Expression of glutathione S-transferases in normal and malignant pancreas: an immunohistochemical study

Glutathione-Depleting Nanomedicines for Synergistic Cancer Therapy

Cancer cells frequently exhibit resistance to various molecular and nanoscale drugs, which inevitably affects the drugs' therapeutic outcomes. Overexpression of glutathione (GSH) has been observed in many cancer cells, and solid evidence has corroborated the resulting tumor resistance to a variety of anticancer therapies, suggesting that this biochemical characteristic of cancer cells can be developed as a potential target for cancer treatments. The single treatment of GSH-depleting agents can potentiate the responses of the cancer cells to different cell death stimuli; therefore, as an adjunctive strategy, GSH depletion is usually combined with mainstream cancer therapies for enhancing the therapeutic outcomes. Propelled by the rapid development of nanotechnology, GSH-depleting agents can be readily constructed into anticancer nanomedicines, which have shown a steep rise over the past decade. Here, we review the common GSH-depleting nanomedicines which have been widely applied in synergistic cancer treatments in recent years. Some current challenges and future perspectives for GSH depletion-based cancer therapies are also presented. With the understanding of the structure-property relationship and action mechanisms of these biomaterials, we hope that the GSH-depleting nanotechnology will be further developed to realize more effective disease treatments and even achieve successful clinical translations.

Downregulation of GSTM2 enhances gemcitabine chemosensitivity of pancreatic cancer in vitro and in vivo

Glutathione-S-transferases (GSTs) not only show cytoprotective role and their involvement in the development of anticancer drug resistance, but also transmit signals that control cell proliferation and apoptosis. However, the role of GST isoforms in chemotherapy resistance remains elusive in pancreatic cancer. Here, we demonstrated that gemcitabine treatment increased the GSTM2 expression in pancreatic cancer cell lines. Knockdown of GSTM2 by siRNA elevated apoptosis and decreased viability of pancreatic cancer cells treated with gemcitabine. Moreover, in vivo experiments further showed that shRNA induced GSTM2 downregulation enhanced drug sensitivity of gemcitabine in orthotopic pancreatic tumor mice. We also found that GSTM2 levels were lower in tumor tissues than in non-tumor tissues and higher GSTM2 expression was significantly associated with longer overall survival. In conclusion, our findings indicate that GSTM2 expression is essential for the survival of pancreatic cancer cells undergoing gemcitabine treatment and leads to chemo resistance. Downregulation of GSTM2 in pancreatic cancer may benefit gemcitabine treatment. GSTM2 expression in patients also shows significant correlation with overall survival. Thus, our study suggests that GSTM2 is a potential target for chemotherapy optimization and prognostic biomarker of pancreatic cancer.

Glutathione S-transferase π: a potential role in antitumor therapy

Glutathione S-transferase π (GSTπ) is a Phase II metabolic enzyme that is an important facilitator of cellular detoxification. Traditional dogma asserts that GSTπ functions to catalyze glutathione (GSH)-substrate conjunction to preserve the macromolecule upon exposure to oxidative stress, thus defending cells against various toxic compounds. Over the past 20 years, abnormal GSTπ expression has been linked to the occurrence of tumor resistance to chemotherapy drugs, demonstrating that this enzyme possesses functions beyond metabolism. This revelation reveals exciting possibilities in the realm of drug discovery, as GSTπ inhibitors and its prodrugs offer a feasible strategy in designing anticancer drugs with the primary purpose of reversing tumor resistance. In connection with the authors' current research, we provide a review on the biological function of GSTπ and current developments in GSTπ-targeting drugs, as well as the prospects of future strategies.

Ruthenium arene complexes with triphenylphosphane ligands: cytotoxicity towards pancreatic cancer cells, interaction with model proteins, and effect of ethacrynic acid substitution

The anticancer behaviour of Ru arene complexes can be tuned by an appropriate choice of the site and linkage of the bioactive group to the phosphane ligand.

