A multiplex real-time PCR method for detection of GSTM1 and GSTT1 copy numbers

Droplet Digital PCR Analysis of GSTM1 Deletion Polymorphism in Psoriatic Subjects Treated with Goeckerman Therapy

Goeckerman therapy (GT) represents an effective treatment of psoriasis including a combination of pharmaceutical grade crude coal tar (CCT) and ultraviolet irradiation (UV-R). Coal tar contains a mixture of polycyclic aromatic hydrocarbons. The best known carcinogenic polyaromate - benzo[a]pyrene is metabolized into a highly reactive benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE). Glutathione S-transferase M1 (GSTM1) catalyses the conjugation of drugs, toxins and products of oxidative stress with glutathione. The aim of the study is to found possible associations between GSTM1 genotypes and the level of BPDE-DNA adducts in 46 psoriatic patients treated with GT. For genotyping, droplet digital PCR was applied. The GSTM1 copy number was normalized to β-globin reference gene. In five GSTM1*1/*1 subjects, the GSTM1 to β-globin ratio moved from 0.99 to 1.03 with a median of 1.01. GSTM1*0/*1 heterozygotes (n = 20) contained only one GSTM1 function allele which conditioned the ratio 0.47-0.53 (median 0.50). GSTM1*0/*0 individuals (n = 21) showed no amplification of the null variants because of the large deletion in GSTM1. BPDE-DNA concentrations ranged from 1.8 to 66.3 ng/µg with a median of 12.3 ng/µg. GSTM1*0/*0 and GSTM1*0/*1 genotypes showed non-significantly higher concentrations of BPDE-DNA adducts than the GSTM1*1/*1 one (12.3 and 12.4 vs 7.8 ng/µg). The non-significant relationship between BPDE-DNA adducts and GSTM1 genotypes in psoriatic patients could be associated with relatively low doses of CCT and short-term UV-R exposures used in GT.

A phase II study of sulforaphane-rich broccoli sprout extracts in men with recurrent prostate cancer

INTRODUCTION

Diets high in cruciferous vegetables are associated with lower risk of incidence of prostate cancer, including aggressive forms of this disease. Human intervention studies with cruciferous vegetable-rich diets also demonstrate modulation of gene expression in important pathways in prostate cells.

PURPOSE

Sulforaphane is a constituent of these foods postulated to harbor the anti-neoplastic activity based on multiple tumor models. Our own work demonstrates that sulforaphane inhibits AR signaling in prostate cancer cells. Here, we report results from the first clinical trial of sulforaphane-rich extracts in men with prostate cancer.

METHODS

We treated 20 patients who had recurrent prostate cancer with 200 μmoles/day of sulforaphane-rich extracts for a maximum period of 20 weeks and determined the proportion of patients with ≥50% PSA declines, the primary endpoint. Only one subject experienced a ≥50% PSA decline. Thus, the primary endpoint was not achieved. Seven patients experienced smaller PSA declines (<50%). There was also a significant lengthening of the on-treatment PSA doubling time (PSADT) compared with the pre-treatment PSADT [6.1 months pre-treatment vs. 9.6 months on-treatment (p = 0.044)]. Finally, treatment with sulforaphane-rich extracts was safe with no Grade 3 adverse events.

CONCLUSIONS

Treatment with 200 μmoles/day of sulforaphane-rich extracts did not lead to ≥50% PSA declines in the majority of patients. However, because of the safety of treatment and the effects on PSADT modulation, further studies, including those with higher doses, may be warranted to clarify the role of sulforaphane as a prevention agent or treatment agent.

Copy number variation of GSTT1 and GSTM1 and the risk of prostate cancer in a Caribbean population of African descent

Background

Deletions of the glutathione S-transferase genes M1 and T1 (GSTM1 and GSTT1) have been studied as potential risk factors for prostate cancer. Conflicting results have been obtained. Moreover, most such studies could not discriminate heterozygous from homozygous carriers of the non-deleted alleles.

Objective

We investigated whether copy number variation (CNV) of the GSTM1 and/or GSTT1 genes contribute to the risk of prostate cancer in the Caribbean population of African descent of Guadeloupe.

