Effects of Histidine on Light-Induced DNA Single-Strand Cleavage by Selected Polycyclic Aromatic Hydrocarbons

The combination of UVA light and 1-aminopyrene, 1-hydroxypyrene, 1-hydroxybenzo[ a ]pyrene, 3-aminofluoranthene, 6-aminochrysene, or 5-, 6-, and 7-methylbenz[ a ]anthracenes causes DNA single-strand cleavage. 1-Hydroxypyrene, 1-hydroxybenzo[ a ]pyrene, and 5-methylbenz[ a ]anthracene have been shown to cause DNA cleavage, at least partially, by generating singlet oxygen. Therefore, the presence of histidine, a singlet oxygen quencher, should inhibit the DNA photocleavage. However, the presence of 50 mM histidine greatly enhances the DNA photocleavage caused by these compounds. This effect is due to the inhibition of the photodegradation of the PAH compounds. Therefore, care must be taken when interpreting the singlet oxygen quenching data by histidine. Histidine may coexist with PAHs that have entered the body. The presence of histidine can alter the photochemical reaction and, possibly, the phototoxicity mechanism of the PAHs.     

Time-Integrated DNA Adduct Levels and Relative Tumorigenic Potencies of Six Polycyclic Aromatic Hydrocarbons in Strain A/J Mouse Lung

We have investigated the induction of DNA adducts and adenomas in the lungs of strain A/J mice following the i.p. administration of several polycyclic aromatic hydrocarbons (PAH): pyrene, dibenz[a,h]anthracene (DBA), benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), 5-methylchrysene (5-MeC), 3-methylcholanthrene (3-MC), and cyclopenta[cd]pyrene (CPP). All of the PAH induced lung adenomas, with relative tumor potency rankings as a function of administered dose: DBA = 3-MC > 5-MeC > CPP > B[a]P > B[b]F. DNA adducts reached maximal levels between 3 and 7 days after injection, followed by a gradual decrease. The time-integrated DNA adduct level (TIDAL) was calculated by numerically integrating the areas under the adduct persistence curves extrapolated out to 240 days for each PAH at each dose level. Tumorigenic potencies as a function of TIDAL values for 5-MeC, B[a]P, B[b]F, and CPP were all equal, while 3-MC was 2.6-fold more potent and DBA was 25.8-fold more potent.     

Effect of the Route of Administration on the Induction of Cytogenetic Damage and DNA Adducts in Peripheral Blood Lymphocytes of Rats and Mice by Polycyclic Aromatic Hydrocarbons

Experiments were designed to investigate how the route of exposure to polycyclic aromatic hydrocarbons (PAHs) in mice and rats affects the induction of cytogenetic end points and DNA adduction. Both mice and rats were exposed to 100 mg/kg of benz[ a ]anthracene (B[ a ]A), benzo[ b ]fluoranthene (B[ b ]F), benzo[ a ]pyrene (B[ a ]P), or chrysene (Chr) by gavage or by intraperitoneal injection (i.p.). Peripheral blood was removed by cardiac puncture 7 days after PAH administration. Blood samples were analyzed in parallel for sister chromatid exchange (SCE) frequency, the frequency of micronuclei in cytochalasin B-induced binucleate cells (MN bn ), and DNA adduction using 32P-postlabeling. The i.p. route of exposure produced both the highest levels of cytogenetic damage and DNA adducts for each PAH. The mouse was more sensitive than the rat to PAH exposure as measured by SCE induction and the total amount of DNA adducts/ w g DNA.     

POLYCYCLIC AROMATIC HYDROCARBONS OF DIESEL AND GASOLINE EXHAUST AND DNA ADDUCT DETECTION IN CALF THYMUS DNA AND LYMPHOCYTE DNA OF WORKERS EXPOSED TO DIESEL EXHAUST

