Limited association between a catechol-O-methyltransferase (COMT) polymorphism and breast cancer risk in Japan

Impact of Catechol-O-Methyltransferase Val 158Met (rs4680) Polymorphism on Breast Cancer Susceptibility in Asian Population

Background:

Catechol-O-methyltransferase (COMT) is an important estrogen-metabolizing enzyme. Numerous case-control studies have evaluated the role COMT Val 158Met (rs4680;472G->A) polymorphism in the risk of breast cancer and provided inconclusive results, hence present meta-analysis was designed to get a more reliable assessment in Asian population.

Methods:

A total of 26 articles were identified through a search of four electronic databases-PubMed, Google Scholar, Science Direct and Springer link, up to March, 2016. Pooled odds ratios (ORs) with 95% con¬fidence intervals (CIs) were used as association measure to find out relationship between COMT Val158Metpolymorphism and the risk of breast cancer. We also assessed between study heterogeneity and publication bias. All statistical analyses were done by Open Meta-Analyst.

Results:

Twenty six case-control studies involving 5,971 breast cancer patients and 7,253 controls were included in the present meta-analysis. The results showed that the COMT Val158Met polymorphism was significantly associated with breast cancer risk except heterozygote model(allele contrast odds ratio (ORAvsG)= 1.13, 95%CI=1.02-1.24,p=0.01; heterozygote/co-dominant ORGAvsGG= 1.03, 95%CI=0.96-1.11,p=0.34; homozygote ORAAvsGG= 1.38, 95%CI= 1.08-1.76,p=0.009; dominant model ORAA+GAvsGG= 1.08, 95%CI=1.01-1.16,p=0.02; and recessive model ORAAvsGA+GG= 1.35, 95%CI=1.07-1.71,p=0.01). In addition, we also performed subgroup analysis based on source of controls and menopausal state of patients.

Conclusions:

In conclusion, the COMT Val158Met polymorphism was related to increased breast cancer susceptibility in the Asian population.

Catechol-O-methyltransferase gene polymorphism and vulvar pain in women with vulvodynia

BACKGROUND

The underlying causes of vulvar pain in women with vulvodynia remain poorly understood. Catechol-O-methyltransferase, an enzyme that metabolizes catecholamines, is a neuromodulator that is involved with perception and sensitivity to pain. The catechol-O-methyltransferase gene is polymorphic, and a single nucleotide polymorphism is associated with low activity and heightened pain sensitivity. The variant allele that encodes this polymorphism commonly is called the "L allele" because of its low enzyme activity as opposed to the normal H (high activity) allele.

OBJECTIVE

The methionine-containing catechol-O-methyltransferase protein coded by the L allele results in elevated catecholamine levels, reduced inactivation of the dopaminergic and adrenergic systems, and increased sensitivity to pain. This polymorphism not only may decrease the pain threshold in response to acute pain but also may facilitate the development of chronic pain. Therefore, the objective of our study was to assess whether a variation in the catechol-O-methyltransferase genotype is involved in increased pain sensitivity in women with vulvodynia.

STUDY DESIGN

We conducted a prospective cohort study.

METHODS

Buccal swabs were collected from 167 white women with vulvodynia and 107 control subjects; the DNA was tested for a single nucleotide polymorphism at position 158 (rs4680) in the catechol-O-methyltransferase gene.

RESULTS

Women with vulvodynia had a marginally increased, yet not significant, prevalence of the catechol-O-methyltransferase genotype that is associated with high activity of the coded protein: 32.9% in the women with vulvodynia, as opposed to 21.5% in the control subjects (odds ratio, 1.80; 95% confidence interval, 1.02-3.15). Subgrouping the cases based on pain frequency revealed that the elevated occurrence of this catechol-O-methyltransferase genotype was present in 40.6% of the subset of women who experienced pain only with sexual intercourse vs only 21.5% of control subjects (odds ratio, 2.50; 95% confidence interval, 1.27-4.93). Also, women with primary vulvodynia had a significantly higher prevalence of the H allele than did the control subjects (62.9% vs 48.1%; odds ratio, 1.82; 95% confidence interval, 1.05-3.17).

CONCLUSION

Increased pain sensitivity in women with vulvodynia is not due to a genetically determined low catechol-O-methyltransferase enzyme activity. Other mechanisms may account for alterations in catechol-O-methyltransferase activity in women with pain that is limited to intercourse or primary vulvodynia that contributes to pain sensitivity.

The Val158Met polymorphism in COMT gene and cancer risk: role of endogenous and exogenous catechols

Catechol-O-methyltransferase, COMT, is an important phase II enzyme catalyzing the transfer of a methyl-group from S-adenosylmethionine to a catechol-containing substrate molecule. A genetic variant Val158Met in the COMT gene leads to a several-fold decrease in the enzymatic activity giving rise to the accumulation of potentially carcinogenic endogenous catechol estrogens and their reactive intermediates and increasing thus the risk of tumorigenesis. However, numerous association studies between the COMT genotype and susceptibility to various malignancies have shown inconsistent and controversial findings indicating that additional gene-gene and gene-environment interactions might be crucial in modulating the physiological role of the COMT. In this review article, the important contribution of dietary catechol-containing flavonoids to modification of the relationships between the COMT genotype and cancer risk is discussed. Whereas, the diverse anticancer activities of common phytochemicals, such as green tea polyphenols, quercetin, fisetin or luteolin, can be markedly changed (both decreased or increased) by the COMT-mediated O-methylation of these exogenous substrates, flavonoids can also behave as potent inhibitors of the COMT enzyme slowing detoxification of endogenous catechol estrogens. Such a many-featured functioning of the COMT and its complex regulation by several different genetic and environmental factors, including plant-based food ingredients, emphasizes the necessity to further stratify the association studies between the COMT genotype and tumor risk by consumption of catechol-containing dietary flavonoids. Currently, it can be only speculated that some of the possible associations might be masked by the regular intake of specific food polyphenols, taking effect in certain communities or populations.

