1-chloro-4-(n-propoxy)-5-thioxanthen-10-one

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Setptember - October 1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1991

Report date:

1991

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

1-chloro-4-(n-propoxy)-5-thioxanthen-10-one

EC Number:

415-890-1

EC Name:

1-chloro-4-(n-propoxy)-5-thioxanthen-10-one

Cas Number:

142770-42-1

Molecular formula:

C16H13ClO2S

IUPAC Name:

1-chloro-4-propoxy-9H-thioxanthen-9-one

Method

Target gene:

Histidine

Species / strain

Species / strain 1

Species / strain / cell type:

S. typhimurium TA 1538

Species / strain 2

Species / strain / cell type:

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

Metabolic activation:

with and without

Metabolic activation system:

Mixed function oxidase systems in the livers of a group of rats (SD male rats) were stimulated by Aroclor 1254, administered as a single intra-peritoneal injection in Arachis oil at a dosage of 500 mg/kg bw. On the fifth day after injection, following an overnight starvation, the rats were killet and their livers aseptically revomed.
The following steps were arried out at 0-4°C under aseptic conditions. The livers were placed in 0.15 M KCl before being trasnferred to an Ultra-Turrax homogeniser. Following preparation, the homogenates were centrifuged at 9000 g for 10 minutes. The supernatant fraction (S9 fraction) was dispensed into aliquots and stored at -80°C until required. The S9-fraction was tested with two carcinogens before use.

S9 mix contained : S9 fraction (10% v/v), MgCl2 (8 mM), KCl (33 mM), sodium phosphate buffer pH 7.4 (100 mM), glucose-6-phodphate (5mM), NADP (4 mM). All the cofactors were filter-sterilised before use.

Vehicle / solvent:

DMSO

Controls

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Details on test system and experimental conditions:

Preliminary toxicity test :
Four concentrations of test substance were assessed for toxicity using the five tester strains. The highest concentration was 50 mg/ml of test substance in the chosen solvent, which provided a final concentration of 5000 µg/plate. Three 10-fold serial dilutions of the highest concentration were also tested. The chosen solvent was used as the negative control.
An aliquot of 0.1 ml of a 10 hour bacterial culture and 0.5 ml S9-mix or 0.5 ml 0.1 M phosphate buffer (pH 7.4) were placed in glass bottles. An aliquot of 0.1 ml of the test substance solution was added followed, immediately, by 2 ml of histidine deficient agar. The mixture was thoroughly shaken and overlaid onto previously prepared petri dishes containing 25 ml minimal agar. A single petri dish was used for each dose level. Plates were also prepared without the additionof bacteria in order to assess the sterility of the test substance, S9 mix and phosphate buffer. All plates were incubated at 37°C for 3 days. After this period the appearance of the background bacterial lawn was examined. Revertant colonies were counted.

Main test
The test substance was added to cultures of the five tester strains at five concentrations. The highest concentration of CPTX used was 5000 µg/plate.
The main test was repeated using the same concentrations of test substance.

Evaluation criteria:

The mean number of revertant colonies for all treatment groups is compared with those obtained for solvent control groups. The mutagenic activity of a test material is assessed by applying the following criteria :
-If treatment with a test material produces an increaase in revertant colony numbers of at least twice the concurrent solvent controls, with some evidence of a positive dose-relationshp in two separate experiments, with any bacterial strain either in the presence or absence of S9 mix, it is considered to show evidence of mutagenic activity in this test system. No statistical analysis is performed.
-If treatment with a test material does not produce reproducible increases of at least 1.5 times the concurrent solvent controls, at any dose level with any bacterial strain, it is considered to show no evidence of mutagenic activity in this test system. No statistical analysis is performed.
-If the results obtained fail to satisfy the criteria for a clear positive or negative response, repeat test and/or use statistics are recommanded.

Statistics:

see Evaluation criteria

Results and discussion

Test results

Test results 1

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Test results 2

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Test results 3

Species / strain:

S. typhimurium TA 1538

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Test results 4

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Test results 5

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

CPTX was not toxic towards the tester strains in the preliminary toxicity test, therefore 5000 µg/plate was chosen as the top dose in the mutation tests.
In the mutation tests, no substantial increases in revertant colony numbers of any of the tester strains were observed following treatment with CPTX at any dose level, either in the presence or absence of S9 mix.

Applicant's summary and conclusion

Conclusions:

It is concluded that CPTX was not mutagenic in the bacterial test system.

Executive summary:

Mutagenic potential of CPTX was evaluated in an Ames test. Histidine dependent auxotrophic mutants of Salmonella typhimurium (strains TA1535, TA1537, TA1538, TA98, TA100) were exposed to the test material, diluted in DMSO which was also used as a negative control. Two independent mutation tests were performed, in the presence and absence of liver preparations from Arochlor 1254-induced rats. 

In the preliminary dose range finding study with dose levels of up to 5000 µg/plate, no toxicity was observed. A top dose level of 5000 µg/plate was chosen for the subsequent mutation study. Other dose levels used in the mutation assays were 1500, 5000, 150 and 50 µg/plate.

No evidence of mutagenic activity was seen at any dose level of CPTX in either mutation test. The concurrent positive control compounds demonstrated the sensitivity of the assay and the metabolising activity of the liver preparations. 

It is concluded that CPTX was not mutagenic in the bacterial test system.