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Herpesvirus saimiri (HVS) is an oncogenic virus for a variety of nonhuman primates. HVS does not produce overt disease upon inoculation in the natural host (squirrel monkey) but consistently induces neoplasms including lymphomas and lymphocytic leukemias in 4 other species of monkeys. Various drugs inhibit replication of HVS in vitro including cytosine arabinoside and adenine arabinoside. In addition, the lymphoma and leukemia induced in owl monkeys responds to vincristine and prednisolone, cyclophosphamide, cytosine arabinoside, and human interferon. Of the various chemical carcinogens studied, the antitumor agent procarbazine induces neoplasms in a variety of species including monkeys. Thus far this compound has induced acute myelogenous leukemia (AML), lymphoma, and hemangiosarcomas in macaques. We have induced primary liver tumors in macaques with several nitrosamines and aflatoxin B1 and these tumors produce alpha-fetoprotein (AFP) which can be assayed for both diagnosis and therapy. Thus far, therapy of hepatocellular carcinoma has been most successful with surgical resection; and the tumor mass and serum AFP have been less responsive to single agent chemotherapy. These nonhuman primate models are useful for an understanding of the cause, diagnosis, prevention, and treatment of the human disease.

The carcinogenic potential of 2‐amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline (MeIQx) was evaluated in cynomolgus monkeys. The animals received MeIQx, beginning at the age of one year, at doses of 10 or 20 mg/kg body weight by gavage five times a week for 84 months and were autopsied 8 months thereafter. Although sporadic development of aberrant crypt foci in the colon and glutathione S‐transferase π‐positive foci in the liver as well as hyper plastic changes of the lymphatic tissue in the lung and gastro‐intestinal tract were observed in several monkeys, this was not treatment‐related. No neoplastic or preneoplastic lesions were found in other organs. Serum chemistry data and organ weights were also within the normal ranges. From these data, it is concluded that MeIQx is not carcinogenic in the cynomolgus monkey under the conditions examined. This lack of carcinogenicity is probably related to the poor activation of MeIQx due to the lack of constitutive expression of CYP1A2 as well as an inability of other cytochrome P450s to catalyze N‐ hydroxylation of MeIQx in the cynomolgus monkey.

Because of reports on tumorigenic activity in different animal species exposed to DDT a decision was made in 1969 to evaluate the long-term effects of DDT on 24 cynomolgus and rhesus monkeys. DDT (20 mg/kg) was given in the diet for 130 months, followed by an observation period that ended in 1994. The two cases of malignant tumor detected in the DDT group included a metastatic hepatocellular carcinoma in a 233-month-old male and a well-differentiated adenocarcinoma of the prostate in a 212-month-old monkey. Benign tumors detected in the DDT group included three cases of leiomyoma, two of which were uterine and one, esophageal. No tumor was detected in the control group of 17 monkeys. Fatty changes in the liver were observed in 52.9% of the DDT group and 29.4% of the control group. More specific signs of hepatotoxicity were documented microscopically in seven DDT monkeys. Severe tremors and histological evidence of CNS and spinal cord abnormalities were observed in six DDT monkeys. The present findings show clear evidence of hepatic and CNS toxicity following long-term DDT administration to cynomolgus and rhesus monkeys. However, the two cases involving malignant tumors of different types are inconclusive with respect to a carcinogenic effect of DDT in nonhuman primates.

