2-ethylhexyl 2-([1,1'-biphenyl]-4-ylcarbonyl)benzoate

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Key CRL AMES 2020

Based on the results of this study it is concluded that C991 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

Key study was conducted according to recognised testing guidelines with GLP.

SS CRL 2019 (non-GLP)

Based on the results of this study it is concluded that C991 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

30 Sep 2019 - 22 November 2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

21 July 1997

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

31 May 2008

Deviations:

no

GLP compliance:

no

Remarks:

GLP study has been performed.

Type of assay:

bacterial reverse mutation assay

Specific details on test material used for the study:

Physical Description: Colourless to pale yellow liquid (determined by Charles River Den Bosch)
Purity/Composition: 96.27%
Storage Conditions: At room temperature
Purity/Composition correction factor: No correction factor required
Test item handling: No specific handling conditions required
Chemical name: 2-Ethylhexyl 2-([1,1'-biphenyl]-4-ylcarbonyl)benzoate
CAS number: 75005-95-7
EC Number: 278-051-5
Molecular formula: C28H30O3
Molecular weight: 414.22

Target gene:

Histidine locus

Species / strain / cell type:

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

Species / strain / cell type:

E. coli WP2 uvr A

Metabolic activation:

with and without

Metabolic activation system:

S9-Fraction
Rat liver microsomal enzymes (S9 homogenate) were obtained from Trinova Biochem GmbH, Giessen, Germany and were prepared from male Sprague Dawley rats that had been injected intraperitoneally with Aroclor 1254 (500 mg/kg body weight). Each S9 batch was characterized with the mutagens benzo-(a)-pyrene (Sigma) and 2-aminoanthracene, which require metabolic activation, in tester strain TA100 at concentrations of 5 µg/plate and 2.5 µg/plate, respectively.

Preparation of S9-Mix
S9-mix was prepared immediately before use and kept refrigerated. S9-mix contained per 10 mL: 30 mg NADP (Randox Laboratories Ltd., Crumlin, United Kingdom) and 15.2 mg glucose-6-phosphate (Roche Diagnostics, Mannheim, Germany) in 5.5 mL Milli-Q water (Millipore Corp., Bedford, MA., USA); 2 mL 0.5 M sodium phosphate buffer pH 7.4; 1 mL 0.08 M MgCl2 solution (Merck); 1 mL 0.33 M KCl solution (Merck). The above solution was filter (0.22 µm)-sterilized. To 9.5 mL of S9-mix components 0.5 mL S9-fraction was added (5% (v/v) S9-fraction) to complete the S9-mix.

Test concentrations with justification for top dose:

Dose range finding test:1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate
Direct plate Assay: 17, 52, 164, 512, 1600 and 5000 µg/plate
Pre-incubation Assay: 17, 52, 164, 512, and 2000 µg/plate

Vehicle / solvent:

dimethyl sulfoxide (Merck, Darmstadt, Germany).

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

2-nitrofluorene

sodium azide

methylmethanesulfonate

other: 2-aminoanthracene, ICR-191

Remarks:

See tables below

Details on test system and experimental conditions:

Preparation of Test Item
No correction was made for the purity/composition of the test item.
A solubility test was performed based on visual assessment. The test item formed a clear colorless solution in dimethyl sulfoxide.
The stock solution of 50 mg/mL was treated with ultrasonic waves until the test item had completely dissolved.
Test item concentrations were used within 2.5 hours after preparation.
Any residual volumes were discarded.

Test System
Test System Salmonella typhimurium bacteria and Escherichia coli bacteria Rationale Recommended test system in international guidelines (e.g. OECD, EC).
Source Trinova Biochem GmbH, Germany [Master culture from Dr. Bruce N. Ames (TA1535, TA1537, TA98, TA100; and Master culture from The National Collections of Industrial and Marine
Bacteria, Aberdeen, UK (WP2uvrA)]
The characteristics of the different Salmonella typhimurium strains were as follows:

