Imidazolidine-2-thione

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in mammalian cells

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study with acceptable restriction

Data source

Reference

Reference Type:

publication

Title:

Responses of the L5178Y tk+/tk- mouse lymphoma cell forward mutation assay: III. 72 coded chemicals.

Author:

McGregor DB, Brown A, Cattanach P, Edwards I, McBride D, Riach C and Caspary WJ.

Year:

1988

Bibliographic source:

Environ. mol. Mutag. 12: 85-154

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

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

Deviations:

yes

Remarks:

one test with DMSO

GLP compliance:

not specified

Type of assay:

mammalian cell gene mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Imidazolidine-2-thione

EC Number:

202-506-9

EC Name:

Imidazolidine-2-thione

Cas Number:

96-45-7

Molecular formula:

C3H6N2S

IUPAC Name:

imidazolidine-2-thione

Details on test material:

Other name = Ethylenethiourea (ETU)
Source : National Toxicology Program Chemical Repository, Radian Corporation, Austin, TX 78766.

Method

Target gene:

Thymidine kinase

Species / strain

Species / strain / cell type:

mouse lymphoma L5178Y cells

Details on mammalian cell type (if applicable):

The tk+/tk-, 3.7.2C heterozygote of L5178Y mouse lymphoma cells was obtained from Dr. D. Clive, Burroughs Wellcome Co., Research Triangle Park, NC 27709, and stored in liquid nitrogen.

Additional strain / cell type characteristics:

not specified

Metabolic activation:

with and without

Metabolic activation system:

10% Post-mitochondrial supernatant fractions of liver homogenates (rats aroclor 1254)

Test concentrations with justification for top dose:

0, 225, 450, 900, 1800, 3600 µg/ml

Vehicle / solvent:

DMSO

Controls

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 3-methylcholanthrene (with S9) and methyl-methanesulphonate (without S9)

Details on test system and experimental conditions:

Each experiment, other than the initial toxicity test, normally consisted of the following groups: vehicle control, four cultures; positive control, two cultures; at least five test compound concentrations, two cultures per concentration. With any chemical, the first experiment was a toxicity test in which cell population expansion was measured. Ten-fold differences in test compound concentrations were used in the toxicity test, the highest being 5 mg/ml unless a much lower concentration was indicated by the poor solubility of a compound.

Evaluation criteria:

See tables 1 and 2

Statistics:

yes

Results and discussion

Test results

Test results 1

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with

Genotoxicity:

positive

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Test results 2

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

Insolubility, rather than toxicity, restricted dosing to 3600 µg/ml, which, in the absence of S9 mix, failed to induce a mutagenic response in two experiments. In the presence of S9 mix statistically significant increases in mutant fraction occurred in two experiments. The LOED was 1800 µg/ml, where toxicity was either slight or not demonstrable. See tables 3-6.

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Any other information on results incl. tables

Table 3 : Results of ETU without S9 (trial no.1)

Concentration µg/ml	Cloning efficiency (%)	Relative total growth (%)	Mutant colony count	Mutant fraction^a	Group average mutation fraction
DMSO	99	103	107	51	-
0	86	96	81	32	37
	86	102	78	30
	85	100	79	52
225	102	108	99	33	33
	92	99	93	34
450	94	107	58	21	28
	95	96	101	36
900	73	85	72	33	-
1800	71	67	86	40	46
	63	80	97	51
3600	64	74	85	44	36
	92	89	76	28
MMS^b	35	24	132	126	154*
	36	21	196	181
^aMutation colonies per 10^6 clonable cells ^bpositive control, Methymethanesulfonate, 2 assays, 15 µg/ml * P<0.05

Table 4 : Results of ETU without S9 (trial no.2)

Concentration µg/ml	Cloning efficiency (%)	Relative total growth (%)	Mutant colony count	Mutant fraction^a	Group average mutation fraction
DMSO	79	99	69	29	-
0	69	93	65	31	26
	69	92	40	19
	80	116	54	21
225	90	104	71	26	21
	83	111	38	15
450	82	109	48	20	19
	90	1014	49	18
900	102	96	55	18	17
	86	102	44	17
1800	86	96	41	16	15
	90	98	36	15
3600	78	98	42	18	16
	84	104	35	14
MMS^b	44	35	172	130	126*
	43	37	157	122
^aMutation colonies per 10^6 clonable cells ^bPositive control, Methymethanesulfonate, 2 assays, 15 µg/ml * P<0.05

Table 5 : Results of ETU with S9 (trial no.1)

Concentration µg/ml	Cloning efficiency (%)	Relative total growth (%)	Mutant colony count	Mutant fraction^a	Group average mutation fraction
DMSO	63	107	28	15	-
0	77	101	46	20	17
	61	81	36	20
	71	111	27	13
225	61	87	53	29	25
	63	97	39	21
450	73	109	35	16	17
	65	104	37	19
900	68	68	51	25	26
	82	92	66	27
1800	91	118	98	36	35*
	73	97	73	35
3600	83	102	81	33	35*
	85	98	94	37
MCA^b	56	32	223	132	130*
	51	32	195	128
^aMutation colonies per 10^6 clonable cells ^bPositive control, 3-mthylcholanthrene, 2 assays, 2.5 µg/ml * P<0.05

Table 6 : Results of ETU with S9 (trial no.2)

Concentration µg/ml	Cloning efficiency (%)	Relative total growth (%)	Mutant colony count	Mutant fraction^a	Group average mutation fraction
DMSO	69	96	45	22	-
0	86	104	71	28	23
	82	106	47	19
	72	95	51	23
225	72	95	48	22	25
	84	109	72	29
450	87	87	103	40	37*
	84	89	88	35
900	75	77	97	43	40*
	65	69	73	38
1800	78	71	103	44	46*
	73	92	104	47
3600	73	80	124	56	55*
	70	68	113	54
MCA^b	69	29	490	238	269*
	47	25	418	300
^aMutation colonies per 10^6 clonable cells ^bPositive control, 3-mthylcholanthrene, 2 assays, 2.5 µg/ml * P<0.05

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information):
positive with metabolic activation
negative without metabolic activation

Positive result was only observed when using metabolic activation.

Executive summary:

Seventy-two chemicals were tested for their mutagenic potential in the L5178Y tk+/- mouse lymphoma cell forward mutation assay. Cultures were exposed to the chemicals for 4 hr, then cultured for 2 days before plating in soft agar with or without trifluorothymidine (TFT), 3 µg/ml. The chemicals were tested at least twice. Significant responses were obtained with ETU with S9 (negative result without S9).