Showing papers on "7,12-Dimethylbenz[a]anthracene published in 1989"

Caloric restriction and 7,12-dimethylbenz(a)anthracene-induced mammary tumor growth in rats: alterations in circulating insulin, insulin-like growth factors I and II, and epidermal growth factor.

Abstract: Caloric restriction (CR) inhibits many neoplastic diseases in rodents, yet the biochemical mechanism(s) for these effects are poorly understood. We have examined the effects of ad libitum (AL) feeding with 25 or 40% CR on the promotion of 7,12-dimethylbenz( a )anthracene-induced mammary tumorigenesis in virgin female Sprague-Dawley rats. Further, we have also studied the influence of chronic CR on temporal alterations in circulating insulin, insulin-like growth factor I/somatomedin C, insulin-like growth factor II/multiplication-stimulating activity, and epidermal growth factor levels at 0, 1, 3, 5, 11, and 20 weeks in carcinogen- and vehicle-treated animals. Tumor incidence and multiplicity were markedly inhibited ( P < 0.05) with increasing CR. Fasting serum insulin-like growth factor I/somatomedin C levels exhibited a significant acute decline with CR at 1 and 3 weeks, but were comparable to AL-fed controls throughout the remainder of the 5-month study, despite continued differences in weight gain between AL and CR rats. Levels of insulin-like growth factor II/multiplication-stimulating activity exhibited no discernible pattern in relation to CR. Serum insulin levels showed age-dependent increases, but were affected by increasing CR at all time points. Insulin levels were significantly ( P < 0.05) reduced in 40% CR rats from 3 weeks onward compared to controls, while 25% CR resulted in nonsignificant ( P < 0.07) reductions throughout the study. No significant differences in growth factor levels were observed between 7,12-dimethylbenz( a )anthracene- and vehicle-treated rats. Circulating epidermal growth factor was not detectable in any treatment group regardless of the nature or duration of the dietary regimen, time of blood collection, or subsequent tumor-bearing status. These data suggest that decreased serum insulin-like growth factor I/somatomedin C and insulin levels with CR and their complex interactions in vivo may play a role in the inhibition of mammary tumor promotion by CR.

Codon 61 mutations in the c-Harvey-ras gene in mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene plus okadaic acid class tumor promoters.

Abstract: Three okadaic acid class tumor promoters, okadaic acid, dinophysistoxin-1, and calyculin A, have potent tumor-promoting activity in two-stage carcinogenesis experiments on mouse skin. DNA isolated from tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) and each of these tumor promoters revealed the same mutation at the second nucleotide of codon 61 (CAA----CTA) in the c-Ha-ras gene, determined by the polymerase chain reaction procedure and DNA sequencing. Three potent 12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoters, TPA, teleocidin, and aplysiatoxin, showed the same effects. These results provide strong evidence that this mutation in the c-Ha-ras gene is due to a direct effect of DMBA rather than a selective effect of specific tumor promoters.

A comparison of the effects of the prostaglandin synthesis inhibitors indomethacin and carprofen on 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis in rats fed different amounts of essential fatty acid.

Abstract: The effects of the cyclooxygenase inhibitors indomethacin and carprofen on the enhancement of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis by dietary linoleate have been compared in female Sprague-Dawley rats. Indomethacin and carprofen, 0.004% and 0.02% (w/w) in the diet, respectively, were fed to rats receiving 20% fat diets containing 0.5, 4 or 12% linoleate starting 7 days after administration of 5 mg DMBA i.g. Indomethacin was shown to have a marked inhibitory effect on mammary tumorigenesis in rats fed the 4 and 12% linoleate diets, but did not alter tumorigenesis in rats fed the 0.5% linoleate diet. In contrast, carprofen was not inhibitory in any of these dietary groups, or in a separate experiment in which a 5% fat--3% linoleate diet was fed. The effect of each drug on prostaglandin E2 (PGE2) levels in normal mammary glands enriched in epithelial cells after a 3-week pretreatment with 17 beta-estradiol and progesterone was also investigated. Carprofen was shown to reduce PGE2 levels to a similar or greater extent than indomethacin at each level of linoleate in the diet. These data demonstrate that a reduction in PGE2 synthesis in the mammary epithelium does not correlate with inhibition of mammary tumorigenesis, and that other factors, including possible alterations in other products of the arachidonic acid cascade, are responsible for this inhibitory effect.