The role of tobacco-derived carcinogens in pancreas cancer

The extremely poor outcome from pancreas cancer is well known. However, its aetiology less well appreciated, and the molecular mechanisms underlying this are poorly understood. Tobacco usage is one of the strongest risk factors for this disease, and this is a completely avoidable hazard. In addition, there are well described hereditary diseases which predispose, and familial pancreas cancer. We have sought here to summarise the role of tobacco-derived carcinogens and the mode of their tumorigenic action on the pancreas. There is compelling evidence from animal and human studies (laboratory including cell line studies and epidemiologic) that tobacco derived carcinogens cause pancreas cancer. However, the manner in which they do so is not entirely apparent. There is also compelling evidence that synergism with genetic and other life-style factors-like diet obesity-results in a multifactorial causation of the disease. Ascertaining the role of tobacco carcinogens in the development of this cancer and their interaction with other risk factors will enable novel therapeutic and preventative strategies to improve outcome from this appalling malignancy.

Expression of the xenobiotic- and reactive oxygen species-detoxifying enzymes, GST-pi, Cu/Zn-SOD, and Mn-SOD in the endocrine cells of colorectal cancer

BACKGROUND AND AIM

The aim of the present work was to analyze the expression of antioxidant enzymes GST-pi, SOD1, and SOD2 in endocrine cells of colorectal cancers and to evaluate the significance of the presence of thus labeled endocrine cells as prognostic factor.

METHODS

The expression of chromogranin A (ChGA), GST-pi, SOD1, and SOD2 was determined in endocrine cells of 128 colorectal cancers using light and electron immunohistochemistry and double immunogold labeling method.

RESULTS

Endocrine cells expressing at least one of the studied antioxidant enzymes were detected in a relatively small proportion of primary colorectal cancers (22 cases, 17%; 14% GST-pi-positive, 14% SOD1-positive, and 9% SOD2-positive). The double immunogold staining and the following electron microscopy showed that GST-pi, SOD1, and SOD2 were co-localized with ChGA to the granules of most endocrine cells. The survival analyses revealed that patients with endocrine cells in primary tumor tissues expressing GST-pi had worse prognosis after the surgical therapy than those without GST-pi-positive endocrine cells (median of 22.70 vs. 49.43 months, p < 0.05, Log-rank test).

CONCLUSIONS

Most of the ChGA-positive endocrine cells in colorectal cancers also expressed some or all of the three studied antioxidant enzymes, GST-pi, SOD1, and SOD2. Moreover, patients having tumors with GST-pi-positive endocrine cells have an unfavorable prognosis. We suggest that not the neuroendocrine differentiation in general, but the presence in the tumors of endocrine cells with activated antioxidant defense and probably metabolically more active might determine a more aggressive type of cancer leading to worse prognosis for patients.

Glutathione S-transferase gene polymorphisms and risk and survival of pancreatic cancer

BACKGROUND

Pancreatic cancer is a multifactorial disease with metastasis-prone and therapy-resistant nature. The authors hypothesized that genetic variants of glutathione S-transferase (GST) affect detoxification of carcinogens and anticancer agents in the human pancreas and, thus, the risk and survival of pancreatic cancer.

METHODS

Genotypes of GSTM1, GSTT1, and GSTP1 were determined in 352 patients with pancreatic ductal adenocarcinoma and in a control group of 315 healthy, non-Hispanic whites (frequency-matched by age and sex). Survival analysis was performed in a subset of 290 patients. Epidemiological and clinical information was obtained. A multiple unconditional logistic regression model, a Cox proportional hazards model, and log-rank tests were used for statistical analysis.

RESULTS

No significant main effects of any of 3 GST genes on the risk of pancreatic cancer were observed. Subgroup analysis showed that older individuals (aged >or=62 years) who carried the GSTP1*C ((105)Val-(114)Val) containing genotype tended to have a reduced risk compared with younger individuals who carried the non-*C genotype (for sex and pack-years of smoking, the adjusted odd ratio was 0.54; 95% confidence interval [95% CI], 0.29-1.02). In a survival analysis of 138 patients who received 5-flurorouracil, patients who carried the GSTP1*C containing genotype had a significantly longer survival than patients who carried the non-*C genotype (multivariate hazard ratio, 0.45; 95% CI, 0.22-0.94).