Background: It was observed in the early 1970s that saccharin produced bladder cancer in rats. However, it has been unclear whether sodium saccharin when consumed by humans poses a substantial carcinogenic hazard. Numerous epidemiologic studies have not shown any evidence of increased urothelial proliferation associated with ingestion of sodium saccharin. Purpose: Our purpose was to determine the effects of long-term feeding of sodium saccharin to three species of nonhuman primates. Methods: Twenty monkeys of three species (six African green, seven rhesus, six cynomolgus, and one hybrid [of rhesus male and cynomolgus female parentage]) were treated with sodium saccharin (25 mg in the diet/kg body weight daily for 5 days a week) beginning within 24 hours after birth and continuing for up to 24 years. Sixteen monkeys (seven rhesus and nine cynomolgus) served as controls. During their last 2 years of life, urine was collected from selected treated and control animals and evaluated for various urinary chemistries and for the presence of calculi, microcrystalluria, and precipitate. Urinary bladders were examined by light microscopy and by scanning electron microscopy. Results: Sodium saccharin treatment had no effect on the urine or urothelium in any of these monkeys. There was no evidence of increased urothelial cell proliferation, and there was no evidence of formation of solid material in the urine. Conclusion: Although the dose of sodium saccharin administered to these monkeys was only five to 10 times the allowable daily intake for humans, the results provide additional evidence that sodium saccharin is without a carcinogenic effect on the primate urinary tract. [J Natl Cancer Inst 1998;90:19‐25]

Forms of 2,4-dichlorophenoxyacetic acid (2,4-D) are herbicides used in the control of a wide variety of broadleaf and woody plants. Subchronic toxicity studies in dogs were conducted on three forms of 2,4-D: the parent form, 2,4-D acid (ACID); 2,4-D dimethylamine salt (DMA); and 2,4-D 2-ethylhexyl ester (2-EHE). The three studies were designed to allow for comparison of the toxicity of the three forms. Doses in the subchronic studies, on an acid equivalent basis, were 0, 0.5 (ACID only), 1.0, 3.75, and 7.5 mg/kg/day. Treatment related findings in the three studies included reductions in body weight gain, and food consumption, and minor increases in blood urea nitrogen, creatinine, and alanine aminotransferase. The data from the three subchronic studies demonstrated the comparable toxicity of ACID, DMA, and 2-EHE and support a subchronic no observed adverse effect level (NOAEL) of 1.0 mg/kg/day for all three forms. Due to the similarity in toxicity of the three forms of 2,4-D, a 1-year chronic toxicity study was performed on the parent ACID to fully characterize the potential toxicity of 2,4-D in the dog. ACID was well tolerated at doses of 0, 1.0, 5.0, and 7.5 mg/kg/day. The clinical pathology alterations were similar to those seen in the subchronic studies and were not progressive. The histopathology alterations observed were not severe in nature and the no observed effect level in the chronic study was determined to be 1.0 mg/kg/day. There was no indication of any immunotoxic or oncogenic response in the studies. In conclusion, the findings of these studies indicate comparable toxicity among representative forms of 2,4-D and their generally low toxicity following subchronic and chronic dietary exposure in the dog.

The carcinogenic potential of 2‐amino‐3‐methylimidazo[4,5f]quinoline (IQ) was evaluated in cynomolgus monkeys. Monkeys received IQ, beginning at the age of one year, at doses of 10 or 20 mg/kg by gavage. Thus far, IQ has induced hepatocellular carcinoma in three monkeys with a latent period of 27 to 37 months. Metastases to the lung occurred in two of the three monkeys. Microscopically, the hepatocellular carcinoma in all three cases demonstrated a trabecular pattern. These data demonstrate that IQ is a potent carcinogen in nonhuman primates and support the idea that it is a potential carcinogen for humans.

Three of 42 (7%) monkeys given aflatoxin B1 (AFB1) for longer than 2 years have developed primary malignant neoplasms of the liver. Liver biopsies performed at intervals during aflatoxin administration revealed that neoplasia was preceded by pathologic lesions of the liver, including toxic hepatitis, proliferation of pseudotubules, and hyperplastic nodules. Serum alpha-fetoprotein levels, monitored in one of the monkeys by radioimmunoassay, paralleled tumor growth and recurrence of the hepatocellular carcinoma. Normal serum alpha-fetoprotein levels were noted for a monkey with hemangioendothelial sarcoma. Our results implicate AFB1 as a liver carcinogen in monkeys and add additional support to the hypothesis that humans exposed to this substance may be at risk of developing liver cancer.

