Glutathione and glutathione-dependent enzymes in cancer drug resistance

Molecular mechanisms of resveratrol as chemo and radiosensitizer in cancer

One of the primary diseases that cause death worldwide is cancer. Cancer cells can be intrinsically resistant or acquire resistance to therapies and drugs used for cancer treatment through multiple mechanisms of action that favor cell survival and proliferation, becoming one of the leading causes of treatment failure against cancer. A promising strategy to overcome chemoresistance and radioresistance is the co-administration of anticancer agents and natural compounds with anticancer properties, such as the polyphenolic compound resveratrol (RSV). RSV has been reported to be able to sensitize cancer cells to chemotherapeutic agents and radiotherapy, promoting cancer cell death. This review describes the reported molecular mechanisms by which RSV sensitizes tumor cells to radiotherapy and chemotherapy treatment.

Effect of Expression of Nuclear-Encoded Cytochrome C Oxidase Subunit 4 Isoforms on Metabolic Profiles of Glioma Cells

Although often effective at treating newly diagnosed glioblastoma (GBM), increasing evidence suggests that chemo- and radiotherapy-induced alterations in tumor metabolism promote GBM recurrence and aggressiveness, as well as treatment resistance. Recent studies have demonstrated that alterations in glioma cell metabolism, induced by a switch in the isoform expression of cytochrome c oxidase subunit 4 (COX4), a key regulatory subunit of mammalian cytochrome c oxidase, could promote these effects. To understand how the two COX4 isoforms (COX4-1 and COX4-2) differentially affect glioma metabolism, glioma samples harvested from COX4-1- or COX4-2-overexpressing U251 cells were profiled using Gas chromatography–mass spectrometry GC-MS and Liquid Chromatography - Tandem Mass Spectrometry LC-MS/MS metabolomics platforms. The concentration of 362 metabolites differed significantly in the two cell types. The two most significantly upregulated pathways associated with COX4-1 overexpression were purine and glutathione metabolism; the two most significantly downregulated metabolic pathways associated with COX4-1 expression were glycolysis and fatty acid metabolism. Our study provides new insights into how Cytochrome c oxidase (CcO) regulatory subunits affect cellular metabolic networks in GBM and identifies potential targets that may be exploited for therapeutic benefit.

Nanoparticles Loaded with Docetaxel and Resveratrol as an Advanced Tool for Cancer Therapy

A growing interest in the use of a combination of chemosensitizers and cytostatics for overcoming cancer resistance to treatment and the development of their delivery systems has been observed. Resveratrol (Res) presents antioxidant, anti-inflammatory and chemopreventive properties but also limits multidrug resistance against docetaxel (Dtx), which is one of the main causes of failure in cancer therapy with this drug. However, the use of both drugs presents challenges, including poor bioavailability, the unfavourable pharmacokinetics and chemical instability of Res and the poor water solubility and dose-limiting toxicity of Dtx. In order to overcome these difficulties, attempts have been made to create different forms of delivery for both agents. This review is focused on the latest developments in nanoparticles for the delivery of Dtx, Res and for the combined delivery of those two drugs. The aim of this review was also to summarize the synergistic mechanism of action of Dtx and Res on cancer cells. According to recent reports, Dtx and Res loaded in a nano-delivery system exhibit better efficiency in cancer treatment compared to free drugs. Also, the co-delivery of Dtx and Res in one actively targeted delivery system providing the simultaneous release of both drugs in cancer cells has a chance to fulfil the requirements of effective anticancer therapy and reduce limitations in therapy caused by multidrug resistance (MDR).

The Roles of microRNAs in Cancer Multidrug Resistance

Simple Summary

The resistance of neoplastic cells to multiple drugs is a serious problem in cancer chemotherapy. The molecular causes of multidrug resistance in cancer are largely known, but less is known about the mechanisms by which cells deliver phenotypic changes that resist the attack of anticancer drugs. The findings of RNA interference based on microRNAs represented a breakthrough in biology and pointed to the possibility of sensitive and targeted regulation of gene expression at the post-transcriptional level. Such regulation is also involved in the development of multidrug resistance in cancer. The aim of the current paper is to summarize the available knowledge on the role of microRNAs in resistance to multiple cancer drugs.

Abstract

Cancer chemotherapy may induce a multidrug resistance (MDR) phenotype. The development of MDR is based on various molecular causes, of which the following are very common: induction of ABC transporter expression; induction/activation of drug-metabolizing enzymes; alteration of the expression/function of apoptosis-related proteins; changes in cell cycle checkpoints; elevated DNA repair mechanisms. Although these mechanisms of MDR are well described, information on their molecular interaction in overall multidrug resistance is still lacking. MicroRNA (miRNA) expression and subsequent RNA interference are candidates that could be important players in the interplay of MDR mechanisms. The regulation of post-transcriptional processes in the proteosynthetic pathway is considered to be a major function of miRNAs. Due to their complementarity, they are able to bind to target mRNAs, which prevents the mRNAs from interacting effectively with the ribosome, and subsequent degradation of the mRNAs can occur. The aim of this paper is to provide an overview of the possible role of miRNAs in the molecular mechanisms that lead to MDR. The possibility of considering miRNAs as either specific effectors or interesting targets for cancer therapy is also analyzed.

Influence of Polymer Structure and Architecture on Drug Loading and Redox-Triggered Release

Disulfide cross-linked nanoassemblies have attracted considerable attention as a drug delivery vehicle due to their responsiveness to the natural redox gradient in biology. Fundamentally understanding the factors that influence the drug loading capacity, encapsulation stability, and precise control of the liberation of encapsulated cargo would be profoundly beneficial to redox-responsive materials. Reported herein are block copolymer (BCP)-based self-cross-linked nanogels, which exhibit high drug loading capacity, high encapsulation stability, and controllable release kinetics. BCP nanogels show considerably higher loading capacity and better encapsulation stability than the random copolymer nanogels at micromolar glutathione concentrations. By partially substituting thiol-reactive pyridyl disulfide into the unreactive benzyl or butyl group, we observed opposite effects on the cross-linking process of BCP nanogels. We further studied the redox-responsive cytotoxicity of our drug-encapsulated nanogels in various cancer cell lines.

