scispace - formally typeset
Search or ask a question

Showing papers on "7,12-Dimethylbenz[a]anthracene published in 1983"


Journal Article
TL;DR: Data suggest that at least part of the stimulatory effect of polyunsaturated fat on 7,12-dimethylbenz(a)anthracene-induced mammary tumorigenesis may be mediated through an increased synthesis of prostaglandins.
Abstract: The effect of the prostaglandin synthetase inhibitor indomethacin on the dietary fat enhancement of 7,12-dimethylbenz(a) anthracene-induced mammary tumorigenesis has been examined in female Sprague-Dawley rats. Rats were fed either a normal-fat or high-fat diet (5 or 18% corn oil, respectively) with or without 0.004% indomethacin, starting 3 days after a single intragastric intubation of 5 mg 7,12-dimethylbenz(a)anthracene. Results of this experiment demonstrated that indomethacin completely blocked the stimulatory effect of fat on tumorigenesis, as measured by a decreased tumor incidence, a decreased number of tumors per group, a decreased tumor size, and an increased latency. No effect of indomethacin was observed in rats fed the normal-fat diet. These data suggest that at least part of the stimulatory effect of polyunsaturated fat on 7,12-dimethylbenz(a)anthracene-induced mammary tumorigenesis may be mediated through an increased synthesis of prostaglandins.

208 citations


Journal Article
TL;DR: Large amounts of deoxyadenosine adducts are formed with the more potent carcinogen, 7,12-dimethylbenz(a)anthracene, in contrast to what is known for benzo( a)pyrene.
Abstract: Primary mouse embryo cell cultures were grown in the presence of [14C]guanine, labeling primarily deoxyguanosine residues in the cellular DNA, or in the presence of [14C]adenine, labeling both deoxyguanosine and deoxyadenosine residues in the cellular DNA. These cultures were subsequently exposed to 7,12-[3H]dimethylbenz(a)anthracene for 24 hr. The DNA was isolated and hydrolyzed to deoxyribonucleosides, and the 7,12-dimethylbenz(a)anthracene:deoxyribonucleoside adducts were separated chromatographically allowing the three major adducts found to be identified as bay-region anti-dihydrodiol-epoxide:deoxyguanosine and :deoxyadenosine adducts and a bay-region syn-dihydrodiol-epoxide:deoxyadenosine adduct. Therefore, in contrast to what is known for benzo(a)pyrene, substantial amounts of deoxyadenosine adducts are formed with the more potent carcinogen, 7,12-dimethylbenz(a)anthracene.

120 citations


Journal Article
TL;DR: The greater reactivity of DMBA with deoxyadenosine residues in mouse skin may play a role in determining its greater tumor initiating potential.
Abstract: 7,12-Dimethylbenz( a )anthracene (DMBA):deoxyribonucleoside-adducts, from enzymatic hydrolysis of DNA from mouse skin exposed to [3H]DMBA in vivo , were analyzed by reversephase high-pressure liquid chromatography. Double-labeling studies showed that the adducts were qualitatively identical to those formed in mouse embryo cell cultures. These have been tentatively identified as bay-region anti -dihydrodiol epoxide: deoxyguanosine- and :deoxyadenosine adducts and a bay-region syn -dihydrodiol epoxide:deoxyadenosine-adduct (where the terms syn and anti define dihydrodiol-epoxides wherein the benzylic hydroxyl group and epoxide oxygen are cis or trans to one another, respectively). The relative amounts of individual adducts did not vary substantially with time or with the sex of the mice. However, the syn -dihydrodiol-epoxide:deoxyadenosine-adduct did increase with dose and constituted as much as 40% of the total DNA binding at high doses of DMBA. This is in contrast to the much lower (2 to 3%) levels of binding to deoxyadenosine residues in mouse skin reported for the less potent tumor initiator benzo( a )pyrene. The greater reactivity of DMBA with deoxyadenosine residues in mouse skin may play a role in determining its greater tumor initiating potential.

86 citations


Journal Article
TL;DR: These findings indicate that both syn- and anti-dihydrodiol-epoxides make a substantial contribution to DMBA binding to DNA in mouse embryo cells.
Abstract: Dimethylbenz(a)anthracene (DMBA):deoxyribonucleo- side adducts, from enzymic hydrolyses of DMA from mouse embryo cells exposed in culture to (3H)DMBA, can be separated into two fractions on the basis of whether or not they bind to the phenyl boronic acid residues of Servacel DHB. This suggests that these two fractions of adducts are derived from ani/ and syn bay-region dihydrodiol-epoxides, respectively. The fluores cence spectra and interactions of the major components of these two fractions with borate ions substantiate this interpretation. These findings indicate that both syn- and anf/-dihydrodiol- epoxides make a substantial contribution to DMBA binding to DNA in mouse embryo cells. For a given mouse embryo cell preparation, the relative contributions of each of these dihydro diol-epoxides to DNA binding did not vary substantially with

