RD 14156

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

The substance was considered to be non-mutagenic under the conditions of an Ames test and in an in vitro mouse lymphoma assay.

The substance was considered to be non-clastogenic to human lymphocytes in an in vitro chromosome aberration test.

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

The study was conducted between 14 April 2016 and 16 June 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)

Version / remarks:

26 September 2014

Deviations:

no

Qualifier:

according to guideline

Guideline:

JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals

Version / remarks:

31 March 2011

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

in vitro mammalian cell transformation assay

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Sponros Lot/Batch number: 5399561P10
- Expiration date of the lot/batch: 25 January 2020
- Purity test date: 25 January 2016

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature in the dark

Species / strain / cell type:

lymphocytes: A&B

Details on mammalian cell type (if applicable):

For each experiment, sufficient whole blood was drawn from the peripheral circulation of a non-smoking volunteer (aged 18-35) who had been previously screened for suitability. The volunteer had not knowingly been exposed to high levels of radiation or hazardous chemicals and had not knowingly recently suffered from a viral infection. Based on over 20 years in-house data for cell cycle times for lymphocytes using BrdU (bromodeoxyuridine) incorporation to assess the number of first, second and third division metaphase cells to calculate the average generation time (AGT) for human lymphocytes it is considered to be approximately
16 hours. Therefore using this average the in-house exposure time for the experiments for 1.5 x AGT is 24 hours.
The details of the donors used are:
Preliminary Toxicity Test: female, aged 33 years
Main Experiment: male, aged 30 years

Cell Culture
Cells (whole blood cultures) were grown in Eagle's minimal essential medium with HEPES buffer (MEM), supplemented “in-house” with L-glutamine, penicillin/
streptomycin, amphotericin B and 10 % foetal bovine serum (FBS), at approximately 37 ºC with 5 % CO2 in humidified air. The lymphocytes of fresh heparinized whole blood were stimulated to divide by the addition of phytohaemagglutinin (PHA).

Metabolic activation:

with and without

Metabolic activation system:

S9 Microsomal fractions

Test concentrations with justification for top dose:

The test item was considered to be a UVCB* and, therefore, the maximum recommended dose was initially set at 5000 μg/mL. The purity of the test item was 100% and was not accounted for in the test item formulations.

The test item was insoluble in aqueous media at 50 mg/mL, and was insoluble in dimethyl sulphoxide and acetone at 125, 250, and 500 mg/mL. However, the test
item could be formulated into a best doseable suspension in acetone at 125 mg/mL in solubility checks performed in-house.
Due to the sensitivity of human lymphocytes to acetone, the formulations were prepared at twice the concentration required in culture and dosed in 50 μl aliquots. Consequently, the maximum practical concentration was 625 μg/mL.
Prior to each experiment, the test item was accurately weighed, formulated in acetone and appropriate serial dilutions prepared.

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: acetone
- Justification for choice of solvent/vehicle: Solubility

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

cyclophosphamide

mitomycin C

Details on test system and experimental conditions:

Culture conditions
Duplicate lymphocyte cultures (A and B) were established for each dose level by mixing the following components, giving, when dispensed into sterile plastic flasks for each culture:
9.05 mL MEM, 10% (FBS)
0.1 mL Li-heparin
0.1 mL phytohaemagglutinin
0.75 mL heparinized whole blood

4-Hour Exposure With Metabolic Activation (S9)
After approximately 48 hours incubation at approximately 37 ºC, 5% CO2 in humidified air, the cultures were transferred to tubes and centrifuged. Approximately 9 mL of the culture medium was removed, reserved, and replaced with the required volume of MEM (including serum) and 0.05 mL of the appropriate solution of vehicle control or test item was added to each culture. For the positive control, 0.1 mL of the appropriate solution was added to the cultures. 1mL of 20% S9¯mix (i.e. 2% final concentration of S9 in standard co-factors) was added to the cultures of the Preliminary Toxicity Test and Main Experiment.

After 4 hours at approximately 37 ºC, 5% CO2 in humidified air, the cultures were centrifuged, the treatment medium removed by suction and replaced with an 8 mL wash of MEM culture medium. After a further centrifugation the wash medium was removed by suction and replaced with the original culture medium. The cells were then re-incubated for a further 20 hours at approximately 37 ºC in 5% CO2 in humidified air.