Association between the COMT Val158Met polymorphism and risk of cancer: evidence from 99 case-control studies

Catechol-O-methyltransferase (COMT) plays a central role in DNA repair and estrogen-induced carcinogenesis. Many recent epidemiologic studies have investigated the association between the COMT Val158Met polymorphism and cancer risk, but the results are inconclusive. In this study, we performed a meta-analysis to investigate the association between cancer susceptibility and COMT Val158Met in different genetic models. Overall, no significant associations were found between COMT Val158Met polymorphism and cancer risk (homozygote model: odds ratio [OR] =1.05, 95% confidence interval [CI] = [0.98, 1.13]; heterozygote model: OR =1.01, 95% CI = [0.98, 1.04]; dominant model: OR =1.02, 95% CI [0.97, 1.06], and recessive model: OR =1.03, 95% CI [0.97, 1.09]). In the subgroup analysis of cancer type, COMT Val158Met was significantly associated with increased risks of bladder cancer in recessive model, and esophageal cancer in homozygote model, heterozygote model, and dominant model. Subgroup analyses based on ethnicities, COMT Val158Met was significantly associated with increased risk of cancer in homozygote and recessive model among Asians. In addition, homozygote, recessive, and dominant models were significantly associated with increased cancer risk in the subgroup of allele-specific polymerase chain reaction genotyping. Significant associations were not observed when data were stratified by the source of the controls. In summary, this meta-analysis suggested that COMT Val158Met polymorphism might not be a risk factor for overall cancer risk, but it might be involved in cancer development at least in some ethnic groups (Asian) or some specific cancer types (bladder and esophageal cell cancer). Further evaluations of more preclinical and epidemiological studies are required.

Genetic polymorphisms of estrogen receptor alpha and catechol-O-methyltransferase genes in Turkish patients with familial prostate carcinoma

OBJECTIVES

Estrogen is one of the most crucial hormones participating in the proliferation and carcinogenesis of the prostate glands. Genetic polymorphisms in the estrogen metabolism pathway might be involved in the risk of prostate carcinoma development. We evaluated the association between genetic polymorphisms in estrogen receptor alpha (ESR1) and catechol-O-methyltransferase (COMT) genes and the risk of developing familial prostate carcinoma.

MATERIALS AND METHODS

In this study, 34 cases with prostate carcinoma whose first-degree relatives had prostate carcinoma and 30 healthy age-matched male controls were enrolled. The genotypes of ESR1 and COMT genes were analyzed employing polymerase chain reaction-restriction fragment length polymorphism method. 34 cases with prostate carcinoma, whose first degree relatives had prostate carcinoma and 14 age-matched male controls were enrolled to analyze the genotype of these two genes.

RESULTS

Among control patients, the ESR1 PvuII genotypes of C/C, C/T and T/T were observed in 37%, 26% and 37%, respectively, whereas the C/C, C/T and T/T genotypes were observed in 18%, 41% and 41% of case patients, respectively. Among controls, the ESR1 PvuII allele frequencies of C and T were equally observed, whereas the C and T allele frequencies were observed in 38% and 62% of patients, respectively. Among ESR1 PvuII genotypes there were not any significant difference in terms of genotype (P = 0.199) and allele (P = 0.181) frequencies. Among controls, the ESR1 XbaI genotypes of G/G, G/A and A/A were observed in 33%, 37% and 33%, respectively, whereas the G/G, G/A and A/A genotypes were observed in 12%, 47% and 41% of patients, respectively. Among controls, the ESR1 XbaI allele frequencies of A and G were observed equally, respectively, whereas the A and G frequencies were observed in 65% and 35% of patients, respectively. Among ESR1 Χ baI, there was not any significant difference in terms of genotype (P = 0.111) and allele (P = 0.093) frequencies. But the C/C genotype of the PvuII site and G/G genotype of the XbaI site in the ESR1 gene were associated significantly with the risk of developing prostate carcinoma. The G/G, G/A and A/A genotypes of the COMT gene were observed in 50%, 29% and 21% of control patients and in 53%, 21% and 26% of case patients, respectively. The A and G allele frequencies of the COMT gene were observed in 36.7%, 63.3% of control patients and in 36.8%, 63.2% of case patients, respectively. In COMT gene, there was not any significant difference in terms of genotype (P = 0.843) and allele (P = 0.991) frequencies. But the G/A genotype of the COMT gene had a weak tendency toward increased risk.

CONCLUSION

Polymorphisms of ESR1 gene in the estrogen metabolism pathway were associated significantly with familial prostate carcinoma risk. Single nucleotide polymorphisms of low-penetrance genes are targets for understanding the genetic susceptibility of familial prostate carcinoma.

Catechol-O-methyltransferase Val158Met polymorphism and breast cancer risk in Asian population

The association between the polymorphism of catechol-O-methyltransferase (COMT) Val158Met and breast cancer risk is still inconclusive. We performed a meta-analysis to derive a more precise estimation of the relationship. A total of 18 studies including 5,175 cases and 6,463 controls were involved in this meta-analysis. When all studies were pooled into the meta-analysis, no significantly elevated breast cancer risk was associated with all genetic models (for additive model: OR = 1.273, 95% CI = 0.947-1.711, P heterogeneity = 0.000; P = 0.110; for dominant model: OR = 1.080, 95% CI = 0.945-1.234, P heterogeneity = 0.001; P = 0.259; for recessive model: OR = 1.242, 95% CI = 0.941-1.641, P heterogeneity = 0.000; P = 0.126; for allele comparison model: OR = 1.096, 95% CI = 0.976-1.230, P heterogeneity = 0.000; P = 0.121). In the subgroup analysis by controls source, the same results were found in all genetic models. In summary, this meta-analysis suggests that the COMT Val158Met polymorphism is not a risk factor for breast cancer development. However, large sample and representative population-based studies with homogeneous breast cancer patients and well-matched controls are warranted to confirm this finding.

Association of COMT Val158Met polymorphism and breast cancer risk: an updated meta-analysis

BACKGROUND

Catechol-O-methyltransferase (COMT) is one of the most important enzymes involved in estrogen metabolism and its functional genetic polymorphisms may be associated with breast cancer (BC) risk. Many epidemiological studies have been conducted to explore the association between the COMT Val158Met polymorphism and breast cancer risk. However, the results remain inconclusive. In order to derive a more precise estimation of this relationship, a large meta-analysis was performed in this study.

METHODS

Systematic searches of the PubMed, Embase and Cochrane Library were performed. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to estimate the strength of the association.

RESULTS

A total of 56 studies including 34,358 breast cancer cases and 45,429 controls were included. Overall, no significant associations between the COMT Val158Met polymorphism and breast cancer risk were found for LL versus HH, HL versus HH, LL versus HL, recessive model LL versus HL+HH, and dominant model LL+HL versus HH. In subgroup analysis by ethnicity, source of controls, and menopausal status, there was still no significant association detected in any of the genetic models.

CONCLUSION

Our meta-analysis results suggest that the COMT Val158Met polymorphism may not contribute to breast cancer susceptibility.

VIRTUAL SLIDES

The virtual slides(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs4806123577708417.

