In vitro metabolism of selected fluoro analogs of 7,12-dimethylbenz[a]anthracene

We have compared the metabolite profiles generated from the rat liver incubation of monofluorinated derivatives of 7,12-dimethylbenz[a]anthracene. These monofluoro analogs are known to exhibit varying degrees of carcinogenicity. In this study we observed that the presence of fluorine substituents blocked metabolism at the fluorinated positions, some of which may be critical for biological activity. Furthermore, we also found that the fluorine substituents affected the chemical reactivity of the 5,6-arene oxide metabolites in terms of their ability to undergo methanolysis.

DNA adduct formation by 7,12-dimethylbenz[a]anthracene and its noncarcinogenic 2-fluoro analogue in female Sprague-Dawley rats

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.

Permanent cell culture lines of rat erythroleukemia and growth inhibition by dexamethasone in vitro

Four erythroleukemia cell lines were established in vitro from rats with primary leukemias induced by a set of intravenous injections of 7,8,12-trimethylbenz[a] anthracene (TMBA). These cell lines were grown in Dulbecco's medium with 20% inactivated fetal calf serum; they were characterized by specific consistent chromosome abnormalities, related to No. 2 chromosome, which were maintained in culture for more than 1 year. Addition of dexamethasone prevented the cell growth of 2 of the cell lines in this medium but failed to alter the growth rate of the other 2 cell lines. These findings are correlated with karyotype abnormalities involving chromosome No. 2.

Specific induction of erythroleukemia and myelogenous leukemia in Sprague-Dawley rats

The experimental induction of leukemias of two sorts by two powerful chemical carcinogens was investigated in rats of a single strain. In Sprague-Dawley rats a series of intravenous injections of N-nitroso-N-methylurea selectively elicited myelogenous leukemia in high yields, whereas erythroleukemia was not evoked. Conversely, a set of intravenous injections of 7,8,12-trimethylbenz[a]anthracene specifically elicited erythro-leukemia in high incidence in the rats, whereas myelogenous leukemia was not produced.

A 7-hydroxymethyl sulfate ester as an active metabolite of 7,12-dimethylbenz[alpha]anthracene

7-Hydroxymethyl-12-methylbenz[alpha]anthracene (7-HMBA), a carcinogenic major metabolite of 7,12-dimethylbenz[alpha]anthracene (DMBA) in liver, was transformed by liver cytosolic sulfotransferase to reactive 7-HMBA sulfate, which is mutagenic toward Salmonella typhimurium strain TA98. The mutagenicity of 7-HMBA in the presence of hepatic sulfotransferase was much higher than that of DMBA or 7-HMBA in the presence of hepatic monooxygenase.

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.

7, 12-dimethylbenz [a] anthracene-deoxyribonucleoside adduct formation in vivo: evidence for the formation and binding of a mono-hydroxymethyl-DMBA metabolite to rat liver DNA

The polycyclic aromatic hydrocarbon, 7,12-dimethyl benz[a] anthracene (DMBA) is a potent carcinogen to the female Sprague-Dawley rat, and when administered under conditions that have been shown to produce cancer, resulted in extensive formation of hydrocarbon-deoxyribonucleoside adducts. Sephadex LH-20 and reverse-phase h.p.l.c. and spectrofluorometric analysis of these adducts demonstrate that at least one adducts results from the binding of 7, 12-dimethylbenz [a] anthracene-1,2,3,4-tetrahydro-3,4,-dihydroxy-1,2,-oxide. In these experiments, employing i.p. administration of the hydrocarbon, a second more polar adduct was observed. Evidence is presented that this adduct results from the formation of a monohydroxymethyl-methyl-benz [a] anthracene-A-ring-diol-epoxide. While both of the monohydroxymethyl-DMBA metabolites have been shown to bind cellular DNA following their administration this is the first evidence of monohydroxymethyl-DMBA-deoxyribonucleoside adducts being formed after the administration of DMBA per se. The evidence suggests that this more polar adduct is a 7-hydroxymethyl-12-methylbenz[a]anthracene-deoxyribonucleoside adduct.

Identification of novel 7,12-dimethylbenz[a]anthracene adducts in cellular ribonucleic acid

The interaction of guanosine with 7,12-dimethylbenz[a]anthracene (DMBA) 5,6-oxide under alkaline conditions resulted in the formation of six derivatives. These six compounds were cochromatographed with nucleosides obtained by hydrolysis of RNA isolated from rat liver cells treated with [3H]DMBA. The cochromatography showed that three of these adducts were formed in cellular RNA. The three products constituted less than 5% of the total nucleoside-DMBA adducts as shown by chromatography on Sephadex LH-20 and high-pressure liquid chromatography. In one of them, the 2'-hydroxy group of the ribose moiety of guanosine was linked to the C-5, and in the second, to the C-6 position of the DMBA 5,6-oxide residue. In the third derivative, the C-8 position of guanosine was linked to the C-5 of the DMBA 5,6-oxide moiety. These results show, for the first time, modifications of the ribose moiety and of the guanine residue at the C-8 position in the cellular RNA by a metabolite of a polycyclic hydrocarbon.

