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Tumor levels of the cell cycle regulators cyclin E and p27 correlate strongly with survival in breast cancer patients and are specifically regulated by the ubiquitin ligases hCDC4 and SKP2. This study was to explore whether genetic susceptibility to breast cancer is associated with polymorphism of these genes and whether gene–gene and gene–risk factor [i.e. full-term pregnancy (FTP)] interactions are important in determining cancer risk. A two-stage case–control study based on single-nucleotide polymorphisms was performed. The first study (560 cases and 1122 controls) was to define the contribution of cell cycle and ubiquitin ligase genes to cancer susceptibility. The second study (926 cases and 923 controls) was to confirm the association identified in the first stage and to map the variant alleles. Increased breast cancer risk was associated with both polymorphism of hCDC4 and a joint effect of cyclin E and hCDC4. These associations were more significant in nulliparous women, and cancer risk associated with a lower number of FTPs was only seen in women with a higher number of high-risk genotypes, providing support for an effect of gene–risk factor interaction in determining susceptibility. Sequence variants of intron 2 in hCDC4 were found to be the most significant polymorphism and high-stage estrogen receptor (ER)-negative patients carrying the homozygous variant genotype manifested significantly poorer survival. This study concludes that polymorphism of hCDC4 is a risk factor for breast cancer development by interacting with either cyclin E or FTP and may also prove useful in predicting progression of patients with high-stage and ER-negative breast cancers. [ABSTRACT FROM PUBLISHER]

A tumorigenic role of the non-homologous end-joining (NHEJ) pathway for the repair of DNA double-strand breaks (DSBs) has been suggested by our finding of a significant association between increased breast cancer risk and a cooperative effect of single-nucleotide polymorphisms in NHEJ genes. To confirm this finding, this case–control study detected both in vivo and in vitro DNA end-joining (EJ) capacities in Epstein-Barr virus-immortalized peripheral blood mononuclear cells (PBMCs) of 112 breast cancer patients and 108 healthy controls to identify individual differences in EJ capacity to repair DSB as a risk factor predisposing women to breast cancer. PBMCs from breast cancer patients consistently showed lower values of in vivo and in vitro EJ capacities than those from healthy women (P < 0.05). Logistic regression, simultaneously considering the effect of known risk factors of breast cancer, shows that the in vitro EJ capacity above the median of control subjects was associated with nearly 3-fold increased risks for breast cancer (adjusted odds ratio, 2.98; 95% confidence interval, 1.64–5.43). Furthermore, a dose–response relationship was evident between risk for breast cancer and EJ capacity, which was analyzed as a continuous variable (every unit decrease of EJ capacity being associated with an 1.09-fold increase of breast cancer risk) and was divided into tertiles based on the EJ capacity values of the controls (P for trend < 0.01). The findings support the conclusion that NHEJ may play a role in susceptibility to breast cancer. [ABSTRACT FROM PUBLISHER]

The enantiomeric compositions of benzo[c]phenanthrene -3,4-dihydrodiol, a metabolic precursor of the ultimate carcinogenic bay-region 3,4-dihydrodiol-1,2-epoxides, formed in the metabolism of BcPh by liver microsomes from untreated, phenobarbital (PB)-treated, 3-methylcholanthrene (MC)-treated and polychlorinated biphenyls (PCB; Aroclor 1254)-treated rats of the Sprague-Dawley and Long-Evans strain were each determined by chiral stationary-phase h.p.l.c. and circular dichroism spectral analyses. The percentage of 3R,4R enantiomer in the -3,4-dihydrodiol metabolite of BcPh varies, depending on the concentration of liver microsomal enzymes used and the time of incubation: 29–30% (control), 46–54% (PB), 94–100% (MC) and 90–99% (PCB). [ABSTRACT FROM PUBLISHER]