CONCLUSIONS

The GSTP1*C variant conferred a possible protective effect against pancreatic cancer in older individuals and a significant survival advantage in patients who received 5-florouracil. The current findings must be confirmed before further inferences can be made.

Gene-environment interactions in pancreatic cancer

Exocrine pancreatic cancer remains a major cause of cancer death in Western populations. Despite many efforts, little is known about its etiology. Tobacco is the only established cause, although the proportion of cases of exocrine pancreatic cancer attributed to it is only 30%. A family history of pancreatic cancer accounts for 10% of the cases of this disease. A large proportion of cases are due to yet unrecognized factors. The combined contribution of genetic susceptibility and environmental factors has rarely been considered. A higher risk of exocrine pancreatic cancer has been observed for patients with hereditary pancreatitis who smoked. It has also been suggested that CFTR mutations and alcohol could interact in the development of exocrine pancreatic cancer. Common variants in a large number of genes could act as low-penetrance alleles. Little is known about their role as susceptibility markers for exocrine pancreatic cancer, except for metabolic enzymes. A few studies have assessed the association between polymorphisms in these genes and exocrine pancreatic cancer. Surprisingly, none of them observed an interaction with tobacco consumption. The reality may be more complex; exocrine pancreatic cancer is genetically heterogeneous and it could involve many somatic and heritable mutations. Gene-gene interactions and endogenous factors, among others, can contribute to tumor development. Future epidemiological studies should consider all of these aspects together.

Differences in the expression of glutathione S-transferases in normal pancreas, chronic pancreatitis, secondary chronic pancreatitis, and pancreatic cancer

INTRODUCTION

In our previous study, glutathione S-transferase-pi (GST-pi), a phase II drug metabolizing enzyme, was found to be expressed in pancreatic ductal and ductular cells but not acinar cells of the normal pancreas, chronic pancreatitis, and secondary pancreatitis caused by pancreatic cancer. A greater percentage of the cells expressing GST-pi was shown in the islets of chronic pancreatitis specimens compared with the normal pancreas and secondary pancreatitis.

AIMS AND METHODOLOGY

To examine whether the increased number of islet cells expressing GST-pi and the absence in the acinar cells are compensated for by other GST isozymes, we investigated the expression of GST-alpha and GST-mu in the same specimens.

RESULTS

Unlike the distribution of GST-pi, the distribution of GST-alpha and GST-mu in islets did not show marked differences between the three groups. However, in four of 18 primary chronic pancreatitis specimens, more islet cells (approximately 25%) expressed GST-alpha than in the normal pancreas and secondary chronic pancreatitis (both approximately 10%). The reactivity of cancer cells to GST-alpha, GST-mu, and GST-pi was similar to the ductal cells in the normal pancreas, chronic pancreatitis, and secondary chronic pancreatitis. Contrary to the expression of GST-pi, no statistically significant differences were found in the distribution of GST-alpha and GST-mu in the normal pancreas, chronic pancreatitis, and secondary chronic pancreatitis.

CONCLUSION

The expression of the other GSTs does not compensate for the variation of expression of GST-pi. There was no specimen in each group that did not express at least one GST isozyme in islet, acinar, and ductal cells.

