Carcinogenesis Bioassay of 2-Biphenylamine Hydrochloride (CAS No. 2185-92-4) in F344/N Rats and B6C3F1 Mice (Feed Study).
2-Biphenylamine (2-aminobiphenyl) is a chemical intermediate used in the manufacture of C.I. Acid Red 15. It is present as a contaminant in 4-biphenylamine (a rubber antioxidant) and in diphenylamine (a dye intermediate, stabilizer for nitrocellulose explosives, and a topical agent for prevention of screwworm infestation in animals). Single-dose, 14-day, and 13-week studies were conducted using technical-grade 2-biphenylamine (2-aminobiphenyl) containing up to 2.5% of the carcinogenic contaminant, 4-biphenylamine. When the contamination was recognized, analytical development was begun to purify the material. The salt, 2-biphenylamine hydrochloride, was prepared to obtain a more pure test product, which contained 0.006%-0.049% 4-biphenylamine. The prechronic tests were completed by the time purification was accomplished, so data from a second 14-day study with 2-biphenylamine hydrochloride were used to help set dose levels for the chronic study. The results of the comparative 14-day studies showed that technical-grade 2-biphenylamine was more toxic to mice than rats than 2-biphenylamine hydrochloride as evidenced by greater incidence of splenomegaly and greater weight gain depression. The technical-grade 2-biphenylamine caused a dose-related decrease in hemoglobin concentration and a dose-related increase in leukocyte count in male and female mice in the 13-week study. Hemosiderosis, congestion, and extramedullary hematopoiesis were present in the spleens of nearly all rats receiving 3,000 ppm or more of the chemical, and in nearly all mice with 1,000 ppm or more 2-biphenylamine in their diets. The chronic study was conducted with the purified 2-biphenylamine hydrochloride by feeding diets containing 1,000 or 3,000 ppm 2-biphenylamine hydrochloride to groups of 49 or 50 F344/N rats and 50 B6C3F1 mice of each sex for 103 weeks. Groups of 50 rats and 50 mice of each sex served as controls. Survival of dosed male and female rats and dosed female mice was comparable with that of the corresponding controls. Survival of high-dose male mice was significantly (P<0.010) less than that of low-dose and control male mice. There were little or no differences in body weight changes for rats or mice between dosed and control groups, although there was a slight decrease in body weight gain at the end of the study for high-dose male (-11%) and female (-8%) rats. Inflammatory cells and interstitial fibrosis were found in increased incidence in the kidneys of dosed male rats as compared with controls and were considered to be compound related. In addition to the increase in renal inflammation and fibrosis, dosed male rats had more focal cellular changes of the liver than did the controls. There were no increased or decreased incidences of tumors in rats that could be associated with chemical administration. Myelomonocytic leukemia in male rats (control, 14/50; low-dose, 1/50; high-dose, 4/50) and fibroadenomas of the mammary gland in female rats (22/50, 10/49, 9/50) occurred with significantly (P<0.03) decreasing trends and the incidences in the dosed groups were significantly (P<0.02) lower than that in the controls. There were no increased or decreased incidences of tumors in rats that could be associated with chemical administration. Hemangiosarcomas from all sites occurred in female mice with a statistically significant (P</=0.002) positive trend. The observed incidence of hemangiosarcomas was 0/49, 1/50, and 7/50 in the control, low-dose, and high-dose groups, respectively. The incidence in the high-dose group was significantly (P<0.01) higher than that in controls. The conclusion that this was due to 2-biphenylamine rather than the contaminant, 4-biphenylamine, is supported by the absence of urinary bladder tumors, which are common to 4-biphenylamine. Hemangiosarcomas also occurred in male mice with a statistically significant positive trend (P=0.040 by a life table test), with incidences of 0/50, 2/50, and 3/50. None of the pairwise comparisons were statistically different. The development of hemangiosarcomas may have been curtailedment of hemangiosarcomas may have been curtailed in the high-dose group of male mice, since only 21/50 survived until the termination of the study. The hemangiosarcomas found in female mice are uncommon with only 6/816 (0.7&percnt;) previously seen in controls at the same laboratory. The rate for control male mice is equally low: 7/803 (0.9&percnt;). Alveolar/bronchiolar adenomas of the lung occurred at a significantly (P&lt;0.01) decreased rate in male mice with an incidence in dose groups lower (P&lt;0.05) than that in controls. Under the conditions of the bioassay, 2-biphenylamine hydrochloride was not carcinogenic for F344/N rats of either sex. 2-Biphenylamine hydrochloride was carcinogenic for B6C3F1 female mice, inducing hemangiosarcomas at various sites. The evidence for an association between the administration of 2-biphenylamine hydrochloride and the increased incidence of hemangiosarcomas in male mice was equivocal. Levels of Evidence of Carcinogenicity: Male Rats: Negative Female Rats: Negative Male Mice: Equivocal Female Mice: Positive