1,3-dibutyl-2-thiourea

Carcinogenicity

Administrative data

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1978

Report date:

1978

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Study was performed to determine whether selected chemicals have the capacity to produce cancer in animals. Mice were exposed to DETU in diet during 103 weeks.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

1,3-diethyl-2-thiourea

EC Number:

203-308-5

EC Name:

1,3-diethyl-2-thiourea

Cas Number:

105-55-5

Molecular formula:

C5H12N2S

IUPAC Name:

1,3-diethylthiourea

Test animals

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River breeding Laboratories, Inc., Wilmington, Massachussets
- Age at study initiation: around 6 weeks-old
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: in polycarbonate cages suspended from aluminium racks.
- Diet (e.g. ad libitum): Wayne Lab-Blox (Allied Mills, Inc. Chicago, Ill.), ad libitum
- Water (e.g. ad libitum): aciduled water (pH 2.5) was suplied to animals in water bottles filled in an automated metering device, ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22-26°C
- Humidity (%):45-55%
- Air changes (per hr):12-15
- Photoperiod (hrs dark / hrs light): fluorescent lighlting 8h/day (9.00 am to 5.00 pm)

Administration / exposure

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

- Concentration: 250 and 500 ppm.
- Positive control: non

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

103 weeks

Frequency of treatment:

daily

Post exposure period:

1 week

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

500 ppm

Doses / concentrations 2

Dose / conc.:

250 ppm

No. of animals per sex per dose:

- Number of animals per dose: 50 males + 50 females
- Control groups: 20 males + 19 females

Control animals:

yes, concurrent no treatment

Positive control:

no

Examinations

Observations and examinations performed and frequency:

- Body weight: immediately prior to initiation of the experiment and then once monthly throughout the bioassay
- Food consumption: collected at monthly intervals from 20 of the animals of the animals in each group.
- Mortality: inspected twice daily

Sacrifice and pathology:

- Animal sacrifice: by CO2 asphyxiation, at the end of the bioassay or when moribund or when animals developed large, palpable masses that jeopardize their health.
- Necropsy: as soon as death occured.
- Gross and microscopic examination of all major tissues, organs and gross lesions.
- Tissues were preserved in a 10 percent neutral buffered formalin solution, embedded in paraffin, sectioned, and stained with hematoxylin and eosin prior to microscopic examination. Slides were prepared from the following tissues: skin, subcutaneous tissue, lungs and bronchi, trachea, bone marrow, spleen, lymph nodes, thymus, heart, salivary gland, liver, pancreas, esophagus, stomach, small intestine, large intestine, kidney, urinary bladder, pituitary, adrenal, thyroid, parathyroid, testis, prostate, brain, tunica vaginalis, uterus, mammary gland and ovary. - A few tissues were not examined for some animals, particularly for those that died early. Besides, some animals were missing, cannibalized, or judged to be in such an advanced state of autolysis as to preclude histopathologic interpretation.

Statistics:

- A Tarone test was performed to evaluate association between dosage and mortality. - Statistical analyses for a possible dose-related effect on survival used the method of Cox (1972) when testing two groups for equality and used Tarone's (1975) extensions of Cox's methods when testing a dose-related trend.
- To determine whether animals receiving the test substance developed a significantly higher proportion of tumors than did the control animals, the one-tailed Fisher exact test was used to compare the tumor incidence of a control group to that of a group of treated animals at each dose level. In practice, the incidence of lesions was analyzed by a Cochran-Armitage test which was used when comparing the dosed groups to the control and which was supported by a Fisher exact test, comparing the high dose group to the control.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Description (incidence and severity):

No abnormal clinical signs were recorded.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

There were no significant positive associations between the dosages of N,N'-diethylthiourea administered and mortality of either sex.
There were adequate numbers of animals in all dose groups survived sufficiently long to be at risk from late-developing tumors.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Dose related mean body weight depression was apparent in both male and female mice after week 30, indicating that the concentrations of N,N'-diethylthiourea administered to mice may have approximated the maximum tolerated dosages (250 and 500 ppm)..

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

The severity and incidence of non-neoplastic lesions were also not unusual (ex: pneumonia, spleen hyperplasia...).

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

In both sexes, the neoplasms observed were similar in type and distribution in dosed and control mice (ex: alveolar/bronchiolar adenoma, hepatocellular adenoma and carcinoma, leukemia or malignant lymphoma...). None of statistical tests for any site revealed a significant positive association between administration of compound and increased tumor incidence.

Other effects:

not examined

Relevance of carcinogenic effects / potential:

The test substance was considered as not carcinogenic in B6C3F1 mice.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

< 250 ppm

Sex:

male/female

Basis for effect level:

other: Decrease of body weight gain was observed at 250 and 500 ppm in mice.

Remarks on result:

other: Systemic toxicity

2

Dose descriptor:

NOAEL

Effect level:

> 500 ppm

Sex:

male/female

Basis for effect level:

other: No tumors was observed in mice after exposure of 250 and 500 ppm of DETU during 103 weeks.

Remarks on result:

other: carcinogenicity

Any other information on results incl. tables

Tables of results: Carcinogenicity study in mice with DETU

 

1/ Analyses of the incidence of primary tumors at specific sites in female mice treated with DETU

 

Topography: morphology	control	Low dose (250 ppm)	High dose (500 ppm)
Hematopoietic system : Leukemia or malignant lymphoma weeks to first observed tumor	8/19 (42%)   93	15/48 (31%)   78	9/41 (22%)   92
Uterus: Endometrial stromal polyp weeks to first observed tumor	0/17 (0%) /	3/45 (7%) 62	2/38 (5%) 91

 

 

2/ Analyses of the incidence of primary tumors at specific sites in male mice treated with DETU

 

Topography: morphology	control	Low dose (250 ppm)	High dose (500 ppm)
Lung: Alveolar/Bronchiloar adenoma or alveolar/bronchiolar carcinoma weeks to first observed tumor	2/13 (15%)     99	4/46 (9%)     104	6/46 (13%)     99
Hematopoietic system : Leukemia or malignant lymphoma weeks to first observed tumor	3/15 (20%)   93	11/48 (23%)   90	12/49 (24%)   76
Circulatory system: Hemangioma or hemangiosarcoma weeks to first observed tumor	1/15 (7%)   104	1/48 (2%)   104	3/49 (6%)   99
Liver: Hepatocellular carcinoma weeks to first observed tumor	2/14 (14%) 104	5/48 (10%) 71	2/49 (4%) 104
Liver: Hepatocellular carcinoma or hepatocellular adenoma weeks to first observed tumor	5/14 (36%)*   /	7/48 (15%)   104	3/49 (6%)*   91

 

* Significative difference between treated and control groups (cochran-Armitage est supported by a Fischer exact test)

 

Applicant's summary and conclusion

Executive summary:

Study was performed to determine whether DETU have the capacity to produce cancer in animals.

Mice were exposed to DETU in diet during 103 weeks at 250 and 500 ppm (12.5 and 25 mg/kg bw/d respectively).

No mortality, no clinical signs were observed during this study, but decrease of body weight gain was observed at each dose.

In both sexes, the neoplasms observed were similar in type and distribution in dosed and control mice (ex: alveolar/bronchiolar adenoma, hepatocellular adenoma and carcinoma, leukemia or malignant lymphoma...). None of statistical tests for any site revealed a significant positive association between administration of compound and increased tumor incidence.

The severity and incidence of non-neoplastic lesions were also not unusual (ex: pneumonia, spleen hyperplasia...).

The test substance was considered as not carcinogenic in B6C3F1 mice.