Species differences in the distribution of drug-metabolizing enzymes in the pancreas

We investigated the cellular expression of 9 cytochrome P450-isozymes (CYP1A1, CYPIA2, CYP2B6, CYP2C8,9,19, CYP2D1, CYP2E1, CYP3A1, CYP3A2, CYP3A4) and 3 glutathione S-transferase-isozymes (GST-pi, GST-alpha. GST-mu) in the pancreas of hamsters, mice, rats, rabbits, pigs, dogs and monkeys, and in comparison with the human pancreas. A wide variation was found in the cellular localization of these enzymes between the 8 species. Most enzymes were expressed in the pancreas of the hamster, mouse, monkey and human, whereas rats, pigs, rabbits and dogs were lacking several isozymes. However, in all of the species the islet cells expressed more enzymes than ductal and acinar cells. An exclusive expression of enzymes in the islet cells was found in the hamster (CYP2E1). mouse (CYP1A1 , CYP1A2, GST-alpha, GST-mu), rat (CYP2C8,9, 19). rabbit (CYP1A2, CYP2B6, GST-pi), and pig (CYP1AI). Although no polymorphism was found in the pancreas of animals, in human tissue four enzymes were missing in about 50% of the cases. The results imply a greater importance of the islet cells in the metabolism of xenobiotics within the pancreas. The differences in the distribution of these drug-metabolizing enzymes in the pancreas between the species call for caution when extrapolating experimental results to humans.

A population-based, case-control study of polymorphisms in carcinogen-metabolizing genes, smoking, and pancreatic adenocarcinoma risk

BACKGROUND

Cigarette smoking is associated with a twofold increased risk of pancreatic cancer. We conducted a population-based case-control study in six San Francisco Bay area counties from 1994 to 2001 to investigate associations between polymorphisms in genes for two carcinogen-metabolizing enzymes (cytochrome P450 1A1 [CYP1A1] and glutathione S-transferase [GST]), smoking, and adenocarcinoma of the exocrine pancreas.

METHODS

We used polymerase chain reaction-based methods to analyze blood samples obtained from 309 case subjects and 964 control subjects to determine their genotypes for three CYP1A1 polymorphisms (m1, m2, and m4) and for homozygous deletions of two GST genes, GSTM1 and GSTT1. Control subjects were frequency matched to case subjects by age and sex. All statistical tests were two-sided.

RESULTS

None of the genetic polymorphisms themselves affected the risk of pancreatic cancer among Caucasian study participants. However, we observed an interaction between GSTT1-null genotype and cigarette smoking among Caucasians that was more prominent among women than among men. Relative to never smokers with the GSTT1-present genotype, the age-adjusted odds ratios (ORs) of pancreatic cancer for heavy smokers with the GSTT1-null genotype were 5.0 (95% confidence interval [CI] = 1.8 to 14.5) for women and 3.2 (95% CI = 1.3 to 8.1) for men; for heavy smokers with the GSTT1-present genotype they were 2.0 (95% CI = 1.0 to 4.0) for women and 2.1 (95% CI = 1.1 to 3.9) for men. ORs for pancreatic cancer among heavy smokers with both GSTT1-null and GSTM1-null genotypes were similar in magnitude to those among heavy smokers with the GSTT1-null genotype alone. There was no evidence of an interaction between CYP1A1 polymorphisms and smoking.

CONCLUSIONS

The combination of heavy smoking and a deletion polymorphism in GSTT1 is associated with an increased risk of pancreatic cancer among Caucasians, with the associations possibly stronger in women than in men.

Increased expression of glutathione S-transferase-pi in the islets of patients with primary chronic pancreatitis but not secondary chronic pancreatitis

The mechanism of tissue alteration in chronic pancreatitis (CP) is still unclear. Different hypotheses have been discussed, including increasing oxidant stress in the acinar cells, often as a result of exposure to xenobiotics. To evaluate the role of oxidative stress in CP, the authors investigated the expression of the drug-metabolizing phase II enzyme, glutathione S-transferase-pi (GST-pi), in the pancreatic tissue of patients with CP and compared it with the healthy pancreatic tissue from age-matched donors. Pancreatic tissue from patients with secondary CP resulting from ductal obstruction by pancreatic cancer (PC) was also examined. The percentage of cells immunoreacting with anti-GST-pi was counted within 15 randomly selected islets in each slide of the three groups. In all specimens, ductal and ductular cells, and in PC, cancer cells, expressed GST-pi in a moderate intensity. Acinar cells did not stain. Various numbers of islet cells in each of the three groups were stained strongly. More islet cells expressed GST-pi in CP (42%) than in healthy pancreatic tissue (16%, p < 0.001) or PC (17%, p < 0.001). Our results imply an important role of islet cells in the metabolism of substances, which are the substrate for GST-pi, and lend support to the hypothesis of oxidative stress as the cause of CP.

