NTP Toxicology and Carcinogenesis Studies of Oxymetholone (CAS NO. 434-07-1) in F344/N Rats and Toxicology Studies of Oxymetholone in B6C3F1 Mice (Gavage Studies).
Oxymetholone is a synthetic anabolic steroid used to treat a variety of conditions, including hypogonadism and delayed puberty. It is also used to correct hereditary angioneurotic edema, manage carcinoma of the breast, promote a positive nitrogen balance following injury or surgery, and stimulate erythropoiesis. Considerable amounts of androgens are consumed by athletes in attempts to improve athletic performance. The National Institute of Environmental Health Sciences and the National Cancer Institute nominated oxymetholone for study based on its extensive illicit pharmaceutical use and the limited evidence that it is a potential human carcinogen. Male and female F344/N rats received oxymetholone (greater than 99% pure) in 0.5% methylcellulose by gavage for 16 days, 14 weeks, or 2 years, and male and female B6C3F1 mice received oxymetholone in 0.5% methylcellulose by gavage for 16 days or 14 weeks. Genetic toxicology studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, and mouse peripheral blood erythrocytes. 16-DAY STUDY IN RATS: Groups of five male and five female F344/N rats were administered 0, 160, 315, 625, 1,250, or 2,500 mg oxymetholone/kg body weight in 0.5% methylcellulose by gavage for 16 days. All male rats survived to the end of the study; one 2,500 mg/kg female died on day 14. The mean body weights of all dosed groups of males were significantly less than those of the vehicle controls, while those of 160 and 315 mg/kg females were significantly greater. 16-DAY STUDY IN MICE: Groups of five male and five female B6C3F1 mice were administered 0, 320, 630, 1,250, 2,500, or 5,000 mg/kg in 0.5% methylcellulose by gavage for 16 days. All mice survived to the end of the study. The final mean body weights of all dosed groups of females were greater than those of the vehicle controls. 14-WEEK STUDY IN RATS: Groups of 10 male and 10 female F344/N rats were administered 0, 80, 160, 315, 625, or 1,250 mg/kg in 0.5% methylcellulose by gavage for 14 weeks. One male rat each in the 625 and 1,250 mg/kg groups died before the end of the study. The mean body weights of males administered 160 mg/kg or greater were significantly less than those of the vehicle controls; in contrast, the mean body weights of all dosed groups of females were significantly greater. A dose-related erythrocytosis, evidenced by increases in erythrocyte counts, total hemoglobin concentrations, and hematocrit values, occurred in dosed groups of rats at week 14. A dose-related hypocholesterolemia occurred at all time points in all dosed groups of rats. Dose- and time-related decreases in 5 -nucleotidase activity occurred in treated rats. There was a transient, treatment-related increase in the activity of alanine aminotransferase in males and females. For male rats administered oxymetholone, cauda epididymis, epididymis, and testis weights and spermatid counts and total spermatid heads per testis were significantly less than those of the vehicle controls, and total spermatid heads per gram testis were significantly greater. Female rats in the 80 mg/kg group spent more time in diestrus and less time in estrus than did the vehicle controls. Kidney weights of males and females and liver and uterus weights of females were increased compared to vehicle controls in rats that received 315 mg/kg or greater; thymus weights of males and females and sartorius muscle and testis weights of males were less. Compared to the vehicle controls, rats that received 160 mg/kg or greater had increased incidences of nonneoplastic lesions of the kidney and mammary gland, and the incidences of hydrometra of the uterus and dysgenesis of the ovary were increased in dosed groups of females. Female rats administered 315 mg/kg or greater had increased incidences of cytoplasmic vacuolization of the adrenal gland and myocardial degeneration of the heart. The severities of these lesions generally increased with increasing dose. 14-WEEK STUDY IN MICE: Groups of 10 male and 10 female B6C3F1 mice were administered 0, 160, 320, 630, 1,250, or 2,500 mg/kged 0, 160, 320, 630, 1,250, or 2,500 mg/kg in 0.5% methylcellulose by gavage for 14 weeks. All mice administered oxymetholone survived until the end of the study. The mean body weights of all dosed groups were similar to those of the vehicle controls. The percentages of motile sperm in 1,250 and 2,500 mg/kg males were significantly less than those of the vehicle