Polymorphisms of phase II xenobiotic-metabolizing and DNA repair genes and in vitro N-ethyl-N-nitrosourea-induced O6-ethylguanine levels in human lymphocytes.

This study tested the hypothesis that genetic variants of phase II detoxification enzymes and DNA repair proteins affect individual response to DNA damage from alkylating agents. In 171 healthy individuals, an immunoslot blot assay was used to measure O6-ethylguanosine (O6-EtGua) adduct levels in peripheral blood lymphocytes treated with N-ethyl-N-nitrosourea (ENU) in vitro. The genotypes of GSTM1, GSTT1, GSTP1 I(105)V and A(114)V, MGMT L(84)F and I(143)V, XPD D(312)N and K(751)Q, and XRCC3 T(241)M were determined. Demographic and exposure information was collected by in-person interview. Student's t-test, analysis of (co)variance, and multiple linear regression models were used in statistical analyses. The mean and median (range) O6-EtGua levels were 94.6 and 84.8 (3.2-508.1)fmol/g DNA, respectively. The adduct level was significantly lower in people who smoked >or=25 years than that in never-smokers (square-root transformed mean values 8.20 versus 9.37, P=0.03). Multiple linear regression models revealed that GSTT1 (beta=-2.36, P=0.009) polymorphism was a significant predictor of the level of adducts in 82 never-smokers, whereas the number of years smoked (beta=-0.08, P=0.005) and XRCC3 T(241)M (beta=2.22, P=0.007) in 89 ever-smokers. The association between GSTP1 I(105)V, MGMT I(143)V, and XPD D(312)N with the level of adducts was not conclusive. Each polymorphism could explain 2-10% of the variation of the adduct level. These observations suggest that GSTT1 null and XRCC3 T(241)M polymorphism may have some functional significance in modulating the level of ENU-induced DNA damage and these effects are smoking-dependent. Results from this exploratory study need to be confirmed in other experimental systems.

Overexpression of oncogenic STK15/BTAK/Aurora A kinase in human pancreatic cancer.

PURPOSE: Multiple chromosome abnormalities, including gain of chromosome20q, have been detected frequently in human pancreatic cancers. Overexpression of the STK15/BTAK/Aurora A gene located on chromosome 20q13, which encodes a centrosome-associated serine/threonine kinase, has been shown to induce chromosomal instability, leading to aneuploidy and cell transformation in multiple in vitro experimental systems. The purpose of this study was to investigate the expression and copy number alteration of STK15 in pancreatic cancer. EXPERIMENTAL DESIGN: STK15 expression at both the mRNA and protein levels together with the copy number of STK15 gene was measured in nine pancreatic carcinoma cell lines: (a) HPAF-II; (b) Aspc-1; (c) Panc-1; (d) Panc-3; (e) Panc-28; (f) Panc-48; (g) HS766T; (h) MIAPaCa-2; and (i) BxPc3. STK15 protein expression was also examined in normal pancreatic tissues and tumors by Western blotting and immunohistochemistry. RESULTS: STK15 was overexpressed in all of the nine cell lines examined, but gene amplification was infrequent. Western Blot analysis of primary tumor tissues revealed 2-10 times overexpression of STK15 protein compared with normal adjacent tissues from pancreatic cancer patients. Concurrent overexpression of cdc20, an STK15-associated protein, and reduced expression of cdc25, a mitosis-activating protein phosphatase, were detected in the same tumor samples. Elevated STK15 protein expression was detected in 22 of 38 tumor sections (58%) from pancreatic cancer patients. The extent of STK15 expression was not significantly correlated with the size, degree of differentiation, and metastasis status of the tumors. CONCLUSIONS: These results show that STK15 is overexpressed in pancreatic tumors and carcinoma cell lines and suggest that overexpression of STK15 may play a role in pancreatic carcinogenesis.

DNA adducts, genetic polymorphisms, and K-ras mutation in human pancreatic cancer.

