Potential biomarker for early risk assessment of prostate cancer.

BACKGROUND: Catechol estrogen quinones (CEQ) derived from 4-hydroxyestrone (4-OHE1) and 4-hydroxyestradiol (4-OHE2) react with DNA to form depurinating--N7Gua and--N3Ade adducts. This damage leads to mutations that can initiate breast and prostate cancer. To determine whether this damage occurs in humans, urine samples from men with prostate cancer and benign urological conditions, and healthy controls were analyzed. The objective was determining whether any of the cancer patients had formed the depurinating 4-OHE1(E2)-1-N3Ade adducts. METHODS: The adducts were extracted from samples by using affinity columns equipped with a monoclonal antibody developed for detecting 4-OHE1(E2)-1-N3Ade adducts. Eluted extracts were separated by capillary electrophoresis with field-amplified sample stacking and/or ultraperformance liquid chromatography. Absorption/luminescence spectroscopies and mass spectrometry were used to identify the adducts. RESULTS: 4-OHE1-1-N3Ade was detected at higher levels in samples from subjects with prostate cancer (n = 7) and benign urological conditions (n = 4) compared to healthy males (n = 5). CONCLUSION: This is the first demonstration that CEQ-derived DNA adducts are present in urine samples from subjects with prostate cancer.

Development of monoclonal antibodies to 4-hydroxyestrogen-2-N-acetylcysteine conjugates: immunoaffinity and spectroscopic studies.

Catechol estrogen quinones (CEQ) derived from oxidation of the catechol estrogens 4-hydroxyestrone (4-OHE1) and 4-hydroxyestradiol (4-OHE2) can conjugate with glutathione (GSH), a reaction that prevents damage to DNA and can provide biomarkers of exposure to CEQs. Monoclonal antibodies (MAb) to 4-OHE1(E2)-2-N-acetylcysteine [4-OHE1(E2)-2-NAcCys] were developed and characterized by immunological and spectroscopic studies. The NAcCys conjugate is the hydrolytic product of the corresponding conjugate with GSH, followed by N-acetylation of cysteine. MAbs were produced by immunizing mice with 4-OHE1(E2)-2-NAcCys attached to an appropriate linker that was conjugated to keyhole limpet hemocyanin (KLH). Hybridoma cell lines were screened using 4-OHE1(E2)-2-NAcCys conjugated to ovalbumin (OA). There is no immunological cross-reactivity between KLH and OA. Hence, positive hybridoma cell lines secreting antibody against 4-OHE1(E2)-2-NAcCys could be rapidly identified using OA-4-OHE1(E2)-2-NAcCys. An affinity column was developed and used to purify MAb against 4-OHE1(E2)-2-NAcCys. The purified MAb was immobilized on an agarose bead column. This column was used to capture and preconcentrate the hapten of interest out of urine samples. A number of structurally related standards were used to estimate the selectivity and specificity of the chosen MAb. Capillary electrophoresis (CE) with field-amplified sample stacking in absorbance detection mode and laser-induced low temperature luminescence measurements were used to identify and quantitate the 4-OHE1(E2)-2-NAcCys conjugates and related compounds released from the affinity column. Femtomole detection limits have been demonstrated. Future prospects in clinical diagnostics for testing human exposure to CEQ by urine analysis are briefly addressed.

Genotoxic metabolites of estradiol in breast: potential mechanism of estradiol induced carcinogenesis.

Long term exposure to estradiol increases the risk of breast cancer in a variety of animal species, as well as in women. The mechanisms responsible for this effect have not been firmly established. The prevailing theory proposes that estrogens increase the rate of cell proliferation by stimulating estrogen receptor-mediated transcription and thereby the number of errors occurring during DNA replication. An alternative hypothesis proposes that estradiol can be metabolized to quinone derivatives which can react with DNA and then remove bases from DNA through a process called depurination. Error prone DNA repair then results in point mutations. We postulate that these two processes, increased cell proliferation and genotoxic metabolite formation, act in an additive or synergistic fashion to induce cancer. If correct, aromatase inhibitors would block both processes whereas anti-estrogens would only inhibit receptor-mediated effects. Accordingly, aromatase inhibitors would be more effective in preventing breast cancer than use of anti-estrogens. Our studies initially demonstrated that catechol estrogen (CE) quinone metabolites are formed in MCF-7 human breast cancer cells in culture. Measurement of estrogen metabolites and conjugates involved utilization of an HPLC separation coupled with an electrochemical detector. We then utilized an animal model that allows dissociation of estrogen receptor-mediated function from that of the effects of estradiol metabolites. Wnt-1 transgenic mice harboring a knock-out of ERalpha provides a means of examining the effect of estrogen deprivation in the absence of the ER in animals with a high incidence of breast tumors. ERbeta was shown to be absent in the breast tissue of these animals by RNase protection assay. In the breast tissue of these estrogen receptor alpha knock-out (ERKO)/Wnt-1 transgenic mice, we demonstrated formation of genotoxic estradiol metabolites. The ERKO/Wnt-1 breast extracts contained picomole amounts of the 4-catechol estrogens, but not their methoxy conjugates nor the 2-CE or their methoxy conjugates. The 4-CE conjugates with glutathione or its hydrolytic products (cysteine and N-acetylcysteine) were detected in picomole amounts in both tumors and hyperplastic mammary tissue, demonstrating the formation of CE-3,4-quinones. These results are consistent with the hypothesis that mammary tumor development is primarily initiated by metabolism of estrogens to 4-CE and, then, to CE-3,4-quinones, which may react with DNA to induce oncogenic mutations. The next set of experiments examined the incidence of tumors formed in Wnt-1 transgenic mice bearing wild type ERalpha (ER+/+), the heterozygous combination of genes (ER+/ER-) or ERalpha knock-out (ER-/-). To assess the effect of estrogens in the absence of ER, half of the animals were oophorectomized on day 15 and the other half were sham operated. Castration reduced the incidence of breast tumors in all animal groups and demonstrated the dependence of tumor formation upon estrogens. A trend toward reduction in tumor number (not statistically significant at this interim analysis) occurred in the absence of functional ER since the number of tumors was markedly reduced in ERKO animals which were castrated early in life. In aggregate, our results support the concept that metabolites of estradiol may act in concert with ER mediated mechanisms to induce breast cancer.

