Novel biomarkers for risk of prostate cancer: results from a case-control study

Hormonal and genotoxic estrogen-androgen carcinogenesis in the NBL rat prostate: A role for aromatase

BACKGROUND

Androgens are generally thought to cause prostate cancer, but the data from animal studies suggest that they must be aromatized to estrogen and act in concert with genotoxic estrogen metabolites. The objective of this study was to determine whether treatment with testosterone (T) combined with a nonestrogenic estrogen metabolite and a nongenotoxic estrogenic compound would all be necessary and sufficient for the induction of a high incidence of prostate cancer in the susceptible NBL rat strain.

METHODS

NBL rats were treated with low-dose testosterone via slow-release Silastic implants and with the marginally estrogenic genotoxic catechol estrogen 4-hydroxyestradiol (4OH-E2) and the nongenotoxic estrogen 2-fluoroestradiol (2F-E2) and in one experiment the aromatase inhibitor letrozole via custom-made slow-release pellets. Animals were euthanized 52 weeks after implantation and their pituitaries and prostate complexes weighed and fixed in formalin. Hematoxylin and eosin (H&E)-stained step sections were prepared and examined microscopically for proliferative lesions.

RESULTS

Animals treated with 2F-E2, with or without the other compounds, had enlarged pituitaries demonstrating its estrogenicity. Animals treated with T, with or without the other compounds, had enlarged prostates consistent with its androgenicity. Rats treated with T plus 2F-E2 and 4OH-E2 developed a high incidence of prostatic cancer (89%), while, surprisingly, rats treated with T plus only 2F-E2 also had a high incidence of prostate cancer (95%) contradicting our initial hypothesis. To test whether the formation of E2 from T by aromatase could lead to estrogen genotoxicity and prostate carcinogenesis we then rats treated with T and 2F-E2 also with letrozole and found that it reduced prostate cancer incidence by about 50%.

CONCLUSIONS

These findings indicate that long-term treatment with a nongenotoxic estrogen (2F-E2) and T as well as uninhibited prostatic aromatase activity generating genotoxic E2 are all required for induction of a high incidence of prostatic adenocarcinomas in NBL rats. These and previous data indicate that androgen receptor-mediated action, estrogen receptor mediation, and estrogen genotoxicity are all required and sufficient for hormonal carcinogenesis in the NBL rat prostate. Interference with the estrogen genotoxicity is a potential approach to prostate cancer chemoprevention.

Chronic coexposure to arsenic and estrogen potentiates genotoxic estrogen metabolic pathway and hypermethylation of DNA glycosylase MBD4 in human prostate epithelial cells

BACKGROUND

Previously we reported that arsenic and estrogen cause synergistic effects in the neoplastic transformation of human prostate epithelial cells. In addition to receptor-mediated pathways, DNA-reactive estrogen metabolites have also been shown to play a critical role in mutagenicity and carcinogenicity. Both estrogen and arsenic are known prostate carcinogens, however, the effect of coexposure to these two chemicals on genes involved in estrogen metabolism is not known. Therefore, the objective of this study was to evaluate the role of arsenic and estrogen coexposure on the expression of estrogen receptors and estrogen metabolism-associated genes. Earlier, we also reported the synergistic effect of arsenic and estrogen on decreased expression of MBD4 genes that play an important role in DNA repair through its DNA glycosylase activity. To further understand the mechanism, the promoter methylation of this gene was also analyzed.

METHODS

Total RNA and protein were isolated from RWPE-1 human prostate epithelial cells that were coexposed to arsenic and estrogen for a chronic duration (6 months). The expression of estrogen receptors, estrogen metabolism associated phase I genes (CYP 1A1, 1A2, 3A4, and 1B1) and phase II gene catechol-O-methyltransferase (COMT), as well as antioxidant MnSOD, were analyzed either at the RNA level by quantitative reverse transcriptase-polymerase chain reaction or at the protein level by western blot. Promoter methylation of MBD4 was analyzed by pyrosequencing.

RESULTS

Expression of MnSOD and phase I genes that convert E₂ into genotoxic metabolites 2-OH-E₂ and 4-OH-E₂ were significantly increased, whereas the expression of phase II gene COMT that detoxifies estrogen metabolites was significantly decreased in arsenic and estrogen coexposed cells. MBD4 promoter was hypermethylated in arsenic and estrogen coexposed cells. Coexposure to arsenic and estrogen has synergistic effects on the expression of these genes as well as in MBD4 promoter hypermethylation.

CONCLUSIONS

These novel findings suggest that coexposure to arsenic and estrogen acts synergistically in the activation of not only the estrogen receptors but also the genes associated with genotoxic estrogen metabolism and epigenetic inactivation of DNA glycosylase MBD4. Together, these genetic and epigenetic aberrations provide the molecular basis for the potentiation of carcinogenicity of arsenic and estrogen coexposure in prostate epithelial cells.

Suppressor effect of catechol-O-methyltransferase gene in prostate cancer

Catechol-estrogens can cause genetic mutations and to counteract their oncogenicity, the catechol-O-methyltransferase (COMT) gene is capable of neutralizing these reactive compounds. In this study, we determined the functional effects and regulation of COMT in prostate cancer. Both the Cancer Genome Atlas (TCGA) and immunohistochemical analysis of clinical specimens demonstrated a reduction of COMT expression in prostate cancer. Also, western analyses of prostate cancer cell lines show COMT levels to be minimal in DuPro and DU145 and thus, these cells were used for further analyses. Re-expression of COMT led to suppressed migration ability (wound healing assay) and enhanced apoptosis (flow cytometric analyses), and when challenged with 4-hydroxyestradiol, a marked reduction of cell proliferation (MTT assay) was observed. Xenograft growth in athymic mice also resulted in inhibition due to COMT. As a mechanism, western analyses show cleaved CASP3 and BID were increased whereas XIAP and cIAP2 were reduced due to COMT. As COMT expression is low in prostate cancer, its regulation was determined. Databases identified several miRNAs capable of binding COMT and of these, miR-195 was observed to be increased in prostate cancer according to TCGA. Real-time PCR validated upregulation of miR-195 in clinical prostate cancer specimens as well as DuPro and DU145 and interestingly, luciferase reporter showed miR-195 capable of binding COMT and overexpressing miR-195 could reduce COMT in cells. These results demonstrate COMT to play a protective role by activating the apoptosis pathway and for miR-195 to regulate its expression. COMT may thus be a potential biomarker and gene of interest for therapeutic development for prostate cancer.

