Bis(dodecylthio)dioctylstannane

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01 December 2009 to 02 March 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Reason / purpose for cross-reference:

other: read-across target

Reference

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study conducted on read-across material

Justification for type of information:

Read-across to DOTE (Dioctyltin bis(2-ethylhexyl thioglycolate)) (CAS 15571-58-1), see attached justification.

Reason / purpose for cross-reference:

read-across source

Key result

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

Key result

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with

Genotoxicity:

negative

Remarks:

But increase at 72 µg/ml but this increase is not indicative for mutagenicity.

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2010

Report date:

2010

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

other: in vitro mammalian cell gene mutation tests using the thymidine kinase gene (migrated information)

Test material

Test material information

Constituent 1

Reference substance name:

Dioctyltin bis(2-ethylhexylmercaptoacetate), purity = 96.3%

IUPAC Name:

Dioctyltin bis(2-ethylhexylmercaptoacetate), purity = 96.3%

Constituent 2

Reference substance name:

2-ethylhexyl 10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate

EC Number:

239-622-4

EC Name:

2-ethylhexyl 10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate

Cas Number:

15571-58-1

Molecular formula:

C36H72O4S2Sn

IUPAC Name:

8-Oxa-3,5-dithia-4-stannatetradecanoic acid, 10-ethyl-4,4-dioctyl-7-oxo-, 2-ethylhexyl ester

Details on test material:

-Purity : 96.3%
-Appearance : colourless liquid
-Batch number: ESOC21.20091
Expiry date : 13 november 2010

Method

Target gene:

TK gene

Species / strain

Species / strain / cell type:

mouse lymphoma L5178Y cells

Details on mammalian cell type (if applicable):

The chromosome number of these cells is 40 (stable aneuploid karyotype, 2n = 40).
The cells were stored as frozen stock cultures in liquid nitrogen.
Each new stock culture is checked for mycoplasma contamination, which was absent.
Cell culturing : The L5178Y cells were grown in culture medium consisting of RPMI 1640 medium (with HEPES and Glutamax-I) supplemented with heat-inactivated horse serum (10 % v/v for growing in flasks, and 20 % for growing in microtiter plates), sodium pyruvate and penicillin/streptomycin.
On the day of exposure, the growth rate (doubling time of 9-14 h) and viability (>90 %; by trypan blue exclusion) of the cells were checked.

Metabolic activation:

with and without

Metabolic activation system:

S9 liver homogenate

Test concentrations with justification for top dose:

FIRST test: Without S9 (24hr of treatment): 0.006-10 µg/ml ; With S9 (4 hr of treatment) : 0.01-20 µg/ml
SECOND test: Without S9 (4hr of treatment): 0.86-20 µg/ml; Without S9 (24hr) : 0.02-0.40µg/ml; With S9 : 1.6-60 µg/ml
THIRD test: Without S9 (24hr of treatment): 0.007-0.5 µg/ml ; With S9 (4hr of treatment): 1.4-100 µg/ml
With S9 (Third test, 4 hr of treatment): 1.4-100 µg/ml (11 concentrations)

Vehicle / solvent:

Ethanol.
The test material was diluted in ethanol to concentrations ranging from 0.04 to 10 mg/ml DOTE. From these stock solutions serial dilutions in ethanol were made and from each of these 0.1 ml were added to a final volume of 10 ml culture medium.

Controls

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

(ethanol)

True negative controls:

no

Positive controls:

yes

Positive control substance:

3-methylcholanthrene

methylmethanesulfonate

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium

DURATION
- Preincubation period: 4 hours or 24 hours (37°C, 5% CO2)
- Exposure duration: 20-24, and 44-48 hours (37°C, 5% CO2)
- Expression time (cells in growth medium): doubling time of 9-14 hours
- Selection time (if incubation with a selection agent): no data

NUMBER OF REPLICATIONS: single culture for each dose, 2 for negative control group, 1 for positive control group

NUMBER OF CELLS EVALUATED: 2000/well

DETERMINATION OF CYTOTOXICITY
- Method: by measuring the relative initial cell yield, the relative suspension growth (RSG) and the relative total growth (RTG)

OTHER EXAMINATIONS:
- Determination of polyploidy: no
- Determination of endoreplication: no

Evaluation criteria:

The following criteria were used to validate the data obtained in the gene mutation assay (Cole et al., 1990; Aaron et al. 1994; Clive et al., 1995):
a) the average cloning efficiency of the negative controls should not be less than 60 % or more than 140 %.
b) the average suspension growth of the negative controls should be between 8 and 32.
c) the average mutant frequency of the negative controls should fall within the range of 40-300 TFT-resistant mutants per 1,000,000 clonable cells.
d) the mutant frequency of the positive controls should be higher than 400 TFTresistant mutants per 1,000,000 clonable cells, and should be at least twice that of the corresponding negative control.
e) unless the test substance shows no cytotoxicity at the highest possible concentration (determined by its solubility, pH and osmolar effects), the highest concentration should result in a clear cytotoxic response. The RTG value of one of the data points should be between 10 and 20 %, or one data point between 1 and 10% and another between 20 and 30 %.

