Showing papers on "7,12-Dimethylbenz[a]anthracene published in 2001"

NAD(P)H : quinone Oxidoreductase 1 Deficiency and Increased Susceptibility to 7,12-Dimethylbenz[a]-anthracene-Induced Carcinogenesis in Mouse Skin

Abstract: BACKGROUND The phase II enzyme NAD(P)H :quinone oxidoreductase 1 (NQO1) catalyzes quinone detoxification, protecting cells from redox cycling, oxidative stress, mutagenicity, and cytotoxicity induced by quinones and its precursors. We have used NQO1(-/-) C57BL/6 mice to show that NQO1 protects them from skin cancer induced by the polycyclic aromatic hydrocarbon benzo[a]pyrene. Herein, we used NQO1(-/-) mice to investigate whether NQO1 also protects them against 7,12-dimethylbenz[a]anthracene (DMBA), where methyl substituents diminish primary quinone formation. METHODS Dorsal skin of NQO1(-/-) or wild-type C57BL/6 mice was shaved. When tested as a complete carcinogen, DMBA (500 or 750 microg in 100 microL of acetone) alone was applied to the shaved area. When tested as a tumor initiator, DMBA (200 or 400 nmol in 100 microL of acetone) was applied to the shaved area; 1 week later, twice-weekly applications of phorbol 12-myristate 13-acetate (PMA)-10 microg dissolved in 200 microL of acetone-to the same area began and were continued for 20 weeks. Tumor development was monitored in all mice (12-15 per group). All statistical tests were two-sided. RESULTS When DMBA (750 microg) was tested as a complete carcinogen, about 50% of the DMBA-treated NQO1(-/-) mice but no DMBA-treated wild-type mouse developed skin tumors. When DMBA (both concentrations) was used as a tumor initiator, NQO1(-/-) mice developed larger tumors at a greater frequency than their wild-type littermates. Twenty-three weeks after the first PMA treatment in the tumor initiator test, all 30 NQO1(-/-) mice given 400 nmol of DMBA had developed skin tumors, compared with 33% (10 of 30) of treated wild-type mice (P<.001). CONCLUSIONS NQO1(-/-) mice are more susceptible to DMBA-induced skin cancer than are their wild-type littermates, suggesting that NQO1 may protect cells from DMBA carcinogenesis.

Lack of promotion of 7,12-dimethylbenz[a]anthracene-initiated mouse skin carcinogenesis by 1.5 GHz electromagnetic near fields.

Abstract: The effects of 1.5 GHz electromagnetic near fields of time division multiple access (TDMA) signal for the Personal Digital Cellular, Japanese cellular telephone standard (PDC) used for cellular phones, on mouse skin carcinogenesis initiated by 7,12-dimethylbenz[a]anthracene (DMBA) were examined. Ten-week-old ICR female mice were treated with a single application of DMBA on shaved dorsal skin by painting at a concentration of 100 microg/100 microl acetone per mouse. One week later, mice were divided into four groups, receiving electromagnetic near fields exposure (DMBA-EMF), sham-exposure (DMBA-Sham), 12-O-tetradecanoylphorbol-13-acetate (TPA, 4 microg /200 microl acetone/mouse), as a positive control (DMBA-TPA), and no-treatment (DMBA-Control). EMF near fields exposure conditions were as follows: skin local peak specific absorption rate (SAR) 2.0 W/kg, whole body average SAR 0.084 W/kg (ratio of peak to average SAR is 24), 90 min a day, 5 days a week, for 19 weeks. At week 20, animals were killed and skin tumors were analyzed histopathologically. The incidences of skin tumors in DMBA-EMF, DMBA-Sham, DMBA-TPA and DMBA-Control groups were 0/48 (0%), 0/48 (0%), 29/30 (96.6%) and 1/30 (3.3%), respectively. Histopathologically, papilloma and squamous cell carcinoma (SCC) were observed in the DMBA-TPA group and only papilloma observed in the DMBA-Control group. The incidences of squamous cell papillomas and squamous cell carcinomas in DMBA-TPA and DMBA-Control groups were 29/30 (96.6%) and 1/30 (3.3%), respectively, numbers of tumors per mouse (tumor multiplicity) being 18.8 +/- 13.4 and 0.1 +/- 0.5. These data clearly demonstrated that near fields exposure to 1.5 GHz EMF, used for cellular phones, does not exert any enhancing effect on skin tumorigenesis initiated by DMBA.

Protective effect of Picroliv, the active constituent of Picrorhiza kurroa, against chemical carcinogenesis in mice.

