DMBA Carcinogenesis Research Articles

Low-Level X-Radiation Effects on Functional Vascular Changes in Syrian Hamster Cheek Pouch Epithelium during Hydrocarbon Carcinogenesis

Effects of repeated low-level X radiation on functional microvascular changes in hamster cheek pouch epithelium during and following carcinogenesis by 7,12-dimethylbenz[a]anthracene (DMBA) were studied. Prior studies showed enhancement of such carcinogenesis by repeated 20 rad head and neck X-radiation exposures, and it was proposed that one possible mechanism was radiogenic alteration of the functional microvasculature in a manner which favored subsequent tumor development. Hamsters were treated with either radiation, DMBA, radiation + DMBA, or no treatment. Animals were sacrificed at 3-week intervals from 0 to 39 weeks after treatments began. Pouch vascular volume and permeability changes were studied by fractional distributions of radiotracers and were analyzed by a variety of statistical methods which explored the vascular parameters, treatment types, elapsed time, presence of the carcinogen, and histopathologic changes. All treatments resulted in significant changes in vascular volume with time, while only DMBA treatments alone resulted in significant changes in vascular permeability with time. Prior to the appearances of frank neoplasms, volumetric changes in DMBA only and radiation only groups were similar, while volume changes in DMBA + radiation groups increased slowly to a peak later than in other groups and then declined steadily to levels similar to the radiation only group. As in prior studies, there were significant vascular volume differences between DMBA and DMBA + radiation groups of tumor-bearing cheek pouches. DMBA maxima were significantly higher than those of DMBA + radiation. Radiation significantly affected DMBA-associated vascular volume and permeability changes during carcinogenesis. Several possible explanations for the relationship of these changes to the enhancement of DMBA carcinogenesis include: radiation blocking normal capillary proliferative and/or dilatory responses to inflammation secondary to neoplastic changes; radiation-induced focal increases in the pericapillary connective tissue histohematic barrier, stimulating angiogenesis but reducing nutrient diffusion; radiation exposures sensitizing vascular endothelium to subsequent angiogenic stimulation from premalignant tissues; DMBA vascular and epithelial effects partially or completely blocking radiation effects on epithelial and/or endothelial cells; and radiation damage to vessel walls partially or fully inhibiting normal physiologic mechanisms of repairing DMBA damage to the vessels.

Effects of Dietary Lipid Saturation on Prolactin Secretion, Carcinogen Metabolism and Mammary Carcinogenesis in Rats

Isoenergetic diets containing 20% corn oil, 20% beef tallow, or an equal mixture of 10% corn oil and 10% beef tallow (mixed fat) were fed to 30 rats per diet for 28 weeks following weaning. DMBA [7,12-dimethylbenz(a)anthracene] was administered (1.75 mg/100 g body weight) in a single oral dose after 4 weeks of feeding. After 28 weeks, 70% of the rats fed corn oil had mammary tumors versus 47% for mixed fat and 30% for tallow. Diet had no effect on the number of tumors per tumor-bearing rat or the proportion of tumors that were adenocarcinomas. Other rats assigned to each of the three diets were killed at the time corresponding to DMBA administration for examination of hepatic mixed-function oxidase activity. NADPH cytochrome c reductase activity and cytochrome P-450 content were higher in rats fed corn oil or mixed fat rather than tallow. However, no significant differences in aryl hydrocarbon hydroxylase, glutathione transferase, and uridine-diphosphoglucuronide transferase activities were observed. The effects of dietary fat saturation on enzyme activity failed to show a clear association with DMBA carcinogenesis. In other rats assigned to the three dietary treatments for 4 or 16 weeks, lipid saturation did not change serum prolactin (PRL) concentrations during diestrus or proestrus. PRL secretion was examined following a provocative stimulus (perphenazine) in rats fed the experimental diets for 4 or 10–22 weeks. Although perphenazine increased serum PRL and depleted the pituitary of PRL, differences in dietary lipid saturation caused no significant changes in these indices. These data show that the incidence of mammary tumors in rats fed high fat diets (20% by weight) was greater in those fed corn oil compared to beef tallow. The effect of dietary lipid source on tumorigenesis was not associated with changes in carcinogen-metabolizing enzyme activity or PRL secretion.

