The carcinogen, 7-hydroxymethyl-12-methylbenz[a]anthracene, is activated and covalently binds to DNA via a sulphate ester

Chemical applicability domain of the local lymph node assay (LLNA) for skin sensitisation potency. Part 4. Quantitative correlation of LLNA potency with human potency

Prediction of skin sensitisation potential and potency by non-animal methods is the target of many active research programmes. Although the aim is to predict sensitisation potential and potency in humans, data from the murine local lymph node assay (LLNA) constitute much the largest source of quantitative data on in vivo skin sensitisation. The LLNA has been the preferred in vivo method for identification of skin sensitising chemicals and as such is potentially valuable as a benchmark for assessment of non-animal approaches. However, in common with all predictive test methods, the LLNA is subject to false positives and false negatives with an overall level of accuracy said variously to be approximately 80% or 90%. It is also necessary to consider the extent to which, for true positives, LLNA potency correlates with human potency. In this paper LLNA potency and human potency are compared so as to express quantitatively the correlation between them, and reasons for non-agreement between LLNA and human potency are analysed. This leads to a better definition of the applicability domain of the LLNA, within which LLNA data can be used confidently to predict human potency and as a benchmark to assess the performance of non-animal approaches.

Structure, function and carcinogenicity of metabolites of methylated and non-methylated polycyclic aromatic hydrocarbons: a comprehensive review

The Unified Theory of PAH Carcinogenicity accommodates the activities of methylated and non-methylated polycyclic aromatic hydrocarbons (PAHs) and states that substitution of methyl groups on meso-methyl substituted PAHs with hydroxy, acetoxy, chloride, bromide or sulfuric acid ester groups imparts potent cancer producing properties. It incorporates specific predictions from past researchers on the mechanism of carcinogenesis by methyl-substituted hydrocarbons, including (1) requirement for metabolism to an ArCH2X type structure where X is a good leaving group and (2) biological substitution of a meso-methyl group at the most reactive center in non-methylated hydrocarbons. The Theory incorporates strong inferences of Fieser: (1) The mechanism of carcinogenesis involves a specific metabolic substitution of a hydrocarbon at its most reactive center and (2) Metabolic elimination of a carcinogen is a detoxifying process competitive with that of carcinogenesis and occurring by a different mechanism. According to this outlook, chemical or biochemical substitution of a methyl group at the reactive meso-position of non-methylated hydrocarbons is the first step in the mechanism of carcinogenesis for most, if not all, PAHs and the most potent metabolites of PAHs are to be found among the meso methyl-substituted hydrocarbons. Some PAHs and their known or potential metabolites and closely related compounds have been tested in rats for production of sarcomas at the site of subcutaneous injection and the results strongly support the specific predictions of the Unified Theory.

Inhibition and binding studies of coenzyme A and bovine phenol sulfotransferase

Phenol sulfotransferases (PSTs, EC 2.8.2.1) catalyze sulfonyl group transfer from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to the hydroxyl oxygen of aromatic acceptor substrates. The structural overlap between PAPS and coenzyme A (CoA) suggested a possible role of this common acyl carrier in modulating PST activity. To test this hypothesis, purified recombinant bovine PST was examined by kinetic and affinity chromatographic approaches. After demonstrating PST enzyme inhibition by CoA, systematic variation of CoA and PAPS concentrations indicated simple competitive inhibition with K(i) = 1. 3 microM. PST bound to CoA-agarose, attached via the pantetheinyl thiol group, was eluted with PAP but not by 2-naphthol. This observation was consistent with the pattern of inhibition. Additional members of the sulfotransferase superfamily, as well as acylated CoAs, should be further investigated.

