N-(2-ethylhexyl)-8,9,10-trinorborn-5-ene-2,3-dicarboximide

Carcinogenicity

Description of key information

Carcinogenicity studies were performed in the mouse and rat according to EPA OPP 83-2 guideline.

Mouse Carcinogenicity study

An 18 -month carcinogenicity study was performed in CD1 mice by the dietary ad-mix route. Groups of 50 male and 50 female CD1 mice were offered 50, 400 or 800 mg/kg bw/day MGK 264 mixed in the diet. Two groups of 50 male and 50 female mice were fed the basal diet and acted as control groups for the study.

There was no difference in survival between treated and control groups. Differences in body weight and food consumption seen to be statistically significantly when comparing control groups to mice treated at 400 and 800 mg/kg bw/day were not considered to be of toxicological significance. Compound consumption in both male and female mice approximated closely to the target doses at around 49, 396 and 790 mg/kg/day.

At terminal kill, when compared to both controls there was a statistically significant increase in liver weight in male mice receiving 800 mg/kg/day and an increased liver to body weight ratio in males and females and liver to brain weight ratio in males of the 400 and 800 mg/kg/day groups.

Test substance related macroscopic and microscopic changes -were found in the liver and/or gallbladder of both sexes in the 400 and 800 mg/kg/day groups. Some of these changes suggested that the liver and bile were involved in the metabolism and excretion of the test substance. Hepatocellular hypertrophy in some animals reflected the additional work load as a consequence of ingestion of large quantities of test substance. MGK 264 can be regarded as mildly toxic to the liver at these high dose levels although there was no increase in liver necrosis. The maximum tolerated dose related to the liver was exceeded.  

The test substance at 800 mg/kg/day slightly increased the incidence of hepatocellular adenomas only in male mice. Such changes are usually found at various incidences in male mice of this substrain in studies of 18 months or longer in duration. The controls from six studies, undertaken between 1986 and 1988, involving 10 control groups for 18 months, the range of the incidence of adenomas was 2-18.3%. Where a differential diagnosis of adenoma and hyperplasia was made the incidence of adenoma was 2-12% and hyperplastic nodules 6-15%. The test substance did not directly induce such changes but arose as a consequence of work hypertrophy and mild toxicity increasing the incidence of hepatocellular proliferative lesions above historical control levels. No such changes were found in the female groups or in the 50 and 400 mg/kg/day male groups. From the peer review it was concluded that there is no compound related effect on the incidence of carcinoma considered either by pairwise comparison or trend analysis. The benign nodular lesions occurring in a single sex at high dosages of the compound are not associated with carcinoma and do not demonstrate a carcinogenic effect of MGK 264 in the CD1 mouse. Therefore the NOEL for carcinogenicity in this study was 800 mg/kg bw/day.  The no toxic effect dose level in this study was 50 mg MGK 264/kg/day to both male and female mice.

 

Rat Carcinogenicity Study

A 2 -year carcinogenicity study was performed in CD(SD) rats by the dietary ad-mix route. Groups of 60 male and 60 female CD1 mice were offered 50, 125 or 450 mg/kg bw/day MGK 264 mixed in the diet. Two groups of 60 male and 60 female rats were fed the basal diet and acted as control groups for the study.

There were no signs of overt toxicity related to the administration of the test article in the diet at levels of 50, 150 and 450 mg/kg/day. Criteria evaluated and considered to be comparable between treated and control groups included survival, clinical pathology determinations and ophthalmological examinations. Body weights were decreased in the 450 mg/kg/day group, particularly in the females. Food consumption was lower at this dosage level in females, but was unaffected in the males.

 Macroscopic pathology findings which were probably test article related included an increased incidence of tan or white liver foci in males and females from the 450 mg/kg/day group and an increased incidence of cysts in the liver of females from 150 and 450 mg/kg/day groups. Liver and kidney weights were increased in the 450 mg/kg/day group. 

Test article-related microscopic findings were observed in the liver of males and females from the 150 and 450 mg/kg/day groups and in the kidneys of females from the 150 and 450 groups. Test article-related liver changes included hepatocellular hypertrophy in males and females from the 150 and 450 mg/kg/day groups, bile stasis in males and females from the 450 mg/kg/day group and in females from the 150 mg/kg/day group, bile duct cysts in females from the 150 and 450 mg/kg/day groups, increased incidence of eosinophilic altered foci in females from the 150 and 450 mg/kg/day groups and males from the 450 mg/kg/day group and increased incidence of clear cell altered foci in males from the 450 mg/kg/day group. The hepatocellular hypertrophy correlated with the increased liver weights.An increased incidence of brown pigment was seen in the convoluted tubule epithelium of the kidney of the females at the 150 and 450 mg/kg/day groups. 

A slight increase in the incidence of adenomas of the follicular epithelium of the thyroid was observed in males from the treated groups. The values did not attain statistical significance nor was a significant positive trend seen. On the basis of the results of this study, the no-effect level was found to be 50 mg/kg/day. There was no evidence of an oncogenic effect related to administration of the test article in this study at any dosage level. Therefore, the no-effect level for oncogenicity was 450 mg/kg/day.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Main study: 6 Oct 1986 to 13 June 1991 (Histopathology peer review subsequently reported on 02 August 1991)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPP 83-2 (Carcinogenicity)

Deviations:

not specified

GLP compliance:

yes

Specific details on test material used for the study:

MGK~ 264
LOT 3843
N-octyl bicycloheptene dicarboximide 98%

Species:

mouse

Strain:

CD-1

Remarks:

Charles River CD-1® mice; Charles River

Details on species / strain selection:

The mouse has been used extensively to evaluate the toxicity of new pesticides. Considerable control data for this species have been accumulated.

Sex:

male/female

Details on test animals or test system and environmental conditions:

Three hundred and forty-five (345) male and 352 female Charles River CD-1® mice (28 days of age) were received from Charles River Breeding Laboratories, Inc., Portage, Michigan on November 13, 1986. The mice were observed during a 20 day acclimation period for any clinical signs of disease and all animals were given a detailed physical and ophthalmological examination. For the first 5 days of the conditioning period, animals were housed 4 per cage to allow for acclimation to the automatic watering system. Five animals/sex were selected for gross necropsy observations and microbiological screening prior to the start of the study. Two hundred fifty (250) males (weighing from 21 to 31 g as measured 1 day prior to study initiation) and 250 females (weighing from 18 to 27 g as measured 1 day prior to study initiation) were randomly selected and assigned.