Inhibition of 7,12-dimethylbenz[a]anthracene-initiated and 12-O-tetradecanoylphorbol-13-acetate-promoted skin papilloma formation in mice by dehydroepiandrosterone and two synthetic analogs

Abstract: Previous work has demonstrated that the adrenal steroid, dehydroepiandrosterone (3-beta-hydroxy-5-androsten-17-one, DHEA), has broad spectrum tumor chemopreventive activity in laboratory mice and rats, inhibiting the development of spontaneous breast cancer and chemically induced tumors of the lung, colon, skin, thyroid and liver. DHEA treatment produces specific side-effects, including estrogenic and androgenic action and an increase in liver weight, which could limit its use as a cancer chemopreventive drug. It is now shown that oral administration of the synthetic steroid 16 alpha-fluoro-5-androsten-17-one, which lacks the side-effects of DHEA treatment, to CD-1 mice inhibits 7,12-dimethylbenz[a]anthracene-initiated and 12-O-tetradecanoylphorbol-13-acetate-promoted skin papilloma formation at both the initiation and promotion stage. The synthetic steroid is more potent as an inhibitor of papilloma formation than comparably administered DHEA.

Growth factor binding to 7,12-dimethylbenz(a)anthracene-induced mammary tumors from rats subject to chronic caloric restriction.

Abstract: Caloric restriction (CR) inhibits tumorigenesis in rodents. To understand the basis for this effect the binding of insulin, insulin-like growth factor I/somatomedin C (IGF-I/Sm-C), insulin-like growth factor II/multiplication stimulating activity (IGF-II/MSA), and epidermal growth factor were examined to membrane preparations of 7,12-dimethylbenz(a)anthracene-induced mammary adenocarcinomas and several normal tissues from female Sprague-Dawley rats. Animals were fed ad libitum (AL) or 25% and 40% calorically restricted diets. Large, palpable (LP) and small, less than or equal to 100 mg, nonpalpable (SNP) tumors were evaluated. Growth factor binding to tumors was differentially affected by CR. IGF-I/Sm-C binding was comparable for AL-LP, AL-SNP, and 25% CR-LP tumors, but elevated in 25% CR-SNP tumors. Scatchard analysis revealed high and low affinity IGF-I/Sm-C binding sites, with AL-SNP and 25% CR-SNP tumors exhibiting similar levels of high affinity sites and at a greater concentration than AL-LP and 25% CR-LP tumors. Insulin binding to mammary tumors was low, i.e., 8- to 13-fold lower than IGF-I/Sm-C binding. The 25% CR-LP and SNP tumors bound 2- to 5-fold more insulin than corresponding AL-LP and SNP tumors. Binding of IGF-II/MSA to these tumor preparations was high, approximately 11- to 25-fold greater than insulin binding, and was unaffected by CR or tumor size. The binding of epidermal growth factor was not detected in any tumor preparations. Receptor binding studies were confirmed with covalent cross-linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses. Normal tissues exhibited tissue- and growth factor-specific alterations in binding with host CR. Thus, alterations in growth factor binding were not tumor specific, but were less pronounced than in mammary tumors. These findings suggest alterations in IGF-I/Sm-C and insulin binding properties to tumors in relation to CR and tumor size may contribute, in part, to the inhibitory effects of CR on tumorigenesis.

Molecular mechanism of 7,12-dimethylbenz[a]anthracene-induced immunosuppression: evidence for action via the interleukin-2 pathway.

Abstract: Previous studies in this laboratory have demonstrated that exposure of mice to the carcinogenic polycyclic aromatic hydrocarbon 7,12-dimethylbenz[a]anthracene results in suppression of both humoral and cell-mediated immunity. This suppression is unaccompanied by any significant alteration in splenic lymphocyte subpopulation composition, suggesting that the immune deficit was due to a modulation of lymphocyte function. Additional studies implicated the T helper lymphocyte as the probable target for 7,12-dimethylbenz[a]anthracene-induced immunosuppression, apparently through an inhibition of interleukin 2 production. The purpose of the present study was to examine the mechanism of 7,12-dimethylbenz[a]anthracene-induced T lymphocyte dysfunction at the molecular level and to determine the consequences of 7,12-dimethylbenz[a]anthracene exposure on the interleukin 2 pathway. In vitro exposure of Con A-activated splenocytes to 7,12-dimethylbenz[a]anthracene resulted in suppression of the mitogenic response, suppressed interleukin 2 production, and reduced the expression of the high affinity receptor for interleukin 2. In contrast, expression of the low affinity interleukin 2 receptor was not affected. In addition, interleukin 2-dependent lymphoblasts and long term cultured splenocytes exhibited a dose-dependent decrease in proliferation following in vitro exposure to 7,12-dimethylbenz[a]anthracene. These results suggest that 7,12-dimethylbenz[a]anthracene-induced immunosuppression may be mediated, at least in part, through the interleukin 2/interleukin 2 receptor pathway.