Methods

In a population-based case-control study, we compared 629 prostate cancer patients and 622 control subjects. Logistic regression was used to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI). Exact copy numbers of GSTM1 and GSTT1 were determined by real-time PCR.

Results

A higher copy number of GSTM1 was marginally associated with prostate cancer risk. Men with 2 and 3 or more GSTT1 genes were at higher risk of prostate cancer (OR: 1.55, 95% CI: 1.11–2.16 and OR: 4.89, 95% CI: 1.71–13.99, respectively; P_trend<0.001). Men with 3, 4 and 5 or more copies of both GSTM1 and GSTT1 genes were at higher risk of prostate cancer (OR: 2.18, 95% CI: 1.21–3.91, OR: 3.24, 95% CI: 1.63–6.46, and OR: 5.77, 95% CI: 1.40–23.84, respectively; P_trend<0.001).

Conclusions

Copy number of GSTT1 and combined GSTM1/GSTT1 appear to be associated with prostate cancer risk in our population study with gene dose relationship. Our results support the hypothesis that variations in copy number of GSTT1 modulate the risk of prostate cancer.

Genetic variants in the glutathione S-transferase genes and survival in colorectal cancer patients after chemotherapy and differences according to treatment with oxaliplatin

INTRODUCTION

The glutathione S-transferase (GST) enzymes are involved in the detoxification of a range of carcinogenic compounds as well as chemotherapeutic agents. Therefore, genetic variants in the GST genes could influence survival in patients with colorectal cancer (CRC). Results from previous studies have been inconsistent and therefore we investigated the association between the GSTP1 ile105val polymorphism and the copy number variants of the GSTM1 and GSTT1 genes and survival in CRC patients treated with adjuvant/palliative chemotherapy.

PATIENTS AND METHODS

We included 755 CRC patients with stage II-IV disease from two population-based studies carried out in Germany. Genotyping of the GSTP1 polymorphism was carried out using fluorescence-based melting curve analysis and copy number variants were determined using a multiplex PCR. Survival analysis was carried out using the Cox regression model, adjusting for age, sex, UICC stage, cancer site, and radiation therapy.

RESULTS

Compared with noncarriers, CRC patients who were homozygote carriers of GSTM1 had significantly poorer survival after treatment with oxaliplatin [hazard ratio (HR) 2.25, 95% confidence interval (CI) 0.93-5.44] than those not treated with oxaliplatin (HR 0.64, 95% CI 0.30-1.34; P for heterogeneity=0.031). The association was significant in metastatic CRC patients treated with oxaliplatin (HR 3.59, 95% CI 1.29-10.03). Neither the GSTP1 105val allele nor the GSTT1 deletion was significantly associated with CRC survival.

CONCLUSION

Our data suggest that GSTM1 may be a predictive marker for oxaliplatin therapy; however, independent large studies are warranted to confirm these results.

Glutathione S-transferase homozygous deletions and relapse in childhood acute lymphoblastic leukemia: a novel study design in a large Italian AIEOP cohort

Aim: In the AIEOP-BFM 2000 trial, 15% of pediatric patients treated according to risk-adapted polychemotherapeutic regimens relapsed. The present study aimed to investigate the influence of GST-M1 and GST-T1 deletions on clinical outcome of children with acute lymphoblastic leukemia treated according to the AIEOP-BFM ALL 2000 study protocol. Materials & methods: A novel-design, two-phase study was applied to select a subsample of 614 children to be genotyped for the deletions of GST genes. Cumulative incidence of relapse was then estimated by weighted Kaplan–Meier analysis, and the Cox model was applied to evaluate the effect of GST-M1 and GST-T1 isoenzyme deletions on relapse. Results: No overall effect was found, but the GST-M1 deletion was associated with better clinical outcome within prednisone poor-responder patients (hazard ratio [HR]: 0.45; 95% CI: 0.23–0.91; p = 0.026), whereas the GST-T1 deletion was associated with worse outcome in the standard-risk group (HR: 4.62; 95% CI: 1.04–20.6; p = 0.045) and within prednisone good responders (HR: 1.62; 95% CI: 1.02–2.58; p = 0.041). Conclusion: Our results show that GST-M1 and GST-T1 homozygous deletions have opposite correlation with relapse, the former being protective and the latter unfavourable in specific subsets of acute lymphoblastic leukemia patients.

