[Specific inhibition of nuclear DNA synthesis with carcinogens (autoradiography studies of a short-term test)]. / Spezifische Hemmung der nuklearen DNS-Synthese durch Karzinogene (Autoradiographische Studien zu einem Kurzzeittest).

Six suckling growing CBA mice 14 days old (5-6 g of body weight) of the same litter served as test animals in each experiment. 0.1 ml of the dissolved chemicals (15-30 per cent of the LD50 were applied by i.p. injection to 3 animals each (experiment) and an equal number of mice was treated with the solvent only (control). 15 hours later the animals were given a single i.p. injection of 3H thymidine (2 microCi/g body weight) and 50 min afterwards they were sacrificed for autopsy and preparation of autoradiographs. Autoradiographs of nuclei of renal tubular epithelia and of liver epithelium were examined by visual silver grain counting (150 nuclei in each experiment and the same number in the corresponding control). We could demonstrate that carcinogenic compounds of different chemical classes partially inhibit the nuclear incorporation of thymidine in a significant manner over a time period longer than 24 hours. This inhibition may be due as a consequence of a prolonged S phase, expressed as a decrease of the mean of silver grain number per nucleus in comparison with the unaltered control. This decrease is used as a criterion for the suppressive effect of carcinogenic substances on the nuclear DNA synthesis rate. Noncarcinogenic compounds did not show this effect.

The thymidine incorporation inhibiting screening system (TSS) to test carcinogenic substances (a nuclear DNA synthesis suppressive short term test).

Suckling mice of the same litter served as test animals. One half received the test substances by i.p-injection, the other half (control) was applied the solvent only. The suppressive effect of carcinogenic substances on nuclear DNA synthesis in tubular renal and in liver epithelia was ascertained in autoradiographs by silver grain counting. The decrease of the mean of silver grain number over the nucleus served as a criterion for the suspicion of carcinogenicity. Non carcinogenic chemicals did not causes this suppressive effect.

[Nuclear DNA synthesis rate and labelling index: effects of carcinogenic and non-carcinogenic chemicals on its behaviour in the organism of growing CBA-mice. The thymidine-incorporation-screening-system (TSS) (author's transl)]. / Kern-DNS-Syntheserate und Markierungsindex in ihrem Verhalten bei Einwirkung carcinogener und nichtcarcinogener Substanzen auf den Organismus wachsender CBA-Mäuse. Das Thymidineinbau-Screening-System (TSS).

During the last few decades there has been an extraordinary accumulation of man-made chemicals in the human environment. There is a growing consensus in oncology that a large proportion of human cancers are environmental in origin by exposure of man to such carcinogenic chemicals. These chemicals in the majority of all cases have not been tested to prove their carcinogenicity. Testing of new chemical compounds is needful prior to their introduction into commerce, foods, agriculture or the working places to prevent human cancer. To test such a large number of possibly carcinogenic chemicals, economical and rapidly practicable bioassays are necessary. In the following we compare some well known bioassays with our autoradiographic thymidine-incorporation-screening-system and other assays based on biochemical quantification of DNA synthesis as parameter for identification of carcinogenic substances. The partial inhibition of the whole DNA synthesis in a proliferating cell population after treatment with toxic and carcinogenic chemicals is an early common response especially in hepatectomized animal, livers caused by the effects of those substances. However, by quantitative evaluation of the nuclear DNA synthesis rate as a basic parameter using autoradiographs of kidney and liver of juvenile growing CBA-mice, it is possible to differentiate carcinogenic from non-carcinogenic chemicals by means of silver grain counting after 3H-TdR incorporation. Contrarily the "whole DNA synthesis" expressed by the percentual 3H-labelling index of kidney and liver did not permit such a differentiation in our experimental arrangement. We could demonstrate that carcinogenic compounds of different chemical classes partially inhibit the nuclear DNA synthesis rate significantly over a time period longer than 24 hours. The tested non-carcinogenic compounds did not show this suppressive effect on the nuclear DNA synthesis rate.

The autoradiographic pattern of DNA synthesis in Papova virus- and N-methyl-N-nitroso urea (MNU)-induced skin tumors of the Syrian hamster (Mesocricetus auratus).

In skin tumors induced in Syrian hamsters by Papova viruses or produced chemically by dripping of methylnitroso urea (MNU) the pattern of DNA synthesis was studied in vitro and in vivo by autoradiography. The greater part of DNA synthesis in the Papova tumor of the hamster is of cellular origin. Only the cells localized adjacent to keratinizing regions of the tumors may be considered as virus-infected with progressive maultiplication of viruses. This also applies to all nuclei with cellular DNA synthesis only in the marginal chromatin. Moreover viral DNA synthesis is supposed in the cytoplasm, too. In methylnitroso urea-induced squamous cell carcinoma labeled cells were likewise found adjacent to keratinizing tumor regions and the pattern of DNA synthesis is generally not limited to the "stratum basale". With increasing malignancy the pattern of DNA synthesis is changing also in chemically induced tumors and is no longer limited to the stratum basale where it still can be demonstrated in the papilloma.

Tumor-inducing effect of trinitroso-trimethylene-triamine (TTT) when orally applied in dimethylsulphoxide (DMSO) for solvent.

By oral application of TTT, disolved in concentrated DMSO, it was possible by means of a long-term experiment to produce tumors in female rats (Wistar strain). Contrary to all previous findings the tumor-inducing effect of this substance has been proved in this way for the first time.

The proliferative activity of the adrenal cortex as influenced by carcinogenic and noncarcinogenic substances.

A single oral toxic dose of carcinogens (N-nitrosomorpholine, aflatoxin B1, N--methyl-N-nitrosourea, urethan) causes a significant increase of the mitotic rate in the adrenal cortex 48 hours after application. Both, the control animals (water via stomach tube) and the animals treated with acetylsalicylic acid, arsenic, phenol and actinomycin D do not produce this effect. These findings confirm our previous results obtained by administration of acetylaminofluorene, diethylnitrosamine, dimethylnitrosamine and trinitroso-trimethylen-triamine. It is possible that the increased mitotic activity of the adrenal cortex is correlated with the substances applied.

Quantitative autoradiographic studies on the competition of diethylnitrosamine (DENA) and 9,10-dimethyl-1,2-benzanthracene (DMBA) in the liver cell of CBA-mice.

In CBA-mice the competition of DENA and DMBA was studied by quantitative autoradiography. During the precancerous phase in DENA-pretreated animals the rate of DMBA-incorporation into DNA/RNA and nuclear proteins was lower as compared to the controls without DENA-pretreatment. Independent of DENA-pretreatment the rate of DMBA-incorporation into the cytoplasm was significantly enhanced in hepatectomized animals. In this experiment the skin as a target organ did not show any quantitatively measurable DMBA-incorporation despite of prolonged autoradiographic exposition time.