Particles present in urban air pollution are mainly derived from diesel- and gasoline-fueled vehicles. Exhaust emission is able to cause several health effects in humans including mutagenicity and carcinogenicity. Polycyclic aromatic hydrocarbons (PAHs) were measured in diesel and gasoline particulate extracts and DNA binding to CT DNA (±S9 and ±XO) was investigated. A large difference in content of 14 PAHs in diesel and gasoline extracts was observed, showing higher concentration of 14 PAHs, 6 carcinogenic PAHs, benzo[a]pyrene (B[a]P) in diesel than in gasoline extracts. Selected PAH standards of B[a]P, benzo[c]fluoranthene (B[c]F), and 3-nitrobenzanthrone (NBA) were used in ³²P-postlabeling/polyacrylamide gel electrophoresis (PAGE) technique to identify CT DNA adducts formed by diesel particulate extracts. CT DNA adduct formation was higher for diesel extracts in comparison with gasoline extracts; however, no clear origin of DNA adducts derived from B[c]F-, 3-NBA-, B[a]P was detected. ³²P-postlabeling/PAGE was a useful assay for analyzing and identifying PAH-DNA adducts. Occupational exposure to particulate and volatile PAH concentrations were evaluated using personal air samples and lymphocyte DNA adducts as markers of exposure. Overall air PAH concentrations were low in all eight workplaces, consisting of 97% of vapor phase compounds. DNA adducts analyzed by ³²P-postlabeling assay were compared between the butanol and nuclease P1 enrichment procedures. Only in winter samples of exposed workers, butanol extraction revealed significantly higher adduct levels in comparison with those of control persons. No differences in adduct levels between exposed and control persons in summer were detected by using either butanol extraction or nuclease P1 treatment. Total concentrations of particulate and volatile PAHs measured in eight workplaces in winter showed a significant correlation with total DNA adducts analyzed in workers' lymphocytes (r = 0.852N = 8, p = .007).     

The Primary Role of Apurinic Sites in Tumor Initiation

The profiles of DNA adducts determined for benzo[a]pyrene (BP), 7,12-dimethylbenz[a]anthracene (DMBA) and dibenzo[a,l]pyrene (DB[a,l]P) reveal that a majority of adducts are released from DNA by depurination. Papillomas were induced in mouse skin by several PAH, and mutations in the c-Harvey-ras oncogene were determined to investigate the relationship between DNA adducts and ras oncogene mutations. The pattern of mutations induced by each PAH correlated with the profile of depurinating adducts. DB[a,l]P and DMBA formed predominantly depurinating adenine adducts (78% and 79%, respectively) and consistently induced a CAA → CTA transversion in codon 61 of ras. In contrast, BP produced both guanine (46%) and adenine (25%) depurinating adducts and induced a GGC → GTC mutation in codon 13 of c-H-ras in 54% of tumors and a CAA → CTA mutation in codon 61 in 15% of tumors. These results support the hypothesis that mis-replication of unrepaired apurinic sites generated by loss of PAH-DNA adducts is responsible for transforming mutations leading to papillomas in mouse skin.     

DETERMINATION OF DIBENZO[A,L]PYRENE AND OTHER FJORD-REGION PAH ISOMERS WITH MW 302 IN ENVIRONMENTAL SAMPLES

Polycyclic aromatic hydrocarbons (PAHs) occur in the environment as complex mixtures including compounds with mutagenic and carcinogenic activity. The PAH profile routinely determined in environmental samples at present encompasses isomers with molecular weight (MW) not greater than 300. However, PAHs with MW >300 have been demonstrated for several matrices to contribute up to 50% of the total activity when tested for carcinogenicity in experimental animals. Recent studies indicate that among the dibenzopyrenes with MW 302 dibenzo[a,l]pyrene, possessing a fjord region, is by far the most carcinogenic PAH hitherto identified. To further elucidate the environmental relevance of this compound we have applied the isotope dilution GC/MS technique as analytical procedure to determine this compound and the related fjord region PAH naphtho[1,2-a]- and naphtho[1,2-e]pyrene in various matrices. Identification was based on comparison of UV and mass spectra as well as retention times of authentic reference materials. Determination of these PAHs was achieved after clean-up by several chromatographic steps including fractionation on a modified TABA-silica gel column. Quantitative data for matrices such as two cigarette smoke condensates, motor vehicle exhaust condensate (Otto-type engines), and tar-cork are reported. Based on toxic equivalent factors the relative contribution of dibenzo[a,l]pyrene (5.4–42.3%) to the total carcinogenic activity of a PAH profile will be discussed comprising 14 selected isomers (benzo[b]naphtho[2,1-d]thiophene; cyclopenta[cd]pyrene; benz[a]anthracene; chrysene/triphenylene; sum of benzo[b]-, benzo[k]-, and benzo[j]fluoranthene; benzo[a]pyrene; indeno[1,2,3-cd]pyrene; dibenz[a,h]anthracene; benzo[ghi]perylene; anthanthrene; dibenzo[a,l]pyrene determined in these matrices.     