Spectral characterization of catechol estrogen quinone (CEQ)-derived DNA adducts and their identification in human breast tissue extract.

Estrogens, including the natural hormones estrone (E(1)) and estradiol (E(2)), are thought to be involved in tumor induction. Catechol estrogen quinones (CEQ) derived from 4-hydroxyestrone (4-OHE(1)) and 4-hydroxyestradiol (4-OHE(2)) react with DNA and form depurinating N7Gua and N3Ade adducts that might be responsible for tumor initiation (Cavalieri, E. L., et al. (2000) J. Natl. Cancer Inst. Monogr. 27, 75). Current detection limits for the CEQ-derived DNA adducts by high-performance liquid chromatography with multichannel electrochemical detection are in the picomole range. To improve the limit of detection (LOD) for CEQ-derived DNA adducts, spectrophotometric monitoring was investigated. Spectroscopic studies of 4-OHE(1)-1-N3Ade, 4-OHE(1)-1-N7Gua, 4-OHE(2)-1-N3Ade, and 4-OHE(2)-1-N7Gua adduct standards were performed at 77 and 300 K. Upon laser excitation at 257 nm, the 4-OHE(1)- and 4-OHE(2)-derived N7Gua and N3Ade adducts are strongly phosphorescent at T = 77 K. No phosphorescence was observed at 300 K. Both N3Ade and N7Gua adduct types have weak phosphorescence origin bands near 383 and 385 nm, respectively. The corresponding phosphorescence lifetimes are 1.11 +/- 0.05 and 0.37 +/- 0.05 s. The LOD, based on phosphorescence measurements, is in the low femtomole range. The concentration LOD is approximately 10(-9) M, i.e., similar to that recently obtained for CEQ-derived N-acetylcysteine conjugates (Jankowiak, R., et al. (2003) Chem. Res. Toxicol. 16, 304). The LOD in capillary electrophoresis (CE) with field-amplified sample stacking and absorbance detection is about 3 x 10(-8) M. To verify whether CEQ-derived DNA adducts are formed in humans or not, tissue extracts from two breast cancer patients were analyzed by CE interfaced with room temperature absorption and low temperature (laser-excited) phosphorescence spectroscopies. For the first time, formation of CEQ-derived DNA adducts is shown in humans. For example, the level of 4-OHE(1)-1-N3Ade in the breast tissue extract from a patient with breast carcinoma (8.40 +/- 0.05 pmol/g of tissue) is larger by a factor of about 30 than that in the breast tissue sample from a woman without breast cancer (0.25 +/- 0.05 pmol/g of tissue). In contrast, similar amounts of 4-OHE(2)-1-N3Ade were observed in both types of tissue. Although more breast tissue samples from women with and without breast cancer need to be studied, these results suggest that the N3Ade adducts could serve as biomarkers to predict the risk of breast cancer.

Initiation of cancer and other diseases by catechol ortho-quinones: a unifying mechanism.

Exposure to estrogens is a risk factor for breast and other human cancers. Initiation of breast, prostate and other cancers has been hypothesized to result from reaction of specific estrogen metabolites, catechol estrogen-3,4-quinones, with DNA to form depurinating adducts at the N-7 of guanine and N-3 of adenine by 1,4-Michael addition. The catechol of the carcinogenic synthetic estrogen hexestrol, a hydrogenated derivative of diethylstilbestrol, is metabolized to its quinone, which reacts with DNA to form depurinating adducts at the N-7 of guanine and N-3 of adenine. The catecholamine dopamine and the metabolite catechol (1,2-dihydroxybenzene) of the leukemogen benzene can also be oxidized to their quinones, which react with DNA to form predominantly analogous depurinating adducts. Apurinic sites formed by depurinating adducts are converted into tumor-initiating mutations by error-prone repair. These mutations could initiate cancer by estrogens and benzene, and Parkinson's disease by the neurotransmitter dopamine. These data suggest a unifying molecular mechanism of initiation for many cancers and neurodegenerative diseases and lay the groundwork for designing strategies to assess risk and prevent these diseases.

