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Toxicological information

Genetic toxicity: in vitro

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Administrative data

Endpoint:
in vitro gene mutation study in bacteria
Remarks:
Type of genotoxicity: gene mutation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2012
Report date:
2012

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Principles of method if other than guideline:
The study was performed to investigate the potential of 1,3-Dihydro-4(or5)-methyl-2Hbenzimidazole-2-thione to induce gene mutations according to the plate incorporation test (experiment I) and the pre-incubation test (experiment II) using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and TA 102.
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay

Test material

Constituent 1
Chemical structure
Reference substance name:
1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione
EC Number:
258-904-8
EC Name:
1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione
Cas Number:
53988-10-6
Molecular formula:
C8H8N2S
IUPAC Name:
1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione
Details on test material:
Identity: 1,3-Dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione
Purity: > 97 % (dose calculation not adjusted to purity)

Method

Species / strain
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102
Additional strain / cell type characteristics:
other: due to the "deep rough" (rfa-) mutation they possess a faulty lipopolysaccharide envelope which enables substances to penetrate the cell wall more easily. A further mutation (deletion of the uvrB gene) causes an inactivation of the excision repair system.
Metabolic activation:
with and without
Metabolic activation system:
S9 mix
Test concentrations with justification for top dose:
In the pre-experiment the concentration range of the test item was 3 – 5000 µg/plate. The pre-experiment is reported as experiment I. Since toxic effects were observed eight concentrations were tested in experiment II and 5000 µg/plate were chosen as maximal concentration.
The concentration range included two logarithmic decades. The following concentrations were tested in experiment II:
3; 10; 33; 100; 333; 1000; 2500; and 5000 µg/plate
Controls
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: Without metabolic activation: sodium azide, NaN3; 4-nitro-o-phenylene-diamine, 4-NOPD; methyl methane sulfonate, MMS; With metabolic activation: 2-aminoanthracene, 2-AA

Results and discussion

Test results
Species / strain:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102
Metabolic activation:
with and without
Genotoxicity:
negative
Vehicle controls validity:
other: 2500 - 5000 µg/plate
Untreated negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
other: other:
Remarks:
Migrated from field 'Test system'.

Any other information on results incl. tables

In experiment I the plates incubated with the test item showed reduced background growth in all strains at higher concentrations. In experiment II normal background growth was observed in all strains with and without metabolic activation.

Toxic effects evident as a reduction in the number of revertants (below the indication factor of 0.5), occurred in the test groups with and without metabolic activation at higher concentrations.

No substantial increase in revertant colony numbers of any of the five tester strains was observed following treatment with 1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione at any dose level, neither in the presence nor absence of metabolic activation (S9 mix). There was also no tendency of higher mutation rates with increasing concentrations in the range below the generally acknowledged border of biological relevance.

Appropriate reference mutagens were used as positive controls and showed a distinct increase of induced revertant colonies.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information):
negative
Executive summary:

The study was performed to investigate the potential of 1,3-Dihydro-4(or5)-methyl-2Hbenzimidazole-2-thione to induce gene mutations according to the plate incorporation test (experiment I) and the pre-incubation test (experiment II) using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and TA 102.

In experiment I the plates incubated with the test item showed reduced background growth in all strains at higher concentrations. In experiment II normal background growth was observed in all strains with and without metabolic activation.

Toxic effects evident as a reduction in the number of revertants (below the indication factor of 0.5), occurred in the test groups with and without metabolic activation at higher concentrations.

No substantial increase in revertant colony numbers of any of the five tester strains was observed following treatment with 1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione at any dose level, neither in the presence nor absence of metabolic activation (S9 mix). There was also no tendency of higher mutation rates with increasing concentrations in the range below the generally acknowledged border of biological relevance.

Appropriate reference mutagens were used as positive controls and showed a distinct increase of induced revertant colonies.

In conclusion, it can be stated that during the described mutagenicity test and under the experimental conditions reported, the test item did not induce gene mutations by base pair changes or frameshifts in the genome of the strains used.

Therefore, 1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione was negative in this Salmonella typhimurium reverse mutation assay.