Original submitted 1 August 2012; Revision submitted 27 September 2012

Association of manganese superoxide dismutase and glutathione S-transferases genotypes with myocardial infarction in patients with type 2 diabetes mellitus

AIM

In the present study we investigated the association between genetic polymorphisms with functional effects on redox regulation: Val16Ala of manganese superoxide dismutase (MnSOD), polymorphic deletions of glutathione S-transferases M1 (GSTM1) and T1 (GSTT1) and Ile105Val of glutathione S-transferase P1 (GSTP1) and myocardial infarction (MI) in a group of patients with type 2 diabetes mellitus.

METHODS

The study population consisted of 463 Caucasian subjects with type 2 diabetes mellitus of more than 10 years' duration: 206 patients with MI and 257 patients with no history of coronary artery disease (CAD). Genotypes were determined by polymerase chain reaction (PCR) with restriction fragment length polymorphism (RFLP) and with multiplex PCR.

RESULTS

The genotype distributions of tested single nucleotide polymorphisms did not show significant difference between cases and controls. After adjustment for age, gender, smoking, BMI, duration of diabetes and lipid parameters carriers of GSTM1/GSTT1-null haplotype showed an increased risk for MI (OR=3.22, 95% CI 1.37-5.04, p=0.03).

CONCLUSIONS

The GSTM1/GSTT1 haplotype might be a genetic risk factor for MI in patients with type 2 diabetes mellitus.

Identification of the GST-T1 and GST-M1 null genotypes using high resolution melting analysis

Glutathione S-transferases, including GST-T1 and GST-M1, are known to be involved in the phase II detoxification pathways for xenobiotics as well as in the metabolism of endogenous compounds. Polymorphisms in these genes have been linked to an increased susceptibility to carcinogenesis and associated with risk factors that predispose to certain inflammatory diseases. In addition, GST-T1 and GST-M1 null genotypes have been shown to be responsible for interindividual variations in the metabolism of arsenic, a known human carcinogen. To assess the specific GST genotypes in the Mexican population chronically exposed to arsenic, we have developed a multiplex High Resolution Melting PCR (HRM-PCR) analysis using a LightCycler480 instrument. This method is based on analysis of the PCR product melting curve that discriminates PCR products according to their lengths and base sequences. Three pairs of primers that specifically recognize GST-T1, GST-M1, and β-globin, an internal control, to produce amplicons of different length were designed and combined with LightCycler480 High Resolution Melting Master Mix containing ResoLight, a completely saturating DNA dye. Data collected from melting curve analysis were evaluated using LightCycler480 software to determine specific melting temperatures of individual melting curves representing target genes. Using this newly developed multiplex HRM-PCR analysis, we evaluated GST-T1 and GST-M1 genotypes in 504 DNA samples isolated from the blood of individuals residing in Zimapan, Lagunera, and Chihuahua regions in Mexico. We found that the Zimapan and Lagunera populations have similar GST-T1 and GST-M1 genotype frequencies which differ from those of the Chihuahua population. In addition, 14 individuals have been identified as carriers of the double null genotype, i.e., null genotypes in both GST-T1 and GST-M1 genes. Although this procedure does not distinguish between biallelic (+/+) and monoallelic (+/-) genotypes, it can be used in an automated workflow as a simple, sensitive, and time and money saving procedure for rapid identification of the GST-T1 and GST-M1 positive or null genotypes.

Glutathione s-transferases in pediatric cancer

The glutathione S-transferases (GSTs) are a family of ubiquitously expressed polymorphic enzymes important for detoxifying endogenous and exogenous compounds. In addition to their classic activity of detoxification by conjugation of compounds with glutathione, many other functions are now found to be associated with GSTs. The associations between GST polymorphisms/functions and human disease susceptibility or treatment outcome, mostly in adults, have been extensively studied and reviewed. This mini review focuses on studies related to GST epidemiology and functions related to pediatric cancer. Opportunities to exploit GST in pediatric cancer therapy are also discussed.

