NTP Toxicology and Carcinogenesis Studies of o-Nitroanisole (CAS No. 91-23-6) in F344 Rats and B6C3F1 Mice (Feed Studies).
o-Nitroanisole is used as an intermediate for the preparation of o-anisidine and in the manufacture of azo dyes. Toxicology and carcinogenesis studies were conducted by administering o-nitroanisole (>99% pure) in the diet to groups of male and female F344 rats and B6C3F1 mice for 14 days, 13 weeks, and 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Chinese hamster ovary cells, and mouse lymphoma cells. 14-DAY STUDIES: Groups of five male and five female F344 rats received diets containing 0, 583, 1,166, 2,332, 4,665, or 9,330 ppm o-nitroanisole. Mean body weight gains and final mean body weights of males in the 4,665 and 9,330 ppm groups were lower than those of the controls. Absolute liver weights were significantly increased in males receiving 1,166 ppm or more and in females receiving 583 ppm or more. Groups of five male and five female B6C3F1 mice received diets containing 0, 250, 500, 1,000, 2,000, or 4,000 ppm o-nitroanisole. Mean body weight gains and final mean body weights of males that received 250 ppm and females that received 4,000 ppm were significantly lower than those of the controls. No other chemical-associated effects were observed. 13-WEEK STUDIES: Groups of 10 male and 10 female F344 rats received diets containing 0, 200, 600, 2,000, 6,000, or 18,000 ppm o-nitroanisole. Final mean body weights and feed consumption by male and female rats receiving 6,000 and 18,000 ppm were lower than those of the controls. Hemoglobin and hematocrit values were significantly lower and methemoglobin levels significantly higher in males in the 6,000 and 18,000 ppm groups than in controls. Absolute liver weights were significantly increased in females that received 200, 600, 2,000, and 6,000 ppm, absolute kidney weights were significantly increased in males that received 600, 2,000, and 6,000 ppm, and absolute spleen weights were significantly increased in males and females that received 6,000 and 18,000 ppm. Groups of 10 male and 10 female B6C3F1 mice received diets containing 0, 60, 200, 600, 2,000, or 6,000 ppm o-nitroanisole. Final mean body weight gains, final mean body weights, and feed consumption by male and female mice receiving 6,000 ppm were lower than those of the controls. Hemoglobin and hematocrit values in males and females that received 2,000 or 6,000 ppm were significantly lower than those in the controls. The absolute and relative liver weights of females in the 600 ppm group and relative liver weights of males and females in the 2,000 and 6,000 ppm groups were significantly greater than those of controls. Lesions associated with exposure to o-nitroanisole were present in the urinary bladder, spleen, kidney, liver, testis, and uterus of rats. Diffuse hyperplasia of the transitional epithelium of the urinary bladder occurred in all male and female rats that received 6,000 and 18,000 ppm. A transitional cell papilloma occurred in one male and transitional cell carcinomas occurred in two males and three females receiving 18,000 ppm. Congestion of the red pulp and capsular hyperplasia of the spleen and hepatocellular hypertrophy of the liver were present in males and females from the 18,000 ppm groups. Multifocal degeneration and necrosis of the renal tubule epithelium with infiltration of mononuclear inflammatory cells were present in male rats that received 600, 2,000, and 6,000 ppm. At the 18,000 ppm level, degeneration of the seminiferous epithelium accompanied by loss of spermatogenic cells and decreased numbers of spermatozoa were observed in the testes of male rats, while uterine atrophy was observed in female rats. Hepatocyte hypertrophy of the centrilobular and midzonal regions of liver lobules was present in mice that received 200 ppm and increased in severity at higher exposure levels. 