NTP Toxicology and Carcinogenesis Studies of Pentachloroanisole (CAS No. 1825-21-4) in F344 Rats and B6C3F1 Mice (Feed Studies).
Pentachloroanisole is a chlorinated aromatic compound which is widely distributed at low levels in the environment and in food products. Formation of pentachloroanisole in the environment may result from the degradation of structurally related, commercially important, ubiquitous chlorinated aromatic compounds such as pentachlorophenol and pentachloronitrobenzene which are known rodent toxins or carcinogens. Toxicology and carcinogenesis studies were conducted by administering pentachloroanisole (>99% pure) in corn oil by gavage to groups of male and female F344/N rats and B6C3F1 mice for 16 days, 13 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium strains, mouse lymphoma cells, and Chinese hamster ovary cells. 16-DAY STUDIES IN RATS: Groups of five male and five female F344/N rats were administered pentachloroanisole in corn oil by gavage once per day, 5 days per week, for 16 days at doses of 0, 100, 125, 150, 175, or 200 mg/kg body weight. Deaths occurred during days 2 and 3 in rats receiving doses of 125 mg/kg or greater; these deaths were considered directly related to pentachloroanisole administration. No biologically significant changes in mean body weight gains or final body weights were noted in the 100 mg/kg groups of rats. Because of the high early mortality rate, valid comparisons of body weight differences in other dose groups could not be made. Inactivity was noted in all dose groups. Rats administered doses of 125 mg/kg or greater also exhibited dyspnea. 16-DAY STUDIES IN MICE: Groups of five male and five female B6C3F1 mice were administered pentachloroanisole in corn oil by gavage once per day, 5 days per week, for 16 days at doses of 0, 100, 175, 250, 325, or 400 mg/kg. Deaths occurred during days 2 and 3 in mice receiving doses of 175 mg/kg or greater; these deaths were considered directly related to chemical administration. No biologically significant changes in mean body weight gains or final body weights were noted in 100 mg/kg males or 100 or 175 mg/kg females. Because of the high early mortality rate, valid comparisons of body weight differences in other dose groups could not be made. Inactivity was noted in dosed mice. 13-WEEK STUDIES IN RATS: Groups of 10 male and 10 female rats were administered pentachloroanisole in corn oil by gavage once per day, 5 days per week, for 13 weeks at doses of 0, 40, 80, 120, 140, or 180 mg/kg body weight. Most rats receiving doses of 120 mg/kg or greater died during the first week of the study as a direct result of pentachloroanisole administration. Mean body weight gains of males administered 40 or 80 mg/kg and of females administered 40, 80, or 120 mg/kg pentachloroanisole were significantly lower than those of the controls. Most dosed rats exhibited temporary inactivity for several hours after dosing. Relative liver and kidney weights of males administered 40 or 80 mg/kg and absolute and/or relative liver and kidney weights of females administered 40 to 120 mg/kg were significantly greater than those of the controls. Lesions observed in males administered 80 mg/kg or more and in females administered 120 mg/kg or more included pulmonary congestion, hemorrhage, and/or edema, meningeal congestion, and hepatocellular necrosis, glycogen depletion, and degeneration of biliary epithelium in the liver. 13-WEEK STUDIES IN MICE: Groups of 10 male and 10 female mice were administered pentachloroanisole in corn oil by gavage once per day, 5 days per week, for 13 weeks at doses of 0, 40, 80, 120, 140, or 180 mg/kg body weight. Most mice administered doses of 120 mg/kg or higher died during the first week of the study as a direct result of pentachloroanisole administration. Mean body weight gains of females administered 40 to 140 mg/kg were significantly greater than that of the controls, but those of dosed males were similar to that of the controls. Most dosed mice exhibited temporary inactivity for several hours after dosing. Absolute and relative liver weights of males administered 80 mg/kg, absolute and relative liver weights of femats of females administered 40 to 180 mg/kg, and absolute and relative kidney weights of females administered 80 to 180 mg/kg pentachloroanisole were also significantly greater than those of the controls. Lesions observed in males administered 40 mg/kg or more and in females administered 80 mg/kg or more included pulmonary congestion and/or edema, adrenal congestion, lymphoid depletion of lymph nodes and thymus, hepatocellular cytomegaly and karyomegaly, and pigment accumulation in hepatocytes and Kupffer cells. 