Endogenous antioxidant enzymes and glutathione S-transferase in protection of mesothelioma cells against hydrogen peroxide and epirubicin toxicity

Control of Oxidative Stress in Cancer Chemoresistance: Spotlight on Nrf2 Role

Chemoresistance represents the main obstacle to cancer treatment with both conventional and targeted therapy. Beyond specific molecular alterations, which can lead to targeted therapy, metabolic remodeling, including the control of redox status, plays an important role in cancer cell survival following therapy. Although cancer cells generally have a high basal reactive oxygen species (ROS) level, which makes them more susceptible than normal cells to a further increase of ROS, chemoresistant cancer cells become highly adapted to intrinsic or drug-induced oxidative stress by upregulating their antioxidant systems. The antioxidant response is principally mediated by the transcription factor Nrf2, which has been considered the master regulator of antioxidant and cytoprotective genes. Nrf2 expression is often increased in several types of chemoresistant cancer cells, and its expression is mediated by diverse mechanisms. In addition to Nrf2, other transcription factors and transcriptional coactivators can participate to maintain the high antioxidant levels in chemo and radio-resistant cancer cells. The control of expression and function of these molecules has been recently deepened to identify which of these could be used as a new therapeutic target in the treatment of tumors resistant to conventional therapy. In this review, we report the more recent advances in the study of Nrf2 regulation in chemoresistant cancers and the role played by other transcription factors and transcriptional coactivators in the control of antioxidant responses in chemoresistant cancer cells.

Metabolic rewiring and redox alterations in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a rare malignancy of mesothelial cells with increasing incidence, and in many cases, dismal prognosis due to its aggressiveness and lack of effective therapies. Environmental and occupational exposure to asbestos is considered the main aetiological factor for MPM. Inhaled asbestos fibres accumulate in the lungs and induce the generation of reactive oxygen species (ROS) due to the presence of iron associated with the fibrous silicates and to the activation of macrophages and inflammation. Chronic inflammation and a ROS-enriched microenvironment can foster the malignant transformation of mesothelial cells. In addition, MPM cells have a highly glycolytic metabolic profile and are positive in 18F-FDG PET analysis. Loss-of-function mutations of BRCA-associated protein 1 (BAP1) are a major contributor to the metabolic rewiring of MPM cells. A subset of MPM tumours show loss of the methyladenosine phosphorylase (MTAP) locus, resulting in profound alterations in polyamine metabolism, ATP and methionine salvage pathways, as well as changes in epigenetic control of gene expression. This review provides an overview of the perturbations in metabolism and ROS homoeostasis of MPM cells and the role of these alterations in malignant transformation and tumour progression.

SILAC-based quantitative proteomics reveals pleiotropic, phenotypic modulation in primary murine macrophages infected with the protozoan pathogen Leishmania donovani

Leishmaniases are major vector-borne tropical diseases responsible for great human morbidity and mortality, caused by protozoan, trypanosomatid parasites of the genus Leishmania. In the mammalian host, parasites survive and multiply within mononuclear phagocytes, especially macrophages. However, the underlying mechanisms by which Leishmania spp. affect their host are not fully understood. Herein, proteomic alterations of primary, bone marrow-derived BALB/c macrophages are documented after 72 h of infection with Leishmania donovani insect-stage promastigotes, applying a SILAC-based, quantitative proteomics approach. The protocol was optimised by combining strong anion exchange and gel electrophoresis fractionation that displayed similar depth of analysis (combined total of 6189 mouse proteins). Our analyses revealed 86 differentially modulated proteins (35 showing increased and 51 decreased abundance) in response to Leishmania donovani infection. The proteomics results were validated by analysing the abundance of selected proteins. Intracellular Leishmania donovani infection led to changes in various host cell biological processes, including primary metabolism and catabolic process, with a significant enrichment in lysosomal organisation. Overall, our analysis establishes the first proteome of bona fide primary macrophages infected ex vivo with Leishmania donovani, revealing new mechanisms acting at the host/pathogen interface. SIGNIFICANCE: Little is known on proteome changes that occur in primary macrophages after Leishmania donovani infection. This study describes a SILAC-based quantitative proteomics approach to characterise changes of bone marrow-derived macrophages infected with L. donovani promastigotes for 72 h. With the application of SILAC and the use of SAX and GEL fractionation methods, we have tested new routes for proteome quantification of primary macrophages. The protocols developed here can be applicable to other diseases and pathologies. Moreover, this study sheds important new light on the "proteomic reprogramming" of infected macrophages in response to L. donovani promastigotes that affects primary metabolism, cellular catabolic processes, and lysosomal/vacuole organisation. Thus, our study reveals key molecules and processes that act at the host/pathogen interface that may inform on new immuno- or chemotherapeutic interventions to combat leishmaniasis.

