Long term tumorigenicity of a single application of indomethacin or Amuno in adolescent and in adult male Sprague Dawley rats.

200 adolescent (Group I) and 200 adult male Sprague Dawley rats (Group II) were divided into 4 subgroups of 50 animals each. Animals were treated on the 29th (Group I) or 98th day of life (Group II) either with acetone or Amuno carrier in acetone or Amuno on acetone (2.5 mg indomethacin/100 g animal weight in acetone) or with the pure substance indomethacin 2.

Comparison of S-phase fractions measured by flow cytometry and autoradiography in human transplant tumors.

The 3H-thymidine labeling index (TLI) and the percentage of cells in the S-phase have been determined by autoradiography and by flow cytometry, (FCM), respectively, in six malignant tumors of human origin transplanted on athymic nude mice. The Dean and Jett model and the graphical model were used to determine the percent of S-phase cells by FCM. Cell cycle analysis was performed using 1) no correction for background; 2) an algebraic function for background correction; and 3) an exponential function for background subtraction.

Benzoyl peroxide promotes the formation of melanotic tumors in the skin of 7,12-dimethylbenz[a]anthracene-initiated Syrian golden hamsters.

A two-stage carcinogenesis experiment was performed in Syrian golden hamsters using a single intragastric initiation with 10 mg/kg body weight of 7,12-dimethylbenz[a]anthracene (DMBA) and repetitive topical promotion on the back skin with two different doses (80 and 160 mg, respectively) of benzoyl peroxide in 1 ml acetone. Benzoyl peroxide was administered three times per week over a period of 16 months. The treatment with benzoyl peroxide alone leads to both a generalized hyperpigmentation and skin scaling without formation of any tumors.

Inhibition of the prenatal dimethylbenz[a]anthracene-induced tumour initiation in mice by prior administration of 7,8-benzoflavone.

7,8-Benzoflavone (BF) was applied orally via stomach tube in doses of 50, 100, 200 and 400 mg/kg body weight to pregnant NMRI mice on the 18th day of gestation. BF application was followed 1 h later by oral administration of 60 mg/kg body weight dimethylbenz[a]anthracene (DMBA). As a rule this dose of DMBA does not lead to prenatal secondary effects and is not carcinogenic to either the mother animals or the F1 generation.

Three-stage tumorigenesis in mouse skin: DNA synthesis as a prerequisite for the conversion stage induced by TPA prior to initiation.

Recent evidence shows that stage I of tumor promotion in NMRI-mouse skin induced by a single dose of 12-O-tetradecanoylphorbol-13-acetate (TPA) can be effected not only after initiation by 7,12-dimethylbenz[a]anthracene (DMBA) but also several weeks prior to initiation. In view of this partial inversion of the initiation-promotion sequence we proposed to replace the term 'stage I of promotion' by the term 'conversion'. The convertogenic effectivity of a single dose of TPA applied after DMBA can be suppressed in a rather characteristic and non-toxic fashion by hydroxyurea (HU).

Suppression of the first stage of phorbol 12-tetradecanoate 13-acetate-effected tumor promotion in mouse skin by nontoxic inhibition of DNA synthesis.

In order to evaluate the significance of epidermal cell proliferation for the first stage of skin tumor promotion, the effect of hydroxyurea (HU), an inhibitor of DNA synthesis, on tumor formation was studied. Mice initiated with 7,12-dimethylbenz[a]anthracene received a single dose of phorbol 12-myristate 13-acetate (PMA) in stage I of promotion, followed by twice weekly application of the irritant skin mitogen phorbol 12-retinoate 13-acetate in stage II. A single dose of HU given intraperitoneally at different times before or after treatment with PMA was found to interfere with tumor formation, exhibiting an almost complete inhibition if administered 18 hr after PMA--i.

Skin tumor formation in the European hamster (Cricetus cricetus L.) after topical initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA).