Meta-analyses of the effect of hormone treatment on cognitive function in postmenopausal women

As we age, most of us experience a certain degree of cognitive decline. In most cases, this decline is gradual. However, in some cases, cognitive impairment is so severe that it can be classified as dementia and this impacts greatly on activities of daily living. Alzheimer's disease, the most common form of dementia, has been linked to the reduction in estrogen levels that comes with aging. More specifically, many researchers have hypothesized that estrogen, and hence estrogen replacement via hormone therapy, could protect against cognitive decline in women. However, recent randomized, controlled trials did not reflect this. In fact, some reports showed that hormone therapy could have detrimental effects on cognitive function in older postmenopausal women. The most publicized of these has been the Women's Health Initiative Memory Study. Studies have thus yielded conflicting results and conclusions. The reasons for this may be due to a number of factors, such as the age of participants, the time of hormone therapy onset ('window of opportunity' theory), type of treatment, type of menopause (surgical or natural) and, possibly, genetic risk factors. We performed quantitative and qualitative meta-analyses and reviewed each of these factors in detail. The future may lie in combining these factors in order to fully understand the potential mechanisms behind estrogen and its effect on cognition.

Catechol-O-methyltransferase Val 108/158 Met polymorphism and breast cancer risk: a case control study in Syria

BACKGROUND

Catechol-O-methyltransferase (COMT) inactivates catechol estrogens by methylation and thus may play a protective role against mutations induced by estrogen metabolites. In this study we investigated the relationship between the Vall58Met polymorphism in the COMT gene and breast cancer risk in a population-based case control study in Syria.

METHODS

We examined 135 breast cancer patients and 107 healthy controls in North Syria to determine the association between the functional genetic Val158Met polymorphism in the COMT gene and female breast cancer risk.

RESULTS

There was no significant overall association between the COMT genotype and individual susceptibility to breast cancer.

CONCLUSIONS

Our data suggest that there may be no overall association between the COMT genotype and breast cancer.

Towards non-surgical therapy for uterine fibroids: catechol-O-methyl transferase inhibitor shrinks uterine fibroid lesions in the Eker rat model

BACKGROUND

Uterine leiomyomas (fibroids) are the most common pelvic tumors in women. We assessed the potential therapeutic utility of Ro 41-0960, a synthetic catechol-O-methyl transferase inhibitor (COMTI), in the Eker rat.

METHODS

We randomized uterine fibroid-bearing Eker rats for treatment with Ro 41-0960 (150 mg/kg/12 h) versus vehicle for 2 and 4 weeks. The fibroids were measured by caliper and subjected to histological evaluation. Urinary levels of 2-hydroxy estrogen (E(2)), 16-hydroxy E2 and DPD (osteoporosis marker) and serum liver enzymes were evaluated. Expressions of Cyclin D1, proliferating cell nuclear antigen (PCNA), Poly [ADP-ribose] polymerase1 (PARP1), tumor suppressor gene (P53) and transforming growth factor (TGFβ3) were assessed in fibroids using immunohistochemical analysis or RT-PCR. Apoptosis was confirmed using terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL).

RESULTS

Ro 41-0960-treated rats exhibited fibroid volumes of 86 ± 7% and 105 ± 12% of initial burden, at 2 and 4 weeks post-treatment, respectively, significantly lower than control group (240 ± 15% and 300 ± 18%; P< 0.01). Ro 41-0960 increased the urinary 2-hydroxy E2/16-hydroxy E(2) ratio, level of p53 mRNA and TUNEL positivity (P< 0.05) and decreased PARP1, PCNA and cyclin D1 proteins and TGFβ3 mRNA (P< 0.05). Ro 41-0960 did not change normal tissue histology, liver functions or urinary DPD level.

CONCLUSIONS

Ro 41-0960 (COMTI) arrested growth/shrunk uterine fibroids in Eker rats. This result may be related to modulation of estrogen-dependent genes involved in apoptosis, proliferation and extracellular matrix deposition via accumulation of 2-hydroxy estrogen. The efficacy and safety of Ro 41-0960 in rats suggest its candidacy for treatment of uterine fibroids.

Soy isoflavones, CYP1A1, CYP1B1, and COMT polymorphisms, and breast cancer: a case-control study in southwestern China

CYP1A1, CYP1B1, and COMT are key enzymes involved in estrogen metabolism. Soy isoflavones, phytoestrogens found in soy foods, may modify the activity of these enzymes. A case-control study was conducted to assess the associations between soy isoflavone intake and the CYP1A1 Ile462Val, CYP1B1 Val432Leu, and COMT Val158Met polymorphisms and breast cancer, as well as their combined effects on breast cancer. A total of 400 newly diagnosed breast cancer cases and 400 healthy controls were recruited. Participants' daily intake of soy isoflavones (DISI [mg/day]) was calculated and transformed to energy-adjusted DISI by the residual method. Gene sequencing was used to analyze CYP1A1, CYP1B1, and COMT polymorphisms. Adjusted odds ratios (aORs) and 95% confidence intervals (95% CIs) were estimated by conditional logistic regression. A strong protective dose-dependent effect of energy-adjusted DISI on breast cancer was found in both pre- and postmenopausal women (P(trend) < 0.05). Among all women and in the postmenopausal subgroup, COMT Met/Met and CYP1B1 Leu/Leu susceptible genotype carriers had higher risk of breast cancer (aORs > 1, OR 95% CIs exclude 1). In premenopausal women, only carrying CYP1B1 Leu/Leu was associated with breast cancer risk (aOR = 2.05, 95% CI: 1.11-3.79). Carrying CYP1A1 Val/Val was related to breast cancer risk only among all women. A stratified analysis was performed at two levels of energy-adjusted DISI, with wildtype homozygous genotypes and low energy-adjusted DISI as the reference. In the high energy-adjusted DISI subgroup, carrying the CYP1B1 Leu/Leu genotype did not affect breast cancer risk in either all women or in the menopausal subgroups, compared with the reference. Overall, in Han Chinese women, carrying CYP1A1 Val/Val and COMT Met/Met appears to be associated with breast cancer risk, especially in postmenopausal women. CYP1B1 susceptible genotypes (Val/Leu or Leu/Leu) also contribute to increased breast cancer risk, regardless of menopausal status, but high soy isoflavone intake may reduce this risk.

Inhibition of catechol-Omicron-methyltransferase activity in human breast cancer cells enhances the biological effect of the green tea polyphenol (-)-EGCG

Tea is one of the most popular beverages in the world and has been studied extensively as a health-promoting beverage that may act to prevent a number of chronic diseases and cancers. (-)-Epigallocatechin gallate [(-)-EGCG], a major component in green tea, is unstable under physiological conditions and methylation of (-)-EGCG by catechol-Omicron-methyltransferase (COMT) is a modification that reduces the biological activity of (-)-EGCG. In the current study, we hypothesized that suppression of COMT activity in human breast cancer cells could increase the proteasome-inhibitory potency of (-)-EGCG and therefore enhance its tumor cell growth-inhibitory activity. We first determined the COMT genotype and basal levels of COMT activity in various human breast cancer cell lines. Furthermore, when breast cancer MDA-MB-231 cells containing high COMT activity were tested, the diminished COMT activity apparently increased the effectiveness of (-)-EGCG via augmented proteasome inhibition and apoptosis induction. This study supplements the previous findings that methylated (-)-EGCG is less bioactive and supports the notion that COMT inhibition may increase the anti-cancer properties of tea polyphenols and the combination may serve as a novel approach or supplemental treatment for breast cancer chemotherapy.

