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Carcinogenicity

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Description of key information

No evidence of carcinogenicity was seen in a 2-year dietary study in rats or in an 80 week dietary study in mice. 

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records
Reference
Endpoint:
carcinogenicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
20 March 1989 to 08 April 1991
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant, guideline study, available as unpublished report, no restrictions, fully adequate for assessment
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
OECD Guideline 451 (Carcinogenicity Studies)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPP 83-5 (Combined Chronic Toxicity / Carcinogenicity)
Deviations:
no
Qualifier:
according to
Guideline:
other: Japan, 59 Nohsan No. 4200
Deviations:
no
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes
Species:
rat
Strain:
other: Tif: RAIf (SPF)
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Age at study initiation: approximately 5 weeks
- Weight at week -1: 74.85-115.4 g (males), 76.33-107.4 g (females)
- Housing: 5 per sex in macrolon type 4 cages
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 11 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22±2°C
- Humidity: 55±10%
- Air changes: 16-20 per hr
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 20 March 1989 To: 08 April 1991
Route of administration:
oral: feed
Vehicle:
other: diet
Details on exposure:
DIET PREPARATION
- Rate of preparation of diet (frequency): every 4 weeks
- Mixing appropriate amounts with (Type of food): certified standard diet (Nafag No. 890 Tox)
- Storage temperature of food: room temperature

VEHICLE
- Justification for use and choice of vehicle (if other than water): not applicable
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Pretest analyses confirmed stability of the diet preparations at room temperature over 35 days. The analysis of the first batch showed that food mixes were homogeneous (-9% to +7% of mean value). The analytically determined concentrations generally ranged from 84.8 to 104.6% of the nominal concentrations. The mean concentrations were 94.2%, 95.6 %, 93.0% and 93.2% of the nominal values in groups 2 to 5, respectively. The analytical data thus indicated that the mixing procedure was adequate and that the variance between nominal and actual dosage was generally acceptable.
Duration of treatment / exposure:
Two years
Frequency of treatment:
Continuous in diet
Post exposure period:
Not applicable
Remarks:
Doses / Concentrations:
10, 100, 1000 or 2000 ppm
Basis:
nominal in diet
Remarks:
Doses / Concentrations:
0.37, 3.77, 36, 73 mg/kg/day (males); 0.43, 4.33, 41, 82 mg/kg/day (females)
Basis:
actual ingested
No. of animals per sex per dose:
80 per sex per group;
50 animals per sex/group for carcinogenicity evaluation;
10 animals for clinical chemistry, haematology and urinalysis;
10 additional animals for haematology only;
10 animals for interim sacrifice after 12 months

Control animals:
yes, plain diet
Details on study design:
- Dose selection rationale: based on the results of previous acute and repeat dose studies
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily for signs of toxicity and mortality

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: at least weekly

BODY WEIGHT: Yes
- Time schedule for examinations: pretest and weekly during the first three months. Thereafter, the weight was recorded monthly

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean diet consumption calculated as g food/kg body weight/week: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes
- Food consumption per cage were recorded pretest and weekly during the first three months. Thereafter, the weight was recorded monthly

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: monthly

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule/dose groups for examinations: eye examinations were conducted in control and high dose group animals pretest, after 26, 52, 78 weeks and at the end of the treatment period. Males and females from intermediate groups were examined prior to terminal sacrifice

HAEMATOLOGY: Yes
- Time schedule for collection of blood: after 13, 26, 52, 78 and 105 weeks
- Anaesthetic used for blood collection: Yes (ether)
- Animals fasted: Yes
- How many animals: 20/sex/group
- Parameters examined: erythrocyte count, haemoglobin, haematocrit, mean corpuscular volume, mean corpuscular haemoglobin, leucocyte count, differential leucocyte count, thrombocyte count, prothrombin time, red cell morphology

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after 13, 26, 52, 78 and 105 weeks
- Anaesthetic used for blood collection: Yes (ether)
- Animals fasted: Yes
- How many animals: 10/sex/group
- Parameters examined: glucose, urea, creatinine, total bilirubin, total protein, albumin, globulins, A/G ratio, cholesterol, sodium, potassium, calcium, chloride, inorganic phosphorus, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma-glutamyl transpeptidase

URINALYSIS: Yes
- Time schedule for collection of urine: pretest and after 13, 26, 52, 78 and 104 weeks
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes (no access to food or water)
- Parameters examined: volume, colour, relative density, pH, protein, glucose, ketones, bilirubin, blood, urobilinogen, urine sediment