Initiation with the carcinogen 7,12-dimethylbenz[a]anthracene followed by promotion with the hyperplasiogenic phorbol ester 12-O-tetradecanoylphorbol-13-acetate carried out on the dorsal skin of European hamsters (Cricetus cricetus L.) led to the formation of a broad spectrum of skin tumors in terms of a two-stage principle. Tumor formation involved the epidermis and its appendages, the connective tissue, and the vascular and pigmentary system.

Interaction of phorbol derivatives with replicating cells.

The significance of the interaction of phorbol derivatives with replicating cells has been studied in HeLa cells and in tumour promotion experiments. Dose-response relationships for the radiomimetic activity of phorbol derivatives in HeLa cells (Kinzel et al., 1980) were obtained by analysis of the degree of transient blockage in G2 phase of the cell cycle.

On the persistence of tumor initiation in two-stage carcinogenesis on mouse skin.

The persistence of the initiated state during two-step carcinogenesis in mouse epidermis is a generally accepted phenomenon, however, conflicting results exist with regard to the degree of irreversibility relative to the age of the animals. Several factors such as age-dependent alterations in the response of the epidermis to the promoter and skin damage following the initiation step have been proposed to account for the observed discrepancies. In the present investigation we have tried to circumvent skin-damaging effects of topically applied 7,12-dimethylbenz[a]anthracene by intragastric administration of the drug.

Effect of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate and its nonpromoting analogue 4-O-methyl-TPA on dorsal dermal melanocytes of the Syrian golden hamster (Mesocricetus auratus).

The effect of the tumor promoter TPA and its inactive structural analogue 4-O-methyl-TPA on the induction of dorsal skin melanosis in the normal Syrian golden hamster and on the promotion of melanomas in DMBA-initiated animals was investigated. Both phenomena were observed in TPA-treated hamsters but could not be detected after exposure of animals to 4-O-methyl-TPA. In contrast to results obtained with a variety of other laboratory animals, neither TPA nor 4-O-methyl-TPA were able to induce epidermal hyperplasia of hamster dorsal skin.

Tumor initiation by 7,12-dimethylbenz[a]anthracene in dermal melanocytes of hamster: inhibition through 7,8-benzoflavone.

Initiation of dermal melanocytes by 7,12-dimethylbenz[a]-anthracene (DMBA) in the dorsal skin of Syrian golden hamsters was investigated for its sensitivity to inhibition by 7,8-benzoflavone (BF). Initiation was carried out by a single intragastric application of DMBA (50 mg/kg body weight) and melanoma development pursued with or without subsequent promotion through repeated topical administration of 12-O-tetradecanoylphorbol-13-acetate (40 nmol/animal, 3 X weekly). A single intragastric application of BF (200 mg/kg body weight) 2 h prior to DMBA resulted in a suppression of melanoma yields by approximately 70%.

7,12-Dimethylbenz[a]anthracene/12-O-tetradecanoyl-phorbol-13-acetate-mediated skin tumor initiation and promotion in male Sprague-Dawley rats.

In contrast to a previous report by Shubik and in accordance with a pilot study from our laboratory with female rats, the 2-stage skin carcinogenesis experiment could be successfully accomplished in male Sprague-Dawley rats. Male animals of this species are better suited for this long-term experiment since, under the conditions used, females are very sensitive to mammary gland tumor formation and show a drastically reduced survival time. A broad spectrum of tumors of epidermal origin could be induced by topical initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetra-decanoyl-phorbol-13-acetate (TPA) as promoter.

Diaplacental initiation of NMRI mice with 7,12-dimethylbenz[a]anthracene during gestation days 6--20 and postnatal treatment of the F1-generation with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate: tumor incidence in organs other than the skin.

The tumor spectrum and tumor incidence in organs other than the skin were investigated in the 12-O-tetradecanoylphorbol-13-acetate (TPA) treated F 1-generation of 13 groups of NMRI mice which had been initiated by a single intragastric dose of 7,12-dimethylbenz[a]anthracene during days 6, 8, and 10--20 of pregnancy. Promotion by topical application of TPA to the back skin was carried out twice per week 12 weeks after birth over a period of 26 weeks. The forestomach epithelium represented the only organ in which statistically significant 2-stage carcinogenesis could be demonstrated.