Strain Histidine mutation Mutation type
TA1537 hisC3076 Frameshift
TA98 hisD3052/R-factor* Frameshift
TA1535 hisG46 Base-pair substitutions
TA100 hisG46/R-factor* Base-pair substitutions
*: R-factor = plasmid pKM101 (increases error-prone DNA repair)

Each tester strain contained the following additional mutations:
rfa : deep rough (defective lipopolysaccharide cellcoat)
gal : mutation in the galactose metabolism
chl : mutation in nitrate reductase
bio : defective biotin synthesis
uvrB: loss of the excision repair system (deletion of the ultraviolet-repair B gene)

The Salmonella typhimurium strains were checked at least every year to confirm their histidine-requirement, crystal violet sensitivity, ampicillin resistance (TA98 and TA100), UV-sensitivity and the number of spontaneous revertants.
The Escherichia coli WP2uvrA strain detects base-pair substitutions. The strain lacks an excision repair system and is sensitive to agents such as UV. The sensitivity of the strain to a wide variety of mutagens has been enhanced by permeabilization of the strain using Tris-EDTA treatment (Ref.1). The strain was checked to confirm the tryptophan-requirement, UV-sensitivity and the number of spontaneous revertants at least every year.
Stock cultures of the five strains were stored in the freezer (-150°C).

Cell Culture
Preparation of bacterial cultures
Samples of frozen stock cultures of bacteria were transferred into enriched nutrient broth (Oxoid LTD, Hampshire, England) and incubated in a shaking incubator (37 ± 1°C, 150 rpm), until the cultures reached an optical density of 1.0 ± 0.1 at 700 nm (109 cells/mL). Freshly grown cultures of each strain were used for a test.

Agar plates
Agar plates (ø 9 cm) contained 25 mL glucose agar medium. Glucose agar medium contained per liter: 18 g purified agar (Oxoid LTD) in Vogel-Bonner Medium E, 20 g glucose (Fresenius Kabi, Bad Homburg, Germany). The agar plates for the test with the Salmonella typhimurium strains also contained 12.5 µg/plate biotin (Merck) and 15 µg/plate histidine (Sigma) and the agar plates for the test with the Escherichia coli strain contained 15 µg/plate tryptophan (Sigma).
Top agar
Milli-Q water containing 0.6% (w/v) bacteriological agar (Oxoid LTD) and 0.5% (w/v) sodium chloride (Merck) was heated to dissolve the agar. Samples of 3 mL top agar were transferred into 10 mL glass tubes with metal caps. Top agar tubes were autoclaved for 20 min at 121 ± 3°C.
Environmental conditions
All incubations were carried out in a controlled environment at a temperature of 37.0 ± 1.0°C (actual range 35.3 - 37.7°C). The temperature was continuously monitored throughout the experiment. Due to addition of plates (which were at room temperature) to the incubator or due to opening and closing the incubator door, temporary deviations from the temperature may occur. Based on laboratory historical data these deviations are considered not to affect the study integrity.
Metabolic Activation System

Experimental Design
Dose-range Finding Test
Selection of an adequate range of doses was based on a dose-range finding test with the strains TA100 and WP2uvrA, both with and without S9-mix. Eightconcentrations, 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate were tested in triplicate.
The highest concentration of the test item used in the subsequent mutation assays was 5000 µg/plate or the level at which the test item exhibited limited solubility. At least five different doses (increasing with approximately half-log steps) of the test item were tested in triplicate in each strain in the absence and presence of S9-mix. The first experiment was a direct plate assay and the second experiment was a pre-incubation assay.
The negative control (vehicle) and relevant positive controls were concurrently tested in each strain in the presence and absence of S9-mix.

First Experiment: Direct Plate Assay
The above mentioned dose-range finding study with two tester strains is reported as a part of the direct plate assay. In the second part of this experiment, the test item was tested both in the absence and presence of S9-mix in the tester strains TA1535, TA1537 and TA98. Top agar in top agar tubes was melted by heating to 45 ± 2°C. The following solutions were successively added to 3 mL molten top agar: 0.1 mL of a fresh bacterial culture (109 cells/mL) of one of the tester strains, 0.1 ml of a dilution of the test item in DMSO and either 0.5 ml S9-mix (in case of activation assays) or 0.5 mL 0.1 M phosphate buffer (in case of non-activation assays). The ingredients were mixed on a Vortex and the content of the top agar tube was poured onto a selective agar plate. After solidification of the top agar, the plates were inverted and incubated in the dark at 37.0 ± 1.0°C for 48 ± 4 h. After this period revertant colonies (histidine independent (His+) for Salmonella typhimurium bacteria and tryptophan independent (Trp+) for Escherichia coli) were counted.