Metabolic Remodelling: An Accomplice for New Therapeutic Strategies to Fight Lung Cancer

Metabolic remodelling is a hallmark of cancer, however little has been unravelled in its role in chemoresistance, which is a major hurdle to cancer control. Lung cancer is a leading cause of death by cancer, mainly due to the diagnosis at an advanced stage and to the development of resistance to therapy. Targeted therapeutic agents combined with comprehensive drugs are commonly used to treat lung cancer. However, resistance mechanisms are difficult to avoid. In this review, we will address some of those therapeutic regimens, resistance mechanisms that are eventually developed by lung cancer cells, metabolic alterations that have already been described in lung cancer and putative new therapeutic strategies, and the integration of conventional drugs and genetic and metabolic-targeted therapies. The oxidative stress is pivotal in this whole network. A better understanding of cancer cell metabolism and molecular adaptations underlying resistance mechanisms will provide clues to design new therapeutic strategies, including the combination of chemotherapeutic and targeted agents, considering metabolic intervenients. As cancer cells undergo a constant metabolic adaptive drift, therapeutic regimens must constantly adapt.

The effects of some cephalosporins on acetylcholinesterase and glutathione S-transferase: an in vivo and in vitro study

BACKGROUND

Glutathione S-transferase (GST) and acetylcholinesterase (AChE) are important enzymes in the metabolism. GSTs are primarily available in phase II metabolism. AChE is vital for neurodegenerative disorders.

SUBJECTS AND METHODS

The in vitro and in vivo effects of cefoperazone sodium (CFP), cefuroxime (CXM), and cefazolin (CZO) were investigated on GST and AChE activity in the present study. GST was purified using Glutathione-Agarose affinity chromatography.

RESULTS

K_i constants of CFP, CXM, and CZO were 0.1392 ± 0.02, 1.5179 ± 0.33, and 1.006 ± 0.11 mM for GST and 0.3010 ± 0.07, 0.3561 ± 0.09, and 0.3844 ± 0.04 mM, for AChE, respectively. The most effective inhibitor was CFP for both enzymes in in vitro. CZO (50 mg/kg), CXM (25 mg/kg), and CFP (100 mg/kg) inhibit in vivo GST and AChE activities. CXM had the most effective in vivo inhibition on AChE and GST.

CONCLUSIONS

CZO, CXM, and CFP are effective AChE and GST inhibitors in both in vitro and in vivo.

Sirtuin 3 enhanced drug sensitivity of human hepatoma cells through glutathione S-transferase pi 1/JNK signaling pathway

SIRT3, a class III histone deacetylase, has been implicated in various cancers as a novel therapeutic target. In hepatocellular carcinoma (HCC), we previously reported that SIRT3 induced cell apoptosis by regulating GSK-3β/Bax signaling pathway. Downregulation of SIRT3 in HCC cells facilitates tumor cell survival. In this study, we found that chemotherapeutic agents (doxorubicin, cisplatin and epirubicin) and sorafenib treatment downregulated SIRT3 mRNA and protein levels in three HCC cell lines. MTS assay found that SIRT3 overexpression sensitized liver cancer cells to chemotherapeutic agents and sorafenib in SMMC-7721, Huh-7 and PLC/PRF/5 cell lines. Moreover, SIRT3 overexpression promoted chemotherapeutic agents-induced or sorafenib-induced apoptosis as evidenced by flow cytometry, enhanced PARP cleavage and enhanced Caspase-9 cleavage in three HCC cells. In contrast, SIRT3 silencing increased drug resistance of HCC cells to chemotherapeutic agents. Mechanistic study found that SIRT3 downregulated the mRNA and protein levels of glutathione S-transferase pi 1 (GSTP1), which is a member of phase II detoxification enzymes families involved in metabolizing for chemotherapeutic agents. Moreover, SIRT3 decreased the amount of GSTP1 that was associated with JNK, which finally contributed the activation of JNK activity and activation of downstream target c-Jun and Bim. Importantly, GSTP1 overexpression or JNK inhibitor abolished SIRT3-induced apoptosis in HCC cells exposed to chemotherapeutic agents. Finally, there was a negative correlation between SIRT3 expression and GSTP1 expression in human HCC tissues. Together, our findings revealed SIRT3 could enhance the drug sensitivity of HCC cells to an array of chemotherapeutic agents. SIRT3 may serve as a potential target for improving the chemosensitivity of HCC patients.