The direct enantiomeric resolution of non-K region trans-1, 2-dihydrodiol, l, 2, 3, 4-tetrahydro-trans-1,2-diol, -3, 4-dihydrodiol and l, 2, 3, 4-tetrahydro--3, 4-diol, K region - and cis-5, 6-dihydrodiols and their monomethyl ethers of chrysene was studied by chiral stationary phase high-performance liquid chromatography (CSP-h.p.l.c). The chiral stationary phase columns were packed with γ-aminopropyl-silanized silica to which either ()--(3,5-dinitrobenzoyl)-phenyiglycine or (S)-AK3, 5-dinitrobenzoyDleucine was bonded either ionically or covalently. Enantiomers of all dihydrodiol derivatives were resolved by one or more, but not all, of the chiral stationary phases utilized. Enantiomeric resolutions were substantially improved when the non-K region dihydrodiols were converted to tetrahydrodiols. The absolute configurations of the K region - and -dihydrodiols were established by the exciton chirality circular dichroism method. The (): () enantiomer ratios, determined by CSP-h.p.l.c, of the 1, 2-, 3, 4- and --dihydrodiols formed in the metabolism of chrysene by liver microsomes from untreated male rats of the Sprague-Dawley strain were found to be 51: 49, 99: 1 and 86: 14, respectively; from phenobarbital-treated rats, 41: 59, 99: 1 and 87: 13, respectively; from 3-methylcholanthrene-treated rats, 96: 4, 99: 1 and 92: 8, respectively. The absolute configurations of chrysene 5, 6-epoxide enantiomers, resolved by CSP-h.p.l.c, were elucidated by the determination of the structures and absolute configurations of their methoxylation products. Both enantiomers of chrysene 5, 6-epoxide were hydrated by micro-somal epoxide hydrolase to chrysene -5, 6-dihydrodiol enriched (67–92%) in the 5R, 6R enantiomer. Chrysene 5R, 6S-epoxide was hydrated to trans-5, 6-dihydrodiol at a rate approximately 6-fold faster than chrysene 55, 6R-epoxide. [ABSTRACT FROM PUBLISHER]

Rat liver microsomes metabolized the weak carcinogen 7-bromobenz[a] (7-Br-BA) to form predominantly -3,4-, 5,6-, 8,9-, and 10,11-dihydrodiols. The dihydrodiol metabolites were isolated by reversed-phase h.p.l.c. for structural and conformational analyses. N.m.r. spectral analysis indicated that the 3,4- and 10,11-dihydrodiols preferentially adopted quasidiequatorial conformations whereas the 5,6- and 8,9-dihydrodiols (which have a bromo substituent) preferred quasidiaxial conformations. Comparison of c.d. spectra with those of quasidiequatorial benz[a]anthracene (BA) 3R,4R-dihydrodiol and 10R,11R-dihydrodiol indicated that the major enantiomeric 7-Br-BA- 3,4- and 10,11-dihydrodiol metabolites have R,R absolute stereochemistry. The absolute conformation of 7-Br-BA-5,6-and -8,9-dihydrodiol metabolites could not be deduced by comparing their c.d. spectra with those of BA 5R,6R- and 8R,9R-dihydrodiols. Catalytic hydrogenolysis converted the enzymalically formed 7-Br-BA -5,6-dihydrodiol to BA -5,6-dihydrodiol which had a c.d. spectrum identical to that of BA 5R,6R-dihydrodiol. Catalytic hydrogenolysis and hydrogenation converted the enzymatically formed 7-Br-BA -8,9-dihydrodiol to a BA 8,9,10,11-tetrahydro--8,9- diol which had a retention time identical to that of BA 8,9,10,11-tetrahydro-8R,9R-diol on a chiral h.p.l.c. column. These results indicate that the major enantiomers of -dihydrodiol metabolites formed in rat liver microsomal metabolism of 7-Br-BA all have R,R absolute stereochemistries. [ABSTRACT FROM PUBLISHER]