Novel nanomedicines to overcome cancer multidrug resistance

Chemotherapy remains a powerful tool to eliminate malignant cells. However, the efficacy of chemotherapy is compromised by the frequent emergence of intrinsic and acquired multidrug resistance (MDR). These chemoresistance modalities are based on a multiplicity of molecular mechanisms of drug resistance, including : 1) Impaired drug uptake into cancer cells; 2) Increased expression of ATP-binding cassette efflux transporters; 3) Loss of function of pro-apoptotic factors; 4) Enhanced DNA repair capacity; 5) Qualitative or quantitative alterations of specific cellular targets; 6) Alterations that allow cancer cells to tolerate adverse or stressful conditions; 7) Increased biotransformation or metabolism of anticancer drugs to less active or completely inactive metabolites; and 8) Intracellular and intercellular drug sequestration in well-defined organelles away from the cellular target. Hence, one of the major aims of cancer research is to develop novel strategies to overcome cancer drug resistance. Over the last decades, nanomedicine, which focuses on targeted delivery of therapeutic drugs into tumor tissues using nano-sized formulations, has emerged as a promising tool for cancer treatment. Therefore, nanomedicine has been introduced as a reliable approach to improve treatment efficacy and minimize detrimental adverse effects as well as overcome cancer drug resistance. With rationally designed strategies including passively targeted delivery, actively targeted delivery, delivery of multidrug combinations, as well as multimodal combination therapy, nanomedicine paves the way towards efficacious cancer treatment and hold great promise in overcoming cancer drug resistance. Herein, we review the recent progress of nanomaterials used in medicine, including liposomal nanoparticles, polymeric nanoparticles, inorganic nanoparticles and hybrid nanoparticles, to surmount cancer multidrug resistance. Finally, the future perspectives of the application of nanomedicine to reverse cancer drug resistance will be addressed.

Molecular Action of Polyphenols in Leukaemia and Their Therapeutic Potential

Leukaemia is a malignant disease of the blood. Current treatments for leukaemia are associated with serious side-effects. Plant-derived polyphenols have been identified as potent anti-cancer agents and have been shown to work synergistically with standard chemotherapy agents in leukaemia cell lines. Polyphenols have multiple mechanisms of action and have been reported to decrease cell proliferation, arrest cell cycle and induce apoptosis via the activation of caspase (3, 8 and 9); the loss of mitochondrial membrane potential and the release of cytochrome c. Polyphenols have been shown to suppress activation of transcription factors, including NF-kB and STAT3. Furthermore, polyphenols have pro-oxidant properties, with increasing evidence that polyphenols inhibit the antioxidant activity of glutathione, causing oxidative DNA damage. Polyphenols also induce autophagy-driven cancer cell death and regulate multidrug resistance proteins, and thus may be able to reverse resistance to chemotherapy agents. This review examines the molecular mechanism of action of polyphenols and discusses their potential therapeutic targets. Here, we discuss the pharmacological properties of polyphenols, including their anti-inflammatory, antioxidant, anti-proliferative, and anti-tumour activities, and suggest that polyphenols are potent natural agents that can be useful therapeutically; and discuss why data on bioavailability, toxicity and metabolism are essential to evaluate their clinical use.

Ibuprofen as an emerging pollutant on non-target aquatic invertebrates: Effects on Chironomus riparius

The concern about pharmaceuticals has been increased over the last decade due to their burgeoning consumption. Ibuprofen has an extensive presence in surface water with risks for the aquatic biota. This study focuses on the effects of ibuprofen at environmental concentrations on the survival, transcriptional level, and enzymatic activity for 24, 96 h on Chironomus riparius. Ibuprofen developed a substantial effect on survival by all the conditions. mRNA levels of EcR, Dronc, and Met (endocrine system), hsp70, hsp24, and hsp27 (stress response), and Proph and Def (immune system) were modified, joined to increased GST and PO activity. The results confirmed alterations on the development of C. riparius, as well as two essential mechanisms, involved in protection against external toxicological challenge. Ibuprofen poses an incipient risk to C. riparius and could at an organismal level by compromising their survival, development, and ability to respond to adverse conditions on the future populations.

Integral Membrane Enzymes in Eicosanoid Metabolism: Structures, Mechanisms and Inhibitor Design

Eicosanoids are potent lipid mediators involved in central physiological processes such as hemostasis, renal function and parturition. When formed in excess, eicosanoids become critical players in a range of pathological conditions, in particular pain, fever, arthritis, asthma, cardiovascular disease and cancer. Eicosanoids are generated via oxidative metabolism of arachidonic acid along the cyclooxygenase (COX) and lipoxygenase (LOX) pathways. Specific lipid species are formed downstream of COX and LOX by specialized synthases, some of which reside on the nuclear and endoplasmic reticulum, including mPGES-1, FLAP, LTC4 synthase, and MGST2. These integral membrane proteins are members of the family "membrane-associated proteins in eicosanoid and glutathione metabolism" (MAPEG). Here we focus on this enzyme family, which encompasses six human members typically catalyzing glutathione dependent transformations of lipophilic substrates. Enzymes of this family have evolved to combat the topographical challenge and unfavorable energetics of bringing together two chemically different substrates, from cytosol and lipid bilayer, for catalysis within a membrane environment. Thus, structural understanding of these enzymes are of utmost importance to unravel their molecular mechanisms, mode of substrate entry and product release, in order to facilitate novel drug design against severe human diseases.

ROS-Mediated Therapeutic Strategy in Chemo-/Radiotherapy of Head and Neck Cancer

Head and neck cancer is a highly genetic and metabolic heterogeneous collection of malignancies of the lip, oral cavity, salivary glands, pharynx, esophagus, paranasal sinuses, and larynx with five-year survival rates ranging from 12% to 93%. Patients with head and neck cancer typically present with advanced stage III, IVa, or IVb disease and are treated with comprehensive modality including chemotherapy, radiotherapy, and surgery. Despite advancements in treatment modality and technique, noisome recurrence, invasiveness, and resistance as well as posttreatment complications severely influence survival rate and quality of life. Thus, new therapeutic strategies are urgently needed that offer enhanced efficacy with less toxicity. ROS in cancer cells plays a vital role in regulating cell death, DNA repair, stemness maintenance, metabolic reprogramming, and tumor microenvironment, all of which have been implicated in resistance to chemo-/radiotherapy of head and neck cancer. Adjusting ROS generation and elimination to reverse the resistance of cancer cells without impairing normal cells show great hope in improving the therapeutic efficacy of chemo-/radiotherapy of head and neck cancer. In the current review, we discuss the pivotal and targetable redox-regulating system including superoxide dismutases (SODs), tripeptide glutathione (GSH), thioredoxin (Trxs), peroxiredoxins (PRXs), nuclear factor erythroid 2-related factor 2/Kelch-like ECH-associated protein 1 (Nrf2/keap1), and mitochondria electron transporter chain (ETC) complexes and their roles in regulating ROS levels and their clinical significance implicated in chemo-/radiotherapy of head and neck cancer. We also summarize several old drugs (referred to as the non-anti-cancer drugs used in other diseases for a long time) and small molecular compounds as well as natural herbs which effectively modulate cellular ROS of head and neck cancer to synergize the efficacy of conventional chemo-/radiotherapy. Emerging interdisciplinary techniques including photodynamic, nanoparticle system, and Bio-Electro-Magnetic-Energy-Regulation (BEMER) therapy are promising measures to broaden the potency of ROS modulation for the benefit of chemo-/radiotherapy in head and neck cancer.

