Adrenocorticolytic derivatives of benz[a]anthracene

Photochemical Reaction of 7,12-Dimethylbenz[a]anthracene (DMBA) and Formation of DNA Covalent Adducts

DMBA, 7,12-dimethylbenz[a]anthracene, is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a probable human carcinogen. It has been found that DMBA is phototoxic in bacteria as well as in animal or human cells and photomutagenic in Salmonella typhimurium strain TA102. This article tempts to explain the photochemistry and photomutagenicity mechanism. Light irradiation converts DMBA into several photoproducts including benz[a]anthracene-7,12-dione, 7-hydroxy-12-keto-7-methylbenz[a]anthracene, 7,12-epidioxy-7,12-dihydro-DMBA, 7-hydroxymethyl-12-methylbenz[a]anthracene and 12-hydroxymethyl-7-methylbenz[a]anthracene. Structures of these photoproducts have been identified by either comparison with authentic samples or by NMR/MS. At least four other photoproducts need to be assigned. Photo-irradiation of DMBA in the presence of calf thymus DNA was similarly conducted and light-induced DMBA-DNA adducts were analyzed by ³²P-postlabeling/TLC, which indicates that multiple DNA adducts were formed. This indicates that formation of DNA adducts might be the source of photomutagenicity of DMBA. Metabolites obtained from the metabolism of DMBA by rat liver microsomes were reacted with calf thymus DNA and the resulting DNA adducts were analyzed by ³²P-postlabeling/TLC under identical conditions. Comparison of the DNA adduct profiles indicates that the DNA adducts formed from photo-irradiation are different from the DNA adducts formed due to the reaction of DMBA metabolites with DNA. These results suggest that photo-irradiation of DMBA can lead to genotoxicity through activation pathways different from those by microsomal metabolism of DMBA.

Rapid induction of mammary cancer by repeated subcutaneous injection of the trans-3,4-dihydrodiol of 7,12-dimethylbenz[a]anthracene in the female Sprague–Dawley rat

The oral administration of a single 20mg dose of 7,12-dimethylbenz[a]anthracene regularly and rapidly induces mammary cancer in 50 day-old Sprague-Dawley female rats [Experimental Leukemia and Mammary Cancer, 1979, p. 74]. Several mechanisms by which 7,12-dimethylbenz[a]anthracene induces mammary cancer have been proposed and various derivatives have been implicated as possible proximate or ultimate electrophilic and carcinogenic forms of this hydrocarbon. Here we show that 7,12-dimethylbenz[a]anthracene-trans-3,4-dihydrodiol rapidly induces mammary cancer by repeated subcutaneous injection in a high proportion of female Sprague-Dawley rats without malignancies at the site of injection, whereas its more lipid soluble diacetate derivative induced injection site sarcomas in addition to distal mammary cancers. By contrast, repeated subcutaneous injection of 7,12-dimethylbenz[a]anthracene and its 7-meso-aldehyde derivative induced subcutaneous sarcoma in most, if not all, rats and a few mammary cancers.

Mass spectrometric analysis of 7-sulfoxymethyl-12-methylbenz[a]anthracene and related electrophilic polycyclic aromatic hydrocarbon metabolites