4-Hour Exposure Without Metabolic Activation (S9)
After approximately 48 hours incubation at approximately 37 ºC with 5% CO2 in humidified air, the cultures were decanted into tubes and centrifuged. Approximately 9 mL of the culture medium was removed and reserved. The cells were then resuspended in the required volume of fresh MEM (including serum) and dosed with 0.05 mL of the appropriate vehicle control, test item solution or 0.1 mL of positive control solution. The total volume for each
culture was a nominal 10 mL.
After 4 hours at approximately 37 ºC, 5% CO2 in humidified air, the cultures were centrifuged the treatment medium was removed by suction and replaced with an 8 mL wash of MEM culture medium. After a further centrifugation the wash medium was removed by suction and replaced with the reserved original culture medium. The cells were then returned to the incubator for a further 20 hours.

24-Hour Exposure Without Metabolic Activation (S9)
As the exposure was continuous the cultures were established, at a nominal volume of 9.9 mL. After approximately 48 hours incubation the cultures were removed from the incubator and dosed with 0.05 mL of vehicle control, test item dose solution or 0.1 mL of positive control solution. The nominal final volume of each culture was 10 mL. The cultures were then incubated at approximately 37 ºC, 5% CO2 in humidified air for 24 hours. The preliminary toxicity test was performed using all three of the exposure conditions as described for the Main Experiment but using single cultures only.

Evaluation criteria:

Data Evaluation
The following criteria were used to determine a valid assay:
 The frequency of cells with structural chromosome aberrations (excluding gaps) in the vehicle control cultures was within the laboratory historical control data range.
 All the positive control chemicals induced a positive response (p≤0.01) and demonstrated the validity of the experiment and the integrity of the S9-mix.
 The study was performed using all three exposure conditions using a top concentration which meets the requirements of the current testing guideline.
 The required number of cells and concentrations were analyzed.

Criteria for determining the Study Conclusion
Providing that all of the acceptability criteria are fulfilled, a test item can be considered to be clearly negative if, in any of the experimental conditions examined:
1) The number of cells with structural aberrations in all evaluated dose groups should be within the range of the laboratory historical control data.
2) No toxicologically or statistically significant increase of the number of cells with structural chromosome aberrations is observed following statistical analysis.
3) There is no concentration-related increase at any dose level

A test item can be classified as genotoxic if:
1) The number of cells with structural chromosome aberrations is outside the range of the laboratory historical control data.
2) At least one concentration exhibits a statistically significant increase in the number of cells with structural chromosome aberrations compared to the concurrent negative control.
3) The observed increase in the frequency of cells with structural aberrations is considered to be dose-related

When all of the above criteria are met, the test item can be considered able to induce chromosomal aberrations in human lymphocytes.

Statistics:

The frequency of cells with aberrations excluding gaps and the frequency of polyploid cells was compared, where necessary, with the concurrent vehicle control value using Fisher's Exact test. (Richardson et al. 1989).
A toxicologically significant response is recorded when the p value calculated from the statistical analysis of the frequency of cells with aberrations excluding gaps is less than 0.05 when compared to its concurrent control and there is a dose-related increase in the frequency of cells with aberrations which is reproducible. Incidences where marked statistically significant increases are observed only with gap-type aberrations will be assessed on a case by case basis.

Key result

Species / strain:

lymphocytes: A&B

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

The assay was considered valid as it met all of the following criteria:
The frequency of cells with chromosome aberrations (excluding gaps) in the vehicle control cultures were within the current historical control data range.
All the positive control chemicals induced a demonstrable positive response (p≤0.01) and confirmed the validity and sensitivity of the assay and the integrity of the S9-mix.
The study was performed using all three exposure conditions using a top concentration which meets the requirements of the current testing guideline.
The required number of cells and concentrations were analyzed.
The test item did not induce any statistically significant increases in the frequency of cells with aberrations either in the absence or presence of metabolic activation.
The test item did not induce any statistically significant increase in the numbers of polyploid cells at any dose level in either of the exposure groups.

