Body weight-tumor incidence correlations in long-term rodent carcinogenicity studies.

Associations between body weight and tumor incidence and among the incidences of selected site-specific tumors were examined for more than 4,000 male and female Fischer-344 rats and B6C3F1 mice in the National Toxicology Program historical control database. Incidences of certain site-specific tumors, most notably mammary gland and pituitary gland tumors in rats and liver tumors in mice, were shown to have a strong positive correlation with 52-wk body weight. Using individual animal data, logistic regression models were derived for predicting site-specific tumor incidence as a function of 52-wk body weight, age, and other factors. This association between body weight and tumor incidence can explain many of the decreased tumor incidences observed in National Toxicology Program carcinogenicity studies. Body weight differences between dosed and control groups can also mask carcinogenic effects for those sites sensitive to body weight changes. Thus, when designing long-term rodent carcinogenicity studies, measures should be taken to minimize potential body weight differences between dosed and control groups. There were a number of small but significant negative correlations among tumor incidences, reflecting primarily the lethality of the tumors in question. None of these correlations (nor the 2 small positive correlations found) are likely to have any impact on the interpretation of experimental results. However, the high negative correlation between pituitary gland and testis tumors in male Fischer-344 rats cannot be dismissed so easily, does not reflect tumor lethality, and is currently being studied further.

Carcinogenicity of glycidol in F344 rats and B6C3F1 mice.

Glycidol, a simple aliphatic epoxide, was administered by gavage in water to groups of male and female F344/N rats and B6C3F1 mice. Rats received 0, 37.5 or 75 mg kg-1 and mice received 0, 25 or 50 mg kg-1 daily, 5 days per week for 2 years. Exposure to glycidol was associated with dose-related increases in the incidences of neoplasms in numerous tissues in both rats and mice. Survival of rats that received glycidol was markedly reduced compared to the control because of the early induction of neoplastic disease. In male rats, mesothelioma arising in the tunica vaginalis and frequently metastasizing to the peritoneum were considered the major cause of early death. Early deaths in female rats were associated with mammary gland neoplasms. Survival of female mice that received 50 mg kg-1 was lower than the control after week 101 due primarily to euthanasia of moribund animals with mammary gland neoplasms. Survival of male mice and female mice that received 25 mg kg-1 was comparable to the control. In mice, exposure to glycidol was associated with increased incidences of neoplasms of the harderian gland in males and females, the forestomach in males and the mammary gland in females.

Toxicity and carcinogenicity of 2,3-dibromo-1-propanol in F344/N rats and B6C3F1 mice.

2,3-Dibromo-1-propanol is a metabolite of the flame retardant tris(2,3-dibromopropyl) phosphate, previously shown to be a mutagen and carcinogen in experimental animals. Toxicology and carcinogenesis studies of 2,3-dibromo-1-propanol were conducted by applying the chemical in 95% ethanol to the interscapular skin of male and female F344/N rats and B6C3F1 mice 5 days a week for 13 weeks in the prechronic study and 48-55 weeks (rats) or 36-42 weeks (mice) in the carcinogenicity study. In the 13-week study, 10 rats and 10 mice of each sex received doses of 0, 44, 88, 177, 375, or 750 mg/kg. Deaths associated with chemical application occurred only in the high-dose (750 mg/kg) male mice. Chemical-related lesions were seen in the kidney of male rats, liver of female rats, and liver and lung of both sexes of mice. Based on the toxicity observed in the 13-week study, 50 rats of each sex received doses of 0, 188, or 375 mg/kg and 50 mice of each sex received 0, 88, or 177 mg/kg in the carcinogenicity study. The planned 2-year study was terminated early because of reduced survival of rats related to chemical-induced neoplasia and because of the appearance of antibodies to lymphocytic choriomeningitis virus in sentinel mice. Nearly all dosed rats had malignant neoplasms at one or more sites, while only one control male and one control female had malignant neoplasms. In rats, neoplasms induced by 2,3-dibromo-1-propanol occurred in the skin, nasal mucosa, Zymbal's gland, oral mucosa, esophagus, forestomach, intestines, liver, kidney, mammary gland (females), clitoral gland (females), spleen (males), and mesothelium (males). In mice, chemical-induced neoplasms occurred in the skin, forestomach, liver (males), and lung (males).