The Meso-region theory of polycyclic aromatic hydrocarbon (PAH) carcinogenesis predicts that the development of pronounced carcinogenicity depends on the introduction of a good leaving group on alkyl side-chains attached to the exceptionally reactive meso-anthracenic or L-region positions of PAHs. Thus, the first step in carcinogenesis by methylated PAHs such as 7,12-dimethylbenz[a]anthracene (DMBA) would be the hydroxylation of the L-region methyl groups, particularly the 7-methyl group. The second would be the formation of a metabolite, e.g. a sulfate ester, which is expected to be a good leaving group capable of generating a highly reactive benzylic carbocation. 7-Hydroxymethyl-12-methylbenz[a]anthracene (7-HMBA) is a metabolite of DMBA, and sulfation of 7-HMBA to a 7-sulfoxymethyl metabolite (7-SMBA) is a known Phase II metabolic process designed to facilitate excretion, but actually enabling more destructive side-reactions. These side-reactions occur with generation of an electrophilic 7-methylene carbonium ion, and/or by in vivo halide exchange to provide neutral side-products more capable of entering cells, especially those of DMBA target tissues. Electrospray ionization mass spectrometry (MS) enabled us to visualize 7-SMBA as an intact m/z 351 conjugate anion by negative mode, and as a released m/z 255 carbonium ion by positive mode. Upon prolonged refrigeration, 7-SMBA accumulated an m/z 383 photooxide, which appeared capable of re-evolving the starting material as visualized by tandem quadrupole MS, or MS/MS. The 7-SMBA carbonium ion provided interpretable fragments when studied by fragment ion MS/MS, including those representing the loss of up to several protons. Subtle differences in this property were encountered upon perturbing 7-SMBA, either by warming it at 37 degrees C for 2 h or by substituting the initial sulfoxy group with an iodo group. Side-reactions accounting for such proton losses are proposed, and are of interest whether they occur in the mass spectrometer, in solution or both; these proposals include acidity at the 12-methyl position and cyclization between the 12-methyl group and the adjacent C-1 position. It is also suggested that such side-reactions may comprise one route to relieving steric strain arising between the 12-methyl group and the angular benzo ring of 7-SMBA.

The metabolism of formyl-substituted benzanthracenes to hydroxymethyl metabolites in rat liver in vitro and in vivo

Hydroxylation of benzylic methyl carbon atoms on drugs and carcinogenic polycyclic aromatic hydrocarbons (PAHs) forms benzylic alcohols. Many carcinogenic and mutagenic PAHs bear a primary or secondary benzylic hydroxyl group attached to the meso-region of the molecule. According to the unified theory, PAHs bearing a benzylic hydroxyl group are proximate carcinogenic metabolites. This paper demonstrates that carcinogenic benz[a]anthracenes bearing a formyl group at the meso-region undergo enzymatic reductive metabolism to the corresponding carcinogenic benzylic alcohol in vitro and in vivo. The unified theory would then predict sulfuric acid esterification of such benzylic alcohols as the final common step in their metabolic activation to generate ultimate electrophilic benzylic carbocations. Finally, oxidative metabolism of 7-formylbenz[a]anthracenes gives rise to corresponding carboxylic acids and other oxygenated metabolites that are carcinogenically inert. Thus, oxidative metabolism of meso-region formyl compounds represents an avenue for the elimination of the carcinogen in a detoxified form.

Biooxidation of 7,12-dimethylbenz[a]anthracene in rat subcutaneous tissue

The present study demonstrates the biooxidation of 7,12-dimethylbenz[a]anthracene to the corresponding hydroxyalkyl metabolites, 7-hydroxymethylbenz[a]anthracene, 7-hydroxymethyl-12-methylbenz[a]anthracene, and 7,12-dihydroxymethylbenz[a]anthracene in the dorsal subcutaneous tissue of the rat, in vivo, a tissue highly susceptible to the carcinogenic action of 7,12-dimethylbenz[a]anthracene.

Mutagenicity of benzylic acetates, sulfates and bromides of polycyclic aromatic hydrocarbons

