3-acetoxymethylen-7-amino-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

The test item is not genotoxic in the Ames test, the in vitro mammalian chromosome aberration test and the in vitro mammalian cell gene mutation test (HPRT assay).

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)

Version / remarks:

2015

Deviations:

no

Principles of method if other than guideline:

Mutant cells deficient in Hprt enzyme activity in the HPRT test are resistant to the cytostatic effects of the purine analogue 6-thioguanine (TG). The Hprt proficient cells are sensitive to TG, which causes the inhibition of cellular metabolism and halts further cell division. Thus, mutant cells are able to proliferate in the presence of TG, whereas normal cells, which contain the Hprt enzyme, are not.

GLP compliance:

yes (incl. QA statement)

Type of assay:

other: HPRT test

Target gene:

Hypoxanthine-guanine phosphoribosyl transferase enzyme locus.

Species / strain / cell type:

Chinese hamster Ovary (CHO)

Details on mammalian cell type (if applicable):

CHO K1: Sub-line (K1) of Chinese hamster ovary cell line CHO
Lot. No.: 12G006
Supplier: ECACC (European Collection of Cell Cultures)

Each batch of frozen cells was purged of HPRT mutants and was free for mycoplasma infections. For each experiment the cells were thawed rapidly, the cells diluted in Ham's F12 medium containing 10 % foetal bovine serum and incubated at 37 °C in a humidified atmosphere of 5 % CO2 in air. Growing cells were subcultured in an appropriate number of flasks. The CHO K1 cells for this study were grown in Ham's F12 medium (F12-10) supplemented with 1 % Antibiotic-antimycotic solution (containing 10000 U/mL penicillin, 10 mg/mL streptomycin and 25 μg/mL amphotericin-B) and heat-inactivated bovine serum (final concentration 10 %). During the 5 treatments with the test item, solvent (negative control) and positive controls, the serum content was reduced to 5 % (F12-5). The selection medium for TG resistant mutants contained 3.4 μg/mL 6-thioguanine (6-TG) (EX-CELL® CD CHO Serum-Free Medium for CHO Cells-SEL).

Metabolic activation:

with and without

Metabolic activation system:

S9 mix of phenobarbital and β-naphthoflavone induced rat liver.

Test concentrations with justification for top dose:

5-hour treatment period without S9-mix: 125, 250, 500, 1000 and 2000 μg/mL
5-hour treatment period with S9-mix: 62.5, 125, 250, 500 and 1000 μg/mL
The concentrations were chosen based on the cytotoxicity and the maximum recommended concentration.

Vehicle / solvent:

The test item was suspended in DMSO.

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

7,12-dimethylbenzanthracene

ethylmethanesulphonate

Details on test system and experimental conditions:

A pre-test on toxicity was performed to select treatment concentrations for the mutation assay.

A 5-hour treatment in the presence and absence of S9-mix was performed. For the 5-hour treatment, 5 x10E6 cells were each placed in sterile dishes and incubated for approximately 24 hours before treatment at 37 °C in a humidified atmosphere of 5 % CO2. Duplicate cultures were used at each test item concentration, for negative (solvent) controls and the positive controls for treatment without and with S9-mix. On the day of treatment the culture medium of exponentially growing cell cultures were replaced with medium (F12-5) containing the test item. The exposure period was 5 hours. Following the exposure period the cells were washed with F12-5 medium and incubated in fresh F12-10 medium for 19 hours. After the 19-hour incubation period, cells were washed twice with F12-10 medium and suspended by treatment with trypsin-EDTA solution and counted using a Bürker chamber. Solubility of the test item in the cultures was assessed by the naked eye, at the beginning and end of treatment. In samples where sufficient cells survived, cell number was adjusted to 10E5 cells/mL. Throughout the expression period, cells were transferred to dishes for growth or diluted to be plated for survival.