Molecular Cloning and Characterization of Five Glutathione S-Transferase Genes and Promoters from Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae) and Their Response to Tannic Acid Stress

Plants accumulate phenolic compounds such as tannic acid to resist insect herbivores. The survival of insects exposed to toxic secondary metabolites depends on the detoxification metabolism mediated by limited groups of glutathione S-transferases (GSTs). Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae) is an important foliar pest of poplar trees. GSTs play an important role in xenobiotic detoxification in M. troglodyta. Five GST genes were identified in M. troglodyta and were classified into five different cytosolic GST classes, delta, omega, sigma, theta, and zeta. Real-time fluorescent quantitative polymerase chain reaction (qPCR) was used to determine the mRNA expression of the five cloned GSTs in the midguts and fat bodies of M. troglodyta. The mRNA expression of the five GSTs was significantly induced when M. troglodyta was exposed to tannic acid. To further understand the tannic acid regulatory cascade, the 5′-flanking promoter sequences of the five MtGSTs were isolated by genome walking methods, and the promoters were very active and induced by tannic acid. In summary, the induction of GST mRNA expression was due to the response of five MtGST promoters to tannic acid. Therefore, MtGST promoters play an important role in the regulation of GST transcription.

In Vitro Inhibition Effect and Molecular Docking Study of Curcumin, Resveratrol, and Quercetin on Human Erythrocyte Glutathione Transferase

Background:

Chemotherapy has shown varying success rates in the treatment of metastatic cancer in the last 50 years. One of the problems in the use of many chemotherapeutic agents is to increase the expression of glutathione transferase enzyme (GST; EC 2.5.1.18). Therefore, the development of GST inhibitors is important to improve the effectiveness of antitumor drugs and to overcome multi-drug resistance.

Introduction:

Glutathione S-transferases (GSTs) are a major member of enzymes serving in the detoxification of exogenous and endogenous substances. But, it has been reported that GSTs are overexpressed in many tumour cells, and it has been found to be related to developing resistance to anticancer drugs by these cells. The development of GST inhibitors is important to increase the efficacy of antitumor drugs and overcome multi-drug resistance. The aim of our study was to investigate the effect of natural compounds including curcumin, resveratrol, and quercetin on GST enzyme activity. We also aimed to specify inhibition mechanism of the compounds on human erythrocytes GST (hGST) with in silico study.

Method:

GST was purified from human erythrocytes using affinity chromatography (glutathione agarose). The enzyme purity was checked with SDS-PAGE. After the inhibitory effect of the curcumin, quercetin, resveratrol was investigated. Lastly, inhibition mechanisms of these natural compound were identified with induced-fit docking method.

Result:

GST was purified with 19.31% yield from human erythrocytes. In inhibition studies, Ki values of curcumin, quercetin, resveratrol were determined as 0.0021 ± 0.0008, 0.0257 ± 0.0011, 663.3301 ± 0.0936 µM respectively. According to our results, all natural products showed the inhibition effect and the order of inhibition is as follows: curcumin ˃ quercetin ˃ resveratrol.

Conclusion:

According to the results of the in vitro and in silico studies, it can be said that curcumin, quercetin, resveratrol are the inhibitors of human erythrocyte GST. In conclusion, these observations may be of great importance for the potential use of these natural compounds as chemopreventive agents.

Glutathione S-transferase omega 1 inhibition activates JNK-mediated apoptotic response in breast cancer stem cells

Glutathione S-transferase omega 1 (GSTO1) contributes to the inactivation of a wide range of drug compounds via conjugation to glutathione during phase reactions. Chemotherapy-induced GSTO1 expression in breast cancer cells leads to chemoresistance and promotes metastasis. In search of novel GSTO1 inhibitors, we identified S2E, a thia-Michael adduct of sulfonamide chalcone with low LC₅₀ (3.75 ± 0.73 μm) that binds to the active site of GSTO1, as revealed by molecular docking (glide score: -8.1), cellular thermal shift assay and fluorescence quenching assay (K_b  ≈ 10 × 10⁵  mol·L^-1 ). Docking studies confirmed molecular interactions between GSTO1 and S2E, and identified the hydrogen bond donor Val-72 (2.14 Å) and hydrogen bond acceptor Ser-86 (2.77 Å). Best pharmacophore hypotheses could effectively map S2E and identified the 4-methyl group of the benzene sulfonamide ring as crucial to its anti-cancer activity. Lack of a thiophenyl group in another analog, 2e, reduced its efficacy as observed by cytotoxicity and pharmacophore matching. Furthermore, GSTO1 inhibition by S2E, along with tamoxifen, led to a significant increase in apoptosis and decreased migration of aggressive MDA-MB-231 cells, as well as significantly decreased migration, invasion and mammosphere formation in sorted breast cancer stem cells (CSCs, CD24^- /CD44⁺ ). GSTO1 silencing in breast CSCs also significantly increased apoptosis and decreased migration. Mechanistically, GSTO1 inhibition activated the c-Jun N-terminal kinase stress kinase, inducing a mitochondrial apoptosis signaling pathway in breast CSCs via the pro-apoptotic proteins BAX, cytochrome c and cleaved caspase 3. Our study elucidated the role of the GSTO1 inhibitor S2E as a potential therapeutic strategy for preventing chemotherapy-induced breast CSC-mediated cancer metastasis and recurrence.

Genome-wide identification and expression of the entire 52 glutathione S-transferase (GST) subfamily genes in the Cu2+-exposed marine copepods Tigriopus japonicus and Paracyclopina nana

In this study, the entire glutathione S-transferases (GSTs), the major phase II detoxification enzyme, were identified in two marine copepod species Tigriopus japonicus and Paracyclopina nana. The genome-wide identification of GSTs in T. japonicus and P. nana resulted in 32 and 20 GSTs in total, respectively. Among the identified GSTs, two specific classes of GSTs, specifically sigma and delta/epsilon GSTs were the dominant form of cytosolic GSTs in T. japonicus, while delta/epsilon and mu classes were dominant cytosolic GSTs in P. nana. In addition, Membrane-Associated Proteins in Eicosanoid and Glutathione metabolism (MAPEG) family were found in relatively higher proportion compared to other classes. Moreover, sigma, delta/epsilon, and microsomal GSTs have shown to expand through tandem duplication. To validate the detoxification function of the identified GSTs, both copepods were exposed to copper (Cu²⁺) and the reactive oxygen species (ROS) level and GST activity were measured. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in two marine copepod species and their important role in marine environmental ecotoxicology.