Second Experiment: Pre-Incubation Assay
The test item was tested both in the absence and presence of S9-mix in all tester strains. Top agar in top agar tubes was melted by heating to 45 ± 2°C. The following solutions were pre-incubated for 30 ± 2 minutes by 70 rpm at 37 ± 1°C, either 0.5 mL S9-mix (in case of activation assays) or 0.5 mL 0.1 M phosphate buffer (in case of non-activation assays), 0.1 mL of a fresh bacterial culture (109 cells/mL) of one of the tester strains, 0.1 mL of a dilution of the test item in DMSO. After the pre-incubation period 3 mL molten top agar was added to the solutions. The ingredients were mixed on a Vortex and the content of the top agar tube was poured onto a selective agar plate. After solidification of the top agar, the plates were inverted and incubated in the dark at 37.0 ± 1.0°C for 48 ± 4 h. After this period revertant colonies (histidine independent (His+) for Salmonella typhimurium bacteria and tryptophan independent (Trp+) for Escherichia coli) were counted.

Colony Counting
The revertant colonies were counted automatically with the Sorcerer Colony Counter. Plates with sufficient test item precipitate to interfere with automated colony counting were counted manually. Evidence of test item precipitate on the plates and the condition of the bacterial background lawn were evaluated when considered necessary, macroscopically and/or microscopically by using a dissecting microscope.

Rationale for test conditions:

According to OECD guideline

Evaluation criteria:

INTERPRETATION
No formal hypothesis testing was done.
In addition to the criteria stated below, any increase in the total number of revertants should be evaluated for its biological relevance including a comparison of the results with the historical control data range.

A test item is considered negative (not mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 or WP2uvrA is not greater than two times the concurrent control, and the total number of revertants in tester strains TA1535, TA1537 or TA98 is not greater than three times the concurrent control.
b) The negative response should be reproducible in at least one follow up experiment.

A test item is considered positive (mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 or WP2uvrA is greater than two times the concurrent control, or the total number of revertants in tester strains TA1535, TA1537 or TA98 is greater than three times the concurrent control.
b) In case a repeat experiment is performed when a positive response is observed in one of the tester strains, the positive response should be reproducible in at least one follow up experiment.

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:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

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:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

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:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

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:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

First Experiment: Direct Plate Assay
The test item was initially tested in the tester strains TA100 and WP2uvrA as a dose-range finding test with concentrations of 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate in the absence and presence of S9-mix. Based on the results of the dose-range finding test, the following dose-range was selected for the mutation assay with the tester strains, TA1535, TA1537 and TA98 in the absence and presence of S9-mix: 17, 52, 164, 512, 1600 and 5000 μg/plate. The results are shown in Table 1 and Table 2 (in Appendix 1, appended to 'attached background information). The individual data are presented in Appendix 3 (appended to 'attached background information).

Precipitate
Precipitation of the test item on the plates was observed at concentrations of 1600 µg/plate and upwards.

Toxicity
To determine the toxicity of the test item, the reduction of the bacterial background lawn, the increase in the size of the microcolonies and the reduction of the revertant colonies were observed. The definitions are stated in Appendix 2(appended to 'attached background information).
No reduction of the bacterial background lawn and no biologically relevant decrease in the number of revertants were observed. In strain TA1537 (absence and presence of S9-mix), fluctuations in the number of revertant colonies below the laboratory historical control data range were observed. However, these reduction are not considered to be caused by toxicity of the test item. It is more likely these reductions are caused by an incidental fluctuation in the number of revertant colonies.

Mutagenicity
In the direct plate test, no increase in the number of revertants was observed upon treatment with the test item under all conditions tested.