The mice were individually housed in stainless steel wire mesh cages in a temperature-, humidity- and light- (12 hours light/12 hours dark) controlled room supplied with 6-12 air changes/hour. Cages were arranged on the racks in dosage level order and the racks rotated every 2 weeks according to a predetermined schedule. Temperatures of 73 ± 4°F, and humidities of 50 ± 20 percent were required by protocol. Temperatures and humidity were continuously recorded throughout the study. Occasionally a deviant value was noted and corrective action taken. Diet (Certified Rodent Chow #5002, Ralston Purina Company, St. Louis, Missouri) and water were available ad libitum.

Route of administration:

oral: feed

Vehicle:

other: No vehicle was used in the dietary ad-mix study. Control animals received the basal diet.

Details on exposure:

Beginning on December 4, 1986, the test article was placed in the diet such that concentrations of 50, 400, and 800 mg/kg/day could be offered. Concentrations were adjusted based on the most recent body weight and food consumption values. Ground diet as received from the supplier was dispensed for the control groups. All animals received freshly prepared diet weekly.

Due to a computer malfunction new dosage calculations could not be calculated for study weeks 41 and 73. Therefore, the previous weeks calculations were used. The remaining 3 weeks of each 4 week period were calculated as required. In addition, doses were not calculated for week 79 due to the scheduled necropsy, so week 78 calculations were used. In the opinion of the Study Director these minor protocol deviations did not affect the quality or integrity of the study.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Homogeneity and stability analysis was conducted pre-test. There was periodic analysis during weeks 1 to 4 and then the diet was analysed weekly thereafter. These samples were analysed in duplicate for test article concentration by GC analysis.

Duration of treatment / exposure:

MGK 264 was offered in the diet such that doses of 50, 400 and 800 mg/kg/day were consumed for 18 months.

Frequency of treatment:

Two control groups received untreated basal diet. Concentrations in the diet were adjusted weekly for the first 16 weeks and then every 4 weeks except at weeks 41 and 73 when the same concentration of test article in the diet was fed for one additional week. Fifty male and fifty female mice were initiated on the study in each of the five groups.

Post exposure period:

N/A

Dose / conc.:

50 mg/kg bw/day (nominal)

Dose / conc.:

400 mg/kg bw/day (nominal)

Dose / conc.:

800 mg/kg bw/day (nominal)

Dose / conc.:

0 mg/kg bw/day

Remarks:

Control group A

Dose / conc.:

0 mg/kg bw/day

Remarks:

Control group B

No. of animals per sex per dose:

50

Control animals:

yes, plain diet

Details on study design:

Dose selection rationale: Dose levels were sleceted based on the findings of a 3 month dietary dose-range finding study in mice in which increased liver weight was evident at 500 mg/kg bw/day and histopathological changes at 1000 mg/kg bw/day.
Asignment to group: Computerized random selection in a block design based on body weights.
Animals with large absolute differences from the quarantine population body weight mean eliminated prior to randomization and homogeneity of group body weight variances used as the criteria for acceptance.

Positive control:

N/A

Observations and examinations performed and frequency:

Observations:
Mortality, moribundity and overt toxicity at least three times daily Monday through Friday and twice daily on weekends and holidays. Detailed observations at least once each week.

Measurements:
Body weights determined pretest and weekly for the first 16 weeks and once every 4 weeks thereafter and at week 78; food consumption determined pretest and weekly for the first 16 weeks and once every 4 weeks thereafter and at week 78. Compound consumption was determined weekly for the fir.st 16 weeks and once every 4 weeks thereafter and at week 78. Food efficiency was calculated for the pretest period and first 16 weeks only.

OPHTHALMOSCOPIC EXAMINATIONS
Examinations conducted pretest, and at termination of study.

Sacrifice and pathology:

CLINICAL PATHOLOGY
Baseline Determinations: 5/ sex; viral screen.
Study Determinations: 10/sex/group at 12 and 18 months of study.
Hematology: Hematocrit; hemoglobin; erythrocyte count; mean corpuscular haemoglobin (MCH), volume (MCV), and haemoglobin concentration (MCHC); total and differential leukocyte count; platelet count.

ANATOMIC PATHOLOGY
Pre-initiation Necropsy: 5/sex.
Terminal Necropsy: All surviving animals at study termination.
Macroscopic Pathology:. On all animals. Tissues fixed in formalin (except eyes in a glutaraldehyde fixative and testis fixed in Bouin' s fluid). Bone marrow smears collected at the terminal sacrifice.

Organ Weights: On mice sacrificed at termination of study. Absolute and relative (to body and brain weights) weights of adrenal ( 2), brain and brain stem, h·eart, kidney (2), liver/gallbladder, testis (2), ovary ( 2) , spleen.

Tissues Preserved: Adrenal (2), aorta (thoracic), bone marrow (femur), bone (femur), brain (fore, mid, hind), eye including optic nerve ( 2), esophagus, stomach (glandular and non glandular) , duodenum, jejunum, ileum, cecum, colon, rectum, ovary (2), testis with epididymis (2), heart, kidney (2), lung with mainstem bronchi (2), liver (2 lobes), lymph nodes (mediastinal, mesenteric and regional), mammary region (females only), pancreas, pituitary, prostate and seminal vesicle (2), salivary gland (mandibular with submandibular lymph node), sciatic nerve, skin, spleen, thyroid/ parathyroid complex, trachea, urinary bladder, gallbladder, uterus, vagina, tissue masses, all gross lesions, skeletal muse le (thigh), spinal cord (cervical, thoracic and lumbar), thymic region, remaining carcass and viscera.

Microscopic Pathology: On all preserved tissue from all animals in control groups. A, B and the 800 mg/kg group, and all animals in the 50 mg/kg and 400 mg/kg groups dying on study or sacrificed during study. Liver, lung (2), kidney (2), gallbladder, gross lesions and masses with adjacent drainage lymph nodes from all animals in the 50 mg/kg and 400 mg/kg groups sacrificed at termination of the study. Tissues sectioned to the block stage and stained with hematoxylin and eosin.

Statistics:

STATISTICS
Body weights, food consumption values, clinical pathology parameters and organ weight values analyzed using analysis of variance and Bartlett's test. Treatment groups compared to the control groups, by sex, using the appropriate t-statistic (equal or unequal variance). Survival and time to tumor data analyzed using life table methods.