76 citations


Journal ArticleDOI
TL;DR: It is found that treating A/J mice with food containing .6% DHEA for 10 weeks or reducing the food intake of non-DHEA treated mice to 60% of ad libitum fed animals significantly reduces the amount of 3H-DMBA bound to mouse skin DNA 12 hours after a topical application of the carcinogen.
Abstract: This study was undertaken to determine whether a reduction in body weight in laboratory mice by regimens that appear to delay the rate of aging (i.e., food restriction and chronic dehydroepiandrosterone (DHEA) treatment), or a production of obesity by the presence of the ob (obese) gene or by gold thioglucose-induced hyperphagia alter the rate of binding of 3H-7,12-dimethylbenz(a)anthracene (3H-DMBA) to mouse skin deoxyribonucleic acid (DNA). We have found that treating A/J mice with food containing .6% DHEA for 10 weeks or reducing the food intake of non-DHEA treated mice to 60% of ad libitum fed animals significantly reduces the amount of 3H-DMBA bound to mouse skin DNA 12 hours after a topical application of the carcinogen. Conversely, A/J mice made obese by a gold thioglucose-induced hyperphagia and C57BL/6J mice with the ob mutation bind significantly increased amounts of 3H-DMBA to skin DNA when compared to their nonobese counterparts.

41 citations


Journal ArticleDOI
TL;DR: The finding of higher levels of chromatographically identical DMBA-DNA adducts in the nontarget (liver) tissue than in the target tissue indicated that adduct formation per se was not a sufficient stimulus for the cancer induction, and implies that certain levels of carcinogen-DNAAdducts may be necessary for carcinogenesis.
Abstract: The potent polycyclic aromatic hydrocarbon 7,12 dimethylbenz[a]anthracene (DMBA) bound to the DNA of numerous organs of the female outbred Sprague-Dawley rat after iv administration under a regimen known to produce a high yield of mammary adenocarcinomas. The maximum DNA binding levels observed following iv administration of 5 mg (20 mumol) DMBA range from approximately 12 mumol hydrocarbon/mol deoxyribonucleic for the liver to approximately 5 mumol hydrocarbon/mol deoxyribonucleotide for the mammary gland, the target tissue. Administered under identical conditions, the noncarcinogenic analogue 2-fluoro-7,12-dimethylbenz[a]anthracene (2F-DMBA) bound to the DNA at levels of about 5-10% that of DMBA (i.e., 0.3-1.6 mumol/mol deoxyribonucleotide). Chromatographic analysis of the hydrocarbon-deoxyribonucleoside adducts produced showed that for DMBA at least two major types of identifiable adducts were observed in all tissues examined, the major one being that resulting from the reaction of a DMBA bay-region diol-epoxide. The other adduct type resulted from the binding of an analogous diol-epoxide of a DMBA metabolite, 7-hydroxymethyl-12-methylbenz[a]anthracene. Adducts from 2F-DMBA were observed on high-pressure liquid chromatography but were in quantities insufficient for characterization. The finding of higher levels of chromatographically identical DMBA-DNA adducts in the nontarget (liver) tissue than in the target tissue indicated that adduct formation per se was not a sufficient stimulus for the cancer induction. However, the failure of the structurally similar 2F-DMBA, which produced only very low levels of DNA adducts, to induce mammary cancer implies that certain levels of carcinogen-DNA adducts may be necessary for carcinogenesis.

35 citations


Journal Article
TL;DR: The results demonstrate the importance of the dose of the challenge carcinogen in revealing the effects of transplacental drug exposure and may have special significance for women who were exposed to DES in utero.
Abstract: Aspects of the development, morphology, and estrogen binding capacity of mammary tumors in rats exposed prenatally to the synthetic estrogen, diethylstilbestrol (DES), and treated postnatally with 7,12-dimethylbenz(a)anthracene (DMBA) were analyzed as part of a project aimed at understanding the effects of transplacental exposure to DES on estrogen-sensitive tissues. Pregnant Sprague-Dawley rats were given injections of DES (total dose, 1.2 micrograms) or vehicle alone on Days 15 and 18 of gestation. All female offspring were given gastric intubations of DMBA, either a single 10-mg dose on Day 50 or two doses (10 mg each) on Days 50 and 57. Among rats treated postnatally with 10 mg of DMBA, the DES-exposed group had a significantly greater incidence of palpable mammary tumors than did the vehicle-exposed controls. In addition, there was an earlier time of appearance of palpable tumors in the DES-exposed group. When the data from rats treated postnatally with two 10-mg doses of DMBA were analyzed, there were no significant differences in palpable mammary tumor incidence or tumor latency between the DES-exposed and vehicle-exposed groups. When the pathology of the mammary tumors produced in rats treated with 10 mg of DMBA was analyzed, the DES-exposed group had a significantly higher proportion of benign tumors (fibroadenoma, adenoma, lobular hyperplasia) than adenocarcinomata compared to vehicle-exposed controls. Both exposure groups had similar numbers of nonpalpable mammary lesions discovered at necropsy. Estrogen binding capacities of representative adenocarcinomata did not differ significantly between the two prenatal exposure groups treated postnatally with 10 mg of DMBA. These results demonstrate the importance of the dose of the challenge carcinogen in revealing the effects of transplacental drug exposure and may have special significance for women who were exposed to DES in utero.