Glutathione Transferases: Potential Targets to Overcome Chemoresistance in Solid Tumors

Multifunctional enzymes glutathione transferases (GSTs) are involved in the development of chemoresistance, thus representing a promising target for a novel approach in cancer treatment. This superfamily of polymorphic enzymes exhibits extraordinary substrate promiscuity responsible for detoxification of numerous conventional chemotherapeutics, at the same time regulating signaling pathways involved in cell proliferation and apoptosis. In addition to upregulated GST expression, different cancer cell types have a unique GST signature, enabling targeted selectivity for isoenzyme specific inhibitors and pro-drugs. As a result of extensive research, certain GST inhibitors are already tested in clinical trials. Catalytic properties of GST isoenzymes are also exploited in bio-activation of specific pro-drugs, enabling their targeted accumulation in cancer cells with upregulated expression of the appropriate GST isoenzyme. Moreover, the latest approach to increase specificity in treatment of solid tumors is development of GST pro-drugs that are derivatives of conventional anti-cancer drugs. A future perspective is based on the design of new drugs, which would selectively target GST overexpressing cancers more prone to developing chemoresistance, while decreasing side effects in off-target cells.

Non-Coding RNAs and Resistance to Anticancer Drugs in Gastrointestinal Tumors

Non-coding RNAs are important regulators of gene expression and transcription. It is well established that impaired non-coding RNA expression especially the one of long non-coding RNAs and microRNAs is involved in a number of pathological conditions including cancer. Non-coding RNAs are responsible for the development of resistance to anticancer treatments as they regulate drug resistance-related genes, affect intracellular drug concentrations, induce alternative signaling pathways, alter drug efficiency via blocking cell cycle regulation, and DNA damage response. Furthermore, they can prevent therapeutic-induced cell death and promote epithelial-mesenchymal transition (EMT) and elicit non-cell autonomous mechanisms of resistance. In this review, we summarize the role of non-coding RNAs for different mechanisms resulting in drug resistance (e.g., drug transport, drug metabolism, cell cycle regulation, regulation of apoptotic pathways, cancer stem cells, and EMT) in the context of gastrointestinal cancers.

Drug metabolizing enzymes and their inhibitors' role in cancer resistance

Despite continuous research on chemotherapeutic agents, different mechanisms of resistance have become a major pitfall in cancer chemotherapy. Although, exhaustive efforts are being made by several researchers to target resistance against chemotherapeutic agents, there is another class of resistance mechanism which is almost carrying on unattended. This class of resistance includes pharmacokinetics resistance such as efflux by ABC transporters and drug metabolizing enzymes. ABC transporters are the membrane bound proteins which are responsible for the movement of substrates through the cell membrane. Drug metabolizing enzymes are an integral part of phase-II metabolism that helps in the detoxification of exogenous, endogenous and xenobiotics substrates. These include uridine diphospho-glucuronosyltransferases (UGTs), glutathione-S-transferases (GSTs), dihydropyrimidine dehydrogenases (DPDs) and thiopurine methyltransferases (TPMTs). These enzymes may affect the role of drugs in both positive as well negative manner, depending upon the type of tissue and cells present and when present in tumors, can result in drug resistance. However, the underlying mechanism of resistance by drug metabolizing enzymes is still not clear. Here, we have tried to cover various aspects of these enzymes in relation to anticancer drugs.

Identification of Novel Pathways of Osimertinib Disposition and Potential Implications for the Outcome of Lung Cancer Therapy

Purpose: Osimertinib is a third-generation inhibitor of the epidermal growth factor receptor used in treatment of non-small cell lung cancer. A full understanding of its disposition and capacity for interaction with other medications will facilitate its effective use as a single agent and in combination therapy.Experimental Design: Recombinant cytochrome P450s and liver microsomal preparations were used to identify novel pathways of osimertinib metabolism in vitro A panel of knockout and mouse lines humanized for pathways of drug metabolism were used to establish the relevance of these pathways in vivoResults: Although some osimertinib metabolites were similar in mouse and human liver samples there were several significant differences, in particular a marked species difference in the P450s involved. The murine Cyp2d gene cluster played a predominant role in mouse, whereas CYP3A4 was the major human enzyme responsible for osimertinib metabolism. Induction of this enzyme in CYP3A4 humanized mice substantially decreased circulating osimertinib exposure. Importantly, we discovered a further novel pathway of osimertinib disposition involving CPY1A1. Modulation of CYP1A1/CYP1A2 levels markedly reduced parent drug concentrations, significantly altering metabolite pharmacokinetics (PK) in humanized mice in vivoConclusions: We demonstrate that a P450 enzyme expressed in smokers' lungs and lung tumors has the capacity to metabolise osimertinib. This could be a significant factor in defining the outcome of osimertinib treatment. This work also illustrates how P450-humanized mice can be used to identify and mitigate species differences in drug metabolism and thereby model the in vivo effect of critical metabolic pathways on anti-tumor response. Clin Cancer Res; 24(9); 2138-47. ©2018 AACR.

Nrf2 is the key to chemotherapy resistance in MCF7 breast cancer cells under hypoxia

Hypoxia leads to reactive oxygen species (ROS) imbalance, which is proposed to associate with drug resistance and oncogenesis. Inhibition of enzymes of antioxidant balancing system in tumor cells was shown to reduce chemoresistance under hypoxia. However, the underlying mechanism remains unknown. The key regulator of antioxidant balancing system is nuclear factor erythroid 2-related factor 2 (NFE2L2, Nrf2). In this study, we showed that hypoxia induced ROS production and increased the Nrf2 activity. Nrf2 activation increased levels of its downstream target antioxidant enzymes, including GCLC and GCLM. The Nrf2-overexpressing also confers chemo-resistant MCF7 cells under normoxia. The in vivo mouse model also demonstrated that the chemical inhibition of Nrf2 can increase cisplatin (CDDP) cytotoxicity. Together, these results showed that Nrf2 serves as a key regulator in chemotherapeutic resistance under hypoxia through ROS-Nrf2-GCLC-GSH pathway. Therefore, targeting Nrf2 can be a potential treatment for hypoxia-induced drug resistance in breast cancer cells.