Preliminary Toxicity Test

The dose range for the Preliminary Toxicity Test was 2.44 to 625 μg/mL. The maximum dose was initially set at the maximum recommended dose level of 5000 μg/mL. Due to solubility issues, the test item could only be formulated into a best doseable suspension at 125 mg/mL in solubility checks performed in-house. Additionally, due to the sensitivity of human lymphocytes to acetone, the formulations were prepared at twice the concentration required in culture and dosed in 50 μl aliquots. Consequently, the maximum practical concentration was 625 μg/mL.

A precipitate of the test item was observed in the parallel blood-free cultures at the end of the exposure at and above 4.88 μg/mL in both the 4(20)-hour and 24-hours exposures in the absence of metabolic activation (S9) and at and above 19.53 μg/mL in the presence of S9. No hemolysis was observed following exposure to the test item in any of the exposure groups.

Microscopic assessment of the slides prepared from the exposed cultures showed that metaphase cells were present up to maximum dose level of 625 μg/mL in the 4(20)-hour exposures in the presence and absence of S9. The maximum dose with metaphases present in the 24-hour continuous exposure was 312.5 μg/mL. The test item induced some evidence of toxicity in all of the exposure groups.

The selection of the maximum dose level for the Main Experiment was based on the lowest precipitating dose level in all three exposure groups.

Chromosome Aberration Test – Main Experiment

The dose levels of the controls and the test item are given in the table below:

Group                                                 Final concentration of RD 14156 (μg/mL)

4(20)-hour without S9               0*, 0.625*, 1.25*, 2.5*, 5*, 10, 20, 30, MMC 0.2*

4(20)-hour with S9 (2%)              0*, 2.5*, 5*, 10*, 20*, 30, 40, 50, CP 1*

24-hour without S9                      0*, 0.625, 1.25, 2.5*, 5*, 10*, 20*, 30, MMC 0.1*

*dose levels selected for metaphase analysis

The qualitative assessment of the slides determined that precipitate was evident at much higher concentrations and the toxicity was greater to that observed in the Preliminary Toxicity Test and that there were metaphases suitable for scoring present in all three exposure groups at the maximum dose level of test item.

Precipitate observations were made at the end of exposure in blood-free cultures and was noted at and above 10 μg/mL in the 4(20)-hour exposure group in the absence of S9 and at and above 20 μg/mL in the 4(20)-hour exposure in the presence of S9 and 24-hour continuous exposure group.

The mitotic index data confirm the qualitative observations in that no explicit dose-related inhibition of mitotic index was observed, however, there were exposure groups where a moderate plateau of toxicity was observed.

In the 4(20)-hour exposure group in the absence of S9, 69%, 73%, 52% and 88% mitotic inhibition was achieved at 1.25, 2.5, 5 and 10 μg/mL, respectively. Therefore, the maximum dose level selected for metaphase analysis was 5 μg/mL as this dose level exhibited optimum toxicity as specified in the OECD 473 test guideline (55±5%).

In the 4(20) hour exposure group in the presence of S9, a slight dose-related inhibition of mitotic index was observed at where 83%, 75% and 45% mitotic inhibition was observed at 5, 10 and 20 μg/mL, respectively. As the lowest precipitating dose level and approximately optimum toxicity was observed at 20 μg/mL, this dose level was chosen as the maximum concentration for metaphase analysis.

In the 24-hour continuous exposure group, 81%, 70% and 65% mitotic inhibition was observed at 5, 10 and 20 μg/mL, respectively. Therefore, the maximum dose level selected for metaphase analysis was 20 μg/mL. Although the inhibition of mitotic index approached optimum toxicity in the 24-hour continuous exposure group, the lowest precipitating dose level was selected as the maximum dose level for metaphase analysis (20 μg/mL).

In the 24-hour continuous exposure group, 81%, 70% and 65% mitotic inhibition was observed at 5, 10 and 20 μg/mL, respectively. Therefore, the maximum dose level selected for metaphase analysis was 20 μg/mL. Although the inhibition of mitotic index approached optimum toxicity in the 24-hour continuous exposure group, the lowest precipitating dose level was selected as the maximum dose level for metaphase analysis (20 μg/mL).

It should be noted that the some of the Mitotic Indices for the duplicate cultures of a single concentration varied but tended to be consistent with the quantitative slide assessment for the presence of metaphases and/or precipitate. It should also be noted that the variability in MI values between duplicates, which was also reflected by the qualitative assessment, was considered not to affect the integrity of the study. This was particularly true for the short term exposure groups. The unequal MI values in the duplicates depressed the overall MI value but not enough to alter the required number of metaphases available for analysis.