Second Experiment: Pre-Incubation Assay
To obtain more information about the possible mutagenicity of the test item, a pre-incubation experiment was performed in the absence and presence of S9-mix. Based on the results of the first mutation assay, the test item was tested up to the dose level of 2000 µg/plate in the tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA. The results are shown in Table 3 (in Appendix 1, appended to 'attached background information), the individual data are presented in Appendix 3.

Precipitate
Precipitation of the test item on the plates was observed at concentrations of 512 and/or 2000 µg/plate. Except for tester strains TA100 and WP2uvrA in the presence of S9-mix (precipitation at the dose level of 2000 µg/plate only) and tester strain TA98 in the absence of S9-mix (precipitation already observed at the dose level of 164 µg/plate).

Toxicity
There was no reduction in the bacterial background lawn and no biologically relevant decrease in the number of revertants at any of the concentrations tested in all tester strains in the absence and presence of S9-mix.

Mutagenicity
In the pre-incubation test, no increase in the number of revertants was observed upon treatment with the test item under all conditions tested.

DISCUSSION
All bacterial strains showed negative responses over the entire dose-range, i.e. no significant dose-related increase in the number of revertants in two independently repeated experiments.
The negative and strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.

Conclusions:

In conclusion, based on the results of this study it is concluded that the test item is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

Executive summary:

The objective of this study was to determine the potential of the test item and/or its metabolites to induce reverse mutations at the histidine locus in several strains of Salmonella typhimurium (S. typhimurium; TA98, TA100, TA1535, and TA1537), and at the tryptophan locus of Escherichia coli (E. coli) strain WP2uvrA in the presence or absence of an exogenous mammalian metabolic activation system (S9).  

The test was performed in two independent experiments, at first a direct plate assay was performed and secondly a pre-incubation assay.

The study procedures described in this report were based on the most recent OECD and EC guidelines.

The test item was a colourless to pale yellow liquid.  The vehicle of the test item was dimethyl sulfoxide.

In the dose-range finding study, the test item was initially tested up to concentrations of 5000 µg/plate in the strains TA100 and WP2uvrA in the direct plate assay.  The test item precipitated on the plates at dose levels of 1600 and 5000 μg/plate.  The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.  Results of this dose-range finding test were reported as part of the first mutation assay.

In the first mutation experiment, the test item was again tested up to concentrations of 5000 µg/plate in the strains TA1535, TA1537 and TA98.  The test item precipitated on the plates at dose levels of 1600 and 5000 μg/plate.  The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.

In the second mutation experiment, the test item was tested up to concentrations of 2000 µg/plate in the tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA in the pre-incubation assay.  The test item was tested up to or beyond a precipitating dose level.  The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.  

The negative and strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.

The test item did not induce a significant dose-related increase in the number of revertant (His+) colonies in each of the four tester strains (TA1535, TA1537, TA98 and TA100) and in the number of revertant (Trp+) colonies in tester strain WP2uvrA both in the absence and presence of S9-metabolic activation.  These results were confirmed in a follow-up experiment.

In conclusion, based on the results of this study it is concluded that the test item is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.  

Reference 2

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 November 2019 - 24 January 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

July 21, 1997

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

31 May 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

bacterial reverse mutation assay

Specific details on test material used for the study:

Physical Description: Colourless to pale yellow liquid (determined by Charles River Den Bosch)
Purity/Composition: 96.27%
Storage Conditions: At room temperature
Solubility in vehicle: Dimethyl sulfoxide: Not indicated
Stability in vehicle: Dimethyl sulfoxide: Not indicated

Target gene:

Hstidine locus (S. typhimurium); tryptophan locus (E. coli)

Species / strain / cell type:

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

Species / strain / cell type:

E. coli WP2 uvr A

Metabolic activation:

with and without

Metabolic activation system:

S9-Fraction
Rat liver microsomal enzymes (S9 homogenate) were obtained from Trinova Biochem GmbH, Giessen, Germany and were prepared from male Sprague Dawley rats that had been injected intraperitoneally with Aroclor 1254 (500 mg/kg body weight).
Each S9 batch was characterized with the mutagens benzo-(a)-pyrene (Sigma) and 2-aminoanthracene, which require metabolic activation, in tester strain TA100 at concentrations of 5 µg/plate and 2.5 µg/plate, respectively.