Lack of association between catechol-O-methyltransferase Val108/158Met polymorphism and breast cancer risk: a meta-analysis of 25,627 cases and 34,222 controls

Epidemiological studies have evaluated the association between catechol-O-methyltransferase (COMT) Val108/158Met polymorphism and breast cancer risk. However, the results remain conflicting rather than conclusive. In order to derive a more precise estimation of the relationship, we performed this meta-analysis. Systematic searches of the PubMed and Medline databases were performed. A total of 41 studies including 25,627 cases and 34,222 controls were identified. Genotype distributions of COMT in the controls of all studies were in agreement with the Hardy-Weinberg equilibrium (HWE) except for three studies. When all 41 studies were pooled into the meta-analysis, there was no evidence for significant association between COMT Val108/158Met polymorphism and breast cancer risk (for Val/Met vs. Val/Val: OR = 0.99, 95% CI = 0.93-1.04; for Met/Met vs. Val/Val: OR = 0.96, 95% CI = 0.88-1.04; for dominant model: OR = 0.97, 95% CI = 0.92-1.03; for recessive model: OR = 0.97, 95% CI = 0.90-1.04). In the subgroup analyses by ethnicity, menopausal status, no significant associations were found in all genetic models. When sensitivity analyses were performed by excluding HWE-violating studies, all the results were not materially altered. In summary, the meta-analysis strongly suggests that COMT Val108/158Met polymorphism is not associated with increased breast cancer risk.

Association of the NPAS3 gene and five other loci with response to the antipsychotic iloperidone identified in a whole genome association study

A whole genome association study was performed in a phase 3 clinical trial conducted to evaluate a novel antipsychotic, iloperidone, administered to treat patients with schizophrenia. Genotypes of 407 patients were analyzed for 334,563 single nucleotide polymorphisms (SNPs). SNPs associated with iloperidone efficacy were identified within the neuronal PAS domain protein 3 gene (NPAS3), close to a translocation breakpoint site previously observed in a family with schizophrenia. Five other loci were identified that include the XK, Kell blood group complex subunit-related family, member 4 gene (XKR4), the tenascin-R gene (TNR), the glutamate receptor, inotropic, AMPA 4 gene (GRIA4), the glial cell line-derived neurotrophic factor receptor-alpha2 gene (GFRA2), and the NUDT9P1 pseudogene located in the chromosomal region of the serotonin receptor 7 gene (HTR7). The study of these polymorphisms and genes may lead to a better understanding of the etiology of schizophrenia and of its treatment. These results provide new insight into response to iloperidone, developed with the ultimate goal of directing therapy to patients with the highest benefit-to-risk ratio.

Estrogens metabolism associated with polymorphisms: influence of COMT G482a genotype on age at onset of canine mammary tumors

Catechol-O-methyltransferase (COMT) is an important enzyme participating in inactivation of carcinogenic oestrogen metabolites. In humans there is a single nucleotide polymorphism in COMT gene (COMT val158met) that has been associated with an increased risk for developing breast cancer. In dogs, there is a single nucleotide polymorphism in COMT gene (G482A), but its relation with mammary carcinogenesis has never been investigated. The aim of this study was to focus on the evaluation of such polymorphism as a risk factor for the development of mammary tumors in bitches and on the analysis of its relationship with some clinicopathologic features (dog's age and weight, number and histologic type of the lesions, lymph node metastasis) of canine mammary neoplasms. A case-control study was conducted analyzing 90 bitches with mammary tumors and 84 bitches without evidence of neoplastic disease. The COMT G482A polymorphism was analyzed by PCR-RFLP. We found a protective effect of the polymorphism in age of onset of mammary tumors, although we could not establish a significant association between COMT genotype and other clinicopathologic parameters nor with mammary tumor risk overall. Animals carrying the variant allele have a threefold likelihood of developing mammary tumors after 9 years of age in comparison with noncarriers. The Kaplan-Meier method revealed significant differences in the waiting time for onset of malignant disease for A allele carrier (12.46 years) and noncarrier (11.13 years) animals. This investigation constitutes the first case-control study designed to assess the relationship between polymorphic genes and mammary tumor risk in dogs. Our results point to the combined effect of COMT genotype with other genetic and/or environmental risk factors as important key factors for mammary tumor etiopathogenesis.

A prospective study of genetic polymorphism in MPO, antioxidant status, and breast cancer risk

Oxidative stress may be involved in breast carcinogenesis. Myeloperoxidase (MPO) is an endogenous oxidant enzyme that generates reactive oxygen species (ROS). A single nucleotide polymorphism (SNP) G-463A in the promoter region has been associated with a decrease in risk of breast cancer. We assessed the association between this polymorphism and breast cancer risk in a nested case-control study within the Nurses' Health Study (1,269 incident breast cancer cases and 1,761 matched controls). We further investigated potential gene-gene and gene-environment interactions. There were no significant associations between MPO or COMT genotypes and risk of breast cancer. However, the combination of a priori hypothesized low-risk genotypes in MPO and COMT genes was associated with a marginally significant decrease in breast cancer risk (OR, 0.28; 95% CI, 0.08-1.00). Dietary intake and plasma antioxidant levels may modify the association between the MPO polymorphism and breast cancer risk. Although the test for departure from multiplicative interaction was not significant, inverse associations with MPO genotype were more pronounced among women who consumed higher amounts of total fruits and vegetables (OR, 0.58; 95% CI, 0.30-1.12); this association was not found among the low-consumption group (OR, 1.11; 95% CI, 0.63-1.96). The relative risk associated with the MPO homozygous variant genotype was 0.44 (95% CI, 0.18-1.09) for women who had the highest level of plasma carotenoids. Results from this study suggest that exogenous and endogenous modulators of oxidative stress may modify the association between the MPO polymorphism and breast cancer risk. Further research is needed to confirm these possible associations.

