(E)-N'-(2-cyano-4-(3-(1-hydroxy-2-methylpropan-2-yl)thioureido)phenyl)-N,N-dimethylformimidamide

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:

15 January 2020 to 07 February 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2020

Report date:

2020

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

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

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:

JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine

Cas Number:

1429755-57-6

Molecular formula:

C15H12N5OS

IUPAC Name:

E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine

Specific details on test material used for the study:

Identification: SPS 5290 (Stage 3)
Batch Number: 80034242B
Chemical Name: (E)-N'-(2-Cyano-4-(3-(1-hydroxy-2-methylpropan-2-yl)thioureido)phenyl)-N,Ndimethylformimidamide
Empirical Formula C15H21N5OS
Molecular Weight: 319.43
Purity: 99.5%
Expiry Date: 05 July 2020
Appearance: Yellow crystalline powder
Storage Conditions: Room temperature, in the dark
No correction for purity was required

Method

Target gene:

histidine or tryptophan locus.

Species / strain

Species / strain 1

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Species / strain 2

Species / strain / cell type:

E. coli WP2 uvr A

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbitone / β-Naphthoflavone induced S9 Microsomal fractions (Sprague-Dawley)

Test concentrations with justification for top dose:

Experiment 1 – Plate Incorporation Method
1.5, 5, 15, 50, 150, 500, 1500 and 5000 μg/plate
The maximum concentration was 5000 μg/plate (the OECD TG 471 maximum recommended dose level)

Experiment 2 – Pre-Incubation Method
The dose range used for Experiment 2 was determined by the results of Experiment 1 and was 15, 50, 150, 500, 1500 and 5000 μg/plate.

Vehicle / solvent:

Dimethyl sulphoxide
The test item was insoluble in sterile distilled water at 50 mg/mL but was fully soluble in dimethyl sulphoxide at the same concentration in solubility checks performed in-house. Dimethyl sulphoxide was therefore selected as the vehicle.

Controls

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

Remarks:

DMSO

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

9-aminoacridine

N-ethyl-N-nitro-N-nitrosoguanidine

benzo(a)pyrene

other: 2-Aminoanthracene (2AA)

Details on test system and experimental conditions:

Test for Mutagenicity: Experiment 1 – Plate Incorporation Method
Without Metabolic Activation
A 0.1 mL aliquot of the appropriate concentration of test item, solvent vehicle or 0.1 mL of the appropriate positive control was added together with 0.1 mL of the bacterial strain culture, 0.5 mL of phosphate buffer and 2 mL of molten, trace amino-acid supplemented media. These were then mixed and overlayed onto a Vogel-Bonner agar plate. Negative (untreated) controls were also performed on the same day as the mutation test. Each concentration of the test item, appropriate positive, vehicle and negative controls, and each bacterial strain, was assayed using triplicate plates.
With Metabolic Activation
The procedure was the same as described previously (see 3.3.2.2) except that following the addition of the test item formulation and bacterial culture, 0.5 mL of S9-mix was added to the molten, trace amino-acid supplemented media instead of phosphate buffer.
Incubation and Scoring
All of the plates were incubated at 37 ± 3 °C for between 48 and 72 hours and scored for the presence of revertant colonies using an automated colony counting system. The plates were viewed microscopically for evidence of thinning (toxicity).

Test for Mutagenicity: Experiment 2 – Pre-Incubation Method
As the result of Experiment 1 was considered negative, Experiment 2 was performed using the pre-incubation method in the presence and absence of metabolic activation (S9-mix).
Without Metabolic Activation
A 0.1 mL aliquot of the appropriate bacterial strain culture, 0.5 mL of phosphate buffer and 0.1 mL of the appropriate concentration of test item formulation, solvent vehicle or 0.1 mL of appropriate positive control were incubated at 37 ± 3 °C for 20 minutes (with shaking) prior to addition of 2 mL of molten, trace amino-acid supplemented media and subsequent plating onto Vogel-Bonner plates. Negative (untreated) controls were also performed on the same day as the mutation test employing the plate incorporation method. All testing for this experiment was performed in triplicate.
With Metabolic Activation
The procedure was the same as described previously (see 3.3.3.2) except that following the addition of the test item formulation and bacterial strain culture, 0.5 mL of S9-mix was added to the tube instead of phosphate buffer, prior to incubation at 37 ± 3 °C for 20 minutes (with shaking) and addition of molten, trace amino-acid supplemented media. All testing for this experiment was performed in triplicate.
Incubation and Scoring
All of the plates were incubated at 37 ± 3 °C for between 48 and 72 hours and scored for the presence of revertant colonies using an automated colony counting system. The plates were viewed microscopically for evidence of thinning (toxicity).

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. A fold increase greater than two times the concurrent solvent control for TA100, TA98 and WP2uvrA or a three-fold increase for TA1535 and TA1537 (especially if accompanied by an out-of-historical range response (Cariello and Piegorsch, 1996)).
5. Statistical analysis of data as determined by UKEMS (Mahon et al., 1989).
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.