The pH and osmolality of the negative (solvent) control and test item solutions were determined in Experiment 1 and Experiment 2.
Plating for survival: Following adjustment of the cultures to 10E5 cells/mL, samples from these cultures were diluted to 40 cells/mL.
A total of 5 mL (200 cells/dish) of the final concentration of each culture was plated into 3 parallel dishes (diameter is approx. 60 mm). The dishes were incubated at 37 °C in a humidified atmosphere of 5 % CO2 in air for 6 days for growing colonies. Then, colonies were fixed with methanol, stained with Giemsa and counted. Survivals were assessed by comparing the cloning efficiency of the test item treated groups to the negative (solvent) control.
Expression of the mutant phenotype: During the phenotypic expression period the cultures were subcultured. Aliquots of approximately 2x10E6 cells were taken on days 1, 3, 6, and evaluated on day 8.
Selection of the mutant phenotype: At the end of the expression period, cultures from each dose level were adjusted to 2 x 10E5 cells / dish ( 4 x five dishes) in selection medium (hypoxanthine Ham's F12-SEL medium) containing 3.4 μg/mL of thioguanine (6-TG).
Plating for viability: At the end of the expression period cell number in the samples were adjusted to 2 × 10E5 cells/mL. Cells were plated in 3 parallel dishes (diameter is approx. 60 mm) for a viability test as described in “Plating for Survival“ section for the survival test.
Fixation and staining of colonies: After the selection period, the colonies were fixed with methanol for five minutes, stained with Giemsa and counted for either mutant selection or cloning efficiency determination.

Rationale for test conditions:

See above.

Evaluation criteria:

Calculation of mutation frequency: The mutation frequency was calculated by dividing the total number of mutant colonies by the number of cells selected (10E6 cells: 5 plates at 2 x 10E5 cells/plate), corrected for the cloning efficiency of cells prior to mutant selection (viability), and was expressed as 6-TG resistant mutants per 10E6 clonable cells.

Key result

Species / strain:

Chinese hamster Ovary (CHO)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

Clear treatment solutions were obtained and no precipitation in the medium was noted at the test item concentrations used. No relevant changes in pH or osmolality were found after treatment with the test item.

On Day 1, there was a clear evidence of toxicity with the test item in the presence of metabolic activation (S9 mix) when compared to the negative (solvent) controls, confirming the response seen in the dose selection cytotoxicity assays. The Day 8 cloning efficiency data indicate that in general the cells had recovered during the expression period.
In the absence of the metabolic activation, no cytotoxicity was observed after test item treatment up to the highest applied concentration, confirming the response seen in the dose selection cytotoxicity assays.
There were no biologically or statistically significant increases in mutation frequency at any concentration tested, either in the absence or in the presence of metabolic activation.
There were no significant differences between treatment and control groups and no dose-response relationships were noted.
All values were within the range of the laboratory historical solvent control data and no dose-related increase was observed in any of the cultures.

The sensitivity of the tests and the efficacy of the S9 mix were demonstrated by a significant increase in mutation frequency in the positive control cultures with Ethyl methanesulfonate (1.0 μL/mL) and 7,12-Dimethyl benz[a]anthracene (20 μg/mL). The mutation frequencies of the positive and negative control cultures were consistent with the historical control data from the previous studies performed at this laboratory. Thus, the study is considered valid.
The osmolality and pH values of test item solutions did not show any significant alterations compared to the concurrent control groups in the Pre-test on Toxicity and Main Mutation Assay.

Conclusions:

The test item was not mutagenic in this in vitro mammalian cell gene mutation test.

Executive summary:

The test item, applied up to the maximum recommended concentration (2000 μg/mL) concentration without metabolic activation system and up to the cytotoxic concentration with metabolic activation system over a 5 hour treatment period did not induce statistically and biologically significant increases in mutant frequency over the background (negative solvent control).

It is concluded that the test item was not mutagenic in this in vitro mammalian cell gene mutation test performed with in Chinese hamster ovary cells.

Reference 2

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

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:

2014

Deviations:

yes

Remarks:

Ethyl methanesulfonate was used as the positive control.