Characteristics of benzo[a]pyrene and A-ring reduced 7,12-dimethyl benz[a]anthracene induced neoplastic transformation of human cells in vitro

The polynuclear aromatic hydrocarbons (PAH) benzo[a]pyrene (BP) and the A-ring reduced analogue of 7,12-dimethylbenz[a]anthracene (DMBA), 1,2,3,4-tetrahydro-7,12-dimethylbenz[a]anthracene (TH-DMBA) are carcinogenic to human cells. The unsaturated PAH, DMBA exhibits no carcinogenic activity on human cells as measured by growth in soft agar. The TH-DMBA and BP treated cells exhibit a colony frequency in soft agar of 84 and 86, respectively. These anchorage independent cells, when seeded on the chick embryonic skin (CES) organ cultures, are invasive and form a fibrosarcoma. It is highly unlikely that TH-DMBA, which does not contain an aromatic A-ring, can undergo metabolism in human cells in culture to form a bay region 3,4-dihydrodiol-1,2-epoxide. These results suggest that an alternate mechanism for the induction of carcinogenesis is appropriate to explain the absence of bay region diol-epoxide metabolite as the ultimate form of the carcinogen in TH-DMBA induced carcinogenesis in human diploid cells.

Effects of neonatally administered-testosterone propionate on the development of target organs of sex hormones and the induction of mammary carcinomas by 7, 8, 12-trimethylbenz (a)anthracene in female Sprague-Dawley rats

Female Sprague-Dawley rats were given 1.25mg testosterone propionate subcutaneously within 24 hours after birth and 30mg 7, 8, 12-trimethylbenz (a) anthracene per 1 kg of body weight intravenously at 50 days of age. In these neonatally androgenized rats, the increase of the anogenital distance, aplasia or hypoplasia of the vagina, persistent estrus on the vaginal smears and eosinophilic substance in mammary glands were observed, with no corpus luteum formation in the ovaries, and the induction of mammary carcinomas by 7, 8, 12-trimethylbenz (a) anthracene was strongly suppressed.

Crystal structure of a carcinogen:nucleoside adduct

The product of reaction between the carcinogen, 7-bromomethyl-12-methylbenz[a]anthracene, and 2'-deoxyadenosine, i.e., N6-(12-methylbenz[a]anthracenyl-7-methyl)deoxyadenosine, has been prepared and characterized, and its structure has been determined by X-ray crystallographic techniques. The major structural features are: (a) the adenine and polycyclic aromatic hydrocarbon residues lie nearly perpendicular to one another; (b) the conformation about the glycosidic bond is syn, rather than anti, and an internal hydrogen bond between the deoxyribose 5'-hydroxyl group and N(3) of the adenine residue is present; and (c) the more planar anthracene portion of the hydrocarbon is stacked between adenine residues of other molecules throughout the crystal.

Metabolism of 7,12-dimethylbenz(a)anthracene and 7-hydroxymethyl-12-methylbenz(a)anthracene by rat liver and microsomes

The metabolism of 7,12-[14C]dimethylbenz(a)anthracene ([14C]DMBA) and 7-[7-CH2-3H]hydroxymethyl-12-methylbenz(a)anthracene ([7-CH2-3H]7-OHM-12-BMA) by rat liver nuclei and microsomes was studied by high-performance liquid chromatography. DMBA and 7-OHM-12-MBA are metabolized at methyl group(s) and at the aromatic ring carbons to form trans-dihyrodiols at positions 3, 4, 5, 6, 8, 9, and 10,11 and phenols at positions 2, 3, and 4 by both nuclear and microsomal enzymes. Both nuclear and microsomal monooxygenase enzyme activities were inducible by pretreatment of the animals with phenobarbital or 3-methylcholanthrene. The rates of formation of all metabolites by microsomes were five- to 20-fold higher than those by nuclei in metabolizing DMBA or 7-OHM-12-MBA. The presence of a hydroxyl group at the 7-methyl position of DMBA markedly decreased the rate of metabolism. The rate of total metabolism of 7-OHM-12-MBA was only 20 to 70% of that of DMBA under identical in vitro incubation conditions. The 3-methylcholanthrene- and phenobarbital-induced enzymes showed a significantly different regioselectivity toward the metabolism of DMBA or 7-OHM-12-MBA and are attributed to different forms of cytochrome P-450 present in the enzyme preparations.

N-Nitroso-N-methylurea elicits mammary cancer in resistant and sensitive rat strains

A single intravenous (i.v.) injection of the water-soluble mammary carcinogen N-nitroso-N-methylurea (NMU; 35 mg/kg of body weight) elicited cancer of the breast in young female rats of two strains in the following incidence: Long-Evans strain, 4%; Sprague-Dawley strain, 70%. In sisters of these rats, a set of 5 i.v. injections of NMU (35 mg/kg at biweekly intervals) evoked mammary carcinoma as follows: Long-Evans strain, 76%; Sprague-Dawley strain, 100%. In its effectiveness in evoking mammary cancer in Sprague-Dawley rats, the lipid-soluble mammary carcinogen 7,8,12-trimethylbenz[a]anthracene exceeded NMU in rapidity of development of cancer and in tumor yield.