34 citations


Journal Article
TL;DR: Results when coupled with the in vivo data suggest that 7-OHM-12-MBA is an intermediate for at least some of the binding of DMBA to epidermal DNA in Sencar mice.
Abstract: The formation of DNA adducts from (/sup 3/H)-7-hydroxymethyl-12-methylbenz(a)anthracene (7-OHM-12-MBA) and (/sup 3/H)-7,12-dimethylbenz(a)anthracene (DMBA) in the epidermis of Sencar mice was analyzed. Comparison of Sephadex LH-20 chromatographic profiles of DNA samples isolated from mice treated with DMBA or 7-OHM-12-MBA suggested that the DMBA-treated animals contained DNA adduct(s) derived from the further metabolism of 7-OHM-12-MBA. Further analysis of DNA samples from DMBA-treated mice by high-pressure liquid chromatography demonstrated the presence of 5 DNA adducts which were chromatographically indistinguishable from the DNA adducts formed in 7-OHM-12-MBA-treated mice. Epidermal homogenates were utilized to catalyze the covalent binding of (/sup 3/H)DMBA and (/sup 3/H)-7-OHM-12-MBA to calf thymus DNA in vitro. Under conditions of limiting concentrations of (/sup 3/H)DMBA, the majority of the DNA adducts formed chromatographed in regions where 7-OHM-12-MBA-DNA adducts eluted. A major DMBA-DNA adduct formed in this in vitro system eluted with the same retention time as did the major 7-OHM-12-MBA-DNA adduct formed in mouse skin in vivo. These results when coupled with the in vivo data suggest that 7-OHM-12-MBA is an intermediate for at least some of the binding of DMBA to epidermal DNA in Sencar mice.

30 citations


Journal Article
TL;DR: The inhibitory effect on DMBA-induced carcinogenesis may be related to the modifications that DBcAMP induces on cAMP level, adenylate cyclase activity, and cAMP-dependent protein kinase of the mammary gland.
Abstract: A single intubation of 7,12-dimethylbenz( a )anthracene (DMBA) (20 mg in 1 ml sesame oil) to female Sprague-Dawley rats at 50 days of age produces primary mammary carcinomas in 80% of rats at 100 to 150 days of age. Administration of N 6, O 2′-dibutyryl cyclic adenosine 3′:5′-monophosphate (DBcAMP) p.o. beginning at 1 day prior to DMBA intubation resulted in marked delay and reduction of tumor production: only 15% as many DBcAMP-treated rats had tumors as in the control group (DMBA only) with 60 days of delay in the first tumor appearance. DMBA-induced tumor production was preceded by changes in the cyclic adenosine 3′:5′-monophosphate (cAMP) metabolism and protein kinase of the mammary gland. Within 24 hr post-DMBA intubation, the intracellular cAMP level and adenylate cyclase activity increased with an increase in type I isozyme of cAMP-dependent protein kinase, a form which has been associated with increased proliferative activity and a less differentiated cellular state in other tissues. The increases in cAMP level, adenylate cyclase activity, and the protein kinase activity were transient, and the values decreased to below the control values by Day 10 post-DMBA intubation. In mammary glands of rats that had received DBcAMP, the cAMP level and protein kinase isozyme pattern were similar to those of older rats that are no longer susceptible to the carcinogen. The inhibitory effect on DMBA-induced carcinogenesis may be related to the modifications that DBcAMP induces on cAMP level, adenylate cyclase activity, and cAMP-dependent protein kinase of the mammary gland.

29 citations


Journal ArticleDOI
TL;DR: 10-F-DMBA is believed to be the first example of a hydrocarbon with a fluoro substituent giving rise to increased tumor initiating activity and structural modifications that alter tumor initiate activity do not alter the ability of TCDD to inhibit tumorigenesis by DMBA.
Abstract: We have determined the skin tumor initiating activity in SENCAR mice of 6 monofluoro derivatives of 7,12-dimethylbenz[a]anthracene (DMBA). 9-Fluoro-DMBA (9-F-DMBA) was approximately as active, and 10-F-DMBA was more active than the parent hydrocarbon, DMBA. The difference between DMBA and 10-F-DMBA was most dramatic at the highest initiating doses of 10-F-DMBA tested. 4-F-DMBA, which was only weakly active as an initiator, was also tested as a complete carcinogen on mouse skin; after 30 weeks of treatment, 50- and 100-nmol weekly doses failed to elicit papillomas or carcinomas. Animals treated with 50 nmol of DMBA weekly exhibited a 100% papilloma incidence and a 42% carcinoma incidence. Pretreatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) effectively inhibited tumor initiation with all of the monofluoro derivatives of DMBA tested. The ED50 (dose of TCDD producing half-maximal inhibition) for the inhibition of DMBA initiation in SENCAR mice was determined to be 1.8 X 10(-3) micrograms/mouse (5.6 pmol). The results indicate that the introduction of a fluorine atom in ring D of DMBA has no effect (positions 9 and 11) or enhances (position 10) tumor initiating activity. We believe 10-F-DMBA to be the first example of a hydrocarbon with a fluoro substituent giving rise to increased tumor initiating activity. The results also indicate that structural modifications that alter tumor initiating activity do not alter the ability of TCDD to inhibit tumorigenesis by DMBA.