Metabolism of PAHs and Methyl-Substituted PAHs by Sphingomonas paucimobilis Strain EPA 505

The ability of Sphingomonas paucimobilis strain EPA 505 (a soil bacterium capable of utilizing fluoranthene as the sole source of carbon and energy for growth) to metabolize 3-methyl-methylfluoranthene, 7-methlybenz[ a ]anthracene, 5-methylchrysene, and their corresponding unsubstituted parent hydrocarbons was investigated. The rate of degradation of 3-methylfluoranthene, 7-methylbenz[ a ]anthracene, and 5-methylchrysene by a resting cell suspension of S. paucimobilis grown on fluoranthene was 20.4, 6.2, and 2.7 nmole/mg of wet cells/hr, respectively. The rate of degradation of fluoranthene, benz[ a ]anthracene, and chrysene was 10.7, 3.4, and 1.4 nmole/mg of wet cells/hr, indicating that methylated PAHs are degraded at a higher rate than the corresponding unsubstituted analogs. Two major isolated metabolites of benz[ a ]anthracene were identified as 2-hydroxy-3-naphthoic acid, and 2-hydroxy-3-phenanthroic acid. Unlike benz[ a ]anthracene, 7-methylbenz[ a ]anthracene was metabolized to its cis -1,2-diol to a significant extent by S. paucimobilis suggesting that the presence of a methyl group at position 7 of benz[ a ]anthracene hinders the action of the enzymes (presumably dehydrogenases), which convert cis -1,2-diol to the corresponding catechol.     

Polycyclic Aromatic Hydrocarbons (PAHs) Occurrence and Toxicity in Camellia sinensis and Herbal Tea

ABSTRACT

This study describes a survey of polycyclic aromatic hydrocarbon (PAH) concentrations in 23 green, herbal, and black tea brands widely consumed in Nigeria by determining the levels of benzo[a]pyrene, chrysene (PAH2), benzo[a]pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene (PAH4), benzo[a]pyrene, benz[a]anthracene, benzo[k]fluoranthene, chrysene, benzo[b]fluoranthene, dibenz[ah]anthracene, benzo[ghi]per-ylene and indeno[1,2,3-cd]pyrene (PA-H8). Toxic equivalence factor and mutagenic equivalence factor were applied to evaluate the toxic equivalence and mutagenic equivalence quotients relative to benzo[a]pyrene. The concentrations of PAHs indicate that Regulation 835/2011/EC was not fulfilled by benzo[a]anthracene, B[a]A, benzo[a]pyrene, B[a]P, benzo[b]fluoranthene, B[b]F, and chrysene, CHR. The PAH4 levels ranged from 1.28 to 44.57, 4.34 to 11.20, and 0.76 to 34.82 µg/kg in green, black, and herbal tea products, respectively. On the other hand, the PAH8 concentration varied between 1.63 and 65.73, 5.02 and 68.83, and 12.43 and 24.92 µg/kg in green, herbal, and black tea samples. The PAH4 and PAH8 provide more reliable indicators for determination of PAH contamination and risk characterization in food than PAH2.     

Evaluation of PAH: DNA Adduct Formation in Rats Fed Coal Tar-Contaminated Diets

Previous studies have demonstrated that mouse lung is a target organ for the tumorigenic and genotoxic effects of coal tar. The present study evaluated PAH:DNA adduct formation in lung, liver, forestomach, and mammary gland of female CD rats fed various types of coal tar-contaminated diets. Coal tar-contaminated soil, an organic extract of contaminated soil, neat coal tar, and diets containing only B[ a ]P were evaluated. Ingestion of coal tar diets resulted in detectable levels of DNA adducts in lung and forestomach tissue. These adducts were primarily derived from benzo[ c ]fluorene and B[ a ]P. The adduct derived from benzo[ c ]fluorene was the most predominant. No adducts were detected in liver and mammary gland under the conditions employed in this study. The formation of a benzo[ c ]fluorene-derived DNA adduct in rat lung following coal tar exposure is consistent with previous studies performed with mice.     