GLP compliance:

yes (incl. QA statement)

Type of assay:

other: In vitro mammalian chromosome aberration test.

Target gene:

Not applicable.

Species / strain / cell type:

Chinese hamster lung fibroblasts (V79)

Details on mammalian cell type (if applicable):

Lot. No.: 10H016
Supplier: ECACC (European Collection of Cells Cultures)
The V79 cell line is well established in toxicology studies. Stability of karyotype and morphology makes it suitable for gene toxicity assays with low background aberrations. These cells were chosen because of their small number of chromosomes (diploid number, 2n=22) and because of the high proliferation rates (doubling time 12-14 h).
The cell stocks were kept in a freezer at -80 +/- 10 °C. Checking for mycoplasma infections was carried out. Trypsin-EDTA (0.25 % Trypsin, 1mM EDTA x 4 Na) solution was used for cell detachment to subculture. The laboratory cultures were maintained in 75 cm2 plastic flasks at 37 +/- 0.5 °C in an incubator with a humidified atmosphere, set at 5 % CO2. The V79 cells for this study was grown in DME (Dulbecco’s Modified Eagle’s) medium supplemented with L-glutamine (2mM) and 1 % of Antibiotic-antimycotic solution (containing 10000 units/mL penicillin, 10 mg/mL streptomycin and 25 μg/mL amphoptericin-B) and heat-inactivated bovine serum (final concentration 10 %). During the 3 and 20 hours treatments with test item, negative and positive controls, the serum content was reduced to 5%.

Additional strain / cell type characteristics:

not specified

Metabolic activation:

with and without

Metabolic activation system:

rodent S9 mix

Test concentrations with justification for top dose:

Experiment A:
Without S9 mix: 0 - 500 - 1000 - 2000 µg/mL (3 h exposure; sampling 20 h after start of exposure).
With S9 mix:0 - 500 - 1000 - 2000 µg/mL (3 h exposure; sampling 20 h after start of exposure).

Experiment B:
Without S9 mix: 0 - 62.5 - 125 - 250 and 500 µg/mL (20 h exposure; sampling 20 h after start of exposure)
With S9 mix: 0 - 62.5 - 125 - 250 and 500 µg/mL (20 h exposure; sampling 28 h after start of exposure)
With S9 mix:0 - 500 - 1000 - 2000 µg/mL (3 h exposure; sampling 28 h after start of exposure).

Selection of doses according to the results of the preliminary test and the maximum recommended concentration.

Vehicle / solvent:

The test item solutions were prepared in the testing laboratory using DMSO. Stock solution: 100 mg/L. The appropriate amount of this stock solution was completed with DME (Dulbecco’s Modified Eagle’s) medium to reach the constant volume. The constant volume was diluted with medium to obtain the examination concentrations.
This vehicle is compatible with the survival of the V79cells and the S9 activity and was chosen based on the results of the preliminary Solubility Test.

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

Remarks:

DMSO

True negative controls:

no

Positive controls:

yes

Positive control substance:

cyclophosphamide

ethylmethanesulphonate

Details on test system and experimental conditions:

Components of Media:
Name: DME (Dulbecco’s Modified Eagle’s) medium
Supplier: Sigma-Aldrich, Germany
Name: Fetal Bovine Serum
Supplier: Sigma-Aldrich, Germany
Name: Antibiotic-antimycotic
Supplier: Sigma-Aldrich, Germany

Rat Liver S9 Fraction
The S9 fraction of phenobarbital (PB) and β-naphthoflavone (BNF) induced rat liver was provided by Trinova Biochem GmbH, Germany; manufacturer: MOLTOX INC., USA. Certificate of Analysis was obtained from the supplier.

