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Administrative data

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
21st July 2021 to 19th August 2021
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2021
Report date:
2021

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Qualifier:
according to guideline
Guideline:
EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay

Test material

Constituent 1
Chemical structure
Reference substance name:
(1R,2S,5S)-6,6-dimethyl-3-[3-methyl-N-(trifluoroacetyl)-L-valyl]-3-azabicyclo[3.1.0]hexane-2-carboxylic acid
EC Number:
955-024-2
Cas Number:
2755812-45-2
Molecular formula:
C16 H23 F3 N2 O4
IUPAC Name:
(1R,2S,5S)-6,6-dimethyl-3-[3-methyl-N-(trifluoroacetyl)-L-valyl]-3-azabicyclo[3.1.0]hexane-2-carboxylic acid
Test material form:
solid

Method

Target gene:
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
Species / strainopen allclose all
Species / strain / cell type:
E. coli WP2 uvr A
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Metabolic activation:
with and without
Metabolic activation system:
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 ug/plate and 2.5 ug/plate, respectively.
Test concentrations with justification for top dose:
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. Eight concentrations, 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 wg/plate were tested in triplicate.
Vehicle / solvent:
dimethyl sulfoxide (DMSO, Merck, Darmstadt, Germany)
Controlsopen allclose all
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Remarks:
WP2uvrA, TA98, TA100, TA1535, TA1537
Positive control substance:
other:
Remarks:
with metabolic action
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Remarks:
WP2uvrA
Positive control substance:
4-nitroquinoline-N-oxide
Remarks:
without metabolic action
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Remarks:
TA1537
Positive control substance:
2-nitrofluorene
other: ICR-191
Remarks:
without metabolic action
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Remarks:
TA1535
Positive control substance:
sodium azide
Remarks:
without metabolic action
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Remarks:
TA100
Positive control substance:
methylmethanesulfonate
Remarks:
without metabolic action
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Remarks:
TA98
Positive control substance:
2-nitrofluorene
Remarks:
without metabolic action
Details on test system and experimental conditions:
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. Eight concentrations, 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 ug/plate were tested in triplicate. The highest concentration of the test item used in the subsequent mutation assays was 5000 ug/plate. 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.

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 (10 9 cells/mL) of one of the tester strains, 0.1 ml of a dilution of the test item in DMSO or control solution 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 +/- 4h. After this period revertant colonies (histidine independent (His+) for Salmonella typhimurium bacteria and tryptophan independent (Trp+) for Escherichia coli) were counted.

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 (10 9 cells/mL) of one of the tester strains, 0.1 mL of a dilution of the test item in DMSO or control solution. 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.
Evaluation 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.

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.

Results and discussion

Test resultsopen allclose all
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
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
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
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
Positive controls validity:
valid
Key result
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
Positive controls validity:
valid
Remarks on result:
not determinable
Remarks:
All bacterial strains showed negative responses over the entire dose-range, 1.e. no 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.

Applicant's summary and conclusion

Conclusions:
In conclusion, based on the results of this study it is concluded that PF-07320267 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 PF-07320267 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.
Batch JR-C200917012-D21001 of the test item was a white to off-white solid with a purity of 99.6%. A correction factor of 1.18 was used according to content (14% isopropylacetate solvate). 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 ug/plate in the strains TA100 and WP2uvrA in the direct plate assay. The test item did not precipitate on the plates at this 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. 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 tested up to concentrations of 5000 ug/plate in the strains TA1535, TA1537 and TA98. The test item did not precipitate on the plates at this 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.
In the second mutation experiment, the test item was tested up to concentrations of 5000 ug/plate in the tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA in the pre-incubation assay. Cytotoxicity, as evidenced by a decrease in the number of revertants, reduction of the bacterial background lawn and/or the presence of microcolonies, was observed in all tester strains in the absence and presence of S9-mix, except in tester strains TA1535, TA98 and WP2uvrA in the presence of S9-mix where no toxicity was observed at any of the dose levels tested.
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 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 PF-07320267 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.