Preparation of S9-Mix
S9-mix was prepared immediately before use and kept refrigerated. S9-mix contained per 10 mL: 30 mg NADP (Randox Laboratories Ltd., Crumlin, United Kingdom) and 15.2 mg glucose-6-phosphate (Roche Diagnostics, Mannheim, Germany) in 5.5 mL Milli-Q water (Millipore Corp., Bedford, MA., USA); 2 mL 0.5 M sodium phosphate buffer pH 7.4; 1 mL 0.08 M MgCl2 solution (Merck); 1 mL 0.33 M KCl solution (Merck). The above solution was filter (0.22 µm)-sterilized. To 9.5 mL of S9-mix components 0.5 mL S9-fraction was added (5% (v/v) S9-fraction) to complete the S9-mix.

Test concentrations with justification for top dose:

Dose-range finding test: 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate in the absence and presence of S9-mix
Mutation assay: 17, 52, 164, 512, 1600 and 5000 μg/plate in the absence and presence of S9-mix
Pre-Incubation Assay: 17, 52, 164, 512 and 2000 μg/plate in the absence and presence of S9-mix

The highest concentration of the test item used in the subsequent mutation assays was 5000 µg/plate or the level at which the test item exhibited limited solubility.

Vehicle / solvent:

The vehicle of the test item was dimethyl sulfoxide (Merck, Darmstadt, Germany)

Solvents for Positive Control Items
Saline = physiological saline (Eurovet Animal Health, Bladel, The Netherlands)
DMSO = dimethyl sulfoxide

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

2-nitrofluorene

sodium azide

methylmethanesulfonate

other: ICR-191 (TA1537 without metabolic activation); 2-aminoanthracene (all strains with metabolic acticvation)

Details on test system and experimental conditions:

NUMBER OF REPLICATIONS:
Number of cultures per concentration: tested in triplicate.


Number of independent experiments :
Eight concentrations in the dose-range finding test (used as part of the direct plate assay) in two strains, with and without S9-mix (32 experiments)
Five concentrations in the direct plate assay in remaining test strains (three), with and without S9-mix (30 experiments)
Five concentrations in the pre-incubation assay in five strains, with and without S9-mix (50 experiments)


METHOD OF TREATMENT/ EXPOSURE - CELL CULTURE
Preparation of bacterial cultures:
Samples of frozen stock cultures of bacteria were transferred into enriched nutrient broth (Oxoid LTD, Hampshire, England) and incubated in a shaking incubator (37 ± 1°C, 150 rpm), until the cultures reached an optical density of 1.0 ± 0.1 at 700 nm (109 cells/mL). Freshly grown cultures of each strain were used for a test.

Agar plates
Agar plates (ø 9 cm) contained 25 mL glucose agar medium. Glucose agar medium contained per liter: 18 g purified agar (Oxoid LTD) in Vogel-Bonner Medium E, 20 g glucose (Fresenius Kabi, Bad Homburg, Germany). The agar plates for the test with the Salmonella typhimurium strains also contained 12.5 µg/plate biotin (Merck) and 15 µg/plate histidine (Sigma) and the agar plates for the test with the Escherichia coli strain contained 15 µg/plate tryptophan (Sigma).

Top agar
Milli-Q water containing 0.6% (w/v) bacteriological agar (Oxoid LTD) and 0.5% (w/v) sodium chloride (Merck) was heated to dissolve the agar. Samples of 3 mL top agar were transferred into 10 mL glass tubes with metal caps. Top agar tubes were autoclaved for 20 min at 121 ± 3°C.