26 citations


Journal Article
TL;DR: Analysis of DNA adducts indicated that these putative proximate carcinogenic metabolites were formed in these cells and subsequently metabolized to DNA-binding products, suggesting that metabolic incompetence may not be an explanation for the relative resistance of the hamster to epidermal carcinogenesis by polycyclic hydrocarbons.
Abstract: Primary cultures of hamster epidermal cells exposed to hydrocarbon, 1 µg/ml, rapidly metabolized [ 3 H]benzo( a )pyrene and [ 14 C]7,12-dimethylbenz( a )anthracene to ethyl acetate:acetone- and water-soluble metabolites. By 24 hr, only 13.6% of the organic solvent-soluble radioactivity recovered in the medium was unchanged [ 3 H]benzo( a )pyrene, and only 5.9% was unchanged [ 14 C]7,12-dimethylbenz( a )anthracene. With both hydrocarbons, the major water-soluble metabolites found extracellularly were conjugated with glucuronic acid; these were primarily phenolic derivatives. Metabolites cochromatographing with 7,8-dihydro-7,8-dihydroxybenzo( a )pyrene or trans -3,4-dihydro-3,4-dihydroxy-7,12-dimethylbenz( a )anthracene were not detectable in high-pressure liquid chromatographic profiles of organic solvent-soluble intracellular and extracellular metabolites. However, analysis of [ 3 H]benzo( a )pyrene: and [ 3 H]7,12-dimethylbenz( a )anthracene:DNA adducts indicated that these putative proximate carcinogenic metabolites were formed in these cells and subsequently metabolized to DNA-binding products. The results suggest that metabolic incompetence may not be an explanation for the relative resistance of the hamster to epidermal carcinogenesis by polycyclic hydrocarbons.

Journal ArticleDOI
TL;DR: In this article, the separation of four 7,12-dimethylbenz(a)anthracene (DMBA) derivatives was compared under identical conditions comprising of a concave gradient (No. 4) from 20 to 70% acetonitrile/water for 75 minutes at flow rate of 1ml/min.
Abstract: This paper presents an evaluation of a number of commercially available octadecylsilane columns. The separation of four 7,12-dimethylbenz(a)anthracene (DMBA) derivatives namelycis- andtrans-5,6-dihydroxy DMBA,trans-8,9-dihydro-8,9-dihydroxy DMBA, and 7,12-dihydroxymethyl benz(a)anthracene (BA) was compared under identical conditions comprising of a concave gradient (No. 4) from 20 to 70% acetonitrile/water for 75 minutes at flow rate of 1ml/min. A direct correlation between percent carbon loading and retention behavior was observed for bonded phases prepared from silica particles with similar surface areas. Other column performance parameters, such as capacity factors, separation ratios and resolution between peaks for the solutes examined were also calculated and are discussed.

Journal ArticleDOI
TL;DR: It is demonstrated that, while bile is not absolutely necessary for the uptake of this orally ingested hydrocarbon carcinogen, it significantly facilitates absorption from a long-chain triglyceride vehicle.
Abstract: This study was undertaken to examine intraluminal factors which might alter the bioavailability of an orally ingested hydrocarbon carcinogen, 7,12-dimethylbenz[a]anthracene, and to assess the extent of its enterohepatic circulation. Rats with biliary and duodenal fistulae were administered radiolabelled hydrocarbon dissolved in olive oil, safflower oil, or medium-chain triglyceride only or with exogenous bile. Subsequent biliary excretion and plasma levels of radiolabel were monitored. Luminal bile significantly enhanced biliary recovery of radiolabel following instillation in both long-chain triglyceride vehicles, but did not affect the recovery from the medium-chain oil. In the presence of luminal bile, plasma levels and biliary recovery of radiolabel using the medium-chain triglyceride were significantly less than with either long-chain triglyceride. Following intraduodenal infusions of the radiolabelled biliary products of the carcinogen, 33% of the administered radiolabel was subsequently reexcreted ...

Journal ArticleDOI
TL;DR: Compared with standard Sephadex LH-20 column chromatography, a newly developed high pressure liquid chromatographic separation of hydrocarbon deoxyribonucleoside adducts derived from the DNA of mouse embryo cell cultures exposed to 7,12-dimethylbenz[a]anthracene (DMBA) provides markedly superior resolution.
Abstract: Compared with standard Sephadex LH-20 column chromatography, a newly developed high pressure liquid chromatographic separation of hydrocarbon deoxyribonucleoside adducts derived from the DNA of mouse embryo cell cultures exposed to 7,12-dimethylbenz[a]anthracene (DMBA) provides markedly superior resolution. Once resolved, the fluorescence spectroscopic properties of the three major DMBA--DNA adducts indicate that the fluorescence exhibited by adducts derived from a bay region syn dihydrodiol epoxide of DMBA differs subtly from that exhibited by adducts derived from the isomeric anti dihydrodiol epoxide.