To test the hypothesis that carcinogen exposure and oxidative stress are involved in pancreatic carcinogenesis in susceptible individuals, aromatic DNA adducts and 8-hydroxyguanosine (8-OH-dG) were measured by (32)P-postlabeling and HPLC-EC, respectively, in 31 pancreatic tumors and 13 normal tissues adjacent to the tumor from patients with pancreatic cancer. Normal pancreatic tissues from 24 organ donors, from six patients with non-pancreatic cancers, and from five patients with chronic pancreatitis served as controls. It was found that tissue samples from patients with pancreatic cancer had significantly higher levels of both aromatic DNA adducts and 8-OH-dG compared with control samples. The mean (+/-S.D.) levels of aromatic DNA adducts were 101.8+/-74.6, 26.9+/-26.6, and 11.2+/-6.6 per 10(9) nucleotides in adjacent tissues, tumors, and controls, respectively. The mean (+/-S.D.) levels of 8-OH-dG were 11.9+/-9.6, 10.8+/-10.6, and 6.7+/-4.6 per 10(5) nucleotides in adjacent tissues, tumors, and controls, respectively. Polymorphisms of the CYP1A1, CYP2E1, NAT1, NAT2, GSTM1, MnSOD, and hOGG1 genes were determined in these patients. The level of aromatic DNA adducts was significantly associated with polymorphism of the CYP1A1 gene. No significant correlation was found between the level of 8-OH-dG and the MnSOD, GSTM1, and hOGG1 polymorphisms. However, one novel polymorphism/mutation of the hOGG1 gene was found in a pancreatic tumor. Mutation at codon 12 of the K-ras gene was found in 25 (81%) of 31 pancreatic tumors, including three G-to-A transitions and 22 G-to-T transversions. Patients with the G-to-T mutation had a significantly higher level of aromatic DNA adducts than those with G-to-A or wild-type codon (P=0.02). On the other hand, the K-ras mutation profile was not related to the level of 8-OH-dG. Given the limitation of sample size, these preliminary data lend further support the hypothesis that carcinogen exposure and oxidative stress are involved in pancreatic carcinogenesis.

Aromatic DNA adducts and polymorphisms of CYP1A1, NAT2, and GSTM1 in breast cancer.

Previous studies by us and others have shown a significantly higher level of aromatic DNA adducts in normal adjacent breast tissue samples obtained from breast cancer patients than in those obtained from non-cancerous controls. The increased amount of DNA damage could be related to excess environmental carcinogen exposure and/or genetic susceptibility to such exposure. In the current study, we investigated the relationship between the levels of aromatic DNA adducts in breast tissues and polymorphisms of the drug-metabolizing genes cytochrome P4501A1 (CYP1A1), N-acetyltransferase-2 (NAT2), and glutathione S-transferase M1 (GSTM1), in 166 women having breast cancer. DNA adducts were measured using (32)P-postlabeling and information on smoking status was obtained from medical records. When pooled data of smokers and non-smokers were analyzed by multiple regression analyses, no significant correlation was found between the level of total DNA adducts and age, race, or polymorphisms of CYP1A1, GSTM1, and NAT2. The only significant predictor of the level of DNA adducts in breast tissues was smoking (P = 0.008). When data were analyzed separately in smokers and non-smokers, however, a significant gene-environment interaction was observed. Smokers with CYP1A1*1/*2 or *2/*2 genotypes had a significantly higher level of DNA adducts than those with the CYP1A1*1/*1 genotype. This effect was not seen among non-smokers. There was also a gene-gene interaction, as smokers with combined CYP1A1*1/*2 or CYP1A1*2/*2 genotypes and GSTM1 null had a much higher level of adducts than those with either CYP1A1 or GSTM1 polymorphism. Genetic polymorphisms of CYP1A1 and NAT2 were also significantly correlated with the frequency of certain types of DNA adducts. For example, a bulky benzo[a]pyrene (B[a]P)-like adduct was detected in 26% of the samples, the presence of which was not related to age, race, smoking status, or GSTM1 and NAT2 genotype. However, a significantly higher frequency of the B[a[P-like adduct was found in individuals having CYP1A1*1/*2 or *2/*2 genotypes than in those having the *1/*1 genotype (P = 0.04). In addition, individuals having slow NAT2 alleles had a significantly higher frequency of the typical smoking-related DNA adduct pattern, i.e. a diagonal radioactive zone (DRZ), than others did (P = 0.008). These findings suggest that polymorphisms of CYP1A1, GSTM1, and NAT2 significantly affect either the frequency or the level of DNA adducts in normal breast tissues of women having breast cancer, especially in smokers. Further large-scale studies are required to determine the exact role of these polymorphisms and types of DNA damage in breast cancer susceptibility.