NEUROBEHAVIOURAL EXAMINATION: No
Sacrifice and pathology:
GROSS PATHOLOGY: Yes (all animals)
- the following organs were weighed: brain, liver, kidneys, adrenals, gonads, spleen (after one year of treatment). At the end of the 2 year period, the thyroid and pituitary glands were also weighed
HISTOPATHOLOGY: Yes (all animals)
- the following tissues were examined microscopically: skin, mammary area, spleen, mesenteric lymph node, axillary lymph node, sternum with bone marrow, femur with joint, skeletal muscle, trachea, lung, heart, aorta, submandibular salivary gland, liver, pancreas, oesophagus, stomach, small intestine, large intestine, kidneys, urinary bladder, prostate, seminal vesicle, testis, epididymis, uterus, ovary, pituitary gland, adrenal gland, thyroid with parathyroid gland, thymus, peripheral nerve, brain, spinal cord, eye with optic nerve, extraorbital lacrimal gland, any tissue with gross lesions
Other examinations:
At autopsy, fat samples were taken to investigate the accumulation of cloquintocet-mexyl after 12 and 24 months.
Statistics:
Univariate standard methods were applied to the data. Each group was compared to controls by Lepage’s two sample test and tested for trends by Jonckheere’s test for ordered alternatives.
Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Water consumption and compound intake (if drinking water study):
no effects observed
Ophthalmological findings:
no effects observed
Haematological findings:
no effects observed
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
no effects observed
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
no effects observed
Details on results:
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
Food consumption was markedly depressed in the high dose group males during the first week of the treatment. Thereafter consumption was similar to that of the control animals throughout the treatment period. The overall food intake of treated groups was within 1.6% of that of the relative controls.

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathology did not reveal any inflammatory or degenerative changes which could be related to the test article. Lymphoid hyperplasia of the thymus was diagnosed in some males. The statistical trend analysis indicated a significant, treatment-related effect in the top dose group. There was no effect on thymic neoplastic lesions.
Among the females, increased incidences of thyroid gland follicle hyperplasia were found. The changes were graded as slight in all cases with no dose-related trend in severity. Statistical analysis indicated a significant effect in the animals treated at 1000 ppm and above. Hyperplasia of the thyroid follicle epithelium is known to occur spontaneously in the rat strain used and the incidence in the 100 ppm dose group was comparable to the incidence usually found in control animals of this rat strain. In the absence of a dose relationship, the observation made in the 10 ppm group was considered to be an outlier and thus incidental. Furthermore there was no correlation between thyroid hyperplasia and proliferative lesions of the pituitary gland. Incidences of thyroid tumours were within the historical control range, indicating that there was no progression of the hyperplasia to neoplastic growth.

HISTOPATHOLOGY: NEOPLASTIC (if applicable)
The incidence of all neoplasms were within the historical control range of the rat strain used and not considered to have been influenced by the treatment.
Cloquintocet-mexyl was devoid of a carcinogenic activity in the rat. The total number of tumour bearing animals and of animals with multiple tumours were similar in all groups
Relevance of carcinogenic effects / potential:
The treatment had no influence on the spontaneous tumour profile of the rat strain used and thus it is concluded that cloquintocet-mexyl is not carcinogenic in the rat.
Dose descriptor:
NOAEL
Effect level:
2 000 ppm (nominal)
Sex:
male/female
Basis for effect level:
other: No treatment-related effects on the spontaneous tumour profile at the highest dose tested (2000 ppm; 73/82 mg/kg bw/day).
Remarks on result:
other: Effect type: carcinogenicity (migrated information)
Dose descriptor:
NOAEL
Effect level:
100 ppm (nominal)
Sex:
male/female
Basis for effect level:
other: Hyperplastic changes in the thymus of males at 2000 ppm and of the thyroid gland in females at 1000 and 2000 ppm.
Remarks on result:
other: Effect type: toxicity (migrated information)

Table 2: Test compound consumption: The average test article intake based on nominal and actual dietary concentrations

Dose of test material

Test article intake (based on nominal concentrations)

Test article intake (based on actual concentrations)

10 ppm

m: 0.387 mg/kg
f: 0.451 mg/kg

m: 0.365 mg/kg
f: 0.425 mg/kg

100 ppm

m: 3.947 mg/kg
f: 4.530 mg/kg

m: 3.773 mg/kg
f: 4.331 mg/kg

1000 ppm

m: 39.10 mg/kg
f: 44.35 mg/kg

m: 36.36 mg/kg
f: 41.25 mg/kg

2000 ppm

m: 78.56 mg/kg
f: 87.49 mg/kg

m: 73.40 mg/kg
f: 81.54 mg/kg

 