Functional studies of single-nucleotide polymorphic variants of human glutathione transferase T1-1 involving residues in the dimer interface

Glutathione transferase T1-1 catalyses detoxication and bioactivation processes in which glutathione conjugates are formed from endogenous and xenobiotic substrates, including alkylating agents and halogenated alkanes. Although the common null polymorphism of the human GSTT1 gene has been studied extensively, little is known about the consequences of GSTT1 single-nucleotide polymorphisms (SNPs). Here, we have examined the effects of two SNPs that alter amino acid residues in the dimer interface of the GST T1-1 protein and one that causes a conservative substitution in the core of the subunit. Variant proteins were expressed in an Escherichia coli strain in which the metabolism of ethylene dibromide to a glutathione conjugate leads to lacZ reversion mutations. We measured the kinetic properties of the enzymes with the characteristic substrate 1,2-epoxy-3-(p-nitrophenoxy)propane (EPNP) and determined the specific activities with several other substrates. Circular dichroism spectroscopy was used to measure protein thermal denaturation profiles. Variant T104P, which has been reported as inactive, showed weak but detectable activity with each substrate. Variant R76S was expressed at lower levels and showed much-reduced thermal stability. The results are interpreted in the context of the three-dimensional structure of human GST T1-1.

Copy number variants in pharmacogenetic genes

Variation in drug efficacy and toxicity remains an important clinical concern. Presently, single nucleotide polymorphisms (SNPs) only explain a portion of this problem, even in situations where the pharmacological trait is clearly heritable. The Human CNV Project identified copy number variations (CNVs) across approximately 12% of the human genome, and these CNVs were considered causes of diseases. Although the contribution of CNVs to the pathogenesis of many common diseases is questionable, CNVs play a clear role in drug-related genes by altering drug metabolizing and drug response. In this review, we provide a comprehensive evaluation of the clinical relevance of CNVs to drug efficacy, toxicity, and disease prevalence in world populations, and discuss the implication of using CNVs as a diagnostic tool in clinical intervention.

Genetic variations in human glutathione transferase enzymes: significance for pharmacology and toxicology

Glutathione transferase enzymes (GSTs) catalyze reactions in which electrophiles are conjugated to the tripeptide thiol glutathione. While many GST-catalyzed transformations result in the detoxication of xenobiotics, a few substrates, such as dihaloalkanes, undergo bioactivation to reactive intermediates. Many molecular epidemiological studies have tested associations between polymorphisms (especially, deletions) of human GST genes and disease susceptibility or response to therapy. This review presents a discussion of the biochemistry of GSTs, the sources-both genetic and environmental-of interindividual variation in GST activities, and their implications for pharmaco- and toxicogenetics; particular attention is paid to the Theta class GSTs.

Dietary glucosinolate intake, polymorphisms in selected biotransformation enzymes, and risk of prostate cancer

A protective role of glucosinolates in prostate cancer development might be mediated by the induction of biotransformation enzymes. These enzymes, enhancing the elimination of carcinogens from the body, are known to be polymorphic. Therefore, we evaluated whether a possible association between glucosinolate intake and prostate cancer risk is modified by polymorphisms in GSTT1, GSTM1, GSTA1, GSTP1, or NOQ1 genes. A case-control study including 248 prostate cancer cases and 492 matched controls was nested in the prospective European Prospective Investigation into Cancer and Nutrition-Heidelberg cohort. At baseline, participants provided dietary and lifestyle data and blood samples, which were used for genotyping and measurement of serum glutathione S-transferase-alpha concentration. Odds ratios and 95% confidence intervals were calculated by conditional logistic regression. We found an inverse association of glucosinolate intake with prostate cancer risk (adjusted odds ratio, 0.72 per 10 mg/d increment; 95% confidence interval, 0.53-0.96). Stratification by genotype showed significantly reduced risks for subjects with wild-type of NQO1 (C609T) compared with CT or TT carriers (P(interaction) = 0.04). Those with deletions in both GSTM1 and GSTT1 genes combined had a significantly reduced risk with increasing glucosinolate intake (P(interaction) = 0.01). There was no effect modification of glucosinolate intake and cancer risk by GSTA1 (G-52A) or GSTP1 (A313G) genotype, but serum glutathione S-transferase-alpha concentrations were inversely associated with prostate cancer. This study showed that the inverse association between glucosinolate intake and prostate cancer risk was modified by NQO1 (C609T) and GSTM1 and GSTT1 deletion polymorphisms. This information will help to further elucidate the mechanism of action of potentially protective substances in vivo.