controls. The estrous cycle lengths of 630, 1,250, and 2,500 mg/kg females were significantly longer, and females in the 1,250 and 2,500 mg/kg groups spent more time in diestrus and less time in estrus. Kidney and liver weights of males and females were greater and thymus weights of females were less than those of the vehicle controls. All dosed females had hyperplasia of the clitoral gland, metaplasia of the parietal layer epithelium of the Bowman's capsule in the kidney, and cytoplasmic alteration of the submandibular gland; these lesions were not observed in the vehicle control group. The incidences of hypoplasia of the ovary in 320 mg/kg or greater females and of parotid gland atrophy in 1,250 and 2,500 mg/kg females were increased. The results of the 14-week oral gavage studies were generally similar in rats and mice, but rats were much more sensitive to oxymetholone. Because it was not likely that a long-term mouse study would provide significant additional toxicity information, the NTP decided to conduct a 2-year study in rats only. 2-YEAR STUDY IN RATS: Groups of 90 male F344/N rats were administered 0, 3, 30, or 150 mg/kg in 0.5% methylcellulose by gavage, and 90 female F344/N rats were administered 0, 3, 30, or 100 mg/kg in 0.5% methylcellulose by gavage for up to 104 weeks, with 9 or 10 rats per group evaluated at 3, 6, 12, or 18 months. Survival and Body Weights: Survival of all dosed groups was similar to that of the vehicle controls. The mean body weights of the 30 mg/kg male group were generally within 10% of those of the vehicle controls, but those of the 150 mg/kg group were markedly decreased. Mean body weights of 3 and 30 mg/kg females were generally greater than those of the vehicle controls throughout the study. Determinations of Oxymetholone in Plasma: The concentrations of oxymetholone in plasma of male and female rats receiving 3 mg/kg for 6, 12, or 18 months were generally below the limits of quantification; therefore, all plasma concentrations in the 3 mg/kg group are considered to be estimates (Table 8). The plasma concentrations at 30 mg/kg were approximately one order of magnitude greater than those of the estimates for males and females receiving 3 mg/kg. There were no dose-related differences in plasma concentrations in female rats receiving 30 or 100 mg/kg, but plasma concentrations in males were significantly elevated in the 150 mg/kg group. It was concluded that oxymetholone kinetics was saturated at 30 mg/kg in female but not male rats. Pathology Findings: A wide spectrum of neoplasms and nonneoplastic lesions was seen in rats administered oxymetholone for 2 years. The incidences of hepatocellular adenoma and hepatocellular adenoma or carcinoma (combined) were significantly increased in 100 mg/kg females as were the incidences of basophilic and clear cell foci in 150 mg/kg males and 100 mg/kg females compared to vehicle controls. The incidences of alveolar/bronchiolar adenoma and adenoma or carcinoma (combined) were significantly increased in 30 mg/kg females. The incidences of mineralization in the lung of 150 mg/kg males and 30 and 100 mg/kg females were significantly increased. The incidence of keratoacanthoma was increased in 30 mg/kg females, and the combined incidence of squamous cell papilloma, keratoacanthoma, basal cell adenoma, squamous cell carcinoma, or carcinoma of the sweat gland was significantly increased in 100 mg/kg females. The incidences of subcutaneous tissue fibroma and fibroma or fibrosarcoma (combined) were significantly increased in 3 mg/kg males. At 2 years, the incidences of benign pheochromocytoma and benign or malignant pheochromocytoma (combined) of the adrenal gland in 150 mg/kg males and medullary hyperplasia in 100 mg/kg females were significantly increased. The incidences of cytoplasmic vacuolization of adrenal cortical cells were significantly increased in 30 and 150 mg/kg males at 18 months and 2 years and in 100 mg/kg females beginning at 12 months and in 30 mg/kg females at 2 years. The incidences of renal tubule adenoma in 3 and 150 mg/kg males were slightly increased. An extended evaluation of the kidney was conducted, and additional incidences of renal tubule adenoma were observed in step sections in vehicle control and dosed male rats. The combined single- and step-section incidence of renal tubule adenoma was significantly increased in 3 mg/kg males. The incidences of nephropathy were significantly increased in 30 and 150 mg/kg males at 2 years and in 100 mg/kg females beginning at 3 months. The severities of nephropathy were significantly