Abstract: Cancer chemoprevention of chemically induced tumours by Picroliv, an iridoid glycoside mixture purified from Picrorhiza kurroa, was studied on 20-methylcholanthrene (20-MC)-induced sarcoma model and 7,12-dimethylbenz[a]anthracene (DMBA)-initiated papilloma formation in BALB/c mice. Administration of Picroliv (100 and 200 mg/kg, p.o) inhibited the sarcoma development by 47 and 53% as estimated on day 200 after 20-MC administration. Control animals started dying of tumour burden 76 days after 20-MC administration and all animals were dead by day 170, while 60 and 66% of the animals survived in the Picroliv treated group, 100 and 200 mg/kg, respectively. Picroliv exhibited anti-tumour-promoting activity on a two-stage carcinogenesis test on mouse skin using DMBA as an initiator and croton oil as a promoter. Topical application of Picroliv (1 and 5 mg/mouse) 30 minutes prior to that of croton oil application resulted in a 50 and 60% reduction in the number of animals that developed papillomas, and 48 and 64% reduction in the number of papillomas per mouse. There was also a delay in the onset of first skin tumour in the group of animals treated with Picroliv. Oral administration of Picroliv (150 mg/kg, p.o.) prior to DMBA application delayed the onset of papillomas and the percent of mice (60%) with tumours indicates that Picroliv inhibited the tumour initiation induced by DMBA. Picroliv administration was also found to increase the life span of transplanted Dalton's Lymphoma Ascites (DLA) and Ehrlich Ascites Carcinoma (EAC) harboring mice and reduced the volume of transplanted solid tumours.

S-Allylcysteine, a Garlic Constituent, Inhibits 7,12-Dimethylbenz[a]Anthracene-Induced Hamster Buccal Pouch Carcinogenesis

Abstract: The effect of S-allylcysteine (SAC), a water-soluble garlic constituent, on 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch (HBP) carcinogenesis was investigated in male Syrian hamstes. Forty hamsters were divided into 4 groups of 10 animals. The right buccal pouches of the animals in Group I were painted with a 0.5% solution of DMBA in liquid paraffin three times a week. The animals in Group II were painted with DMBA as in Group I and, in addition, received 200 mg/kg body wt p.o. SAC three times a week on days alternate to DMBA application. Group III animals received SAC as in Group II. Group IV animals received neither DMBA nor SAC and served as the control. The hamsters were killed after an experimental period of 14 wk. Measurement of lipid peroxidation, the antioxidant enzymes superoxide dismutase (SOD) and catalase, in the buccal pouch mucosa, liver, and circulation was used to monitor the chemopreventive potential of SAC. All hamsters painted with DMBA alone developed tumors identified histologically as well-differentiated squamous cell carcinomas. In hamsters bearing DMBA-induced buccal pouch tumors, diminished lipid peroxidation in the tumor tissue was accompanied by decreased activities of SOD and catalase, whereas in the liver and circulation, enhanced lipid peroxidation was associated with compromised antioxidant defenses. Administration of SAC suppressed the incidence of DMBA-induced HBP tumors as revealed by the absence of carcinomas. Histologically, only keratosis was observed. SAC modulated DMBA-induced decreased susceptibility of the HBP to lipid peroxidation while simultaneously enhancing SOD and catalase activities, whereas in the liver and circulation, SAC decreased the extent of lipid peroxidation and significantly enhanced antioxidant activities. We suggest that SAC exerts its chemopreventive effects by modulating lipid peroxidation and enhancing antioxidant activities in the target organ as well as in the liver and circulation.

Mechanistic studies on the inhibitory action of dietary dibenzoylmethane, a beta-diketone analogue of curcumin, on 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis.

Abstract: Dietary factors play important roles in the carcinogenic process. The results of epidemiological data and some laboratory animal studies indicate that certain naturally occurring and synthetic components are able to block the carcinogenic process and inhibit the development of certain cancers. Dibenzoylmethane (DBM), a curcumin-related beta-diketone analogue has been reported to exhibit a remarkable inhibitory effect on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumorigenesis in Sencar mice. The present study investigated the possible mechanisms of inhibitory action of DBM on DMBA-induced mammary tumorigenesis in mice. The summarized results indicate that: (1) in in-vitro studies. DBM inhibited DMBA metabolism and the formation of DMBA-DNA adducts in a dose-dependent manner; (2) in the assay of competitive binding to estrogen receptors with [3H]-estradiol in vitro, DBM showed weak binding affinity; (3) in vivo, feeding of 1% DBM in the diet of immature Sencar mice for 4 -5 weeks decreased the uterine and parametrial fat pad weights, and lowered the serum estrogen and triglyceride levels. This study provides insight into the mechanisms involved in the inhibitory action of DBM in mouse mammary tumorigenesis.