Dead-end complex, lipid interactions and catalytic mechanism of microsomal glutathione transferase 1, an electron crystallography and mutagenesis investigation

Microsomal glutathione transferase 1 (MGST1) is a detoxification enzyme belonging to the Membrane Associated Proteins in Eicosanoid and Glutathione Metabolism (MAPEG) superfamily. Here we have used electron crystallography of two-dimensional crystals in order to determine an atomic model of rat MGST1 in a lipid environment. The model comprises 123 of the 155 amino acid residues, two structured phospholipid molecules, two aliphatic chains and one glutathione (GSH) molecule. The functional unit is a homotrimer centered on the crystallographic three-fold axes of the unit cell. The GSH substrate binds in an extended conformation at the interface between two subunits of the trimer supported by new in vitro mutagenesis data. Mutation of Arginine 130 to alanine resulted in complete loss of activity consistent with a role for Arginine 130 in stabilizing the strongly nucleophilic GSH thiolate required for catalysis. Based on the new model and an electron diffraction data set from crystals soaked with trinitrobenzene, that forms a dead-end Meisenheimer complex with GSH, a difference map was calculated. The map reveals side chain movements opening a cavity that defines the second substrate site.

A Facile and Efficient Approach for the Production of Reversible Disulfide Cross-linked Micelles

Nanomedicine is an emerging form of therapy that harnesses the unique properties of particles that are nanometers in scale for biomedical application. Improving drug delivery to maximize therapeutic outcomes and to reduce drug-associated side effects are some of the cornerstones of present-day nanomedicine. Nanoparticles in particular have found a wide application in cancer treatment. Nanoparticles that offer a high degree of flexibility in design, application, and production based on the tumor microenvironment are projected to be more effective with rapid translation into clinical practice. The polymeric micellar nano-carrier is a popular choice for drug delivery applications. In this article, we describe a simple and effective protocol for synthesizing drug-loaded, disulfide cross-linked micelles based on the self-assembly of a well-defined amphiphilic linear-dendritic copolymer (telodendrimer, TD). TD is composed of polyethylene glycol (PEG) as the hydrophilic segment and a thiolated cholic acid cluster as the core-forming hydrophobic moiety attached stepwise to an amine-terminated PEG using solution-based peptide chemistry. Chemotherapy drugs, such as paclitaxel (PTX), can be loaded using a standard solvent evaporation method. The O2-mediated oxidation was previously utilized to form intra-micellar disulfide cross-links from free thiol groups on the TDs. However, the reaction was slow and not feasible for large-scale production. Recently, an H2O2-mediated oxidation method was explored as a more feasible and efficient approach, and it was 96 times faster than the previously reported method. Using this approach, 50 g of PTX-loaded, disulfide cross-linked nanoparticles have been successfully produced with narrow particle size distribution and high drug loading efficiency. The stability of the resulting micelle solution is analyzed using disrupting conditions such as co-incubation with a detergent, sodium dodecyl sulfate, with or without a reducing agent. The drug-loaded, disulfide cross-linked micelles demonstrated less hemolytic activity when compared to their non-cross-linked counterparts.

The Essential Role of H19 Contributing to Cisplatin Resistance by Regulating Glutathione Metabolism in High-Grade Serous Ovarian Cancer

Primary and acquired drug resistance is one of the main obstacles encountered in high-grade serous ovarian cancer (HGSC) chemotherapy. Cisplatin induces DNA damage through cross-linking and long integrated non-coding RNAs (lincRNAs) play an important role in chemical induced DNA-damage response, which suggests that lincRNAs may be also associated with cisplatin resistance. However, the mechanism of long integrated non-coding RNAs (lincRNAs) acting on cisplatin resistance is not well understood. Here, we showed that expression of lin-RECK-3, H19, LUCAT1, LINC00961, and linc-CARS2-2 was enhanced in cisplatin-resistant A2780-DR cells, while transcriptome sequencing showed decreased Linc-TNFRSF19-1 and LINC00515 expression. Additionally, we verified that different H19 expression levels in HGSC tissues showed strong correlation with cancer recurrence. H19 knockdown in A2780-DR cells resulted in recovery of cisplatin sensitivity in vitro and in vivo. Quantitative proteomics analysis indicated that six NRF2-targeted proteins, including NQO1, GSR, G6PD, GCLC, GCLM and GSTP1 involved in the glutathione metabolism pathway, were reduced in H19-knockdown cells. Furthermore, H19-knockdown cells were markedly more sensitive to hydrogen-peroxide treatment and exhibited lower glutathione levels. Our results reveal a previously unknown link between H19 and glutathione metabolism in the regulation of cancer-drug resistance.

MicroRNAs and Cancer Drug Resistance

The discovery of small regulatory noncoding RNAs revolutionized our thinking on gene regulation. The class of microRNAs (miRs), a group of small noncoding RNAs (20-22 nt in length) that bind imperfectly to the 3'-untranslated region of target mRNA, has been insistently implicated in several pathological conditions including cancer. Indeed, major hallmarks of cancer, such as cell differentiation, cell proliferation, cell cycle, cell survival, and cell invasion, has been described as being regulated by miRs. Recent studies have also implicated miRs in cancer drug resistance. Regardless of the several studies done until now, drug resistance still is a burden for cancer therapy and patients' outcome, often resulting in more aggressive tumors that tend to metastasize to distant organs. Hence, with this review, we aim to summarize the miRs that influence molecular pathways that are involved in cancer drug resistance, such as drug metabolism, drug influx/efflux, DNA damage response (DDR), epithelial-to-mesenchymal transition (EMT), and cancer stem cells.

Smokeless tobacco consumption impedes metabolic, cellular, apoptotic and systemic stress pattern: A study on Government employees in Kolkata, India

Smokeless tobacco (SLT) remains a threat amongst a large population across the globe and particularly in India. The oral use of tobacco has been implicated to cause physiological stress leading to extreme toxicological challenge. The study included 47 SLT-users and 44 non-users providing a spectrum of pathophysiological, clinico-biochemical, antioxidant parameters, cell cycle progression study of PBMC and morphological changes of red blood cells (RBC). The expressions of p53, p21, Bax, Bcl-2, IL-6, TNF- α, Cox-2, iNOS were analyzed from thirteen representative SLT-users and twelve non-users. Difference in CRP, random glucose, serum cholesterol, TG, HLDL-C, LDL-C, VLDL-C, neutrophil count, monocyte count, ESR, SOD (PBMC) and TBARS (RBC membrane) were found to be statistically significant (p < 0.05) between the studied groups. The current study confers crucial insight into SLT mediated effects on systemic toxicity and stress. This has challenged the metabolic condition leading to a rise in the inflammatory status, increased apoptosis and RBC membrane damage. The above findings were substantiated with metabolic, clinical and biochemical parameters. This is possibly the first ever in-depth report and remains an invaluable document on the fatal effects of SLT.