Evidence that a burst of DNA depurination in SENCAR mouse skin induces error-prone repair and forms mutations in the H-ras gene.

Treatment of SENCAR mouse skin with dibenzo[a,l]pyrene results in abundant formation of abasic sites that undergo error-prone excision repair, forming oncogenic H-ras mutations in the early preneoplastic period. To examine whether the abundance of abasic sites causes repair infidelity, we treated SENCAR mouse skin with estradiol-3,4-quinone (E(2)-3,4-Q) and determined adduct levels 1 h after treatment, as well as mutation spectra in the H-ras gene between 6 h and 3 days after treatment. E(2)-3,4-Q formed predominantly (> or =99%) the rapidly-depurinating 4-hydroxy estradiol (4-OHE(2))-1-N3Ade adduct and the slower-depurinating 4-OHE(2)-1-N7Gua adduct. Between 6 h and 3 days, E(2)-3,4-Q induced abundant A to G mutations in H-ras DNA, frequently in the context of a 3'-G residue. Using a T.G-DNA glycosylase (TDG)-PCR assay, we determined that the early A to G mutations (6 and 12 h) were in the form of G.T heteroduplexes, suggesting misrepair at A-specific depurination sites. Since G-specific mutations were infrequent in the spectra, it appears that the slow rate of depurination of the N7Gua adducts during active repair may not generate a threshold level of G-specific abasic sites to affect repair fidelity. These results also suggest that E(2)-3,4-Q, a suspected endogenous carcinogen, is a genotoxic compound and could cause mutations.

Role of human cytochrome P450 1A1, 1A2, 1B1, and 3A4 in the 2-, 4-, and 16alpha-hydroxylation of 17beta-estradiol.

The steady-state kinetics and specific activity of 2-, 4-, and 16alpha-hydroxylation of 17beta-estradiol (E(2)) were evaluated for human cytochrome P450 (CYP) 1A1, 1A2, 1B1, and 3A4 enzymes, using complementary DNA-expressed CYP isoforms. CYP1A2 showed the highest 2-hydroxylation activity, followed by CYP1A1, 1B1, and 3A4. CYP1B1 had the highest 4-hydroxylation activity, followed by CYP1A2, 1A1, and 3A4. The 16alpha-hydroxylation reaction was catalyzed mainly by CYP1A2 and, to a similar, slightly lower extent, CYP3A4 and 1A1, with a lesser contribution by CYP1B1. The E(2) 2-, 4-, and 16alpha-hydroxylation activities of human liver microsomes were 1.3 +/- 0.3, 0.5 +/- 0.06, and 0.3 +/- 0.05 nmol metabolite/min/nmol P450, respectively. The contribution of CYP1A1 and 1B1 (mainly extrahepatic) to the E(2) hydroxylation reactions, relative to CYP1A2 and 3A4 (predominantly hepatic), may be relevant to understanding the process of hormonal carcinogenesis both in liver and in extrahepatic tissues.

Imbalance of estrogen homeostasis in kidney and liver of hamsters treated with estradiol: implications for estrogen-induced initiation of renal tumors.

Reaction of endogenous catechol estrogen quinones (CE-Q) with DNA may initiate cancer by generation of oncogenic mutations. Treatment of male Syrian golden hamsters with estrogens or 4-catechol estrogens (4-CE), but not 2-CE, induces kidney, but not liver, tumors. The hamster provides an excellent model for studying activation and deactivation (protection) of estrogen metabolites in relation to formation of CE-Q. Several factors can unbalance estrogen homeostasis, thereby increasing the oxidative pathway leading to the carcinogenic CE-3,4-Q. Hamsters were injected with 8 micromol of estradiol (E(2)), and liver and kidney extracts were analyzed for 31 estrogen metabolites, conjugates, and depurinating DNA adducts by HPLC with electrochemical detection. Neither liver nor kidney contained 4-methoxyCE, presumably due to the known inhibition of catechol-O-methyltransferase by 2-CE. More O-methylation of 2-CE was observed in the liver and more formation of CE-Q in the kidney. These results suggest less protective methylation of 2-CE and more pronounced oxidation of CE to CE-Q in the kidney. To investigate this further, hamsters were pretreated with L-buthionine(S,R)-sulfoximine to deplete glutathione levels and then treated with E(2). Compared to the liver, a very low level of CE and methoxyCE was observed in the kidney, suggesting little protective reductase activity. Most importantly, reaction of CE-3,4-Q with DNA to form the depurinating 4-hydroxyE(2)(E(1))-1-N7Gua adducts was detected in the kidney, but not in the liver. Therefore, tumor initiation in the kidney appears to arise from relatively poor methylation of 2-CE and poor reductase activity in the kidney, resulting in high levels of CE-Q. Thus, formation of depurinating DNA adducts by CE-3,4-Q may be the first critical event in the initiation of estrogen-induced kidney tumors.

