Skin Tumor Initiation Research Articles

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

In contrast to a previous report by Shubik and in accordance with a pilot study from our laboratory with female rats, the 2-stage skin carcinogenesis experiment could be successfully accomplished in male Sprague-Dawley rats. Male animals of this species are better suited for this long-term experiment since, under the conditions used, females are very sensitive to mammary gland tumor formation and show a drastically reduced survival time. A broad spectrum of tumors of epidermal origin could be induced by topical initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetra-decanoyl-phorbol-13-acetate (TPA) as promoter. The tumors were not only localized in the interfollicular epidermis but to a large extent also in the epidermal appendages. More importantly, the DMBA - TPA treatment led to the development of a variety of tumors of the connective tissue and the angiofibrous matrix. The incidence of these tumors was almost comparable to that found for epidermal tumors. In some animals we observed up to 12 histologically different tumors. Compared to the mouse, the tumor incidence in organs other than the skin was definitely lower. Ethyldiazoacetate (EDA), a substance which has been shown to induce skin tumors when administered i.v. to rats, was tested with regard to its initiating capacity. The combination EDA-TPA led to a skin tumor spectrum comparable to that produced by DMBA-TPA. However, the survival time of the EDA-TPA treated animals was significantly higher than those exposed to DMBA-TPA. EDA, therefore, seems to be a suitable alternative to DMBA for systemic initiation of skin tumors.

Tumor-initiating activity of 4-fluoro-7,12-dimethylbenz[a]anthracene and 1,2,3,4-tetrahydro-7,12-dimethylbenz[a]anthracene in female SENCAR mice.

We have determined the skin tumor-initiating activity in SENCAR mice of two A-ring derivatives of 7,12-dimethylbenz[a]anthracene (DMBA). 4-Fluoro-7,12-dimethylbenz[a]anthracene at a dose of 200 nmol per mouse exhibited weak activity, producing 0.6 papillopmas per mouse; doses of 10 and 20 nmol per mouse had no activity. A derivative of DMBA with the A-ring reduced, 1,2,3,4-tetrahydro-7,12-dimethylbenz[a]anthracene (1,2,3,4,-H-DMBA), had substantial tumor-initiating activity when compared with the parent hydrocarbon. In one experiment, doses of 10 and 100 nmol per mouse gave rise to 1.6 and 9.5 papillomas per mouse, respectively; similar results were obtained in 3 additional experiments. Although the tumor-initiating activity of 1,2,3,4,-H4-DMBA was approximately one-tenth that of DMBA, this derivative was slightly (17%) more active than benzo[a]pyrene. 1,2,3,4-H4-DMBA was tested for the ability to induce mutations to 6-thioguanine-resistance in Chinese hamster V79 cells. In the absence of feeder cells capable of metabolizing polycyclic hydrocarbons, it was not mutagenic. However, in a cell-mediated mutation assay with secondary hamster embryo cells as activators, this derivative produced mutations in a dose-dependent manner and was approximately one-tenth as active as DMBA. These results indicate that metabolism of DMBA at positions 1-, 3-, 2- and 4- is important for biological activity and that for certain derivatives (i.e., 1,2,3,4-H4-DMBA), alternate pathways of metabolic activation may also be important.

Anticarcinogenic and cocarcinogenic effects of benzo[e]pyrene and dibenz[a,c]anthracene on skin tumor initiation by polycyclic hydrocarbons.

