4-methylbenzothiazol-2-ylamine

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-11-16 - 2017-03-16 (Experimental)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

1997

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)

Version / remarks:

2008

Deviations:

no

Test guideline 3

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.5100 - Bacterial Reverse Mutation Test (August 1998)

Deviations:

no

Test guideline 4

Qualifier:

according to guideline

Guideline:

other: Japanese Ministry of Economy, Trade and Industry, Japanese Ministry of Health, Labour and Welfare and Japanese Ministry of Agriculture, Forestry and Fisheries.

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

1

Reference substance name:

4-methylbenzothiazol-2-ylamine

EC Number:

216-028-3

EC Name:

4-methylbenzothiazol-2-ylamine

Cas Number:

1477-42-5

Molecular formula:

C8H8N2S

IUPAC Name:

4-methyl-1,3-benzothiazol-2-amine

Test material form:

solid: particulate/powder

Method

Target gene:

histidine / tryptophan

Species / strain

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2

Metabolic activation:

with and without

Metabolic activation system:

rat liver homogenate metabolizing system (10% liver S9 in standard co-factors)

Test concentrations with justification for top dose:

1.5, 5, 15, 50, 150, 500, 1500 and 5000 μg/plate (in all experiments)

Vehicle / solvent:

dimethyl sulphoxide- Vehicle(s)/solvent(s) used: DMSO

Controls

Untreated negative controls:

yes

Remarks:

untreated

Negative solvent / vehicle controls:

yes

Remarks:

DMSO

True negative controls:

no

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

9-aminoacridine

N-ethyl-N-nitro-N-nitrosoguanidine

benzo(a)pyrene

other: 2-Aminoanthracene

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation, 1st experiment); preincubation (2nd, 3rd & 4th experiment)

DURATION
- Preincubation period: 20 Min
- Exposure duration: 48h

SELECTION AGENT (mutation assays):
His-negative plates

NUMBER OF REPLICATIONS: Per strain and dose, three plates with and three plates without S9 mix were used.

DETERMINATION OF CYTOTOXICITY
- Method: Toxicity of the test item results in a reduction in the number of spontaneous revertants or a clearing of the bacterial background lawn.

- OTHER
- Study controls: The solvent (vehicle) control used was dimethyl sulphoxide. The negative (untreated) controls were performed to assess the spontaneous revertant colony rate. The solvent and negative controls were performed in triplicate.
The positive control items used demonstrated a direct and indirect acting mutagenic effect depending on the presence or absence of metabolic activation. The positive controls were performed in triplicate.
- Concentrations of positive controls:
N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) - 2 μg/plate for WP2uvrA, 3 μg/plate for TA100, 5 μg/plate for TA1535
9-Aminoacridine (9AA) - 80 μg/plate for TA1537
4-Nitroquinoline-1-oxide (4NQO) - 0.2 μg/plate for TA98
2-Aminoanthracene (2AA) - 1 μg/plate for TA100, 2 μg/plate for TA1535 and TA1537, 10 μg/plate for WP2uvrA
Benzo(a)pyrene (BP) - 5 μg/plate for TA98
- The sterility controls were performed in triplicate as follows:
Top agar and histidine/biotin or tryptophan in the absence of S9-mix;
Top agar and histidine/biotin or tryptophan in the presence of S9-mix; and
The maximum dosing solution of the test item in the absence of S9-mix only (test in singular only).

Evaluation criteria:

There are several criteria for determining a positive result. Any, one, or all of the following can be used to determine the overall result of the study:
1. A dose-related increase in mutant frequency over the dose range tested (De Serres and Shelby, 1979).
2. A reproducible increase at one or more concentrations.
3. Biological relevance against in-house historical control ranges.
4. Statistical analysis of data as determined by UKEMS (Mahon et al., 1989).
5. Fold increase greater than two times the concurrent solvent control for any tester strain (especially if accompanied by an out-of-historical range response (Cariello and Piegorsch, 1996)).
A test item will be considered non-mutagenic (negative) in the test system if the above criteria are not met.
Although most experiments will give clear positive or negative results, in some instances the data generated will prohibit making a definite judgment about test item activity. Results of this type will be reported as equivocal.

Statistics:

Statistical significance was confirmed by using Dunnetts Regression Analysis (* = p < 0.05) for those values that indicate statistically significant increases in the frequency of revertant colonies compared to the concurrent solvent control.