Analysis of potential biomarkers of estrogen-initiated cancer in the urine of Syrian golden hamsters treated with 4-hydroxyestradiol.

Estrone (E1) and 17beta-estradiol (E2) are metabolized to catechol estrogens (CE), which may be oxidized to semiquinones and quinones (CE-Q). CE-Q can react with glutathione (GSH) and DNA, or be reduced to CE. In particular, CE-3,4-Q react with DNA to form depurinating adducts (N7Gua and N3Ade), which are cleaved from DNA to leave behind apurinic sites. We report the determination of 22 estrogen metabolites, conjugates and adducts in the urine of male Syrian golden hamsters treated with 4-hydroxyestradiol (4-OHE2). After initial purification, urine samples were analyzed by HPLC with multichannel electrochemical detection and by capillary HPLC/tandem mass spectrometry. 4-Hydroxyestrogen-2-cysteine [4-OHE1(E2)-2-Cys] and N-acetylcysteine [4-OHE1(E2)-2-NAcCys] conjugates, as well as the methoxy CE, were identified and quantified by HPLC, whereas the 4-OHE1(E2)-1-N7Gua depurinating adducts and 4-OHE1(E2)-2-SG conjugates could only be identified by the mass spectrometry method. Most of the administered 4-OHE2 was metabolically converted to 4-OHE1. Formation of thioether (GSH, Cys and NAcCys) conjugates and depurinating adducts [4-OHE1(E2)-1-N7Gua] indicates that oxidation of 4-CE to CE-3,4-Q and subsequent reaction with GSH and DNA, respectively, do occur. The major conjugates in the urine were 4-OHE1(E2)-2-NACCYS: The oxidative pathway of 4-OHE1(E2) accounted for approximately twice the level of products compared with those from the methylation pathway. The metabolites and methoxy CE were excreted predominantly (>90%) as glucuronides, whereas the thioether conjugates were not further conjugated. These results provide strong evidence that exposure to 4-OHE1(E2) leads to the formation of E1(E2)-3,4-Q and, subsequently, depurinating DNA adducts. This process is a putative tumor initiating event. The estrogen metabolites, conjugates and adducts can be used as biomarkers for detecting enzymatic oxidation of estrogens to reactive electrophilic metabolites and possible susceptibility to estrogen-induced cancer.

Detection and quantification of depurinated benzo[a]pyrene-adducted DNA bases in the urine of cigarette smokers and women exposed to household coal smoke.

Polycyclic aromatic hydrocarbons (PAH) are metabolized to electrophiles that can bind to DNA bases and destabilize the N-glycosyl bond, causing rapid depurination of the adducted bases. Recent studies support depurination of DNA as a mechanism central to the genesis of H-ras mutations in PAH-treated mouse skin. Depurinating adducts account for 71% of all DNA adducts formed in mouse skin treated with benzo[a]pyrene (BP). This study analyzed urine of cigarette smokers, coal smoke-exposed women, and nonexposed controls for the presence and quantities of the depurinated BP-adducted DNA bases, 7-(benzo[a]pyren-6-yl)guanine (BP-6-N7Gua) and 7-(benzo[a]pyren-6-yl)adenine (BP-6-N7Ade). Since these adducted bases originate from reaction of the BP radical cation with double-stranded DNA and not with RNA or denatured DNA, their presence in urine is indicative of DNA damage. Urine samples were fractionated by a combination of SepPak extraction and reverse-phase HPLC, and then analyzed by tandem mass spectrometry and capillary electrophoresis with laser-induced fluorescence. BP-adducted bases were detected in the urine from three of seven cigarette smokers and three of seven women exposed to coal smoke, but were not detected in urine from the 13 control subjects. Concentrations were estimated to be 60-340 and 0.1-0.6 fmol/mg of creatinine equivalent of urine for coal smoke-exposed women (maximum possible BP intake of ca. 23 000 ng/day) and cigarette smokers (BP intake of ca. 800 ng/day), respectively, exhibiting a sensitive response to BP exposures. BP-6-N7Gua was present at ca. 20-300 times the concentration of BP-6-N7Ade in the urine of coal smoke-exposed women, but was not detected in the urine of cigarette smokers. This difference may be due to the remarkably different BP exposures experienced by the two groups of PAH-exposed individuals. These results justify more extensive studies of depurinated BP-adducted DNA bases as potential biomarkers of PAH-associated cancer risk.

Catechol estrogen conjugates and DNA adducts in the kidney of male Syrian golden hamsters treated with 4-hydroxyestradiol: potential biomarkers for estrogen-initiated cancer.