Diarachidonoylphosphoethanolamine induces apoptosis of malignant pleural mesothelioma cells through a Trx/ASK1/p38 MAPK pathway

1,2-Diarachidonoyl-sn-glycero-3-phosphoethanolamine (DAPE) induces both necrosis/necroptosis and apoptosis of NCI-H28 malignant pleural mesothelioma (MPM) cells. The present study was conducted to understand the mechanism for DAPE-induced apoptosis of NCI-H28 cells. DAPE induced caspase-independent apoptosis of NCI-H28 malignant pleural mesothelioma (MPM) cells, and the effect of DAPE was prevented by antioxidants or an inhibitor of NADPH oxidase (NOX). DAPE generated reactive oxygen species (ROS) and inhibited activity of thioredoxin (Trx) reductase (TrxR). DAPE decreased an association of apoptosis signal-regulating kinase 1 (ASK1) with thioredoxin (Trx), thereby releasing ASK1. DAPE activated p38 mitogen-activated protein kinase (MAPK), which was inhibited by an antioxidant or knocking-down ASK1. In addition, DAPE-induced NCI-H28 cell death was also prevented by knocking-down ASK1. Taken together, the results of the present study indicate that DAPE stimulates NOX-mediated ROS production and suppresses TrxR activity, resulting in the decrease of reduced Trx and the dissociation of ASK1 from a complex with Trx, allowing sequential activation of ASK1 and p38 MAPK, to induce apoptosis of NCI-H28 MPM cells.

Proteomic biomarkers of endometrial cancer risk in women with polycystic ovary syndrome: a systematic review and biomarker database integration

There is a need for research studies into the molecular mechanisms underpinning the link between polycystic ovary syndrome (PCOS) and endometrial cancer (EC) to facilitate screening and to encourage the development of novel strategies to prevent disease progression. The objective of this review was to identify proteomic biomarkers of EC risk in women with PCOS. All eligible published studies on proteomic biomarkers for EC identified through the literature were evaluated. Proteomic biomarkers for EC were then integrated with an updated previously published database of all proteomic biomarkers identified so far in PCOS women. Nine protein biomarkers were similarly either under or over expressed in women with EC and PCOS in various tissues. These include transgelin, pyruvate kinase M1/M2, gelsolin-like capping protein (macrophage capping protein), glutathione S-transferase P, leucine aminopeptidase (cytosol aminopeptidase), peptidyl-prolyl cis-transisomerase, cyclophilin A, complement component C4A and manganese-superoxide dismutase. If validated, these biomarkers may provide a useful framework on which the knowledge base in this area could be developed and will facilitate future mathematical modelling to enhance screening and prevention of EC in women with PCOS who have been shown to be at increased risk.

Evaluation of platinum-ethacrynic acid conjugates in the treatment of mesothelioma

Malignant pleural mesothelioma (MPM) cells are characterized by chemoresistance associated with glutathione (GSH) metabolism. Ethacrynic acid (EA) is able to inhibit the detoxifying enzyme glutathione-S-transferase (GST), which catalyzes the conjugation between GSH and Pt-based drugs. With the aim of obtaining active bifunctional drugs, a Pt(II) complex containing two EA moieties as leaving groups, namely cis-diamminobis(ethacrynato)platinum(II), was synthesized, characterized, and tested on four MPM cell lines. The resulting antiproliferative activity was compared with that elicited by the analogue Pt(IV) complex, cis,cis,trans-diamminodichloridobis(ethacrynato)platinum(IV) (ethacraplatin) and by the co-administration of free EA and cisplatin. The Pt(II) and Pt(IV) bifunctional complexes showed poorer performance than the reference drug cisplatin alone or in combination with EA. After treatment, cellular GST activity remained consistently unchanged, while the GSH level increased.

Drug resistance in lung cancer

Resistance to chemotherapy drugs is a major problem in cancer treatment. Scientific advances made in the last two decades have resulted in the identification of genes and molecular signaling mechanisms that contribute to drug resistance. This has resulted in a better understanding of the biology of cancer cells and the way these cells adapt or undergo subtle molecular changes thereby protecting themselves from the cytotoxic effects of the anticancer drugs. Based on the knowledge gained to-date new molecularly targeted drugs are being developed and tested in clinical studies, in an attempt to overcome drug resistance and improve drug efficacy. Despite these attempts the overall 5-year survival of patients diagnosed with cancer, such as lung cancer, remains dismal and is less than 15%. It is evident that additional mechanisms contributing to drug resistance exist which are yet to be discovered. It is hoped that identification of new targets and understanding their contribution to drug resistance will provide opportunities for innovative therapies in overcoming drug resistance. In an attempt to broaden our knowledge and understanding on drug resistance we have, in this review article, summarized the most common mechanisms associated with drug resistance in lung cancer.