Mutagenicity of 6-sulfooxymethylbenzo[a]pyrene in Salmonella typhimurium and Chinese hamster V79 cells

6-Sulfooxymethylbenzo[a]pyrene (SMBP) is an ultimate and reactive form of 6-hydroxymethybenzo[a]pyrene (HMBP), which is converted into SMBP by the mediation of sulfotransferase. SMBP and HMBP with metabolic activation were mutagenic to S. typhimurium TA98 and TA100. The number of mutation per plate in strain TA98 was proportional to the concentrations of SMBP ranging from 0.2 to 1.0 nmol/plate, whereas that in strain TA100 was decreased at concentrations above 0.6 nmol/plate. The mutation frequencies by HMBP was also increased in a dose dependent manner in both strains. Furthermore, SMBP and HMBP were highly mutagenic and cytotoxic to Chinese hamster lung fibroblast (V79) cells. A dose-dependent increase in mutation frequencies at both hypoxanthine:guanine phosphoribosyltransferase (HGPRT) and sodium/potassium-ATPase (Na/K-ATPase) loci were found in V79 cells treated with SMBP and HMBP. The cytotoxicity of SMBP was increased with the increasing concentrations up to 2.5 microM, where the survival frequency and growth rate were decreased to almost 40% and 30% of the control value, respectively. The survival frequencies of V79 cells by HMBP were also decreased in a dose dependent manner up to 180 microM as similar to those of SMBP but the effects were less remarkable. SMBP was progressively accumulated in V79 cells, reaching plateau in just 30 min. A dose dependent increase in complex formation with DNA or proteins was observed by treatment with SMBP. The mutagenicity and cytotoxicity of SMBP and HMBP may be derived from their binding capacity to DNA in V79 cells and S. typhimurium.

7-Sulfooxymethylbenz[a]anthracene is an ultimate electrophilic and carcinogenic form of 7-hydroxymethylbenz[a]anthracene

The hypothesis was tested that 7-sulfooxymethylbenz[a]anthracene (7-SBA) is an ultimate electrophilic and carcinogenic form of 7-hydroxymethylbenz[a]anthracene. In conformity with this hypothesis, 7-SBA was more carcinogenic than 7-HBA in inducing sarcomas at the site of repeated subcutaneous injection. These metabolites were individually administered to female Sprague-Dawley rats, beginning at 30 days of age, in 0.2 mumol doses given three times each week for 20 doses. One year after the first injection of 7-SBA, seven of thirteen female Sprague-Dawley rats had developed sarcomas. 7-HBA, on the other hand, had induced sarcomas at the site of injection in only two of tweleve rats. No tumors developed either in the control group given sesame oil:DMSO only or in the untreated control group. It would appear from the results summarized here that the search for an ultimate electrophilic and carcinogenic form of 7-HBA has been successful.

7-Sulfooxymethyl-12-methylbenz[a]anthracene is an exceptionally reactive electrophilic mutagen and ultimate carcinogen

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.

Major hydroxysteroid sulfotransferase STa in rat liver cytosol may consist of two microheterogeneous subunits

The possible existence of two microheterogeneous subunits, designated ST-40P and ST-41P, of hydroxysteroid sulfotransferases in female Sprague-Dawley rat liver cytosol was demonstrated by cloning and sequencing of cDNAs, both isolated from two rat liver cDNA libraries. These subunits consisted of an equal number of amino acid residues with only one amino acid substitution. ST-40P and ST-41P expressed as homodimers from the ST-40 and ST-41 cDNAs in Escherichia coli had enzyme activities toward all of the examined 20 hydroxysteroids, 13 bile acids, and the carcinogen 5-hydroxymethylchrysene (5-HCR), with formation of the reactive metabolite 5-HCR sulfate, at rates very similar to those by STa, the major hydroxysteroid sulfotransferase in rat liver cytosol. This strongly suggested that they are essential components of STa. The present study carried out by using the recombinant enzymes provides the first direct evidence for the identity of sulfotransferases catalysing the sulfation of hydroxysteroids and bile acids and proposes that the current nomenclature system used for distinguishing hydroxysteroid sulfotransferases from bile acid sulfotransferases should be improved.