2-YEAR STUDIES IN RATS: Based on the chemical-related mortality and liver lesions seen in the 16-day and 13-week studies, doses selected for the 2-year studies were 0, 10, 20, and 40 mg/kg for males and 0, 20, and 40 mg/kg for females. Groups of 70 male and 70 female rats were administered pentachloroanisole in corn oil by gavage 5 days per week for up to 2 years. At 9 and 15 months, up to 10 animals per group were selected for interim evaluations. Survival, Body Weights, and Clinical Findings: The survival of high-dose males was significantly decreased (vehicle control, 24/50; low-dose, 20/50; mid-dose, 24/50; high-dose, 14/50); most deaths in the high-dose group occurred at or before week 16. The majority of deaths in the mid- and high-dose groups may have been due to pentachloroanisole-related hyperthermia. The survival of dosed females was greater than that of the controls (29/50, 35/50, 44/50). Final mean body weights of mid- and high-dose males were 7% and 10% lower than that of the controls; final mean body weight of high-dose females was 11% lower than that of the controls. Final mean body weights of other dose groups were similar to those of the vehicle controls. At the 9-month interim evaluation, mean rectal temperature of males administered 40 mg/kg was significantly greater than that of the controls. Relative liver and kidney weights of males and females administered 20 or 40 mg/kg were significantly greater than those of controls. At the 15-month interim evaluation, relative liver weights of dosed females and absolute liver weights of 40 mg/kg females were significantly greater than those of the controls, as were relative liver and kidney weights of 40 mg/kg males. Pathology Findings: In the 2-year studies, administration of pentachloroanisole to males was associated with significant increases in the incidences of benign adrenal medulla pheochromocytomas. The incidence of benign adrenal medulla pheochromocytomas was marginally increased in high-dose females and slightly exceeded the range of the historical controls. Incidences of adrenal medulla hyperplasia were increased in dosed female rats, but not in dosed males. The incidences of pancreatic adenomas and focal hyperplasia were decreased in dosed males. The incidences of mammary gland fibroadenomas and uterine stromal polyps and sarcomas (combined) were decreased in high-dose females. Treatment-related increased incidences of intracytoplasmic pigmentation occurred in renal tubule epithelium, olfactory epithelium, and hepatocytes of males and females. Congestion and hemorrhage of the lungs, lymph nodes, thymus, adrenal cortex, and meninges, as well as hepatocellular centrilobular necrosis occurred almost exclusively in mid- and high-dose males that died or were killed moribund before the end of the studies. 2-YEAR STUDIES IN MICE: Based on the chemical-related mortality and liver lesions seen in the 16-day and 13-week studies, doses selected for the 2-year studies were 0, 20, and 40 mg/kg. Groups of 70 male and 70 female mice were administered pentachloroanisole in corn oil by gavage 5 days per week for up to 2 years. At 9 and 15 months, up to 10 animals per group were selected for interim evaluations. Survival, Body Weights, and Clinical Findings: The survival of dosed males was similar to that of the controls; survival of high-dose females was lower than that of the controls (24/50, 25/50, 16/50). The decreased survival of the high-dose females was attributed primarily to ovarian abscesses which were observed after moribund sacrifice. At the 9-month interim evaluation, the mean body weight of males administered 40 mg/kg was significantly lower than that of the vehicle controls. Absolute and relative liver weights of females and the relative liver weight of males administered 40 mg/kg were significantly greater than those of the controls. Final mean body weights of low- and high-dose males were 11% and 17% lower than that of the controls. Final mean body weights of dosed females were similar to that of the controls. There were no clinical findings attributed to pentachloroanisole administration. Pathology Findings: Centrilobular hepatocyte cytomegaly and pigment accumulation in hepatocytes and