Clinical signs:

no effects observed

Description (incidence and severity):

See table 2 of the attached report for details of clinical observations. No changes in behavior or physical appearance were observed that would differentiate the groups.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Survival data are presented in Table 1 of the attached report. A record of animal fate and disposition is presented in Appendix I of the attached report. Survival between treated and control groups was comparable.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Considered to be of no toxicological significance.
Body weights are illustrated in Figure 1 and summarized in Table 3 of the attached report. Individual body weights are presented in Appendix K of the attached report. Group mean body weights at study week 78 were similar at all male and female dosage levels when compared to the controls. Statistically significant differences in mean values were noted at the 400 and 800 mg/kg/day dosage levels frequently in males and occasionally in the females. These body weight differences were less than ten percent and were not toxicologically significant.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Considered to be of no toxicological significance.
Food consumption data are illustrated in Figure 2 and summarized in Tables 4-5 of the attached report.
Mean food consumption (g/animal/day) for the 400 and 800 mg/kg/day groups were frequently statistically significant for males and females through 78 weeks of study. These differences were not toxicologically significant.

Food efficiency:

no effects observed

Description (incidence and severity):

Food efficiency values are illustrated in Figure 3 and presented in Table 6 of the attached report. Mean food consumption (g/kg/day) in males and females was occasionally statistically significant at the 50, 400 and 800 mg/kg/day dosage level when compared to the controls. These differences were not toxicologically significant.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

Individual ophthalmoscopic examination findings are presented Appendix M of the attached report.
No test article related ophthalmoscopic abnormalities were detected; the observations noted were representative of pathology that would be expected for this group of mice considering age, sex and strain.

Haematological findings:

no effects observed

Description (incidence and severity):

Hematology
Mean hematological values are summarized in Table 8. Individual hematological values are presented in Appendix N of the attached report.
There were no test substance related changes present in the hematological data for either sex at study month 12 and 18. Occasionally a value for a test substance treated group was found to be statistically different from that of one of the control groups. However, the absolute differences were small and considered to result from normal biological variation. No toxicological significance was attributed at 12 months to variations in values for mean corpuscular hemoglobin, platelet count, segmented neutrophil and leukocyte counts. The only variation detected at 18 months was for lymphocyte count. Mean count for Control Group B was statistically significantly greater than those for Control Group A and the 400 mg/kg/day female groups.

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Statistically significnt differences were observed in multiple organs at botht he 400 and 800 mg/kg/day - see "any other information on results" for tables and further information.

The liver was the site of test article related morphologic changes and some of the organ weight variations in the liver (increased liver weight in 800 mg/kg/day males, increased liver:brain weight ratio in 400 and 800 mg/kg/day males) may represent a test article effect. Other organ weight variations probably reflect decreased body weights in the 400 and 800 mg/kg/day groups or normal biological variations.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Macroscopic
Macroscopic pathology data are summarized in Table 9. Individual macroscopic findings are presented in Appendix P. No macroscopic lesions were observed in any of the 10 mice which were necropsied at the pretest sacrifice. Test article related macroscopic findings in treated mice were limited to an increased incidence of liver nodules and/or masses in the 400 and 800 mg/kg/day males. Other macroscopic findings were typical of the usual background age-related lesions in mice of this strain.

Some of the more common spontaneous lesions included cloudy corneas "'*1ich were seen primarily in mice sacrificed at termination; lung nodules, granular and/or pale kidneys in males and females and ovarian cysts and uterine cysts in females tAlich died or were sacrificed in extremis or "'*1ich were terminally sacrificed.

Microscopic
Microscopic pathology data are summarized in Tables 11-13. Individual microscopic findings are presented in Appendix P and the tissue inventory is presented in Appendix Q. Sponsor consultant Dr. Butler's report is presented in Appendix S. Test article related microscopic changes were observed in the liver and gallbladder of males and females from the 800 mg/kg/day groups, in the 1 iver and gal lb ladder of males from the 400 mg/kg/day group and in the gallbladder of females from the 400 mg/kg/day group. No test article related changes were observed in mice from the 50 mg/kg/day group. At the 800 mg/kg/day level, 19 of 49 males and 9 of 49 females in which the gallbladder was available for examination had dark brown single or multiple biliary calculi contained within the gallbladder. The incidence of calculi in the gallbladder at 400 mg/kg/day was 11 of 48 in males and 3 of 49 in females. Two males from control group B also had calculi within the gallbladder. Intrahepatic bile stasis occurred in the 1 iver of 5 males from the 400 mg/kg/day group and 45 males from the 800 mg/kg/day group and biliary calculi in large intrahepatic bile duct were observed in 9 males and 2 females from the 800 mg/kg/day group. Other test article related liver changes included an increased incidence of hepatocellular hypertrophy in males and females from the 800 mg/kg/day level. The incidence of this condition in males was 2, 3, 1, 2 and 30 from the control A, control B, 50, 400 and 800 mg/kg/day groups, respectively.
In females, hepatocellular hypertrophy was only observed in s1x 800 mg/kg/day mice. Several other conditions which were considered test article related occurred only in 800 mg/kg/day males. These conditions included portal bile duct proliferation which occurred in 30 800 mg/kg/day males, portal mononuclear cell infiltration which occurred in thirteen males and spongiosis hepatis (a microcytic degenerative lesion) which was found in four males. There was also a test article related increased incidence of hepatocellular adenomas at the 800 mg/kg/day level in male mice. The incidence of this tumor was 3, 1, 1, 6, and 12 in the control A, control B, 50, 400 and 800 mg/kg/day levels, respectively. The increased incidence of hepatocellular adenomas at 800 mg/kg/day correlated with the macroscopic observation of an increase in liver nodules/masses at these levels in males.