Two-stage skin carcinogenesis by systemic initiation of pregnant mice with 7,12-dimethylbenz(a)anthracene during gestation days 6-20 and postnatal promotion of the F 1-generation with the phorbol ester 12-tetradecanoylphorbol-13-acetate.

The DMBA-TPA-mediated two-stage skin carcinogenesis experiment was modified in that pregnant mice were systemically treated once during pregnancy with the carcinogen. Intragastric application times were fetal days 6, 8, and 10-20. A control group of pregnant mice received repeated doses (from days 8-20) of sesame oil, which was used as a solvent for DMBA.

Systemic two-stage carcinogenesis in the epithelium of the forestomach of mice using 7,12-dimethylbenz(a)anthracene as initiator and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate as promoter.

In a modified two-stage carcinogenesis experiment, the effectiveness of the initiator 7,12-dimethylbenz(a)anthracene (DMBA) and the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in the epithelium of the forestomach of the mouse has been investigated. Fifty mice were treated intragastrically with a single dose of DMBA (50 mg/kg body weight), followed by repeated intragastric administration of TPA (10 mg/kg body weight) over a period of 35 weeks. In comparison with the corresponding control groups (no treatment, DMBA initiation only, and TPA treatment only), the initiated and promoted group clearly showed the highest tumor incidence in the target organ (45 tumor-bearing animals of 50 animals).

Transmaternal modification of the Berenblum/Mottram experiment in mice.

The classical 2-stage carcinogenesis experiment has been modified in that the carcinogen DMBA was applied to pregnant mother animals at different dose levels and different time intervals during pregnancy. Promotion with the phorbol ester TPA was performed as usual by application of the promoter on the back skin of mice of the F-1 generation. It can be shown that it is possible to initiate fetal epidermal cells by transmaternal route and to promote them to produce visible skin tumors post natum.

Diaplacental carcinogenesis: initiation with the carcinogens dimethylbenzanthracene (DMBA) and urethane during fetal life and postnatal promotion with the phorbol ester TPA in a modified 2-stage Berenblum/Mottram experiment.

Diaplacental initiation with the carcinogens DMBA or urethane followed by topical treatment of mice of F-1 generation with the tumor promotor TPA led to the formation of benign and malignant tumors on the back skin and also in various internal organs. (This system constitutes a modified 2-stage experiment based on the early schemes of Berenblum and Mottram.) Application of either the carcinogens or the tumor promoter alone did not lead to the formation of tumors within one year.

Transmaternal variation of the Berenblum experiment with NMRI-mice: tumour initiation with DMBA via mothers milk followed by promotion with the phorbol ester TPA.

DMBA which is applied transmaternally via the mothers milk can initiate tumour cells in the F-1 generation. Subsequent application of the tumour promoter TPA to the back skin of the young animals induced the formation of skin papillomas and carcinomas. Animals treated according to this scheme also developed malignant neoplasms in the other organs.

Improved tumour yields by means of a TPA-DMBA-TPA variation of the Berenrlum-Mottram experiment on the back skin of NMRI mice. The effect of stationary hyperplasia without inflammation.

Application of the phorbol ester TPA to the back skin of NMRI mice 14 times within a period of 7 weeks causes a stationary hyperplasia, with a corresponding increase in the labelling index of the basal cells from 1% to 14%. By initiation of skin, which has been pretreated with TPA in this way, with the carcinogen DMBA, followed by continued treatment with TPA (initiation-promotion corresponding to the classical Berenblum-Mottram experiment) the tumour yield (papillomas, carcinomas) is very much higher than that obtained using the scheme of the normal Berenblum-Mottram experiment. The preliminary induction of a stationary hyperplasia with high rates of nucleic acid synthesis must be considered an important co-factor in epidermal carcinogenesis.