In the present study, we have examined the effects of benzo[e]pyrene (B[e]P) and dibenz[a,c]anthracene (DB[a,c]A) on the skin tumor-initiating activities of methylated and non-methylated polycyclic aromatic hydrocarbons (PAH). B[e]P, when applied 5 min prior to initiation with seven different PAH skin carcinogens, effectively inhibited the tumor-initiating activities of 7,12-dimethylbenz[a]anthracene (DMBA) and dibenz[a,h]anthracene (DB[a,h]A) but had little or no effect on the tumor-initiating activities of 3-methyl-cholanthrene (MCA), 7-methylbenz[a]anthracene (7-MBA), 12-methylbenz[a]anthracene (12-MBA), and 5-methyl-chrysene (5-MeC). B[e]P potentiated the tumor-initiating activity of benzo[a]pyrene (B[a]P) by approximately 30%, DB[a,c]A, when applied 5 min prior to initiation, inhibited the tumor-initiating activities of DMBA, MCA, and DB[a,h]A but had little or no effect on the tumor-initiating activities of B[a]P, 7-MBA, 12-MBA, and 5-MeC. DB[a,c]A, when applied 12, 24, or 36 h prior to initiation with B[a]P, which allowed time for induction of epidermal monooxygenase enzymes, inhibited tumor initiation. The covalent binding of DMBA and B[a]P to epidermal DNA was examined under the influence of B[e]P. Doses of 20 and 200 nmol B[e]P given 5 min prior to 10 nmol [3H]DMBA reduced binding to 47 and 22%, respectively, of the control value. In contrast, doses of 200 or 2000 nmol B[e]P given 5 min prior to 200 nmol [3H]B[a]P had little or no effect on total binding. The data indicate that one cannot predict anti and cocarcinogenic effects of B[e]P and DB[a,c]A on the basis of a presence or absence of a methyl substituent. In addition, fundamental differences exist in the processing and metabolism of DMBA and B[a]P by mouse epidermal cells.

Mutagenic and carcinogenic potency of extracts of diesel and related environmental emissions: Summary and discussion of the results

The proposed conversion from gasoline powered automobiles to diesel powered vehicels has prompted the Environmental Protection Agency to evaluate the potential health effects associated with exposure to diesel emissions. At present, there is no direct epidemiological link between this exposure and human health. Therefore, a research program was constructed to compare the health effects associated with diesel emissions with those from other emission sources for which epidemiological information was available. The emission sources chosen were cigarette smoke, roofing tar, and coke oven. An additional comparative emission source which was a gasoline catalyst engine. Respirable particles from a variety of combustion sources have the potential of being carcinogenic and mutagenic. The objective of these studies was to determine the relative biological activity of the organic material adsorbed on these particles in both in vitro mutagenesis and in vitro and in vivo bioassays. The organic extracts from the following series of emission sources were quantitatively bioassayed in a matrix of tests for their carcinogenic and mutagenic activity: (1) a light-duty Oldsmobile diesel 350 engine; (2) a heavy-duty Caterpillar diesel engine; (3) a light-duty Nissan engine; (4) a Volkswagen Rabbit diesel engine; (5) cigarette smoke; (6) roofing tar; (7) coke oven; and (8) a gasoline catalyst Mustang. The test matrix consisted of the following bioassay: reverse mutation in Salmonella typhimurium; mitotic recombination in Saccharomyces cerevisiae; DNA damage in Syrian hamster embryo cells (SHE); sister chromatid exchange in CHO cells; gene mutation in L5178Y mouse lymphoma cells, Balb/c 3T3 mouse embryo fibroblasts and CHO cells; viral enhancement of SHE cells; oncogenic transformation in Balb/c 3T3 cells; and skin tumor initiation in SENCAR and C57 black mice. The results of this test matrix are discussed.

Extent of skin tumour initiation in mice by 7,12-dimethylbenz[ a]anthracene and induction of arylhydrocarbon monooxygenase are not causally related

In order to clarify further the relation between extent of arylhydrocarbon monooxygenase (AHM) induction and tumour initiation by polycyclic aromatic hydrocarbons, AHM activity and concentration of 7,12-dimethylbenz[ a]anthracene (DMBA) equivalents in dorsal epidermis were determined after both intragastric and topical administration of DMBA. Although in each case the dose applied caused comparable tumor incidences, both the extent of AHM induction and the concentration of DMBA equivalents were remarkably different: while topically applied DMBA stimulated AHM several-fold, intragastric instillation led to only a slight increase, if any. The concentration of DMBA equivalents in epidermis was about 100-fold higher after topical DMBA application than after intragastric administration. These data provide further evidence that extent of tumour initiation by DMBA and of AHM induction are not causally related; positive correlations found in certain cases appear to be fortuitous. Induction of AHM seems to be rather a function of DMBA concentration adjustment in epidermis and to indicate, if anything, elevated detoxification.