increased in dosed groups of males at 2 years and in 100 mg/kg females at 18 months and 2 years. The incidences of mineralization of the kidney were significantly increased in 150 mg/kg males at all time points. The incidences of ovarian dysgenesis were significantly increased in 100 mg/kg females beginning at 3 months and in 30 mg/kg females beginning at 6 months, and severities increased with increasing dose. The incidences of chronic myocardial degeneration (cardiomyopathy) were significantly increased in 100 mg/kg females at 6 months and 2 years and the severity was increased at 2 years. The incidences of lobular hyperplasia were increased in 150 mg/kg males at 18 months and 2 years and in 30 and 100 mg/kg females at all time points. The incidences of seminiferous tubule degeneration were significantly increased in 30 and 150 mg/kg males at 2 years, and the incidences of mineralization of the testis were increased in 150 mg/kg males at 12 months and in 30 mg/kg males at 18 months and at 2 years. Decreased incidences of neoplasms occurred in male and female rats. The incidence of uterine stromal polyp or stromal sarcoma (combined) was significantly decreased in 100 mg/kg females at 2 years. The incidences of mammary gland fibroadenoma and fibroadenoma or carcinoma (combined) were significantly decreased in all dosed groups of females. The incidences of pituitary gland pars distalis adenoma were significantly decreased in 30 and 100 mg/kg females at 2 years. The incidences of testicular interstitial cell adenoma were significantly decreased in 30 and 150 mg/kg males at 18 months and in all dosed groups at 12 months and 2 years. The incidences of mononuclear cell leukemia were significantly decreased in 30 and 150 mg/kg males and 100 mg/kg females at 2 years. GENETIC TOXICOLOGY: Oxymetholone was not mutagenic in S. typhimurium strain TA97, TA98, TA100, or TA1535, with or without S9 metabolic activation. It did not induce chromosomal aberrations in cultured Chinese hamster ovary cells, with or without S9, and no increase in the frequency of micronucleated normochromatic erythrocytes was noted in peripheral blood samples from male or female mice treated for 14 weeks with oxymetholone. CONCLUSIONS: Under the conditions of this 2-year gavage study, there was equivocal evidence of carcinogenic activity of oxymetholone in male F344/N rats based on increased incidences of subcutaneous tissue fibromas and fibromas or fibrosarcomas (combined) of the skin, variably increased incidences of benign and benign or malignant pheochromocytomas (combined) of the adrenal gland, and increased incidences of renal tubule adenomas. There was clear evidence of carcinogenic activity of oxymetholone in female F344/N rats based on increased incidences of hepatocellular neoplasms. Increased incidences of alveolar/bronchiolar neoplasms and skin neoplasms in female rats were also related to oxymetholone administration. Decreased incidences of alveolar/bronchiolar neoplasms and testicular interstitial cell adenomas in males; uterine stromal polyps or stromal sarcomas (combined), mammary gland neoplasms, and pituitary gland pars distalis adenomas in females; and mononuclear cell leukemia in males and females were related to oxymetholone administration. In addition, gavage administration of oxymetholone to male and female F344/N rats resulted in a spectrum of nonneoplastic effects frequently reported with administration of synthetic anabolic androgens. Synonyms: Adroidin; anadroyd; anasteron; anasteronal; anasterone; androstan-3-one, androstano[2,3-c]1,2,5-oxadiazol-17-ol, 17-methyl-, (5-a,17-b)-; becorel; 4,5-dihydro-2-hydroxymethylene-17-a-methyltestosterone; dynasten; HMD; 17b-hydroxy-2- (hydroxymethyl)-17-methyl-5-a-androstan-3-one; 17-hydroxy-2-(hydroxymethylene)-17-methyl-(5-a,17-b)-; 17-hydroxy- 2-(hydroxymethylene)-17-methyl-5-a-17-b-androst-3-one; 17b-hydroxy-2-(hydroxymethylene)-17-a-methyl-5-a-androstan-3-one; 17b-hydroxy-2-(hydroxymethylene)-17-methyl-5a-androstan-3-one; 17-hydroxy-2-(hydroxymethylene)-17-methyl-5-a-17- b-androstan-3-one; 17b-hydroxy-2-hydroxymethylene-17a-methyl-3-androstanone; 2-hydroxymethylene-17-a-methyl-5- a-androstan-17-b-ol-3-one; 2-hydroxymethylene-17a-methyl dihydrotestosterone; 2-hydroxymethylene-17-a-methyl-17-b- hydroxy-3-androstanone; methabol; 17a-methyl-2-hydroxymethylene-17-hydroxy-5-a-androstan-3-one; oximetholonum; oximetolona; oxitosona-50; oxymethenolone; roboral; zenalosyn Trade names: Adroyd; Anadrol; Anapolon; Anapolon 50; Nastenon; Pardroyd; Pavisoid; Plenastril; Protanabol; Synasteron