Influence of dietary antioxidants on the mutagenicity of 7,12-dimethylbenz[a]anthracene and bleomycin in female rats.

Abstract: Studies on agents that modulate carcinogen-induced genotoxic effects in experimental animals provide end points that can be used for assessing the antimutagenic or anticarcinogenic properties of putative chemopreventive compounds and for predicting their protective efficacy in humans. In this study, we investigated the ability of the dietary antioxidant Vitamins C, E, beta-carotene and the mineral selenium to inhibit the mutant frequency (MF) induced by treatment of rats with 7,12-dimethylbenz[a]anthracene (DMBA), a mammary carcinogen and bleomycin (BLM), an anti-tumor agent that can damage DNA by free radical mechanisms. Both chemicals have been previously shown to be mutagenic in the rat lymphocyte Hprt assay. Adult female Fischer 344 rats were given the antioxidants singly or in a combination 2 weeks prior to mutagen treatment. Antioxidant intake continued for an additional 4 weeks post-mutagen treatment. At sacrifice, spleens were aseptically removed for the isolation of lymphocytes to conduct the mutagenesis assay at the Hprt locus. The DMBA and BLM treatment induced a marked increase in MF, 52.8 x 10(-6) and 19.2 x 10(-6), respectively, over the controls. The MFs seen in the individual antioxidants alone (single or mixture) were relatively similar to the controls, with the exception of Vitamins C and E, that had 1.7- and 1.5-fold increase, respectively. The degree of inhibitory response was dependent on the type of mutagen and the particular antioxidant. BLM/antioxidant combination had inhibitions ranging from 44 to 80%, while DMBA/antioxidant system ranged from 60 to 93%, with Vitamins C and E achieving the highest inhibition in both systems. The mixture displayed low inhibitory responses, 44.6% for BLM/mix and 47% DMBA/mix. On the whole, the results indicate that the dietary constituents tested are antimutagenic; however, because of the gradations seen with the responses, the protective efficacy of these antioxidants may depend on the type of mutagen/carcinogen they encounter. Pending molecular analysis of mitochondrial DNA mutations will also indicate whether there is a shift in the mutational spectra produced by the carcinogens in the presence of antioxidants.

Analysis of c-Ha-ras gene mutations in skin tumors induced in carcinogenesis-susceptible and carcinogenesis-resistant mice by different two-stage protocols or tumor promoter alone.

Abstract: In the present study we describe the molecular analysis of c-Ha-ras gene mutations in 47 papillomas and 17 carcinomas developed in two lines of mice, carcinogenesis-susceptible (Car-S) and carcinogenesis-resistant (Car-R), selectively bred for extreme susceptibility or resistance to chemical skin carcinogenesis initiated and promoted with different doses of 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). This study also presents the analysis of c-Ha-ras gene mutations in 22 papillomas and 22 carcinomas in Car-S mice initiated with DMBA and promoted with benzoyl peroxide (BzPo) and in seven papillomas and one carcinoma from a group of uniniated Car-S mice that received only BzPo treatment. The data showed that a A(182)-->T transversion in the c-Ha-ras gene was present in 100% and 81% of the skin tumors developed in Car-S and Car-R mice, respectively, after DMBA initiation and TPA promotion, suggesting that differences in genetic susceptibility can influence the frequency of c-Ha-ras mutations in the skin tumors produced. The same A(182)-->T mutation with an incidence of 68% was found in papillomas from DMBA-initiated and BzPo-promoted Car-S mice. The difference in the mutation frequency between DMBA/BzPo and DMBA/TPA papillomas suggested that the promotion step contributes to the final mutation pattern. The tumor induction experiment with BzPo alone showed that this compound can induce tumor development in 26% of Car-S mice, and the molecular analysis of the tumors showed a broad mutation spectrum, including mutations in codons 12, 13, and 61 of the c-Ha-ras gene. Mol. Carcinog. 30:111-118, 2001.

Role of iron-dextran on 7,12-dimethylbenz(a) anthracene-initiated and croton oil-promoted cutaneous tumorigenesis in normal and pregnant mice.