The 3,4-Quinones of Estrone and Estradiol Are the Initiators of Cancer whereas Resveratrol and N-acetylcysteine Are the Preventers

This article reviews evidence suggesting that a common mechanism of initiation leads to the development of many prevalent types of cancer. Endogenous estrogens, in the form of catechol estrogen-3,4-quinones, play a central role in this pathway of cancer initiation. The catechol estrogen-3,4-quinones react with specific purine bases in DNA to form depurinating estrogen-DNA adducts that generate apurinic sites. The apurinic sites can then lead to cancer-causing mutations. The process of cancer initiation has been demonstrated using results from test tube reactions, cultured mammalian cells, and human subjects. Increased amounts of estrogen-DNA adducts are found not only in people with several different types of cancer but also in women at high risk for breast cancer, indicating that the formation of adducts is on the pathway to cancer initiation. Two compounds, resveratrol, and N-acetylcysteine, are particularly good at preventing the formation of estrogen-DNA adducts in humans and are, thus, potential cancer-prevention compounds.

Urinary oestrogen steroidome as an indicator of the risk of localised prostate cancer progression

BACKGROUND

Prostate cancer (PCa) is the most common cancer in North American men. Beyond the established contribution of androgens to disease progression, growing evidence suggest that oestrogen-related pathways might also be of clinical importance. The aim of this study was to explore the association of urinary oestrogen levels with clinical outcomes.

METHODS

Urine samples from the prospective multi-institutional PROCURE cohort were collected before RP for discovery (n = 259) and validation (n = 253). Urinary total oestrogens (unconjugated + conjugated), including oestrone and oestradiol, their bioactive and inactive catechol and methyl derivatives (n = 15), were measured using mass spectrometry (MS).

RESULTS

The median follow-up time for the discovery and replication cohorts was 7.6 and 6.5 years, respectively. Highly significant correlations between urinary oestrogens were observed; however, correlations with circulating oestrogens were modest. Our findings indicate that higher levels of urinary oestriol and 16-ketoestradiol were associated with lower risk of BCR. In contrast, higher levels of 2-methoxyestrone were associated with an increased risk of development of metastasis/deaths.

CONCLUSIONS

Our data suggest that urinary levels of oestriol and 16-ketoestradiol metabolites are associated with a more favourable outcome, whereas those of 2-methoxyestrone are associated with an elevated risk of metastasis after RP. Further studies are required to better understand the impact of oestrogens on disease biology and as easily accessible urine-based risk-stratification markers.

Steroidomics for the Prevention, Assessment, and Management of Cancers: A Systematic Review and Functional Analysis

Steroidomics, an analytical technique for steroid biomarker mining, has received much attention in recent years. This systematic review and functional analysis, following the PRISMA statement, aims to provide a comprehensive review and an appraisal of the developments and fundamental issues in steroid high-throughput analysis, with a focus on cancer research. We also discuss potential pitfalls and proposed recommendations for steroidomics-based clinical research. Forty-five studies met our inclusion criteria, with a focus on 12 types of cancer. Most studies focused on cancer risk prediction, followed by diagnosis, prognosis, and therapy monitoring. Prostate cancer was the most frequently studied cancer. Estradiol, dehydroepiandrosterone, and cortisol were mostly reported and altered in at least four types of cancer. Estrogen and estrogen metabolites were highly reported to associate with women-related cancers. Pathway enrichment analysis revealed that steroidogenesis; androgen and estrogen metabolism; and androstenedione metabolism were significantly altered in cancers. Our findings indicated that estradiol, dehydroepiandrosterone, cortisol, and estrogen metabolites, among others, could be considered oncosteroids. Despite noble achievements, significant shortcomings among the investigated studies were small sample sizes, cross-sectional designs, potential confounding factors, and problematic statistical approaches. More efforts are required to establish standardized procedures regarding study design, analytical procedures, and statistical inference.

Role of Estrogen in Androgen-Induced Prostate Carcinogenesis in NBL Rats

Androgens are thought to cause prostate cancer, but the underlying mechanisms are unclear. Data from animal studies suggest that for androgens to cause prostate cancer, they must be aromatized to estrogen and act in concert with estrogen metabolites. We tested the hypothesis that androgen-receptor and estrogen receptor-mediated effects of androgen and estrogen are necessary, as well as genotoxicity of estrogen metabolites. NBL rats were treated with androgenic and estrogenic compounds for 16-75 weeks through slow-release silastic implants or pellets. Testosterone alone induced cancer in the prostate of 37% of rats. 5α-Dihydrotestosterone, which cannot be converted to estradiol or testosterone, did not cause a significant prostate cancer incidence (4%). Addition of estradiol to 5α-dihydrotestosterone treatment did not markedly enhance prostate cancer incidence (14%), unlike adding estradiol to testosterone treatment which induced a 100% tumor incidence. Testosterone plus estradiol treatment induced a DNA adduct detectable by ³²P-postlabeling, oxidative DNA damage (8-hydroxyguanosine), and lipid peroxidation at the site within the prostate where this treatment causes cancers, preceding later cancer formation. The non-estrogenic 4-hydroxy metabolite of estradiol, when combined with testosterone, induced prostatic dysplasia within 16 weeks and, after long-term treatment, a very low incidence of prostate cancer (21%). When an estrogen that cannot be hydroxylated (2-fluoroestradiol) was added to this combined treatment with testosterone and 4-hydroxyestradiol, dysplasia frequency after 16 weeks was doubled. These results strongly support the hypothesis, but additional definitive studies are needed which may identify new targets to interfere with these mechanisms that are clinically feasible in humans.

Etiology and prevention of prevalent types of cancer

Endogenous estrogens become carcinogens when excessive catechol estrogen quinone metabolites are formed. Specifically, the catechol estrogen-3,4-quinones can react with DNA to produce a large amount of specific depurinating estrogen-DNA adducts, formed at the N-3 of Ade and N-7 of Gua. Loss of these adducts leaves apurinic sites in the DNA, which can generate subsequent cancer-initiating mutations. Unbalanced estrogen metabolism yields excessive catechol estrogen-3,4-quinones, increasing formation of the depurinating estrogen-DNA adducts and the risk of initiating cancer. Evidence for this mechanism of cancer initiation comes from studies in vitro, in cell culture, in animal models and in human subjects. High levels of estrogen-DNA adducts have been observed in women with breast, ovarian or thyroid cancer, and in men with prostate cancer or non-Hodgkin lymphoma. Observation of high levels of depurinating estrogen-DNA adducts in high risk women before the presence of breast cancer indicates that adduct formation is a critical factor in breast cancer initiation. Two dietary supplements, N-acetylcysteine and resveratrol, complement each other in reducing formation of catechol estrogen-3,4-quinones and inhibiting formation of estrogen-DNA adducts in cultured human and mouse breast epithelial cells. They also inhibit malignant transformation of these epithelial cells. In addition, formation of adducts was reduced in women who followed a Healthy Breast Protocol that includes N-acetylcysteine and resveratrol. Blocking initiation of cancer prevents promotion, progression and development of the disease. These results suggest that reducing formation of depurinating estrogen-DNA adducts can reduce the risk of developing a variety of types of human cancer.