Ellagic acid effects on the carcinogenicity, DNA-binding and metabolism of 7,12-dimethylbenz(a)anthracene (DMBA).

Abstract: Naturally-occurring components of the human food supply have recently received attention as possible agents for cancer chemoprevention. The plant phenol ellagic acid has been reported to be an effective inhibitor of carcinogen metabolism and certain chemically-induced tumors. Therefore, we evaluated the efficacy of ellagic acid in inhibiting DMBA metabolism, DNA-binding and the initiation of DMBA-induced carcinogenesis in rat mammary tissue. Mammary epithelial cell aggregates were isolated from rats fed control and ellagic acid (0.4 and 0.8%) containing diets. When incubated with DMBA, aggregates from ellagic acid-fed rats exhibited a significant but modest inhibition of DMBA metabolism and DNA-binding. An inhibition of DMBA-DNA binding and DMBA metabolism in secondary cultures of mammary epithelial cells also was detected only when ellagic acid was added at 150 molar excess compared to DMBA. The feeding of ellagic acid (0.8%) to rats for 28 days prior to the administration of DMBA resulted in a 21% reduction in mammary tumor incidence at 21 weeks which was, however, not statistically significant. Together, these results indicate that, in contrast to its effects with other carcinogens in other tissues, ellagic acid is not a potent inhibitor of DMBA metabolism, DNA-binding and carcinogenicity with rat mammary tissue.

7,12-Dimethylbenz[a]anthracene-induced perinatal carcinogenesis and its modulation by butylated hydroxyanisole in mice.

Abstract: We discuss the transplacental and transmammary carcinogenicity of 7,12-dimethylbenz[a]anthracene (DMBA) in Swiss albino mice and its modulation by butylated hydroxyanisole (BHA). Transmission of the carcinogen by either route elicits the development of tumour in F1 individuals, and in either situation the incidence of tumours is dependent upon the dose of DMBA administered to gestating or lactating mothers or foster mothers. However, for a given dose of carcinogen, its transplacental carcinogenicity is much greater than its transmammary carcinogenicity. Transmammary carcinogenicity is evident in F1 progeny whether they are nursed by DMBA-exposed mothers, syngenic foster mothers (Swiss albino strain) or allogenic foster mothers (C57BL/6 strain), but the incidence of tumours is appreciably lower when allogenic females are the foster mothers. DMBA administered to females during gestation appears to remain as a residue, then to find its way through the transmammary route into normal F1 individuals being foster-nursed, and to produce tumours. We have also shown the influence of age, but not of parity, of foster mothers on DMBA-induced transmammary carcinogenesis in F1 individuals. In these experiments, BHA has a chemopreventive action against DMBA-induced transplacental and transmammary carcinogenesis in mice.

Modulation of 7,12-dimethylbenz[a]anthracene-induced transmammary carcinogenesis by disulfiram and butylated hydroxyanisole in mice.

Abstract: The individual as well as combined chemopreventive actions of disulfiram (DSF) and butylated hydroxyanisole (BHA) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced transmammary carcinogenesis in mice were examined. When nursing mothers receiving normal diet were treated with DMBA (1 mg/mouse) on days 6, 8 and 10 postpartum, the tumor incidence in their 50-week-old F1 progeny was 44.1%. When nursing mothers receiving 0.75% BHA diet, 0.5% DSF diet and 0.75% BHA + 0.5% DSF diet were similarly treated with DMBA, the tumor incidences in their 50-week-old F1 progeny were 14.7% (P less than 0.05), 12.5% (P less than 0.05) and 5.8% (P less than 0.01), respectively. It is concluded that diets containing BHA (0.75%) and DSF (0.5%), singly or in combination, can inhibit transmammary carcinogenesis in Swiss albino mice.

Sodium o-phenylphenate (OPP-Na) promotes skin carcinogenesis in CD-1 female mice initiated with 7,12-dimethylbenz[a]anthracene.