Tumorigenicity of 7,12-dimethylbenz[a]anthracene, its hydroxymethylated derivatives and selected dihydrodiols in the newborn mouse

The newborn mouse lung adenoma model has been shown to be a sensitive test for studying the tumorigenicity of bay region diol epoxides and their precursor dihydrodiols. When a total dose of 28 nmol of 7,12-dimethylbenz[a]anthracene (DMBA) or its derivatives was injected i.p. into the preweaning mice, it was found that the 3,4-dihydrodiols of both DMBA and 7-hydroxymethyl-12-methylbenz[a]anthracene caused 13.3 and 4.1 times more lung adenomas than DMBA, respectively. The mice treated with the 5,6- and 8,9-dihydrodiols of DMBA, 7-hydroxymethyl-12-methylbenz[a]anthracene and its 5,6- and 8,9- and 10,11-dihydrodiols, 7-methyl-12-hydroxymethylbenz[a]anthracene and 7,12-dihydroxymethylbenz[a]anthracene developed a level of lung adenomas/mouse less than 2-fold higher than that found in the DMSO-treated control group. Liver tumors also developed in some of the mice. The percentage of mice with liver tumors also indicated that the 3,4-dihydrodiols of both DMBA and 7-hydroxymethyl-12-methylbenz[a]anthracene were more tumorigenic than DMBA itself. These data indicate that the 3,4-dihydrodiols of both DMBA and its 7-hydroxymethyl derivative may be proximate carcinogenic metabolites of DMBA in the newborn mouse.

Mutagenicity of benzo[a]pyrene 7,8-dihydrodiol and 7,12-dimethylbenz[a]anthracene 3,4-dihydrodiol in S. typhimurium mediated by microsomes from rat liver and mouse skin

The mutagenic activities of trans-7,8-dihydro-7,8-dihydroxybenzo[a]-pyrene (BP 7,8-diol) and of trans-3,4-dihydroxy-7,12-dimethylbenz[a]-anthracene (DMBA 3,4-diol) towards S. typhimurium TA100 were measured in assays that were carried out on a micro-scale in liquid medium in the presence of microsomal fractions prepared from mouse skin or rat liver. In the presence of an NADPH-generating system, microsomal enzymes converted both diols into mutagens that were probably the respective 'bay-region' diol-epoxides. The rate of the enzyme-catalysed conversion of the BP 7,8-diol into mutagens by microsomal preparations from mouse epidermis was similar to that occurring with microsomes from rat liver. Pretreatment of mice by the topical application of benz[a]anthracene (BA) or 7,12-dimethylbenz[a]-anthracene (DMBA) increased the mutagenic activity of BP 7,8-diol mediated by mouse skin microsomal preparations by 2-fold and this was paralleled by a 4-fold increase in epidermal aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) activity. The results are discussed in relation to the high susceptibility of mouse skin to polycyclic aromatic hydrocarbon (PAH) carcinogenesis.

DNA excision repair in human cells treated with ultraviolet radiation and 7,12-dimethylbenz[a]anthracene 5,6-oxide

Excision repair was measured in normal human and xeroderma pigmentosum group C cells treated with 7,12-dimethylbenz[a]-anthracene 5,6-oxide and with ultraviolet radiation by the techniques of unscheduled DNA synthesis, repair replication, a modification of bromodeoxyuridine photolysis employing the dye Hoechst 33258 and 365 nm radiation, and endonuclease-sensitive sites assay. Radioautography and repair replication showed that in normal cells the magnitude of repair after a saturation dose of epoxide (approx. 10 microM) to be 0.1-0.2 that after a saturating ultraviolet dose (20 J/m2 at 254), though survival data showed that both doses gave nearly similar killings. Repair was of the long-patch type and repair kinetics after the epoxide treatment were similar to ultraviolet. After a combined treatment with both agents, unscheduled synthesis in normal cells was more than additive, although, considering the experimental errors, these data and those of repair replication are consistent with additivity. The epoxide did not inhibit loss of sites sensitive to the ultraviolet endonuclease. However, after a combined treatment to xeroderma pigmentosum cells there was appreciably less unscheduled synthesis than for the sum of both treatments and the epoxide inhibited the loss of nuclease-sensitive sites. We interpret the data to indicate that there are different rate-limiting steps in the removal of the ultraviolet and the epoxide damages, and that the residual repair activity in xeroderma pigmentosum cells is accomplished by different, not just fewer, enzymes than in normal cells.