Pre-test for Cytotoxicity (Concentration selection)
The pre-experiments on solubility of the test item (non GLP) and GLP Pre-test for Cytotoxicity (Concentration selection) were performed.
In order to determine the treatment concentrations of test item in the cytogenetic study a dose selection (cytotoxicity assay) was performed. During the cytotoxicity assay the cells were seeded into 92 x 17 mm dishes (for tissue cultures in TC sterile quality) at 5 x 105 cells each and were incubated for 24 hours in 10 mL of DME (Dulbecco’s Modified Eagle’s) medium containing 10 % foetal bovine serum.After 24 hours the cells were treated using increasing concentrations of test item in the absence or presence of S9 mix (100 mg/mL) and were incubated at 37 °C for 3 hours. After treatment the cultures were washed with DME medium and covered with DME (Dulbecco’s Modified Eagle’s) medium containing 10 % foetal bovine serum. Cell counts were performed after 20 hours (approximately 1.5 normal cell cycles from the beginning of treatment). The cells were counted using a Bürker chamber. Additional groups of cells were treated for 20 hours without metabolic and for 3 hours with metabolic activation, with cell counts conducted after 20 hours (without S9 mix only) and 28 hours (without and with S9 mix).Additionally, 4 cultures were set up for determining the initial cell count. At harvest the cells were trypsinised, collected and cell counts were determined. Based on the cell counts Relative Increase in Cell Counts (RICC) was calculated, which is an indicator of cytotoxicity. The volume of culture medium was 5 mL/dish for each per group. The results obtained were used for dose selection of the test item used in the Chromosome Aberration Assays (Experiments A and B). In addition, the pH and osmolality was measured in this pre-test.

Chromosome Aberration Assays. The Chromosome Aberration Assays were conducted in two independent experiments in the presence and in the absence of S9 mix.
Experiment A: The test item was suspended in DMSO for the treatment (stock solution: 100 mg/mL). The appropriate amount of this stock solution was completed with DME (Dulbecco’s Modified Eagle’s) medium to reach the constant volume. The constant volume was diluted with medium to obtain the examination concentrations. Duplicate cultures were used at each concentration and the negative control cultures as well as the positive controls for treatment without and withS9 mix. 5 x 10E5 cells were set up at each group. The culture medium of exponentially growing cell cultures was replaced with medium containing the test item. The exposure period was 3 hours. The exposure period was followed by washing the cells with DME (Dulbecco’s Modified Eagle’s) medium and then growth medium was added. Sampling was made at 20 hours after treatment start (approximately 1.5 normal cell cycles from the beginning of treatment). For concurrent measures of cytotoxicity for all treated and negative control cultures, 5 x 10E5 cells were set up.

Experiment B: In the cytogenetic Experiment B the exposure period without metabolic activation was 20 hours. The exposure period with metabolic activation was 3 hours.
Experiment B, as Experiment A, included a concurrent S9 non-activated and S9 activated positive and negative control. For each group 5 x 105 cells/dish cells were seeded. Sampling was made at 1.5 cell cycles (20 hours, without S9 mix only) and at approximately 2 normal cell cycles (28 hours, without and with S9 mix) from the beginning of treatment to cover a potential mitotic delay.

Measurement of pH and Osmolality: The pH value and osmolality of negative (solvent) control and test item treatment solutions (for every treatment concentrations) were measured in the Pre-test for Cytotoxicity (Concentration selection) and in the Chromosome Aberration Assay.

Preparation of Chromosomes
Cell cultures were treated with Colchicine (0.2 μg/mL) 2.5 hours prior to harvesting. Following the selection time, cells were swollen with 0.075 M KCl hypotonic solution, then washed in fixative (approx. 10 min. in 3:1 mixture of methanol: acetic-acid until the preparation becomes plasma free) and dropped onto slides and air-dried. The preparation was stained with 5 % Giemsa for subsequent scoring of chromosome aberration frequencies.

Analysis of Methaphase Cells
All slides were independently coded before microscopic analysis and scored blind. 300 well-spread metaphase cells containing 22 ± 2 chromosomes were scored per test item concentration as well as the negative and positive controls and were equally divided among the duplicates (150 metaphases/slide). Chromatid and chromosome type aberrations (gaps, deletions and exchanges) were recorded separately. Additionally, the number of polyploid and endoreduplicated cells were scored. The nomenclature and classification of chromosome aberrations were given based upon ISCN, 1985, and Savage, 1975, 1983.