Interactions between 7,12-Dimethylbenz(a)anthracene (DMBA) and Repeated Low-Level X Radiation in Hamster Cheek Pouch Carcinogenesis: Dependence on the Relative Timing of DMBA and Radiation Treatments

peated Low-Level X Radiation in Hamster Cheek Pouch Carcinogenesis: Dependence on the Relative Timing of DMBA and Radiation Treatments. Radiat. Res. 90, 155-164 (1982). Low-level X radiation was shown to enhance Syrian hamster cheek pouch carcinogenesis by 7,12-dimethylbenz(a)anthracene (DMBA) when radiation was administered concurrently with and following DMBA applications. We studied the effects of altering the timing of radiation and DMBA applications on this enhancement. DMBA in mineral oil was applied twice weekly for 10 weeks and 20 R head and neck X radiation once weekly for 17 weeks. In duplicate studies, animals received radiation, DMBA, or DMBA plus X radiation. In the DMBA plus X-ray group, there were 9 weeks of preirradiation and 7 weeks of concurrent treatments. Radiation alone did not result in any histologically detectable changes. In one study, preirradiation may have reduced the carcinogenic activity of DMBA, while in the second study there were no significant differences in tumor incidences between X radiation plus DMBA and DMBA only groups. Thus, while repeated 20-R X-ray exposures during and following DMBA applications enhance DMBA carcinogenesis, identical X-ray exposures prior to and during DMBA applications appear either to slightly inhibit or to have no appreciable effect on DMBA carcinogenesis.

Quantitative studies of hemidesmosomes during progressive DMBA carcinogenesis in hamster cheek-pouch mucosa.

The present study was designed to establish whether there are changes in hemidesmosomal distribution during defined stages of chemical carcinogenesis in hamster cheek-pouch epithelium. 0.5% DMBA in liquid paraffin was applied thrice weekly to hamster pouches and tissue samples were obtained at regular intervals and assigned to hyperplastic, dysplastic and carcinomatous groups on the basis of histological criteria. Untreated pouches served as controls. Following a strict sampling regime, electron micrographs were obtained from the epithelial-connective tissue junction and, using stereological intersection counting, the relative surface area of basal plasma membrane (BPM) occupied by hemidesmosomes was estimated. In normal epithelium 40% of the BPM is occupied by hemidesmosomes. During carcinogenesis, values decrease progressively and significantly to 35% in hyperplasia, 28% in dysplasia and 13% in carcinoma. A decrease in the relative area of hemidesmosomes would therefore appear to contribute to the increased motility of epithelial cells during a connective-tissue invasion and cellular metastasis.

Inhibition of DMBA carcinogenesis of hamster buccal pouch by phenanthrene and dimethylnaphthalene.

Phenanthrene (Phe) and to a lesser degree 1,4-dimethylnaphthalene (DMeN) were each found to retard the development of epidermoid carcinomas in hamster buccal pouch induced by the thrice weekly application of a 0.5 per cent solution of 7,12-dimethylbenz[a]anthracene (DMBA) in heavy mineral oil.

Inhibition of hamster buccal pouch carcinogenesis by 13-cis-retinoic acid.

Sixty-four male and female Syrian hamsters, 3 months of age and weighing 90 to 120 grams, were divided into four equal experimental groups. In animals of Groups 1 and 2 the left buccal pouch was painted three times weekly with a 0.5% solution of DMBA in heavy mineral oil. Group 2 animals also received 10 mg. of 13-cis-retinoic acid in peanut oil administered orally twice a week by pipette. Carcinogen retinoid were administered on alternate days. Group 3 animals served as controls, receiving only 13-cis-retinoic acid. Group 4 animals served as untreated controls. Four animals in each group (two males and two females) were killed at 10, 12, 14, and 16 weeks. The Group 2 animals, which received 13-cis-retinoic acid, exhibited a significant delay in DMBA carcinogenesis of buccal pouch mucosa, as studied both grossly and histologically. Both groups eventually demonstrated well-differentiated epidermoid carcinomas, but the tumors were smaller in the DMBA-retinoid animals.

Induction of mouse epidermal ornithine decarboxylase activity and skin tumors by 7,12-dimethylben.

Application of a single large dose (3.6 micromol) or smaller weekly repeated doses (0.2 micromol) of 7,12-dimethylbenz[a]anthracene (DMBA) to the skin of CD-1 mice led to a 20 to 50-fold increase in epidermal ornithine decarboxylase (ODC) (EC 4.1.1.17) activity as well as tumor formation. Retinoic acid (0.17-68 nmol), a potent inhibitor of both the induction of ODC activity and tumor formation by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), failed to inhibit both the induction of ODC activity and tumor formation by DMBA. In contrast, 7,8-benzoflavone (367 nmol), which did not inhibit the induction of ODC activity by TPA, effectively inhibited the induction of ODC activity as well as the formation of skin tumors caused by DMBA. These results indicate that (a) the mechanism of the induction of ODC activity and tumor formation by a complete carcinogen appears to be different from that of the tumor promoter TPA, (b) DMBA-induced ODC activity may be an important component of the mechanism of DMBA carcinogenesis, and (c) the protective effect of retinoic acid on skin carcinogenesis is not universal; it inhibits skin tumor formation by some agents and not by others.

Influence of surface lipids on skin carcinogenesis in rats.