[Synthesis of alpha-fetoprotein in rat liver after a single injection of the liver carcinogen 4-dimethylaminoazobenzene and its noncarcinogenic isomer 4-diethylaminoazobenzene]

Single injection of the hepatospecific carcinogen 4-dimethylaminobenzene and its noncarcinogenic isomer 4-dimethylaminoazobenzene induced the foci of oval and transitional cells in the rat liver. Part of the cells synthesized alpha-fetoprotein. It is suggested that induction of the foci of the above cells and alpha-fetoprotein synthesis are likely to be due to the toxic effect of the two carcinogenic agents.

Electrophoretic mobility of PM2 DNA treated with ultimate chemical carcinogens or with ultraviolet light

Superhelical DNA of the Pseudomonas phage PM2 was irradiated with UV-light or reacted with covalently binding carcinogens, such as 7-bromomethyl-benz[a]anthracene, (Ac)2ONFln, K-region epoxides, and alkylating agents. Migration velocity of the DNA products was determined using agarose gel electrophoresis. In gels of more than 1.3%-1.9% agarose, modified PM2 DNA exhibited a dose-(concentration-)dependent decrease of migration velocity. This phenomenon is probably due to a decrease in superhelix density which caused the compact DNA coil to assume eventually an open-circular conformation. Comparison of the extent of DNA modification with the decrease of migration velocity revealed that the superhelical structure sensitively reflected the chemical DNA alterations. DNA species exhibiting, in 1.6% agarose gels, a migration velocity of up to 30% of that of control DNA showed an increase of velocity in 0.4% agarose. Therefore, in 1.3%-1.9% agarose gels, the decrease os superhelix density is accompanied by an increase of the frictional coefficient, whereas in 0.4%-0.9% agarose gels the same decrease of superhelix density apparently led to a higher degree of flexibility of the macromolecule and/or exposure of additional electric charges.

Evaluation of metabolic activation of 7,12-dimethylbenz(a)anthracene in vitro by aroclor 1254-induced rat liver S-9 fraction

Short-term assays for detection of chemical carcinogens frequently rely on an Aroclor 1254-induced rat liver S-9 fraction for metabolic activation of test compounds. The ability of this in vitro system to reproduce the activation occurring in target tissue was investigated by examining the DNA adducts produced when the polycyclic aromatic hydrocarbon carcinogen, 7,12-dimethylbenz(a)anthracene (DMBA), was incubated with the S-9 fraction and calf thymus DNA. Analyses by Sephadex LH-20 column chromatography of hydrocarbon-deoxyribonucleoside adducts obtained after enzymic digestion of the [3H]DMBA-modified DNA revealed that the products of binding of DMBA to DNA in the presence of the S-9 fraction vary with the relative concentration of DMBA to S-9 fraction. Further analyses of these adducts by high-pressure liquid chromatography in the presence of the diol-epoxide-DNA adduct (isolated from mouse embryo cells exposed to [14C]DMBA) and chemically synthesized ultraviolet-absorbing markers of DMBA 5,6-oxide-deoxyribonucleoside adducts showed that, at high DMBA-S-9 ratios, DMBA 5,6-oxide-deoxyriboiucleoside adducts were prominent among the products while, at low DMBA-S-9 ratios, the products included the diol-epoxide-DNA adduct found in target tissue. However, this adduct was always accompanied by other adducts not found in intact cellular systems. Inclusion of a metabolic inhibitor (1,1,1-trichloropropylene oxide) in the Salmonella mutagenicity assay demonstrated that high levels of revertants can be obtained from rat liver S-9 fraction-activated DMBA under conditions which should prohibit formation of the diol-epoxide. These results suggest that Aroclor 1254-induced rat liver S-9 fraction does not exactly reproduce the metabolic activation of this particular carcinogen in vivo and therefore should not be assumed to do this for other carcinogens.

Synthesis and mutagenicity of A-ring reduced analogues of 7,12-dimethylbenz[a]anthracene

The synthesis and mutagenicity of two derivatives of 7,12-dimethylbenz[a]anthracene (DMBA; 1), i.e., 1,2-H2DMBA (4) and 1,2,3,4-H4DMBA (5), are reported. These analogues (4 and 5) represent dihydro and tetrahydro A-ring reduced forms of DMBA, a region in the parent hydrocarbon (1) proposed to be involved in metabolism to the ultimate carcinogen. The synthesis for 4 without isolation of intermediates from the tosylhydrazone of 1,2,3,4-tetrahydrobenz[a]anthracene-4,7,12-trione (10) by successive reaction with 8 molar equiv of CH3Li, HI, and NaBH4 represents a novel approach to this hydrocarbon now available in sufficient quantity for biological studies. Interestingly, both of these reduced analogues 4 and 5 exhibited mutagenic activity in the Ames assay in the presence or absence of microsomal activation for strains TA98 and TA100. In these strains, DMBA was active only in the presence of S-9 fraction. In the plasmid-deficient strain TA1537, only tetrahydro analogue 5 exhibited mutagenic activity both in the absence and presence of S-9 fraction.

