2-isopropyl-9H-thioxanthen-9-one

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01 June 2003 to 15 October 2003

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2003

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)

Version / remarks:

not indicated

Deviations:

no

GLP compliance:

not specified

Type of assay:

in vitro mammalian chromosome aberration test

Test material

Test material information

Constituent 1

Reference substance name:

2-isopropyl-9H-thioxanthen-9-one

EC Number:

226-827-9

EC Name:

2-isopropyl-9H-thioxanthen-9-one

Cas Number:

5495-84-1

Molecular formula:

C16H14OS

IUPAC Name:

2-isopropyl-9H-thioxanthen-9-one

Method

Species / strain

Species / strain / cell type:

mammalian cell line, other: CHL/IU

Metabolic activation:

with and without

Metabolic activation system:

Induced rat liver microsomal fraction

Test concentrations with justification for top dose:

Test 1 (With activation): 37.5, 70 and 150 µg/mL
Test 1 (Without activation): 15, 30 and 60 µg/mL
Test 2 (Without activation): 10, 20 and 40 µg/mL
Test 3 (Without activation): 2.5, 5 and 10 µg/mL

Vehicle / solvent:

- Vehicle/solvent used: DMSO

Controls

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:

WITH METABOLIC ACTIVATION
Test 1- Exposure time: 6 hours and Harvest time: 24 hours

WITHOUT METABOLIC ACTIVATION
Test 1- Exposure time: 6 hours and Harvest time: 24 hours

WITHOUT METABOLIC ACTIVATION
Test 2- Exposure time: 24 hours and Harvest time: 24 hours

WITHOUT METABOLIC ACTIVATION
Test 3- Exposure time: 48 hours and Harvest time: 48 hours

DETERMINATION OF CYTOTOXICITY
- Method: Cytotoxicity was determined with or without metabolic activation using viable cell counts.

Results and discussion

Test results

Key result

Species / strain:

mammalian cell line, other: CHL/IU

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

True negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

- In the cytotoxicity measurement, it was determined that concentrations of the test material at 60 µg/mL, 40 µg/mL and 10 µg/ml respectively for 6 hours, 24 hours and 48 hours without metabolic activator and at 150 µg/mL with metabolic activator could result in a significant inhibition of cell growth by 50 percent.
- Without metabolic activator, the test material did not cause structural chromosome aberration in CHL cells exposed for 6 hours, 24 hours and 48 hours respectively, but it could induce the increase of gap in CHL cells treated for 48 hour. The test material didn't induce structural chromosome aberration in CHL cells with metabolic activator.
- The test material caused a significant increase of polyploidy in CHL cells at 60 µg/mL in the case of CHL cells exposed for 6 hours without metabolic activation (P<0.05). No other abnormality was observed.

- In this study, it was observed that without metabolic activation, polyploidy of CHL cells increased significantly exposed for 6 hours at 60 µg/mL of test material, while this case didn't occur when exposed for 24 hours and 48 hours. Since the polyploidy ratio is as low as 2.5 % and there was no obvious dose-response relationship, it is therefore concluded that the 6 hours result may be not related to action of the test material.

Any other information on results incl. tables

Table 1: Effect of the Test Material on Structural Chromosome Aberration in CHL Cells

Metabolic activation	Exposure period	Dose (µg/mL)	Cell no. scored	Gaps	No. of structural aberrations	Ratio of aberration (%)	Result
+	6 hours	0	200	3	2	1.0	-
		37.5	200	6	3	1.5	-
		75	200	12	1	0.5	-
		150	200	8	8	4.0	-
		CP (20)	200	28	118	59.0	+
-	6 hours	0	200	0	3	1.5	-
		15	200	6	3	1.5	-
		30	200	2	1	0.5	-
		60	200	3	6	3.0	-
		MMC (0.2)	200	5	73	36.5	+
-	24 hours	0	200	3	3	1.5	-
		10	200	2	4	2.0	-
		20	200	5	2	1.0	-
		40	200	2	2	1.0	-
		MMC (0.1)	200	30	106	53.0	+
-	48 hours	0	200	0	2	1.0	-
		2.5	200	14	2	1.0	-
		5	200	10	7	3.5	-
		10	200	18	8	4.0	-
		MMC (0.05)	200	4	41	20.5	+

 

Table 2: Effect of the Test Material on Polyploidy in CHL Cells

Metabolic activation	Exposure period	Dose (µg/mL)	Cell no. scored	Number of polyploid	Ratio of polyploidy (%)	X^2
+	6 hours	0	200	4	2.0	5.44 P > 0.05
		37.5	200	5	2.5
		75	200	2	1.0
		150	200	0	0.0
		CP (20)	200	0	0.0
-	6 hours	0	200	0	0.0	9.09 P > 0.05
		15	200	3	1.5
		30	200	0	0.0
		60	200	5	2.5*
		MMC (0.2)	200	0	0.0
-	24 hours	0	200	2	1.0	2.74 P > 0.05
		10	200	3	1.5
		20	200	2	1.0
		40	200	0	0.0
		MMC (0.1)	200	0	0.0
-	48 hours	0	200	0	0.0	3.0 P > 0.05
		2.5	200	1	0.5
		5	200	0	0.0
		10	200	0	0.0
		MMC (0.05)	200	0	0.0

Compared with Negative Control:*, P<0.05

Applicant's summary and conclusion

Conclusions:

Under the conditions of this study, the test material is not clastogenic in either the presence or absence of metabolic activation.

Executive summary:

The potential of the test material to cause chromosome aberrations in cultured mammalian cells was investigated in accordance with the standardised guideline OECD 473.

CHL/IU cells were treated with the test material according to the following:

Test 1 (with metabolic activation) for exposure time 6 hours and harvest time 24 hours at 37.5, 70 and 150 µg/mL;

Test 1 (without metabolic activation) for exposure time 6 hours and harvest time 24 hours at 15, 30 and 60 µg/mL;

Test 2 (without metabolic activation) for exposure time of 24 hours and harvest time 24 hours; and

Test 3 (without metabolic activation) for exposure time 48 hours and harvest time 48 hours.

Metabolic activation was provided in the form of Induced rat liver microsomal fraction. The test material was prepared in DMSO and this was used as the solvent control. Mitomycin C was used as a positive control in the absence of exogenous metabolic activation and Cyclophosphamide was used for the presence of exogenous metabolic activation. Cytotoxicity was determined with or without metabolic activation using viable cell counts.

In the cytotoxicity measurement, it was determined that concentrations of the test material at 60 µg/mL, 40 µg/mL and 10 µg/mL respectively for 6 hours, 24 hours and 48 hours without metabolic activation and at 150 µg/mL with metabolic activator could result in a significant inhibition of cell growth by 50 percent.

Without metabolic activation, the test material did not cause structural chromosome aberration in CHL cells exposed for 6 hours, 24 hours and 48 hours respectively, but it could induce the increase of gaps in CHL cells treated for 48 hours. The test material didn't induce structural chromosome aberration in CHL cells with metabolic activator.

The test material caused a significant increase of polyploidy in CHL cells at 60 µg/mL in the case of CHL cells exposed for 6 hours without metabolic activation (P<0.05). No other abnormality was observed.

In this study, it was observed that without metabolic activation, polyploidy of CHL cells increased significantly when exposed for 6 hours at 60 µg/ml of test material, while this case didn't occur when exposed for 24 hours and 48 hours, respectively. Since the polyploidy ratio is as low as 2.5 % and there was no obvious dose-response relationship it is therefore concluded that the 6 hours results may not be related to action of the test material.

Under the conditions of this study, the test material is not clastogenic in either the presence or absence of metabolic activation.