Abstract: Sodium o-phenylphenate (OPP-Na) was applied at a dose level of 5.0 mg/animal dermally to the fur-clipped dorsal area of female CD-1 mice twice weekly for 47 weeks after applications of 10 micrograms of 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator twice weekly for 5 weeks. A total of 25 skin tumors (21 papillomas and four carcinomas) developed in 15 out of 20 mice (75%). The incidence and yield of skin tumors in this DMBA/OPP-Na group were significantly higher than in the DMBA/acetone-treated group where only six tumors (five papillomas and one carcinoma) were observed in five out of 20 mice (25%). Only one papilloma developed in OPP-Na/12-o-tetradecanoylphorbol 13-acetate (TPA) treated animals (initiation testing group), and no tumors were observed in mice receiving OPP-Na/acetone. OPP-Na elevated 5-bromodeoxyuridine(BrdU) incorporation in basal cells of mouse epidermis dose-relatedly and the thickness of the skin in the treated group was also increased to approximately 2- or 3-fold that of controls. In addition, high dose application (20 mg/mouse) caused ulceration. O-Phenylphenol (OPP) administration was associated with extensive corrosive effects. The data suggest that OPP-Na is an ulcerogenic agent which induces epidermal proliferation and which can act as a promoter, but not as an initiator or a complete carcinogen, in two-stage mouse skin carcinogenesis.

Effect of dehydroepiandrosterone (DHEA) on the metabolism of 7,12-dimethylbenz[a]anthracene (DMBA) in rats

Abstract: The influence of dehydroepiandrosterone (DHEA), an adrenal steroid, on the biotransformation of the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) in rats has been investigated. Male Sprague-Dawley rats (2-3 months old) were fed DHEA for 14 days at a dietary level of 0.8%. There was an increase in liver weights with increases per whole liver, in total protein, microsomal and cytosolic protein and cytochrome P-450, and cytosolic glutathione transferase activity in DHEA fed rats. DNA content of the liver, however, remained constant. Forty-eight hours after a single i.p. dose of [3H]DMBA (133 mumol/kg body weight, 102 muCi/rat) binding of DMBA derived metabolites to DNA decreased significantly both per unit of DNA (605 versus 194 pmol/mg DNA) as well as per whole liver DNA (25.4 versus 8.5 nmol) in DHEA fed rats. However, a significantly higher amount of DMBA-derived metabolites were bound to total hepatic protein (455 versus 288 nmol) in the steroid fed rats. Microsome mediated binding of DMBA to DNA was 3-fold higher in DHEA fed rats. Excretion of DMBA-derived metabolites in urine was 2-fold higher in DHEA fed rats. The results of this study demonstrate that DHEA inhibits binding of DMBA to hepatic DNA in vivo in spite of the increased metabolic activation of the carcinogen perhaps due to increased detoxification and competitive binding of its active species to proteins.

In vitro and in vivo effects of sodium selenite on 7,12-dimethylbenz[a]anthracene--DNA adduct formation in isolated rat mammary epithelial cells.

Abstract: Supplementation with increasing quantities of selenium (Se), as sodium selenite, to cultures of rat mammary epithelial cells resulted in a proportional depression in 7,12-dimethylbenz[a]anthracene (DMBA) binding to DNA. A depression in the two major anti bay-region dihydrodiol epoxide-deoxyribonucleoside adducts largely accounted for the reduced binding. DMBA-DNA binding in freshly isolated mammary cells from rats fed a diet containing 2.0 p.p.m. Se and incubated in culture with DMBA for 24 h was decreased 32% compared to binding in cells obtained from rats fed 0.1 p.p.m. Se. DMBA-DNA binding in mammary cells obtained from rats fed supplemental Se for 2 weeks or more was depressed compared to that occurring in cells from unsupplemented rats. The reduced ability of cells obtained from rats previously fed a 2.0 p.p.m. Se diet to activate DMBA to intermediates capable of binding to DNA became increasingly apparent with the duration of exposure to the carcinogen. Consistent with the in vitro supplementation study, cells isolated from rats previously fed a diet containing 2.0 p.p.m. Se had a reduced occurrence of the two major anti dihydrodiol epoxide adducts. The depression in DMBA binding following selenite supplementation, both in vitro and in vivo, supports the ability of Se to inhibit the initiation phase of carcinogenesis.

Fate of 7,12-dimethylbenz(a)anthracene in the mouse mammary gland during initiation and promotion stages of carcinogenesis in vitro.