The increased incidence of hepatocellular adenomas in males from the 800 mg/kg/day group in association with other evidence of liver toxicity at both 400 and 800 mg/kg/day, suggests that the test article probably caused increased turnover of hepatocytes. In the 50 mg/kg/day dosage group where there was no evidence of liver toxicity, there was also a decrease ln hepatocellular adenomas. Other microscopic findings were typical of normal background lesions commonly found in an aging population of mice of this strain. Some of the more commonly occurring spontaneous lesions observed included subcapsular A cell proliferation and brown degeneration ln the adrenal cortex, corneal mineralization in the eye, chronic nephritis and lymphocytic infiltration in the kidneys, lung adenomas, chronic inflammation and cystic dilatation of glands in the glandular mucosa of the stomach, seminiferous tubule atrophy and aspermatogenesis in the testes and ovarian cysts and cystic hyperplasia of the uterus. Amyloidosis was frequently found in multiple sites, primarily in the adrenal cortex, small intestine, heart, kidney, liver, thyroid and ovaries. Amyloidosis of the kidney, primarily involving the glomeruli, was the single most common cause of death. There was no evidence of significant infectious disease which would have had an effect upon the validity of the study in any of the organs or tissues examined.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Macroscopic patholoqy findings which were probably test article related included an increased incidence of tan or white liver foci in males and females from the 450 mg/kg/day qroup and an increased incidence of cysts in the liver of females from 150 and 450 mg/kg/day groups. Liver and kidney weights were increased in the 450 mg/kg/day qroup.

Test article-related microscopic findings were observed in the liver of males and females from the 150 and 450 mg/kg/day groups and in the kidneys of females from the 150 and 450 groups. Test article-related liver changes included hepatocellular hypertrophy in males and females from the 150 and 450 mg/kg/day groups, bile stasis in males and females from the 450 mg/kg/day group and in females from the 150 mg/kg/day group, bile duct cysts in females from the 150 and 450 mg/kg/day groups, increased incidence of eosinophilic altered foci in females from the 150 and 450 mg/kg/day groups and males from the 450 mg/kg/day qroup and increased incidence of clear cell altered foci in males from the 450 mg/kg/day group. The hepatocellular hypertrophy correlated with the increased liver weiqhts. An increased incidence of brown pigment was seen in the convoluted tubule epithelium of the kidney of the females at the 150 and 450 mg/kg/day groups.

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

A slight increase in the incidence of adenomas of the follicular epithelium of the thyroid was observed in males from the treated groups. The values did not attain statistical significance nor was a significant positive trend seen.

Relevance of carcinogenic effects / potential:

A peer review of the histopathological examination was performed by an independent organisation. The peer review conclued the following:
Under the conditions of the study MGK 264 results in centrilobular hepatocyte hypertrophy most commonly observed in the male. There is also evidence of deranged biliary metabolism recognised by the presence of bile lakes and biliary proliferation. The mechanism of this effect is not known. The peer review pathologist would consider that the increase of benign nodules (hyperplasia and adenoma) only in one sex (male) at the highest dose (800 mg/kg/day) is secondary to the hepatoxicity of MGK 264 at the dose employed in the study.
In this study the incidence of hyperplasia and adenoma combined is 18% and 10% for control groups A and B respectively. These are common lesions. When considered separately both lesions are common and fall within the reported historical control range.
Only when adenomas and carcinomas are combined is there a statistical difference (P=0.041) at 400 mg/kg/day. In the peer review pathologist’s opinion, stated above, there is no biological justification for combining the benign and malignant lesions in this instance. Further, even when combined for statistical purposes, the level of significance (P=0.041) does not achieve the level of significance required for a common tumour of P<0.01 (Haseman, 1983, Fundamental and Applied Toxicology, 334-339).
There is no compound related effect on the incidence of carcinoma considered either by pairwise comparison or trend analysis. The benign nodular lesions occurring in a single sex at high dosages of the compound are not associated with carcinoma and do not demonstrate a carcinogenic effect of MGK 264 in the CD1 mouse.

Key result

Dose descriptor:

NOEL

Effect level:

50 mg/kg bw/day (nominal)

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Key result

Dose descriptor:

NOEL

Effect level:

800 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

histopathology: neoplastic

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

400 mg/kg bw/day (nominal)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

The liver was the site of test article related morphologic changes and some of the organ weight variations in the liver (increased liver weight in 800 mg/kg/day males, increased liver:brain weight ratio in 400 and 800 mg/kg/day males) may represent a test article effect. Other organ weight variations probably reflect decreased body weights in the 400 and 800 mg/kg/day groups or normal biological variations.

 

Male -Statistically Significant Organ Weight Differences Against Both Control Groups

Body Weight decreased	400, 800 mg/kg/day
Brain:Body increased	400 mg/kg/day
Adrenal ,left : Body increased	400 mg/kg/ day
Adrenal ,left :Brain increased	400 mg/kg/day
Adrenal, right :Body increased	400 mg/kg/day
Heart : Body increased	400 mg/kg/day
Liver/Gall bladder increased	800 mg/kg/day
Liver/Gallbladder:Body increased	400, 800 mg/kg/day
Liver/Gallbladder:Brain increased	400, 800 mg/kg/day

 

Female - Statistically Significant Organ Weight Differences Against Both Control Groups

Body Weight decreased	800 mg/kg/day
Brain:Body increased	800 mg/kg/day
Kidney, Left:Brain decreased	800 mg/kg/day
Liver/Gall bl adder :Body increased	400, 800 mg/kg/day

 

Conclusions:

Mice offered MGK 264 in the diet such that around 400 and 800 mg/kg/day were consumed had slightly lower body weight values than those of the control groups. Test substance related macroscopic and microscopic changes -were found in the liver and/or gallbladder of both sexes in the 400 and 800 mg/kg/day groups. Some of these changes suggested that the liver and bile were involved in the metabolism and excretion of the test substance. Hepatocellular hypertrophy in some animals reflected the additional work load as a consequence of ingestion of large quantities of test substance. MGK 264 can be regarded as mildly toxic to the liver at these high dose levels although there was no increase in liver necrosis. The maximum tolerated dose related to the liver was exceeded.
 
The test substance at 800 mg/kg/day slightly increased the incidence of hepatocellular adenomas only in male mice. Such changes are usually found at various incidences in male mice of this substrain in studies of 18 months or longer in duration. The controls from six studies, undertaken between 1986 and 1988, involving 10 control groups for 18 months, the range of the incidence of adenomas was 2-18.3%. Where a differential diagnosis of adenoma and hyperplasia was made the incidence of adenoma was 2-12% and hyperplastic nodules 6-15%. The test substance did not directly induce such changes but arose as a consequence of work hypertrophy and mild toxicity increasing the incidence of hepatocellular proliferative lesions above historical control levels. No such changes were found in the female groups or in the 50 and 400 mg/kg/day male groups.
 