Formation of depurinating adducts by reaction of catechol estrogen-3,4-quinones with DNA was proposed to be a tumor initiating event by estrogens [E.L. Cavalieri et al. (1997) Proc. Natl Acad. Sci. USA, 94, 10937-10942]. Under estrogenic imbalance, oxidation of catechol estrogens to quinones may compete with their detoxification by protective enzymes. The quinones formed can be detoxified by reaction with glutathione (GSH) or can covalently bind to DNA. To provide more support for this hypothesis, we developed a method to identify and quantify GSH, cysteine (Cys) and N-acetylCys conjugates of 4-hydroxyestrogens (4-OHE) in the kidneys of male Syrian hamsters treated with 4-hydroxyestradiol (4-OHE2) by intraperitoneal injection. The highest level of conjugates was observed 1 h after treatment, and almost none was detected after 24 h. Dose-response studies indicated conjugate formation after treatment with 0.5 micromol of 4-OHE2/100 g body weight, and formation increased up to a treatment level of 12 micromol/100 g body weight. GSH, Cys and N-acetylCys conjugates of 4-OHE were identified in the picomole range by high-performance liquid chromatography (HPLC) with multichannel electrochemical detection and confirmed by HPLC/tandem mass spectrometry. Treatment of tissue homogenates with beta-glucuronidase/sulfatase at 37 degrees C for 6 h before extraction resulted in a 12- to 20-fold increase in Cys conjugates from picomole to nanomole levels. Similar enhancement was observed by just incubating the tissue at 37 degrees C for 6 h. Evidence for the 4-OHE-1-N7Gua depurinating adducts was obtained by mass spectrometry. We conclude that GSH and Cys conjugates of the 4-OHE and the 4-OHE-N7Gua adducts can be utilized as biomarkers to detect estrogenic imbalance and potential susceptibility to tumor initiation.

Evidence that error-prone DNA repair converts dibenzo[a,l]pyrene-induced depurinating lesions into mutations: formation, clonal proliferation and regression of initiated cells carrying H-ras oncogene mutations in early preneoplasia.

Initiation of skin tumors in mice is associated with the formation of oncogenic mutations in the H-ras gene. Mice treated on the dorsal skin with the potent polycyclic aromatic hydrocarbon (PAH) carcinogen dibenzo[a,l]pyrene (DB[a,l]P) form papillomas carrying the H-ras codon 61 (CAA to CTA) mutations. These mutations are induced in early preneoplastic skin within 1 day after DB[a,l]P treatment (Oncogene 16 (1998) 3203-3210) and appear to be related to DB[a,l]P-Ade-depurinating adducts (Proc. Natl. Acad. Sci. U. S. A. 92 (1995) 10422-10426). The rapid kinetics of mutation induction suggests that abasic sites generated from base depurination may undergo error-prone excision repair in pre-S-phase cells to induce these mutations. Analysis of mutations in the H-ras exon 1 and 2 region in DB[a,l]P-treated early preneoplastic skin indicated great changes in mutation spectra in the preneoplastic period. The initial spectra contained abundant A-->G mutations, which frequently occurred 3' to a putative conserved sequence (TGN-doublet). These mutations appeared to be induced initially as mismatched (G.T) heteroduplexes and then converted into double-stranded mutations by one round of replication. Unlike the A-->G mutations found in DB[a, l]P-treated skin (which forms 99% depurinating adducts), A-->G mutations found in anti-DB[a,l]P-diol epoxide-treated skin (forms 97% stable adducts) did not appear to be G.T heteroduplexes. These results, therefore, suggest that under these conditions, the repair errors occurred only from abasic sites but not from stable adducts. Initiated cells carrying specific oncogenic mutations, formed presumably by misrepair, underwent rapid clonal expansion and regression (transient clonoplasia). The multiplication of initiated stem cells during transient clonoplasia may be a factor determining the tumor-initiating potential of some PAH carcinogens.

Synthesis and structure determination of 6-methylbenzo[a]pyrene-deoxyribonucleoside adducts and their identification and quantitation in vitro and in mouse skin.

Activation of the moderate carcinogen 6-methylbenzo[a]pyrene (6-CH(3)BP) by one-electron oxidation to form DNA adducts was studied. Iodine oxidation of 6-CH(3)BP in the presence of dGuo produces BP-6-CH(2)-N(2)dGuo, BP-6-CH(2)-N7Gua and a mixture of 6-CH(3)BP-(1&3)-N7Gua, whereas in the presence of Ade the adducts BP-6-CH(2)-N1Ade, BP-6-CH(2)-N3Ade, BP-6-CH(2)-N7Ade and 6-CH(3)BP-(1&3)-N1Ade are obtained. Furthermore, for the first time an aromatic hydrocarbon radical cation afforded an adduct with dThd, the stable adduct BP-6-CH(2)-N3dThd. Formation of these adducts indicates that the 6-CH(3)BP radical cation has charge localized at the 6, 1 and 3 position. When 6-CH(3)BP was activated by horseradish peroxidase in the presence of DNA, two depurinating adducts were identified, BP-6-CH(2)-N7Gua (48%) and 6-CH(3)BP-(1&3)-N7Gua (23%), with 29% unidentified stable adducts. In the binding of 6-CH(3)BP catalyzed by rat liver microsomes, the same two depurinating adducts, BP-6-CH(2)-N7Gua (22%) and 6-CH(3)BP-(1&3)-N7Gua (10%), were identified, with 68% unidentified stable adducts. In 6-CH(3)BP-treated mouse skin, the two depurinating adducts, BP-6-CH(2)-N7Gua and 6-CH(3)BP-(1&3)-N7Gua, were identified. Although quantitation of these two adducts was not possible due to coelution of metabolites on HPLC, they appeared to be the major adducts found in mouse skin. These results show that 6-CH(3)BP forms depurinating adducts only with the guanine base of DNA, both in vitro and in mouse skin. The weaker reactivity of 6-CH(3)BP radical cation vs. BP radical cation could account for the weaker tumor-initiating activity of 6-CH(3)BP in comparison to that of BP.