1,2,3-Trichloropropane: a multisite carcinogen in rats and mice.

1,2,3-Trichloropropane was evaluated in 2-year toxicology and carcinogenesis studies by the National Toxicology Program. The selection of this chemical for study was based on the potential for human exposure, its positive in vitro genotoxicity, and the carcinogenicity of structurally related chemicals. During the 2-year study 1,2,3-trichloropropane was administered in corn oil by gavage 5 days per week; groups of 60 F344/N rats received 0, 3, 10, or 30 mg/kg, while groups of 60 B6C3F1 mice received 0,6,20, or 60 mg/kg. Because of reduced survival associated with the development of chemical-related neoplasms, rats that received 30 mg/kg were terminated at 65 weeks (females) or 76 weeks (males). Similarly, mice that received 60 mg/kg were terminated at 73 weeks (females) or 79 weeks (males), while groups of mice that received 20 mg/kg were terminated at 88 weeks. 1,2,3-Trichloropropane induced benign and/or malignant neoplasms at multiple sites in both rats and mice; this included increased incidences of benign and malignant neoplasms of the squamous epithelium of the oral mucosa and forestomach of male and female rats, benign neoplasms of the kidney and pancreas and benign or malignant neoplasms of the preputial gland in male rats, malignant neoplasms of the mammary gland, and benign or malignant neoplasms of the clitoral gland in female rats. In mice, 1,2,3-trichloropropane induced a low incidence of malignant neoplasms of the oral mucosa in females, high incidences of benign and malignant neoplasms of the forestomach in males and females, benign neoplasms of the liver and harderian gland of males and females, and uterine neoplasms in females.

The utility of multiple-section sampling in the histopathological evaluation of the kidney for carcinogenicity studies.

In a recent review of 379 carcinogenicity studies in rodents conducted under the auspices of the National Cancer Institute and, later, the National Toxicology Program (NTP), the kidneys were the third most frequent site for chemical-related neoplasia. While some potent carcinogens induced high incidences of renal neoplasms with shortened latency in Fischer-344 (F-344) rats or B6C3F1 mice, other usually nonmutagenic compounds produced marginally increased incidences of renal neoplasms that were difficult to interpret. As an aid to the interpretation of 16 recent studies, additional kidney sections from rats or mice were prepared and examined microscopically. The remaining pieces of formalin-fixed kidney were embedded and sectioned at intervals of 1 mm (rats) or 0.5 mm (mice) to produce an additional 6-8 (rats) or 4-6 (mice) H&E-stained sections per kidney per animal for microscopic examination. The average number of additional sections per animal was similar between dosed and control groups to avoid sampling bias. The supplemental evaluation of these additional kidney sections was clearly useful in determining potential renal carcinogenicity in male F-344 rats in these NTP studies. Of the 13 studies in male rats in which step-sections of kidney were evaluated, the supplemental data demonstrated conclusively an association between chemical administration and renal tubule hyperplasia, adenoma, or both in 9 studies. For 3 chemicals, the evidence of an association with renal proliferative lesions in male rats remained uncertain. In contrast, the supplemental evaluation of step-sections was less useful for female rats, male mice, and female mice, largely because such evaluations generally revealed few if any additional neoplasms. For these sex-species groups, there were only two instances, both involving male mice, in which the additional data confirmed an association with kidney neoplasia.

Gender differences in animal bioassays for carcinogenicity.