The optically pure (−) and (+)-1,2-dihydroxy-1,2-dihydrobenz[a]anthracenes (BA -1,2-dihydrodiol) were obtained through the resolution of their diastereomeric di(−)menthoxyacetates by normal-phase h.p.l.c, followed with base-catalyzed hydrolysis. The (−)-BA -1,2-dihydrobiol has been determined to have 1R,2R absolute stereochemistry by exciton chirality method. Each of the enantiomeric and racemic BA -1,2-dihydrodiol was incubated with liver microsomes from untreated, phenobarbital (PB)-, and 3-methylcholanthrene (MC)-treated male Sprague-Dawley rats. The racemic and enantiomeric BA -1,2-dihydrodiols were each metabolized to two 1,2,3,4-tetrahydroxy-1,2,3,4-tetrahydrobenz[a]anthracenes (BA 1,2,3,4-tetrol) derived from the hydrolysis of BA -1,2-dihydrodiol -3,4-epoxide (the 3,4-epoxy oxygen is trans to the 1-hydroxyl group) and -3,4-epoxide (the 3,4-epoxy oxygen is to the 1-hydroxyl group), respectively. All the BA 1,2,3,4-tetrols were identified by comparing the reversed-phase h.p.l.c. retention times of tetrols and their vicinal acetonides with the hydrolysis products of the chemically synthesized BA -1,2-dihydrodiol -3,4-epoxide, BA -1,2-dihydrodiol -3,4-epoxide, BA -3,4-dihydrobiol -1,2-epoxide, and BA -3,4-dihydrodiol -1,2-epoxide, respectively, by their modes of forming vicinal acetonides, and by ultraviolet absorption and mass spectral analyses. From the metabolism of (−)-BA -1,2-dihydrodiol, a BA -l,2-dihydrodiol -3,4-epoxide was the major product formed by liver microsomes from MC-treated rats whereas a BA -l,2-dihydrodiol -3,4-epoxide was the major product formed by liver microsomes from either untreated or PB-treated rats. In contrast, BA -l,2-dihydrodiol -3,4-epoxide was the major product formed from the metabolism of (+)-BA -1,2-dihydrodiol by all three rat liver microsomal preparations. Liver microsomes from PB-treated rats were found to catalyze the metabolism of both the racemic and the enantiomeric BA -l,2-dihydrodiols at a rate higher than those by liver microsomes from untreated and MC-treated rats. All BA 1,2,3,4-tetrol metabolites were found to be optically active by circular dichroism spectral analysis. The results indicate that the ‘bay-region’ BA -l,2-dihydrodiol is metabolized by rat liver microsomes predominantly at the vicinal 3,4-double bond and that each enantiomeric BA -1,2-dihydrodiol is metabolized to a pair of diastereomeric -l,2-dihydrodiol 3,4-epoxides with varying degrees of stereoselectivity depending on the constitutive forms of cytochrome P-450 in the rat liver microsomal preparations. [ABSTRACT FROM PUBLISHER]

The rat liver microsomal metabolism of 3-deutero-6-nitro-benzo[a]pyrene ([3-H]6-NO-BaP) was studied. The metabolites were separated by h.p.l.c. The 500 MHz H n.m.r. spectral analysis of the metabolites indicated that the 3-hydroxy-6-NO-BaP and 6-NO-BaP-3,9-hydroquinone each retained 33% of the deuterium label at the C-2 position. It is proposed that the migration of deuterium occurs via an NIH shift mechanism. These results indicate that a 2,3-epoxide is a common intermediate. [ABSTRACT FROM PUBLISHER]

The effects of butylated hydroxyanisole (BHA) on the metabolism of benzo[a]pyrene (BP) were investigated with mouse hepatic microsomes. Microsomes from BHA-fed mice showed a higher activity in catalyzing the formation of most metabolites from BP but a much lower activity in the formation of 9-hydroxyBP than control microsomes. Dietary BHA treatment enhanced the total metabolism of BP but decreased the microsomal metabolism of BP-7,8-diol, especially the formation of BP--7,8-diol--9,10-oxide. The altered metabolism of BP is believed to be due to the induction of new cytochrome P-450 species by dietary BHA. Consistent with this interpretation is the observation that the treatment also decreased the and increased the of ethoxycou-marin O-dealkylase. Short-term treatment (BHA administered p.o.) and added BHA were shown to inhibit BP metabolism. Thus, BHA can affect BP metabolism by exerting its inhibitory effect directly and by altering the composition of microsomal monooxygenase enzymes after a few days of exposure. [ABSTRACT FROM PUBLISHER]

The newborn mouse lung adenoma model has been shown to be a sensitive test for studying the tumor-igenicity of bay region diol epoxides and their precursor dihydrodiols. When a total dose of 28 nmol of 7, 12-dimethylbenz[a]anthracene (DMBA) or its derivatives was injected i.p. into the preweaning mice, it was found that the 3, 4-dihydrodiols of both DMBA and 7-hy-droxymethyl-12-methylbenz[a]anthracene caused 13.3 and 4.1 times more lung adenomas than DMBA, respectively. The mice treated with the 5, 6- and 8, 9-dihydro-diols of DMBA, 7-hydroxymethyl-12-methylbenz[a]-anthracene and its 5, 6- 8,9- and 10,11-dihydrodiols, 7-methyl-12-hydroxymethylbenz[a]an-thracene and 7,12-dihydroxymethylbenz[a]anthracene developed a level of lung adenomas/mouse less than Mold higher than that found in the DMSO-treated control group. Liver tumors also developed in some of the mice. The percentage of mice with liver tumors also indicated that the 3, 4-dihydrodiols of both DMBA and 7-hydroxymethyl-12-methylbenz[a]anthracene were more tumorigenic than DMBA itself. These data indicate that the 3, 4-dihydrodiols of both DMBA and its 7-hydroxymethyl derivative may be proximate carcinogenic metabolites of DMBA in the newborn mouse. [ABSTRACT FROM PUBLISHER]