The no toxic effect dose level in this study was 50 mg MGK 264 Insecticide Synergist/kg/day to both male and female mice.
 
From the peer review it was concluded that there is no compound related effect on the incidence of carcinoma considered either by pairwise comparison or trend analysis. The benign nodular lesions occurring in a single sex at high dosages of the compound are not associated with carcinoma and do not demonstrate a carcinogenic effect of MGK 264 in the CD1 mouse.

Executive summary:

An 18-month carcinogenicity study was performed in CD1 mice by the dietary ad-mix route. Groups of 50 male and 50 female CD1 mice were offered 50, 400 or 800 mg/kg bw/day MGK 264 mixed in the diet. Two groups of 50 male and 50 female mice were fed the basal diet and acted as control groups for the study.

There was no difference in survival between treated and control groups. Differences in body weight and food consumption seen to be statistically significantly when comparing control groups to mice treated at 400 and 800 mg/kg bw/day were not considered to be of toxicological significance. Compound consumption in both male and female mice approximated closely to the target doses at around 49, 396 and 790 mg/kg/day.

At terminal kill, when compared to both controls there was a statistically significant increase in liver weight in male mice receiving 800 mg/kg/day and an increased liver to body weight ratio in males and females and liver to brain weight ratio in males of the 400 and 800 mg/kg/day groups.

Test substance related macroscopic and microscopic changes -were found in the liver and/or gallbladder of both sexes in the 400 and 800 mg/kg/day groups. Some of these changes suggested that the liver and bile were involved in the metabolism and excretion of the test substance. Hepatocellular hypertrophy in some animals reflected the additional work load as a consequence of ingestion of large quantities of test substance. MGK 264 can be regarded as mildly toxic to the liver at these high dose levels although there was no increase in liver necrosis. The maximum tolerated dose related to the liver was exceeded.

The test substance at 800 mg/kg/day slightly increased the incidence of hepatocellular adenomas only in male mice. Such changes are usually found at various incidences in male mice of this substrain in studies of 18 months or longer in duration. The controls from six studies, undertaken between 1986 and 1988, involving 10 control groups for 18 months, the range of the incidence of adenomas was 2-18.3%. Where a differential diagnosis of adenoma and hyperplasia was made the incidence of adenoma was 2-12% and hyperplastic nodules 6-15%. The test substance did not directly induce such changes but arose as a consequence of work hypertrophy and mild toxicity increasing the incidence of hepatocellular proliferative lesions above historical control levels. No such changes were found in the female groups or in the 50 and 400 mg/kg/day male groups.

 

The no toxic effect dose level in this study was 50 mg MGK 264/kg/day to both male and female mice.

An independent peer review of the histopathology was performed and has been reported in the end point record. The review was in aggreement with the study pathologist and did not find that administration of MGK 264 at high dosages in the mouse was associated with a carcinogenic effect.

Reference 2

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

02 November 1989 to 08 October 1993

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPP 83-2 (Carcinogenicity)

GLP compliance:

yes

Specific details on test material used for the study:

MGK 264
Lot Number: 7437
Purity: 100%

Species:

rat

Strain:

Crj: CD(SD)

Remarks:

Charles River CD rats

Details on species / strain selection:

The rat is a standard laboratory animal used to evaluate the chronic toxicity and oncogenicity of test substances and it has been demonstrated that this strain has been sensitive to chemical carcinogens of various types. This laboratory has historical data on the tumor incidence and survival for rats of this strain and source.

Sex:

male/female

Details on test animals or test system and environmental conditions:

The rats were individually housed in wire-mesh cages in an environmentally controlled room with a 12 hour light/12 hour dark cycle. Beginning October 31, 1990 (study week 42, day 3), the rats were housed in extended front cages. The animals were moved to clean cages once every two weeks and the feeder jars were changed and sanitized weekly. The cages were arranged in racks in group order and the racks were rotated every two weeks. The racks were spaced approximately four feet apart and away from the wall. The temperature and humidity were continuously recorded and the recordings were monitored for conformance with protocol specifications (73 ± 5°F for the temperature and 50 ± 20% for the humidity). Appropriate corrective action was taken whenever the readings were outside acceptable limits. The graphs of temperature and humidity are maintained in the study record. Diet (Certified Rodent Chow #5002, Purina Mills, Inc., St. Louis, Missouri) and water were available ad libitum, except prior to clinical pathology testing and necropsy, when food only was removed.

Certification analysis of each lot of diet was performed by the manufacturer. The IRDC water supply was analyzed on a quarterly basis for the presence of heavy metals, pesticides and bacterial contaminants. The results of food and water analysis applicable to the study are retained in the Archives of IRDC.

Each rat was identified by cage, group and individually by ear tag. Ear tags were verified after initial tagging, before and after blood and urine sample collections, at each cage change and prior to necropsy.

Route of administration:

oral: feed

Vehicle:

other: No vehicle was used in the dietary ad-mix study. Control animals received the basal diet.

Details on exposure:

Beginning on January 15, 1990, the test article was offered in the diet at dosage levels of 50, 150 and 450 mg/kg/day. Two control groups received the basal diet on a comparable regimen. The control and treated diets were offered ad libitim seven days a week for at least 24 months. The concentrations for each sex group were adjusted weekly for the first 14 weeks and then every two weeks thereafter, based on the projected mean weekly food consumption measurements and body weight to maintain a constant mg/kg/day intake. Initially, a correction factor based on historical data was used in calculations; however, based on actual study data, use of the correction factor resulted in slightly elevated (16-22% at week 11) dosages. Beginning at week 12, the correction factor was not used.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

At the time test article:diet mixtures were prepared for each study week 100 g samples were taken from the top, middle and bottom of the prepared diet. These samples were mixed thoroughly to form a 300 g composite sample. Each composite sample was then subdivided into three 100 g samples. At study weeks 1-4 and every four weeks thereafter, one 100 g composite sample from each test diet was analyzed in duplicate for determination of test article concentration, and the other two 100 g samples were stored frozen.

At all other study weeks all three sets of 100 g samples were stored frozen. If the results of the analysis for any prepared diet ware outside of the specified limits of acceptability, the affected diet was re-prepared and re-analyzed. Any test diet outside of specification was not administered.

Analytical Methods are presented in Appendix B of the attached report.

Duration of treatment / exposure:

At least 24 months

Frequency of treatment:

The control and treated diets were offered ad libitim seven days a week for at least 24 months.