Soy isoflavones decrease the catechol-O-methyltransferase-mediated inactivation of 4-hydroxyestradiol in cultured MCF-7 cells

The tissue concentrations of the female sex hormone 17beta-estradiol (E2) and its reactive catechol metabolites such as 4-hydroxyestradiol (4-HO-E2) play important roles in hormonal carcinogenesis. They are influenced by the activity of local enzymes involved in the metabolic activation and inactivation of E2. In the mammary gland, catechol estrogens are predominately inactivated by catechol-O-methyltransferase (COMT). Food supplements containing the soy isoflavones genistein and daidzein are consumed because they are believed to protect from breast cancer; however, this proposed benefit is controversial. The aim of the present study was to investigate the influence of soy isoflavones on the gene expression and activity of COMT in cultured human mammary adenocarcinoma MCF-7 cells. Levels of COMT messenger RNA (mRNA) were determined by reverse transcription/competitive polymerase chain reaction and COMT activity was determined by high-performance liquid chromatography analysis of the methylation products of both the model substrate quercetin and the physiological relevant substrate 4-HO-E2. Our study demonstrates for the first time that soy isoflavones at hormonally active concentrations cause a significant reduction of both COMT mRNA levels and COMT activity as well as of the methylation of 4-HO-E2. Experiments using the estrogen receptor (ER) antagonist ICI 182,780 support a role of the ER in the isoflavone-induced down-regulation of COMT expression. Thus, this study not only demonstrates that hormonally active concentrations of soy isoflavones inhibit the detoxification of catechols in this human breast cancer cell line but also implies that diet might influence COMT activity to a greater extent than heretofore recognized.

The Val158Met polymorphism of the catechol-O-methyltransferase gene is not associated with the risk of sporadic or latent prostate cancer in Japanese men

AIM

Since catechol estrogens possess carcinogenetic potential, their detoxification may lead to reduced risk of carcinogenesis. Catechol-O-methyltransferase (COMT) catalyzes the O-methylation of catechol estrogens. The enzymatic activity of COMT has been shown to be governed by a functional single-nucleotide polymorphism represented by a G-to-A transition at codon 158, that results in a valine to methionine substitution; this variant form is associated with an up to 4-fold decrease in enzymatic activity. We attempted to investigate whether the Val158Met polymorphism of COMT was associated with the risk of prostate cancer.

METHODS

We analysed genomic DNA samples from 324 sporadic prostate cancer patients; 342 controls who had died from causes unrelated to cancer; and 95 Japanese men who were diagnosed as latent prostate cancer by autopsy. The genotyping method we used was a TaqMan assay.

RESULTS

Age adjusted odds ratios for sporadic prostate cancer susceptibility were 1.047 (95% CI: 0.630-1.741) for the G/A genotype and 0.858 (95% CI: 0.407-1.804) for the A/A genotype, as compared with those for the G/G genotype. There was no significant association between this polymorphism and latent prostate cancer susceptibility either.

CONCLUSIONS

Our results suggested that the Val158Met polymorphism of COMT was not associated with the risk of sporadic or latent prostate cancer in Japanese men.

A multigenic study on breast cancer risk associated with genetic polymorphisms of ER Alpha, COMT and CYP19 gene in BRCA1/BRCA2 negative Shanghai women with early onset breast cancer or affected relatives

High penetrance genes such as BRCA1 or BRCA2 account for only a small proportion of familial breast cancer in Chinese population. Estrogen has been proposed to participate in the proliferation and carcinogenesis of breast cancer. To investigate the association between genetic polymorphisms in genes encoding estrogen metabolizing, estrogen biosynthesizing enzyme and estrogen receptor and the breast cancer risk in BRCA1/BRCA2 negative Shanghai women, we conducted a case-control study including 114 cases with early-onset breast cancer or affected relatives and 121 healthy controls. The genotypes of estrogen receptor alpha (ERalpha), aromatase (CYP19), and catechol-O-methyltransferase (COMT) genes were analyzed by direct DNA-sequencing. Compared with H/H genotype of COMT Val158Met, COMT Val158Met L/L genotype was associated with a nonsignificantly elevated risk of breast cancer (OR: 3.72; 95% CI: 0.99-13.96, P=0.051). There was no statistically significant difference in genotype frequency of the ERalpha PvuII, ERalpha XbaI and CYP19 Arg264Cys polymorphism between controls and cases. When stratified by menopausal status, COMT Val158Met L/L (OR: 11.94; 95% CI: 1.48-96.03, P=0.02) and ERalpha PvuII P/p genotypes (OR: 2.67; 95% CI: 1.01-7.05, P=0.048) were associated with a significantly elevated risk of breast cancer in premenopausal women, and there was a association between ERalpha XbaI x/x genotype and the nonsignificantly increased risk of breast cancer in premenopausal women (OR: 6.88; 95% CI: 0.80-59.15, P=0.079). The multigenic analysis showed maybe these high risk genotypes had combined effect on breast cancer risk. Our findings suggest that polymorphism of genes involving estrogen-metabolizing pathway, estrogen- biosynthesizing pathway and estrogen receptor pathway may play an important role in the etiology of BRCA1/2 negative breast cancer with hereditary predisposing factors.

Functional maternal catechol-O-methyltransferase polymorphism and fetal growth restriction

OBJECTIVES

The pathophysiologic processes that occur at the cellular and molecular levels in intrauterine fetal growth restriction are largely unknown. Catechol-O-methyltransferase (COMT) is a phase II enzyme that inactivates catechol estrogens by transfer of a methyl group. A functional Val158Met polymorphism in the COMT gene has been known as a susceptible marker for breast cancer. The aim of this study was to examine the association between this polymorphism and fetal growth.

METHODS

A consecutive series of 412 women who experienced singleton deliveries was assessed in the birth cohort study. Genotyping of COMT and CYP17A1 polymorphisms was determined by allelic discrimination using fluorogenic probes and the 5'nuclease assay.

RESULTS

The adjusted odds ratio for the risk of low birth weight (<2.500 g) in women with homozygous low-activity (COMT-L) alleles was 2.98 (95% confidence interval, 1.10-8.11). The mean birth weight of infants whose mothers were homozygous for COMT-L was less than that of infants whose mothers had at least one high-activity (COMT-H) allele (2.610 versus 2.800 g, P=0.07). The odds ratio for the risk of intrauterine fetal growth restriction, defined as birth weight <10th percentile or <mean-1.5 SD, in women homozygous for COMT-L alleles was 2.63/2.57 (95% confidence interval, 1.14-6.05/0.96-6.88). In the recessive genotype model, the odds ratios for the risk of low birth weight and intrauterine fetal growth restriction in women homozygous for COMT-L were 3.36 (95% confidence interval, 1.30-8.65) and 2.89/2.65 (95% confidence interval, 1.31-6.34/1.06-6.65), respectively. A positive association exists between birth weight and the homozygous CYP17A1 A2 genotype (P<0.01). When both COMT and CYP17A1 genotypes were considered, the highest risk of low birth weight/intrauterine fetal growth restriction was found among women with the homozygous COMT-L and CYP17A1 A1 genotype. The odds ratio for the risk of intrauterine fetal growth restriction (<10th percentile) in those women was 5.35 (95% confidence interval, 1.15-25.0).

CONCLUSION

Our findings suggest that the allele encoding low-activity COMT may be a susceptible marker for intrauterine fetal growth restriction.

