Do single nucleotide polymorphisms in xenobiotic metabolizing genes determine breast cancer susceptibility and treatment outcomes?

Genotypes of CYP1A1, SULT1A1 and SULT1A2 and risk of squamous cell carcinoma of esophagus: outcome of a case-control study from Kashmir, India

Studies on associations of various polymorphism in xenobiotic metabolizing genes with different cancers including esophageal squamous cell carcinoma (ESCC) are mixed and inconclusive. To evaluate the association of CYP1A1*4, SULT1A1*2 and SULT1A2*2 genotypes with ESCC risk and their modifying effects on different risk factors of ESCC, we conducted a case-control study in Kashmir, India, an area with relative high incidence of ESCC. We recruited 404 histopathologically confirmed ESCC cases, and equal number of controls, individually matched for sex, age and district of residence to respective case. Information was obtained on various dietary, lifestyle and environmental factors in face-to-face interviews, using a structured questionnaire, from each subject. Genotypes were analyzed by polymerase chain reaction, restriction fragment length polymorphism and direct sequencing. Conditional logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs). A higher risk was observed in the subjects who harbored variant genotype of CYP1A1*4 (OR = 2.06; 95% CI: 1.28-3.32); and the risk was further enhanced in ever smokers (OR = 3.47; 95% CI: 1.62-7.42), adobe dwellers (OR = 6.71; 95% CI: 3.02-14.89), and biomass fuel users (OR = 5.11; 95% CI: 1.34-19.50). We did not find any significant differences in the polymorphic variants of SULT1A1*2 and SULT1A2*2 between cases and controls. The study indicates that, unlike SULT1A1*2 and SULT1A2*2, the polymorphism of CYP1A1*4 is associated with ESCC risk. However, replicative studies with larger sample size are needed to substantiate our findings.

Association of MTHFR (C677T) Gene Polymorphism With Breast Cancer in North India

BACKGROUND

Breast cancer is one of the most common malignancies in women and is associated with a variety of risk factors. The functional single-nucleotide polymorphism (SNP) C677T in the gene encoding 5,10-methylenetetrahydrofolate reductase (MTHFR) may lead to decreased enzyme activity and affect the chemosensitivity of tumor cells. This study was designed to investigate the association of MTHFR gene polymorphism (SNP) in the pathogenesis of breast cancer among the North Indian women population.

MATERIALS AND METHODS

Genotyping was performed by polymerase chain reaction (PCR) using genomic DNA, extracted from the peripheral blood of subjects with (275 cases) or without (275 controls) breast cancer. Restriction fragment length polymorphism was used to study C677T polymorphism in the study groups.

RESULTS

The distribution of MTHFR (C677T) genotype frequencies, ie, CC, TT, and CT, among the patients was 64.7%, 2.18%, and 33.09%, respectively. In the healthy control group, the CC, TT, and CT frequencies were 78.91%, 1.09%, and 20.1%, respectively. The frequencies of C and T alleles were 81.2% and 18.7%, respectively, in the patient subjects, while they were 88.9% and 11.09%, respectively, among the healthy control group. Frequencies of the CT genotype and the T allele were significantly different (P = 0.007 and P = 0.005, respectively) between the control and the case subjects.

CONCLUSION

This study shows an association of the CT genotype and the T allele of the MTHFR (C667T) gene with increased genetic risk for breast cancer among Indian women.

Association of the MTHFR Gene C677T Polymorphism with Breast Cancer in a Turkish Population

BACKGROUND

Breast cancer is the most common cancer among women. 1 in every 8 women in the United States have a lifetime risk of getting breast cancer. MTHFR is a key enzyme that regulates the folate metabolism which has an important role in DNA synthesis, repair, and methylation. The aim of the current study was to analyze the association between the MTHFR gene C677T (Ala222Val, rs1801133) polymorphism and breast cancer.

PATIENTS AND METHODS

199 breast cancer patients and 195 healthy controls were included in this study. The MTHFR gene C677T polymorphism was analyzed using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) methods. A meta-analysis including 707 breast cancer patients and 880 controls from Turkish populations was also carried out. Statistical analyses were performed using the χ2 test.