The test material was considered to be mutagenic in the gene mutation test at the TK-locus if a concentration-related increase in mutant frequency was observed, or if a reproducible positive response for at least one of the test substance concentrations was observed.
The test material was considered not to be mutagenic in the gene mutation test at the TK-locus if it produced neither a dose-related increase in the mutant frequency nor a reproducible positive response at any of the test material concentrations.

Statistics:

no statistical analysis was performed.

Results and discussion

Test results

Test results 1

Key result

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

Test results 2

Key result

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with

Genotoxicity:

negative

Remarks:

But increase at 72 µg/ml but this increase is not indicative for mutagenicity.

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

Results without S9 (see tables 1 and 2) :
In the absence of S9-mix three assays were performed in which mutagenicity was evaluated; two with 24 hours exposure and one with 4 hours exposure. In the first assay with 24 hours exposure the RTG at the highest concentration was 22 % (not between 10 and 20 %) and only six concentrations could be evaluated due to severe cytotoxicity. In the second assay with 24 hours exposure (results obtained in third test), sufficient cytotoxicity was observed at the highest concentration (RTG of 13 %) and nine concentrations could be evaluated resulting in clear to hardly any cytotoxic response. In the assay with 4 hours exposure (second test) at and above 5 μg/mL no clear dose response in cytotoxicity was observed, however, sufficient toxicity (RTG between 10 and 20 %) was observed for a valid test.
In none of the three assays performed in the absence of S9-mix any increase in mutant frequency (MF) by more than 88 or 126 mutants per 1,000,000 clonable cells, i. e. no equivocal or positive response, compared to the negative control was observed at any dose level.

Results with S9 (see table 3) :
In the presence of S9-mix two assays were performed in which mutagenicity was evaluated. In the first assay not sufficient cytotoxicity was observed at the highest concentration of 20 μg/mL (RTG was 38 %; not between 10 and 20 %). In the second assay (results obtained in third test), although relatively small intervals between the concentrations were used, none of the concentrations resulted in an RTG between 10 and 20 %. Above 44 μg/mL no dose response in cytotoxicity was observed. The RTG at 85 μg/ml was 30% whereas at 72 μg/ml the RTG was 5%. In addition, the relative suspension growth (RSG) at 61 and 85 μg/mL were 24 and 21%, respectively. This means that already in this phase almost 80 % cytotoxicity was observed, however, since the initial cell yield and cloning efficiencies at these concentrations were above 100 % (which is very unusual) this resulted not in RTG values below 20 %. In the presence of S9-mix at 72 μg/mL the mutant frequency was significantly increased by 238 mutants per 1,000,000 clonable cells compared to the negative control. Since relatively small intervals (0.85) were used and the increase was observed at a single concentration causing more than 90% cytotoxicity, it is concluded that this increase is not indicative for mutagenicity.

Colony sizing :
Colony sizing was performed in the third test at 2 concentrations in the presence of S9-mix, since a positive response in mutant frequency was observed. Both at 72 and 85 μg/mL relatively more small then large colonies were formed; 68 and 65 % compared to 32 and 35 %, respectively.
Since the increase in mutant frequency at 72 μg/mL was considered to be not relevant, no conclusions were drawn from these findings.

Positive and negative controls :
Methyl methanesulphonate (MMS) and 3-methylcholanthrene (MCA) were used as positive control substances in the absence and in the presence of S9-mix, respectively; Ethanol served as negative control. The negative controls were within historical background ranges and treatment with the positive controls yielded the expected significant increase in mutant frequency compared to the negative controls.

RANGE-FINDING/SCREENING STUDIES:
Prior to the main study two dose range finding studies were performed; single cultures were exposed for 24 hours in the absence of S9-mix to 5 concentrations of DOTE ranging from 312 to 5000 μg/mL and 9.4 to 150 μg/mL, in the first and second study, respectively.

COMPARISON WITH HISTORICAL CONTROL DATA:
The negative controls were within historical background ranges and treatment with the positive controls yielded the expected significant increase in mutant frequency compared to the negative controls.

Any other information on results incl. tables

Table 1 : Summary of the results after 24 hours exposure in the absence of S9-mix.