Effect of chlorinated hydrocarbons on expression of cytochrome P450 1A1, 1A2 and 1B1 and 2- and 4-hydroxylation of 17beta-estradiol in female Sprague-Dawley rats.

Chlorinated hydrocarbons (CHCs) are environmental contaminants that bioaccumulate and hence are detected in human tissues. Epidemiological evidence suggests that the increased incidence of a variety of human cancers, such as lymphoma, leukemia and liver and breast cancers, might be attributed to exposure to these agents. The ability of CHCs to disrupt estrogen homeostasis is hypothesized to be responsible for their biological effects. The present study examined the effect of CHCs on the expression of cytochrome P450 (CYP)1A1, CYP1A2 and CYP1B1 mRNAs and the consequent 2- and 4-hydroxylation of 17beta-estradiol (E(2)) in female Sprague-Dawley rats. Animals were administered a single dose of the LD(50) of 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) (25 microg/kg), 2, 4-dichlorophenoxyacetic acid (2,4-D) (375 mg/kg) and dieldrin (DED) (38 mg/kg) by gavage. Seventy-two hours after treatment, increased expression of CYP1A1, CYP1A2 and CYP1B1 was observed in the liver, kidney and mammary tissue. Since CYP1A and CYP1B1 are the major enzymes catalyzing 2- and 4-hydroxylation of E(2), respectively, the effect of these CHCs on the metabolism of E(2) was investigated in rat tissues. Formation of 2- and 4-catechol estrogens was increased in a tissue-specific manner in response to treatment. TCDD was the most potent inducer for CYP1 enzyme mRNA and for the 2- and 4-hydroxylation of E(2). 2,4-D and DED induced similar responses, but less than that of TCDD. These results suggest that induction of CYP1 family enzymes and consequent increases in estrogen metabolism by CHCs in target tissues may be factors contributing to the biological effects associated with exposure to these agents.

Profiles of cytokine mRNAs in the skin and lymph nodes of SENCAR mice treated epicutaneously with dibenzo[a,l]pyrene or dimethylbenz[a]anthracene reveal a direct correlation between carcinogen-induced contact hypersensitivity and epidermal hyperplasia.

The potent carcinogenicity of dibenzo[a,l]pyrene (DB[a,l]P) in mouse skin is associated with an inflammatory response and a striking epidermal hyperplasia. The mechanism of these tissue responses is not known. However, a recent study has shown DB[a,l]P to be a contact sensitizer. In view of the programmed expression of cytokines during induction of contact hypersensitivity (CHS) and elicitation of CHS reactions, we analyzed cytokine mRNAs in treated skin and draining lymph nodes of SENCAR mice, at selected times after a single, epicutaneous application of DB[a,l]P or dimethylbenz[a]anthracene (DMBA), a substantially weaker carcinogen and a weaker contact sensitizer than DB[a,l]P. Cytokine mRNAs were quantified by first-strand DNA synthesis with reverse transcriptase (RT) and DNA amplification by the polymerase chain reaction (PCR). Histopathology of treated skin was determined in the same experiments. Time-response profiles of interferon (IFN) gamma and interleukin (IL) 2 in the DLN and IL1beta, IL10, tumor necrosis factor (TNF) alpha, and IL4 mRNAs in the skin of mice treated with 200 nmol of DB[a,l]P were in remarkable agreement with established profiles in mice treated with conventional contact sensitizers, e.g., oxazolone or dinitrochlorobenzene. Strong upregulation of DLN IFNgamma mRNA coupled with little change in IL 2 mRNA suggested a CD8(+) T-cell response characteristic of CHS induction. Coordinate expression of epidermal IL1beta, TNFalpha, and IL10 mRNAs, 24 h after DB[a,l]P treatment, was also characteristic of CHS induction. IL1beta and IL10 are upregulated by allergens and not by chemical irritants. Time-response profiles of epidermal IL1beta, TNFalpha, IL10, and IL4 mRNAs, 3-14 d after DB[a,l]P treatment, corresponded with expression of these cytokines during elicitation of CHS reactions. Epidermal IL4 is specifically upregulated during CHS reactions. Cytokine mRNA responses were dose-dependent (50, 100, and 200 nmol of DB[a,l]P) and markedly weaker in animals treated with 400 nmol of DMBA. Significantly, the intensity of epidermal hyperplasia correlated with the strength of the cytokine mRNA signals in DLN and skin. In conclusion, our data support carcinogen-specific CHS as a mechanism by which the very potent carcinogen DB[a,l]P induces epidermal hyperplasia, a requirement for tumor promotion in mouse skin.