A mutation of Keap1 found in breast cancer impairs its ability to repress Nrf2 activity

Keap1 is the substrate recognition module of a Cullin 3-based E3 ubiquitin ligase. Its primary role is to catalyze the ubiquitylation of the Nrf2 transcription factor. Oxidative stress blocks the E3 ligase activity of Keap1 which stabilizes Nrf2 allowing it to drive the expression of certain antioxidant and drug metabolizing enzymes. A recent study identified a mutation in the Keap1 gene (Keap1C23Y) that is present in breast cancer. Using reporter gene assays we show that Keap1C23Y is impaired in its ability to repress Nrf2 dependent transcription. Unlike wild-type Keap1, we found that Keap1C23Y failed to stimulate the degradation of Nrf2. Co-immunopreciptation experiments showed that Keap1C23Y retains its ability to interact with Nrf2 and Cullin 3. In contrast, we found that Keap1C23Y could not efficiently promote the ubiquitylation of Nrf2, suggesting that its intrinsic biological activity might have been compromised. These results revealed an unexpected role for the N-terminal region of Keap1 in regulating its E3 ligase activity. Importantly, our findings suggest that a paradox exists whereby Nrf2 activity is beneficial in non-malignant cells but in cancer cells it may provide a selective advantage for clonal expansion.

Combined effect of epirubicin and lymphokine-activated killer cells on the resistant human breast cancer cells

Accumulating evidence suggests the concept that epirubicin and lymphokine-activated killer (LAK) cells cytotoxicity may be mediated by free radicals generation and P-glycoprotein-positive (Pg-p+) cancer cells are more sensitive for LAK cells than their drug-sensitive parental lines. We tested this hypothesis further by exposing drug-sensitive (WT) and epirubicin-resistant MCF-7 human breast tumor cells to epirubicin and LAK cells. Subsequently, we monitored cell proliferation as a measure of cytotoxicity. The cytotoxicity of epirubicin, LAK, and LAK + epirubicin (1/10 of IC50) was evaluated in 400-fold epirubicin resistant MCF-7 EPI(R) (P-glycoprotein overexpressing) and drug-sensitive MCF-7 WT cells. IC50 values were measured using the MTT cytotoxicity test. The MCF-7 EPI(R) cells exhibited an increased susceptibility to LAK cells than did the MCF-7 WT cells. P-gp+ MCF-7 EPI(R) cells were lysed by human LAK cells to a greater extend than were their drug-sensitive counterparts. LAK + epirubicin combined treatment increased susceptibility of MCF-7 WT and MCF-7 EPI(R) cells to LAK cells cytotoxicity. For both cell lines, cytotoxicity was dependent upon the concentration of the epirubicin and effector cell/target cell (E/T) ratio. The resistance of MCF-7 EPI(R) cells to epirubicin appears to be associated with a developed tolerance to superoxide, most likely because of a tree-fold increase in superoxide dismutase (SOD) activity and 13-fold augmented selenium dependent glutathione peroxidase (GSH-Px) activity. Acting in concert, these two enzymes would decrease the formation of hydroxyl radical from reduced molecular oxygen intermediates. The addition of SOD decreased cytotoxicity of epirubicin and LAK cells. Taken together, these observations support the role of oxygen radicals in the cytotoxicity mechanism of epirubicin and suggest further that the development of resistance to this drug by the MCF-7 EPI(R) tumor cells may have a component linked to oxygen free radicals. It is proposed that production of reactive oxygen species by the treatment of epirubicin and LAK cells can cause cytotoxicity of MCF-7 WT and MCF-7 EPI(R) cells. SOD, catalase, GSH-Px, GST (glutathione S-transferase), and GSH (reduced glutathione) must be considered as part of the intracellular antioxidant defense mechanism of MCF-7 WT and MCF-7 EPI(R) cells against reactive oxygen species.