TREATMENT AND HARVEST SCHEDULE:
First Experiment: Direct Plate Assay (including dose range finder)
Top agar in top agar tubes was melted by heating to 45 ± 2°C. The following solutions were successively added to 3 mL molten top agar: 0.1 mL of a fresh bacterial culture (109 cells/mL) of one of the tester strains, 0.1 ml of a dilution of the test item in DMSO and either 0.5 ml S9-mix (in case of activation assays) or 0.5 mL 0.1 M phosphate buffer (in case of non-activation assays). The ingredients were mixed on a Vortex and the content of the top agar tube was poured onto a selective agar plate. After solidification of the top agar, the plates were inverted and incubated in the dark at 37.0 ± 1.0°C for 48 ± 4 h. After this period revertant colonies (histidine independent (His+) for Salmonella typhimurium bacteria and tryptophan independent (Trp+) for Escherichia coli) were counted.

Second Experiment: Pre-Incubation Assay
Top agar in top agar tubes was melted by heating to 45 ± 2°C. The following solutions were pre-incubated for 30 ± 2 minutes by 70 rpm at 37 ± 1°C, either 0.5 mL S9-mix (in case of activation assays) or 0.5 mL 0.1 M phosphate buffer (in case of non-activation assays), 0.1 mL of a fresh bacterial culture (109 cells/mL) of one of the tester strains, 0.1 mL of a dilution of the test item in DMSO. After the pre-incubation period 3 mL molten top agar was added to the solutions. The ingredients were mixed on a Vortex and the content of the top agar tube was poured onto a selective agar plate. After solidification of the top agar, the plates were inverted and incubated in the dark at 37.0 ± 1.0°C for 48 ± 4 h. After this period revertant colonies (histidine independent (His+) for Salmonella typhimurium bacteria and tryptophan independent (Trp+) for Escherichia coli) were counted.


COLONY COUNTING
The revertant colonies were counted automatically with the Sorcerer Colony Counter. Plates with sufficient test item precipitate to interfere with automated colony counting were counted manually. Evidence of test item precipitate on the plates and the condition of the bacterial background lawn were evaluated when considered necessary, macroscopically and/or microscopically by using a dissecting microscope.

ACCEPTABILITY CRITERIA
A Salmonella typhimurium reverse mutation assay and/or Escherichia coli reverse mutation assay is considered acceptable if it meets the following criteria:
a) The vehicle control and positive control plates from each tester strain (with or without S9-mix) must exhibit a characteristic number of revertant colonies when compared against relevant historical control data generated at Charles River Den Bosch.
b) The selected dose-range should include a clearly toxic concentration or should exhibit limited solubility as demonstrated by the preliminary toxicity range-finding test or should extend to 5 mg/plate.
c) No more than 5% of the plates are lost through contamination or some other unforeseen event. If the results are considered invalid due to contamination, the experiment will be repeated.

All results presented in the tables of the report are calculated using values as per the raw data rounding procedure and may not be exactly reproduced from the individual data presented.

Rationale for test conditions:

According to OECD guidelines

Evaluation criteria:

INTERPRETATION
No formal hypothesis testing was done.
In addition to the criteria stated below, any increase in the total number of revertants should be evaluated for its biological relevance including a comparison of the results with the historical control data range. A test item is considered negative (not mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 or WP2uvrA is not greater than two times the concurrent control, and the total number of revertants in tester strains TA1535, TA1537 or TA98 is not greater than three times the concurrent control.
b) The negative response should be reproducible in at least one follow up experiment.

A test item is considered positive (mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 or WP2uvrA is greater than two times the concurrent control, or the total number of revertants in tester strains TA1535, TA1537 or TA98 is greater than three times the concurrent control.
b) In case a repeat experiment is performed when a positive response is observed in one of the tester strains, the positive response should be reproducible in at least one follow up experiment.

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity, but tested up to precipitating concentrations

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity, but tested up to precipitating concentrations

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity, but tested up to precipitating concentrations

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity, but tested up to precipitating concentrations

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity, but tested up to precipitating concentrations

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

FIRST EXPERIMENT: Direct Plate Assay
The test item was initially tested in the tester strains TA100 and WP2uvrA as a dose-range finding test with concentrations of 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate in the absence and presence of S9-mix. Based on the results of the dose-range finding test, the following dose-range was selected for the mutation assay with the tester strains, TA1535, TA1537 and TA98 in the absence and presence of S9-mix: 17, 52, 164, 512, 1600 and 5000 μg/plate. The results are shown in Table 1 and Table 2. The individual data are presented in Appendix 3.