Observation of two sibling rhesus monkeys, Macaca mulatta, indicated that they were intolerant to lactose. While on a lactose formula the monkeys had severe diarrhea and weight loss but were otherwise healthy. When a lactose-free formula was instituted, the diarrhea abated and there was a steady weight gain.

A fecal filtrate of human origin containing the Norwalk agent of epidemic viral gastroenteritis was administered by stomach tube to chimpanzees in an attempt to induce diarrheal disease. Significant postchallenge serum antibody rises against Norwalk viral antigens were demonstrated in all animals using the techniques of immune electron microscopy and radioimmunoassay. In addition, viral antigens were detected in feces from five of nine animals using radioimmunoassay. Clinical illness characterized by diarrhea and/or vomiting did not occur. Infection was transmitted subsequently by feeding four additional chimpanzees a fecal filtrate prepared from one of the previously infected animals. Development of an antibody response in four animals and detection of viral antigen in two animals that received this passage filtrate indicated that viral replication had occurred in the absence of clinical illness. The availability of the chimpanzee as an experimental animal host susceptible to infection with the Norwalk agent should facilitate the study of epidemic viral gastroenteritis.

10 monkeys (macaques) received adriamycin by monthly intravenous injections at 12 mg/m2 (1 mg/kg). 8 of the 10 monkeys developed congestive heart failure at an average cumulative adriamycin dose (310 mg/m2) well below that considered the safe upper limit (550 mg/m2) in man. Histologically, the myocardial lesions resembled those found in human anthracycline-induced cardiomyopathy. 1 of the 10 monkeys developed acute myeloblastic leukemia after receiving 324 mg/m2 of adriamycin; the 10th monkey is alive and well 26 months after the last dose of drug. Our results suggest that adriamycin is a more potent cardiotoxin in monkeys than in man, and that leukemia may be a consequence of prolonged treatment with this drug.

The carcinogenic potential of cycasin and methylazoxymethanol (MAM) acetate was investigated in nonhuman primates. Old-world monkeys (rhesus, cynomolgus, and African green monkeys) received cycasin and/or MAM acetate by oral or ip routes up to 11 years. Eighteen monkeys survived longer than 2 months after initiation of treatment with cycasin (50-75 mg/kg) or MAM acetate (1.5-3.0 mg/kg) given orally 5 days/week; 9 of the animals were necropsied. Histopathologic examination of a liver tumor from 1 of these monkeys revealed well-differentiated hepatocellular carcinoma. A second monkey had multiple tumors, including hepatocellular carcinoma, intrahepatic bile duct adenocarcinoma, renal carcinoma and adenomas, and adenomatous polyps of the colon. Although liver tumors were not observed in the other monkeys, all but 1 monkey had hepatic lesions such as toxic hepatitis and cirrhosis. These monkeys had received cycasin and/or MAM acetate for an average of 57 months (range, 2-133 mo). A group of 10 monkeys received MAM acetate by weekly ip injections (3-10 mg/kg). Six of these animals developed tumors after receiving an average of 6.14 g (range, 3.58-9.66 g) of MAM acetate for an average of 75 months (range, 50-89 mo). Four of the monkeys developed hepatocellular carcinomas, and 2 had multiple primary tumors including hepatocellular carcinomas, renal carcinomas, squamous cell carcinomas of the esophagus, and adenocarcinomas of the small intestine. Our results showed that long-term administration of cycasin and/or MAM acetate by oral and ip routes was hepatotoxic and carcinogenic in old-world monkeys.

Although esophageal cancer has been induced experimentally in rodents [1–5], the findings are difficult to extrapolate to humans in a way that could have applicability to clinical medicine. This report briefly describes, a model of experimental induction of squamous cell carcinoma in non-human primates, emphasizing the precursor stages and discussing similarities and differences from human experience.