Studies were performed to determine the direct mutagenicity of the acetates and some bromides and sulfates of hydroxymethyl polycyclic aromatic hydrocarbons in S. typhimurium strains TA98 and TA100. Benzylic acetates, bromides and sulfates were synthesized and characterized. The compounds tested were benzyl alcohol, 5-hydroxymethylchrysene, 1-hydroxymethylpyrene, 6-hydroxymethylbenzo[a]pyrene, 6-(2-hydroxyethyl)benzo[a]pyrene, 6-hydroxymethylanthanthrene, 9-hydroxymethylanthracene, 9-hydroxymethyl-10-methylanthracene, 7-hydroxymethylbenz[a]anthracene, 7-(2-hydroxyethyl)benz[a]anthracene, 12-hydroxymethylbenz[a]anthracene, 7-hydroxymethyl-12-methylbenz[a]anthracene, 12-hydroxymethyl-7-methylbenz[a]anthracene, 1-hydroxy-3-methylcholanthrene, 2-hydroxy-3-methylcholanthrene, 3-hydroxy-3, 4-dihydrocyclopental[cd]pyrene and 4-hydroxy-3, 4-dihydrocyclopental[cd]pyrene. The benzylic sulfate esters of 6-hydroxymethylbenzo[a]pyrene and 7-hydroxymethylbenz[a]anthracene were the most mutagenic compounds, whereas the aliphatic sulfate ester of 7-hydroxyethylbenz[a]anthracene did not cause an increase in mutations above background. All meso-anthracenic benzylic acetate esters were mutagenic in both strains with various degrees of activity, whereas the corresponding non-benzylic esters were inactive, as expected. Of the non-meso-benzylic acetate esters, only the 3-acetoxy-3, 4-dihydrocyclopenta[cd]pyrene was mutagenic. In the benzylic bromide series, only the eight mesoanthracenic were mutagenic, whereas benzyl bromide and 5-bromomethylchrysene were inactive. The aliphatic bromides, 6-(2-bromoethyl)benzo[a]pyrene and 7-(2-bromoethyl)benz[a]anthracene did not display significant activity. The potencies of the acetate esters more accurately reflect the mutagenicity because the rate of solvolysis did not compete with the reactivity of the esters with bacterial DNA. In the case of benzylic sulfates and bromides, the rate of solvolysis was very rapid and could have diminished the level of mutagenicity, depending on the assay conditions. These results demonstrate that meso-anthracenic benzylic acetates, sulfates and bromides are mutagenic, whereas benzylic acetate esters attached to other carbon atoms are inactive.

Combined reversed-phase and normal-phase high-performance liquid chromatography in the purification and identification of 7,12-dimethylbenz[a]anthracene metabolites

A total of 37 compounds have been identified as rat liver microsomal metabolites of the potent carcinogen 7,12-dimethylbenz[a]anthracene and its hydroxymethyl derivatives 7-methyl-12-hydroxymethylbenz[a]anthracene, 7-hydroxymethyl-12-methylben[a]anthracene and 7,12-dihydroxymethylbenz[a]anthracene. The metabolites were characterized by: (i) retention times on reversed-phase (with a C18 column) and normal-phase (with a silica gel column) high-performance liquid chromatography (HPLC); (ii) ultraviolet absorption and fluorescence spectra; (iii) mass spectral analysis; (iv) optical activity; and (v) comparison of the physicochemical properties of the metabolites with those of some available synthetic standards. The 37 identified metabolites include four trans-3,4-dihydrodiols, four trans-5,6-dihydrodiols, four trans-8,9-dihydrodiols, four trans-10,11-dihydrodiols, two methyl carboxylic acids, two methyl aldehydes, two hydroxymethyl aldehydes, four 2-phenols, four 3-phenols, four 4-phenols and three hydroxymethyl derivatives. The trans configuration of the dihydrodiols was determined by their inability to form vicinal cisacetonides. Seven dihydrodiol metabolites were found to be optically active. Detailed physicochemical properties, such as ultraviolet absorption spectra, fluorescence spectra measured in methanol and in 0.1 N NaOH, major mass ions from mass spectral analysis and the retention times on two HPLC systems, are presented in support of the structural assignments.

The binding of benz(a)anthracene derivatives to glyceraldehyde-3-phosphate dehydrogenase and mammary tissue following exposure to laboratory light

7,12-Dimethylbenz(a)anthracene (DMBA) and 7-methoxymethyl-12-methylbenz(a)anthracene (MeO-DMBA) are converted to a number of products during short exposures in aqueous suspension to laboratory illumination. The mixture of products binds to glyceraldehyde-3-phosphate dehydrogenase (GPDH) while inhibiting its activity but there is no apparent relationship between the binding and inhibition of enzyme activity. There is little, or no, binding or enzyme inhibition when the compounds are protected from light. 7-Bromomethyl-12-methylbenz(a)anthracene (Br-DMBA) binds to GPDH whether photoactivated or not but enzyme inhibition depends upon light exposure. The binding of light-exposed DMBA by surviving rat mammary tissue was five-times greater than with the unchanged hydrocarbon. Binding of MeO-DMBA products also occurred after light exposure but not in the dark.