Dose (µg/mL)	First assay (first test)		Dose (µg/mL)	First assay (first test)
	MF	RTG		MF	RTG
			0.36	115	13
			0.31	64	29
			0.26	63	36
0.2	89	22	0.22	93	60
0.1	72	81	0.16	115	79
0.05	76	95	0.11	59	100
0.03	57	84	0.079	93	99
0.01	74	96	0.055	80	108
0.006	58	81	0.027	72	110
0	93*	100*	0	74*	100*

*Mean of duplicate cultures.

MF = mutant frequency ; RTG = Relative total growth.

Table 2 : Summary of the results after 4 hours exposure in the absence of S9-mix.

Dose (µg/mL)	Second test
	MF	RTG
20	105	20
17	88	9
14	154	11
10	121	20
7.3	72	21
5.1	81	21
3.6	124	30
1.8	105	42
0.86	76	64
0	66*	100*

*Mean of duplicate cultures.

MF = mutant frequency ; RTG = Relative total growth.

Table 3 : Summary of the results after 4 hours exposure in the presence of S9-mix.

Dose (µg/mL)	First assay (first test)		Dose (µg/mL)	Second assay (third test)
	MF	RTG		MF	RTG
			85	143	30
20	117	38	72	318	5
14	105	49	61	89	39
9.8	83	60	44	111	35
6.9	80	80	32	140	42
3.4	73	88	22	71	57
1.6	75	93	11	103	85
0.8	69	101	5.4	83	89
0.4	87	84	2.7	95	83
0.2	78	93	1.4	100	71
0	86*	100*	0	80*	100*

*Mean of duplicate cultures.

MF = mutant frequency ; RTG = Relative total growth.

Applicant's summary and conclusion

Conclusions:

It is concluded that under the conditions used in this study, the test material DOTE is not mutagenic at the TK-locus of mouse lymphoma L5178Y cells.
The test material DOTE was tested and evaluated for mutagenicity in both the absence and presence of metabolic activation (S9-mix). In the absence of S9-mix beside treatment for 4 hours, an extended treatment for 24 hours was used. In the three assays performed sufficient cytotoxicity was observed to validate the concentrations used and in none of the assays any indication for a mutagenic potential was observed.

Executive summary:

The test material DOTE was examined for its potential to induce gene mutations at the TK-locus of cultured mouse lymphoma L5178Y cells, in both the absence and the presence of a metabolic activation system (S9-mix). Three tests were conducted; in the first and third test single cultures were treated for 24 hours and 4 hours in the absence and presence of S9-mix, respectively; in the second test cultures were treated for 24 hours and 4 hours in the absence of S9-mix and 4 hours in the presence of S9-mix. The test material was dissolved in ethanol prior to testing.

The highest concentrations of DOTE evaluated for mutagenicity in the absence of S9-mix, were 20 μg/mL and 0.36 μg/mL at 4 and 24 hours exposure, respectively. In the presence of S9-mix and 4 hours exposure, the highest concentration evaluated was 85 μg/mL. The maximum concentrations were limited by cytotoxicity.

DOTE was cytotoxic in both the absence and presence of S9-mix. In the absence of S9-mix and 24 hours exposure cytotoxicity, resulting in a reduction in initial cell yield and/or suspension growth, was observed at and above 0.1 μg/mL. The relative total growth (RTG) at the highest concentration evaluated in the first and third test were 22 and 13 %, respectively. In the absence of S9-mix and 4 hours exposure cytotoxicity was observed at all concentrations included (as from 0.86 μg/mL). The relative total growth (RTG) at the highest concentration evaluated in the second test was 20 %.

In the presence of S9-mix cytotoxicity was observed at and above 1.4 μg/mL. The relative total growth (RTG) at the highest concentration evaluated in the first and third test were 38 and 30 %, respectively. In the absence of S9-mix no increase in mutant frequency was observed at any test substance concentration evaluated. In the presence of S9-mix at 72 μg/mL the mutant frequency was significantly increased by 238 mutants per 1,000,000 clonable cells compared to the negative control. Since relatively small intervals (0.85) were used and the increase was observed at a single concentration causing more than 90 % cytotoxicity compared to six concentrations causing 50-70 % cytotoxicity which showed no increase in mutant frequency, it is concluded that this increase is not indicative for mutagenicity. It is very likely a secondary effect to cytotoxicity and thus not indicative for mutagenicity.

Methyl methanesulphonate (MMS) and 3-methylcholanthrene (MCA) were used as positive control substances in the absence and presence of the S9-mix, respectively; ethanol (vehicle) served as negative control. The negative controls were within historical background ranges and treatment with the positive control yielded the expected significant increase in mutant frequency compared to the negative controls.

It is concluded that under the conditions used in this study, the test material DOTE is not mutagenic at the TK-locus of mouse lymphoma L5178Y cells.