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on data from the registered substance and on read-across from the structurally similar substance, the available data on genetic toxicity do not meet the classification criteria according to Regulation (EC) 1272/2008 or Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.