Roles of electrophilic sulfuric acid ester metabolites in mutagenesis and carcinogenesis by some polynuclear aromatic hydrocarbons

Hydroxylation of meso-methyl groups with subsequent formation of reactive benzylic esters bearing a good leaving group (e.g. sulfate) was proposed as a possible biochemical mechanism of activation and tumorigenicity of methyl-substituted polycyclic aromatic hydrocarbons (PAHs). In support of this postulation, recent studies have demonstrated the formation by rodent hepatic sulfotransferase activity of electrophilic, mutagenic, and carcinogenic sulfuric acid esters of several hydroxymethyl aromatic hydrocarbons including hydroxymethyl derivatives of benz[a]anthracene, 6-hydroxymethylbenzo[a]pyrene, 5-hydroxymethylchrysene, 9-hydroxymethyl-10-methylanthracene, and 1-hydroxymethylpyrene. Besides these hydroxymethyl PAHs containing a primary benzylic alcoholic group, some aromatic hydrocarbons with secondary benzylic hydroxyl functional group(s) are also metabolically activated through sulfuric acid esterification.

Transport, binding, and metabolism of sulfate conjugates in the liver

Sulfate conjugates are a heterogeneous class of polar, anionic metabolites that result from the conjugation of endogenous and exogenous compounds. Sulfate conjugates exhibit a high degree of binding to albumin, the extent of which usually exceeds those of their parent compounds. Preponderant direct and indirect evidence suggests that sulfation activity is slightly higher in the periportal than in the perivenous (centrilobular) region of the liver, but recent immunohistochemical studies imply that specific isoforms of the sulfotransferases may also be preferentially localized in the perivenous region. Entry of sulfate conjugates into the liver cell is poor unless discrete carriers are present. Although known transport carriers exist for the sulfated bile acids, the specificity of the carriers for drug sulfate conjugates is presently unknown. The removal of sulfates is usually by way of biliary excretion while, on occasion, sulfates can be desulfated and participate in futile cycling with their parent compounds. The binding, transport, and hepatic elimination of various drug sulfate conjugates are examined. Non-recirculating studies carried out in the perfused rat liver with the multiple indicator dilution technique under varying input sulfate conjugate concentrations have provided essential information on the effects of vascular (red blood cells and plasma protein) binding on transport and removal of the conjugates. These studies clearly demonstrate the need to study protein binding, transmembrane transfer characteristics across the liver basolateral (sinusoidal) and canalicular membranes, and enzyme zonation in a distributed-in-space fashion in order to properly define the handling of sulfate conjugates in the liver.

Sulfonation in chemical carcinogenesis--history and present status

Many laboratories have characterized the electrophilic metabolites of chemical carcinogens and their covalently bound adducts with genomic DNA in vivo. Recent studies from our laboratory have shown that enzymatic sulfonation of members of several classes of proximate carcinogens containing C- or N-hydroxy groups converts them to electrophilic, mutagenic, and carcinogenic sulfuric acid ester metabolites in mouse liver. These compounds form the subject of this report.

Molecular cloning and functions of rat liver hydroxysteroid sulfotransferases catalysing covalent binding of carcinogenic polycyclic arylmethanols to DNA

Three sulfotransferases (STs) catalysing the metabolic activation of potent carcinogenic polycyclic arylmethanols were purified from female Sprague-Dawley (SD) rat liver cytosol without loss of their enzyme activities in the presence of Tween 20 used for preventing the enzymes from aggregation during purification and identified as hydroxysteroid sulfotransferases (HSTs). All the purified HSTs, STa, STb, and STc, with different electric charges had an apparently equal size of subunit (30.5 kDa) and cross-reacted with polyclonal antibody raised against STa. Our study on molecular cloning of cDNA libraries from two female SD rat livers indicated that both contained cDNA inserts coding for 5 different HST subunits, consisting of 284-285 amino acid residues (M(r), 33,084-33,535) and sharing strong amino acid sequence identity (> 83%). Of the 5 HST subunits, two had an identical amino acid sequence except for only one amino acid residue, and the other two contained only 6 amino acid substitutions in their sequences.