Post exposure period:

N/A

Dose / conc.:

50 mg/kg bw/day (nominal)

Dose / conc.:

150 mg/kg bw/day (nominal)

Dose / conc.:

450 mg/kg bw/day (nominal)

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

Control group A

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

Control group B

Control animals:

yes, plain diet

Details on study design:

60 per sex per dose

Positive control:

N/A

Observations and examinations performed and frequency:

Observations:
Mortality, moribundity and overt toxicity at least twice daily; detailed observations at least once each week.

Measurements:
Body weights determined pretest, weekly for the first 14 weeks of study and once every two weeks thereafter.
Food consumption determined pretest, weekly for the first 14 weeks of study and every two weeks thereafter; food efficiency calculated study weeks 1-14.

OPHTHALMOSCOPIC EXAMINATIONS
Once pretest and at study termination.

CLINICAL PATHOLOGY
Pretest Microbiological
Screen: 5 rats/sex.
Study Determinations: At 6, 12, 18 and 24 months of study.

Hematology:
Hematocrit; hemoglobin; erythrocyte count; mean corpuscular haemoglobin (MCH), volume (MCV), and haemoglobin concentration (MCHC); total and differential leukocyte counts; platelets; reticulocytes·

Biochemistry:
Aspartate aminotraneferase, alanine aminotransferase, alkaline phosphatase, glucose, urea nitrogen, total bilirubin, cholesterol, albumin, globulin (calculated), albumin/globulin ratio (calculated), total protein, creatinine, creatine phosphokinase, calcium, sodium, potassium, chloride, inorganic phosphate.

Urinalysis:
Volume, color and appearance, pH, specific gravity, protein, glucose, ketones, urobilinogen, nitrite, bilirubin, occult blood, microscopic elements.

Sacrifice and pathology:

ANATOMIC PATHOLOGY
All animals surviving until the scheduled sacrifice and all animals sacrificed in extremis were euthanased and received a complete necropsy examination.

Macroscopic Pathology: On all animals. Tissues fixed in formalin (except eye, in a glutaraldehyde fixative, and testis, in Bouin's fluid). Bone marrow smears collected at the terminal sacrifice.

Organ Weights: on all animals at the terminal sacrifice. Absolute and relative (to body and brain weights) weights of adrenal (2), brain and brain stem, heart, kidney (2), liver, ovary (2), testis (2), spleen.

Tissues Preserved: Adrenal (2), aorta, bone (femur), bone marrow (femur), brain (fore, mid and hind), eye including optic nerve (2), esophagus, stomach (glandular and nonglandular), duodenum, jejunum, ileum, cecum, colon, rectum, ovary (2), testis with epididymis (2), heart, kidney (2), liver (one section from each lobe), lung with mainstem bronchi, lymph nodes (mediastinal, mesenteric, regional), mammary region (female only), pancreas, pituitary, prostate and seminal vesicle (2), salivary gland (mandibular [2] with mandibular lymph node [2]), sciatic nerve, skeletal muscle (thigh), skin, spinal cord (cervical, thoracic and lumbar), spleen, thymic region, thyroid/parathyroid (2), trachea, urinary bladder, uterus, vagina, tissue masses, gross lesions.

Microscopic Pathology: Tissues listed above sectioned at 5 microns and stained with hematoxylin and eosin for animals in the control groups and 450 mg/kg/day group and for all animals dying or euthanized in extremis. Liver and thyroid/ parathyroid, lungs, kidneys, tissue masses (and adjacent drainage lymph nodes) and gross lesions from all animals at terminal sacrifice.

Statistics:

Body weights, food consumption and food efficiency values, clinical pathology parameters and organ weights analyzed using analysis of variance and Bartlett's test. Treatment groups compared to the control groups, by sex, using the appropriate t-statistic (equal or unequal variance). Nonparametric analysis, when appropriate, using rank transformation.

Tumor incidence data analyzed using life table test, Hoel-Walburg, Fisher's exact and Cochran-Armitage tests.

Clinical signs:

no effects observed

Description (incidence and severity):

There were no signs of overt toxicity and no test-article related differences in the incidences of clinical findings.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Survival in the treated groups was comparable to the control groups.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean body weights of the 450 mg/kg/day group rats were lower, with statistical significance occurring frequently, after week 18 for the males, and after week 10 for the females compared to both control groups throughout the study. Body weights at lower dosage levels were considered comparable to both control groups throughout the study. At weeks 100, 102 and 104 the 150 mg/kg/day group male body weight mean was lower than both male control values, however this pattern was not seen earlier in the study.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Mean food consumption values (g/animal/day) of the 450 mg/kg/day group females were significantly lower than values of both control groups throughout most of the study. Values for males at this dosage level and males and females at the 50 and 150 mg/kg/day dosage levels ware similar to control group values throughout the study, although occasional statistically significant differences were seen.

Food efficiency:

effects observed, non-treatment-related

Description (incidence and severity):

Statistically significant increases and decreases in food efficiency values occurred between males and females at all dosage levels compared to the control group throughout the first 14 weeks of study. These differences, however, were sporadic and not indicative of a treatment affect.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No test article related ophthalmoscopic abnormalities were detected; the observations noted were representative of pathology that would be expected for this group of rats considering age, sex and strain.

Haematological findings:

no effects observed

Description (incidence and severity):

There were no test article related changes present in the hematological data for either sex at any interval. No statistically significant differences were detected for any male group treated with the test substance. Occasionally a value for a test substance treated female group was found to be statistically different from that of a control group. However, the absolute differences were small and considered to result from normal biological variation. No toxicological significance was attributed to these differences.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

No test article related trends were discerned in mean values of clinical chemistry parameters. No statistically significant differences were detected for any male group treated with the test substance. Occasionally statistically significant differences were detected between the mean for a test article substance female group compared to that of a control group. However, with a few exceptions; all absolute differences were small and considered within the range of normal biological variations. The few exceptions were slight increases in the 450 mg/kg/day group in cholesterol, total protein, and globulin at the 12 month interval only.

Urinalysis findings:

no effects observed

Description (incidence and severity):

The urinalysis values for all groups were considered normal. No toxicological significance was attributed to variations in urine pH values.