Critical depurinating DNA adducts: Estrogen adducts in the etiology and prevention of cancer and dopamine adducts in the etiology and prevention of Parkinson's disease

Endogenous estrogens become carcinogens when dangerous metabolites, the catechol estrogen quinones, are formed. In particular, the catechol estrogen-3,4-quinones can react with DNA to produce an excess of specific depurinating estrogen-DNA adducts. Loss of these adducts leaves apurinic sites in the DNA, generating subsequent cancer-initiating mutations. Unbalanced estrogen metabolism yields excessive catechol estrogen-3,4-quinones, increasing formation of depurinating estrogen-DNA adducts and the risk of initiating cancer. Evidence for this mechanism of cancer initiation comes from various types of studies. High levels of depurinating estrogen-DNA adducts have been observed in women with breast, ovarian or thyroid cancer, as well as in men with prostate cancer or non-Hodgkin lymphoma. Observation of high levels of depurinating estrogen-DNA adducts in high risk women before the presence of breast cancer indicates that adduct formation is a critical factor in breast cancer initiation. Formation of analogous depurinating dopamine-DNA adducts is hypothesized to initiate Parkinson's disease by affecting dopaminergic neurons. Two dietary supplements, N-acetylcysteine and resveratrol complement each other in reducing formation of catechol estrogen-3,4-quinones and inhibiting formation of estrogen-DNA adducts in cultured human and mouse breast epithelial cells. They also inhibit malignant transformation of these cells. In addition, formation of adducts was reduced in women who followed a Healthy Breast Protocol that includes N-acetylcysteine and resveratrol. When initiation of cancer is blocked, promotion, progression and development of the disease cannot occur. These results suggest that reducing formation of depurinating estrogen-DNA adducts can reduce the risk of developing a variety of types of human cancer.

Interaction of bisphenol A 3,4-quinone metabolite with glutathione and ribonucleosides/deoxyribonucleosides in vitro

Bisphenol A is a monomer used in the manufacture of polycarbonate plastic products, epoxy resin-based food can liners and flame retardants. To determine the genotoxic potential of bisphenol A, the mechanism of the reactions between the reactive electophilic bisphenol A 3,4-quinone (BPAQ) with glutathione and ribonucleosides/deoxyribonucleosides were studied. The obtained results demonstrated that BPAQ reacted with 2'-deoxyguanosine (dG)/guanosine (G), 2'-deoxyadenosine (dA)/adenosine (A), but not with 2'-deoxycytidine (dC)/cytidine (C) and thymidine (T)/uridine (U) in aqueous acetic acid. The reactions were accompanied by loss of deoxyribose, and the rate of depurination by deoxyribonucleoside adducts were faster than that of ribonucleoside adducts. In mixtures of ribonucleosides and deoxyribonucleosides treated with BPAQ, reactions occurred more readily with dG/G than dA/A. The structures of the modified bases were confirmed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). We also found that BPAQ reacted readily with glutathione (GSH) in aqueous acetic acid, and characterized the BPAQ-GSH conjugate by ESI-MS/MS. The in vitro data of depurinating DNA/RNA adducts and BPAQ-GSH adducts may provide appropriate reference for the identification of BPAQ adducts in environmental and biological systems.

Formation and Biological Targets of Quinones: Cytotoxic versus Cytoprotective Effects

Quinones represent a class of toxicological intermediates, which can create a variety of hazardous effects in vivo including, acute cytotoxicity, immunotoxicity, and carcinogenesis. In contrast, quinones can induce cytoprotection through the induction of detoxification enzymes, anti-inflammatory activities, and modification of redox status. The mechanisms by which quinones cause these effects can be quite complex. The various biological targets of quinones depend on their rate and site of formation and their reactivity. Quinones are formed through a variety of mechanisms from simple oxidation of catechols/hydroquinones catalyzed by a variety of oxidative enzymes and metal ions to more complex mechanisms involving initial P450-catalyzed hydroxylation reactions followed by two-electron oxidation. Quinones are Michael acceptors, and modification of cellular processes could occur through alkylation of crucial cellular proteins and/or DNA. Alternatively, quinones are highly redox active molecules which can redox cycle with their semiquinone radical anions leading to the formation of reactive oxygen species (ROS) including superoxide, hydrogen peroxide, and ultimately the hydroxyl radical. Production of ROS can alter redox balance within cells through the formation of oxidized cellular macromolecules including lipids, proteins, and DNA. This perspective explores the varied biological targets of quinones including GSH, NADPH, protein sulfhydryls [heat shock proteins, P450s, cyclooxygenase-2 (COX-2), glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1, (NQO1), kelch-like ECH-associated protein 1 (Keap1), IκB kinase (IKK), and arylhydrocarbon receptor (AhR)], and DNA. The evidence strongly suggests that the numerous mechanisms of quinone modulations (i.e., alkylation versus oxidative stress) can be correlated with the known pathology/cytoprotection of the parent compound(s) that is best described by an inverse U-shaped dose-response curve.

Depurinating estrogen-DNA adducts, generators of cancer initiation: their minimization leads to cancer prevention

Estrogens can initiate cancer by reacting with DNA. Specific metabolites of endogenous estrogens, the catechol estrogen-3,4-quinones, react with DNA to form depurinating estrogen-DNA adducts. Loss of these adducts leaves apurinic sites in the DNA, generating mutations that can lead to the initiation of cancer. A variety of endogenous and exogenous factors can disrupt estrogen homeostasis, which is the normal balance between estrogen activating and protective enzymes. In fact, if estrogen metabolism becomes unbalanced and generates excessive catechol estrogen 3,4-quinones, formation of depurinating estrogen-DNA adducts increases and the risk of initiating cancer is greater. The levels of depurinating estrogen-DNA adducts are high in women diagnosed with breast cancer and those at high risk for the disease. High levels of depurinating estrogen-DNA adducts before the presence of breast cancer indicates that adduct formation is a critical factor in breast cancer initiation. Women with thyroid or ovarian cancer also have high levels of estrogen-DNA adducts, as do men with prostate cancer or non-Hodgkin lymphoma. Depurinating estrogen-DNA adducts are initiators of many prevalent types of human cancer. These findings and other discoveries led to the recognition that reducing the levels of estrogen-DNA adducts could prevent the initiation of human cancer. The dietary supplements N-acetylcysteine and resveratrol inhibit formation of estrogen-DNA adducts in cultured human breast cells and in women. These results suggest that the two supplements offer an approach to reducing the risk of developing various prevalent types of human cancer. Graphical abstract Major metabolic pathway in cancer initiation by estrogens.