Conclusions:

RD 14156 did not induce a statistically significant increase in the frequency of cells with chromosome aberrations, in either the absence or presence of a liver enzyme metabolizing system. The test item was, therefore, considered to be non-clastogenic to human lymphocytes in vitro.

Executive summary:

This report describes the results of an in vitro study for the detection of structural chromosomal aberrations in cultured mammalian cells. It supplements microbial systems insofar as it identifies potential mutagens that produce chromosomal aberrations rather than gene mutations (Scott et al., 1990).

Methods

Duplicate cultures of human lymphocytes, treated with the test item, were evaluated for chromosome aberrations at four dose levels, together with vehicle and positive controls. In this study, three exposure conditions were investigated; 4 hours exposure in the presence of an induced rat liver homogenate metabolizing system (S9), at a 2% final concentration with cell harvest after a 20-hour expression period, 4 hours exposure in the absence of metabolic activation (S9) with a 20-hour expression period and a 24-hour exposure in the absence of metabolic activation.

The dose levels used in the Main Experiment were selected using data from the preliminary toxicity test where the results indicated that the maximum concentration should be limited on toxicity for the 4-hour exposure group, in the absence of S9-mix and precipitate for the other two exposure groups.

Results

All vehicle (acetone) controls had frequencies of cells with aberrations within the range expected for normal human lymphocytes. All the positive control items induced statistically significant increases in the frequency of cells with aberrations. Thus, the sensitivity of the assay and the efficacy of the S9-mix were validated.

The test item was toxic but did not induce any statistically significant increases in the frequency of cells with aberrations, using a dose range that included a dose level that was the lowest precipitating dose level or optimum toxicity.

Conclusion

The test item, RD 14156 was considered to be non-clastogenic to human lymphocytes in vitro.

Reference 2

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

The study was conducted between 24 March 2016 and 25 April 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 490 (In Vitro Mammalian Cell Gene Mutation Tests Using the Thymidine Kinase Gene)

Version / remarks:

28 July 2015

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

EU Method B.17 (Mutagenicity - In Vitro Mammalian Cell Gene Mutation Test)

Version / remarks:

30 May 2008

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.5300 - In vitro Mammalian Cell Gene Mutation Test

Deviations:

not specified

GLP compliance:

yes (incl. QA statement)

Remarks:

No analysis to determine homogeneity, concentration or stability of RD14156 formulation. Formulated within 2h of use and assumed stable - not considered to affect purpose or integrity of study

Type of assay:

in vitro mammalian cell micronucleus test

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Sponsor Lot/Batch no. 5399561P10
- Expiration date of the lot/batch: 25 January 2020
- Purity test date: 25 Jan 2016

RADIOLABELLING INFORMATION (if applicable)
- Radiochemical purity:
- Specific activity:
- Locations of the label:
- Expiration date of radiochemical substance:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature in the dark
- Stability under test conditions:
- Solubility and stability of the test substance in the solvent/vehicle:
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium:

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing:
- Preliminary purification step (if any):
- Final dilution of a dissolved solid, stock liquid or gel:
- Final preparation of a solid:

FORM AS APPLIED IN THE TEST (if different from that of starting material)

OTHER SPECIFICS:

Species / strain / cell type:

mouse lymphoma L5178Y cells

Remarks:

+/- 3.7.2c

Details on mammalian cell type (if applicable):

CELLS USED
- Source of cells: MRC Cell Mutation Unit, University of Sussex, UK
- Suitability of cells:
- Cell cycle length, doubling time or proliferation index: ~12h
- Sex, age and number of blood donors if applicable:
- Whether whole blood or separated lymphocytes were used if applicable:
- Number of passages if applicable:
- Methods for maintenance in cell culture if applicable:
- Modal number of chromosomes:
- Normal (negative control) cell cycle time:

MEDIA USED
- Type and identity of media including CO2 concentration if applicable: RPMI 1640 medium, 37 degC, 5% CO2
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes
- Periodically checked for karyotype stability: [yes/no)
- Periodically 'cleansed' against high spontaneous background: yes

Additional strain / cell type characteristics:

not specified

Metabolic activation:

with and without

Metabolic activation system:

S9

Test concentrations with justification for top dose:

The test item was considered to be a complex mixture and maximum ecommended dose level was 500 mg/mL. Low soulbility indicated this was not suitable thus concentration was reduced to 125 mg/mL. Acetone is toxic to L5178Y cells at greater than 0.5% total culture volume, therefore test item was formulated at 125 mg/mL and dosed at 0.5% to gve a maximum achievable dose of 625 µg/mL

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: acetone
- Justification for choice of solvent/vehicle: solubility of test item

Negative solvent / vehicle controls:

yes

Remarks:

Acetone

Positive controls:

yes

Positive control substance:

ethylmethanesulphonate

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium;
- Cell density at seeding (if applicable):

DURATION
- Preincubation period:
- Exposure duration: 4h +/- S9 and 24h -S9
- Expression time (cells in growth medium):
- Selection time (if incubation with a selection agent):
- Fixation time (start of exposure up to fixation or harvest of cells):

SELECTION AGENT (mutation assays):

SPINDLE INHIBITOR (cytogenetic assays):

STAIN (for cytogenetic assays):

NUMBER OF REPLICATIONS:

METHODS OF SLIDE PREPARATION AND STAINING TECHNIQUE USED:

NUMBER OF CELLS EVALUATED:

NUMBER OF METAPHASE SPREADS ANALYSED PER DOSE (if in vitro cytogenicity study in mammalian cells):

CRITERIA FOR MICRONUCLEUS IDENTIFICATION:

DETERMINATION OF CYTOTOXICITY
- Method: mitotic index; cloning efficiency; relative total growth; other:
- Any supplementary information relevant to cytotoxicity:

OTHER EXAMINATIONS:
- Determination of polyploidy:
- Determination of endoreplication:
- Methods, such as kinetochore antibody binding, to characterize whether micronuclei contain whole or fragmented chromosomes (if applicable):

- OTHER:

Evaluation criteria:

Dose selection for the mutagenicity experiments was made using data from the preliminary toxicity test in an attempt to obtain the desired levels of toxicity. This optimum toxicity is approximately 20% survival (80% toxicity), but no less than 10% survival (90% toxicity). Relative Total Growth (RTG) values are the primary factor used to designate the level of toxicity achieved by the test item for any individual dose level. However, under certain circumstances, %RSG values may also be taken into account when designating the level of toxicity achieved. Dose levels that have RTG survival values less than 10% are excluded from the mutagenicity data analysis, as any response they give would be considered to have no biological or toxicological relevance.

Key result

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

The dose range of the test item used in the preliminary toxicity test was 2.44 to 625 µg/mL. There was evidence of reductions in the Relative Suspension Growth (%RSG) of cells treated with the test item when compared to the concurrent vehicle controls in all three of the exposure groups. However, the reductions were observed at dose levels beyond the onset of the test item precipitate observed at and above 19.53 µg/mL. Therefore, the dose levels in the subsequent Mutagenicity Test were limited by the onset of test item precipitate.

There was no evidence of any marked dose-related toxicity following exposure to the test item in any three of the exposure groups, as indicated by the %RSG and RTG values. There was also no evidence of any marked dose-related reductions in viability (%V) in any of the exposure groups, indicating that residual toxicity had not occurred. Acceptable levels of toxicity were seen with the positive control substances.

The vehicle controls had mutant frequency values that were considered acceptable for the L5178Y cell line at the TK +/- locus. The positive controls produced marked increases in the mutant frequency per viable cell achieving the acceptability criterion, indicating that the test system was operating satisfactorily, and that the metabolic activation system was functional.

The test item did not induce any toxicologically significant or dose related (linear-trend) increases in the mutant frequency x 10-6 per viable cell at any of the dose levels, in any of the three exposure groups. Precipitate of the test item was observed at 20 and 30 µg/mL

Conclusions:

The test item did not induce any increases in the mutant frequency at the TK +/- locus in L5178Y cells that exceeded the GEF, consequently it is considered to be non-mutagenic in this assay

Executive summary:

The study was conducted according to a method that was designed to assess the potential mutagenicity of the test item on the thymidine kinase, TK +/-, locus of the L5178Y mouse lymphoma cell line. The method was designed to be compatible with the OECD Guidelines for Testing of Chemicals No 490 "In Vitro Mammalian Cell Gene Mutation Tests Using the Thymidine Kinase Gene" adopted 28 July 2015, Method B17 of Commission Regulation (EC) No. 440/2008 of 30 May 2008, the US EPA OPPTS 870.5300 Guideline, and in alignment with the Japanese MITI/MHW guidelines for testing of new chemical substances.