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Statistically significant increases in absolute liver weight, liver/body weight and liver/brain weight ratios occurred in males and females from the 450 mg/kg/day group when compared to both control groups. Liver weight, liver/body and liver/brain weight ratios also were significantly increased in the 150 mg/kg/day group males when compared to control 1 group and the liver/body weight ratio of the 150 mg/kg/day group females was significantly increased when compared to Control 2 group. The liver weight of the 50 mg/kg/day group males was significantly increased when compared to control 1 group. The left kidney, left kidney/body and left kidney/brain weight ratios of the 450 mg/kg/day group males were increased when compared with both control groups. The same parameters for the right kidney in the 450 mg/kg/day group males were significantly increased only when compared to Control 2 group. In females, the left and right kidney/body weight ratios, heart/body weight ratio and brain/body weight ratio of the 450 mg/kg/day group were significantly increased when compared to both control groups. The body weight of the 450 mg/kg/day group females was significantly decreased when compared to both control groups.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Macroscopic findings which were probably test article related included an increased incidence of tan or white liver foci in males and females from the 450 mg/kg/day group and an increased incidence of cysts in the liver of females from the 150 and 450 mg/kg/day groups. Other macroscopic findings were typical of spontaneous lesions in an aging population of rats of this strain. Some of the more commonly observed spontaneous macroscopic lesions included enlarged pituitary glands; skin masses; decubital ulcers on the hind legs; galactoceles and thickened, enlarged mammary glands; enlarged adrenal glands; ovarian and uterine cysts; tan or yellow foci in the prostate and small, soft testes·

Histopathological findings: non-neoplastic:

not specified

Description (incidence and severity):

Test article related microscopic findings were observed in the liver of males and females from the 150 and 450 mg/kg/day groups and in the kidneys of females from the 150 and 450 mg/kg/day groups. Test article related liver changes included hepatocellular hypertrophy in males and females from the 150 and 450 mg/kg/day groups, bile stasis in males and females from the 450 mg/kg/day group and in females from the 150 mg/kg/day group, bile duct cysts in females from the 150 and 450 mg/kg/day groups, increased incidence of eosinophilic altered foci in females from the 150 and 450 mg/kg/day groups and males from the 450 mg/kg/day group and increased incidence of clear cell altered foci in males from the 450 mg/kg/day group. Hepatocellular hypertrophy occurred in 47/60 males and 46/60 females from the 450 mg/kg/day group and in 26/60 males 22/60 females from the 150 mg/kg/day group. The finding was most prominent in the centrilobular hepatocytes and was considered to result from enzyme induction involved in metabolism of the test article. It correlated with increased liver weight observed at terminal sacrifice in these groups. Bile stasis was characterized by reddish-brown calculi within intrahepatic bile ducts in portal areas· This lesion occurred in 20/60 males and 23/60 females from the 450 mg/kg/day group and in 1/60 females from the 150 mg/kg/day group.
Incidence of foci of clear hepatocyte cytoplasmic alteration was 11, 9, 6, 7 and 18 in males and 8, 5, 5, 5 and 9 in females from the control 1, control 2, 50, 150 and 450 mg/kg/day groups, respectively. Incidence of foci of eosinophilic hepatocyte cytoplasmic alteration was 3, 1, 6, 5 and 16 in males and 3, 1, 8, 7 and 9 in females from the control 1, control 2, 50, 150, 450 mg/kg/day groups, respectively. Incidence of cysts of intrahepatic bile ducts was 2, 0, 1, 1 and 4 in males and 1, 2, 0, 5 and 8 in females from the control 1, control 2, 50, 150 and 450 mg/kg/day groups, respectively. Incidence of brown pigment observed in the convoluted tubule epithelium of the kidney was 2, 6, 4, 11 and 33 in females from the control 1, control 2, 50, 150 and 450 mg/kg/day groups.

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

There was an increased incidence of adenomas of the follicular epithelium of the thyroid in males from the treated groups. The incidence of follicular adenomas was 2, 1, 4, 5 and 6 in males from Control 1, Control 2, 50 mg/kg/day, 150 mg/kg/day, and 450 mg/kg/day groups, respectively, per 60 animals in each dosage group. No increase in follicular adenomas occurred in females. Other microscopic findings were consistent with the spontaneous lesions which commonly occur in an aging population of rats of this strain. Some of the more commonly occurring non-neoplastic spontaneous lesions included congestion, degeneration, vacuolar change and hematocyst formation in the adrenal cortex; ultimobranchial cysts in the thyroid; nematodiasis of the colon and rectum; retinal atrophy in the eye; cardiomyopathy; chronic mineralization in the kidney; portal bile duct proliferation, cholangiofibrosis, portal mononuclear cell infiltrate, telanqiectasis and spongiosis hepatis in the liver; chronic interstitial pneumonia and alveolar macrophage accumulation in the lung; medullary plammacytosis in lymph nodes; increased splenic hematopoiesis and hemosiderosis; demyelination in the sciatic nerve and in spinal nerve roots included with sections of the spinal cord; arteritis, tubule atrophy and aspermatogenesis in the testis; cysts in the ovary and uterus; ulcerative pododermatitis of the hind legs; physiologic involution of the thymus; and galactoceles and lobular hyparplasia of the mammary gland. Adenomas of the pituitary were the most commonly occurring spontaneous neoplasm and were responsible for most of the deaths which occurred during the course of study. Other common spontaneous neoplasms included mammary fibroadenomas and adenocarcinomas, keratoacanthomas in the skin, Leydig cell tumors in the testis and uterine polyps.

Details on results:

There was no indication of significant infectious disease which would have affected the validity of the study in any of the tissues examined from any of the rats from any of the control or experimental groups.

Relevance of carcinogenic effects / potential:

A slight increase in the incidence of adenomas of the follicular epithelium of the thyroid was observed in males from the treated
groups. The values did not attain statistical significance nor was a significant positive trend seen.

On the basis of the results of this study, the no-effect level was found to be 50 mg/kg/day. There was no evidence of an oncogenic effect related to administration of the test article in this study at any dosage level. Therefore, the no-effect level for oncogenicity was 450 mg/kg/day.

Key result

Dose descriptor:

NOEL

Effect level:

50 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

gross pathology

histopathology: non-neoplastic

Key result

Dose descriptor:

NOEL

Effect level:

450 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: There was no evidence of an oncogenic effect related to administration of the test article in this study at any dosage level. Therefore, the no-effect level for oncogenicity was 450 mg/kg/day.