Rationale for test conditions:

See above.

Evaluation criteria:

– Different types of structural chromosome aberrations are listed, with their numbers and frequencies for experimental and control cultures.
– Gaps were recorded separately and reported, but generally not included in the total aberration frequency.
– Concurrent measures of cytotoxicity for all treated and negative control cultures in the main aberration experiment (s) were recorded.
– Individual culture data were summarised in tabular form.
– There were no equivocal results in this study.
– pH and Osmolality data were summarised in tabular form.

Interpretation of Results
Providing that all acceptability criteria are fulfilled, a test item is considered to be clearly positive if:
– at least one of the test concentrations exhibits a statistically significant increase compared with the concurrent negative control,
– the increase is dose-related when evaluated with an appropriate trend test,
– any of the results are outside the distribution of the laboratory historical negative control data.
Providing that all acceptability criteria are fulfilled, a test chemical is considered clearly negative because:
– none of the test concentrations exhibits a statistically significant increase compared with the concurrent negative control,
– there is no concentration-related increase when evaluated with an appropriate trend test

Statistics:

For statistical analysis CHI2 test was utilized. The parameters evaluated for statistical analysis were the number of aberrations (with and without gaps) and number of cells with aberrations (with and without gaps). The number of aberrations in the treatment and positive control groups were compared to the concurrent negative control. The concurrent negative and positive controls and the treatment groups were compared to the laboratory historical controls, too.

Key result

Species / strain:

Chinese hamster lung fibroblasts (V79)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

There was no precipitation in the medium at any concentration tested. The concentration selection cytotoxicity assay was performed as part of this study to establish an appropriate concentration range for the Chromosome Aberration Assays.

In Experiment A, there were no biologically significant increases in the number of cells showing structural chromosome aberrations, neither in the absence nor in the presence of metabolic activation, up to the maximum recommended concentration. There were no statistical differences between treatment and concurrent solvent and historical control groups and no dose-response relationships were noted.
In Experiment B, the frequency of the cells with structural chromosome aberrations did not show significant alterations compared to concurrent controls, up to the cytotoxic concentration without S9 mix over a prolonged treatment period of 20 hours with harvest at 20 or 28 hours following treatment start. Further, a 3-hour treatment up to the maximum recommended concentration in the presence of S9 mix with 28-hour harvest from the beginning of treatment did not cause an increase in the number of cells with structural chromosome aberrations.

In both experiments, no statistically significant differences between treatment and concurrent solvent control groups and no dose-response relationships were noted. The observed chromosome aberration were inside the distribution of the laboratory historical negative control data.
There were no biologically relevant increases in the rate of polyploid or endoreduplicated metaphases in either experiment in the presence or absence of metabolic activation.
There was no precipitation of the test item at any dose level tested. No biologically relevant changes in pH or osmolality of the test system were noted at the different dose levels tested.
The number of aberrations found in the solvent controls was compatible with the laboratory historical laboratory control data.
The concurrent positive controls ethyl methanesulphonate (0.4 and 1.0 μL/mL) and Cyclophosphamide (5 μg/mL) caused the expected biologically relevant increases of cells with structural chromosome aberrations as compared to solvent controls and were compatible with the historical positive control data.

pH and osmolality values of control and test item treatment solutions were measured. In Experiments A and B no significant differences between test item treatment and control groups were observed.

Conclusions:

The test substance, with and without mammalian metabolic activation system, did not induce structural chromosome aberrations in Chinese Hamster lung cells. The test item is not clastogenic in this system.

Executive summary:

A Chromosome Aberration Assay in V79 cells was performed. The test item was dissolved in DMSO and then in Dulbecco’s Modified Eagle’s medium and the following concentrations were selected on the basis of cytotoxicity investigations made in a preliminary study. In two independent experiments (both run in duplicate with concurrent negative and positive controls) at least 300 (150-150) well-spread metaphase cells were analysed at concentrations and treatment (exposure)/sampling (expression) intervals given below:

Experiment A:

Without S9 mix: 0 - 500 - 1000 - 2000 µg/mL  (3 h exposure; sampling 20 h after start of exposure).