One main Mutagenicity Test was performed. In this main test, L5178Y TK +/- 3.7.2c mouse lymphoma cells (heterozygous at the thymidine kinase locus) were treated with the test item at six dose levels in duplicate, together with vehicle (acetone), and positive controls using 4 hour exposure groups both in the absence and presence of metabolic activation (2% S9), and a 24 hour exposure group in the absence of metabolic activation.

The dose levels of test item used in the main test was selected following the preliminary toxicity test and were 1.25, 2.5, 5, 10, 20 and 30µg/mL.

The maximum dose level used in the Mutagenicity Test was limited by the presence of test item precipitate. Precipitate of the test item was observed at 20 and 30 µg/mL at the end of the exposure period in the Mutagenicity Test. The vehicle control cultures had mutant frequency values that were acceptable for the L5178Y cell line at the TK +/- locus. The positive control substances induced marked increases in the mutant frequency, sufficient to indicate the satisfactory performance of the test and of the activity of the metabolizing system.

The test item did not induce any increases in the mutant frequency at the TK +/- locus in L5178Y cells that exceeded the GEF, consequently it is considered to be non-mutagenic in this assay.

Reference 3

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

The study was conducted between 23 March 2016 and 11 April 2016

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:

1997

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

30 May 2008

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

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

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals

Deviations:

not specified

GLP compliance:

yes (incl. QA statement)

Type of assay:

bacterial reverse mutation assay

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Sponsor Lot/Batch no.: 5399561P10
- Expiration date of the lot/batch: 25 January 2020
- Purity test date: 25 January 2016

RADIOLABELLING INFORMATION (if applicable)
- Radiochemical purity:
- Specific activity:
- Locations of the label:
- Expiration date of radiochemical substance:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature in the dark
- Stability under test conditions:
- Solubility and stability of the test substance in the solvent/vehicle:
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium:

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing:
- Preliminary purification step (if any):
- Final dilution of a dissolved solid, stock liquid or gel:
- Final preparation of a solid:

FORM AS APPLIED IN THE TEST (if different from that of starting material)

OTHER SPECIFICS:

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

Test concentrations with justification for top dose:

The test item was insoluble in sterile distilled water, dimethyl sulphoxide, dimethyl formamide and acetonitrile at 50 mg/mL, acetone at 100 mg/mL and tetrahydrofuran at 200 mg/mL in solubility checks performed in–house. The test item formed the best doseable suspension in dimethyl formamide, therefore, this solvent was selected as the vehicle.
The maximum concentration was 5000 .g/plate (the maximum recommended dose level). Eight concentrations of the test item (1.5, 5, 15, 50, 150, 500, 1500 and 5000 .g/plate) were assayed in triplicate against each tester strain, using the direct plate incorporation method.

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: dimethyl formamide
- Justification for choice of solvent/vehicle: Solubility of test material

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

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:

Test for Mutagenicity: Experiment 1 - Plate Incorporation Method
Dose selection
The test item was tested using the following method. The maximum concentration was 5000 µg/plate (the maximum recommended dose level). Eight concentrations of the test item (1.5, 5, 15, 50, 150, 500, 1500 and 5000 µg/plate) were assayed in triplicate against each tester strain, using the direct plate incorporation method.
Without Metabolic Activation
0.1 mL of the appropriate concentration of test item, solvent vehicle or appropriate positive control was added to 2 mL of molten, trace amino-acid supplemented media containing 0.1 mL of one of the bacterial strain cultures and 0.5 mL of phosphate buffer. 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 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.
3.3.2.4 Incubation and Scoring
All of the plates were incubated at 37 ± 3 C for approximately 48 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). Manual counts were performed at and above 500 .g/plate because of test item precipitation. A number of additional manual counts were also performed due to colonies on the edge of the plates and artefacts on the plates, thus distorting the actual count.