Hexamethoxylated Monocarbonyl Analogues of Curcumin Cause G2/M Cell Cycle Arrest in NCI-H460 Cells via Michael Acceptor-Dependent Redox Intervention

Curcumin, derived from the dietary spice turmeric, holds promise for cancer prevention. This prompts much interest in investigating the action mechanisms of curcumin and its analogues. Two symmetrical hexamethoxy-diarylpentadienones (1 and 2) as cucumin analogues were reported to possess significantly enhanced cytotoxicity compared with the parent molecule. However, the detailed mechanisms remain unclear. In this study, compounds 1 and 2 were identified as the G2/M cell cycle arrest agents to mediate the cytotoxicity toward NCI-H460 cells via Michael acceptor-dependent redox intervention. Compared with curcumin, they could more easily induce a burst of reactive oxygen species (ROS) and collapse of the redox buffering system. One possible reason is that they could more effectively target intracellular TrxR to convert this antioxidant enzyme into a ROS promoter. Additionally, they caused up-regulation of p53 and p21 and down-regulation of redox-sensitive Cdc25C along with cyclin B1/Cdk1 in a Michael acceptor- and ROS-dependent fashion. Interestingly, in comparison with compound 2, compound 1 displayed a relatively weak ability to generate ROS but increased cell cycle arrest activity and cytotoxicity probably due to its Michael acceptor-dependent microtubule-destabilizing effect and greater GST-inhibitory activity, as well as its enhanced cellular uptake. This work provides useful information for understanding Michael acceptor-dependent and redox-mediated cytotoxic mechanisms of curcumin and its active analogues.

Glutathione S-Transferase (GST) Gene Diversity in the Crustacean Calanus finmarchicus--Contributors to Cellular Detoxification

Detoxification is a fundamental cellular stress defense mechanism, which allows an organism to survive or even thrive in the presence of environmental toxins and/or pollutants. The glutathione S-transferase (GST) superfamily is a set of enzymes involved in the detoxification process. This highly diverse protein superfamily is characterized by multiple gene duplications, with over 40 GST genes reported in some insects. However, less is known about the GST superfamily in marine organisms, including crustaceans. The availability of two de novo transcriptomes for the copepod, Calanus finmarchicus, provided an opportunity for an in depth study of the GST superfamily in a marine crustacean. The transcriptomes were searched for putative GST-encoding transcripts using known GST proteins from three arthropods as queries. The identified transcripts were then translated into proteins, analyzed for structural domains, and annotated using reciprocal BLAST analysis. Mining the two transcriptomes yielded a total of 41 predicted GST proteins belonging to the cytosolic, mitochondrial or microsomal classes. Phylogenetic analysis of the cytosolic GSTs validated their annotation into six different subclasses. The predicted proteins are likely to represent the products of distinct genes, suggesting that the diversity of GSTs in C. finmarchicus exceeds or rivals that described for insects. Analysis of relative gene expression in different developmental stages indicated low levels of GST expression in embryos, and relatively high expression in late copepodites and adult females for several cytosolic GSTs. A diverse diet and complex life history are factors that might be driving the multiplicity of GSTs in C. finmarchicus, as this copepod is commonly exposed to a variety of natural toxins. Hence, diversity in detoxification pathway proteins may well be key to their survival.

Selective redox-responsive drug release in tumor cells mediated by chitosan based glycolipid-like nanocarrier

The redox responsive nanocarriers have made a considerable progress in achieving triggered drug release by responding to the endogenous occurring difference between the extra- and intra- cellular redox environments. Despite the promises, this redox difference exists both in normal and tumor tissue. So a non-selective redox responsive drug delivery system may result in an undesired drug release in normal cells and relevant side-effects. To overcome these limitations, we have developed a chitosan based glycolipid-like nanocarrier (CSO-ss-SA) which selectively responded to the reducing environment in tumor cells. The CSO-ss-SA showed an improved reduction-sensitivity which only fast degraded and released drug in 10mM levels of glutathione (GSH). The CSO-ss-SA could transport the drug fast into the human ovarian cancer SKOV-3 cells and human normal liver L-02 cells by internalization, but only fast release drug in SKOV-3 cells. By regulating the intracellular GSH concentration in SKOV-3 cells, it indicated that the cellular inhibition of the PTX-loaded CSO-ss-SA showed a positive correlation with the GSH concentration. The CSO-ss-SA was mainly located in the liver, spleen and tumor in vivo, which evidenced the passive tumor targeting ability. Despite the high uptake of liver and spleen, drug release was mainly occurred in tumor. PTX-loaded CSO-ss-SA achieved a remarkable tumor growth inhibition effect with rather low dose of PTX. This study demonstrates that a smartly designed glycolipid-like nanocarrier with selective redox sensitivity could serve as an excellent platform to achieve minimal toxicity and rapid intracellular drug release in tumor cells.

Jadomycin breast cancer cytotoxicity is mediated by a copper-dependent, reactive oxygen species-inducing mechanism

Jadomycins are natural products biosynthesized by the bacteria Streptomyces venezuelae which kill drug-sensitive and multidrug-resistant breast cancer cells in culture. Currently, the mechanisms of jadomycin cytotoxicity are poorly understood; however, reactive oxygen species (ROS)–induced DNA cleavage is suggested based on bacterial plasmid DNA cleavage studies. The objective of this study was to determine if and how ROS contribute to jadomycin cytotoxicity in drug-sensitive MCF7 (MCF7-CON) and taxol-resistant MCF7 (MCF7-TXL) breast cancer cells. As determined using an intracellular, fluorescent, ROS-detecting probe, jadomycins B, S, SPhG, and F dose dependently increased intracellular ROS activity 2.5- to 5.9-fold. Cotreatment with the antioxidant N-acetyl cysteine lowered ROS concentrations to below baseline levels and decreased the corresponding cytotoxic potency of the four jadomycins 1.9- to 3.3-fold, confirming a ROS-mediated mechanism. Addition of CuSO₄ enhanced, whereas addition of the Cu(II)-chelator d-penicillamine reduced, the ROS generation and cytotoxicity of each jadomycin. Specific inhibitors of the antioxidant enzymes, superoxide dismutase 1, glutathione S-transferase, and thioredoxin reductase, but not catalase, enhanced jadomycin-mediated ROS generation and anticancer activity. In conclusion, the results indicate that jadomycin cytotoxicity involves the generation of cytosolic superoxide via a Cu(II)-jadomycin reaction, a mechanism common to all jadomycins tested and observed in MCF7-CON and drug-resistant MCF7-TXL cells. The superoxide dismutase 1, glutathione, and peroxiredoxin/thioredoxin cellular antioxidant enzyme pathways scavenged intracellular ROS generated by jadomycin treatment. Blocking these antioxidant pathways could serve as a strategy to enhance jadomycin cytotoxic potency in drug-sensitive and multidrug-resistant breast cancers.