Human AKR1C Isoforms Oxidize the Potent Proximate Carcinogen 7,12-DMBA-3,4-diol in the Human Lung A549 Carcinoma Cell Line

Aldo-keto reductases (AKRs) oxidize structurally diverse PAH trans -dihydrodiols to yield reactive and redox active o -quinones. This study examined the ability of AKR1C2 and AKR1C4 to oxidize PAH trans -dihydrodiols of the benz[ a ]anthracene series. The enzymes oxidized 100% of the racemic trans -dihydrodiols and the highest utilization ratios were observed for the more potent proximate carcinogens 7,12-dimethylbenz[ a ]anthracene-3,4-diol (DMBA-3,4-diol) and 7-methylbenz[ a ]anthracene-3,4-diol (7-MBA-3,4-diol). Human multiple tissue expression array analysis revealed high expression of AKR1C isoforms in the human lung carcinoma cell line A549. Both Western blot analysis using AKR1C9 antisera and enzymatic assays using 1-acenapthanol as substrate confirmed the presence of active AKR1C enzymes in A549 cells. To determine the importance of AKR1C-mediated trans -dihydrodiol oxidation in A549 cells, DMBA-3,4-diol was incubated with cell lysates in the presence of 2-mercaptoethanol. Liquid chromatography/mass spectrometric analysis identified peaks that corresponded to the synthetically prepared mono- and bis -thioether conjugates of DMBA-3,4-dione confirming the ability of these cells to oxidize DMBA-3,4-diol to the corresponding o -quinone. Together, these studies demonstrate the importance of human AKR1Cs in PAH activation and their possible role in lung cancer.     

EFFICIENT NEW SYNTHESES OF POLYCYCLIC AROMATIC HYDROCARBON ORTHO-QUINONES AND THEIR 2′-DEOXYRIBONUCLEOSIDE ADDUCTS

Three mechanisms have been proposed to explain the carcinogenic activities of polycyclic aromatic hydrocarbons (PAHs). On the basis of the nature of the active metabolites involved, they may be termed: the diol epoxide mechanism, the quinone mechanism, and the radical-cation mechanism. In connection with studies to evaluate the relative importance of these pathways, we required practical methods for the syntheses of the active PAH metabolites involved. We now report efficient new synthesis of the o-quinones of benzo[a]pyrene (BPQ), 7,12-dimethylbenz[a]anthracene (DMBAQ), and benz[a]anthracene (BAQ). These quinones are convenient synthetic precursors of the related o-catechols, trans-dihydrodiols, and diol epoxides, as well as the stable adducts of the o-quinones with 2-deoxyadenosine and 2′-deoxyguanosine.     

An Abbreviated Synthesis of 7,12-Dimethylbenz[ a ]anthracene and Benzo[ c ]chrysene Metabolites Using the Suzuki Reaction

Efficient syntheses of important metabolites of 7,12-dimethylbenz[ a ]anthracene (DMBA) and benzo[ c ]chrysene (B[ c ]C), via Suzuki coupling reaction are described. This approach provides an excellent method for the preparation of 3-methoxy-DMBA 5 , 10-methoxy-B[ c ]C 14 and 2-methoxy B[ c ]C 20 , and hence for the corresponding dihydrodiols 6 , 15 , and 21 . Following a similar Suzuki reaction, DMBA-6(5 H )-one 8 was also synthesized in high yield.     

THE ROLE OF PAH-DNA ADDUCTS IN CAUSING CANCER

This article addresses the evidence for the mechanism of activation of polycyclic aromatic hydrocarbons (PAH) to “ultimate carcinogenic” DNA-binding metabolites in cells and describes how analysis of DNA adducts allowed the determination that the metabolites are dihydrodiol epoxides of PAH. Initially, the PAH-DNA adduct analysis techniques we developed allowed us to establish that the reactive form of PAH that bind to DNA in cells was not the K-region epoxide. Further development of PAH-DNA adduct analysis techniques allowed us to determine that in the case of the very potent carcinogen dibenzo[a,l]pyrene, the reactive metabolite was a diol epoxide with “fjord region” of the molecule. Collaborative studies of DNA adducts in cells from a mouse in which cytochrome P450 1B1 levels were knocked out demonstrated that DB[a,l]P activation to DNA binding intermediates was reduced to undetectable levels demonstrating the great importance of this enzyme in activating fjord region containing PAH.     