Animal bioassays for carcinogenicity are essential components of occupational health studies. Animal data that have been collected under controlled experimental conditions provide definitive information about the carcinogenic activities of individual substances or defined mixtures and their relative potencies in the test species. Such information serves as a frame of reference for clinical and epidemiologic studies, pointing to potential adverse health effects and to the types of substances that might produce them. This article alerts the occupational and environmental health communities to 20 substances that produced breast tumors, 13 substances that produced uterine tumors, and 8 substances that produced ovarian tumors in long-term National Toxicology Program animal studies. Each of the substances also produced neoplasms at other body sites. Follow-up studies of molecular measures of exposure and response in people and in animals will reduce the uncertainties of transspecies extrapolations.

Effect of individual housing and other experimental design factors on tumor incidence in B6C3F1 mice.

The effects of individual housing and other experimental design factors on body weight, survival, and tumor incidence in 72 control groups of B6C3F1 mice were evaluated. Individually housed males showed a greatly reduced incidence of dermal/subcutaneous tumors and an improved survival relative to group-housed animals. However, there were significant body weight increases in individually housed males and females and an associated marked increase in liver tumor incidence in both sexes and a lesser increase in lung neoplasms in males. Body weights of mice as young as 19 weeks of age were predictive of subsequent liver tumor incidence. There were no major differences in tumor rates among the various types of control groups, and differences in tumor rates among laboratories were not significant for most tumors. Differences among animal suppliers may have contributed to the time-related decreased incidence of malignant lymphoma observed in control mice, particularly in females. Comparisons with earlier control tumor rates suggest that there has been little change in tumor incidence for control groups having approximately equivalent body weights. However, control groups with heavier animals have shown a striking increase in the incidence of liver tumors. The National Toxicology Program recently returned to its earlier practice of group-housing female mice, and this should reduce the incidence of liver tumors in this sex-species group. However, if measures are not taken to reduce body weights, male mice (which continue to be individually housed because of fighting problems among group-housed animals) will likely continue to show a high incidence of liver tumors and possibly also lung neoplasms.

Evaluation of reduced protocols for carcinogenicity testing of chemicals: report of a joint EPA/NIEHS workshop.

The current U.S. Environmental Protection Agency (EPA) and other national/international guidelines specify the use of two species and two sexes rodents (usually the rat and the mouse) for carcinogenicity testing of chemicals. In view of the enormous number of chemicals to be tested, the high cost of testing, and the large number of animals used in the present protocol, many academic, industrial, and government authorities are examining the possibility of using a reduced protocol (less than two species and two sexes of rodents) for carcinogenicity testing of chemicals. The use of a reduced protocol offers many advantages as well as some disadvantages. To pursue further the potential implications and impacts of using a reduced protocol for carcinogenicity testing on the processes of hazard identification and risk assessment, a workshop entitled "Evaluation of Reduced Protocols for Carcinogenicity Testing of Chemicals" was held at the Embassy Suites Hotel in Alexandria, Virginia on September 22 and 23, 1992. It was cosponsored by EPA's Office of Prevention, Pesticides and Toxic Substances (OPPTS) and the National Toxicology Program of the National Institutes of Environmental Health Sciences (NTP/NIEHS) and attended by more than 60 participants from government, industry, academia, and the general public. The Expert Consensus Panel and most of the participants supported the use of reduced protocols in carcinogenicity testing. However, it was recognized that reduced protocols may not be appropriate for the testing of all chemicals and that additional analyses/data may be needed for selection of the most appropriate reduced protocol for certain chemicals/chemical classes.

Rodent carcinogenicity bioassay: past, present, and future.

Toxicity/carcinogenicity studies in rodents have played a pivotal role in identifying chemicals that are potentially hazardous to humans. In fact, nearly all of the known human carcinogens are also carcinogenic in 1 or more rodent species. During the past 20 yr the quality and consistency of rodent studies has improved considerably, and much has been learned about mechanisms whereby chemicals initiate or promote the carcinogenic process in rats and mice. The process of identifying chemicals that cause toxicity or carcinogenicity in rodents is quite well established, but the procedures for extrapolating this data for risk management decisions in the protection of human health have lagged far behind. While many would accept the assumptions that genotoxic chemicals that cause cancer in animals pose a cancer risk to humans and that genotoxic chemicals causing cancer at high doses pose a risk at lower doses, there is much less certainty with respect to nongenotoxic chemicals. The confusion about risk extrapolation for nongenotoxic chemicals has often lead to criticism of the hazard identification process for chemicals in general. There is increasing awareness of the complexity of the carcinogenic process that has made species extrapolation and dose extrapolation from rodent studies to humans more complex. Although newer molecular biological techniques and cell kinetic measurements offer exciting possibilities for better risk assessment, it is the combination of well-designed rodent studies with appropriate mechanistic studies that offers the best hope for regulatory decisions based on sound scientific principles.