RESULTS

No statistically significant differences in allele and genotype frequencies were observed between patients and controls (p > 0.05). Although not statistically significant, TT homozygous variants were encountered more frequently in patients than in controls. A statistically significant association was observed between the MTHFR gene C677T polymorphism and the tumor histology of breast cancer patients (p = 0.038). The results of the meta-analysis suggested that there was a high association between breast cancer and the MTHFR gene C677T polymorphism in Turkish populations (p < 0.0001).

CONCLUSION

In our study, we did not find any association between the MTHFR gene C677T polymorphism and breast cancer. However, a meta-analysis of the 6 association studies carried out in Turkish populations with 707 patients and 880 controls showed a significant association between breast cancer and the MTHFR gene C677T polymorphism.

Association of CYP1A1 A4889G and T6235C polymorphisms with the risk of sporadic breast cancer in Brazilian women

OBJECTIVES

We examined the influence of CYP1A1 A4889G and T6235C polymorphisms on the risk of sporadic breast cancer.

METHODS

DNA from 742 sporadic breast cancer patients and 742 controls was analyzed using the polymerase chain reaction, followed by the restriction fragment length polymorphism technique.

RESULTS

More patients had the CYP1A1 4889AG+GG genotype compared to controls (29.0% versus 23.2%, p=0.004). The G allele carriers had a 1.50-fold increased risk (95% CI: 1.14-1.97) of sporadic breast cancer compared to the other study participants. The frequency of the 4889AG+GG genotype among the Caucasian patients was higher than in the non-Caucasian patients (30.4% versus 20.2%, p=0.03) and controls (30.4% versus 23.2%, p=0.002). Caucasians and G allele carriers had a 1.61-fold increased risk (95% CI: 1.20-2.15) of sporadic breast cancer compared to other subjects. The CYP1A1 4889AG+GG genotype was more common among patients with a younger median age at first full-term pregnancy than among controls (33.8% versus 23.2%, p=0.001) and subjects whose first full-term pregnancies occurred at an older age (33.8% versus 26.1%, p=0.03). Women with the CYP1A1 4889AG+GG genotype and earlier first full-term pregnancies had a 1.87-fold (95% CI: 1.32-2.67) increased risk of sporadic breast cancer compared to the other study participants. Excess CYP1A1 4889AG+GG (39.8% versus27.1%, p=0.01) and 6235TC+CC (48.4% versus 35.9%, p=0.02) genotypes were also observed in patients with grade I and II tumors compared to patients with grade III tumors and controls (39.8% versus 23.2%, p=0.04; 48.4% versus 38.6%, p=0.04). The G and C allele carriers had a 2.44-fold (95% CI: 1.48-4.02) and 1.67-fold (95% CI: 1.03-2.69) increased risk, respectively, of developing grade I and II tumors compared to other subjects.

CONCLUSIONS

The CYP1A1 A4889G and T6235C polymorphisms may alter the risk of sporadic breast cancer in Brazilian women.

Comparative study and meta-analysis of meta-analysis studies for the correlation of genomic markers with early cancer detection

A large number of common disorders, including cancer, have complex genetic traits, with multiple genetic and environmental components contributing to susceptibility. A literature search revealed that even among several meta-analyses, there were ambiguous results and conclusions. In the current study, we conducted a thorough meta-analysis gathering the published meta-analysis studies previously reported to correlate any random effect or predictive value of genome variations in certain genes for various types of cancer. The overall analysis was initially aimed to result in associations (1) among genes which when mutated lead to different types of cancer (e.g. common metabolic pathways) and (2) between groups of genes and types of cancer. We have meta-analysed 150 meta-analysis articles which included 4,474 studies, 2,452,510 cases and 3,091,626 controls (5,544,136 individuals in total) including various racial groups and other population groups (native Americans, Latinos, Aborigines, etc.). Our results were not only consistent with previously published literature but also depicted novel correlations of genes with new cancer types. Our analysis revealed a total of 17 gene-disease pairs that are affected and generated gene/disease clusters, many of which proved to be independent of the criteria used, which suggests that these clusters are biologically meaningful.