A self-assembled polymeric micellar immunomodulator for cancer treatment based on cationic amphiphilic polymers

Here, we report a self-assembled polymeric micellar immunomodulator (SPI) for enhanced cancer treatment based on cationic amphiphilic polymers. To obtain the cationic amphiphilic polymer, the hydrophobic all-trans-retinoic acid (ATRA) was conjugated with a hydrophilic low-molecular-weight PEI (LowPEI, Mn = 1.8 kDa). The ATRA-LowPEI conjugates could self-assemble in aqueous media, forming micelles with a strong positive charge (∼+40 mV) and particle sizes of ~70 nm. Compared to conventional therapeutic agents (e.g., cisplatin), the SPI exhibited enhanced anti-cancer activity regardless of drug resistance. After mechanistic in vitro cell death studies, we revealed that the mechanical disruptive force generated by the cationic charge of SPI primarily induced necrotic cell death. Furthermore, the organelle fragments induced by the necrotic cell death triggered antitumoral immune responses. Therefore, SPI induced synergistic effects of the cationic charge-induced necrosis and antitumoral immune responses could produce an effective cancer treatment. In addition, the SPI was shielded by hyaluronic acid (HA/SPI complex) to enhance its tumor selectivity in vivo. Finally, the HA/SPI complex accumulated selectively into tumor sites after systemic administration into tumor-bearing mice, exhibiting effective antitumoral effects without systemic toxicity. Therefore, this technology holds great potential for translation into a clinical cancer treatment.

Glutathione S-transferase P1 (GSTP1) directly influences platinum drug chemosensitivity in ovarian tumour cell lines

BACKGROUND

Chemotherapy response in ovarian cancer patients is frequently compromised by drug resistance, possibly due to altered drug metabolism. Platinum drugs are metabolised by glutathione S-transferase P1 (GSTP1), which is abundantly, but variably expressed in ovarian tumours. We have created novel ovarian tumour cell line models to investigate the extent to which differential GSTP1 expression influences chemosensitivity.

METHODS

Glutathione S-transferase P1 was stably deleted in A2780 and expression significantly reduced in cisplatin-resistant A2780DPP cells using Mission shRNA constructs, and MTT assays used to compare chemosensitivity to chemotherapy drugs used to treat ovarian cancer. Differentially expressed genes in GSTP1 knockdown cells were identified by Illumina HT-12 expression arrays and qRT-PCR analysis, and altered pathways predicted by MetaCore (GeneGo) analysis. Cell cycle changes were assessed by FACS analysis of PI-labelled cells and invasion and migration compared in quantitative Boyden chamber-based assays.

RESULTS

Glutathione S-transferase P1 knockdown selectively influenced cisplatin and carboplatin chemosensitivity (2.3- and 4.83-fold change in IC50, respectively). Cell cycle progression was unaffected, but cell invasion and migration was significantly reduced. We identified several novel GSTP1 target genes and candidate platinum chemotherapy response biomarkers.

CONCLUSIONS

Glutathione S-transferase P1 has an important role in cisplatin and carboplatin metabolism in ovarian cancer cells. Inter-tumour differences in GSTP1 expression may therefore influence response to platinum-based chemotherapy in ovarian cancer patients.

In vivo regulation of human glutathione transferase GSTP by chemopreventive agents

Relatively little progress has been made in determining the in vivo regulation of glutathione S-transferase P (GSTP), particularly the human enzyme hGSTP1, despite being identified as a significant factor in carcinogenesis and development of drug resistance in tumor cell lines. Here, we report the characterization of a transgenic reporter mouse that reveals how hGSTP1 is regulated in vivo by chemopreventive agents. Basal expression was found in crypts and villi of the small and large intestine, bronchiolar epithelial cells, the epidermis and hair follicles, gall bladder epithelium, choroid plexus, and biliary epithelium. Expression was induced in different tissues by the antioxidant chemopreventive agents ethoxyquin and butylated hydroxyanisole. However, genetic deletion of the Nrf2 transcription factor, which directs central genetic programs of detoxification and protection against oxidative stress, increased rather than attenuated GSTP1 expression. In vitro investigations with mouse embryonic fibroblasts revealed factors, in addition to Nrf2, that control the expression of GSTP1, offering further insights into regulation. The new reporter mouse described here provides a useful tool to gain deeper insights into the mechanisms of action of chemopreventive compounds and other environmental agents.

Carvacrol modulates instability of xenobiotic metabolizing enzymes and downregulates the expressions of PCNA, MMP-2, and MMP-9 during diethylnitrosamine-induced hepatocarcinogenesis in rats

Hepatocellular carcinoma is the fifth most common malignant tumor in the world, both in terms of incidence and mortality in Asian and Western countries. There are currently limited therapeutic regimens available for effective treatment of this cancer. Carvacrol is a predominant monoterpenoic phenol believed to impede cancer promotion and progression. The present study was conducted to decipher the role of carvacrol during diethylnitrosamine (DEN)-induced hepatocarcinogenesis in male wistar albino rats. Carvacrol (15 mg/kg body weight) suppressed the elevation of serum tumor marker enzymes, carcinoembryonic antigen, and α-feto protein induced by DEN. The activities of phase I enzymes increased markedly during DEN induction, but was found to be significantly lowered upon carvacrol treatment. On the contrary, the phase II enzymes decreased in DEN-administered animals, which was improved normalcy upon carvacrol-treated animals. DEN-administered animals showed increased mast cell counts, argyrophilic nucleolar organizing regions, proliferating cell nuclear antigen, and matrix metalloproteinases (MMPs-2/9), whereas carvacrol supplementation considerably suppressed all the above abnormalities. The results suggest that the carvacrol exhibited the potential anticancer activity by inhibiting cell proliferation and preventing metastasis in DEN-induced hepatocellular carcinogenesis.

Role of glutathione in cancer progression and chemoresistance

Glutathione (GSH) plays an important role in a multitude of cellular processes, including cell differentiation, proliferation, and apoptosis, and disturbances in GSH homeostasis are involved in the etiology and progression of many human diseases including cancer. While GSH deficiency, or a decrease in the GSH/glutathione disulphide (GSSG) ratio, leads to an increased susceptibility to oxidative stress implicated in the progression of cancer, elevated GSH levels increase the antioxidant capacity and the resistance to oxidative stress as observed in many cancer cells. The present review highlights the role of GSH and related cytoprotective effects in the susceptibility to carcinogenesis and in the sensitivity of tumors to the cytotoxic effects of anticancer agents.

The redox state of cytochrome c modulates resistance to methotrexate in human MCF7 breast cancer cells

Background

Methotrexate is a chemotherapeutic agent used to treat a variety of cancers. However, the occurrence of resistance limits its effectiveness. Cytochrome c in its reduced state is less capable of triggering the apoptotic cascade. Thus, we set up to study the relationship among redox state of cytochrome c, apoptosis and the development of resistance to methotrexate in MCF7 human breast cancer cells.