Catechol-O-methyltransferase haplotypes and breast cancer among women on Long Island, New York

The gene encoding catechol-O-methyltransferase (COMT), critical to the inactivation of reactive catechol estrogens, has several single nucleotide polymorphisms (SNPs) that influence enzyme activity. A 3-SNP haplotype (IVS1+255 C>T; Ex4-12 G>A; 3'UTR-521 A>G), which has been shown to reduce COMT expression in the human brain, has been identified. To evaluate the influence of genetic variation of COMT on breast cancer risk, these 3-SNPs were genotyped in 1052 cases and 1098 controls. We estimated the associations between breast cancer and individual SNPs, as well as, multilocus haplotypes. We also examined surrogates of hormone exposure as potential modifiers of the putatively functional Ex4-12 SNP-breast cancer association. Odds ratios (OR) and 95% confidence intervals (CI) were based on age-adjusted unconditional logistic regression models. We found no association between the individual SNPs alone and breast cancer. When examining the association between breast cancer and the 3-SNP haplotypes, we observed a 19% increase in risk associated with each copy of the TGG haplotype (OR=1.19, 95% CI 0.96-1.49), relative to the common TAA haplotype, which was statistically significant when assuming a dominant model (OR=1.32, 95% CI 1.05-1.67, p-value=0.02). In this report of COMT haplotypes and breast cancer, we found some evidence that additional genetic variability beyond the Ex4-12 G>A SNP contributes to risk of breast cancer among a small subgroup of women; however, these results need to be replicated in additional studies.

Departure from multiplicative interaction for catechol-O-methyltransferase genotype and active/passive exposure to tobacco smoke among women with breast cancer

BACKGROUND

Women with homozygous polymorphic alleles of catechol-O-methyltransferase (COMT-LL) metabolize 2-hydroxylated estradiol, a suspected anticarcinogenic metabolite of estrogen, at a four-fold lower rate than women with no polymorphic alleles (COMT-HH) or heterozygous women (COMT-HL). We hypothesized that COMT-LL women exposed actively or passively to tobacco smoke would have higher exposure to 2-hydroxylated estradiol than never-active/never passive exposed women, and should therefore have a lower risk of breast cancer than women exposed to tobacco smoke or with higher COMT activity.

METHODS

We used a case-only design to evaluate departure from multiplicative interaction between COMT genotype and smoking status. We identified 502 cases of invasive incident breast cancer and characterized COMT genotype. Information on tobacco use and other potential breast cancer risk factors were obtained by structured interviews.

RESULTS

We observed moderate departure from multiplicative interaction for COMT-HL genotype and history of ever-active smoking (adjusted odds ratio [aOR] = 1.6, 95% confidence interval [CI]: 0.7, 3.8) and more pronounced departure for women who smoked 40 or more years (aOR = 2.3, 95% CI: 0.8, 7.0). We observed considerable departure from multiplicative interaction for COMT-HL genotype and history of ever-passive smoking (aOR = 2.0, 95% CI: 0.8, 5.2) or for having lived with a smoker after age 20 (aOR = 2.8, 95% CI: 0.8, 10).

CONCLUSION

With greater control over potential misclassification errors and a large case-only population, we found evidence to support an interaction between COMT genotype and tobacco smoke exposure in breast cancer etiology.

The Val158Met polymorphism of the catechol-O-methyltransferase gene is associated with the PSA-progression-free survival in prostate cancer patients treated with estramustine phosphate

OBJECTIVE

The aim of our study is to find out the good responders for estramustine phosphate (EMP) therapy in patients with prostate cancer. We have focused on the metabolism of EMP and studied the association between a functional single-nucleotide polymorphism in the catechol-O-methyltransferase gene (Val158Met of COMT) and PSA-progression-free survival in Japanese patients with prostate cancer treated by EMP.

METHODS

Seventy-two Japanese patients with previously untreated prostate cancer who were found to be eligible for low-dose EMP therapy were enrolled in the study. Genotyping of the Val158Met polymorphism of COMT was conducted by both the polymerase chain reaction-based restriction fragment length polymorphism method and TaqMan assay.

RESULTS

Patients with the Val/Val genotype of COMT had a significantly higher PSA-progression-free rate as compared to those with the Val/Met or Met/Met genotype (p=0.027). The adjusted hazard ratio of biochemical PSA failure for the Val158Met genotype of COMT was 2.164 (95% CI, 1.111 to 5.525).

CONCLUSIONS

The Val158Met polymorphism of COMT is associated with the PSA-progression-free rate of EMP-treated patients in prostate cancer.

Cytochrome P450 1B1 and catechol-O-methyltransferase genetic polymorphisms and breast cancer risk in Chinese women: results from the shanghai breast cancer study and a meta-analysis

Cytochrome P450 1B1 (CYP1B1) and catechol-O-methyltransferase (COMT) are important estrogen-metabolizing enzymes and, thus, genetic polymorphisms of these enzymes may affect breast cancer risk. A population-based case-control study was conducted to assess the association of breast cancer risk with CYP1B1 and COMT polymorphisms. A meta-analysis was done to summarize the findings from this and previous studies. Included in this study were 1,135 incident breast cancer cases diagnosed from August 1996 through March 1998 among female residents of Shanghai and 1,235 randomly selected, age frequency-matched controls from the same general population. The common alleles of the CYP1B1 gene were Arg (79.97%) in codon 48, Ala (80.53%) in codon 119, and Leu (86.57%) in codon 432. The Val allele accounted for 72.46% of the total alleles identified in codon 108/158 of the COMT gene. No overall associations of breast cancer risk were found with any of the single nucleotide polymorphisms described above. This finding was supported by a meta-analysis of all previous published studies. No gene-gene interactions were observed between CYP1B1 and COMT genotypes. The associations of breast cancer risk with factors related to endogenous estrogen exposure, such as years of menstruation and body mass index, were not significantly modified by the CYP1B1 and COMT genotypes. We observed, however, that women who carried one copy of the variant allele in CYP1B1 codons 48 or 119 were less likely to have estrogen receptor-positive breast cancer than those who carried two copies of the corresponding wild-type alleles. The results from this study were consistent with those from most previous studies, indicating no major associations of breast cancer risk with CYP1B1 and COMT polymorphisms.

No association of estrogen receptor α and cytochrome P450c17α polymorphisms with age at menopause in a Dutch cohort

BACKGROUND

Age at menopause is under strong genetic control. So far, genetic variations of only one gene, the PvuII polymorphism of the estrogen receptor alpha (ERalpha) gene, have been shown to be associated with age at onset of menopause. This study aims to investigate whether PvuII, XbaI and B-variant polymorphisms of the ERalpha gene, and the MspAI polymorphism of the cytochrome P450c17alpha (CYP17) gene are associated with age at menopause in a Dutch cohort.