Journal Article
TL;DR: DMBA may lastingly alter capillary endothelium in a manner which allows or aids in its subsequent dilatory and proliferative responses to angiogenic stimulation from malignant tumors, and possibly from premalignant or malignantly transformed cells.
Abstract: Anatomical and functional vascular changes during hamster cheek pouch carcinogenesis were studied by light microscopy; scanning electron microscopy of vascular casts; transmission electron microscopy of cheek pouch capillaries; and fractional distributions of 51 Cr-erythrocytes, 125 I-human serum albumin, and 86 RbCl which were used to determine vascular volume, permeability, and perfusion. Histopathological changes and focal capillary changes in vascular casts were measured quantitatively by an image analyzer. Male Syrian hamsters received 0.5% 7,12-dimethylbenz[a]anthracene (DMBA) in mineral oil for 11 weeks and were sacrificed at periodic intervals from 2 to 20 weeks after initial treatment. Simple hyperplasia was first seen at Week 1. The area of hyperplastic epithelium, expressed as percentage, increased to about 60% by Week 8 and then decreased to 30% at Week 20. Dysplastic foci were first seen at Week 2. The percentage of the area of dysplasia increased with time to 41% at Week 20. Squamous cell carcinomas occurred from Week 10, increased with time, and were found in all animals at Week 20. Vascular cast diameters of normal-looking capillaries were larger during than after DMBA treatment. Type 3 vascular proliferations were found beneath dysplasia and cancer. Capillaries beneath simple hyperplasia and type 3 capillaries beneath dysplasia and cancers were dilated but not fenestrated. Changes in vascular volume were independent of changes in permeability and perfusion and also occurred in contralateral untreated pouches of treated animals. While 86 Rb values initially correlated with 125 I values, the 86 Rb values were unstable in intermediate and later time periods. Changes of vascular volume were accompanied initially by the presence of DMBA and were coincident with increased areas of dilated capillaries beneath simple hyperplasia and later with areas of type 3 capillary proliferation beneath dysplasia and cancer. Changes of vascular permeability were related to inflammation indices throughout the study. DMBA may lastingly alter capillary endothelium in a manner which allows or aids in its subsequent dilatory and proliferative responses to angiogenic stimulation from malignant tumors, and possibly from premalignant or malignantly transformed cells.

Journal ArticleDOI
TL;DR: The data suggest that the susceptibility of young virgin rat mammary cells to DMBA may be due in part to the conversion of a greater percentage of DMBA to phenolic compounds and to water- and ethyl acetate-soluble polar metabolites, and event known to influence the susceptibility to cytotoxic effects of cultured cells.
Abstract: These in vitro metabolism studies of 7,12-dimethylbenz[a]anthracene (DMBA) by rat mammary epithelial cells were initiated to determine whether differences in the incidence of DMBA-induced mammary carcinomas observed between young virgin, old virgin and parous Sprague-Dawley rats can be explained through variations in their ability to metabolize DMBA. The results show that: (a) qualitatively, the metabolic profiles produced by epithelial cells from the 3 groups of rats were similar; (b) the level of metabolism with cells from young virgin and parous rats was similar but was 1.5-2.0 times higher than that obtained with cells from old virgin rats; c) the major ethyl acetate-soluble metabolite detected by h.p.l.c. from cells of old virgin and parous rats was the trans-8,9-dihydrodiol (50-65% of total metabolites), whereas the majority of the radioactivity following incubation with cells from young virgin rats co-eluted with very polar metabolites (65% of total metabolites); and (d) the amount of phenolic metabolites produced by young virgin rat cells was higher than in old virgin or parous rat cells. The data suggest that the susceptibility of young virgin rat mammary cells to DMBA may be due in part to the conversion of a greater percentage of DMBA to phenolic compounds and to water- and ethyl acetate-soluble polar metabolites, and event known to influence the susceptibility of cultured cells to the cytotoxic effects of DMBA.