Genetic polymorphisms of CYP2E1, GST, and NAT2 enzymes are not associated with risk of breast cancer in a sample of Lebanese women

Changes in the activity of drug metabolizing enzymes (DMEs) are potentially associated with cancer risk. This relationship is attributed to their involvement in the bioactivation of multiple procarcinogens or the metabolism of multiple substrates including an array of xenobiotics and environmental carcinogens. 326 Lebanese women of whom 99 were cancer free (controls) and 227 were diagnosed with breast cancer (cases) were included. Blood for DNA was collected and medical charts were reviewed. Three genotyping methods were employed including: (1) restriction fragment length polymorphism (RFLP) for CYP2E1*5B, CYP2E1*6, NAT2*5 and NAT2*6; (2) gel electrophoresis for GSTM1 and GSTT1; and (3) real-time PCR for GSTP1 Ile/Val polymorphism. We analyzed the relationship between genetic susceptibilities in selected xenobiotic metabolizing genes and breast cancer risk. Allele frequencies were fairly similar to previously reported values from neighboring populations with relevant migration routes. There were no statistically significant differences in the distribution of variant carcinogen metabolizing genes between cases and controls even after adjusting for age at diagnosis, menopausal status, smoking, and alcohol intake. Despite its limitations, this is the first study that assesses the role of genetic polymorphisms in DMEs with breast cancer in a sample of Lebanese women. Further studies are needed to determine the genetic predisposition and gene-environment interactions of breast cancer in this population.

Revolving door action of breast cancer resistance protein (BCRP) facilitates or controls the efflux of flavone glucuronides from UGT1A9-overexpressing HeLa cells

Cellular production of flavonoid glucuronides requires the action of both UDP-glucuronosyltransferases (UGT) and efflux transporters since glucuronides are too hydrophilic to diffuse across the cellular membrane. We determined the kinetics of efflux of 13 flavonoid glucuronides using the newly developed HeLa-UGT1A9 cells and correlated them with kinetic parameters derived using expressed UGT1A9. The results indicated that, among the seven monohydroxylflavones (HFs), there was moderately good correlation (r(2) ≥ 0.65) between the fraction metabolized (fmet) derived from HeLa-UGT1A9 cells and CLint derived from the UGT1A9-mediated metabolism. However, there was weak or no correlation between these two parameters for six dihydroxylflavones (DHFs). Furthermore, there was weak or no correlation between various kinetic parameters (Km, Vmax, or CLint) for the efflux and the metabolism regardless of whether we were using seven HFs, six DHFs, or a combination thereof. Instead, the cellular excretion of many flavonoid glucuronides appears to be controlled by the efflux transporter, and the poor affinity of glucuronide to the efflux transporter resulted in major intracellular accumulation of glucuronides to a level that is above the dosing concentration of its aglycone. Hence, the efflux transporters appear to act as the "Revolving Door" to control the cellular excretion of glucuronides. In conclusion, the determination of a flavonoid's susceptibility to glucuronidation must be based on both its susceptibility to glucuronidation by the enzyme and resulting glucuronide's affinity to the relevant efflux transporters, which act as the "Revolving Door(s)" to facilitate or control its removal from the cells.

