Carcinogenesis in rats by nitrosodialkylureas containing methyl and ethyl groups given by gavage and in drinking water

The carcinogenic effects in male and female F344 rats of four nitrosodialkylureas containing methyl or ethyl groups have been compared by two modes of administration, gavage in oil solution or dissolved in drinking water. Weekly doses of 20 and 40 mumol were given to each rat by either route and treatment lasted usually 30 wk, resulting in a total dose per rat of 0.6 or 1.2 mmol. Nitrosodimethylurea and nitroso-1-methyl-3-ethylurea gave rise primarily to tumors of the nervous system, whereas nitrosodiethylurea and nitroso-1-ethyl-3-methylurea gave rise to tumors of the mammary gland, lung, intestinal tract, nervous system, and testicular mesotheliomas. The effect of nitrosodimethylurea was weaker than that of the other three compounds, as measured by rate of mortality with tumors. Drinking water treatment was less effective than treatment by gavage, by the same criterion. The tumorigenic effects paralleled those of the corresponding monoalkylnitrosourea, suggesting the presence in the target organs of receptors for which ethylnitrosoureas or methylnitrosoureas, respectively, have affinity.     

Carcinogenesis in rats by asymmetric nitrosamines containing an allyl group

Four asymmetric nitrosamines containing 1 allyl group were administered to rats in drinking water to aid in understanding the failure of nitrosodiallylamine ( NDAA ) to induce tumors in rats. Three of the compounds were given at equimolar doses, the fourth at somewhat lower dose. All four nitrosamines induced tumors of the esophagus and/or nasal cavity. Nitrosoallylethanolamine (NAE) induced a 30% incidence of hepatocellular carcinomas, while nitrosoallyl -2- hydroxypropylamine induced 70% hepatocellular carcinomas and a much lower dose of nitrosoallyl -2- oxopropylamine induced 80% of hepatocellular carcinomas, several of which metastasized. Nitrosoallyl -2,3- dihydroxypropylamine , which increased the mortality from tumors much more than the other compounds, failed to induce tumors in the liver, but induced a high incidence (85%) of tumors of the esophagus. The conclusion is that the allyl group is not metabolically inert, but that its presence in these molecules modifies their metabolism so as to give rise to tumors in a variety of organs. It does not seem that formation of an allylating agent is the common mechanism of carcinogenesis by these compounds.     

Carcinogenesis by nitrosobis-(2-oxopropyl)amine labeled with deuterium and by nitroso-2-hydroxypropyl-2-oxopropylamine in rats and hamsters

The effects of the labeling with deuterium of the alpha-methylene groups of the carcinogen nitrosobis-(2-oxopropyl)amine (NBOP) on its carcinogenic effectiveness in rats and hamsters have been studied. The greater strength of the C-D bond compared with the C-H bond often leads to slower metabolism and lesser carcinogenic activity. When NBOP and NBOP-d4 were given to male and female rats in drinking water at equimolar doses, the mortality rate from tumors was lower in the rats given the deuterium-labeled compound, although the results were statistically significant (P = 0.012) only in males. The incidences of tumors of several groups was similar for NBOP and NBOP-d4, but there was a marked difference between males and females, females having a high incidence of liver tumors, and males very few. When NBOP and NBOP-d4 were given by gavage to rats or Syrian hamsters at identical doses there was no difference in rate of mortality from tumors, or in the pattern of tumors induced by either compound. In rats, both compounds were given at two dose rates, and in neither was a difference seen. To complement the studies with NBOP, a normal reduction product formed metabolically in vivo, nitroso-(2-hydroxypropyl) (2-oxopropyl)amine (NHPOP) was administered to rats in drinking water at the same dose rate. In male rats, the mortality rate was lower with NHPOP than with NBOP, while with female rats the opposite was the case (P less than 0.01 in both cases) and there was little difference in the pattern of tumors induced in either sex. NHPOP appears to have a quite distinct carcinogenic effect from NBOP, suggesting that the metabolic conversion of one to the other does not play a large role. The weak deuterium-isotope effect of NBOP-d4 given to rats in drinking water, but not detected in rats or hamsters treated by gavage, suggests that alpha-oxidation of NBOP is not likely to be a rate-limiting step in carcinogenesis by NBOP.     

Carcinogenicity of nitrosothiomorpholine and 1-nitrosopiperazine in rats

Summary Two cyclic nitrosamines, nitrosothiomorpholine and 1-nitrosopiperazine, have been tested by long term feeding to rats in drinking water, at 50 mg/l and 200 mg/l. Nitrosothiomorpholine produced tumors, both benign and malignant, of the esophagus and tongue. Nitrosopiperazine appeared to be definitely tumorigenic, although it showed no selectivity of site for tumor induction and induced tumors in a wide range of organs and tissues. Nitrosopiperazine was very much less acutely toxic than dinitrosopiperazine.