Additional evidence for the involvement of the 3,4-diol 1,2-oxides in the metabolic activation of 7,12-dimethylbenz[a]anthracene in mouse skin

The role of vicinal diol-epoxides in the metabolic activation of 7,12-dimethylbenz[a]anthracene to intermediates that react with nucleic acids was investigated using Sephadex LH-20 column chromatography and high pressure liquid chromatography. The results show that some of the hydrocarbon-DNA products formed in mouse skin treated in vivo with 7,12-dimethylbenz[a]anthracene arise from the reaction of DNA with 3,4-dihydro-3,4-dihydroxy-7,12-dimethylbenz[a]anthracene 1,2-oxides which, on the basis of this and other evidence, appears to be a biologically-active metabolite of 7,12-dimethylbenz[a]anthracene. However, since other nucleic acid-hydrocarbon adducts were also present that have not been identified as resulting from the reaction of the 3,4-diol 1,2-oxides with DNA, other mechanisms may also be involved in the metabolic activation of 7,12-dimethylbenz[a]anthracene in mouse skin.

Biotransformation and bioactivation of 7, 12-dimethylbenz[a]anthracene (7, 12-DMBA)

As the result of rapidly developing technological advances, our understanding of the biotransformation and bioactivation of 7, 12-DMBA has increased markedly in recent years. In terms of the metabolic conversion of this polynuclear aromatic hydrocarbon to reactive mutagen/carcinogens, the "bay region" generalization appears to apply, although the candidacy of a number of other intermediary metabolites as ultimate biologically-active forms still remains viable. Large gaps remain in knowledge concerning the nonoxidative metabolic transformations of 7, 12-DMBA, and these require closing in order to further our understanding of the regulation of mechanics controlling steady-state levels of reactive intermediates. Studies on the photooxidation of the hydrocarbon have allowed a stronger appreciation of its chemical reactivity and instability and promise to help resolve many of the apparently conflicting observations of the past. 7, 12-DMBA remains a highly interesting and valuable tool in investigations of bioactivation processes as they relate to the etiology of several important pathologic conditions, including chemically induced tissue necrosis, mutagenesis, carcinogenesis, teratogenesis, atherogenesis, and, possibly, other pathogenic phenomena as well. It is hoped that this review will serve to benefit research in these areas and hasten the reduction of such pathologic phenomena in our society.

Fluorescence of hydrocarbon-deoxyribonucleoside adducts

In comparison with the fluorescence emission spectra of 7-methylbenz[a]-anthracene-nucleoside adducts, the fluorescence emission spectra of hydrocarbon-deoxyribonucleoside adducts containing a methyl substituent in the "bay region" lack spectral resolution at room temperature and appear at substantially longer wavelength. This spectral resolution is improved when spectra are measured at 77 K and an irreversible spectral shift to shorter wavelength, accompanied by improved resolution, results from mild acid hydrolysis. These spectral properties peculiar to the "bay region-substituted" adducts presumably result from an intramolecular interaction between the hydrocarbon fluorophore and the attached nucleoside brought about, in the examples studied here, by the presence of the 12-methyl group in 7,12-dimethylbenz[awanthracene (DMBA) and in 7-hydroxymethyl-12-methylbenz[a]anthracene. This interaction suggests that the site of nucleoside attachment is in close proximity to the 12-methyl group and that binding occurs, therefore, through the intermediacy of a 3,4-diol-1,2-oxide, i.e. a "bay region" diol-epoxide in each case.

Excision of DNA damage arising from chemicals of different carcinogenic potencies

Primary cultures of mouse embryo cells are more efficient in excising DNA-carcinogen adducts resulting from exposure to either 7-bromomethylbenz-[alpha]anthracene or the more carcinogen 7-bromomethyl-12-methylbenz[alpha]anthracene than are mouse L 929 cell suspension cultures. However, within each of these systems, the excisabilities of the adducts formed by either bromo-compound are similar, so differences in carcinogenic potency of the compounds cannot be attributed to differences in the excisability of their DNA-adducts.

The formation of dihydrodiols by the chemical or enzymic oxidation of 7-hydroxymethyl-12-methylbenz[alpha]anthracene and the possible role of hydroxymethyl dihydrodiols in the metabolic activation of 7,12-dimethylbenz[alpha]anthracene

The formation of dihydrodiols from 7-hydroxymethyl-12-methylbenz[alpha]anthracene by rat-liver microsomal fractions, by mouse skin in short-term organ culture and by chemical oxidation in an ascorbic acid/ferrous sulphate/EDTA system has been studied using a combination of thin-layer chromatography and high pressure liquie chromatography. The 3,4-, 8,9- and 10,11-dihydrodiols were formed in all three systems. The 5,6-dihydrodiol was formed in rat-liver microsomal fractions and in chemical oxidation but was not detected as a metabolite of [7-3H]hydroxymethyl-12-methylbenz[alpha]anthracene when this compound was incubated with mouse skin in short-term organ culture. The possible role of hydroxymethyl dihydrodiols in the in vivo metabolic activation of 7,12-dimethylbenz[alpha]anthracene in mouse skin has been studied using Sephadex LH-20 column chromatography. The results show that the hydrocarbon-nucleic acid products formed following the treatment of mouse skin in vivo with [7,12-3H]dimethylbenz[alpha]anthracene are not the same as those that are formed following the treatment of mouse skin under the same conditions with either 7-hydroxymethyl-12-methylbenz[alpha]anthracene or 7-methyl-12-hydroxymethylbenz[alpha]anthracene.