9-Hydroxyellipticine: Inhibitory effect on skin carcinogenesis induced in Swiss mice by 7,12-dimethylbenz[ a]anthracene

9-Hydroxyellipticine (9-hydroxy-5,11-dimethyl-6- H-pyrido[4,3 b]carbazole), a potent inhibitor of monooxygenases, strongly inhibits the initiation of skin tumors by 7,12-dimethylbenz[ a]anthracene (DMBA) in male NMRI Swiss mice. 9-Hydroxyellipticine has no effect on promotion step.

Carcinogenicity of Halogenated Olefinic and Aliphatic Hydrocarbons in Mice<xref ref-type="fn" rid="FN2">2</xref>

A series of 15 halogenated hydrocarbons of industrial and environmental importance were tested for carcinogenicity by chronic administration by one or more routes in Ha:ICR Swiss mice. Not all compounds were tested by the four routes of administration used. Allyl chloride, 1,2-dibromo-3-chloropropane, and vinylidene chloride were active as skin tumor initiators in the two-stage carcinogenesis assays; phorbol myristate acetate was used as a promoter. 1,2-Dibromoethane was the only compound that induced a significant incidence (p less than 0.05) of skin papillomas, skin carcinomas, and lung tumors by repeated skin application. 1,2-Dichloroethane, 1,1,2,2-tetrabromoethane, and 1,2-dibromo-3-chloropropane induced lung and/or stomach tumors by repeated skin application. Two compounds showed sarcomagenic activity by sc injection; they were cis-1,3-dichloropropene and 2-chloropropanal. By intragastric intubation, 1-chloropropene and 2-chloropropanal induced significant numbers of stomach tumors. Vehicle, no-treatment, and positive control groups were included in these tests. The following compounds were also tested by one or more of the four routes but were inactive by the criteria used; i.e., they showed P = 0.05 or greater than 0.05: trichloroethylene, tetrachloroethylene, hexachlorobutadiene, chloroacetaldehyde, 1-chloropropene oxide (cis and trans), and trichloroethylene oxide.

The effects of weak or non-carcinogenic polycyclic hydrocarbons on 7, 12-dimethylbenz[ a]anthracene and benzo[ a]pyrene skin tumor-initiation

Benzo[e]pyrene (B[e]P) inhibited 7,12-dimethylbenz[a]anthracene (DMBA) skin tumor-initiation in mice by 84%, whereas pyrene and fluoranthene inhibited DMBA initiation by 50 and 34%, respectively. However, B[e]P, pyrene and fluoranthene had either no significant effect or a slight enhancing effect on benzo[a]pyrene (B[a]P) skin tumor-initiation. In addition, B[e]P had essentially no effect on the initiating ability of (+/-)B[a]P-7 beta,8 alpha-diol-9 alpha,10 alpha-epoxide. As a tumor-initiator, B[e]P was found to have very weak activity at a 252 microgram/level (0.4 papillomas/mouse at 40 weeks) and no activity at 100 microgram. When given at a dose of 100 microgram twice weekly, B[e]P induced 2.1 papillomas/mouse at 30 weeks, and 25% of the mice had carcinomas at 40 weeks. However, B[e]P carcinogenic activity is weak when compared to B[a]P, which can induce a comparable tumor response at a dose of 5 microgram twice weekly. When B[e]P was tested as a tumor promoter at a dose of 100 microgram twice weekly after DMBA initiation, it induced 4.5 papillomas/mouse at 30 weeks and a 45% carcinoma incidence at 40 weeks, which was approximately twice as effective as B[e]P alone. The data show that B[e]P is a very weak tumor initiator, a weak complete carcinogen, a moderate tumor promoter, possibly a weak co-tumor-initiator when given with B[a]P, and a potent anit-tumor-initiator when given with DMBA. The anti-tumor initiating and co-tumor-initiating effects of B[e]P appear to be related to its ability to modify the conversion of the tumor initiator into an electrophilic intermediate(s) which are capable of covalently binding to DNA. In addition, B[e]P induced epidermal cellular proliferation which may be related to its promoting ability.