The bay-region hydroxyl groups of benz[a]anth-racene (±)-l, 2-dihydrodiol are known to be exclusively in quasi-axial conformations. This dihydro-diol was stereoselectively metabolized in rat liver microsomes to form two optically active 1, 2, 3, 4-tetrahydrotetrols as the predominant products. Thus, the bay-region axial hydroxyl groups of benz[a]-anthracene -l, 2-dihydrodiol do not direct metabolism away from the vicinal 3, 4-double bond. [ABSTRACT FROM PUBLISHER]

The 12 possible monomethylbenz[a]anthracenes (MBAs) were examined for their tumor-initiating activity in the classical two-stage initiation-promotion experiment. Based on the average number of tumors/mouse, 7-MBA was the most tumorigenic compound of the series causing 4.9 papillomas/mouse at an initiating dose of 400 nmol/mouse. At this same dose level 8-MBA and 12-MBA were equally potent causing 1.0 papillomas/mouse. 6- and 9-MBAs caused ∼0.6 papillomas/mouse at this dose level. These data are in general agreement with previous experiments using other model systems. Of interest is the low tumorigenicity of the 1-, 2-, 3- and 4-MBAs which has been cited in support of the bay region theory of polycyclic aromatic hydrocarbon carcinogenesis. The tumor-initiating ability of anthracene and 9,10-dimethylanthracene was also examined. Neither of these compounds possessed tumor-initiating activity. [ABSTRACT FROM PUBLISHER]

The tumor-initiating activity of the 3, 4-dihydrodiols (diols) as well as other metabolites of 8-methylbenz[a]-anthracene (8-MBA) and 8-hydroxymethylbenz[a)-anthracene (8-OHMBA) were examined in the classical 2-stage initiation-promotion model on mouse skin. The 3,4-diol of 8-MBA caused 2.2 times as many papillomas/mouse as did 8-MBA. The 3,4-diol of 8-OHMBA was not more tumorigenic than either 8-MBA or 8-OHMBA. None of the other diols tested, including the 5,6- and 8,9-diol of 8-MBA and the 5,6 and 10,11-diol of 8-OHMBA were remarkably tumor-igenic. These data indicate that the 3,4-diol of 8-MBA is a good candidate as a proximate carcinogen of 8-MBA and further suggest that the bay region 3,4-diol-1,2-epoxide is a likely ultimate carcinogen of this compound on mouse skin. [ABSTRACT FROM PUBLISHER]

Cyclopenta-polycyclic aromatic hydrocarbons (cyclopenta-PAHs) are a group of compounds that have been detected as environmental pollutants. Perturbation molecular orbital (PMO) calculations on their presumed ultimate carcinogenic metabolites, the cyclopenta-PAH expoxides, predict that they may have a greater biological hazard than the classic PAHs. [ABSTRACT FROM PUBLISHER]

The role of the familial breast cancer susceptibility genes, BRCA1 and BRCA2, in the homologous recombination (HR) pathway for DNA double-strand break (DSB) repair suggests that the mechanisms involved in HR and DNA DSB repair are of etiological importance during breast tumorigenesis. Bloom (BLM) helicase directly interacts with RAD51 recombinase, which is involved in regulating HR, and it is thus of particular interest to examine whether this interaction is associated with breast cancer susceptibility. This single-nucleotide polymorphism (SNP)-based case–control study was performed to examine this hypothesis using specimens from 933 patients with breast cancer and 1539 healthy controls. The results showed that one SNP (rs2380165) in BLM and two (rs2412546 and rs4417527) in RAD51 were associated with breast cancer risk. Furthermore, haplotype and diplotype analyses based on combinations of five SNPs in RAD51 revealed a strong association between RAD51 polymorphisms and breast cancer risk (P < 0.05). Support for the interaction between BLM and RAD51 in determining breast cancer risk came from the finding that the association between cancer risk and at-risk genotypes/haplotype pairs of RAD51 was stronger and more significant in women harboring homozygous variant alleles of BLM (P for interaction < 0.05). Interestingly, not only the intronic SNP located within the region encoding the helicase domain of BLM but also those within the RAD51-interaction domain-encoding region showed an interaction with RAD51 polymorphisms in determining breast cancer susceptibility. Our results suggest a contribution of BLM and RAD51 to breast cancer development and provide support for the tumorigenic significance of the functional interaction between these two HR proteins. [ABSTRACT FROM AUTHOR]