Clinical response to chemotherapy in locally advanced breast cancer was not associated with several polymorphisms in detoxification enzymes and DNA repair genes

Evaluation of molecular markers GSTM1 and GSTT1 and clinical factors in breast cancer: case-control study and literature review

The study was conducted to evaluate the frequency of polymorphisms in GSTM1 and GSTT1 genes in patients with breast cancer compared with individuals without history of cancer, and the association of these polymorphisms with clinical/epidemiological parameters.There were evaluated 752 women (219 patients and 533 controls). Molecular analysis was performed by the Polymerase Chain Reaction (PCR). Statistical analysis was used multiple logistic regression and descriptive statistics.Age ≥50 years (OR =3.22, 95% CI =2.30 - 4.51, p <0.001) and alcohol consumption (OR =1.60, 95% CI =1.13 - 2.27, p = 0.008) were associated to the development of breast cancer, while smoking and null genotypes GSTM1 and GSTT1 presented no association. GSTM1 and GSTT1 polymorphisms presented no relationship with the clinical and histopathological parameters or molecular subtypes of breast cancer. Ninety-two percent of tumors were invasive ductal, 66% were grade II, 65% were larger than 2 cm, the stages II (35.3%) and III (31.2%) were the most prevalent, and 47.7% were molecular subtype luminal B.Individuals aged ≥50 years and alcohol consumers have more chance to developing breast cancer. GSTM1 and GSTT1 polymorphisms are not associated to the risk of breast cancer.

GSTP1, GSTM1, and GSTT1 polymorphisms as predictors of response to chemotherapy in patients with breast cancer: a meta-analysis

Several studies have investigated the effects of polymorphisms in the GSTP1, GSTT1, and GSTM1 genes on responsiveness to chemotherapy in breast cancer, but the results have been inconsistent. The aim of this study was to determine the association between polymorphisms of GSTP1, GSTT1, and GSTM1 genes and response to chemotherapy in patients with breast cancer. The relevant studies were retrieved from PubMed, Embase, ISI Web of Knowledge, China National Knowledge Infrastructure, and Wanfang databases. The articles evaluating the correlations between response to chemotherapy and GSTP1, GSTT1, and GSTM1 polymorphisms in breast cancer patients were comprehensively reviewed. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to measure the strength of the associations. These associations were assessed with the χ ² test in this meta-analysis. Subgroup analysis by chemotherapy protocol and ethnicity were conducted to explore the source of heterogeneity among studies. A total of 14 articles with 31 studies involving GSTP1, GSTT1, and GSTM1 polymorphisms with response to chemotherapy were identified in the final meta-analysis. In the overall analysis, a significant association of GSTM1-present/GSTM1-null polymorphism with responsiveness to chemotherapy was observed in breast cancer patients (OR 0.74, CI 0.60-0.92, P = 0.006), whereas the GSTT1-present/GSTT1-null and GSTP1rs1695 polymorphisms were not significantly associated with clinical response to chemotherapy. The subgroup analysis by chemotherapy protocol indicated that the patients who harboring GSTP1rs1695 AA or AG variant had a higher response rate to anthracycline-based chemotherapy than those carrying GSTP1rs1695 GG variant [AA vs. GG: OR 0.48, CI 0.29-0.80, P < 0.05; AA vs. AG: OR 0.60, CI 0.43-0.83, P < 0.05; A vs. G: OR 0.60, CI 0.47-0.77, P < 0.05; AA vs. (AG + GG): OR 0.56, CI 0.42-0.76, P < 0.05; (AA + AG) vs. GG: OR 0.57, CI 0.34-0.94, P < 0.05]. In addition, the heterogeneity existed among studies for GSTP1 polymorphism, while no obvious heterogeneity was detected for GSTT1 and GSTM1 polymorphisms. And the heterogeneity present in different studies, evaluating the association of GSTP1 polymorphism with response to anthracycline-based chemotherapy, disappeared in breast cancer patients after subgroup analysis by chemotherapy regimen was performed. In conclusion, this meta-analysis suggested that GSTP1rs1695 and GSTM1-present/GSTM1-null polymorphisms could be considered as reliable predictors of response to anthracycline-based chemotherapy in patients with breast cancer.