With S9 mix:0 - 500 - 1000 - 2000 µg/mL (3 h exposure; sampling 20 h after start of exposure).

Experiment B:

Without S9 mix: 0 - 62.5 - 125 - 250 and 500 µg/mL (20 h exposure; sampling 20 h after start of exposure)

With S9 mix: 0 - 62.5 - 125 - 250 and 500  µg/mL (20 h exposure; sampling 28 h after start of exposure)

With S9 mix:0 - 500 - 1000 - 2000 µg/mL (3 h exposure; sampling 28 h after start of exposure).

Results:

The test item, tested up to the maximum recommended concentration of 2000 μg/mL, both with and without mammalian metabolic activation system (three hour treatment) and up to the cytotoxic concentration without mammalian metabolic activation system (twenty hours treatment) , did not induce structural chromosome aberrations in Chinese Hamster lung cells.

Reference 3

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

March 28, 1995 to June 22, 1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study (OECD 471) with acceptable restrictions.

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Species / strain / cell type:

S. typhimurium TA 97

Species / strain / cell type:

S. typhimurium TA 98

Species / strain / cell type:

S. typhimurium TA 100

Species / strain / cell type:

S. typhimurium TA 102

Species / strain / cell type:

S. typhimurium TA 1535

Metabolic activation:

with and without

Metabolic activation system:

S9-mix

Test concentrations with justification for top dose:

In a preliminary experiment the strain TA100 was mixed with the test substance and top-agar
and plated on standard agar. The growth of the bacterial lawn was recorded. 9 concentrations
ranging from 0.8 pg to 5000 pg test substance per plate were used.
"7-ACA" was toxic at concentrations of 5000 pg/plate (no growth of bacteria). At
1700 pg/plate a reduced bacterial lawn was seen. The lower concentrations allowed normal
growth of the bacteria.

So it was decided for the first experiment to use 2000 pg "7-ACA" per plate as the highest concentration which would possibly be slightly toxic, and to use 4 lower concentrations, obtained by subsequent dilution to one third (one part solution + two parts solvent). As the obtained toxicity was not clearly pronounced in the first experiment, a higher concentration, 5000 pg per plate, was added in the second experiment for all strains. 5000 pg per plate is the highest recommended concentration for the Ames test according to the OECD guideline.

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

Water

True negative controls:

no

Positive controls:

yes

Positive control substance:

sodium azide

other: 4NOPD: 4-Nitro-o-phenylene-diarnine. tBHPO: t-Butyl-hydroperoxide. 2AA: 2-Amino-anthracene. DHA: 1,8-Dihydoxy-anthraquinone.

Details on test system and experimental conditions:

Reference substances:
• 2-Aminoanthracene, (Sigma, article A-1381. Practical grade).
• Sodium azide (Aldrich, Gillingham, England, article 19,993-1, 99%).
• 4-Nitro-o-phenylenediamine (Sigma, article N-9504).
• 1,8-Dihydroxy-anthraquinone (Danthron, Sigma, article D-5636, 95%).
• t-Butyl-hydroperoxide (Sigma, article B-2633, 70% aqu. solution).
1,8-Dihydroxy-anthraquinone and 2-aminoanthracene are mutagenic only when activated by a metabolising system; 4-nitro-o-phenylenediamine, t-butyl-hydroperoxide and sodium azide are directly acting mutagens.

Test and reference substance solutions - preparation
250 mg of test substance were dissolved in 4.0 ml of sterile H20. 1.0 ml of 1 Mol/1 NaOH was added to solve the test substance. This solution contained 5000 ug in 100 ul and was used for the highest concentration group. From this solution 0.6 ml were combined with 0.9 ml of sterile water. The resulting solution contained 2000 ug in 100 ul and was used for the second concentration group. The lower concentrations were obtained by subsequent dilution to one third each (one volume of solution plus two volumes of H2O).