Abstract: Metabolic conversion and distribution of the products of 7,12-dimethylbenz( a )anthracene (DMBA) were analyzed in the mouse mammary cell transformation model in organ culture In order to determine the levels of uptake of DMBA, the glands were exposed to the transforming dosage of the procarcinogen (78 µm, 20 µCi/ml) for 24 h, and the level of uptake was determined to be 8 × 10 4 cpm/mg of tissue Subsequently, the glands were incubated in DMBA-free medium, and distribution of the radioactivity in DNA and in the acid-insoluble materials was measured Data showed that, in addition to the 24-h DMBA treatment period, the initiation stage extends for another 3 h when the incubation is continued in DMBA-free medium A saturation level of uptake of [ 3 H]DMBA into the whole gland was observed at 12 h, while DMBA was continually metabolized with the products being bound to DNA and to the acidinsoluble fractions throughout the entire incubation period with or without DMBA The three major adducts identified were anti -DMBA-3,4-diol-1,2-epoxide (DMBADE):deoxyguanosine, syn -DMBADE:deoxyadenosine, and anti -DMBADE:deoxyadenosine Qualitatively the adduct profiles remained similar However, with the additional 3-h incubation in DMBA-free medium, the three major DMBA-DNA adducts increased slightly by 65 to 75% Thus the total 27-h time period can be considered as the duration of the initiation stage in the DMBA-induced carcinogenesis of mouse mammary cells in organ culture Therefore the subsequent 6-h incubation in DMBA-free medium may be considered as within the promotional stage, and at the same time period the levels of the three DNA adducts decreased significantly by 675 to 841% ( P

[Suppressor activity of bone marrow and spleen cells in C57Bl/6 mice during carcinogenesis induced by 7,12-dimethylbenz(a)anthracene].

Abstract: The nonspecific suppressor activity of bone marrow cells (BMC) and spleen cells (SC) of C57B1/6 mice was studied at 7,12-dimethylbenz(a)anthracene-induced carcinogenesis. It is established that in the latent period of the tumour development and with its appearance the suppressor activity of BMC decreases, while SC-increases. The activity of the BMC suppressor factor which is determined by the inhibition of proliferation of mastocytoma P-815 cells in vitro did not change significantly.

Administration-route-related difference in the micronucleus test with 7,12-dimethylbenz[a]anthracene.

Abstract: The effect of route of administration on the outcome of the mouse micronucleus test was evaluated in 2 laboratories by administering a model chemical, 7,12-dimethylbenz[a]anthracene (DMBA) by intraperitoneal injection (i.p.) and oral gavage administration (p.o.) to males of 2 mouse strains, MS/Ae and CD-1. On the basis of a small-scale acute toxicity study and a pilot micronucleus test, a full-scale micronucleus test was performed with a 48-h sampling time at doses of 25, 50, 100, and 200 mg/kg by both administration routes in the 2 strains. At each dose level and in both strains, higher frequencies of micronucleated polychromatic erythrocytes (MNPCEs) were found after use of the i.p. route. In the MS/Ae strain, a linear, positive dose response was obtained by both routes. In the CD-1 strain, the maximum response was reached at 100 mg/kg and a downturn occurred at 200 mg/kg by both routes. The comparison of maximum responses indicated that MS/Ae was the higher responder for both routes of application. Although DMBA induced micronuclei more efficiently by the i.p. route than after oral administration on a mg/kg base, this route-related difference was reversed in both strains when the comparison was made on the basis of LD50 values and when the maximum responses were neglected.

Increased tumour incidence and skin tumour promotion in two generations of descendants of 7,12-dimethylbenz[a]anthracene-treated pregnant mice.

Abstract: Many experiments suggest the possibility of hereditary transmission of a predisposition to developing cancer. If this is the case, the progeny of animals exposed to carcinogens during embryogenesis should bear initiated cells. In order to examine this possibility, offspring of mice exposed to 7,12-dimethyl-benz[a]anthracene in utero were treated cutaneously with a tumour promoter, 12-O-tetradecanoylphorbol-13-acetate. This treatment resulted in the development of skin tumours, i.e., papillomas and carcinomas. Moreover, various tumours also developed in many internal organs, and particularly in the lung. These findings suggest that exposure to carcinogens may not only increase cancer risk in subsequent generations, but also considerably reinforce sensitivity to tumour-promoting factors, which by themselves may pose no threat to an unexposed population.