Precipitate
Precipitation of the test item on the plates was observed at concentrations of 1600 µg/plate and upwards.

Toxicity
To determine the toxicity of the test item, the reduction of the bacterial background lawn, the increase in the size of the microcolonies and the reduction of the revertant colonies were observed. The definitions are stated in Appendix 2.
No reduction of the bacterial background lawn and no biologically relevant decrease in the number of revertants were observed. In strain TA1537 (absence and presence of S9-mix), fluctuations in the number of revertant colonies below the laboratory historical control data range were observed. However, these reduction are not considered to be caused by toxicity of the test item. It is more likely these reductions are caused by an incidental fluctuation in the number of revertant colonies.

Mutagenicity
In the direct plate test, no increase in the number of revertants was observed upon treatment with the test item under all conditions tested.


SECOND EXPERIMENTt: Pre-Incubation Assay
To obtain more information about the possible mutagenicity of the test item, a pre-incubation experiment was performed in the absence and presence of S9-mix. Based on the results of the first mutation assay, the test item was tested up to the dose level of 2000 µg/plate in the tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA. The results are shown in Table 3, the individual data are presented in Appendix 3.

Precipitate
Precipitation of the test item on the plates was observed at concentrations of 512 and/or 2000 µg/plate. Except for tester strains TA100 and WP2uvrA in the presence of S9-mix (precipitation at the dose level of 2000 µg/plate only) and tester strain TA98 in the absence of S9-mix (precipitation already observed at the dose level of 164 µg/plate).

Toxicity
There was no reduction in the bacterial background lawn and no biologically relevant decrease in the number of revertants at any of the concentrations tested in all tester strains in the absence and presence of S9-mix.

Mutagenicity
In the pre-incubation test, no increase in the number of revertants was observed upon treatment with the test item under all conditions tested.

Conclusions:

In conclusion, based on the results of this study it is concluded that the test item is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

Executive summary:

The objective of this study was to determine the potential of the test item and/or its metabolites to induce reverse mutations at the histidine locus in several strains of Salmonella typhimurium (S. typhimurium; TA98, TA100, TA1535, and TA1537), and at the tryptophan locus of Escherichia coli (E. coli) strain WP2uvrA in the presence or absence of an exogenous mammalian metabolic activation system (S9).  

The test was performed in two independent experiments, at first a direct plate assay was performed and secondly a pre-incubation assay.

The study procedures described in this report were based on the most recent OECD and EC guidelines.

The test item was a colourless to pale yellow liquid.  The vehicle of the test item was dimethyl sulfoxide.

In the dose-range finding study, the test item was initially tested up to concentrations of 5000 µg/plate in the strains TA100 and WP2uvrA in the direct plate assay.  The test item precipitated on the plates at dose levels of 1600 and 5000 μg/plate.  The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.  Results of this dose-range finding test were reported as part of the first mutation assay.

In the first mutation experiment, the test item was again tested up to concentrations of 5000 µg/plate in the strains TA1535, TA1537 and TA98.  The test item precipitated on the plates at dose levels of 1600 and 5000 μg/plate.  The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.

In the second mutation experiment, the test item was tested up to concentrations of 2000 µg/plate in the tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA in the pre-incubation assay.  The test item was tested up to or beyond a precipitating dose level.  

The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.  

The negative and strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.

The test item did not induce a significant dose-related increase in the number of revertant (His+) colonies in each of the four tester strains (TA1535, TA1537, TA98 and TA100) and in the number of revertant (Trp+) colonies in tester strain WP2uvrA both in the absence and presence of S9-metabolic activation.  These results were confirmed in a follow-up experiment.

In conclusion, based on the results of this study it is concluded that C991 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

The substance does not meet the criteria for classification as mutagenic according to the EU Classification, Labelling, and Packaging regulation 1272/2008.