Table 3: Cloquintocet-mexyl – 24-month rat study - Survival 

% survival after 104 weeks

0

10

100

1000

2000

Males

Females

52%

56%

46%

58%

42%

62%

26%

42%

46%

58%

 

Table 4: Histopathological findings in the chronic rat study with cloquintocet-mexyl

0

10

100

1000

2000

Historic control values

Males

Thymus

- Lymphoid hyperplasia

- severity

 

0

 

0

 

1

1

 

2

1

 

5

2

- Lymphoma

0

2

0

1

0

Thyroid

- hyperplasia follicular epithelium

 

2

 

6

 

7

 

5

 

3

- adenoma

4

1

1

4

3

- carcinoma

1

0

2

0

1

Females

Thymus

- Lymphoid hyperplasia

 

2

 

2

 

0

 

0

 

0

Thyroid

- hyperplasia follicular epithelium

- severity

 

0

0

 

8

1.4

 

5

1.6

 

10

1.5

 

11

1.4

 

0-4/76

- adenoma

0

1

2

0

2

0-3/77

- carcinoma

0

0

0

1

2

2/77

Table 5: Occurrence of primary tumours in the chronic rat study with cloquintocet-mexyl

males

females

ppm

0

10

100

1000

2000

0

10

100

1000

2000

Number of tumour-bearing animals

55

48

51

55

56

60

63

63

59

63

Number of animals with one tumour

28

25

32

28

31

31

36

37

34

35

Number of animals with two tumours

17

18

13

19

19

22

21

19

19

22

Number of animals with three tumours

6

3

4

7

4

6

4

6

5

5

Number of animals with four tumours

0

2

1

1

0

1

2

1

1

1

Number of animals with five tumours

3

0

1

0

2

0

0

0

0

0

Conclusions:
There were no treatment-related effects on the spontaneous tumour profile and it is concluded that 2000 ppm cloquintocet-mexyl is a NOEL for carcinogenicity in the rat. There were treatment-related hyperplastic changes in the thymus of males at 2000 ppm and of the thyroid gland in females at 1000 and 2000 ppm. The toxicity NOAEL was 100 ppm, equivalent to a mean daily dose of 3.77 mg/kg bw/day in males and 4.33 mg/kg bw/day in females.
Executive summary:

Groups of 80 male and 80 female Tif:RAIf (SPF) rats were fed diet containing 0 (control), 10, 100, 1000 or 2000 ppm cloquintocet-mexyl. Mortality, clinical appearance and behaviour, bodyweights, bodyweight changes, food consumption, ophthalmology, haematology, blood and urine biochemistry, organ weights, gross pathology and histopathology were assessed. Ten animals per group per sex were killed after 52 weeks of treatment for interim examination.

Cloquintocet-mexyl was well tolerated at dietary concentrations up to 2000 ppm (73.4/81.5 mg/kg bwt/day in males and females respectively). The effects of toxicological significance were hyperplasic changes in the thymus of males treated at 2000 ppm and of the thyroid gland in females treated at 1000 and 2000 ppm. The treatment had no influence on the spontaneous tumour profile of the rat strain used and thus it is concluded that cloquintocet-mexyl is not carcinogenic in the rat.

Based on the histopathological findings of the thyroid follicular epithelial hyperplasia at 1000 ppm in females the toxicity NOAEL was 100 ppm, equivalent to a mean daily dose of 3.77/4.33 mg/kg bw/day in males and females respectively.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
73 mg/kg bw/day
Study duration:
chronic
Species:
rat

Carcinogenicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Carcinogenicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Dietary studies in rats (Fankhauser, 1992) and mice (Fankhauser, 1992) have been performed. No evidence of carcinogenicity was seen at the highest dose tested in either species. In rats, hyperplastic changes were seen in the thymus of males at 2000 ppm and of the thyroid gland in the females at 1000 and 2000 ppm. Dietary administration to mice over 18 months resulted in reduced body weights in both sexes, lower food consumption in females, increased water consumption in both sexes and chronic inflammatory changes in the urinary bladder in males at 5000 ppm. No statistically significant treatment-related increase in any tumour type was seen in either study.


Justification for selection of carcinogenicity via oral route endpoint:
The combined chronic toxicity/carcinogenicity study in the rat has been selected. The carcinogenicity study in the mouse was also negative at the highest dose tested.

Justification for classification or non-classification

Cloquintocet-mexyl is considered not to be carcinogenic and no classification is warranted:

- under Directive 67/548/EEC, as amended for the 28th time in Directive 2001/59/EC, Annex VI, 4.2.1.

- under Regulation (EC) 1272/2008, Annex I, Part 3, 3.6.2.