Results and discussion

Test results

Key result

Species / strain:

bacteria, other: S.typhimurium TA98, TA100, TA1535, TA1537 and E. coli WP2uvrA

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

5000µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Remarks:

untreated

Positive controls validity:

valid

Applicant's summary and conclusion

Conclusions:

The study was conducted under GLP according to OECD guideline 471 on the registered substance itself. The method is to be considered scientifically reasonable with no deficiencies in documentation or any deviations, the validity criteria are fulfilled, positive and negative controls gave the appropriate response. Hence, the results can be considered as reliable to assess the potential of the test item to induce reverse mutations in bacteria. The test substance was non-mutagenic in the Salmonella typhimurium test strains TA1535, TA1537, TA98 and TA100 and Escherichia coli strain WP2uvrA in the absence and presence of metabolic activation under the experimental conditions in the present study.

Executive summary:

In a reverse gene mutation assay in bacteria (OECD 471, GLP), Salmonella typhimurium strains TA1535, TA1537, TA98 and TA100 and Escherichia coli strain WP2uvrA were treated with the test item using both the Ames plate incorporation and pre-incubation methods at eight dose levels, in triplicate, both with and without the addition of a rat liver homogenate metabolizing system (10% liver S9 in standard co-factors). The dose range for Experiment 1 was predetermined and was 1.5 to 5000 μg/plate. The experiment was repeated on a separate day (pre-incubation method) using fresh cultures of the bacterial strains and fresh test item formulations. The dose range was the same as Experiment 1 (1.5 to 5000 μg/plate). Eight test item dose levels were selected in the second mutation test in order to achieve both a minimum of four non-toxic dose levels and the toxic limit of the test item following the change in test methodology.

Third and fourth, confirmatory experiments were performed, in triplicate, in response to small, non-reproducible increases in TA1535 revertant colony frequency (presence of S9 only) noted in the second mutation test. Both experiments utilised a dose range of 1.5 to 5000 μg/plate using the pre-incubation method.

The vehicle (dimethyl sulphoxide) control plates gave counts of revertant colonies within the normal range. All of the positive control chemicals used in the test induced marked increases in the frequency of revertant colonies, both with or without metabolic activation. Thus, the sensitivity of the assay and the efficacy of the S9-mix were validated.

The maximum dose level of the test item in the first experiment was selected as the maximum recommended dose level of 5000 μg/plate. In the first mutation test (plate incorporation method), the test item caused a visible reduction in the growth of the bacterial background lawns of all of the tester strains at 5000 μg/plate in both the absence and presence S9-mix. These results were not indicative of toxicity sufficiently severe enough to prevent the test item being tested up to the maximum recommended dose level of 5000 μg/plate in the second mutation test. Results from Experiment 2 (pre-incubation method) showed that the test item again induced a toxic response with reductions in the bacterial background lawns noted in the absence of S9-mix from 1500 μg/plate (TA100, WP2uvrA and TA1535) and at 5000 μg/plate (TA98 and TA1537). In the presence S9-mix, reductions in the bacterial background lawns were noted at 5000 μg/plate for all of the tester strains. An identical toxic response was noted in both confirmatory tests (Experiments 3 and 4) with weakened bacterial background lawns noted to TA1535 at 5000 μg/plate (presence of S9-mix only). The sensitivity of the bacterial tester strains to the toxicity of the test item varied slightly between strain type, exposures with or without S9-mix and experimental methodology. No test item precipitate was observed on the plates at any of the doses tested in either the presence or absence of S9-mix.

There were no increases in the frequency of revertant colonies recorded for any of the bacterial strains, with any dose of the test item, either with or without metabolic activation (S9-mix) in Experiment 1 (plate incorporation method). Similarly, no substantial increases in the frequency of revertant colonies were recorded for any of the bacterial strains, with any dose of the test item, either with or without metabolic activation (S9-mix) in Experiment 2 (pre-incubation method). Small, statistically significant increases in TA1535 revertant colony frequency were observed in the second mutation test at 150, 500 and 1500 μg/plate in the presence of S9-mix only. However, these increases could not be reproduced in either a third or fourth, confirmatory experiment. The responses noted in Experiment 2 were considered to be of no biological relevance because there was no clear evidence of a dose-response relationship, reproducibility or a twofold increase in revertant colony frequency over the concurrent vehicle control. Hence, the test substance was considered to be non-mutagenic under the conditions of this test.