5-Methoxy, 7-methylbenz[a]anthracene: Crystal Structure of a Planar Weak Carcinogen

Abstract

The crystal and molecular structure of 5-methoxy,7-methylbenz[a]anthracene has been determined by X-ray diffraction at room temperature to an R-index of 0.062 over 936 reflections. The molecule, the first methoxy-substituted methylbenz[a]anthracene to be analysed, is highly planar, with the carbon and oxygen atoms of substituents lying within 0.04 Å of the mean plane of the polycyclic skeleton. Carbon–oxygen bond lengths in the methoxy group are unequal at 1.372(7) and 1.426(9) Å and the C_aromatic–O bond makes dissimilar angles of 113.5(7) and 124.3(7)° at C(5). The shortest C–C bonds are C(5)–C(6) = 1.351(9) at the substituted K-region, C(8)–C(9) = 1.352(9), C(10)–C(11) = 1.362(9) Å, and C(3)–C(4) = 1.361(10) Å. In the unsubstituted bay region, the long beach bond C(13)–C(18) = 1.454(9) Å is flanked by beach bond angles C(12)–C(18)–C(13) = 121.2(6) and C(18)–C(13)–C(1) = 123.1(6)°.     

Selective Recognition of Substituted Chrysene-Diol Epoxide-2-DNA Adducts by Antiserum prepared Against DNA Adducts of Benzo[c]Phenanthrene-Diol Epoxide-2

Polyclonal antiserum prepared against DNA that was modified with racemic benzo[c]phenanthrene-3,4-diol-1,2-epoxide-2 (B[c]PhDE-2; benzylic hydroxyl and epoxide oxygen trans) was characterized for specificity of antigen recognition. Previous studies have demonstrated that the antisera stereoselectively recognized B[c]PhDE-2-DNA and failed to recognize DNA modified with racemic benzo[c]phenanthrene-3,4-diol-1,2-epoxide-1 (B[c]PhDE-1-DNA, benzylic hydroxyl and epoxide oxygen cis), benzo[a]pyrene-7,8-diol-9, 10-epoxide-2-DNA (B[a]PDE-2-DNA) and 7,12-dimethylbenz[a]anthracene-3,4-diol-1,2-epoxide-1-DNA (DMBADE-1-DNA). DNA samples modified by diol-epoxide-2 diastereomers of several hydrocarbons were tested in competitive ELISA assays utilizing B[c]PhDE-2-DNA (270 fmol adducts per well). DNA modified with racemic diol-epoxide-2 of various substituted chrysenes (including chrysene, benzo[g]chrysene (B[g]C), 6-methylchrysene (6-MeC), and 5-methychrysene (5-MeC), gave 50% inhibition of antisera binding at significantly higher concentrations (5 to 7-fold) than the parent B[c]PhDE-2-DNA or 5,6-diMeCDE-DNA. DNA modified with 5,7-dimethylchryseneDE-2 (5,7-diMeCDE-2) and dibenzo[a,l]pyreneDE-2 (DB[a,l] PDE-2) required 20 and > 100-fold greater levels of adducts to give 50% inhibition. Results with B[c]Pb, 5,6-diMeC, chrysene, 6-MeC and 5-MeC diol epoxide-2-DNA     

Preparation of schiff base adducts of phosphatidylcholine core aldehydes and aminophospholipids, amino acids, and myoglobin

We have prepared Schiff base adducts of the core aldehydes of phosphatidylcholine and aminophospholipids, free amino acids, and myoglobin. The Schiff bases of the ethanolamine and serine glycerophospholipids were obtained by reacting sn-1-palmitoyl(stearoyl)-2-[9-oxo]nonanoyl-glycerophosphocholine (PC-Ald) with a twofold excess of the aminophospholipid in chloroform/methanol 2∶1 (vol/vol) for 18 h at room temperature. The Schiff bases of the amino acids and myoglobin were obtained by reacting the aldehyde with an excess of isoleucine, valine, lysine, methyl ester lysine and myoglobin in aqueous methanol for 18 h at room temperature. Prior to isolation, the Schiff bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4°C. The reaction products were characterized by normal-phase high-performance liquid chromatography and on-line mass spectrometry with electrospray ionization. The amino acids and aminophospholipids yielded single adducts. A double adduct was obtained for myoglobin, which theoretically could have accepted up to 23 PC-Ald groups. The yields of the products ranged from 12 to 44% for the aminophospholipids and from 15–57% for the amino acids, while the Schiff base of the myoglobin was estimated at 5% level. The new compounds are used as reference standards for the detection of high molecular weight Schiff bases in lipid extracts of natural products. Based on presentation at the AOCS Annual Meeting & Expo in Indianapolis, Indiana, April 28–May 1, 1996.     

