STUDY ABSTRACT: MECHANISTIC STUDY USING CARCINOGENIC ENDPOINTS IN p53+/- MICE GIVEN p-CRESIDINE BY ORAL GAVAGE FOR 26 WEEKS

The purpose of this study was to validate this model at Redfield Laboratories to demonstrate that p53+/-C57BL/6TacfBR-[KO]p53 N5 heterozygous transgenic mice will respond to p-cresidine, a known carcinogen, by developing bladder tumors when given by oral gavage for 26 weeks.
Sixty young adult p53+/- transgenic mice, thirty males and thirty females, were used in this evaluation and treated according to the following scheme:

Group Number Dosage Level
(mg.kg)
Dosage Volume
(mL/kg)
Number of Animals
Males / Females
1 Vehicle, corn oil 10 15 15
2 400 p-cresidine 10 15 15

All mice were given a physical examination prior to study start. Body weights were recorded prestudy, weekly during the treatment period and prior to necropsy. Feed consumption was recorded weekly. The mice were examined daily for pharmacological, toxicological or behavioral effects. Examination and palpation for tumors was performed weekly beginning week 14. Each mouse received its respective dose via oral gavage once daily for 26 consecutive weeks. In order to prevent the animal from struggling every time it was dosed due to the "adverse" taste of the test material, after the p-cresidine was drawn up into the dosing syringe, the dosing needle was wiped off and then the animal was dosed. All animals were subjected to a gross postmortem examination, protocol specified organs were weighed and tissues were fixed in 10% neutral buffered formalin or Bouin's, embedded in paraffin, sectioned and stained for microscopic examination by a Board Certified Veterinary Pathologist (ACVP).

The daily treatment with p-cresidine did not result in any consistent or distinct adverse clinical signs or palpable tumors. The group mean body weight of the males was decreased compared to the controls from Study Day 92 until termination of the study. This consistent treatment-related effect was not noted in the females. Analysis of the data indicated no consistent adverse effect on feed consumption of either sex. The weight (absolute and relative to body and brain) of the kidneys in both sexes was reduced whereas the weight of the liver was increased compared to the controls. These treatment-related effects were associated with the histological finding of hepatocellular hypertrophy in the liver and glomerulonephropathy in the kidneys.

Gross tissue changes associated with the presence of tumors were noted in the urinary bladder and kidneys at necropsy. Histologically, the macrophages of the spleen contained golden yellow pigmentation, which was thought to represent hemosiderin possibly from the breakdown of the erythrocytes.

Histological evaluation indicated treatment with p-cresidine resulted in bladder tumors in 67% of the male and in 47% of the female p53+/- transgenic mice compared to the controls. These tumors which generally occurred along the ventral surface of the bladder were primarily transitional cell carcinomas and transitional cell carcinomas with squamous metaplasia.

In summary, 400 mg/kg p-cresidine given to p53+/- transgenic mice for 26 weeks resulted in the production of bladder tumors in 67% of the males and 47% of the females. This chemical also caused the expected effect of increased liver weight (hepatocellular hypertrophy) and decreased kidney weights (glomerulonephropathy). The expected effect from using p-cresidine as a positive control has been confirmed in this strain of transgenic mouse in this laboratory.