Journal Article
TL;DR: Investigation of the effect of the promoter 12- O -tetradecanoylphorbol-13-acetate (TPA) on the evolution of different types of 7,12-dimethylbenz( a )anthracene-initiated rat tracheal epithelial cells in vivo shows that initiation can be viewed as a series of complex cellular changes.
Abstract: The aim of these studies was to investigate the effect(s) of the promoter 12- O -tetradecanoylphorbol-13-acetate (TPA) on the evolution of different types of 7,12-dimethylbenz( a )anthracene (DMBA)-initiated rat tracheal epithelial cells in vivo . As described previously, upon exposure to carcinogens, cells appear in the tracheal epithelium which are distinguishable from the majority of the epithelial cells by a markedly enhanced in vitro growth capacity. In the present study, tracheal transplants were exposed in vivo to 35 µg DMBA for 2 weeks and subsequently to 100 µg TPA. Controls were exposed to DMBA alone, TPA alone, or blank pellets alone. Tracheal cells were harvested by enzymatic procedures at 0, 3, 6, 12, or 18 months after the end of exposure to DMBA and at the same time points after the beginning of exposure to TPA or control pellets and were assayed in vitro with the epithelial focus (EF) assay for the frequency of different types of EF-forming units. Control tracheas yielded 4 viable cells harvested. Of these EFs, 10 to 28% were subculturable (EF s ), and no EF s derived from control tracheas exhibited growth in soft agarose EF s,ag + ). Exposure to TPA alone did not increase the yield of EF, EF s , or EF s,ag + above control levels. Carcinogen exposure resulted in a 6- to 20-fold increase in yield of EF, a 2- to 3-fold increase in EF s , and a ≥15-fold increase in yield of EF s,ag + above control levels. Neither the yield of EF nor the yield of EF s was affected by subsequent exposure to TPA. In contrast, there was a marked effect of subsequent TPA exposure on the maintenance and size of the cell pool giving rise to anchorage-independent offspring (EF s,ag + ). By 3 months after DMBA exposure, 15% of EF s were EF s,ag + in both the DMBA and DMBA-TPA exposure groups. However, in cultures established 12 months following exposure to DMBA alone, only 2% of EF s s were EF s,ag + following exposure to DMBA alone. In contrast, at this same time following exposure to DMBA and TPA, 18% of EF s s were EF s,ag + . In a parallel two-stage carcinogenesis study with tracheal transplants, a significant enhancement of the DMBA-induced tumor response by TPA was observed. At 20 months after exposure, 4 and 37%, respectively, of DMBA- and DMBA-TPA-exposed tracheas developed invasive carcinomas. In summary, it appears that initiation can be viewed as a series of complex cellular changes. With time, some of these changes are reversible. Exposure to TPA of cell populations initiated with low doses of DMBA results in the persistence of altered cell populations in the intact tissue. Without TPA treatment, some phenotypically altered cells appear to revert to a more normal state and/or fail to replicate.

Journal ArticleDOI
TL;DR: There is considerable potential for dietary fiber to interact with DMBA and its metabolites in the lumen of the gastrointestinal tract, possibly influencing hydrocarbon carcinogen bioavailability.
Abstract: This in vitro study examined the ability of various dietary fiber components to bind 7,12-dimethylbenz[a]anthracene (DMBA), a hydrocarbon carcinogen known to contaminate food. Bile salt solutions of DMBA were incubated with individual fiber materials under various conditions, and the degree of binding was assessed. Binding of DMBA from simple bile salt solution was greatest with delipidated bran greater than acid lignin greater than alpha-cellulose greater than unprocessed bran. Binding to acid lignin was slowly reversible, was constant within the pH range 4-8, and appeared independent of a bile salt-fiber interaction. Acid lignin bound DMBA from a mixed lipid-bile salt solution significantly, but less effectively than from pure bile salt solutions. DMBA biliary metabolites from Sprague-Dawley rats were bound less extensively to all the fiber materials than was the parent hydrocarbon, but following hydrolysis of the metabolites by beta-glucuronidase binding was significantly increased. These results indicate that there is considerable potential for dietary fiber to interact with DMBA and its metabolites in the lumen of the gastrointestinal tract, possibly influencing hydrocarbon carcinogen bioavailability.

Journal ArticleDOI
TL;DR: The marked increase in carcinogenicity of aromatic hydrocarbons by a methyl substituent is observed not only with BA but also with other aromatic hydro carbons, such as chrysene and anthrabene, and 5-Methylchrysene, for instance, has as highly carcinogenic activity as 3-MC whereas carcinogenivity of chrysese is very weak.
Abstract: Many attentions have long been paid to the question about the reason why benz [a]-anthracene (BA), a very weak carcinogen, increases its carcinogenic activity to the level of the most potent carcinogenic hydrocarbons, such as benzo [a] pyrene (BP) and 3-methylcholanthrene (3-MC), by the substitution of methyl group(s) for the "L-region" (7-and 12-positions) hydrogens, e.g. 7, 12-dimethyl-BA (DMBA) has a higher carcinogenic activity than BP, and 7-methyl-BA (7-MBA) is as carcinogenic as 3-MC (Cavalieri, 1979; Selkirk, 1980). In addition, 3-MC is also an alkyl-substituted BA. The marked increase in carcinogenicity of aromatic hydrocarbons by a methyl substituent is observed not only with BA but also with other aromatic hydrocarbons, such as chrysene and anthrabene (Cavalieri, 1979; Selkirk, 1980). 5-Methylchrysene, for instance, has as highly carcinogenic activity as 3-MC whereas carcinogenicity of chrysese is very weak. Similarly, 9, 10-dimethylanthracene is carcinogenic whereas the mother compound; anthracene, is not carcinogenic (Fig. 1). Several attempts have been made to know active metabolites of DMBA in relation to epoxide formation. DMBA 5, 6-oxide has been isolated and identified as an active metabolite from a hepatic mitrosomal reaction mixture (Keysell et al., 1973). DMBA 3, 4-diol-1, 2-epokide was also strongly assumed to be an active metabolite, but has not been detected yet from the in vitro system (Jerina et al., 1978 ; Malaveille et al., 1978 ; Wislocki bt al:, 1980). These studies, however, were carried out by using liver microsomes from rats pretreated with the P-448 inducer, 3-MC or polychlorinated biphenyls. 8, 9- and 10, 11-epoxides of DMBA might also be candidates for the active metabolites since their hydrolysis products, 8, 9- and 10, 11-dihydrodiols, have been isolated from a rat liver microsomal system (DiGiovanni and Juchau, 1980).