Synthesis and structure determination of the adducts formed by electrochemical oxidation of Dibenzo[a,l]pyrene in the presence of adenine.

Because the radical cations of polycyclic aromatic hydrocarbons (PAH) are involved in tumor initiation, determination of the structures of biologically formed PAH-DNA adducts is important and relies on comparison of their properties with those of synthesized adducts. One of the possible sites of adduct formation is the N-3 position of Ade, but this depurinating adduct is not obtained by one-electron oxidation of dibenzo[a,l]pyrene (DB[a,l]P) in the presence of deoxyadenosine. Therefore, we turned to electrochemical oxidation of DB[a,l]P in the presence of Ade in dimethylformamide and produced the following adducts: DB[a,l]P-10-N1Ade (47%), DB[a, l]P-10-N3Ade (5%), DB[a,l]P-10-N7Ade (2%), and DB[a,l]P-10-N(6)Ade (6%). In Me(2)SO, this reaction afforded the same four adducts, but in slightly different yields: DB[a,l]P-10-N1Ade (44%), DB[a, l]P-10-N3Ade (9%), DB[a,l]P-10-N7Ade (1%), and DB[a,l]P-10-N(6)Ade (3%). These adducts were purified by reverse-phase HPLC, and the subtle differences between the isomers were revealed by NMR, tandem mass spectrometry, and fluorescence line-narrowing spectroscopy. The relative yields of the N1Ade, N3Ade, and N7Ade adducts reflect the nucleophilicity and steric accessibility of these three nitrogen atoms in Ade.

Structure elucidation of the adducts formed by fjord-region Dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides and deoxyadenosine.

Model adducts to be used in the identification of biologically formed adducts were synthesized by reaction of fjord-region dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE) and deoxyadenosine (dA). The (+/-)-anti-DB[a,l]PDE was reacted with dA in dimethylformamide at 100 degrees C for 30 min to give four DB[a, l]PDE-14-N(6)dA adducts: (-)-anti-trans (26%), (+)-anti-trans (26%), (-)-anti-cis (17%), and (+)-anti-cis (17%). The (+/-)-syn-DB[a,l]PDE was reacted with dA under the same conditions to yield four DB[a, l]PDE-14-N(6)dA adducts and one N7Ade adduct: (+)-syn-cis (19%), (+)-syn-trans (13%), (-)-syn-cis (19%), (-)-syn-trans (13%), and (+/-)-syn-DB[a,l]PDE-14-N7Ade (22%). The structures of the eight stereoisomers of DB[a,l]PDE-14-N(6)dA were unequivocally assigned by reacting optically pure (-)-anti-DB[a,l]PDE and (+)-syn-DB[a,l]PDE with dA and by a combination of NMR, circular dichroism, and fast atom bombardment mass spectrometry. Reactions at 100 degrees C yielded mainly the trans-opened adducts at the benzylic C-14 position for both (+/-)-anti-DB[a,l]PDE and (-)-anti-DB[a,l]PDE, whereas (+/-)-syn-DB[a,l]PDE and (+)-syn-DB[a,l]PDE afforded mainly cis-opened adducts. At room temperature, however, only trans-opened adducts were obtained from (+/-)-anti-DB[a,l]PDE and only cis-opened adducts from (+/-)-syn-DB[a,l]PDE. Steric hindrance created by the fjord region may be an important factor for the stereoselectivity observed at room temperature.

Structure elucidation of the adducts formed by fjord region Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxides with deoxyguanosine.

(+/-)-anti-Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(+/-)-anti-DB[a,l]PDE} was reacted with deoxyguanosine (dG) in dimethylformamide at 100 degrees C for 30 min, and two sets of adducts were isolated: a mixture of (+/-)-anti-cis- & -trans-N(2)dG (43%) and a mixture of (+/-)-anti-cis- & -trans-N7Gua (45%). Both are mixtures of four stereoisomers that cannot be separated by HPLC. Similarly, (+/-)-syn-DB[a,l]PDE was reacted with dG under the same conditions, and (+/-)-syn-cis- & -trans-N(2)dG (38%) and (+/-)-syn-cis- & -trans-N7Gua (59%) were obtained. The structures of the adducts were determined by a combination of NMR and fast atom bombardment mass spectrometry. By reacting (-)-anti-DB[a,l]PDE or (+)-syn-DB[a,l]PDE with dG under the same conditions, however, optically pure N(2)dG and N7Gua isomers were obtained: (-)-anti-cis-N(2)dG (12%), (-)-anti-trans-N(2)dG (17%), (-)-anti-trans-N7Gua (43%), (+)-syn-cis-N(2)dG (7%), (+)-syn-trans-N(2)dG (3%), (+)-syn-cis-N7Gua (36%), and (+)-syn-trans-N7Gua (22%). The structures of the optically pure adducts were assigned by NMR. syn- and anti-DB[a,l]PDE-N(2)dG adducts can be distinguished by fluorescence line-narrowing spectroscopy (FLNS). Moreover, distinction between cis- and trans-stereochemistry of the adducts is also straightforward by FLNS, because the FLN spectra for the four DB[a,l]PDE-N(2)dG adducts, anti-cis, anti-trans, syn-cis, and syn-trans, are spectroscopically unique.