The importance of the “bay region” diol-epoxide in 7,12-dimethylbenz[ a]anthracene skin tumor initiation and mutagenesis

The skin tumor-initiating and V79 mutagenic activities of various derivatives of 7,12-dimethylbenz[a]anthracene (DMBA) were investigated to determine what possible cellular metabolite(s) may be responsible for its carcinogenicity and/or mutagenicity. 1-,2-,3-,4- and 5-hydroxyDMBA were found to be essentially inactive as skin tumor initiators whereas 9- and 10-hydroxyDMBA had weak activity. The (+/-)-trans DMBA 8,9- and 5,6-dihydrodiols were also essentially inactive as skin tumor initiators and (+/-)-DMBA 8beta,9alpha-diol-10alpha-11alpha-epoxide had weak skin tumor initiating activity. All of the above tested derivatives of DMBA were essentially inactive as mutagens in the cell-mediated or direct V79 mutagenesis systems. A methyl or fluoro addition to the 1, 2 or 5 positions almost completely blocked the skin tumor initiating and V79 mutagenic activities of DMBA, whereas a fluoro addition to position 11 did not. From our data we suggest that a 'bay region' diol-epoxide may be important in DMBA carcinogenicity and mutagenicity.

2,3,7,8-Tetrachlorodibenzo-p-dioxin: Potent anticarcinogenic activity in CD-1 mice

Topical pretreatment with non-toxic doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin, a contaminant formed in the commercial synthesis of the herbicide 2,4,5-trichlorophen-oxyacetic acid, strongly inhibited the initiation of skin tumors by 7,12-dimethylbenz(a)-anthracene and benzo(a)pyrene in female CD-1 mice. 2,3,7,8-tetrachlorodibenzo-p-dioxin also produced marked induction of epidermal monooxygenase enzymes functional in the conversion of 7,12-dimethylbenz(a)anthracene to a variety of hydroxylated products. The time course of anticarcinogenic effects resulting from pretreatment with the dioxin correlated with the magnitude of induction as well as with a singnificant reduction in the quantity of 7,12-dimethylbenz(a)anthracene metabolites covalently bound in vivo to epidermal DNA and RNA but not protein.

Lack of Involvement of 6-Hydroxymethylation in Benzo[<italic>a</italic>]pyrene Skin Tumor Initiation in Mice<xref ref-type="fn" rid="FN2">2</xref>

The skin tumor-initiating activities of benzo[a]pyrene (BP), 6-hydroxymethylbenzo[a]pyrene (6-OH-CH2-BP), and 6-methylbenzo[a]pyrene (6-CH3-BP), as well as the effects of 7,8-benzoflavone (7,8-BF), quercetin, and 1-benzylimidazole on their activity, were determined in outbred female CD-1 mice by use of a two stage system of tumorigenesis. The skin tumor-initiating activity of 6-OH-CH2-BP and 6-CH3-BP was 12.5 and 20%, respectively, of the activity of BP, 7,8-BF had little effect on the skin tumor-initiating activity of 6-OH-CH2-BP and 6-CH3-BP. However, a dose-dependent inhibition of BP tumorigenesis by 7,8-BF was noted. Quercetin and 1-benzylimidazole also inhibited BP skin tumor-initiating activity. These findings indicated that direct hydroxymethylation of BP is not an important pathway in the activation of BP in mouse skin tumor initiation.

Effects of 7, 8-benzoflavone on skin tumor-initiating activities of various 7- and 12-substituted derivatives of 7, 12-dimethylbenz[a]anthracene in mice.