---

Carcinogene Wirkung von Nitrosothiomorpholine und 1-Nitrosopiperazine bei Ratten

Zusammenfassung Zwei cyclische Nitrosamine, nitroso-thiomorpholine und 1-Nitrosopiperazine, wurden Ratten in Langzeit-Versuchen im Trinkwasser appliziert (50 mg/l bzw. 200 mg/l). Nitroso-thiomorpholine führte zu benignen und malignen Tumoren des Oesophagus und der Zunge. Nitroso-pieerazine zeigte ebenfalls tumorigene Wirkung für eine große Zahl von Organen und Geweben, allerdings keine Organ-Spezifität. Nitroso-piperazine erwies sich als von sehr viel geringerer akuter Toxicität als Dinitroso-piperazin.

---

---

This investigation was supported by Contract # 43-68-959 from the National Cancer Institute, U.S.P.H.S.

---

We wish to thank Miss P. Johns, Mrs. J. Stroud for skilled technical assistance.     

Carcinogenicity of methylated derivatives of N-nitrosodiethylamine and related compounds in Sprague-Dawley rats.

Five nitrosamines, which can be considered alkyl derivatives of N-nitrosodiethylamine, were tested for carcinogenicity by administration to Sprague-Dawley rats in drinking water at approximately equimolar concentrations. N-Nitrosodi-n-propylamine was a potent carcinogen but less so than N-nitrosodiethylamine and gave the same spectrum of tumors. N-Nitrosodiisopropylamine was very much weaker than N-nitrosodiethylamine and induced only tumors of the nasal turbinates in significant incidence. At the doses given, neither N-nitrosodiisobutylamine nor N-nitrosodi-sec-butylamine was significantly carcinogenic. In contrast, the cyclic nitrosamine N-nitrosohexamethyleneimine was equally potent with N-nitrosodiethylamine and gave the same spectrum of tumors in liver, esophagus, and nasal turbinates. The results support the concept that oxidation at the alpha carbon atom of nitrosamines is a significant step in carcinogenesis.     

Relative carcinogenic effectiveness of derivatives of nitrosodiethylamine in rats

The carcinogenicity of five derivatives of nitrosodiethylamine was compared with that of the parent compound by p.o. administration to rats. All were less potent than was nitrosodiethylamine. When nitrosobis(2-methoxyethyl)amine and nitrosobis(2-ethoxyethyl)amine were administered at equimolar doses in drinking water, there was a high incidence of liver tumors, but the animals died later than they did after nitrosodiethylamine treatment, which also induced esophageal tumors. Nitrosoiminodipropionitrile and nitrosobis(2,2-diethoxyethyl)amine failed to induce tumors at the same dose level. Nitrosobis(2-chloroethyl)amine was administered in oil by gavage at a dose lower than that of nitrosodiethylamine and produced a much weaker tumor response; 5 of 15 treated rats had forestomach papillomas, and 1 had olfactory adenocarcinoma and no other induced tumors.     

Similar carcinogenic effects in rats of 1-ethyl-1-nitroso-3-hydroxyethylurea and 1-hydroxyethyl-1-nitroso-3-ethylurea

The two isomeric N-nitroso derivatives of the dialkylurea, 1-ethyl-3-(2-hydroxyethyl)urea,were given by gavage to 20 male F344 rats for 30 weeks at equimolardoses. The tumorigenic responses were compared with those toa similar dose of nitrosoethylurea or nitroso-2-hydroxyethylurea.Each of the nitrosomonoalkylureas caused death from tumors morerapidly than the analogous nitrosodialkylurea. Each of the nitrosodialkylureasinduced a broader spectrum of tumors in the rats than did eithernitrosoethylurea or nitroso-2-hydroxyethylurea, including neoplasmsof the thyroid, lung, skin, colon, mesotheliomas and neoplasmsof the brain and liver in high incidence, the last two of whichwere not seen in animals given the nitrosomonoalkylureas. Onthe other hand, there were fewer tumors of the forestomach inrats given the nitrosodialkylureas than with the nitrosomo-noalkylureas.The major difference between 1-nitroso-1-eth-yl-3-hydroxyethylureaand 1-nitroso-1-hydroxyethyl-3-ethyl- urea was that the formerinduced only neoplastic nodules in the,liver of 30% of the rats,while the latter induced hepatocellular carcinomas in 55% ofthe rats; approximately half of the rats given either compoundhad brain neoplasms, which included astrocytomas, gliomas andoligoden drogliomas.