Experiment 2 – Pre-Incubation Method
As Experiment 1 was deemed negative, Experiment 2 was performed using the pre-incubation method in the presence and absence of metabolic activation. The dose range used for Experiment 2 was determined by the results of Experiment 1 and was 15 to 5000 µg/plate. Six test item concentrations were selected in Experiment 2 in order to achieve both four non-toxic dose levels and the potential toxic limit of the test item following the change in test methodology
Without Metabolic Activation:
0.1 mL of the appropriate bacterial strain culture, 0.5 mL of phosphate buffer and 0.1 mL of the 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. As an aid to dosing and maintenance of the test item in suspension, the maximum concentration (50 mg/mL) was dosed first for all of the tester strains. 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 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 approximately 48 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). Manual counts were performed at and above 1500 µg/plate because of test item precipitation.

Evaluation criteria:

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.

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.

Key result

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

Key result

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

Key result

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

Key result

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

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

The maximum dose level of the test item in the first experiment was selected as the maximum 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) and consequently the same maximum dose level was used in the second mutation test. 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), in the second mutation test (pre-incubation method). In the first mutation test (plate incorporation method), a test item precipitate (particulate in appearance) was noted by eye from 150 µg/plate. After employing the pre-incubation modification in the second mutation test, a particulate test item precipitate was noted under a low-power microscope at 150 µg/plate and by eye from 500 µg/plate. The precipitate observations did not prevent the scoring of revertant colonies. There were no toxicologically 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) in Experiment 1 (plate incorporation method). 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). Small, statistically significant increases in revertant colony frequency were observed in the first mutation test at 1500 µg/plate (TA100) and 1.5 and 5 µg/plate (TA98) in the absence of S9-mix only. These increases were considered to be of no biological relevance because there was no evidence of a dose-response relationship and the individual revertant counts at the statistically significant dose levels were within the in-house historical untreated/vehicle control range for each tester strain. Furthermore, the maximum fold increase was only 1.8 times the concurrent vehicle controls.

The vehicle (dimethyl formamide) 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.

RD 14156 was considered to be non-mutagenic under the conditions of this test.

Conclusions:

RD 14156 was considered to be non-mutagenic under the conditions of this test.

Executive summary:

Salmonella typhimurium strains TA1535, TA1537, TA98 and TA100 and Escherichia coli strain WP2uvrA were treated with suspensions of 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 was predetermined and was 1.5 to 5000 .g/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 achieve both four non-toxic dose levels and the potential toxic limit of the test item following the change in test methodology.

Results

The vehicle (dimethyl formamide) 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. 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) and consequently the same maximum dose level was used in the second mutation test. 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), in the second mutation test (pre-incubation method). In the first mutation test (plate incorporation method), a test item precipitate (particulate in appearance) was noted by eye from 150 .g/plate. After employing the pre-incubation modification in the second mutation test, a particulate test item precipitate was noted under a low-power microscope at 150 µg/plate and by eye from 500 .g/plate. The precipitate observations did not prevent the scoring of revertant colonies. There were no toxicologically 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) in Experiment 1 (plate incorporation method). 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). Small, statistically significant increases in revertant colony frequency were observed in the first mutation test at 1500 µg/plate (TA100) and 1.5 and 5 µg/plate (TA98) in the absence of S9-mix only. These increases were considered to be of no biological relevance because there was no evidence of a dose-response relationship and the individual revertant counts at the statistically significant dose levels were within the in-house historical untreated/vehicle control range for each tester strain. Furthermore, the maximum fold increase was only 1.8 times the concurrent vehicle controls.

Conclusion

RD 14156 was considered to be non-mutagenic under the conditions of this test.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

Testing is unnecessary because a negative result, with and without metabolic activation, was obtained in in vitro tests for gene mutation and chromosomal aberrations.

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In an Ames test 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 either Experiment 1 (plate incubaiton method) or Experiment 2 (pre-incubation method).

During testing in a mouse lymphoma assay the test item did not induce any increases in the mutant frequency at the TK +/- locus in L5178Y cells that exceeded the GEF.

In a chronosome aberration test, the substance did not induce a statistically significant increase in the frequency of cells with chromosome aberrations, in either the absence or presence of a liver enzyme metabolizing system.

Justification for classification or non-classification

The substance produced a negative result, with and without metabolic activation, in three in vitro tests for gene mutagenicty or chromosomal aberration.