Sex steroid hormone metabolism in relation to risk of aggressive prostate cancer

BACKGROUND

The combined action of androgens and estrogens-specifically their balance-may play a role in prostate carcinogenesis, but existing evidence is sparse and inconsistent. We investigated associations between serum sex steroid hormones, including estrogen metabolites, and risk of aggressive prostate cancer.

METHODS

In a case-control study nested within the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial cohort, we measured serum estrone, estradiol, and 13 estrogen metabolites, in the 2-, 4-, or 16-hydroxylation pathways, using an LC/MS-MS assay. Cases (n = 195) were non-Hispanic white men ages 55 to 70 years when diagnosed with aggressive prostate cancer (stage III or IV and/or Gleason ≥7). Controls (n = 195) were non-Hispanic white men without prostate cancer who were frequency matched to cases by age and year at blood draw, and time since baseline screen. Only men with serum testosterone and sex hormone-binding globulin measured previously were eligible. Logistic regression models were used to estimate ORs and 95% confidence intervals (95% CI).

RESULTS

Risk of aggressive prostate cancer was strongly inversely associated with estradiol:testosterone ratio (OR4th quartile vs. 1st = 0.27; 95% CI, 0.12-0.59, Ptrend = 0.003) and positively associated with 2:16α-hydroxyestrone ratio (OR4th quartile vs. 1st = 2.44; 95% CI, 1.34-4.45, Ptrend = 0.001). Individual estrogen metabolites were unrelated to risk.

CONCLUSIONS

Our findings suggest that sex steroid hormones, specifically the estrogen-androgen balance, may be important in the development of aggressive prostate cancer.

IMPACT

Improved understanding of the hormonal etiology of prostate cancer is critical for prevention and therapeutic interventions.

The molecular etiology and prevention of estrogen-initiated cancers: Ockham's Razor: Pluralitas non est ponenda sine necessitate. Plurality should not be posited without necessity

Elucidation of estrogen carcinogenesis required a few fundamental discoveries made by studying the mechanism of carcinogenesis of polycyclic aromatic hydrocarbons (PAH). The two major mechanisms of metabolic activation of PAH involve formation of radical cations and diol epoxides as ultimate carcinogenic metabolites. These intermediates react with DNA to yield two types of adducts: stable adducts that remain in DNA unless removed by repair and depurinating adducts that are lost from DNA by cleavage of the glycosyl bond between the purine base and deoxyribose. The potent carcinogenic PAH benzo[a]pyrene, dibenzo[a,l]pyrene, 7,12-dimethylbenz[a]anthracene and 3-methylcholanthrene predominantly form depurinating DNA adducts, leaving apurinic sites in the DNA that generate cancer-initiating mutations. This was discovered by correlation between the depurinating adducts formed in mouse skin by treatment with benzo[a]pyrene, dibenzo[a,l]pyrene or 7,12-dimethylbenz[a]anthracene and the site of mutations in the Harvey-ras oncogene in mouse skin papillomas initiated by one of these PAH. By applying some of these fundamental discoveries in PAH studies to estrogen carcinogenesis, the natural estrogens estrone (E1) and estradiol (E2) were found to be mutagenic and carcinogenic through formation of the depurinating estrogen-DNA adducts 4-OHE1(E2)-1-N3Ade and 4-OHE1(E2)-1-N7Gua. These adducts are generated by reaction of catechol estrogen quinones with DNA, analogously to the DNA adducts obtained from the catechol quinones of benzene, naphthalene, and the synthetic estrogens diethylstilbestrol and hexestrol. This is a weak mechanism of cancer initiation. Normally, estrogen metabolism is balanced and few estrogen-DNA adducts are formed. When estrogen metabolism becomes unbalanced, more catechol estrogen quinones are generated, resulting in higher levels of estrogen-DNA adducts, which can be used as biomarkers of unbalanced estrogen metabolism and, thus, cancer risk. The ratio of estrogen-DNA adducts to estrogen metabolites and conjugates has repeatedly been found to be significantly higher in women at high risk for breast cancer, compared to women at normal risk. These results indicate that formation of estrogen-DNA adducts is a critical factor in the etiology of breast cancer. Significantly higher adduct ratios have been observed in women with breast, thyroid or ovarian cancer. In the women with ovarian cancer, single nucleotide polymorphisms in the genes for two enzymes involved in estrogen metabolism indicate risk for ovarian cancer. When polymorphisms produce high activity cytochrome P450 1B1, an activating enzyme, and low activity catechol-O-methyltransferase, a protective enzyme, in the same woman, she is almost six times more likely to have ovarian cancer. These results indicate that formation of estrogen-DNA adducts is a critical factor in the etiology of ovarian cancer. Significantly higher ratios of estrogen-DNA adducts to estrogen metabolites and conjugates have also been observed in men with prostate cancer or non-Hodgkin lymphoma, compared to healthy men without cancer. These results also support a critical role of estrogen-DNA adducts in the initiation of cancer. Starting from the perspective that unbalanced estrogen metabolism can lead to increased formation of catechol estrogen quinones, their reaction with DNA to form adducts, and generation of cancer-initiating mutations, inhibition of estrogen-DNA adduct formation would be an effective approach to preventing a variety of human cancers. The dietary supplements resveratrol and N-acetylcysteine can act as preventing cancer agents by keeping estrogen metabolism balanced. These two compounds can reduce the formation of catechol estrogen quinones and/or their reaction with DNA. Therefore, resveratrol and N-acetylcysteine provide a widely applicable, inexpensive approach to preventing many of the prevalent types of human cancer.