Rapid complexing of oxoacylglycerols with amino acids peptides and aminophospholipids

We prepared model Schiff bases from 2-[9-oxo]nonanoyl glycerol (2-MAG-ALD) and various amino compounds. 2-MAG-ALD was obtained by pancreatic lipase hydrolysis of trioleoyl glycerol and reductive ozonolysis of the resulting 2-monooleoyl glycerol. The reaction products were purified by thin-layer chromatography. Schiff bases were synthesized in greater than 50% yield by reacting 2-MAG-ALD with twofold molar excess of valine, Nα-acetyl-l-lysine methyl ester and the tripeptides glycyl-glycyl-glycine, glycyl-glycyl-histidine, and glycyl-histidyl-lysine in aqueous methanol and with 1-palmitoyl-2-stearoyl glycerophosphoethanolamine (PE) in chloroform.methanol for 16 h at room temperature. Prior to analysis the bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4°C. Reaction products were analyzed by high-performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI/MS). Reduced Schiff bases of 2-MAG-ALD with PF and amino acids were analyzed by normal-phase HPLC/ESI/MS and those with peptides by reversed-phase HPLC/ESI/MS. Single adducts were obtained in all cases and both the α-amino group of valine and the ε-amino group of Nα-acetyl-l-lysine methyl ester were reactive. Molecular ions of reaction products were the only detected ions in the negative ionization mode, whereas in the positive ion mode sodiated molecular ions were also detected. The present study suggests that 2-MAG-ALD may form Schiff base adducts with amino compounds in other aqueous media, such as the intestinal lumen and in the hydrophobic environment of cell membranes.     

NMR Conformational Analysis of DNA Duplexes Containing Diol Epoxide Adducts of Polycyclic Aromatic Hydrocarbons

The principal adducts formed between DNA and polycyclic aromatic hydrocarbon diol epoxides result from N-alkylation of the exocyclic amino groups of the purine bases by the benzylic carbon atom of the epoxide. To date, the solution conformations of more than a dozen alkylated DNA duplexes have been examined by 2D NMR spectroscopy. For trans opened diol epoxides, oligomer duplexes containing N²-adducts at deoxyguanosine have the hydrocarbon residue lying in the minor groove whereas those containing N⁶-adducts at deoxyadenosine have the hydrocarbon intercalated within the DNA helix. Absolute configuration at the site of attachment appears to be a major determinant in establishing whether the hydrocarbon lies to the 3′- or the 5′-side of the adducted base. For trans opened deoxyadenosine adducts with R-absolute configuration, the hydrocarbon residue is positioned toward the 5′-end of the adducted strand whereas trans opened deoxyguanosine adducts with R-absolute configuration have the hydrocarbon located toward the 3′-end of the adducted strand.     

Responses of Human Cells to PAH-Induced DNA Damage

Benzo[ a ]pyrene (B[ a ]P) and dibenzo[ a,l ]pyrene (DB[ a,l ]P) induce cytochrome P450 (CYP) CYP1A1 and CYP1B1, which metabolize these polycyclic aromatic hydrocarbons (PAHs) into DNA-binding species. In order to detail roles of CYP1A1 and CYP1B1 in activation of DB[ a,l ]P to the diol epoxide, we here report the inhibition of CYP1A1 in human MCF-7 cells with phosphorodiamidate morpholino antisense oligomers (morpholinos). PAH-DNA adduct formation was also determined after treatment with morpholinos and B[ a ]P or DB[ a,l ]P. p53 is involved in DNA repair, cell cycle arrest, and apoptosis. Cells with normal p53 protein arrest in the G1 phase of the cell cycle on exposure to DNA-damaging agents (presumably allowing the cell sufficient time to repair damaged DNA prior to replication). Previous studies in human MCF-7 cells indicate that cells with PAH-DNA adducts escape cell cycle arrest and accumulate in the S phase. In the present study the effect of PAH-DNA adducts on the cell cycle were observed in human diploid fibroblasts (HDF). We found that treatment of HDF with the diol epoxide of DB[ a,l ]P causes cell cycle arrest in G 1 . An increase in DNA adduct formation with increase in concentration of dibenzo[ a,l ]pyrene diol epoxide {( m )- anti -DB[ a,l ]PDE} was also observed.