Kupffer cells were seen in dosed mice, but not in controls at the 9- and 15-month interim evaluations. In the 2-year studies, the incidence of benign pheochromocytomas was significantly increased in high-dose males. Dosed males also exhibited increased incidences of adrenal medulla hyperplasia and hypertrophy. The incidences of hemangiosarcomas of the liver were significantly increased in dosed males. Increased incidences of hepatocellular cytologic alteration, biliary tract hyperplasia, and Kupffer cell pigmentation occurred in dosed males and females; the incidences of mixed cell foci were also increased in dosed males. Cytologic alteration encompassed hepatocellular cytomegaly, karyomegaly, hepatocyte degeneration and necrosis, and multinucleated giant cell formation, and was considered an advanced stage of the pathologic process observed at 13 weeks. GENETIC TOXICOLOGY: Pentachloroanisole was mutagenic in Salmonella typhimurium strains TA98 and TA1537 in the absence but not in the presence of exogenous metabolic activation (S9). No clear mutagenic activity was observed in TA100 with hamster S9, without S9, or in TA1535 with or without S9. An equivocal response was observed in TA100 with rat S9. Pentachloroanisole was positive for induction of trifluorothymidine resistance in mouse lymphoma L5178Y cells with S9; the response observed without S9 was weak and inconsistent. In cytogenetic tests with Chinese hamster ovary cells, pentachloroanisole induced sister chromatid exchanges, but not chromosomal aberrations, with and without S9. TOXICOKINETICS: Male and female F344/N rats and B6C3F1 mice were administered 10, 20, or 40 mg/kg pentachloroanisole by gavage or 10 mg/kg pentachloroanisole intravenously (Appendix H). A rapid elimination of pentachloroanisole and a rapid formation of its main metabolite, pentachlorophenol, were seen in both species after an intravenous or an oral dose of pentachloroanisole. The area under the concentration-versus-time curve of pentachloroanisole increased with dosage in each species but the dose proportionality was lost above 20 mg/kg. No sex-related differences were found in the rate of absorption of pentachloroanisole from the GI tract, in the area under the concentration-versus-time curve, or in the overall rate elimination of pentachloroanisole. However, in female rats the area under the concentration-versus-time curve of pentachlorophenol was significantly larger than in male rats. No such difference was observed in mice. CONCLUSIONS: Under the conditions of these 2-year gavage studies, there was some evidence of carcinogenic activity of pentachloroanisole in male F344/N rats based on increased incidences of benign pheochromocytomas of the adrenal medulla. There was equivocal evidence of carcinogenic activity of pentachloroanisole in female F344/N rats based on marginally increased incidences of benign pheochromocytomas of the adrenal medulla. There was some evidence of carcinogenic activity of pentachloroanisole in male B6C3F1 mice based on increased incidences of benign pheochromocytomas of the adrenal medulla and hemangiosarcomas of the liver. There was no evidence of carcinogenic activity of pentachloroanisole in female B6C3F1 mice given doses of 20 or 40 mg/kg. Pentachloroanisole administration was associated with increased incidences of adrenal medulla hyperplasia in female rats and increased incidences of pigmentation in the renal tubule epithelium, olfactory epithelium, and hepatocytes of male and female rats. In addition, decreased incidences of pancreatic adenomas and focal hyperplasia in male rats and decreased incidences of mammary gland fibroadenomas and uterine stromal polyps and sarcomas (combined) in female rats were observed. Hyperthermia-related lesions in male rats receiving 20 or 40 mg/kg were considered indirectly related to pentachloroanisole administration. Pentachloroanisole administration was associated with increased incidences of adrenal medulla hyperplasia and hypertrophy and hepatocellular mixed cell foci in male mice. In male and female mice, nonneoplastic liver lesions associated with pentachloroanisole administration included hepatocellular cytologic alteration, Kupffer cell pigmentation, biliary tract hyperplasia, and subacute inflammation. Synonyms: 2,3,4,5,6-pentachloroanisole; methyl pentachlorophenate; methyl pentachlorophenyl ether; o-methylpentachlorophenol; pentachloromethoxybenzene; pentachlorophenyl methyl ether