Expression of glutathione S-transferase alpha, P1-1 and T1-1 in the human gastrointestinal tract

Glutathione S-transferases (GSTs) form a family of enzymes, which play an important role in the prevention of cancer by detoxifying numerous potentially carcinogenic compounds. GSTs catalyze the conjugation of glutathione to such harmful molecules, and enable their secretion. Human GSTs can be divided into five main classes. The theta class of isoenzymes was only recently identified and limited (immunohistochemical) data on these enzymes are available. In the present study, paraffin-embedded sections of different gastrointestinal tissues were analyzed immunohistochemically for GSTalpha, GSTP1-1 and GSTT1-1 expression using specific antibodies. GSTalpha, GSTP1-1 and GSTT1-1 were highly expressed in all gastrointestinal tissues examined, with a unique cellular distribution. GSTT1-1 is the first GST isoenzyme demonstrated in duodenal Paneth cells and glands of Brunner. The common expression of GSTalpha, GSTT1-1 and GSTP1-1 in many cell types along the human gastrointestinal tract suggests an important role in the protection against carcinogens and other xenobiotics.

Glutathione S-transferase expression in malignant mesothelioma and non-neoplastic mesothelium: an immunohistochemical study

Expression of the glutathione S-transferase (GST) subclasses alpha, mu and pi was investigated immunohistochemically in 20 normal or hyperplastic mesothelium and in 57 malignant mesothelioma cases. These results were correlated with survival and also with P-170 glycoprotein expression. Nearly all the non-neoplastic mesothelium cases were positive for GST alpha and pi. About half of the non-neoplastic cases were positive for mu. Twenty-nine (51%) malignant mesotheliomas were positive for at least one of the GST species; 21 (37%) showed immunoreactivity for alpha, 18 (31.5%) for mu and 21 (37%) for pi. A total of 54 mesothelioma cases displayed immunoreactivity for the P-170 glycoprotein. For GST pi and GST mu, a statistical significance between expression and increased survival was found (respectively P = 0.012 and 0.024) while for GST alpha no significance was found. The results of this study demonstrate that expression of GST pi correlates positively with increased survival in malignant mesothelioma. It is also concluded that, in mesothelioma, GST and P-170 glycoprotein may contribute to the resistance to cytotoxic drugs frequently observed in these tumours. No correlation between GST and P-170 expression was demonstrated.

Immunohistochemical study of metallothionein in pancreatic carcinomas

Metallothioneins are a family of intracellular metalloproteins that have been thought to be involved in anticancer drug resistance. However, the role of metallothioneins in pancreatic cancer has not been investigated in detail. The immunohistochemical localization of metallothionein was examined in normal human adult pancreas tissue and in 75 pancreatic duct cell carcinomas, using monoclonal anti-metallothionein antibody. Furthermore, in vitro studies on the sensitivity of pancreatic cancer to cisplatin were performed in 10 cases of pancreatic carcinoma. Metallothionein staining was weakly positive in the acinar and islet cells and intralobular ducts but was negative in the large pancreatic ducts. In pancreatic carcinomas, metallothionein staining was diffusely positive in 6 (8%), focally positive in 25 (33%) and negative in 44 (59%) of the 75 pancreatic carcinomas. The expression of metallothioneins in pancreatic tumors was related to metastasis, poor prognosis and poor histological grading (poorer glandular differentiation and nuclear anaplasia). The in vitro study of tumor sensitivity to cisplatin showed no significant correlation between metallothionein expression and resistance to cisplatin. Metallothionein-positive pancreatic carcinoma will be potentially highly malignant or acquire an enhanced ability to produce metallothioneins as the malignant potential increases. The expression of metallothionein could be a prognostic indicator in pancreatic carcinomas.