Results and discussion

Test results

Test results 1

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Test results 2

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Test results 3

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Test results 4

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Test results 5

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

Prior to use, the relevant strains were checked for characteristics (deep rough character, ampicillin resistance, UV light sensitivity and histidine or tryptophan auxotrophy), viability and spontaneous reversion rate (all were found to be satisfactory). The amino acid supplemented top agar and the S9-mix used in both experiments were shown to be sterile. The test item formulation was also shown to be sterile. These data are not given in the report.
Results for the negative controls (spontaneous mutation rates) and viability are presented in Table 1 and were considered to be acceptable. These data are for concurrent untreated control plates performed on the same day as the Mutation Test.
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 and without metabolic activation. Thus, the sensitivity of the assay and the efficacy of the S9-mix were validated

Experiment 1 (plate incorporation)
The maximum dose level of the test item in the first experiment was selected as the OECD TG 471 recommended dose level of 5000 μg/plate.
There was no visible reduction in the growth of the bacterial background lawn at any dose level, either in the presence or absence of metabolic activation (S9-mix).
No test item precipitate was observed on the plates at any of the doses tested in either the presence or absence of metabolic activation (S9-mix).
There were no biologically relevant 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). One statistically significant value was noted (TA98 at 500 μg/plate in the absence of metabolic activation (S9-mix), however as the maximum fold increase was only 1.8 times the concurrent vehicle control and the mean colony count was within the in-house historical vehicle/untreated control range for the strain the response was considered of no biological relevance.

Experiment 2 (pre-incubation)
The maximum dose level of the test item in the second experiment was the same as for Experiment 1 (5000 μg/plate).
There was no visible reduction in the growth of the bacterial background lawn at any dose level, either in the presence or absence of metabolic activation (S9-mix).
No test item precipitate was observed on the plates at any of the doses tested in either the presence or absence of metabolic activation (S9-mix).
There were no significant 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).

Applicant's summary and conclusion

Conclusions:

In this Reverse Mutation Assay ‘Ames Test’ using strains of Salmonella typhimurium and Escherichia coli (OECD TG 471) the test item SPS 5290 (Stage 3) did not induce an increase in the frequency of revertant colonies that met the criteria for a positive result, either with or without metabolic activation (S9-mix). Under the conditions of this test SPS 5290 (Stage 3) was considered to be non-mutagenic.

Executive summary:

Introduction

The test method was designed to be compatible with the guidelines for bacterial mutagenicity testing published by the major Japanese Regulatory Authorities including METI, MHLW and MAFF, the OECD Guidelines for Testing of Chemicals No. 471 "Bacterial Reverse Mutation Test", Method B13/14 of Commission Regulation (EC) number 440/2008 of 30 May 2008, the ICH S2(R1) guideline adopted June 2012 (ICH S2(R1) Federal Register. Adopted 2012; 77:33748-33749) and the USA, EPA OCSPP harmonized guideline - Bacterial Reverse Mutation Test.

Methods

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 up to 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 (plate incorporation) was based on OECD TG 471 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 amended following the results of Experiment 1 and was 15 to 5000 μg/plate. Six test item concentrations were selected in Experiment 2 in order to ensure the study achieved both four non-toxic dose levels as required by the test guideline, the lack of cytotoxicity noted in Experiment 1, and the potential for a change in the cytotoxicity of the test item following the change in test methodology from plate incorporation to pre-incubation.

Results

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 and 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 OECD TG 471 recommended dose level of 5000 μg/plate. There was no visible reduction in the growth of the bacterial background lawn at any dose level, either in the presence or absence of metabolic activation (S9-mix), in the first mutation test (plate incorporation method).

Based on the results of Experiment 1, the same maximum dose level (5000 μg/plate) was employed in the second mutation test (pre-incubation method). Similarly, there was no visible reduction in the growth of the bacterial background lawn at any dose level, either in the presence or absence of metabolic activation (S9-mix).

No test item precipitate was observed on the plates at any of the doses tested in either the presence or absence of metabolic activation (S9-mix) in Experiments 1 and 2.

There were no biologically relevant 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). One statistically significant value was noted (TA98 at 500 μg/plate in the absence of metabolic activation (S9-mix)), however as the maximum fold increase was only 1.8 times the concurrent vehicle control and the mean colony count was within the in-house historical vehicle/untreated control range for the strain the response was considered of no biological relevance. Therefore, this value has not been highlighted in Table 2 as it did not meet the required criteria for a positive response.

Similarly, no significant 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).

Conclusion

In this Reverse Mutation Assay ‘Ames Test’ using strains of Salmonella typhimurium and Escherichia coli (OECD TG 471) the test item SPS 5290 (Stage 3) did not induce an increase in the frequency of revertant colonies that met the criteria for a positive result, either with or without metabolic activation (S9-mix). Under the conditions of this test SPS 5290 (Stage 3) was considered to be non-mutagenic.