Unbalanced estrogen metabolism in ovarian cancer

Greater exposure to estrogens is a risk factor for ovarian cancer. To investigate the role of estrogens in ovarian cancer, a spot urine sample and a saliva sample were obtained from 33 women with ovarian cancer and 34 age-matched controls. Thirty-eight estrogen metabolites, conjugates and DNA adducts were analyzed in the urine samples using ultraperformance liquid chromatography/tandem mass spectrometry, and the ratio of adducts to metabolites and conjugates was calculated for each sample. The ratio of depurinating estrogen-DNA adducts to estrogen metabolites and conjugates was significantly higher in cases compared to controls (p < 0.0001), demonstrating high specificity and sensitivity. DNA was purified from the saliva samples and analyzed for genetic polymorphisms in the genes for two estrogen-metabolizing enzymes. Women with two low-activity alleles of catechol-O-methyltransferase plus one or two high-activity alleles of cytochrome P450 1B1 had higher levels of estrogen-DNA adducts and were more likely to have ovarian cancer. These findings indicate that estrogen metabolism is unbalanced in ovarian cancer and suggest that formation of estrogen-DNA adducts plays a critical role in the initiation of ovarian cancer.

Unbalanced estrogen metabolism in thyroid cancer

Well-differentiated thyroid cancer most frequently occurs in premenopausal women. Greater exposure to estrogens may be a risk factor for thyroid cancer. To investigate the role of estrogens in thyroid cancer, a spot urine sample was obtained from 40 women with thyroid cancer and 40 age-matched controls. Thirty-eight estrogen metabolites, conjugates and DNA adducts were analyzed by using ultraperformance liquid chromatography/tandem mass spectrometry and the ratio of adducts to metabolites and conjugates was calculated for each sample. The ratio of depurinating estrogen-DNA adducts to estrogen metabolites and conjugates significantly differed between cases and controls (p < 0.0001), demonstrating high specificity and sensitivity. These findings indicate that estrogen metabolism is unbalanced in thyroid cancer and suggest that formation of estrogen-DNA adducts might play a role in the initiation of thyroid cancer.

Metabolomic profiling unravels DNA adducts in human breast that are formed from peroxidase mediated activation of estrogens to quinone methides

Currently there are three major hypotheses that have been proposed for estrogen induced carcinogenicity, however exact etiology remains unknown. Based on the chemical logic, studies were undertaken to investigate if estrogens could generate quinone methides in an oxidative environment which then could cause DNA damage in humans. In presence of MnO2 estrogens were oxidized to quinone methides. Surprisingly quinone methides were found to be stable with t1/2 of 20.8 and 4.5 min respectively. Incubation of estrogens with lactoperoxidase (LPO) and H2O2 resulted in formation of respective quinone methides (E1(E2)-QM). Subsequent addition of adenine to the assay mixture lead to trapping of E1(E2)-QM, resulting in formation of adenine adducts of estrogens, E1(E2)-9-N-Ade. Targeted ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) based metabolomic analysis of the breast tissue extracts showed the presence of adenine adducts of estrogens, E1(E2)-9-N-Ade, along with other estrogen related metabolites. Identity of E1(E2)-N-Ade in LPO assay extracts and breast tissue extracts were confirmed by comparing them to pure synthesized E1(E2)-9-N-Ade standards. From these results, it is evident that peroxidase enzymes or peroxidase-like activity in human breast tissue could oxidize estrogens to electrophilic and stable quinone methides in a single step that covalently bind to DNA to form adducts. The error prone repair of the damaged DNA can result in mutation of critical genes and subsequently cancer. This article reports evidence for hitherto unknown estrogen metabolic pathway in human breast, catalyzed by peroxidase, which could initiate cancer.

Ultra performance liquid chromatography-tandem mass spectrometry method for profiling of steroid metabolome in human tissue

In humans, steroids play a broad and vital role in regulation of gene expression, secondary sexual characteristics, maturation, reproduction, cardiovascular health, neurological functions, etc., but imbalance in steroid metabolism is also linked to development and progression of many diseases, such as cancer, neurodegenerative diseases, and cardiovascular diseases. Hence, measurement of steroids in biological samples is essential to monitor human health. Currently, there is radioimmunoassay, gas chromatography-mass spectrometry (GC/MS), and liquid chromatography-mass spectrometry (LC-MS) methods developed for steroid measurements in biological samples. However, these methods require elaborate sample preparation procedures and have concerns(s) related to reproducibility, dynamic range, time, costs, and most importantly the total coverage of steroids. Also currently, there is no method available for comprehensive steroid profiling in a single LC-MS run that includes androgens, corticosteroids, progestogens, estrogens, estrogen metabolites, estrogen conjugates, and estrogen-DNA adducts as well as exogenous steroid derivatives. Here, I present a global steroid metabolic profiling method based on liquid-liquid extraction (LLE) followed by ultra performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS) for simultaneous measurement of over 100 indigenous as well as exogenous steroids in about 12 min, without derivatization. The method was successfully applied to determine steroid hormone levels in the breast tissue of healthy women. Overall presence of all major classes of steroids as well as estrogen derivatives was detected in breast tissue.

A perspective on the role of estrogen in hormone-induced prostate carcinogenesis

Androgens are thought to cause prostate cancer, but the precise mechanisms by which they do so are unclear. Data, mostly from animal studies, suggest that for androgens to cause prostate cancer they must be aromatized to estrogen and act in concert with these estrogen metabolites. Androgen-receptor mediated activity of androgens and estrogen receptor-mediated effects of estrogen metabolites are likely to be necessary, but estrogen genotoxicity appears to be a probable critical factor as well. Only when all these mechanisms are active, may prostate carcinogenesis result. Convincing proof-of-concept studies are needed to definitively test this concept which, if proven, may lead to clinically feasible chemoprevention approaches interfering with these mechanisms.

Peroxidase-mediated dealkylation of tamoxifen, detected by electrospray ionization-mass spectrometry, and activation to form DNA adducts

Tamoxifen (TAM) is extensively used for the treatment and prevention of breast cancer. Associated with TAM treatment is a two- to eightfold increase in risk of endometrial cancer. To understand the mechanisms associated with this increased risk several pathways for TAM metabolism and DNA adduct formation have been studied. The purpose of this study was to investigate the role of peroxidase enzymes in the metabolism of TAM and its activation to form DNA adducts. Using advanced tandem mass spectrometry we have investigated the peroxidase-mediated metabolism of TAM. Incubation of TAM with horseradish peroxidase (HRP) and H(2)O(2) produced multiple metabolites. Electrospray ionization-MS/MS analysis of the metabolites demonstrated a peak at 301.3m/z with daughter ions at 183.0, 166.9, 128.9, and 120.9m/z, which identified the metabolite as metabolite E (ME). The levels of ME were significantly inhibited by the addition of ascorbic acid to the incubation mixture. Co-incubation of either TAM or ME and DNA with HRP and H(2)O(2) produced three DNA adducts with a RAL of 1.97±0.01×10(-7) and 8.45±2.7×10(-7). Oxidation of ME with MnO(2) produced metabolite E quinone methide (MEQM). Furthermore, incubation of either TAM or ME with HRP and H(2)O(2) resulted in formation of MEQM. Reaction of calf thymus DNA with MEQM produced three DNA adducts with a RAL of 9.8±1.0×10(-7). Rechromatography analyses indicated that DNA adducts 1, 2, and 3 formed in the HRP activation of either TAM or ME were the same as those formed by the chemical reaction of DNA with MEQM. The results of these studies demonstrate that peroxidase enzymes can both metabolize TAM to form the primary metabolite ME and activate ME to a quinone methide intermediate, which reacts with DNA to form adducts. It is possible that peroxidase enzymes or peroxidase-like activity in endometrium could contribute to the formation of DNA damage and genotoxic effects in endometrium after TAM administration.