2-YEAR STUDIES: The doses selected for the 2-year study of o-nitroanisole in rats were based on lower mean body weights, reduced feed consumption, and increased severity of regenerative anemia in male and female rats receiving 6,000 and 18,000 ppm during the 13-week study. Groups of 6roups of 60 male and 60 female F344 rats received diets containing 0, 222, 666, or 2,000 ppm o-nitroanisole. Groups of 60 male and 60 female B6C3F1 mice received diets containing 0, 666, 2,000, or 6,000 ppm o-nitroanisole. After 15 months, up to 10 animals from each group were evaluated for chemical-related lesions. Survival, Body Weights, Feed Consumption, and Clinical Findings: Survival of male rats receiving 2,000 ppm was significantly lower than that of the controls due to increased severity of nephropathy. Survival of 222 and 666 ppm male rats and all exposed female rats was similar to that of the controls. Survival of groups of exposed male and female mice was similar to that of the controls. The final mean body weight of male rats receiving 2,000 ppm was lower than that of the controls. Final mean body weights of male and female mice that received 2,000 and 6,000 ppm were lower than those of the controls. Feed consumption by male and female rats was similar to that by the controls. The only clinical finding in male or female mice attributable to chemical administration was discolored urine. Neoplasms and Nonneoplastic Lesions: The incidence of mononuclear cell leukemia was significantly increased in male rats that received 666 and 2,000 ppm and in female rats that received 2,000 ppm (males: 0 ppm, 26/50; 222 ppm, 25/50; 666 ppm, 42/50; 2,000 ppm, 34/50; females: 14/50, 11/50, 14/50, 26/50). Nephropathy occurred in all male rats; the severity increased with exposure level. Focal hyperplasia of the renal tubule epithelium was present in three males receiving 222 ppm and two males receiving 2,000 ppm. Renal tubule adenomas occurred in one male from each of the 222, 666, and 2,000 ppm groups, and renal tubule carcinomas occurred in two males from the 2,000 ppm group. Focal hyperplasia of the transitional epithelium of the urinary bladder was present in one female rat that received 222 ppm and two male rats and six female rats that received 2,000 ppm. A transitional cell papilloma occurred in the urinary bladder of one female rat from the 2,000 ppm group, and a transitional cell carcinoma occurred in another female from the 2,000 ppm group. The incidence of forestomach ulcers increased in male rats that received 2,000 ppm, and the incidence of focal hyperplasia of the forestomach increased with exposure level in male and female rats. In addition, squamous cell papillomas of the forestomach were present in one female receiving 222 ppm, one male receiving 666 ppm, and one male and one female receiving 2,000 ppm, while squamous cell carcinomas were present in one male receiving 666 ppm and one male and one female receiving 2,000 ppm. The incidences of pituitary gland adenomas in male rats and mammary gland fibroadenomas in female rats decreased with exposure level. The incidence of cellular alteration in the liver was significantly increased in exposed groups of male and female mice. The incidences of hepatocellular adenoma, hepatocellular adenoma or carcinoma (combined), and hepatocellular carcinoma or hepatoblastoma (combined) were significantly increased in male mice receiving 2,000 and 6,000 ppm. The incidences of hepatocellular adenoma or carcinoma were significantly increased in female mice that received 2,000 ppm. STOP-EXPOSURE STUDY: Groups of 60 male and 60 female F344 rats received diets containing 0, 6,000, or 18,000 ppm o-nitroanisole for 27 weeks and were then maintained on control feed without further chemical exposure for up to an additional 77 weeks. Up to 10 rats from each group were evaluated for the presence of chemical-related lesions at 3, 6, 9, and 15 months. Survival and Body Weights: Survival of exposed male and female rats was significantly lower than that of the controls as a result of moribund deaths associated with significantly increased incidences of urinary bladder neoplasms, primarily transitional cell carcinomas. All male rats that received 18,000 ppm were dead by week 48 and all females that received 18,000 ppm were dead by week 61. Mean body weights of exposed male and female rats were lower than those of the controls throughout the study. Neoplasms and Nonneoplastic Lesions: Hyperplasia of the transitional epithelium of the urinary bladder was present in nearly all exposed male and female rats examined at the interim evaluations. A transitional cell carcinoma was first observed at the 3-month interim evaluation in a male rat that received 18,000 ppm. At the 6- and 9-month interim evaluations, transitional cell papillomas or carcinomas were observed in both