The skin tumor-initiating activities of various 7- and 12-substituted derivatives of 7,12-dimethylbenz(a)anthracene (DMBA) were investigated in female outbred Charles River CD-1 mice. 7-Formyl-12-methylbenz(a)anthracene (7-CHO-12-MBA) at 740 nmoles/mouse was an effective tumor initiator, at a dose 74-fold greater than that of DMBA. 7,8-Benzoflavone (7,8-BF) inhibited the tumor-initiating activity of 7-CHO-12-MBA by 51%. 12-Formyl-7-methylbenz(a)anthranene and 7,12-diformylbenz(a)anthracene, applied at initiating doses of 740 nmoles and 704 nmoles/mouse, respectively, were much less active than 7-CHO-12-MBA. 7-Bromomethyl-12-methylbenz(a)anthracene (7-BRME-12-MBA) and 7-bromomethylbenz(a)anthracene (7-BRMEBA) were also investigated. 7-BRME-12-MBA was a more effective tumor initiator than 7-BRMEBA, but both were less active than DMBA. 7,8-BF inhibited the tumor-initiating activity of 7-BRME- 12-MBA and 7-BRMEBA by 34 and 54%, respectively. 12-Bromomethyl-7-methylbenz(a)anthracene (12-BRME-7-MBA) was as active an initiator as 7-BRME-12-MBA. 7,8-BF inhibited tumor initiation with 12-BRME-7-MBA by 29%. Three naturally occurring flavones, quercetin, myricetin, and 4',5,7-trihydroxyflavonone, and the cytochrome P/sub 450/, inhibitor 1-benzylimidazole were investigated after topical application(100 ..mu..g) for their effects on tumor initiation with DMBA. Quercetin inhibited tumor initiation with DMBA. Quercetin inhibited tumor initiation with DMBA by 22%, whereas myricetin and 4',5,7-trihydroxyflavanone enhanced tumor initiation with DMBA by 54 and 29%, respectively. 1-Benzylimidazole had no effect. The abilities of the flavones and 1-benzylimidazole to inhibit aryl hydrocarbon hydroxylasemore » in vitro did not correlate with their effects on tumor initiation with DMBA.« less

Croton oil enhancement of skin tumor initiation by N-methyl-N'-nitro-N-nitrosoguanidine: possible role of DNA replication.

SummaryAn application of 0.5% croton oil at times from 6 hr before until 24) hr after initiation with 4 μmoles MNNG led to a threefold increase in papilloma yield and a substantial shortening of the latent period in two-stage tumor induction experiments in mouse skin. Since DNA replication was not stimulated by croton oil until 2-4 days after application of MNNG, this enhancement cannot be explained by an increased uptake of the MNNG by DNA-synthesizing cells or by increased susceptibility of these cells. If DNA replication is involved in initiation, then our results suggest that the critical DNA replication occurs after the interaction of MNNG with DNA, but before the initial damage can be repaired, perhaps resulting in a nonrepairable mutation.

The effects of benzoflavones on polycyclic hydrocarbon metabolism and skin tumor initiation

The effects of benzoflavones on skin tumor initiation by polycyclic hydrocarbons and epidermal aryl hydrocarbon hydroxylase were investigated. 7,8-Benzoflavone (7,8-BF) was found to be a potent inhibitor of the inhibition of skin tumors by 3-methylcholanthrene (MC) as well as 7,12-dimethylbenz(a)anthracene (DMBA). 5,6-Benzoflavone(5,6-BF) inhibited tumor initiation by MC and DMBA, but to a lesser degree than 7,8-BF. Dose-response studies of the capacity of 7,8-BF to inhibit DMBA tumor initiation revealed that 7,8-BF was an effective inhibitor at 2.5 μg and a maximum inhibition of 90% occurred at 100 μg of 7,8-BF. The tumor initiating ability of 7-hydroxymethyl-12-methylbenz(a)anthracene (7-OHMe-12MeBA) was not inhibited by 7,8-BF. Epidermal aryl hydrocarbon(benzo(a)pyrene hydroxylase(AHH) was increased by 5,6-BF and either had no effect or was slightly inhibited by 7,8-BF when given either topically or i.p. Both flavones when added directly to the assay tubes inhibited the in vitro epidermal AHH activity from control and MC pretreated mice by greater than 75%. When added in vitro, 7,8-BF and 5,6-BF inhibited epidermally mediated covalent binding of radioactive DMBA and dibenz(a,h)anthracene to DNA by 50% or more. The inhibition of skin tumor initiation by 7,8-BF and 5,6-BF appears to be partially related to its ability to inhibit the formation of electrophilic intermediates.