Skin tumours were indeuced in female Wistar SPF-rats by different polycyclic aromatic hydrocarbons, benzo[alpha]pyrene (BP), dibenz[alpha, h]anthracene (DBA), 7,12-dimethylbenz]alpha]anthracene (DMBA), and 3-methylcholanthrene (MCA) being applied on the dorsal skin of 20 rats each. DBA was not carcinogenic under the experimental conditions. DMBA proved the most potent carcinogen, and MCA was more potent than BP. Half of the animals in each group underwent skin-surface lipid extraction (SSLE) before the application of carcinogen. SSLE did not influence the cumulative number of rats with skin tumours during an observation period of 15 months nor the type of tumours induced. The lipid extraction, however, increased the latency period and decreased the rate of tumour development when BP and MCA acted as carcinogens. On the contrary, SSLE enhanced the rate of tumour production by DMBA and reduced the latency period. The role of sebum and its composition in skin carcinogenesis is discussed, and an explanation of the different influence of SSLE on BP and MCA carcinogenesis is discussed, and and explanation of the different influence of SSLE on BP and MCA carcinogenesis in contrast to DMBA carcinogenesis is sought in differences in metabolic activation of the carcinogens.

Effect of Age of Non-Skin Tissues on Susceptibility of Skin Grafts to 7,12-Dimethylbenz[ a ]anthracene (DMBA) Carcinogenesis in BALB/c Mice, and Effect of Age of Skin Graft on Susceptibility of Surrounding Recipient Skin to DMBA 2

The influence of age-dependent alterations in non-skin tissues on chemical carcinogen-induced skin papilloma development was studied by treatment with 7,12-dimethylbenz[alpha]anthracene (DMBA) of 4-month-old skin grafts sewed onto 4- and 20-month-old syngeneic recipients. Skin of 4- and 20-month-old BALB/c female mice differed in susceptibility to DMBA carcinogenesis, but the 4-month-old grafts showed the same papilloma incidence independent of the age of the recipient mice. In a different experiment, the influence of age of skin grafts on papilloma development on DMBA-treated recipient skin was studied. Fourteen- and 26-month-old skin grafts were carried by 14-month-old recipients. Grafts of those two ages are known to differ in susceptibility to DMBA carcinogenesis, but no effect of the grafts on papilloma development on DMBA-treated recipients was detectable. It was concluded that certain age-dependent differences in skin susceptibility to chemical carcinogens are solely a reflection of alterations in the skin at the site of carcinogen treatment.

Immunological phenomena in harmless mice during experimental carcinogenesis induced with long-term topical application of 7, 12-dimethylbenzanthracene (DMBA)

To estimate the influence of topical treatment with DMBA and induced tumors on delayed hypersensitivity, the response of spleen lymphocytes to PHA in vitro and macrophage migration inhibition with PHA were studied in DMBA-treated hairless mice. DNA synthesis and blastic transformation of cultured lymphocytes decreased after 6-12 weeks of DMBA application. Lymphocyte response to PHA gradually diminished during the experiment, as compared with control animals. Since the malignant transformation of skin tumors was not observed before 16 weeks of DMBA carcinogenesis, it seems that derangements in cellular immunity preceded the malignant proliferation. The increase in spleen weight and the absence of PHA-induced inhibition of macrophage migration in hairless mice with malignant tumors may also be related to the influence of the tumor itself on the lymphatic system of experimental animals.

Aging increases susceptibility of mouse skin to DMBA carcinogenesis independent of general immune status.

The dependence of chemical carcinogenesis on age of target tissue was studied by repeated DMBA-treatment of mouse skin grafted from old and young syngeneic donors to young recipients. Carcinomas developed on 39 percent (1.6/41) of grafts from old donors and on 12 percent (5/41) of grafts from young donors. The incidence of nonskin lymphoid tumors was highest in male recipients bearing grafts from old donors.

Suppression by Vitamins D<sub>2</sub> and D<sub>3 </sub>of Hamster Cheek Pouch Carcinoma Induced with 9,10-Dimethyl-1,2-benzanthracene

Local application of vitamins D<sub>2</sub> and D<sub>3</sub> caused inhibition of tumor formation in the hamster cheek pouch, induced by topical treatment with DMBA. These results and data from the literature are used in an attempt to explain the mechanism of carcinogenesis by DMBA, and the inhibition of this process by vitamin D. In tumor cells the amount of alkaline phosphatase and the amount of calcium bound to the cell membrane are both decreased. It is probable that the protein molecule alkaline phosphatase can also act as calcium binding protein. The decreased amount of calcium bound to the membrane of tumor cells leads to increased permeability, with an increased and less controlled flow of metabolites to and from the cytoplasm, resulting in a decreased control of the mitotic process. Vitamins D cause induction of the synthesis of alkaline phosphatase/calcium binding protein, and this may explain the marked inhibition of DMBA carcinogenesis in animals treated simultaneously with DMBA and vitamin D. This effect of vitamin D is probably not specific, and there are indications that other substances which cause induction of alkaline phosphatase also inhibit tumor formation.