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Genetic toxicity in vitro

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Reference
Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
17th January 2017 to 30th March 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of assay:
bacterial reverse mutation assay
Specific details on test material used for the study:
Identification:
4,4’-(1,3-phenylenediisopropylidene) diphenylcyanate
Batch No.:
FAR366085A
Purity:
Substance of Unknown or Variable Composition, Complex Reaction Products and Biological Materials
99.8% (per Certificate of analysis)
Description:
Blackish, yellow-orange, viscous liquid
Storage Conditions:
Room temperature, protected from light
Receipt Date:
13 December 2016
Target gene:
All Salmonella tester strain cultures must demonstrate the presence of the deep rough mutation (rfa) and the deletion in the uvrB gene. Cultures of tester strains TA98 and TA100 must demonstrate the presence of the pKM101 plasmid R-factor. All WP2 uvrA cultures must demonstrate the deletion in the uvrA gene.
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Details on mammalian cell type (if applicable):
Salmonella tester strains were derived from Dr. Bruce Ames’ cultures;
Species / strain / cell type:
E. coli WP2 uvr A
Details on mammalian cell type (if applicable):
E. coli tester strains were from the National Collection of Industrial and Marine Bacteria, Aberdeen, Scotland.
Metabolic activation:
with and without
Metabolic activation system:
Aroclor 1254-induced rat liver S9 was used as the metabolic activation system.
Test concentrations with justification for top dose:
The results of the preliminary toxicity assay conducted at dose levels of 6.67, 10.0, 33.3, 66.7, 100, 333, 667, 1000, 3333 and 5000 μg per plate in DMSO
The maximum dose of 5000 μg per plate was achieved using a concentration of 50.0 mg/mL and a 100 μL plating aliquot.

Based upon the results of the preliminary toxicity assay, the dose levels selected for the mutagenicity assay were 5.00, 15.0, 50.0, 150, 500, 1500 and 5000 μg per plate.
Vehicle / solvent:
DMSO was the vehicle of choice based on the solubility of the test substance and compatibility with the target cells. The test substance formed a clear solution in DMSO at a concentration of approximately 350 mg/mL in the solubility test conducted at BioReliance.
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
Positive control substance:
9-aminoacridine
2-nitrofluorene
sodium azide
methylmethanesulfonate
other: 2-aminoanthracene
Details on test system and experimental conditions:
The tester strains used were the Salmonella typhimurium histidine auxotrophs TA98, TA100, TA1535 and TA1537 as described by Ames et al. (1975) and Escherichia coli WP2 uvrA as described by Green and Muriel (1976).
Tester strains TA98 and TA1537 are reverted from histidine dependence (auxotrophy) to histidine independence (prototrophy) by frameshift mutagens. Tester strain TA1535 is reverted by mutagens that cause basepair substitutions. Tester strain TA100 is reverted by mutagens that cause both frameshift and basepair substitution mutations. Specificity of the reversion mechanism in E. coli is sensitive to basepair substitution mutations, rather than frameshift mutations (Green and Muriel, 1976).
Salmonella tester strains were derived from Dr. Bruce Ames’ cultures; E. coli tester strains were from the National Collection of Industrial and Marine Bacteria, Aberdeen, Scotland.
Evaluation criteria:
The Mutation Factor is calculated by dividing the mean value of the revertant counts through the mean values of the solvent control (the exact and not the rounded values are used for calculation).
A test item is considered as mutagenic if:
- a clear and dose-related increase in the number of revertants occurs and/or
- a biologically relevant positive response for at least one of the dose groups occurs
in at least one tester strain with or without metabolic activation.
A biologically relevant increase is described as follows:
- if in tester strains TA 98, TA 100 and TA 102 the number of reversions is at least twice as high
- if in tester strains TA 1535 and TA 1537 the number of reversions is at least three times higher
than the reversion rate of the solvent control.
Statistics:
According to OECD guidelines, the biological relevance of the results is the criterion for the interpretation of results, a statistical evaluation of the results is not regarded as necessary.
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:
other: yes with metabolic activation
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
Key result
Species / strain:
E. coli WP2 uvr A
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
other: yes with metabolic activation
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Conclusions:
All criteria for a valid study were met as described in the protocol. The results of the Bacterial Reverse Mutation Assay indicate that, under the conditions of this study, 4,4’-(1,3-phenylenediisopropylidene) diphenylcyanate did not cause a positive mutagenic response with any of the tester strains in either the presence or absence of Aroclor-induced rat liver S9. The study was concluded to be negative without conducting a confirmatory (independent repeat) assay because the results were clearly negative; hence, no further testing was warranted.
Executive summary:

The test substance, 4,4’-(1,3-phenylenediisopropylidene) diphenylcyanate, was tested to evaluate its mutagenic potential by measuring its ability to induce reverse mutations at selected loci of several strains of Salmonella typhimurium and at the tryptophan locus of Escherichia coli strain WP2 uvrA in the presence and absence of an exogenous metabolic activation system. Dimethyl sulfoxide (DMSO) was used as the vehicle.

In the preliminary toxicity assay, the dose levels tested were 6.67, 10.0, 33.3, 66.7, 100, 333, 667, 1000, 3333 and 5000 μg per plate. Precipitate was observed beginning at 667 or 1000 μg per plate. Toxicity was observed, as reductions in revertant counts, beginning at 333, 3333 or at 5000 μg per plate with most test conditions. Based upon these results, the maximum dose tested in the mutagenicity assay was 5000 μg per plate.

In the mutagenicity assay, the dose levels tested were 5.00, 15.0, 50.0, 150, 500, 1500 and 5000 μg per plate. Precipitate was observed beginning at 1500 μg per plate. Toxicity was observed, as reductions in revertant counts, at 5000 μg per plate with tester strains TA100 and WP2 uvrA in the presence of S9 activation. No positive mutagenic responses were observed with any of the tester strains in either the presence or absence of S9 activation.

These results indicate 4,4’-(1,3-phenylenediisopropylidene) diphenylcyanate was negative for the ability to induce reverse mutations at selected loci of several strains of Salmonella typhimurium and at the tryptophan locus of Escherichia coli strain WP2 uvrA in the presence and absence of an exogenous metabolic activation system.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Justification for classification or non-classification