Preparation, isolation, and characterization of Dibenzo[a,l]pyrene diol epoxide-deoxyribonucleoside monophosphate adducts by HPLC and fluorescence line-narrowing spectroscopy.

Dibenzo[a,l]pyrene (DB[a,l]P) is the most potent carcinogenic polycyclic aromatic hydrocarbon that has been identified in the environment. Earlier studies in our laboratory indicated that more than 80% of the DB[a,l]P-DNA adducts formed in vitro were depurinating adducts and that most of the stable adducts were formed from diol epoxide intermediates. To complete the profile of both stable and depurinating adducts of DB[a,l]P, we have synthesized standard adducts by reacting 3'-dAMP or 3'-dGMP with either (+/-)-anti- or (+/-)-syn-dibenzo[a,l]pyrene 11,12-dihydrodiol 13, 14-epoxide (DB[a,l]PDE). The adducts were separated by HPLC with an ion-pair column and were identified by fluorescence line-narrowing spectroscopy (FLNS). A total of six pairs of stereoisomers along with another stable DB[a,l]PDE-DNA adduct were successfully isolated and identified. Pairs of (+/-)-trans and (+/-)-cis isomers were expected to be formed from the reaction of anti-DB[a,l]PDE with either dAMP or dGMP. While we were able to identify two pairs of stereoisomeric (+/-)-syn-DB[a,l]PDE-dAMP (cis and trans) and two pairs of stereoisomeric (+/-)-anti-DB[a,l]PDE-dAMP (cis and trans) adducts, identification of all the stereoisomers of dGMP adducts proved to be impossible. A pair of (+/-)-syn-trans-DB[a,l]PDE-dGMP adducts, a pair of (+/-)-anti-cis-DB[a,l]PDE-dGMP adducts, and one syn-cis-DB[a,l]PDE-dGMP adduct were conclusively identified by FLNS. These standard adducts will be used to identify the stable DNA adducts formed by DB[a,l]P and DB[a,l]PDE in vitro and in vivo.

A novel method for the isolation and identification of stable DNA adducts formed by Dibenzo[a,l]pyrene and Dibenzo[a,l]pyrene 11, 12-dihydrodiol 13,14-epoxides in vitro.

Our laboratory previously reported the identification and quantification of depurinating DNA adducts of dibenzo[a,l]pyrene (DB[a,l]P) in vitro, which comprise about 84% of all the DNA adducts that are formed [Li, K.-M., et al. (1995) Biochemistry 34, 8043-8049]. To determine a complete adduct profile and identify both stable and depurinating DNA adducts, we have developed a relatively simple, nonradioactive method for the identification of stable DNA adducts by combining enzymatic digestion, HPLC, and fluorescence line-narrowing spectroscopy (FLNS) techniques. Calf thymus DNA, bound to either (+/-)-anti- or (+/-)-syn-DB[a,l]PDE or rat liver microsome-activated DB[a,l]P, was first digested to 3'-mononucleotides with micrococcal nuclease and spleen phosphodiesterase. The adducts were then separated by HPLC with an ion-pair column and identified by FLNS by using the spectra of standards for comparison. In reactions with (+/-)-anti-DB[a,l]PDE, three adducts, an anti-cis-DB[a,l]PDE-dGMP, an anti-trans-DB[a, l]PDE-dAMP, and an anti-cis-DB[a,l]PDE-dAMP, were identified by HPLC and FLNS. In reactions with (+/-)-syn-DB[a,l]PDE, a pair of syn-trans-DB[a,l]PDE-dGMP adducts as well as a syn-cis-DB[a, l]PDE-dGMP, a syn-cis-DB[a,l]PDE-dAMP, and a pair of syn-trans-DB[a, l]PDE-dAMP adducts were identified. From the digest of microsome-activated DB[a,l]P-bound DNA, a syn-trans-DB[a,l]PDE-dGMP, an anti-cis-DB[a,l]PDE-dGMP, a syn-trans-DB[a,l]PDE-dAMP, and a syn-cis-DB[a,l]PDE-dAMP adduct were identified. An anti-cis-DB[a, l]PDE-dAMP adduct was identified only by (32)P-postlabeling. A total of five of the stable adducts formed by DB[a,l]P and nine of the stable adducts formed by DB[a,l]PDE in vitro have been identified. These adducts were also correlated to adduct spots in the (32)P-postlabeling method by cochromatography with standards. Approximately 93% of the stable adducts formed in reactions with (+/-)-anti-DB[a,l]PDE, 90% of adducts with (+/-)-syn-DB[a,l]PDE, and 85% of adducts formed with microsome-activated DB[a,l]P have been identified as Gua or Ade adducts. Equal amounts of stable Gua and Ade adducts were observed in the microsome-catalyzed binding of DB[a, l]P to calf thymus DNA, while 1.4 times more Gua adducts than Ade adducts were obtained in reactions with (+/-)-anti- or (+/-)-syn-DB[a,l]PDE.