Distribution of antioxidant enzymes in developing human lung, respiratory distress syndrome, and bronchopulmonary dysplasia

We studied cell-specific protein expression of all the major antioxidant enzymes (AOEs) and related proteins, such as copper-zinc superoxide dismutase (CuZnSOD), manganese SOD (MnSOD), extracellular SOD (ECSOD), catalase, the heavy and light chains of gamma-glutamylcysteine synthetase (gamma-GCS-l and gamma-GCS-h, also called glutamate cysteine ligase), the rate-limiting enzyme in glutathione synthesis, hemeoxygenase-1 (HO-1), and thioredoxin (Trx), in developing human lung, respiratory distress syndrome, and bronchopulmonary dysplasia by immunohistochemistry. Generally, after 17 weeks of gestational age, MnSOD was predominantly expressed in bronchial epithelium, alveolar epithelium, and macrophages, CuZnSOD was expressed in bronchial epithelium, ECSOD was expressed in bronchial epithelium, vascular endothelium, and the extracellular matrix, catalase was expressed in bronchial epithelium and alveolar macrophages, gamma-GCS-h was expressed in bronchial epithelium and endothelium, and gamma-GCS-l was expressed in bronchial epithelium. Trx was restricted to bronchial epithelium and to a lesser extent to alveolar macrophages, and HO-1 found in alveolar macrophages. Basically, the expression of these enzymes was similar in normal and diseased lung. It can be concluded that various AOEs and related proteins differ in their distribution and expression in lung before term, but generally it seems that infants are better adapted to high oxygen tension than might be expected.

Antioxidant enzymes and redox regulating thiol proteins in malignancies of human lung

Oxidants are known to modulate cell proliferation and apoptosis, and induce synthesis of growth factors that play an important role in tumor growth and invasion. Antioxidant enzymes and thiol proteins regulating cellular redox state constitute the major cellular protection against oxidants. Consequently, they are also associated both with carcinogenesis and tumor progression. Superoxide dismutases, glutamate cysteine ligase, catalase, thioredoxins and peroxiredoxins, which are the most important of these enzymes, are expressed in lung malignancies, and especially in pleural mesothelioma. This has consequences not only for tumor behavior but also for resistance of tumor cells to cytotoxic drugs and radiation.

Superoxide dismutases in malignant cells and human tumors

Reactive oxygen metabolites have multifactorial effects on the regulation of cell growth and the capacity of malignant cells to invade. Overexpression of the superoxide dismutases (SODs) in vitro increases cell differentiation, decreases cell growth and proliferation, and can reverse a malignant phenotype to a nonmalignant one. The situation in vivo is more complex due to multiple interactions of tumor cells with their environment. Numerous in vivo studies show that the superoxide dismutases can be highly expressed in aggressive human solid tumors. Furthermore, high SOD has occasionally been associated with a poor prognosis and with resistance to cytotoxic drugs and radiation. Most of the apparent conflicts between the above in vitro and in vivo observations can be reconciled by considering the net redox status of tumor cells in different environments. Administering high concentrations of SOD to cells in vitro is usually associated with a non- or less malignant phenotype, whereas secondary induction of SOD in tumors in vivo can be associated with an aggressive malignant transformation probably due to the altered (oxidative) redox state in the malignant cells. This concept suggests that for many types of tumors antioxidants could be used to diminish the invasive capability of malignant cells.

Overexpression of gamma-glutamylcysteine synthetase in human malignant mesothelioma

Mesothelioma is a fatal tumor resistant to all treatment modalities for reasons that are still unresolved. Glutathione (GSH)-associated pathways are induced by oxidants and cytotoxic drugs, and they are also involved in the progression and resistance of some tumor cells in vitro. The rate-limiting enzyme in GSH biosynthesis is gamma-glutamylcysteine synthetase (gamma GCS). However, the expression of this enzyme has not been systematically investigated in malignant tumors, and there are no studies of gamma GCS in biopsy specimens of malignant mesothelioma. We investigated the immunohistochemical distribution and expression of both subunits of gamma GCS in healthy pleural mesothelium, pleural mesothelioma tumor biopsy samples (34 cases), and mesothelioma cells in culture (7 cell lines). Nonmalignant mesothelium showed no immunoreactivity for either subunit in any of the cases. The heavy (catalytic) subunit of gamma GCS was highly immunostained in 29 and weakly positive in 5 cases. High-moderate and weak immunoreactivity of the light (regulatory) subunit of gamma GCS was found in 15 and 7 tumors, respectively, whereas 12 cases showed no reactivity. There was no correlation with either catalytic or regulatory subunit expression and patient survival. There was, however, a significant correlation between the heavy chain and multidrug resistance protein (MRP) 2 (P =.048), whereas no correlation was observed between the light chain and MRP1 or MRP2. Treatment of cultured mesothelioma cells with buthionine sulfoximine (BSO), to inhibit gamma GCS, significantly potentiated cisplatin-induced cytotoxicity mainly by nonapoptotic mechanism when assessed by counting the living cells, TUNEL (terminal deoxytransferase-mediated dUTP nick-end labeling) assay, and caspase-3 cleavage. In conclusion, gamma GCS is highly positive in most cases of malignant mesothelioma and may play an important role in the primary drug resistance of this tumor in vivo.

Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers

We investigated the role of glutathione and nitric oxide synthase (NOS) in fiber-induced cell and DNA toxicity using alkaline (pH 13) single-cell gel electrophoresis (the Comet assay). Transformed cultured human pleural mesothelial (MeT-5A) cells and alveolar epithelial cells (A549) were exposed to crocidolite asbestos fibers (1-10 microg/cm(2)) in the presence of buthionine sulfoximine (BSO) or L-arginine-methyl ester (L-NAME). BSO inhibits gamma-glutamylcysteine synthetase (gamma-GCS) and causes glutathione depletion, and L-NAME inhibits nitric oxide generation. Studies were also conducted to assess the expression of the heavy and light subunits of gamma-GCS in human pleural mesothelium and bronchial epithelium in vivo and the induction of inducible NOS (iNOS) by asbestos fibers. Asbestos fibers caused DNA single-strand breaks, and the process was significantly enhanced by BSO (69% compared to the non-treated cells). A549 cells had a 3.5-fold glutathione content compared to MeT-5A cells, which was consistent with the higher resistance of these cells against oxidants and fibers. Flow cytometry of iNOS showed no change of iNOS by the fibers in either cell type in vitro. L-NAME had no effects on the DNA single-strand breaks in the Comet assay, either. Studies on lung biopsies showed that the immunoreactivities of both gamma-GCS subunits were very low in healthy human mesothelium in vivo. We conclude that glutathione may play an essential role in protecting intact cells against fiber-induced oxidative DNA alterations, and low gamma-GCS reactivity in pleural mesothelium may be associated with the high sensitivity of mesothelial cells to fiber-induced toxicity.

Pharmacogenomics: the inherited basis for interindividual differences in drug response

It is well recognized that most medications exhibit wide interpatient variability in their efficacy and toxicity. For many medications, these interindividual differences are due in part to polymorphisms in genes encoding drug metabolizing enzymes, drug transporters, and/or drug targets (e.g., receptors, enzymes). Pharmacogenomics is a burgeoning field aimed at elucidating the genetic basis for differences in drug efficacy and toxicity, and it uses genome-wide approaches to identify the network of genes that govern an individual's response to drug therapy. For some genetic polymorphisms (e.g., thiopurine S-methyltransferase), monogenic traits have a marked effect on pharmacokinetics (e.g., drug metabolism), such that individuals who inherit an enzyme deficiency must be treated with markedly different doses of the affected medications (e.g., 5%-10% of the standard thiopurine dose). Likewise, polymorphisms in drug targets (e.g., beta adrenergic receptor) can alter the sensitivity of patients to treatment (e.g., beta-agonists), changing the pharmacodynamics of drug response. Recognizing that most drug effects are determined by the interplay of several gene products that govern the pharmacokinetics and pharmacodynamics of medications, pharmacogenomics research aims to elucidate these polygenic determinants of drug effects. The ultimate goal is to provide new strategies for optimizing drug therapy based on each patient's genetic determinants of drug efficacy and toxicity. This chapter provides an overview of the current pharmacogenomics literature and offers insights for the potential impact of this field on the safe and effective use of medications.

The expression of P-glycoprotein and multidrug resistance proteins 1 and 2 (MRP1 and MRP2) in human malignant mesothelioma

BACKGROUND

Malignant mesothelioma is a malignancy with a primary resistance to chemo- and radiotherapies for reasons which are still unclear. Multidrug resistance proteins might explain the observed resistance, but no studies have assessed their expression in mesothelioma.

PATIENTS AND METHODS

Immunohistochemical expression of P-glycoprotein (P-gp), and the multidrug resistance proteins 1 and 2 (MRP1 and MRP2) were investigated in 36 cases of malignant mesothelioma and in samples from normal mesothelium.

RESULTS

P-gp immunopositivity was found in 61%, MRP1 immunopositivity in 58% and MRP2 positivity in 33% of the cases. Normal mesothelium did not express these multidrug-resistant proteins. There was a significant association between P-gp and MRP2 (P = 0.022) expression. No or weak P-gp, MRP1 or MRP2 immunostaining was significantly more frequent in sarcomatoid mesothelimas than in epithelial or biphasic mesotheliomas (P = 0.031, P = 0.034 and P = 0.024, respectively). There was no significant association between patient survival and expression of the multidrug-resistant proteins.