Key result

Critical effects observed:

not specified

Lowest effective dose / conc.:

150 mg/kg bw/day (nominal)

System:

hepatobiliary

Organ:

bile duct

kidney

liver

There were no signs of overt toxicity related to the administration of the test article in the diet at levels of 50, 150 and 450 mg/kg/day. Criteria evaluated and considered to be comparable between treated and control groups included survival, clinical pathology determinations and ophthalmological examinations. Body weights were decreased in the 450 mg/kg/day group, particularly in the females. Food consumption was lower at this dosage level in females, but was unaffected in the males.

 

Macroscopic pathology findings which were probably test article related included an increased incidence of tan or white liver foci in males and females from the 450 mg/kg/day group and an increased incidence of cysts in the liver of females from 150 and 450 mg/kg/day groups. Liver and kidney weights were increased in the 450 mg/kg/day group.

 

Test article-related microscopic findings were observed in the liver of males and females from the 150 and 450 mg/kg/day groups and in the kidneys of females from the 150 and 450 groups. Test article-related liver changes included hepatocellular hypertrophy in males and females from the 150 and 450 mg/kg/day groups, bile stasis in males and females from the 450 mg/kg/day group and in females from the 150 mg/kg/day group, bile duct cysts in females from the 150 and 450 mg/kg/day groups, increased incidence of eosinophilic altered foci in females from the 150 and 450 mg/kg/day groups and males from the 450 mg/kg/day group and increased incidence of clear cell altered foci in males from the 450 mg/kg/day group. The hepatocellular hypertrophy correlated with the increased liver weights. An increased incidence of brown pigment was seen in the convoluted tubule epithelium of the kidney of the females at the 150 and 450 mg/kg/day groups.

 

A slight increase in the incidence of adenomas of the follicular epithelium of the thyroid was observed in males from the treated groups. The values did not attain statistical significance nor was a significant positive trend seen. On the basis of the results of this study, the no-effect level was found to be 50 mg/kg/day. There was no evidence of an oncogenic effect related to administration of the test article in this study at any dosage level. Therefore, the no-effect level for oncogenicity was 450 mg/kg/day.

Conclusions:

There were no signs of overt toxicity related to the administration of the test article in the diet at levels of 50, 150 and 450 mg/kg/day. Criteria evaluated and considered to be comparable between treated and control groups included survival, clinical pathology determinations and ophthalmological examinations. Body weights were decreased in the 450 mg/kg/day group, particularly in the females· Food consumption was lower at this dosage level in females, but was unaffected in the males·

Macroscopic pathology findings which were probably test article related included an increased incidence of tan or white liver foci in males and females from the 450 mg/kg/day group and an increased incidence of cysts in the liver of females from 150 and 450 mg/kg/day groups. Liver and kidney weights were increased in the 450 mg/kg/day group.

Test article-related microscopic findings were observed in the liver of males and females from the 150 and 450 mg/kg/day groups and in the kidneys of females from the 150 and 450 groups. Test article-related liver changes included hepatocellular hypertrophy in males and females from the 150 and 450 mg/kg/day groups, bile stasis in males and females from the 450 mg/kg/day group and in females from the 150 mg/kg/day group, bile duct cysts in females from the 150 and 450 mg/kg/day groups, increased incidence of eosinophilic altered foci in females from the 150 and 450 mg/kg/day groups and males from the 450 mg/kg/day group and increased incidence of clear cell altered foci in males from the 450 mg/kg/day group. The hepatocellular hypertrophy correlated with the increased liver weights. An increased incidence of brown pigment was seen in the convoluted tubule epithelium of the kidney of the females at the 150 and 450 mg/kg/day groups.

A slight increase in the incidence of adenomas of the follicular epithelium of the thyroid was observed in males from the treated groups. The values did not attain statistical significance nor was a significant positive trend seen. On the basis of the results of this study, the no-effect level was found to be 50 mg/kg/day. There was no evidence of an oncogenic effect related to administration of the test article in this study at any dosage level. Therefore, the no-effect level for oncogenicity was 450 mg/kg/day.

Executive summary:

A 2 -year carcinogenicity study was performed in CD(SD) rats by the dietary ad-mix route. Groups of 60 male and 60 female rats were offered 50, 150 or 450 mg/kg bw/day MGK 264 mixed in the diet. Two groups of 60 male and 60 female rats were fed the basal diet and acted as control groups for the study.

There were no signs of overt toxicity related to the administration of the test article in the diet at levels of 50, 150 and 450 mg/kg/day. Criteria evaluated and considered to be comparable between treated and control groups included survival, clinical pathology determinations and ophthalmological examinations. Body weights were decreased in the 450 mg/kg/day group, particularly in the females· Food consumption was lower at this dosage level in females, but was unaffected in the males·

 

Macroscopic pathology findings which were probably test article related included an increased incidence of tan or white liver foci in males and females from the 450 mg/kg/day group and an increased incidence of cysts in the liver of females from 150 and 450 mg/kg/day groups. Liver and kidney weights were increased in the 450 mg/kg/day group.

 

Test article-related microscopic findings were observed in the liver of males and females from the 150 and 450 mg/kg/day groups and in the kidneys of females from the 150 and 450 groups. Test article-related liver changes included hepatocellular hypertrophy in males and females from the 150 and 450 mg/kg/day groups, bile stasis in males and females from the 450 mg/kg/day group and in females from the 150 mg/kg/day group, bile duct cysts in females from the 150 and 450 mg/kg/day groups, increased incidence of eosinophilic altered foci in females from the 150 and 450 mg/kg/day groups and males from the 450 mg/kg/day group and increased incidence of clear cell altered foci in males from the 450 mg/kg/day group. The hepatocellular hypertrophy correlated with the increased liver weights.Anincreased incidence of brown pigment was seen in the convoluted tubule epithelium of the kidney of the females at the 150 and 450 mg/kg/day groups.

 

A slight increase in the incidence of adenomas of the follicular epithelium of the thyroid was observed in males from the treated groups. The values did not attain statistical significance nor was a significant positive trend seen. On the basis of the results of this study, the no-effect level was found tobe50 mg/kg/day. There was no evidence of an oncogenic effect related to administration of the test article in this study at any dosage level. Therefore, the no-effect level for oncogenicity was 450 mg/kg/day.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Quality of whole database:

Both mouse and rat carcinogenicity studies were guideline compliant studies perofrmed according to the principles of GLP.