Simultaneous genotyping of GSTT1 and GSTM1 null polymorphisms by melting curve analysis in presence of SYBR Green I

Due to their ability to metabolize xenobiotics, glutathione S-transferases (GSTs) play an important role in cellular protection. GST family members mu (GSTM1) and theta (GSTT1) exhibit a common polymorphism that results in the complete deletion of the gene (null allele). Homozygous deletions, which result in the absence of the enzyme, are considered a risk factor for several diseases, including cancer. We report a simple, low cost, and high throughput assay for the simultaneous analysis of the GSTM1 and GSTT1 null polymorphisms in a single step. The assay is based on multiplex real-time PCR in the presence of SYBR Green I and genotype discrimination by melting curve analysis in a LightCycler. We have genotyped 792 samples to compare this new approach with conventional PCR followed by gel electrophoresis. Comparison of the methods gave a good agreement, with kappa values of 0.88 for GSTM1 and 0.64 for GSTT1. Reanalysis of discrepant samples indicated that absence of amplification of the larger GSTT1 fragment by conventional PCR accounted for most of the discrepancies. Moreover, the improved amplification efficiency of the real-time PCR results in a significant reduction of missing values. Due to its simplicity and low cost, this assay is well suited for the rapid analysis of GST-null genotypes in studies that involve large number of samples.

Genetic polymorphisms in GST genes and survival of colorectal cancer patients treated with chemotherapy

Glutathione S-transferases (GSTs) participate in the detoxification of chemotherapeutic agents. Genetic polymorphisms in GST genes (GSTP1 Ile105Val, copy-number variants of GSTM1 and GSTT1) that lead to diminished enzyme activity have been associated with increased chemotherapeutic treatment benefit in colorectal cancer patients.

AIMS

We assessed the effect of genetic polymorphisms in GST genes on survival in colorectal cancer patients treated with adjuvant/palliative chemotherapy. As GSTs participate in the metabolism of platinum metabolites, we also assessed the association between genetic variants in GST genes and survival of colorectal cancer patients who received treatment with oxaliplatin.

MATERIALS & METHODS

We followed 338 colorectal cancer patients treated with chemotherapy for a median of 36.4 months since treatment start. A total of 65 of the patients received treatment with oxaliplatin. Polymorphisms were genotyped by fluorescence-based melting curve analysis (GSTP1 Ile105Val), a relative quantification method (copy-number variants of GSTM1 and GSTT1), and PCR followed by gel electrophoresis (null/non-null genotypes for GSTM1 and GSTT1). Associations between genotypes and overall survival were assessed using Kaplan-Meier curves and Cox proportional hazards regression.

RESULTS

As hypothesized, GSTM1 copy number variant was inversely associated with survival in colorectal cancer patients treated with chemotherapy. Mortality was significantly reduced in patients with one GSTM1 copy (hazard ratio: 0.45, 95% CI: 0.23-0.90, p = 0.02) and nonsignificantly reduced in those with the null genotype (HR: 0.67, 95% CI: 0.35-1.27, p = 0.22) compared with carriers of two copies. Both GSTP1 genotype and GSTT1 genotype were not associated with survival.

CONCLUSION

This is the first study to provide suggestive evidence for an effect of copy-number variation of GSTM1 on survival in colorectal cancer patients who received chemotherapy. Large studies are warranted to establish the impact of GST genotypes on treatment outcome in colorectal cancer patients.