Carcinogenic effect of N-butyl-N-nitrosourethan on CDF1 mice

Studies were made on the induction of tumors in mice by N-butyl-N-nitro-sourethan (BNUR), with the following results. 1) Oral administration of 0.04% BNUR in deionized water to CDF1 mice for 20 weeks produced papillomas in the esophagus and forestomach of all 58 mice, and 24 of the mice had squamous cell carcinoma. 2) No skin tumors developed when 0.1%, 0.5%, or 1% BNUR in acetone was painted on the skin on the back of CDF1 mice three times a week for 25 weeks. 3) No sarcomas developed within 30 weeks when a dose of 10, 60, or 120 mg/ml of BNUR in dimethyl sulfoxide solution was injected subcutaneously into the back of CDF1 mice, 10 times at 1-week intervals. 4) In the in vitro malignant transformation test, golden hamster lung fibroblast cells did not show malignant transformation during an observation period of 150 days after treatment with BNUR at a final concentration of 30 and 60 mug/ml for 24 hr. The carcinogenicity and possible mode of action of BNUR are discussed on the basis of these results.