CONCLUSIONS

The results show that P-gp, MRP1 and MRP2 are induced and expressed in malignant mesothelial cells. Regardless of their expression no association with survival of the patients was seen, suggesting that the primary resistance of malignant mesotheliomas is not solely dependent on their expression or function.

Up-regulation of thioredoxin and thioredoxin reductase in human malignant pleural mesothelioma

Thioredoxin (Trx) with a redoxactive dithiol together with NADPH and thioredoxin reductase (TrxR) is a major disulfide reductase regulating cellular redox state and cell proliferation and possibly contributing to the drug resistance of malignant cells. We assessed the Trx system in malignant pleural mesothelioma cell lines, in nonmalignant pleural mesothelium and in biopsies of malignant pleural mesothelioma. The mRNA and immunoreactive proteins of Trx and cytosolic and mitochondrial TrxR were positive in all four human mesothelioma cell lines investigated. Six cases of nonmalignant, histologically healthy pleural mesothelium showed no Trx or TrxR immunoreactivity, whereas immunohistochemistry on 26 biopsies of human malignant pleural mesothelioma showed positive Trx in all cases and positive TrxR in 23 (88%) of the cases. Moderate or strong immunoreactivity for Trx or TrxR was detected in 85% (22 cases) and 61% (14 cases) of the mesothelioma cases, respectively. Both Trx and TrxR staining patterns were mainly diffuse and cytoplasmic, but in 39% of the mesothelioma cases prominent nuclear staining could also be detected. Although staining for Trx and TrxR was seen in tumor cells, no significant association could be demonstrated between Trx or TrxR expression and tumor cell proliferation or apoptosis in the biopsies of mesothelioma. There was no significant association between the intensity of Trx or TrxR immunoreactivity and patient survival, which may possibly be related to moderate or intense Trx and TrxR reactivity in most of the cases. Although the Trx system may have an important role in the drug resistance of malignant mesothelioma, these studies also suggest that multiple factors contribute to the promotion, cell proliferation and apoptosis of malignant mesothelioma cells in vivo.

Expression and prognostic significance of catalase in malignant mesothelioma

BACKGROUND

Free radicals and antioxidant enzymes (AOEs) may play a critical role in cell proliferation and in the resistance of malignant cells against cytotoxic drugs and radiation. Malignant mesothelioma is a resistant tumor with high levels of manganese superoxide dismutase, a central superoxide scavenging AOE. In the current study, the authors assessed the expression and prognostic role of catalase, an important hydrogen peroxide scavenging AOE, in malignant pleural mesothelioma.

METHODS

Catalase expression was investigated by immunohistochemistry in 5 cases of nonmalignant healthy pleura and in tumor tissue of 32 mesothelioma patients, and by Western blot in 7 continuous human mesothelioma cell lines. The distribution of catalase in mesothelioma cells was assessed by immunoelectron microscopy. Furthermore, to investigate the effect of catalase inhibition in the drug resistance of these cells in vitro, the authors exposed mesothelioma cells with the highest catalase level to epirubicin with and without aminotriazole pretreatment.

RESULTS

Nonmalignant mesothelial cells showed no catalase immunoreactivity whereas most mesothelioma cases (24 of 32, 75%) were catalase positive, 17 cases (53%) showing moderate or high expression. Higher catalase expression in mesothelioma was associated with a better prognosis, mean survival rate from diagnosis being 6 and 24 months for negative/low expression and moderate/high expression, respectively. Furthermore, a coordinately high expression of both manganese-superoxide dismutase (Mn-SOD) and catalase predicted even more favorable outcome of the mesothelioma patients. Catalase also could be detected in all mesothelioma cell lines, the most resistant cell line showing the highest protein expression and compartmentalization of catalase mainly to peroxisomes. Aminotriazole inhibition of catalase had a marginal effect on the toxicity caused by epirubicin.

CONCLUSIONS

Catalase may have multifactorial effects in malignant cells; high catalase and/or coordinated high expression of Mn-SOD and catalase may decrease tumor progression by modulating the cellular redox state, but enhanced antioxidant capacity of mesothelioma cells also may protect tumor cells against exogenous oxidants, at least in vitro.