Mechanism of DNA depurination by carcinogens in relation to cancer initiation

Depurinating DNA adducts formed by aromatic hydrocarbons and catechol estrogen quinones play a major role in cancer initiation. Most of these adducts depurinate instantaneously, but some guanine adducts depurinate from DNA with half-lives of hours. We report here, that after 10 h at 37 °C, reaction of estradiol-3,4-quinone (E(2)-3,4-Q) with ds-DNA to yield N7Gua and N3Ade adducts was complete and more efficient than with ss-DNA. When E(2)-3,4-Q reacted with t-RNA, no adducts were detected after 10 h, and the level of N3Ade and N7Gua adducts after 10 days was less than half that with ss-DNA after 10 h. Reaction of E(2)-3,4-Q and dG yielded 4-OHE(2)-1-N7dG, which spontaneously depurinated to yield 4-OHE(2)-1-N7Gua. To investigate the mechanism of depurination, E(2)-3,4-Q was reacted with carbocyclicdeoxyguanosine, in which the ring oxygen of the deoxyribose moiety is substituted with CH(2) , and depurination was observed. The results from this experiment demonstrate that the oxocarbenium ion mechanism plays the major role in depurination and provides the first experimental evidence for this mechanism. A newly discovered β-elimination mechanism also plays a minor role in depurination. Understanding why the depurinating estrogen-DNA adducts come from DNA, and not from RNA, underscores the critical role that these adducts play in initiating cancer.

Hormones and prostate carcinogenesis: Androgens and estrogens

Prostate cancer is the leading non-skin malignancy detected in US males and the second cause of death due to male cancer in the US. Androgenic hormones are generally believed to be causatively associated with prostate carcinogenesis, but human evidence, mostly epidemiological, for this is minimal. Circulating hormone levels are not associated with the risk of prostate cancer and neither are polymorphisms in various genes encoding the androgen metabolizing enzymes or androgen receptors. Evidence in support of the involvement of androgens in prostate cancer development is derived from clinical trials with 5α-reductase inhibitors, which reduced the risk by approximately 25%. Animal studies using rat models, however, provide clear evidence that testosterone can induce prostate cancer and can act as a strong tumor promoter in concert with genotoxic carcinogens. One such genotoxic factor may be 17β-estradiol, which is generated from testosterone by the aromatase enzyme. Estradiol can be converted to catecholestrogens, which through redox cycling, generate reactive metabolites that can adduct the DNA and potentially lead to mutations. Animal studies and limited human evidence suggest that estrogens can be involved in prostate carcinogenesis by such a genotoxic mechanism. However, how androgens exert their tumor-promoting effect is not clear. It is likely that hormonal and non-hormonal factors as well as genetic and non-genetic (environmental) factors interact in a highly complex and poorly understood manner to determine the risk of prostate cancer.

Unbalanced metabolism of endogenous estrogens in the etiology and prevention of human cancer

Among the numerous small molecules in the body, the very few aromatic ones include the estrogens and dopamine. In relation to cancer initiation, the estrogens should be considered as chemicals, not as hormones. Metabolism of estrogens is characterized by two major pathways. One is hydroxylation to form the 2- and 4-catechol estrogens, and the second is hydroxylation at the 16α position. In the catechol pathway, the metabolism involves further oxidation to semiquinones and quinones, including formation of the catechol estrogen-3,4-quinones, the major carcinogenic metabolites of estrogens. These electrophilic compounds react with DNA to form the depurinating adducts 4-OHE(1)(E(2))-1-N3Ade and 4-OHE(1)(E(2))-1-N7Gua. The apurinic sites obtained by this reaction generate the mutations that may lead to the initiation of cancer. Oxidation of catechol estrogens to their quinones is normally in homeostasis, which minimizes formation of the quinones and their reaction with DNA. When the homeostasis is disrupted, excessive amounts of catechol estrogen quinones are formed and the resulting increase in depurinating DNA adducts can lead to initiation of cancer. Substantial evidence demonstrates the mutagenicity of the estrogen metabolites and their ability to induce transformation of mouse and human breast epithelial cells, and tumors in laboratory animals. Furthermore, women at high risk for breast cancer or diagnosed with the disease, men with prostate cancer, and men with non-Hodgkin lymphoma all have relatively high levels of estrogen-DNA adducts, compared to matched control subjects. Specific antioxidants, such as N-acetylcysteine and resveratrol, can block the oxidation of catechol estrogens to their quinones and their reaction with DNA. As a result, the initiation of cancer can be prevented.

Imbalanced estrogen metabolism in the brain: possible relevance to the etiology of Parkinson's disease

Damage to DNA by dopamine quinone and/or catechol estrogen quinones may play a significant role in the initiation of Parkinson's disease (PD). Depurinating estrogen-DNA adducts are shed from cells and excreted in urine. The aim of this study was to discover whether higher levels of estrogen-DNA adducts are associated with PD. Forty estrogen metabolites, conjugates, and DNA adducts were analyzed in urine samples from 20 PD cases and 40 matched controls by using ultra performance liquid chromatography/tandem mass spectrometry. The levels of adducts in cases versus controls (P < 0.005) suggest that unbalanced estrogen metabolism could play a causal role in the initiation of PD.

Urinary estrogen metabolites and prostate cancer risk: a pilot study

BACKGROUND

The high incidence of and few identified risk factors for prostate cancer underscore the need to further evaluate markers of prostate carcinogenesis. The aim of this pilot study was to evaluate urinary estrogen metabolites as a biomarker of prostate cancer risk.

METHODS

Using a liquid chromatography-tandem mass spectrometry method, urinary concentrations of 15 estrogen metabolites were determined in 77 prostate cancer cases, 77 healthy controls, and 37 subjects who had no evidence of prostate cancer after a prostate biopsy.