Carcinogen activation by sulfate conjugate formation

The foregoing pages presented a substantial body of data that established that sulfotransferase conjugation can transform many xenobiotics into agents that can modify cellular macromolecules. However, activation by sulfation is rarely the only metabolic pathway that is open to these compounds; other pathways can become more important in response to a variety of factors. This metabolic switching can be produced by substrate concentration, cofactor availability, kinetic factors that dictate the velocity of the various possible conjugation reactions, and, in some cases, competition between Phase-I and Phase-II metabolism. Also, it is important to realize that demonstration of activation by sulfate ester formation in vitro does not necessarily mean that a similar activation process will occur in vivo. Experience also teaches that argument by analogy can be very misleading in the case of sulfate activation. Small structural differences can upset the delicate balance between sulfate activation and the various other competing pathways. Nevertheless, sulfation is an important mechanism by which a number of chemicals are transformed to their activated forms.

Phenol sulfotransferase expression in the airways: enzymological and immunohistochemical demonstration

Phenol (aryl) sulfotransferases (PSTs) provide a conjugative pathway that detoxifies hydroxylated aromatic xenobiotics by esterification with sulfate. Both human and bovine airways have been reported to use this pathway, and in this investigation the bovine system is examined. PST activity in tracheal through fourth generation bronchial mucosal cytosols was 0.1-0.35 nmol/mg protein/min. Activity was generally greater in more distal bronchi and in parenchymal extracts, which contained 0.6-3 nmol/mg/min PST activity. Comparison of the PST activities of bronchial and parenchymal cytosols indicated similar pH activity profiles, although steady state kinetic measurements revealed different Km values for the acceptor substrate 2-naphthol (13.7 microM for bronchial, 31.3 microM for parenchymal). Anion exchange chromatography indicated two PST isoforms being expressed in different ratios. Immunoblot analysis with mouse anti-bovine PST revealed a closely spaced doublet at 32 kDa in both bronchial mucosal and parenchymal cytosolic extracts; however, this doublet was unequally stained in parenchymal extracts. Immunohistochemical analyses revealed faint positive staining of the tracheobronchial epithelium. Greatest immunostaining was observed in the nonciliated secretory epithelial cells of the bronchioles, whereas surrounding smooth muscle, endothelial cells, and alveoli were immunonegative. These results are consistent with the known locations of other detoxification enzymes within the airways.

Inhibition of rat hepatic aryl sulphotransferase IV by dihydrodiol derivatives of benzo[a]pyrene and naphthalene

1. Although neither the (+)- nor (-)-enantiomer of trans-benzo[a]pyrene-7,8-dihydrodiol was a substrate for aryl sulphotransferase IV from rat liver, both enantiomers inhibited the enzyme-catalysed sulphation of 1-naphthalene-methanol with Ki values of 3.7 +/- 0.4 microM for the (+)-enantiomer, and 4.4 +/- 0.3 microM for the (-)-enantiomer. 2. Based on the magnitude of the Ki values, the binding affinity of these dihydrodiols for the aryl sulphotransferase was significantly greater than that for the corresponding phenolic derivatives of benzo[a]pyrene. That is 7-hydroxybenzo[a]pyrene and 8-hydroxybenzo[a]pyrene were both substrates for aryl sulphotransferase IV, with apparent Km values of 280 +/- 41 microM and 370 +/- 72 microM, respectively. 3. Both (+)- and (-)-trans-naphthalene-1,2-dihydrodiols were also inhibitors of aryl sulphotransferase IV, but with higher Ki values than would be expected from previously determined apparent Km and Ki values for (R)-(-)- and (S)-(+)-1,2,3,4-tetrahydro-1-naphthols, respectively.

