7-(hydroxymethyl)-12-methylbenz(a)anthracene-sulfate-ester and 7-hydroxymethyl-12-methylbenz(a)anthracene

The hypothesis was tested that an ultimate carcinogen of 7-hydroxymethyl-12-methylbenz[a]anthracene (HMBA), a major metabolite of 7,12-dimethylbenz[a]anthracene (DMBA), is a benzylic carbonium ion generated from an exceptionally reactive aralkylating metabolite, such as an electrophilic sulfate ester. In conformity with this hypothesis, sarcomas were rapidly induced in rats following repeated subcutaneous injection of HMBA (67%) or its electrophilic sulfate ester, sodium 7-sulfooxymethyl-12-methylbenz[a]anthracene (SMBA) (100%). It would appear from the results summarized here that the search for a carcinogenic metabolite of DMBA has been successful. In addition, an aralkylating electrophilic mutagen and carcinogen has been prepared from HMBA, which is itself either an ultimate carcinogen or a direct precursor of an ultimate carcinogen, i.e., a benzylic carbonium ion.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Carcinogens; Female; Mutagens; Rats; Rats, Sprague-Dawley; Sarcoma, Experimental

Metabolic activation of 7-hydroxymethyl-12-methylbenz[a]anthracene (HMBA) and related hydroxymethyl polycyclic aromatic hydrocarbons to electrophilic and mutagenic sulfuric acid esters has been demonstrated previously (Watabe et al., In: Xenobiotic Metabolism and Disposition (Eds. Kato R, Estabrook RW and Cayen MN), pp. 393-400. Taylor & Francis, London, 1989). In the present study, the rat hepatic sulfotransferase activity catalyzing the formation of such reactive sulfuric acid esters was inhibited strongly by dehydroepiandrosterone, a typical substrate hydroxysteroid sulfotransferases (HSSTs). Pentachlorophenol, a potent phenol sulfotransferase inhibitor, had little effect in this regard. A marked sex difference was observed for the hepatic cytosolic sulfotransferase activity for HMBA in rats. This sex difference was age-related; no significant difference was observed in preweanling rats, whereas in adult rats female rat liver showed a much higher enzyme activity. These age- and sex-related differences in the sulfonation of HMBA reflect the regulation of HMBA sulfotransferase activity by gonadal hormones as previously demonstrated with HSSTs. Thus, pretreatment with estradiol benzoate significantly enhanced the sulfotransferase activity for HMBA in both male and female rats, (P less than 0.01 and P less than 0.05 respectively), whereas testosterone propionate pretreatment decreased this activity. Castration of male rats increased the HMBA sulfotransferase activity 2- to 3-fold compared with that in control animals. By contrast, ovariectomy reduced the enzyme activity 38% in females. These results imply that rat liver HSST activity is responsible for the sulfonation of HMBA. Intraperitoneal injection of HMBA (0.25 mumol/g body wt) into infant rats produced benzylic DNA adducts in the liver which were chromatographically identical with those obtained from incubations of HMBA with deoxyguanosine and deoxyadenosine in the presence of hepatic cytosolic sulfotransferase activity. Intraperitoneal administration of sodium 7-sulfooxymethyl-12-methylbenz[a]anthracene resulted in much higher levels of these adducts and the deoxycytidine adduct in the liver DNA than did an equimolar amount of the parent hydroxymethyl hydrocarbon. The levels of hepatic benzylic DNA adducts formed from HMBA were reduced markedly by pretreatment of rats with dehydroepiandrosterone, a strong inhibitor of hepatic sulfotransferase activity for this hydrocarbon.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Age Factors; Animals; Biotransformation; Castration; Dehydroepiandrosterone; Estradiol; Female; Liver; Male; Pentachlorophenol; Rats; Rats, Inbred Strains; Sex Factors; Sulfotransferases; Sulfurtransferases; Testosterone

Although a bay-region dihydrodiolepoxide metabolite has been considered as a principal ultimate electrophilic and carcinogenic form of 7,12-dimethylbenz[a]anthracene (DMBA), other reactive metabolites might also play a role in the activation of this hydrocarbon in vivo. Earlier studies suggested the hydroxylation of a meso-anthracenic methyl group with subsequent formation of a benzylic ester bearing a good leaving group (e.g. sulfate) as a metabolic activation pathway for DMBA. In support of this hypothesis, the formation of an electrophilic and mutagenic sulfuric acid ester of 7-hydroxymethyl-12-methylbenz[a]anthracene (HMBA) by rat liver cytosolic sulfotransferase activity has previously been demonstrated, but no data have been reported on the carcinogenicity of this reactive ester. In the present study, we compared the carcinogenicity of chemically synthesized sodium 7-sulfooxymethyl-12-methylbenz[a]anthracene (SMBA) with that of the parent methyl and hydroxymethyl hydrocarbons. For this purpose, tests were made in several animal tumor models: induction of hepatomas in male B6C3F1 mice, lung adenoma induction in A/J mice, initiation of mouse skin tumors, development of sarcomas in rats at the injection sites, and initiation of preneoplastic enzyme-altered foci in rat liver. Data from all of these studies indicate that SMBA is not more carcinogenic than DMBA or HMBA. In addition, the carcinogenic activity of HMBA was not altered by dehydroepiandrosterone, a strong inhibitor of sulfotransferase activity for HMBA. DMBA produced only a low level of hepatic benzylic DNA adducts in rats when a relatively high dose was administered. These adducts constitute less than 5% of total DMBA residues bound to hepatic DNA. The rest of the adducts appear to be associated with other electrophilic intermediates including the dihydrodiol epoxide metabolites. Based on the results of our present study, it is unlikely that DMBA exerts its carcinogenic activity via metabolic activation to SMBA.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Adenoma; Administration, Topical; Animals; Chlorides; Cytosol; DNA; Female; Injections, Intraperitoneal; Injections, Subcutaneous; Liver; Liver Neoplasms, Experimental; Lung Neoplasms; Male; Mice; Mice, Inbred Strains; Mutagens; Papilloma; Rats; Rats, Inbred Strains; Salmonella typhimurium; Skin Neoplasms; Sulfotransferases

DNA and RNA adducts that were chromatographically identical to those formed in vitro on reaction of 7-sulfooxymethyl-12-methyl-benz[a]anthracene with guanine and adenine nucleosides were formed in the livers of rats and mice given i.p. injections of 7-hydroxymethyl- or 7-sulfooxymethyl-12-methyl-benz[a]anthracene. Considerably higher levels of these hepatic adducts were obtained from the latter short-lived electrophilic ester than from the hydroxymethyl compound. These observations are consistent with the finding of rat liver cytosolic sulfotransferase activity for 7-hydroxymethyl-12-methylbenz[a]anthracene (Watabe et al., Science 215, 403, 1982). Formation of these hepatic adducts from 7-hydroxymethyl-12-methylbenz[a]anthracene was inhibited by prior administration to rats of dehydroepiandrosterone, an inhibitor of the sulfotransferase activity for this hydroxymethyl hydrocarbon.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Carcinogens; Chromatography, High Pressure Liquid; DNA; Female; Liver; Male; Mice; Rats; RNA; Sulfurtransferases; Tritium

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Benz(a)Anthracenes; Carcinogens; Chemical Phenomena; Chemistry; Cytosol; In Vitro Techniques; Liver; Male; Protein Binding; Proteins; Rats; Rats, Inbred Strains

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.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Benz(a)Anthracenes; Biotransformation; Mutagenicity Tests; Mutagens; Salmonella typhimurium; Structure-Activity Relationship; Sulfuric Acids