RESULTS

We observed an inverse association between the urinary 16-ketoestradiol (16-KE2) and 17-epiestriol (17-epiE3)--metabolites with high estrogenic activity--and prostate cancer risk. Men in the lowest quartile of 16-KE2, had a 4.6-fold risk of prostate cancer (OR=4.62, 95% CI=1.34-15.99), compared with those in the highest quartile.

CONCLUSIONS

We observed modest differences in estrogen metabolite concentrations between prostate cancer patients and subjects without cancer. Larger studies with both androgen and estrogen measurements are needed to confirm these results to clarify further whether estrogen metabolites are independent biomarkers for prostate cancer risk and whether androgen/estrogen imbalance influences prostate cancer risk.

Circulating steroid hormones in prostate carcinogenesis. Part 2: Estrogens

The aim of this review is to describe the associations between circulating plasma estrogens and prostate cancer (PCa). We recall the origins of estrogens, which derive from the aromatization of androgens, but also by sulfatase hydrolysis of estrone sulfate (E1-S), the main circulating plasma estrogen. We evoke that the carcinogenic effects of estrogens were demonstrated in the rat and murine prostate when estrogens and androgens were simultaneously administered to them. We also describe estrogen proliferative activity and the genotoxicity of estrogen-hydroxylated metabolites with the formation of DNA adducts. We report published aromatase and CYP1B1 polymorphisms found in men with PCa. We published a bibliography on the relation between PCa and prostate inflammation, as well as the possible role of obesity in the aggressiveness of PCa. In this review, we provide an exhaustive list of assays carried out in subjects at high risk for PCa compared with Caucasians, showing that higher estrogen levels were found in the plasma of these subjects at high risk for PCa. Plasma estrone was the estrogen for which plasma concentration was highest in subjects of African descent. We recall the links observed between plasma estrogens, particularly E1-S, and PCa aggressiveness. Finally, we describe assays for determining hydroxylated estrogens and DNA adducts in the urine of men with PCa. We insist on the importance of the technology employed in estrogen measurement and propose the use of mass spectrometry methods to carry out estrogen assays, in order to decrease variability in the results of plasma estrogen assays.

Resveratrol and N-acetylcysteine block the cancer-initiating step in MCF-10F cells

Substantial evidence suggests that catechol estrogen-3,4-quinones react with DNA to form predominantly the depurinating adducts 4-hydroxyestrone (estradiol)-1-N3Ade [4-OHE(1)(E(2))-1-N3Ade] and 4-OHE(1)(E(2))-1-N7Gua. Apurinic sites resulting from these adducts generate critical mutations that can initiate cancer. The paradigm of cancer initiation is based on an imbalance in estrogen metabolism between activating pathways that lead to estrogen-DNA adducts and deactivating pathways that lead to estrogen metabolites and conjugates. This imbalance can be improved to minimize formation of adducts by using antioxidants, such as resveratrol (Resv) and N-acetylcysteine (NAcCys). To compare the ability of Resv and NAcCys to block formation of estrogen-DNA adducts, we used the human breast epithelial cell line MCF-10F treated with 4-OHE(2). Resv and NAcCys directed the metabolism of 4-OHE(2) toward protective pathways. NAcCys reacted with the quinones and reduced the semiquinones to catechols. This pathway was also carried out by Resv. In addition, Resv induced the protective enzyme quinone reductase, which reduces E(1)(E(2))-3,4-quinones to 4-OHE(1)(E(2)). Resv was more effective at increasing the amount of 4-OCH(3)E(1)(E(2)) than NAcCys. Inhibition of estrogen-DNA adduct formation was similar at lower doses, but at higher doses Resv was about 50% more effective than NAcCys. Their combined effects were additive. Therefore, these two antioxidants provide an excellent combination to protect catechol estrogens from oxidation to catechol quinones.

Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms

Development of breast cancer involves genetic factors as well as lifetime exposure to estrogen. The precise molecular mechanisms whereby estrogens influence breast tumor formation are poorly understood. While estrogen receptor alpha (ERalpha) is certainly involved, nonreceptor mediated effects of estradiol (E(2)) may also play an important role in facilitating breast tumor development. A "reductionist" strategy allowed us to examine the role of ERalpha independent effects of E(2) on mammary tumor development in ERalpha knockout (ERKO) mice bearing the Wnt-1 oncogene. Exogenous E(2) "clamped" at early follicular and midluteal phase levels (i.e., 80 and 240 pg/ml) accelerated tumor formation in a dose-related fashion in ERKO/Wnt-1 animals (p = 0.0002). Reduction of endogenous E(2) by oophorectomy (p < 0.001) or an aromatase inhibitor (AI) (p = 0.055) in intact ERKO/Wnt-1 animals delayed tumorigenesis as further evidence for an ER-independent effect. The effects of residual ERalpha or beta were not involved since enhancement of tumor formation could not be blocked by the antiestrogen fulvestrant. 17alpha-OH-E(2), a metabolizable but ER-impeded analogue of E(2) stimulated tumor development without measurable uterine stimulatory effects. Taken together, our results suggest that ER-independent actions of E(2) can influence breast tumor development in concert with ER dependent effects. These observations suggest 1 mechanism whereby AIs, which block E(2) synthesis, would be more effective for breast cancer prevention than use of antiestrogens, which only block ER-mediated effects.

N-acetylcysteine blocks formation of cancer-initiating estrogen-DNA adducts in cells

Catechol estrogens, especially 4-hydroxylated metabolites of 17beta-estradiol (E(2)), are responsible for estrogen-induced carcinogenesis. 4-Hydroxyestradiol (4-OHE(2)), a major metabolite of E(2) formed preferentially by cytochrome P-450 1B1, is oxidized to E(2)-3,4-quinone, which can react with DNA to yield the depurinating adducts 4-OHE(2)-1-N3Ade and 4-OHE(2)-1-N7Gua. The apurinic sites generated by the loss of these depurinating adducts induce mutations that could lead to cancer initiation. In this study, we have evaluated the effects of N-acetylcysteine (NAcCys) on the metabolism of two cell lines, MCF-10F (a normal human breast epithelial cell line) and E6 (a normal mouse mammary epithelial cell line), treated with 4-OHE(2) or its reactive metabolite, E(2)-3,4-quinone. Extensive HPLC with electrochemical detection and UPLC-MS/MS analyses of the cell media demonstrated that the presence of NAcCys very efficiently shifted the estrogen metabolism toward protective methoxylation and conjugation pathways in multiple ways, whereas formation of depurinating DNA adducts was inhibited. Protection by NAcCys seems to be similar in both cell lines, irrespective of their origin (human or mouse) or the presence of estrogen receptor-alpha. This finding suggests that NAcCys, a common dietary supplement, could be used as a potential chemopreventive agent to block the initial step in the genotoxicity caused by catechol estrogen quinones.