Bioactivation of 7-hydroxymethyl-12-methylbenz[a]anthracene by rat liver bile acid sulfotransferase I

The bioactivation of 7-hydroxymethyl-12-methylbenz[a]anthracene (HMBA) to an electrophilic sulfuric acid ester metabolite has been shown to be catalyzed by rat liver bile acid sulfotransferase I (BAST I). The sulfation and activation of HMBA by BAST I was determined by the ability of sulfated HMBA to form DNA adducts. The BAST I was also shown to react with rabbit anti-human dehydroepiandrosterone sulfotransferase antisera and to represent a major form of hydroxysteroid/bile acid sulfotransferase in female rat liver cytosol. Higher levels of BAST I activity and immunoreactivity as well as HMBA-DNA adduct formation were detected in female rat liver cytosol than in male rat liver cytosol. The bioactivation of HMBA by pure BAST I was dependent on the presence of 3'-phosphoadenosine 5'-phosphosulfate (PAPS) in the reaction and was inhibited by dehydroepiandrosterone, a physiological substrate for BAST I. Glutathione, a cellular nucleophile with important protective properties, decreased DNA adduct formation in the HMBA sulfation reaction in the absence of glutathione S-transferase activity. These results indicate the usefulness of BAST I to investigate the sulfation and activation of HMBA and probably other hydroxymethylated polyaromatic hydrocarbons to electrophilic and mutagenic metabolites under defined reaction conditions.

Age- and sex-related differences in activation of the carcinogen 7-hydroxymethyl-12-methylbenz[a]anthracene to an electrophilic sulfuric acid ester metabolite in rats. Possible involvement of hydroxysteroid sulfotransferase activity

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.

Activation mechanisms to chemical toxicity

The pathobiology of chemical toxicity may involve "acute lethal injury" (necrosis), "autoxidative injury" (oxygen toxicity), "immunological injury" (neoantigen formation), and malignancy. Toxic chemicals may be activated by reduction, conjugation, radical formation, or oxidation. Oxidative activation may be effected by cytochromes P-450/P-448, flavoprotein monooxygenases, or hydroxyl radicals. The alternative pathways of oxidative metabolism of toxic chemicals, namely, detoxication and activation, are catalysed by the phenobarbital-induced cytochromes P-450 and by the 3-methylcholanthrene-induced cytochromes P-448 respectively. Oxidative metabolism by cytochromes P-450 is followed by conjugation and detoxication, whereas oxidative metabolism by cytochromes P-448 yields reactive intermediates which are not readily conjugated, and thus react with vital intracellular macromolecules, resulting in necrosis, redox cycling and oxygen radical formation, neoantigen production, and mutations. The molecular dimensions of specific substrates, inhibitors and inducers of the PB-cytochromes P-450 indicate that they are globular and are different from those of the cytochromes P-448 which are planar, suggesting that the active sites of the two families of enzymes are different. Oxidative metabolism of planar substrates of cytochromes P-448 results in conformationally-hindered oxygenations, which inhibits subsequent conjugations. Cytochrome P-448 activity may be quantified by the oxidative deethylation of 7-ethoxyresorufin which, unlike benzo(a)pyrene hydroxylation (AHH) is a specific reaction for this family of enzymes. Oxidative metabolism of chemicals varies inversely with the body weight of the animal species, so that chemical toxicity involving oxidative activation, redox cycling, and reactive oxygen is greater the smaller the animal species.

Enzyme-catalyzed detoxication reactions: mechanisms and stereochemistry

Enzyme catalyzed detoxication reactions are one of the primary defenses organisms have against chemical insult. This article reviews current chemical approaches to understanding the cooperative role of enzymes in the metabolism of foreign compounds. Emphasis is placed on chemical and stereochemical studies which help elucidate the mechanism of action and active-site topologies of the detoxication enzymes. The stereoselectivity of the cytochromes P-450 and flavin containing monooxygenases as well as the role of hemoglobin and lipid peroxidation in the primary metabolism of xenobiotics is discussed. Current knowledge of the mechanism and stereoselectivity of epoxide hydrolase is also presented. Three enzymes involved in secondary metabolism of xenobiotics, UDP-glucuronosyltransferase, sulfotransferase and glutathione S-transferase are discussed with particular emphasis on active site topology and cooperative participation with the enzymes of primary metabolism.

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.