Peer review in carcinogenicity bioassays: uses/abuses.

"Truth is the essence of science," and "peer review" is a key element in assuring the "truth". Peer review is particularly important with regard to diagnostic pathology in bioassays used for regulatory purposes and approval of drugs and medical devices for at least 2 reasons: (a) If a study is designed correctly and conducted properly, the bottom-line results rely almost entirely on pathological interpretations, and (b) diagnostic pathology is a subjective science that relies on the training and experience of the pathologist and therefore is subject to individual bias. "Bias" can be introduced during the collection and preparation of pathological materials, use of inconsistent terminology during the pathology evaluation and interpretation of the results. Peer review can help in reducing this bias. However, peer review is also subject to bias by knowledge of treatment groups, selection of inappropriate slides for review, in the type of question asked of the reviewers, and in the selection of the reviewers. When done correctly, pathology peer review can be an effective and important part of a process to assure the results of a study, but when done improperly it can cloud the issue and have a negative impact on the credibility of the study.

Toxicity and carcinogenicity of chronic exposure to tris(2-chloroethyl)phosphate.

Previous short-term studies of tris(2-chloroethyl)phosphate (TRCP), a flame retardant used in industrial and consumer products, demonstrated that repeated administration of 350 mg TRCP/kg body wt by oral gavage resulted in necrosis of pyramidal neurons in the CA1 region of the hippocampus of F344 rats, but not in B6C3F1 mice. The 2-year studies reported here were designed to characterize the chronic toxicity and potential carcinogenicity of TRCP in each sex of F344 rats and B6C3F1 mice. Groups of 60 rats per sex received 0, 44, or 88 mg/kg by oral gavage, once per day, 5 days per week, for up to 103 weeks. Groups of 60 mice per sex received 0, 175, or 350 mg/kg by oral gavage on the same dosing schedule. Each of these groups contained 10 animals which were euthanized at 66 weeks. The principal toxic effects of chronic exposure of rats to TRCP occurred in the brain and kidney. In contrast to the findings in the 16-week studies, a hippocampal lesion was not observed in the brain, although degenerative lesions were widely distributed in the gray and white matter of the brain stem and cerebral cortex of high-dose female and, to a lesser extent, male rats. These findings suggest that the hippocampal necrosis may be dependent upon the size of the individual doses or may have a pathogenesis different from that of the lesions in the brain stem and cerebral cortex. The other primary effect of chronic exposure was a dose-dependent increased incidence of renal tubule hyperplasia and adenoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity and carcinogenicity of hydroquinone in F344/N rats and B6C3F1 mice.