Mass spectral characterization of the K-region and non K-region dihydrodiols of 7,12-dimethylbenz (a) anthracene

Dihydrodiols are derived from intermediary arene oxides during the metabolism of polycyclic aromatic hydrocarbons. In this study, the mass spectra of the trimethylsilyl ether derivatives obtained from the 5,6-dihydrodiol and 8,9-dihydrodiol of 7,12-dimethylbenz [a] anthracene were compared. The mass spectral fragmentation patterns indicate some key features in distinguishing a K-region dihydrodiol from its non K-region isomer. The 8,9-dihydrodiol, a non K-region metabolite, exhibits a greater tendency to undergo a ring contraction fragmentation process while the K-region 5,6-dihydrodiol participates preferably in other fragmentation pathways. The data presented in this report will be useful in charcterizing K-region and nonK-region metabolic epoxidation of polycyclic aromatic hydrocarbons.

The induction of sister chromatid exchanges by dihydrodiols derived from 7,12-dimethylbenz[a]anthracene and 3-methylcholanthrene

The in vitro induction of sister chromatid exchanges (SCEs) in Chinese hamster ovary (CHO) cells by the polycyclic hydrocarbons, 7,12-dimethylbena[a]anthracene and 3-methylcholanthrene and some of the related dihydrodiols was investigated. Increased numbers of SCEs were seen in the chromosomes of cells exposed to non-K-region dihydrodiols. The most active compounds were the 3,4-dihydrodiol of 7,12-dimethylbenza[a]anthracene and the 7,8- and 9,10-dihydrodiols of 3-methylcholanthrene: the parent hydrocarbons and their corresponding K-region dihydrodiols were relatively less active. The results are consistent with others that suggest that the metabolic activation of both hydrocarbons proceeds through the conversion of non-K-region dihydrodiols into vicinal diol-epoxides.

Estrogenic properties of 3,9-dihydroxy-7,12-dimethylbenz[a]anthracene in rats

Previously, the 3,9-dihydroxy derivative of benz[a]-anthracene was shown to be weakly estrogenic. The availability of the related diol of the mammary carcinogen dimethylbenz[a]-anthracene, i.e., 3,9-dihydroxy-7,12-dimethylbenz[a]anthracene (3,9-diOHDMBA), prompted a similar study of its estrogenic properties. The competitive binding studies of 3,9-diOHDMBA with 17beta-estradiol in the uterine cytosol of immature SD rats gave a Ka of 1.7 x 10(8) M-1. 17beta-Estradiol (10(-9) M) binding to the 8S binding protein was inhibited by 3,9-diOHDMBA at concentrations similar to those of nafoxidine HCl (1 x 10(-5) M). Bioassay demonstrated that the diol possesses 1/4,464 the activity of 17beta-estradiol.

Potent tumor-initiating activity of the 3,4-dihydrodiol of 7,12-dimethylbenz(a)anthracene in mouse skin

The abilities of the racemic trans-3,4-, 5,6-, and 8,9-dihydrodiols of 7,12-dimethylbenz(a)anthracene to initiate skin tumors in mice were determined by using a two-stage system of tumorigenesis. The 7,12-dimethylbenz(a)anthracene trans-3,4-dihydrodiol was found to be much more active as a tumor initiator than the parent hydrocarbon. The 7,12-dimethylbenz(a)anthracene trans-5,6- and 8,9-dihydrodiols were essentially inactive as skin tumor initiators. Our results suggest that the 3,4-dihydrodiol of 7,12-dimethylbenz(a)anthracene is a proximal carcinogen and that the "bay region" diol-epoxide may be the ultimate carcinogenic form of DMBA.

Comparison of mutagenesis and malignant transformation by dihydrodiols from benz[a]anthracene and 7,12-dimethylbenz[a]anthracene

Five dihydrodiols derived from benz[a]anthracene (BA) and 4 dihydrodiols derived from 7,12-dimethylbenz[a]anthracene (DMBA) have been tested, together with the parent hydrocarbons, for their abilities to induce mutations to 8-azaguanine resistance in V79 (Chinese hamster cells and malignant transformation in M2 mouse fibroblasts. The syn- and anti-isomers of benz[a]anthracene 8,9-diol 10,11-oxide were also tested for biological activity in these two systems. The non-K-region 1,2- and 3,4-dihydrodiols of BA induced mutations but the non-K-region 8,9-dihydrodiol and the K-region 5,6-dihydrodiol were inactive as mutagens; none of these BA diols transformed M2 mouse fibroblasts. The 3,4- and the 8,9-dihydrodiols derived from 7,12-dimethylbenz[a]anthracene induced mutations in V79 cells and malignant transformation in M2 mouse fibroblasts and both were more active than the hydrocarbon itself. The K-region 5,6-dihydrodiol and the non-K-region 10,11-dihydrodiol of DMBA were inactive in both test systems. The results are not inconsistent with other data suggesting that the metabolic activation of both BA and DMBA occurs through conversion of the respective 3,4-dihydrodiols into the related vicinal diol-epoxides, although other dihydrodiols may also be involved in vivo. Both the BA diol-epoxides tested were mutagenic, but although the anti-isomer transformed M2 fibroblasts, the syn-isomer was inactive.