Journal ArticleDOI
TL;DR: Analysis of DMBA--DNA adducts by Servacel DHB chromatography and high-pressure liquid chromatography showed that treatment of cells with BHA, but not with BHT, resulted in a decreased contribution from the syn bay region dihydrodiol epoxide to overall binding.

Journal Article
TL;DR: This study showed 7,12-dimethylbenz[a]anthracene-induced mammary tumor cells were highly sensitive to doxorubicin (Dx) (adriamycin); Dx induced specific ultrastructural effects on the nuclei, mitochondria, and membranes of the cells; and the in vitro response of the primary culture may be useful for prediction of theresponse of the source tumor to chemotherapy.
Abstract: For the determination of their response to doxorubicin (Dx) (adriamycin), monodispersed mammary tumor cells (from female outbred Sprague-Dawley rats) were maintained as monolayer primary culture. Dose-response curves and [3H]thymidine labeling indices showed the antimitotic and cytocidal effects of the drug varied in a dose-dependent fashion. Dose-response curves revealed that the median lethal dose concentration was 10(-4) M. A 24-hour treatment at concentrations of 10(-4) to 10(-5) M completely arrested DNA synthesis of the tumor cells. Surviving cells exhibited chromatin abnormalities, accumulation of cytoplasmic myelin bodies, vacuolization of endoplasmic reticulum, and increased density of mitochondrial matrix. This study showed 1) 7,12-dimethylbenz[a]anthracene-induced mammary tumor cells were highly sensitive to Dx; 2) Dx induced specific ultrastructural effects on the nuclei, mitochondria, and membranes of the cells; and 3) the in vitro response of the primary culture may be useful for prediction of the response of the source tumor to chemotherapy.

Journal ArticleDOI
TL;DR: The metabolic profile described in this report contrasts with those obtained in earlier experiments in which the incubation of DMBA with Pseudomonas aeruginosa and Penicillium notatum produced no dihydrodiol metabolites but only methyl-hydroxylated metabolites.
Abstract: The metabolites of 7,12-dimethylbenz[a]anthracene (DMBA), a carcinogenic polycyclic aromatic hydrocarbon, in cultures of Cunninghamella elegans were isolated by high-pressure liquid chromatography and characterized by UV spectroscopy and mass spectrometry. The major metabolites were DMBA-trans-8,9-dihydrodiol and DMBA-trans-3,4-dihydrodiol. The 7-hydroxymethyl and the 12-hydroxymethyl derivatives of these dihydrodiol metabolites were also formed. The metabolic profile described in this report contrasts with those obtained in our earlier experiments in which the incubation of DMBA with Pseudomonas aeruginosa and Penicillium notatum produced no dihydrodiol metabolites but only methyl-hydroxylated metabolites.

Journal ArticleDOI
TL;DR: The metabolism of 7,12-dimethylbenz[ a ]anthracene and its non-carcinogenic 2-fluoro analogue (2F-DMBA) by Syrian hamster embyro (SHE) cells has been studied using high pressure liquid chromatography (HPLC) and fluorescence spectroscopy.

Journal ArticleDOI
TL;DR: Although the overall extents of metabolism of the substrates by the two types of homogenate were similar, there was twice as much binding to protein in incubations with the 7-hydroxymethyl derivative, which converted much more of the parent hydrocarbon into water-soluble derivatives.

Journal ArticleDOI
TL;DR: The incidences of DMBA-induced dominant lethals were markedly reduced in pre-meiotic germ cells by the pretreatment with PB, whereas a significant reduction of the lethal events in post-meiotics germ cells was observed with MC.
Abstract: The effects of pretreatment with either phenobarbital (PB) or 3-methylcholanthrene (MC) on the induction of dominant lethal events by 7, 12-dimethylbenz[a]anthracene (DMBA) in male mice were studied. DMBA induced dominant lethals in both post- and pre-meiotic germ cells of mice. The incidences of DMBA-induced dominant lethals were markedly reduced in pre-meiotic germ cells by the pretreatment with PB, whereas a significant reduction of the lethal events in post-meiotic germ cells was observed with MC. No significant reduction of living implants was detected in pre-meiotic germ cells on pretreatment with PB. The contents of liver microsomal cytochrome p-450 of mice pretreated with PB or MC were about twice those of non-treated mice.