exposed groups of male rats. Transitional cell carcinomas were observed at the 6-month interim evaluation in females receiving 18,000 ppm and at the 9-month interim evaluation in females receiving 6,000 and 18,000 ppm. Adenomatous polyps of the large intestine were observed in a small number of exposed rats at the 6-, 9-, and 15-month interim evaluations. At the end of the study, the incidence of adenomatous polyps of the large intestine was significantly increased in all exposed groups and carcinomas of the large intestine were present in four males and two females from the 18,000 ppm groups. The incidence of hyperplasia of the transitional epithelium of the kidney pelvis was significantly increased in exposed male and female rats and transitional cell papillomas were present in three males and one female that received 18,000 ppm. Transitional cell carcinomas of the kidney were present in one male receiving 6,000 ppm and six males and one female receiving 18,000 ppm. Transitional cell carcinomas of the urinary bladder were seen in nearly all exposed male and female rats. Of the males and females receiving 6,000 ppm which were without carcinomas, three males and one female had transitional cell papillomas. Generalized centrilobular hypertrophy, focal hepatocellular necrosis, multifocal hepatocellular cytoplasmic vacuolation, and Kupffer cell pigmentation were observed in the livers of male and female rats at the 3- and 6-month interim evaluations; however, only Kupffer cell pigmentation was observed at the end of the study. Congestion of the red pulp of the spleen was observed in nearly all exposed male and female rats at the 3-, 6-, and 9-month interim evaluations but the incidence was only slightly increased in the 18,000 ppm groups at the end of the study. Degeneration and atrophy of the seminiferous tubule epithelium of the testes were observed at the 3- and 6-month interim evaluations in all male rats receiving 18,000 ppm. GENETIC TOXICOLOGY: o-Nitroanisole was tested in two laboratories for mutagenicity in Salmonella typhimurium strains TA97, TA98, TA100, TA1535, and TA1537 with and without exogenous metabolic activation (S9). Positive responses were observed at both laboratories in TA100 with and without S9 activation. One laboratory found no increase in mutations, while the second laboratory detected a weakly positive response in TA1535 without S9. No mutagenic activity was observed in the other tester strains. o-Nitroanisole was positive in the mouse lymphoma assay for induction of trifluorothymidine resistance in L5178Y cells without S9 activation. In cytogenetic tests with Chinese hamster ovary cells, o-nitroanisole induced a significant increase in chromosomal aberrations at the highest dose tested in the presence of S9 activation; sister chromatid exchanges were induced both with and without S9. CONCLUSIONS: Under the conditions of these feed studies there was clear evidence of carcinogenic activity of o-nitroanisole in male and female F344 rats that received diets containing 6,000 or 18,000 ppm for 6 months based on overall increased incidences of benign and malignant neoplasms of the urinary bladder, transitional cell neoplasms of the kidney, and benign and malignant neoplasms of the large intestine. There was a chemical-related increased incidence of mononuclear cell leukemia in male and female rats receiving diets containing 222, 666, or 2,000 ppm o-nitroanisole for 2 years. Marginally increased incidences of uncommon renal tubule neoplasms in male rats and forestomach neoplasms in male and female rats were considered uncertain findings. There was clear evidence of carcinogenic activity of o-nitroanisole in male B6C3F1 mice based on increased incidences of benign and malignant hepatocellular neoplasms. There was some evidence of carcinogenic activity of o-nitroanisole in female B6C3F1 mice based on increased incidences of hepatocellular adenomas. Increased severity of nephropathy in male rats, and increased incidences of focal hyperplasia of the renal tubule epithelium and forestomach ulcers in male rats, and of transitional cell hyperplasia of the urinary bladder, focal hyperplasia of the forestomach, and hyperplasia of transitional epithelium of the kidney pelvis in male and female rats were associated with exposure to o-nitroanisole. Synonyms: Methoxynitrobenzene, nitrophenyl methyl ether