CYP1A1 regulates breast cancer proliferation and survival

Cytochrome P450-1A1 (CYP1A1) is an extrahepatic phase I metabolizing enzyme whose expression is suppressed under physiologic conditions but can be induced by substrates via the aryl hydrocarbon receptor (AhR). Recent studies have shown that the majority of breast cancer tumors constitutively express CYP1A1. These findings led us to test the hypothesis that CYP1A1 promotes breast cancer progression by evaluating the effects of CYP1A1 knockdown on the proliferation and survival of the MCF7 and MDA-MB-231 lines. Independently of estrogen receptor status, CYP1A1 knockdown decreased colony formation, decreased cell proliferation, blocked the cell cycle at G0-G1 associated with reduction of cyclin D1, and increased apoptosis associated with reduction of survivin. CYP1A1 knockdown markedly increased phosphorylation of AMP-activated protein kinase (AMPK) and decreased phosphorylation of AKT, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and 70-kDa ribosomal protein S6 kinase (P70S6K). AMPK inhibition by compound C partially abrogated the proapoptotic effects of CYP1A1 knockdown, suggesting that effects of CYP1A1 knockdown are mediated in part through AMPK signaling. Consistent with CYP1A1 knockdown, pharmacologic reduction of CYP1A1 levels by the phytopolyphenol carnosol also correlated with impaired proliferation and induced AMPK phosphorylation. These results indicate that reduction of basal CYP1A1 expression is critical for inhibition of proliferation, which is not affected by α-naphthoflavone-mediated inhibition of CYP1A1 activity nor modulated by AhR silencing. This study supports the notion that CYP1A1 promotes breast cancer proliferation and survival, at least in part, through suppression of AMPK signaling and that reduction of CYP1A1 levels is a potential strategy for breast cancer therapeutics.

Melphalan as a treatment for BRCA-related ovarian carcinoma: can you teach an old drug new tricks?

Late-stage ovarian carcinoma is almost universally fatal. BRCA mutations are associated with an improved outcome and enhanced sensitivity to platinum chemotherapy, yet recurrence and platinum resistance remain a major problem and highly effective regimens following platinum failure do not yet exist. Here we report a remarkable case of cure following platinum-resistant stage III ovarian carcinoma in a woman with a BRCA2 mutation. The patient was subsequently treated with oral melphalan therapy and has not recurred in over 25 years. Melphalan is a bifunctional alkylator that creates inter- and intra-strand DNA cross-links. In a pharmaceutical screen, melphalan was shown to be selectively toxic to BRCA2-deficient breast cancer cell lines and produced a longer relapse-free survival in mice than did cisplatin or olaparib. There is increasing evidence to consider BRCA mutation status when selecting chemotherapy regimens, and melphalan treatment for BRCA-related ovarian cancer merits further investigation. Focusing attention on long-term survivors may provide new mechanistic insights into the biology of chemo-responsiveness.

No evidence for glutathione S-transferases GSTA2, GSTM2, GSTO1, GSTO2, and GSTZ1 in breast cancer risk

Breast cancer is a complex disease and in recent years a number of breast cancer susceptibility genes have been identified, but the role of low penetrance susceptibility genes has not been completely resolved. Glutathione S-transferases (GSTs) are phase II xenobiotic metabolizing enzymes involved in the detoxification of chemical carcinogens and environmental pollutants and play an important role in cell defense mechanisms against oxidative stress. They have been in the spot light for the investigation of a potential association with breast cancer risk but so far, sparse or even no data for a potential contribution of GSTA2, GSTM2, GSTO, and GSTZ to breast cancer risk are available. We genotyped GSTA2_448_C > G (rs2180314), GSTA2_742_A > C (rs6577), GSTM2_-832_T > C (rs638820), GSTO1_-1242_G > A (rs2164624), GSTO1_419_A > C (rs4925), GSTO2_-183_A > G (rs2297235), GSTO2_342_A > G (rs156697), GSTZ1_-4378_A > G (rs1046428), and GSTZ1_94_G > A (rs3177427) by MALDI-TOF MS in the German GENICA breast cancer case-control collection of 1021 cases and 1015 controls and performed breast cancer risk association in general and with respect to the stratifications: menopausal status, family history of breast or ovarian cancer, use of oral contraceptives, use of hormone therapy, body mass index, and smoking as well as histopathological tumor characteristics including hormone receptor status, grade, histology, and node status. We did not observe any breast cancer risk associations and conclude that it is unlikely that glutathione S-transferases GSTA2, GSTM2, GSTO1, GSTO2, and GSTZ1 participate in breast cancer susceptibility.