Toxicology and carcinogenesis studies were conducted by administering hydroquinone (more than 99% pure) by gavage to groups of F344/N rats and B6C3F1 mice of each sex for 14 days, 13 wk or 2 yr. 14-day studies were conducted by administering hydroquinone in corn oil to rats at doses ranging from 63 to 1000 mg/kg body weight and to mice at doses ranging from 31 to 500 mg/kg, 5 days/wk. In the 13-wk studies, doses for rats and mice ranged from 25 to 400 mg/kg. At those doses showing some indication of toxicity in the 14-day and 13-wk studies, the central nervous system, forestomach and liver were identified as target organs in both species and renal toxicity was observed in rats. Based on these results, 2-yr studies were conducted by administering 0, 25 or 50 mg hydroquinone/kg in deionized water by gavage to groups of 65 rats of each sex, 5 days/wk. Groups of 65 mice of each sex were given 0, 50 or 100 mg/kg on the same schedule. 10 rats and 10 mice from each group were killed and evaluated after 15 months. Mean body weights of high-dose male rats and high-dose mice were approx. 5-14% lower than those of controls during the second half of the study. No differences in survival were observed between dosed and control groups of rats or mice. Nearly all male rats and most female rats in all vehicle control and exposed groups had nephropathy, which was judged to be more severe in high-dose male rats. Hyperplasia of the renal pelvic transitional epithelium and renal cortical cysts were increased in male rats. Tubular cell hyperplasia of the kidney was seen in two high-dose male rats, and renal tubular adenomas were seen in 4/55 low-dose and 8/55 high-dose male rats; none was seen in vehicle controls or in female rats. Mononuclear cell leukaemia in female rats occurred with increased incidences in the dosed groups (vehicle control, 9/55; low dose, 15/55; high dose, 22/55). Compound-related lesions observed in the liver of high-dose male mice included anisokaryosis, syncytial alteration and basophilic foci. The incidences of hepatocellular neoplasms, primarily adenomas, were increased in dosed female mice (3/55; 16/55; 13/55). Follicular cell hyperplasia of the thyroid gland was increased in dosed mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of renal toxicity in F344 rats gavaged with mercuric chloride for 2 weeks, or 2, 4, 6, 15, and 24 months.

Both sexes of F344 rats were gavaged with maximal tolerated doses of mercuric chloride for periods from 2 wk to up to 2 yr to investigate chronic nephrotoxicity and potential carcinogenicity. The toxicity of mercuric chloride was excessive after 2 wk of exposure to doses ranging from 1.25 to 20 mg/kg, compromising renal function by selectively destroying cells of the proximal tubules, and eliciting marked elevations in urinary biomarker enzymes diagnostic for acute renal tubule necrosis. In the 2-wk studies, urinary alkaline phosphatase and aspartate amino-transferase were most sensitive to renal mercury toxicity among a panel of six enzymes, exhibiting twofold increases above controls at the 5.0 mg/kg dose, before changes in the other enzymes occurred. Urinary lactate dehydrogenase was the most responsive enzyme, with up to 11-fold increases in activity above controls. In response to mercuric chloride exposure of 5.0 mg/kg for 2-6 mo, the greatest and most persistent increases in elevation of urinary enzyme activities were exhibited by alkaline phosphatase and gamma-glutamyl transferase, which increased two-to threefold above controls. At this interval, the maximal severity of the renal lesions in both sexes of rats was graded as minimal to mild. Beyond 6 mo none of the urinary enzymes measured in this study was adequate as biomarkers of nephrotoxicity, although the severity of the renal lesions had progressed. Mercury accumulated in a dose-related fashion primarily in the kidney, and to a lesser extent in the liver. The severity of the renal lesions was increased by continued exposure to mercuric chloride, as tissue concentrations of mercury rose in proportion to dose. Mercuric chloride treatment for 2 yr clearly exacerbated the severity of the spontaneous nephrotoxicity prevalent in aging F344 rats. The excessive mortality that occurred in the male rats was probably due to a combination of these factors. No renal tumors were detected in rats, possibly because the potential for their development was reduced; however, direct tissue contact with mercury induced squamous-cell papillomas of the forestomach in both sexes.

Toxicity of monochloroacetic acid administered by gavage to F344 rats and B6C3F1 mice for up to 13 weeks.

Groups of 20 rats and 20 mice of each sex were administered monochloroacetic acid (MCAA) once daily, 5 days per week, in water by gavage for up to 13 weeks. Doses used were 0, 30, 60, 90, 120, or 150 mg/kg for rats and 0, 25, 50, 100, 150, or 200 mg/kg for mice. Compound-related deaths occurred at the four highest dose levels in rats and at the highest dose level in mice. Mean body weights of treated groups of rats and mice surviving until the end of the study were similar to those of the controls. A dose-related increase in blood urea nitrogen, alanine aminotransferase, aspartate aminotransferase, as well as a dose-related increase in the relative liver and kidney weights was observed in rats but not in mice. A dose-related increase in the incidence and severity of cardiomyopathy occurred in rats. This lesion may be related to the inhibition of heart mitochondrial aconitase activity. No compound-related lesions were observed in mice. The results of this study indicate that F344 rats are more sensitive than B6C3F1 mice; sexes within the species were equally sensitive. The no-observable-effect level was estimated as 30 mg MCAA/kg body weight for rats and 100 mg MCAA/kg body weight for mice.