4-Nitro-o-phenylenediamine, 1,8-dihydroxy-anthraquinone and 2- aminoanthracene were prepared from stock solutions in DMSO (dimethylsulfoxide). 4-Nitro-o-phenylenediamine was diluted with H20, 1,8-dihydroxy-anthraquinone with 80% DMSO and 2-aminoanthracene with 50 % DMSO.
Sodium azide and t-butyl-hydroperoxide were dissolved in sterile water.

Test system:
Bacterial strains of salmonella typhimurium TA97a, TA98, TA100, TA102 and TA1535, obtained in Nov. 1988 from Prof. Bruce N. Ames, Berkeley, California.

The bacteria were stored in small portions in a solution of 6 % DMSO in phosphate buffered saline in liquid nitrogen.
The strains were tested for ampicillin resistance, UV - sensitivity and sensitivity against crystal violet, for spontaneous mutation frequencies and for sensitivities against the positive control substances on December 1994 (TA97a, TA98, TA100 and TA102) and on January 1995 (TA1535). The bacteria were stored frozen since that time.

The main genetic properties of these strains are:

Strain: his-Mutation: rfa: uvrB: pkMlOl:
TA97a D6610 yes yes yes
TA98 D3052 yes yes yes
TA100 G46 yes yes yes
TA102 G428 yes no yes
TA1535 G46 yes yes no

D6610 and D3052 are frameshift mutations, G46 is a base pair mutation, G428 is an ochre-mutation.

The rfa mutation leads to a reduced lipopolysaccharide barrier in the cell wall and allows larger molecules to pass the cell wall. Bacteria with this mutation are sensitive to crystal violet.

UvrB results in a loss of the DNA-excision repair system. This increases the sensitivity to mutagenic influences. Bacteria with this mutation are sensitive to UV light.

The plasmide pkMlOl also disturbs the ability of the bacteria to repair genetic damage and therefore increases its sensitivity to mutagens. Bacteria with this plasmide are resistant against ampicillin.

Justification for the bacterial strains used:
The OECD guideline requires at least the strains TA1535, TA1537 or TA97a (or TA97), TA98 and TA100 for the test. TA102 is recommended because it detects some mutagens which are not detected or are detected poorly by the standard set of tester strains.

Conditions of cultivation:
A small amount from each of the frozen bacterial cultures was transferred with a spatula to ten ml of nutrient broth. They were incubated overnight (about 16 hours) at 37 °C and then used for the exposure.

Metabolic system:
The microsomal fraction of homogenised livers of rats treated once with 500 mg/kg of aroclor 1254 was used. The treatment was on Sept. 9,1994 (for the first experiment) and April 12, 1995 (for the second experiment). 5 days after treatment, the feed was withdrawn for one night. The livers of the animals were removed and homogenised in cold 0,15 mol/1 KC1. 3 ml of homogenate were obtained per gram of liver. Then the homogenate was centrifuged for 10 minutes at 9.000 x g. The supernatant contained the microsomes. Portions of one ml of the microsomes were stored in liquid nitrogen. Immediately before use they were thawed and mixed with the cofactor solution.

Exposure
Groups, concentrations, number of samples:

high concentration 1 5000 ug/plate 3 samples
concentration 2 2000 -"- 3 -"-
concentration 3 667 -"- 3 -"-
concentration 4 222 -"- 3 -"-
concentration 5 74 3 -"-
low concentration 6 25 -"- 3
control (H20) 100 ul/plate 6 -"-
positive control * * 3 -"-

* Positive-controls (ug per plate):

Strain: without S9 with S9
TA97a 4NOPD, 20 ug 2AA, 3 pg
TA98 4NOPD, 5 ug 2AA, 3 ug
TA100 Sodium-azide, 5 pg 2AA, 3 ug
TA102 tBHPO, 50 ug DHA, 50 pg
TA1535 Sodium-azide, 5 pg 2AA, 3 us

4NOPD: 4-Nitro-o-phenylene-diarnine. tBHPO: t-Butyl-hydroperoxide. 2AA: 2-Amino-anthracene. DHA: 1,8-Dihydoxy-anthraquinone.