Comparative metabolism and DNA binding of 7,12-dimethylbenz[a]anthracene and its weakly carcinogenic 5-fluoro analog

Cultured Syrian hamster embryo cells readily convert both the carcinogenic polycyclic aromatic hydrocarbon, 7,12-dimethylbenz[a]anthracene (DMBA), and its weakly carcinogenic analogue, 5-fluoro-7,12-dimethylbenz[a]anthracene (5F-DMBA), to water soluble metabolites. DMBA, however, binds to the hamster cell DNA at least 2.8-3.0 times more extensively than 5F-DMBA. Likewise, 5F-DMBA is converted to water soluble metabolites by liver microsomal preparations at a rate equal to DMBA, but the latter compound binds to DNA 2.6-3.2 times more effectively.

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.

Comparison of metabolism-mediated binding to DNA of 7-hydroxymethyl-12-methylbenz(a)anthracene and 7, 12-dimethylbenz(a)anthracene

Comparison of the binding to DNA of 7-hydroxymethyl-12-methylbenza(a)anthracene and 7, 12-dimethylbenz(a)anthracene (DMBA) catalyzed by mouse embryo cells in culture or by rat liver microsomes indicates that the products formed are different for the two hydrocarbons. Thus, the hydroxy compound is not an intermediate in the binding of DMBA to DNA in these systems. Binding of the hydroxy compound to DNA in mouse embryo cells is less efficient than for DMBA and is inhibited by 1,1,1-trichloropropylene 2,3-oxide, an inhibitor of epoxide hydrase. This and the fluorescence spectra of the hydroxy compound-DNA adducts indicate that the hydroxy compound is activated for DNA binding through the formation of a diol-epoxide in the 1,2,3,4-ring. As previously found for DMBA, this is consistent with the activation of this compound through a bay-region diol-epoxide.

DNA repair in Syrian hamster embryo cells treated with 7,12-dimethylbenz[a]anthracene and its weakly carcinogenic 5-fluoro analog

The postreplication repair capacity of Syrian hamster embryo cells in culture was determined after treatment with the potent carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) and its weakly carcinogenic analog 5-F-DMBA. The size and amount of daughter DNA sedimenting as high-molecular-weight DNA were found to be less in the DMBA treated cells than in the 5-F-DMBA-treated cells. This difference probably depends upon the types of adducts entering DNA replication.

Identification of 7,12-dimethylbenz[a]anthracene metabolites that lead to mutagenesis in mammalian cells

The mutagenicity of 7,12-dimethylbenz[a]-anthracene (DMBA) and 11 of its enzymatically derived metabolites was tested with Chinese hamster V79 cells for identification of mutagenic metabolites. The metabolites consisted of 7-hydroxymethyl-12-methylbenz[a]anthracene, 7-methyl-12-hydroxymethylbenz[a]anthracene, 7,12-dihydroxymethylbenz[a]anthracene, three trans-3,4-diols, two trans-5,6-diols, and three trans-8,9-diols, all of which derived from DMBA or from the hydroxymethyl derivatives. Mutations were characterized by resistance to ouabain and 6-thioguanine. None of the tested metabolites were mutagenic in V79 cells, which do not metabolize polycyclic aromatic hydrocarbons. Therefore, mutagenesis in the V79 cells was tested in the presence of golden hamster cells capable of metabolizing polycyclic aromatic hydrocarbons (cell-mediated assay). In this assay, DMBA, 7-hydroxymethyl-12-methylbenz[a]anthracene, 7-methyl-12-hydroxymethylbenz[a]anthracene, and their trans3,4-diols were mutagenic for both genetic markers, and the mutagenic response increased as a function of the hydrocarbon dose. All other metabolites were either inactive or showed up to a 4-fold higher mutation frequency than the untreated V79 cells for ouabain and 6-thioguanine resistance. The DMBA-trans-3,4-diol was the only metabolite that was more active than DMBA itself; at 0.05 muM it was 6-8 times more active than DMBA itself; at 0.05 muM it was 6-8 times more active than DMBA in inducing both ouabain and 6-thioguanine resistance. This diol was mutagenic at a dose as low as 0.01 muM. Mutagenesis by DMBA and the trans-3,4-diols was inhibited by 7,8-benzoflavone, an inhibitor of mixed-function oxidases. Analysis of DMBA metabolism in intact golden hamster cells indicated that DMBA-trans-3,4-diol is one of the major metabolites produced. Our results therefore suggest that DMBA-trans-3,4-diol may be metabolized to a diol-epoxide, presumably the trans-3,4-diol-1,2-epoxide, which may be a major reactive metabolite responsible for DMBA mutagenicity in mammalian cells.