Comparative toxicity and carcinogenicity studies of tetracycline and oxytetracycline in rats and mice.

Two-year toxicity and carcinogenicity studies of oxytetracycline hydrochloride and tetracycline hydrochloride, two structurally similar and widely used antibiotics, were performed in F344/N rats and B6C3F1 mice. Rats and mice were continuously exposed via their diet to the following levels of antibiotic: oxytetracycline HCl--rats 0, 25,000, or 50,000 ppm; mice 0,6,300, or 12,500 ppm; tetracycline HCl--rats and mice 0, 12,500, or 25,000 ppm. On a milligram per kilogram of body weight basis these exposures represent doses that are 20 to 140 times daily human therapeutic doses. Dose-related increased survival was noted among oxytetracycline-treated male rats and tetracycline-treated female rats and male mice, while treatment-related reduced body weight gain occurred in oxytetracycline- and tetracycline-treated mice. Microscopic changes included fatty metamorphosis and focal cellular change in livers of oxytetracycline-treated male rats and basophilic cytoplasmic and clear cell change in livers of tetracycline-treated male rats. The only neoplastic changes were a marginally increased trend in pheochromocytoma of the adrenal medulla (equivocal evidence only) among oxytetracycline-exposed male rats (12/50 controls, 19/50 low dose, 24/50 high dose) and an increased incidence of pituitary adenoma or adenocarcinoma among high-dose oxytetracycline-treated female rats (20/50 controls, 32/50 high dose). Although oxytetracycline and tetracycline appeared to increase the incidence of pituitary hyperplasia in high-dose male and female rats, respectively, the total incidence of proliferative changes (hyperplasia, adenoma, and adenocarcinoma) was not affected by antibiotic exposure. The results from these studies therefore support the notion that neither antibiotic is carcinogenic in rodents. There were several negative trends suggesting possible protective effects by both these tetracycline analogs against certain spontaneous neoplastic and non-neoplastic changes.

Results and conclusions of the National Toxicology Program's rodent carcinogenicity studies with sodium fluoride.

The US National Toxicology Program (NTP) has conducted toxicity and carcinogenicity studies with sodium fluoride administered in the drinking water to F344/N rats and B6C3F1 mice. The drinking water concentrations used in the 2-year studies were 0, 25, 100, or 175 ppm sodium fluoride (equivalent to 0, 11, 45 or 79 ppm fluoride). Survival and weight gains of rats and mice were not affected by fluoride treatment. Animals receiving sodium fluoride developed effects typical of dental fluorosis, and female rats given 175 ppm had increased osteosclerosis. There were no increases in neoplasms in female rats or in male or female mice that were attributed to sodium fluoride administration. There was equivocal evidence of carcinogenic activity of sodium fluoride in male rats based on the occurrence of a small number of osteosarcomas in treated animals.

Decreases in spontaneous tumors in rats and mice after treatment with amphetamine.