METHODS

DNA was isolated from urine samples of 385 Caucasian women with natural menopause and the genotypes of the four polymorphisms were determined. A questionnaire was used for background characteristics. The genotypes of PvuII, XbaI, MspAI were obtained by PCR restriction fragment length polymorphism analysis. The B-variant was determined with an allele-specific oligonucleotide hybridization method. Two-sided t-tests were performed to assess the association between the four polymorphisms and menopausal age. The PvuII and XbaI polymorphisms were analysed separately as well as in a combined score.

RESULTS

The results show that none of the polymorphisms independently, nor the combined genotypes for PvuII and XbaI, were associated with age at natural menopause.

CONCLUSION

No evidence was found for a relationship between common variants of the ERalpha gene and the CYP17 gene with age at natural menopause.

Polymorphic catechol-O-methyltransferase gene, duration of estrogen exposure, and breast cancer risk: A nested case–control study in Taiwan

BACKGROUND

Polymorphic catechol-O-methyltransferase (COMT) catalyzes the O-methylation of catechol estrogens, which are hypothesized to participate in estrogen-induced carcinogenesis.

METHODS

We examined 87 cases and 341 population controls in Taiwan to determine the association between the functional genetic Val158Met polymorphism in membrane-bound form of COMT gene and female breast cancer risk. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by conditional logistic regression.

RESULTS

There was no overall association between COMT genotype and individual susceptibility to breast cancer. However, COMT-L variant genotypes appear to pose increased risk of breast cancer in women with greater duration from menarche to first full-term pregnancy (>8 years) (OR, 2.67; 95% CI, 1.00-7.36).

CONCLUSIONS

This study based on limited sample sizes suggests that there may be no overall association of COMT genotype with breast cancer, but the COMT-L allele could pose enhanced risk of breast cancer in the presence of relevant environmental exposures, as most low penetrance gene are expected to act through gene-environment interactions.

Catechol-O-methyltransferase Val 108/158 Met polymorphism in premenopausal breast cancer patients

There is compelling evidence to suggest that catecholestrogens may play a role in the development of breast cancer. Particularly, inactivation of catecholestrogens may prevent the genesis and arrest the development of breast cancer. Catechol-O-methyltransferase (COMT) is polymorphic and responsible for the detoxification of catecholestrogens. In the present study, we examined what role COMT gene polymorphisms may play in the development of breast cancer in a case-control study of 130 sporadic unrelated premenopausal Turkish breast cancer patients with 233 unrelated healthy controls. The frequency of COMT-L allele was more significantly represented in the breast cancer cases (48.08%) than in the controls (38.20%). The genotype frequencies of COMT-HH, HL and LL were 25.4, 53.1 and 21.5% in the breast cancer subjects and 26.6, 62.7 and 10.7% in the controls respectively. In conclusion, the COMT-L allele and COMT-LL genotype are genetic risk factors for sporadic breast cancer in premenopausal Turkish women.

A family-based genetic association study of variants in estrogen-metabolism genes COMT and CYP1B1 and breast cancer risk

In this paper, we report findings from a family-based association study examining the association between polymorphisms in two key estrogen-metabolism genes CYP1B1 (codon 432 G --> C and codon 453 A --> G variants) and COMT (codon 158 G --> A variant) and female breast cancer. We conducted the study among 280 nuclear families containing one or more daughters with breast cancer with a total of 1124 family members (702 with available constitutional DNA and questionnaire data and 421 without). These nuclear families were selected from breast cancer families participating in the Metropolitan New York Registry (MNYR) - one of the six centers of NCI's Breast Cooperative Family Registry. We used likelihood-based statistical methods to examine the allelic associations. We found none of the variant alleles of the CYP1B1 and COMT genes to be associated with breast cancer in these families. This was consistent with results from matched case-control analyses using all available sib-ships in these families. However, we found that parental carrier status of the CYP1B1 codon 453 variant G allele and the COMT codon 158 variant A allele was associated with breast cancer risk in daughters (independent of the daughters' own genotype). In conclusion, findings from this family-based study indicate that a woman's own CYP1B1 or COMT genotypes are not associated with her breast cancer risk. Although the study found that parental carrier status of certain CYP1B1 or COMT genotypes might be associated with daughter's breast cancer risk, the biological basis as well as independent confirmation of this finding need to be investigated in future larger family-based studies before making meaningful inferences.

An evolutionary perspective on single-nucleotide polymorphism screening in molecular cancer epidemiology

Given that there are millions of single-nucleotide polymorphisms (SNPs) in the entire human genome, a major difficulty faced by scientists in planning costly population-based genotyping is to choose target SNPs that are most likely to affect phenotypic functions and ultimately contribute to disease development. Although it is widely accepted that sequences with important functionality tend to be less variable across species because of selective pressure, to what extent evolutionary conservation is mirrored by epidemiological outcome has never been demonstrated. In this study, we surveyed odds ratios detected for 46 SNPs in 39 different cancer-related genes from 166 molecular epidemiological studies. The conservation levels of amino acid that these SNPs affected were calculated as a tolerance index by comparing sequences from different species. Our results provide evidence of a significant relationship between the detected odds ratios associated with cancer risk and the conservation levels of the SNP-affected amino acids (P = 0.002; R(2) = 0.06). Tolerance indices were further calculated for 355 nonsynonymous SNPs identified in 90 human DNA repair genes, of which 103 caused amino acid changes in very conserved positions. Our findings support the concept that SNPs altering the conserved amino acids are more likely to be associated with cancer susceptibility. Using such a molecular evolutionary approach may hold great promise for prioritizing SNPs to be genotyped in future molecular epidemiological studies.

Polymorphisms of estrogen synthesizing and metabolizing genes and breast cancer risk in Japanese women

Recent success of chemoprevention with tamoxifen has opened a new era wherein prevention of breast cancer is much more emphasized than treatment of established breast cancer. Since tamoxifen has been shown to reduce the risk of estrogen receptor (ER)-positive, but not ER-negative, breast cancer in the chemoprevention trial (P-1), it seems to be important to develop risk factors for ER-positive breast cancer in order to select the candidates for chemoprevention more appropriately. Estrogens, the major risk factors for breast cancer, are speculated to affect breast cancer risk through ER, thus, genetic polymorphisms of the genes involved in the estrogens biosynthesis and metabolism are expected as risk factors for ER-positive breast cancer. Significance of polymorphisms of the genes involved in estrogens biosynthesis (CYP17, CYP19) and metabolism (CYP1A1, CYP1B1, COMT) in modulating the susceptibility to breast cancer is reviewed. The ethnic difference of the variant allele frequencies between Caucasian women and Asian women is also discussed.