All concentrations of the test substance were tested without as well as with an external metabolising system (S9-mix). The results were verified by a second, independent experiment.

Exposure technique:
The exposure is performed according to the 'Plate Incorporation Assay', in which bacteria, test substance (and microsomes) are in contact on the plate without preceding incubation in the liquid state.
For each sample the following solutions were combined:
• 0.1 ml of the overnight culture of the bacteria,
• 0.5 ml of S9-mix (or phosphate buffered saline for samples without metabolic activation),
• 0.1 ml of the appropriate test- or reference substance solution and
• 2 ml of top agar.
The combined solutions were mixed and spread over a plate with minimal agar (9 cm diameter). After the top agar had solified, the plates were incubated at 37 °C until the colonies were visible (2 days)

Evaluation criteria:

Counting of colonies:
The plates were counted visually by marking the colonies with a felt tipped pen. From plates with more then about 300 colonies a fraction of the total area was counted visually and the total amount of colonies was calculated.

Statistics:

Means and standard deviation were calculated for the number of mutants in every concentration group.
For comparison of the control group and the test substance groups the analysis of variance was used followed by the test of Scheffe. For comparison of the control group and the positive control group, the t-test was used, p = 0.05 was used as the significance level.
The criteria for a positive result are:
A reproducible statistically significant increase of the number of revertants to more then twice the amount of the spontaneous revertants for at least one of the concentrations.

Species / strain:

S. typhimurium TA 97

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

not specified

Additional information on results:

Bacteria:
The used strains of Salmonella typhimurium showed the expected genetic properties and were sensitive against several mutagenic chemicals.

Reference substances:
The positive control substances increased the mutation frequency statistically significantly. As 2-aminoanthracene is non mutagenic without metabolic activation and the mutagenicity of 1,8-dihydroxy-anthraquinone is lower without metabolic activation, the results of these substances demonstrate also the efficiency of the metabolising system.
The mutation frequencies of the negative control groups were in the usual range for the different strains.

Test substance:
Toxicity:
The test substance was slightly toxic at the concentration of 2000 µg per plate in the first experiment, resulting in reduced numbers of spontaneous revertants. As the toxicity however was pronounced only in strain TA100, a further, higher concentration was added at the second experiment for all strains except TA100. This concentration - 5000 µg per plate - was clearly toxic. 5000 µg per plate is also the limit concentration for the Ames test.
Mutagenicity:
This is the parameter of major interest, because a substance is called mutagenic in the Ames test when a reproducible statistically significant increase in the number of revertants to more than twice the amount of the spontaneous revertants for at least one of the concentrations occurs.
There was no statistically significant increase in the number of mutants in any of the tested bacterial strains with any of the tested concentrations. The addition of an external metabolising system did not change this results.

Conclusions:

7-ACA is not mutagenic in the Ames test with the strains of Salmonella typhimurium TA97a, TA98, TA100, TA102 and TA1535 up to the concentration of 5000 pg per plate which is the limit of toxicity as well as the limit concentration for the Ames test.

Executive summary:

7-ACA was tested for mutagenic action with the "Salmonella typhimurium Reverse Mutation Assay" (Ames Test). The study was conducted in accordance with the OECD-guideline 471. Results:

Positive controls:

All positive control groups showed significantly increased mutation frequencies which demonstrates the sensitivity of the test system.

Test substance:

In none of the tested concentrations and with none of the used strains a statistically significant increase of the mutation frequency was obtained. Metabolic activation did not change these results.

7-ACA is therefore non-mutagenic in the Ames test with the strains TA97a, TA98, TA100, TA102 and TA1535 up to 5000 µg per plate which is the limit of toxicity and the limit of this kind of test.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Justification for classification or non-classification

No indications were obtained to justify a classification of the test item.