Proliferation, apoptosis, and manganese superoxide dismutase in malignant mesothelioma

Proliferation and apoptotic indices of tumour cells may have important prognostic significance. Manganese superoxide dismutase (MnSOD), an important anti-oxidant enzyme, has been shown to decrease proliferation of malignant cells transfected with the MnSOD gene. The aim of the present study was to investigate the indices of cell proliferation and apoptosis and their prognostic significance in human mesothelioma and to assess the effect of MnSOD on the proliferation and apoptosis of the mesothelioma cells expressing high constitutive MnSOD activity. Tissue sections from 35 subjects with malignant pleural mesothelioma were studied for cell proliferation by Ki-67 immunohistochemistry and for apoptosis by the TUNEL assay. In additional experiments, 2 mesothelioma cell lines expressing either low (M14K) or high (M38K) MnSOD levels were assessed for proliferative and apoptotic responses to epirubicin. The median proliferation and apoptotic indices of the mesothelioma tissue were 8.2% and 0.75%, respectively. Patients with a high proliferation (>8%) or apoptotic index (>0.75%) showed a worse prognosis (p < 0.001). MnSOD expression was inversely correlated with cell proliferation (p = 0.02). Our cell line experiments indicated that cells expressing high MnSOD levels were more resistant to apoptosis and showed lower proliferation when exposed to epirubicin in vitro. These findings show that high proliferation and apoptosis are associated with a poor prognosis of mesothelioma and that a high MnSOD level is associated with low proliferation of tumour cells. Furthermore, experiments with cultured mesothelioma cells suggest the importance of MnSOD in the proliferation and apoptosis caused by drug exposure.

Antioxidant defense mechanisms of human mesothelioma and lung adenocarcinoma cells

The development of drug resistance of tumors is multifactorial and still poorly understood. Some cytotoxic drugs generate free radicals, and, therefore, antioxidant enzymes may contribute to drug resistance. We investigated the levels of manganese superoxide dismutase (Mn SOD), its inducibility, and its protective role against tumor necrosis factor-alpha and cytotoxic drugs (cisplatin, epirubicin, methotrexate, and vindesin) in human pleural mesothelioma (M14K) and pulmonary adenocarcinoma (A549) cells. We also studied other major antioxidant mechanisms in relation to oxidant and drug resistance of these cells. A549 cells were more resistant than M14K cells toward both oxidants (hydrogen peroxide and menadione) and all the cytotoxic drugs tested. M14K cells contained higher basal Mn SOD activity than A549 cells (28.3 +/- 3.4 vs. 1.8 +/- 0.3 U/mg protein), and Mn SOD activity was significantly induced by tumor necrosis factor-alpha only in A549 cells (+524%), but the induction did not offer any protection during subsequent oxidant or drug exposure. Mn SOD was not induced significantly in either of these cell lines by any of the cytotoxic drugs (0.007-2 microM, 48 h) tested when assessed by Northern blotting, Western blotting, or specific activity. A549 cells contained higher catalase activity than M14K cells (7.6 +/- 1.3 vs. 3.6 +/- 0.5 nmol O(2). min(-1). mg protein(-1)). They also contained twofold higher levels of glutathione and higher immunoreactivity of the heavy subunit of gamma-glutamylcysteine synthetase than M14K cells. Experiments with inhibitors of gamma-glutamylcysteine synthetase and catalase supported our conclusion that mechanisms associated with glutathione contribute to the drug resistance of these cells.

Generation of reactive oxygen species by human mesothelioma cells

Malignant mesothelioma cells contain elevated levels of manganese superoxide dismutase (MnSOD) and are highly resistant to oxidants compared to non-malignant mesothelial cells. Since the level of cellular free radicals may be important for cell survival, we hypothesized that the increase of MnSOD in the mitochondria of mesothelioma cells may alter the free radical levels of these organelles. First, MnSOD activity was compared to the activities of two constitutive mitochondrial enzymes; MnSOD activity was 20 times higher in the mesothelioma cells than in the mesothelial cells, whereas the activities of citrate synthase and cytochrome c oxidase did not differ significantly in the two cell lines. This indicates that the activity of MnSOD per mitochondrion was increased in the mesothelioma cells. Superoxide production was assayed in the isolated mitochondria of these cells using lucigenin chemiluminescence. Mitochondrial superoxide levels were significantly lower (72%) in the mesothelioma cells compared to the mesothelial cells. Oxidant production in intact cells, assayed by fluorimetry using 2',7'-dichlorodihydrofluorescein as a fluorescent probe, did not differ significantly between these cells. We conclude that mitochondrial superoxide levels are lower in mesothelioma cells compared to nonmalignant mesothelial cells, and that this difference may be explained by higher MnSOD activity in the mitochondria of these cells. Oxidant production was not different in these cells, which may be due to the previously observed increase in H2O2-scavenging mechanisms of mesothelioma cells.