Genetic polymorphisms of estrogen receptor alpha,CYP19, catechol-O-methyltransferase are associated with familial prostate carcinoma risk in a Japanese population

BACKGROUND

Estrogen is one of the crucial hormones participating in the proliferation and carcinogenesis of the prostate glands. Genetic polymorphisms in the estrogen metabolism pathway might be involved in the risk of prostate carcinoma development. The authors evaluated the association between genetic polymorphisms in estrogen-related enzymes and receptors and the risk of developing familial prostate carcinoma.

METHODS

In the current study, 101 cases with prostate carcinoma whose first-degree relatives had prostate carcinoma and 114 healthy age and residence-matched male controls were enrolled. The genotypes of estrogen receptor (ER) alpha, aromatase (CYP19), and catechol-O-methyltransferase (COMT) genes were analyzed.

RESULTS

For single polymorphisms, a significant association of the T/T genotype of the PvuII site in the ER alpha gene (odds ratio [OR], 3.44; 95% confidence interval [CI], 1.97-5.99; P = 0.0028), and the C/T and T/T genotypes of the CYP19 gene (OR, 1.77; 95% CI, 1.02-3.09; P = 0.037) with prostate carcinoma risk, was observed. The G/A genotype of the COMT gene showed a weak tendency toward increased risk (OR, 1.48; 95% CI, 0.85-2.57; P = 0.18). Stratification of cases according to clinical stage and pathologic grade showed that the C/T and T/T genotypes of the CYP19 gene were associated significantly with high-grade carcinoma (OR, 2.59; 95% CI, 1.47-4.46; P = 0.048). The number of high-risk genotypes (the T/T in ER alpha, the C/T and T/T in CYP19, and the G/A in COMT) significantly increased the risk of developing prostate carcinoma (2 genotypes: OR, 3.00; 95% CI, 1.72-5.23; P = 0.008; 3 genotypes: OR, 6.30; 95% CI, 3.61-10.99; P = 0.002).

CONCLUSIONS

Genetic polymorphisms of genes in the estrogen metabolism pathway were associated significantly with familial prostate carcinoma risk. Single nucleotide polymorphisms of low-penetrance genes are targets for understanding the genetic susceptibility of familial prostate carcinoma.

Inhibition of aromatase: insights from recent studies

Aromatase is the rate limiting enzyme that catalyzes the conversion of androgens to estrogens. Blockade of this step allows treatment of diseases that are dependent upon estrogen. Over the past two decades, highly potent and specific aromatase inhibitors have been developed which block total body aromatization by over 99%. An important recent question is whether aromatase inhibitors are superior to the antiestrogens for treatment of hormone-dependent breast cancer. The third generation aromatase inhibitors have been compared to tamoxifen for the treatment of breast cancer in the advanced, adjuvant, and neoadjuvant settings. All of these studies suggest the superiority of aromatase inhibitors over tamoxifen. The mechanism responsible for the superiority of the aromatase inhibitors relates to the estrogen agonistic effects of tamoxifen. During exposure to estrogen deprived conditions and to tamoxifen, breast cancer cells adapt and upregulate the MAP kinase and PI-3 kinase pathways. These growth factor signaling pathways potentiate the estrogen agonistic properties of tamoxifen. Data from a large adjuvant therapy trial (ATAC trial) provide evidence that the aromatase inhibitors may also be superior for breast cancer prevention. The mechanism for superiority in this setting probably relates to the genotoxic effects of estradiol metabolites. The aromatase inhibitors may be also useful for the treatment of endometriosis and for ovulation induction as evidenced by preliminary data. The recent advances in development of the aromatase inhibitors clearly demonstrate the utility of these agents for treatment of breast cancer and potentially for other indications.

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.

Transforming growth factor B1 T29C polymorphism and breast cancer risk in Japanese women

BACKGROUND

A cohort study for Caucasians aged 65 years or older demonstrated a marked breast cancer risk reduction for those with the CC genotype of transforming growth factor B1 (TGF B1) T29C polymorphism. This is a prevalent case-control study to examine the reported risk reduction for Japanese women.

PATIENTS AND METHODS

A total of 232 histologically diagnosed breast cancer patients who visited Aichi Cancer Center Hospital between June 1999 and March 2000 were enrolled. The controls were 172 female outpatients without cancer at the same hospital. DNA was extracted from peripheral blood, and TGF B1 genotype was determined by PCR-CTPP.

RESULTS

The genotype frequency was 23.7% for TT, 49.2% for TC, and 27.1% for CC among controls, and 28.9%, 46.1%, and 25.0%, respectively, among cases. Age-adjusted odds ratio (OR) relative to the TT genotype was 0.81 (95% confidence interval, 0.50-1.31) for the TC genotype and 0.77 (0.45-1.34) for the CC genotype. For premenopausal women, the CC genotype was significantly associated with reduced risk of breast cancer in comparison with the TT genotype (OR=0.45, 0.20-0.98). The association was not observed for postmenopausal women (OR=1.40, 0.64-3.08).

CONCLUSION

The present study showed risk reduction for Japanese premenopausal women with the CC genotype, but not for postmenopausal Japanese women.

Characterization of human soluble high and low activity catechol-O-methyltransferase catalyzed catechol estrogen methylation

The major detoxification pathway of the carcinogenic catechol estrogens is methylation by catechol- -methyltransferase (COMT). It has been hypothesized that the enzyme encoded by the low-activity allele (COMT(L) ) has a lower catalytic activity for catechol estrogen methylation than that encoded by the high activity allele (COMT(H) ). We expressed and purified human soluble (S)-COMT(H) and S-COMT(L) in and characterized the methylation of 2- and 4-hydroxyestradiol (2- and 4-OH-E2). There were no differences between the kinetic parameters for COMT(H) and COMT(L). The kinetic parameters for S-adenosylmethionine (SAM), the methyl donor in these reactions, also did not differ for COMT(H) and COMT(L). S-adenosylhomocysteine, the demethylated SAM metabolite, inhibited methylation of the catechol estrogens in a non-competitive manner similarly for COMT(H) and COMT(L). Each COMT substrate tested inhibited the methylation of other substrates in a mixed competitive and non-competitive fashion similarly for COMT(H) and COMT(L). Furthermore, in cytosolic fractions of COMT(HH)(MCF-10A and ZR-75-1) and COMT(LL)(MCF-7 and T47D) human breast epithelial cell lines, no differences were detected between the kinetic parameters of COMT with respect to 2- and 4-OH-E2 methylation; nor were COMT protein levels associated with the COMT genotype. These data suggest that the decreased COMT enzymatic activity that has been detected in human tissue in association with the COMT(L) allele is not reflected by differences in the affinity or capacity of COMT(H) and COMT(L) for catechol estrogen methylation. These results raise the question of what accounts for the difference in COMT activity associated with the COMT(HH) and COMT(LL) genotypes in human tissue.