Toxicology and carcinogenesis studies of dl-amphetamine sulfate, a drug used in the treatment of weight control, narcolepsy, and behavioral syndromes in children, were performed in F344/N rats and B6C3F1 mice. In these studies, amphetamine was administered for 2 years at doses of 0, 20, or 100 ppm in the feed to groups of 50 animals/dose/sex/species. The average amount of amphetamine consumed per day was estimated to be 1 or 5 mg/kg for low or high dose rats, 4 or 30 mg/kg for low or high dose male mice, and 3 or 19 mg/kg for low or high dose female mice. Survival was similar in dosed and control groups. The most notable effect of long-term treatment with this drug was the reduction of body weight in comparison to controls, and reduction in spontaneous tumors including pheochromocytomas of the adrenal gland in male rats, fibroadenomas of the mammary gland in female rats, adenomas of the anterior pituitary gland in male and female rats and female mice, endometrial stromal polyps of the uterus of female rats, adenomas or carcinomas of the liver in male and female mice, adenomas of the Harderian gland in male and female mice, and adenomas or carcinomas of the lung in male and female mice. Decreases in spontaneous tumors have previously been seen in 2-year rodent studies in groups of animals that have a reduced body weight in comparison to controls, but the spectrum of reduction in spontaneous neoplasms after treatment with amphetamine is broader than has previously been observed.

Tumors of the skin in the HRA/Skh mouse after treatment with 8-methoxypsoralen and UVA radiation.

8-Methoxypsoralen (8-MOP) with and without UVA radiation was administered to HRA/Skh mice (36 animals per treatment group) three times a week in the feed for a total dose of 9-80 mg/kg/week for 52 weeks. Most of the animals at the top dose of 8-MOP with UVA radiation had developed skin toxicity and/or skin tumors by 52 weeks. The skin lesions seen after treatment with 8-MOP and UVA radiation were characterized as squamous cell hyperplasia, squamous cell papilloma, and squamous cell carcinoma and are similar to what has been reported in humans after exposure to 8-MOP and UVA. Squamous cell hyperplasia and acute inflammation of the cornea were also seen in some of the treated female mice. Oral administration of 8-MOP and UVA did not result in a carcinogenic response to other organ systems. There were no increases in skin neoplasms after 8-MOP or UVA radiation alone. 8-MOP given in combination with UVA was carcinogenic to the skin of mice at dose levels similar to those used to treat psoriasis in humans.

Neurotoxicity and carcinogenicity of N-methylolacrylamide in F344 rats and B6C3F1 mice.

Toxicology and carcinogenicity studies of N-methylolacrylamide were conducted by administering the chemical by gavage in water to both sexes of F344/N rats and B6C3F1 mice 5 times per week for 16 d, 13 wk, or 2 yr. In 16-d studies, rats receiving doses of 200 mg/kg or higher and mice receiving 400 mg/kg died. In 13-wk studies, all rats given 100 mg/kg or higher doses died. Rats receiving 50 mg/kg or higher doses developed hindlimb ataxia progressing to paralysis. In neurobehavioral assessments, decreased forelimb and hindlimb grip strength occurred in rats at doses as low as 12.5 mg/kg. Landing footspread was also increased in dosed rats compared to controls. Axon filament and myelin sheath degeneration in the spinal cord and/or peripheral nerves occurred in rats receiving doses of 25 mg/kg or higher. Necrosis in the granular cell layer of the cerebellum was seen in rats given 200 mg/kg. Mice receiving 200 mg/kg in 13-wk studies died. Decreased grip strength was noted in mice at doses as low as 25 mg/kg, and rotarod performance was also affected by N-methylolacrylamide administration, but no neuropathology was seen microscopically. Testicular weights were decreased at doses as low as 12.5 mg/kg, and hepatocellular necrosis, thymic lymphocyte necrosis, and hemorrhage, necrosis, and mineralization of the zona reticularis of the adrenal gland were seen in mice that died (200 mg/kg). In 2-yr studies, survival and weight gains in male and female rats receiving doses of 6 or 12 mg/kg/d were minimally affected. No biologically important clinical signs or neoplastic or nonneoplastic lesions were attributed to N-methylolacrylamide administration to rats, suggesting that higher doses could have been tolerated. In mice, survival was not different between dosed and control groups (0, 25, or 50 mg/kg/d). Body weights were higher by as much as 25% in dosed compared to control groups. No compound-related clinical signs were observed, but increases in neoplasms of the harderian gland, liver, and lung were clearly related to chemical administration in both sexes of mice. Benign granulosa-cell neoplasms of the ovary were also increased in dosed female mice.