Therapeutic applications of dichloroacetate and the role of glutathione transferase zeta-1

Dichloroacetate (DCA) has several therapeutic applications based on its pharmacological property of inhibiting pyruvate dehydrogenase kinase. DCA has been used to treat inherited mitochondrial disorders that result in lactic acidosis, as well as pulmonary hypertension and several different solid tumors, the latter through its ability to reverse the Warburg effect in cancer cells and restore aerobic glycolysis. The main clinically limiting toxicity is reversible peripheral neuropathy. Although administration of high doses to rodents can result in liver cancer, there is no evidence that DCA is a human carcinogen. In all studied species, including humans, DCA has the interesting property of inhibiting its own metabolism upon repeat dosing, resulting in alteration of its pharmacokinetics. The first step in DCA metabolism is conversion to glyoxylate catalyzed by glutathione transferase zeta 1 (GSTZ1), for which DCA is a mechanism-based inactivator. The rate of GSTZ1 inactivation by DCA is influenced by age, GSTZ1 haplotype and cellular concentrations of chloride. The effect of DCA on its own metabolism complicates the selection of an effective dose with minimal side effects.

GSTT1 and GSTM1 polymorphisms predict treatment outcome for breast cancer: a systematic review and meta-analysis

Observational studies have reported controversial results on the association between GSTT1 and GSTM1 genotypes and treatment outcome of breast cancer. The purpose of this study is to evaluate the association between GSTT1 and GSTM1 and treatment outcome in breast cancer patients. Eligible studies were searched in PubMed, EMBASE, Cochrane Library, and China National Knowledge Infrastructure databases. A random-effect model or fixed-effect model was used to calculate the overall combined risk estimates. Twenty-one studies with a total of 4990 patients were included in this meta-analysis. The GSTM1 null genotype (odds ratio (OR) = 1.33, 95 % confidence interval (CI) 1.01-1.75, P = 0.046) and GSTT1/GSTM1 double null genotype (OR = 2.22, 95 % CI 1.02-4.84, P = 0.045) were significantly associated with an increased tumor response. A reduced overall survival (hazard ratio (HR) = 0.84, 95 % CI 0.72-0.98, P = 0.024) was observed in GSTM1 null genotype, especially in mixed descent (HR = 0.77, 95 % CI 0.61-0.96, P = 0.018) and large sample size (HR = 0.85, 95 % CI 0.72-0.99, P = 0.033). Evidence of publication bias was observed in GSTM1 genotype rather than in GSTT1 genotype. This meta-analysis suggests that GSTM1 null and GSTT1/GSTM1 double null polymorphisms might be significantly associated with an increased tumor response. However, the GSTM1 null genotype might be significantly associated with a reduced overall survival. Future studies are warranted to confirm these findings.

Functional polymorphisms in xenobiotic metabolizing enzymes and their impact on the therapy of breast cancer

Breast cancer is the top cancer among women, and its incidence is increasing worldwide. Although the mortality tends to decrease due to early detection and treatment, there is great variability in the rates of clinical response and survival, which makes breast cancer one of the most appealing targets for pharmacogenomic studies. The recognition that functional CYP2D6 polymorphisms affect tamoxifen pharmacokinetics has motivated the attempts of using CYP2D6 genotyping for predicting breast cancer outcomes. In addition to tamoxifen, the chemotherapy of breast cancer includes combinations of cytotoxic drugs, which are substrates for various xenobiotic metabolizing enzymes. Because of these drugs’ narrow therapeutic window, it has been postulated that impaired biotransformation could lead to increased toxicity. In the present review, we performed a systematic search of all published data exploring associations between polymorphisms in xenobiotic metabolizing enzymes and clinical outcomes of breast cancer. We retrieved 43 original articles involving either tamoxifen or other chemotherapeutic protocols, and compiled all information regarding response or toxicity. The data indicate that, although CYP2D6 polymorphisms can indeed modify tamoxifen pharmacokinetics, CYP2D6 genotyping alone is not enough for predicting breast cancer outcomes. The studies involving other chemotherapeutic protocols explored a great diversity of pharmacogenetic targets, but the number of studies for each functional polymorphism is still very limited, with usually no confirmation of positive associations. In conclusion, the application of pharmacogenetics to predict breast cancer outcomes and to select one individual’s chemotherapeutic protocol is still far from clinical routine. Although some very interesting results have been produced, no clear practical recommendations are recognized yet.