Abstract: Skin chemical carcinogenesis has been divided into the process of initiation, promotion and progression. Earlier, we showed the role of iron overload in the promotion stage of skin carcinogenesis. In this communication, we report that iron overload does not augment croton oil-mediated tumor promotion in 7,12-dimethylbenz(a)anthracene (DMBA)-initiated pregnant mice skin tumorigenesis. Virgin female Swiss mice were given 1 mg iron/mouse/day parenterally for 2 weeks to induce iron overload. After the last injection, a group of mice was left with male mice for 10 days. These animals showed an increase in cutaneous iron concentration as compared to normal mice. Papillomas were induced in mice skin by a single topical application of DMBA as initiator. A week after the initiation, promoting agent, croton oil was applied twice per week for 20 weeks. The appearance of the first tumor (papilloma), number of tumors/mouse and percentage incidence were recorded. When compared to the iron unloaded control and iron overload pregnant groups, the iron overload virgin animals showed an increased incidence of tumors. In iron overload virgin animals, tumors appeared earlier and also the numbers of tumors/mouse were significantly higher. However, in iron overload pregnant animals, diminished tumor incidence was observed and the numbers of tumors matched the result of normal pregnant animals. Our results show that iron overload in pregnant mice does not participate in the augmentation of DMBA- and croton oil-induced skin tumorigenesis.

Effect of a combined administration of 5-fluorouracil and medroxyprogesterone acetate on pyrimidine nucleoside phosphorylases and thymidylate synthetase in 7,12-dimethylbenz[a]anthracene-induced rat mammary tumors

Abstract: The effect of a combined therapy of medroxyprogesterone acetate (MPA) and 5-fluorouracil (5-FU) on tumor size, pyrimidine nucleoside phosphorylase (PyNPase) activity, and thymidylate synthetase (TS) activity was examined in Sprague-Dawley (SD) rats with 7,12-dimethyl-benz[a]anthracene (DMBA)-induced mammary tumors. MPA augmented the antitumor activity of 5-FU and protected against body weight-loss due to 5-FU administration. PyNPase activity of both the MPA group and the MPA+5-FU group tended to increase compared with that of the 5-FU alone group. TS inhibition levels in the MPA+5-FU group tended to increase compared with those in the 5-FU alone group. These results indicate that MPA tended to augment antitumor activity of 5-FU and to reduce the side effects caused by 5-FU.

The comparative mutagenic action of 7,12- dimethylbenz(a)anthracene in the Armenian hamsters and mice

Abstract: he Armenian hamster (AH), Cricetulus migratorius, was first used in biomedical research by Yerganian and Papoyan (1). This rodent has a low diploid number of 22 chromosomes, like the Chinese hamster, and was analyzed using routine and differential staining (1,2). The AHs are successfully used in mutagenesis studies such as detection of reciprocal translocations in the germ cells (3), chromosomal aberrations induced by cyclophosphamide (CP) and thiotepa in bone marrow cells (4,5). These experiments show the increased resistance of AHs to clastogenic action of drugs and metaphase arresting ability of colchicine compared to mice, rats, guinea pigs and the Chinese hamsters. The aim of our work was to study comparative mutagenic action of strong rodent carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) in AHs and mice. The experiments were performed with AHs, trapped in the region of Yerevan (Armenia) and maintained in our animal room (20 male AHs, weighing 25 g). We used also 20 male random-bred albino mice (22 g b.w.) from animal room of Cancer Research Center, Yerevan (Armenia). The animals were maintained in our animal room on standard rodent diet (specific for each species) and water ad libitum. To study the comparative mutagenic action of DMBA (Fluka, Buchs, Switzerland), the carcinogen was dissolved in olive oil and was injected twice apart intraperitoneally into rodents at doses equal to 1/10 of LD50 (22 mg/kg and 40 mg/kg for mice and AHs, respectively) (6). As a negative control the vehicle of DMBA was used (olive oil). For positive control we used the CP (Mosmedpreparati, Russia) dissolved in saline and injected intraperitoneally at single dose of 25 mg/kg b.w. for mice, and 50 mg/kg for AHs. Bone marrow sampling was done 24 h after the last chemical agent injection and processed as described earlier (7). Slides were stained with acridine orange according to Tinwell and Ashby (8). We used the LM-4 fluorescence microscope (USSR) to observe the slides. Each slide was assessed for micronucleated (MN) polychromatic erythrocytes (PEs) among 1000 erythrocytes. In addition, the per cent content of PE was calculated. Statistical analysis was performed by using Student's t tests. The data concerning MN inducing action of DMBA are presented in Table 1.