Identification of four trans-3,4-dihydrodiol metabolites of 7,12-dimethylbenz[a]anthracene and their in vitro DNA-binding activities upon further metabolism

Trans-3,4-dihydrodiols of 7,12-dimethylbenz[a]anthracene (7,12-Me2BA), 7-methyl-12-hydroxymethylbenz[a]anthracene (7-Me-12-OHMeBA), 7-hydroxymethyl-12-methylbenz[a]anthracene (7-OHMe-12-MeBA), and 7,12-di(hydroxymethyl)benz[a]anthracene [7,12-(OHMe)2BA] have been identified as metabolites of the potent carcinogenic and adrenocorticolytic agent 7,12-MeBA. The four trans-3,4-dihydrodiols were identified by their (i) ultraviolet-visible absorption and fluorescence properties, (ii) different retention times on both reversed-phase and normal-phase high-pressure liquid chromatography, (iii) mass spectral analysis, and (iv) inability to form vicinal cis-acetonides. Upon further metabolism by liver microsomes, the trans-3,4-dihydrodiols of 7,12-Me2BA, 7-Me-12OHMeBA, and 7-OHMe-12-MeBA were found to give rise to products that bind more strongly to DNA in vitro than do the products of 7,12-Me2BA. The evidence suggests that one or more of the four trans-3,4-dihydrodiols may be the proximate carcinogenic and adrenocorticolytic metabolites.

Reduction of respiratory tract binding of benzo[a]pyrene in mice by immunization

Male inbred A/J mice immunized by combined ip and intranasal administration of a bovine serum albumin conjugate of 5-fluoro-12-methylbenzanthryl-7-acetic acid developed tracheal antibodies capable of binding the carcinogen benzo[a]pyrene (BP). Immunized mice administered 92 ng of [3H]BP intranasally exhibited a one-third reduction in BP content in respiratory tract tissues (nose and trachea) when compared with control mice 20 hours after BP administration.

Synthesis and carcinogenic activity of 5-fluoro-7-(oxygenated methyl)-12-methylvenz[a]anthracenes

Treatment of 7,12-benz[a]anthraquinone (2) with methylmagnesium iodide or methyllithium yields mixtures of cis- and trans-7,12-dihydro-7,12-dihydroxy-7,12-dimethylbenz[a]anthracenes (3a,b), in which the ratio of cis to trans lies in the 3--4:1 region. Each isomer afforded high yields of 7-chloromethyl-12-methylbenz[a]anthracene (5) on treatment with hydrogen chloride in ethyl acetate. Similarly, 5-fluoro-7,12-benz[a]anthraquinone (8) afforded a mixture of cis- and trans-5-fluoro-7,12-dihydro-7,12-dihydroxy-7,12-dimethylbenz[a]anthracenes (9) which yielded 7-chloromethyl-5-fluoro-12-methylbenz[a]anthracene (10) on treatment with HCl. The chloromethyl compounds, 5 and 10, yielded 7-acetoxymethyl-12-methylbenz[a]anthracene (6) and 7-acetoxymethyl-5-fluoro-12-methylbenz[a]anthracene (11) on treatment with acetate ion. Hydrolysis of 6 and 11 yielded 7-hydroxymethyl-12-methylbenz[a]anthracene (7) and 5-fluoro-7-hydroxymethyl-12-methylbenz[a]anthracene (12), respectively. Since neither 11 nor 12 is appreciably carcinogenic, the carcinogenic metabolism of 7,12-dimethylbenz[a]anthracene (DMBA) probably does not involve attack at the 7-methyl group.

Formation of glucuronic acid conjugates of 7,12-dimethylbenz(a)anthracene phenols in 7,12-dimethylbenz(a)anthracene-treated hamster embryo cell cultures

Secondary cultures of hamster embryo cells exposed to 0.5 nmol [G-3H]7,12-dimethylbenz(a)anthracene (DMBA) per ml medium metabolized more than 90% of the DMBA within 48 hr. Samples of medium were extracted with chloroform, methanol, and water. The chloroform phases contained about one-third of the DMBA metabolites; the major chloroform-extractable metabolite was 8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz(a)anthracene. Beta-glucuronidase treatment of the aqueous methanol-soluble metabolites converted almost one-half of them to chloroform-soluble metabolites, of which more than 80% were identified as phenolic derivatives of DMBA. Similar metabolite profiles were obtained by treating the medium with beta-glucuronidase before chloroform extraction. Separation of the methyl group-hydroxylated derivatives of DMBA from the phenolic derivatives was accomplished by high-pressure liquid chromatography. Small amounts of hydroxymethyl derivatives were detected only in the chloroform-extractable material, whereas DMBA phenols were the major component of the beta-glucuronidase-released mateirla. These results indicate that the major pathway of DMBA metabolism in hamster embryo cells is oxidation of the aromatic rings and not oxidation of the methyl groups.