Depurinating estrogen-DNA adducts in the etiology and prevention of breast and other human cancers

Experiments on estrogen metabolism, formation of DNA adducts, mutagenicity, cell transformation and carcinogenicity have led to and supported the hypothesis that the reaction of specific estrogen metabolites, mostly the electrophilic catechol estrogen-3,4-quinones, with DNA can generate the critical mutations to initiate breast and other human cancers. Analysis of depurinating estrogen-DNA adducts in urine demonstrates that women at high risk of, or with breast cancer, have high levels of the adducts, indicating a critical role for adduct formation in breast cancer initiation. Men with prostate cancer or non-Hodgkin lymphoma also have high levels of estrogen-DNA adducts. This knowledge of the first step in cancer initiation suggests the use of specific antioxidants that can block formation of the adducts by chemical and biochemical mechanisms. Two antioxidants, N-acetylcysteine and resveratrol, are prime candidates to prevent breast and other human cancers because in various M in vitro and in vivo experiments, they reduce the formation of estrogen-DNA adducts.

Urinary biomarkers suggest that estrogen-DNA adducts may play a role in the aetiology of non-Hodgkin lymphoma

A variety of evidence suggests that estrogens may induce non-Hodgkin lymphoma (NHL). The reaction of catechol estrogen quinones with DNA to form depurinating estrogen-DNA adducts is hypothesized to initiate this process. These adducts are released from DNA, shed from cells into the bloodstream and excreted in urine. The aim of this study was to determine whether or not the depurinating estrogen-DNA adducts might be involved in the aetiology of human NHL. Estrogen metabolites, conjugates and depurinating DNA adducts were identified and quantified in spot urine samples from 15 men with NHL and 30 healthy control men by using ultraperformance liquid chromatography/tandem mass spectrometry. The levels of estrogen-DNA adducts were significantly higher in the men with NHL than in the healthy control men. Thus, formation of estrogen-DNA adducts may play a critical role in the aetiology of NHL, and these adducts could be potential biomarkers of NHL risk.

Urinary estrogen metabolites and prostate cancer: a case-control study and meta-analysis

OBJECTIVE

To investigate prostate cancer (Pca) risk in relation to estrogen metabolism, expressed as urinary 2-hydroxyestrone (2-OHE1), 16alpha-hydroxyestrone (16alpha-OHE1) and 2-OHE1 to 16alpha-OHE1 ratio.

METHODS

We conducted a case-control study within the Western New York Health Cohort Study (WNYHCS) from 1996 to 2001. From January 2003 through September 2004, we completed the re-call and follow-up of 1092 cohort participants. Cases (n = 26) and controls (n = 110) were matched on age, race and recruitment period according to a 1:4 ratio. We used the unconditional logistic regression to compute crude and adjusted odds ratios (OR) and 95% confident interval (CI) of Pca in relation to 2-OHE1, 16alphaOHE1 and 2-OHE1 to 16alpha-OHE1 by tertiles of urine concentrations (stored in a biorepository for an average of 4 years). We identified age, race, education and body mass index as covariates. We also conducted a systematic review of the literature which revealed no additional studies, but we pooled the results from this study with those from a previously conducted case-control study using the DerSimonian-Laird random effects method.

RESULTS

We observed a non-significant risk reduction in the highest tertile of 2-OHE1 (OR 0.72, 95% CI 0.25-2.10). Conversely, the odds in the highest tertile of 16alpha-OHE1 showed a non-significant risk increase (OR 1.76 95% CI 0.62-4.98). There was a suggestion of reduced Pca risk for men in the highest tertile of 2-OHE1 to 16alpha-OHE1 ratio (OR 0.56, 95% CI 0.19-1.68). The pooled estimates confirmed the association between an increased Pca risk and higher urinary levels of 16alpha-OHE1 (third vs. first tertile: OR 1.82, 95% CI 1.09-3.05) and the protective effect of a higher 2-OHE 1 to 16alpha-OHE1 ratio (third vs. first tertile: OR 0.53, 95% CI 0.31-0.90).

CONCLUSION

Our study and the pooled results provide evidence for a differential role of the estrogen hydroxylation pathway in Pca development and encourage further study.

Mechanism of metabolic activation and DNA adduct formation by the human carcinogen diethylstilbestrol: the defining link to natural estrogens

Diethylstilbestrol (DES) is a human carcinogen, based on sufficient epidemiological evidence. DES is mainly metabolized to its catechol, 3'-hydroxyDES (3'-OH-DES), which can further oxidize to DES-3',4'-quinone (DES-3',4'-Q). Similarly to estradiol-3,4-quinone, the reaction of DES-3',4'-Q with DNA would form the depurinating 3'-OH-DES-6'-N3Ade and 3'-OH-DES-6'-N7Gua adducts. To prove this hypothesis, synthesis of DES-3',4'-Q by oxidation of 3'-OH-DES with Ag(2)O was tried; this failed due to instantaneous formation of a spiro-quinone. Oxidation of 3'-OH-DES by lactoperoxidase or tyrosinase in the presence of DNA led to the formation of 3'-OH-DES-6'-N3Ade and 3'-OH-DES-6'-N7Gua adducts. These adducts were tentatively identified by LC-MS/MS as 3'-OH-DES-6'-N3Ade, m/z = 418 [M+H](+), and 3'-OH-DES-6'-N7Gua, m/z = 434 [M+H](+). Demonstration of their structures derived from their oxidation by MnO(2) to the DES quinone adducts and subsequent tautomerization to the dienestrol (DIES) catechol adducts, which are identical to the standard 3'-OH-DIES-6'-N3Ade, m/z = 416 [M+H](+), and 3'-OH-DIES-6'-N7Gua, m/z = 432 [M+H](+), adducts. The reaction of DIES-3',4'-Q or lactoperoxidase-activated 3'-OH-DIES with DNA did not produce any depurinating adducts, due to the dienic chain being perpendicular to the phenyl planes, which impedes the intercalation of DIES into the DNA. Enzymic oxidation of 3'-OH-DES suggests that the catechol of DES intercalates into DNA and is then oxidized to its quinone to yield N3Ade and N7Gua adducts. These results suggest that the common denominator of tumor initiation by the synthetic estrogen DES and the natural estrogen estradiol is formation of their catechol quinones, which react with DNA to afford the depurinating N3Ade and N7Gua adducts.