Journal Article
TL;DR: The organotropic, but not the strain, selectivity of DMBA-induced carcinogenicity appears to be attributed in part to metabolic activation.
Abstract: The biotransformation of DMBA in uninduced and induced 10,000g organ supernatants derived from female Sprague-Dawley and Long-Evans rats, which are respectively sensitive and resistant to DMBA-induced carcinogenesis, was studied. Qualitative and quantitative differences in the metabolism of DMBA are summarized as a function of organ (liver, lung, kidney, and mammary) and strain and oxidative enzyme induction protocol utilized and are attributed to the differential induction of various cytochrome P-450s. The percent production of 7,12-dimethylbenz(a)anthracene-3,4-dihydrodiol (DMBA-3,4-DHD) and phenol metabolites in 10,000g organ supernatants from beta-napthoflavone induced animals correlated with organ susceptibility to DMBA-induced carcinogenesis in both SD and LE rat strains. A negative correlation was observed between 8,9-DHD production and reported sensitivity to specific organ tumorigenesis, but no other relationship was observed with other metabolites (7- and 12-hydroxymethyl, K-region DHD, and 10,11-DHDs). Similar DMBA metabolite hplc profiles were observed in the same organ S-10 fractions isolated from either SD or LE rats. Thus, the organotropic, but not the strain, selectivity of DMBA-induced carcinogenicity appears to be attributed in part to metabolic activation.

Journal ArticleDOI
TL;DR: Data show that the 1,2-dihydrodiol of 7,12-dimethylbenz[a]anthracene is formed as a metabolite of this hydrocarbon by rodent and human skin maintained in short-term organ culture.
Abstract: Rodent and human skin maintained in short-term organ culture was treated with 3H-labelled 7,12-dimethylbenz[a]-anthracene. Extracts of the rodent tissue and culture fluid in which either mouse, rat or human skin had been maintained were found to contain radioactive material that possessed the chromatographic characteristics of trans-1,2-dihydro-1,2-dihydroxy-7,12-dimethylbenz[a]anthracene when it was examined in two different h.p.l.c. systems. When the metabolite was treated with hot mineral acid, the two radioactive products formed co-chromatographed with the phenols that were formed when the reference dihydrodiol was similarly treated. Acetylation of the isolated metabolite yielded a single product that had chromatographic properties identical to those of the diacetate of the reference dihydrodiol. Taken together these data show that the 1,2-dihydrodiol of 7,12-dimethylbenz[a]anthracene is formed as a metabolite of this hydrocarbon by rodent and human skin maintained in short-term organ culture.

Journal ArticleDOI
TL;DR: Primary cell cultures from a density-defined cell subpopulation of the DMBA-induced rat mammary tumors were exposed to tamoxifen during their log phase of growth and growth inhibition and the ultrastructure of surviving cells were examined along with the influence of this antiestrogen on the secreted proteins.
Abstract: Primary cell cultures from a density-defined cell subpopulation of the DMBA-induced rat mammary tumors were exposed to tamoxifen during their log phase of growth. Growth inhibition and the ultrastructure of surviving cells were examined along with the influence of this antiestrogen on the secreted proteins as determined by pulse labeling with [35S]methionine and fluorography. Cell growth was remarkably inhibited at clinically achievable concentrations. However, ultrastructural changes in the surviving cells were minimal, the most noteworthy being the accumulation of myelin bodies. Protein secretion was affected in the defined subpopulation of several tumors by the reduced production of a high-molecular-weight protein. These tumors may represent a population of estrogen-sensitive tumors within the DMBA-induced mammary tumor model.

Journal ArticleDOI
TL;DR: Results demonstrate that the frequency of chromosome aberrations of V79 cells was much greater in the presence of hamster cells at late passages than inThe presence of cells at early passages.

Journal ArticleDOI
TL;DR: The results suggest that PRL may stimulate DMBA-induced tumor growth independently of ER and that a part of the inhibiting effect of tamoxifen on tumor growth may be explained by the decreased PRL secretion.
Abstract: The role of prolactin (PRL) and estrogen in the growth of 7, 12-dimethylbenz (a)-anthracene (DMBA)-induced rat mammary tumors was investigated. Tumor growth was suppressed by both bromocriptine and tamoxifen. Combined administration of ovine PRL and tamoxifen attenuated the inhibitory action of tamoxifen on tumor growth. Serum PRL levels were decreased by both bromocriptine and tamoxifen administration. Estrogen receptors (ER) in tumor tissues were decreased in number by tamoxifen, but not by bromocriptine. Progesterone receptors (PgR) in DMBAinduced mammary tumors were abolished by tamoxifen and significantly reduced by bromocriptine. Combined administration of ovine PRL with tamoxifen attenuated the inhibition of PgR induced by tamoxifen alone, while ER remained undetectable. Specific PRL binding to the liver was significantly reduced by treatment with bromocriptine, tamoxifen and tamoxifen plus ovine PRL, whereas PRL receptors in mammary tumor were not influenced by these drugs. These results suggest that PRL may stimulate DMBA-induced tumor growth independently of ER and that a part of the inhibiting effect of tamoxifen on tumor growth may be explained by the decreased PRL secretion.