Results

Cell incubation with cytochrome c-reducing agents, such as tetramethylphenylenediamine, ascorbate or reduced glutathione, decreased the mortality and apoptosis triggered by methotrexate. Conversely, depletion of glutathione increased the apoptotic action of methotrexate, showing an involvement of cytochrome c redox state in methotrexate-induced apoptosis. Methotrexate-resistant MCF7 cells showed increased levels of endogenous reduced glutathione and a higher capability to reduce exogenous cytochrome c. Using functional genomics we detected the overexpression of GSTM1 and GSTM4 in methotrexate-resistant MCF7 breast cancer cells, and determined that methotrexate was susceptible of glutathionylation by GSTs. The inhibition of these GSTM isoforms caused an increase in methotrexate cytotoxicity in sensitive and resistant cells.

Conclusions

We conclude that overexpression of specific GSTMs, GSTM1 and GSTM4, together with increased endogenous reduced glutathione levels help to maintain a more reduced state of cytochrome c which, in turn, would decrease apoptosis, thus contributing to methotrexate resistance in human MCF7 breast cancer cells.

Inhibition and induction of glutathione S-transferases by flavonoids: possible pharmacological and toxicological consequences

Many studies reviewed herein demonstrated the potency of some flavonoids to modulate the activity and/or expression of glutathione S-transferases (GSTs). Because GSTs play a crucial role in the detoxification of xenobiotics, their inhibition or induction may significantly affect metabolism and biological effects of many drugs, industrials, and environmental contaminants. The effect of flavonoids on GSTs strongly depends on flavonoid structure, concentration, period of administration, as well as on GST isoform and origin. Moreover, the results obtained in vitro are often contrary to the vivo results. Based on these facts, the revelation of important flavonoid-drug or flavonoid-pollutant interaction has been complicated. However, it should be borne in mind that ingestion of certain flavonoids in combination with drugs or pollutants (e.g., acetaminophen, simvastatin, cyclophosphamide, cisplatine, polycyclic aromatic hydrocarbons, chlorpyrifos, acrylamide, and isocyanates), which are GST substrates, could have significant pharmacological and toxicological consequences. Although reasonable consumptions of a flavonoids-rich diet (that may lead to GST induction) are mostly beneficial, the uncontrolled intake of high concentrations of certain flavonoids (e.g., quercetin and catechins) in dietary supplements (that may cause GST inhibition) may threaten human health.

Unique structure and regulation of the nematode detoxification gene regulator, SKN-1: implications to understanding and controlling drug resistance

Nematodes parasitize an alarming number of people and agricultural animals globally and cause debilitating morbidity and mortality. Anthelmintics have been the primary tools used to control parasitic nematodes for the past several decades, but drug resistance is becoming a major obstacle. Xenobiotic detoxification pathways defend against drugs and other foreign chemicals in diverse organisms, and evidence is accumulating that they play a role in mediating resistance to anthelmintics in nematodes. Related antioxidation pathways may also provide filarial parasites with protection against host free-radical-mediated immune responses. Upstream regulatory pathways have received almost no attention in nematode parasites, despite their potential to coregulate multiple detoxification and antioxidation genes. The nuclear eurythroid 2-related factor 2 (NRF2) transcription factor mediates inducible detoxification and antioxidation defenses in mammals, and recent studies have demonstrated that it promotes multidrug resistance in some human tumors. Recent studies in the free-living model nematode, Caenorhabditis elegans, have defined the homologous transcription factor, SKN-1, as a master regulator of detoxification and antioxidation genes. Despite similar functions, SKN-1 and NRF2 have important differences in structure and regulatory pathways. Protein alignment and phylogenetic analyses indicate that these differences are shared among many nematodes, making SKN-1 a candidate for specifically targeting nematode detoxification and antioxidation.

Naturally occurring flavonoids as inhibitors of purified cytosolic glutathione S-transferase

Flavonoids are known to modulate catalytic activity and expression of various enzymes. Glutathione S-transferases (GSTs) are the important biotransformation enzymes defending cells against potentially toxic xenobiotics. Therefore, the modulation of GST activity may influence detoxification of xenobiotics. The aim of this study was to evaluate the in vitro inhibitory activity of several dietary flavonoids towards purified equine liver cytosolic GST. Pure GST was incubated in the presence or absence of flavonoids (10 nM-100 µM), its activity was assayed using 1-chloro-2,4-dinitrobenzene (CDNB) as a substrate, and half maximal inhibitory concentrations (IC(50)) were determined. The obtained results were confirmed by GST activity staining of native polyacrylamide gel electrophoresis (PAGE) gels. For the most potent inhibitor, the inhibition kinetics study was performed. From 24 flavonoids tested, the most potent GST inhibitor was gallocatechin gallate (IC(50) = 1.26 µM). The inhibition kinetics of this compound followed noncompetitive mechanism versus both glutathione (K(i) = 35.9 µM) and CDNB (K(i) = 34.1 µM). The inhibitory potency of different flavonoids for GST activity depended mainly on the pattern of hydroxylation and number of hydroxyl groups in the ring B. Especially, pyrogallol-type catechins with 3-OH group esterified with gallic acid showed strong potential to inhibit GST in vitro.

Chemopreventive efficacy of geraniol against 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The status of lipid peroxidation, antioxidants, and detoxification enzymes were used as biochemical end points to assess the chemopreventive potential of geraniol, a monoterpene, in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. Topical application of 0.5% DMBA in liquid paraffin, three times a week, for 14 weeks developed well-differentiated squamous cell carcinoma in the buccal pouch of golden Syrian hamsters. Although 100% tumor formation was noticed in hamsters treated with DMBA alone, intragastric administration of geraniol, at a dose of 250 mg/kg body weight (b.w.) to DMBA-treated hamster completely prevented the formation of oral tumors. Furthermore, geraniol significantly reduced lipid peroxidation by-products and improved the status of enzymatic and non-enzymatic antioxidants as well as modulated the status of phase I and phase II detoxification enzymes, favoring the excretion of carcinogenic metabolite, during DMBA-induced oral carcinogenesis. The present study concludes that the chemopreventive potential of geraniol relies on its anti-lipid peroxidative and antioxidant function as well as modulatory effects on phase I and II detoxification enzymes to excrete the carcinogenic metabolite, during DMBA-induced hamster buccal pouch carcinogenesis.

Knockout and transgenic mice in glutathione transferase research

Glutathione transferases (GSTs) are a multigene family of ubiquitously expressed, polymorphic enzymes responsible for the metabolism of a wide range of both endogenous and exogenous substrates, play a central role in the adaptive response to chemical and oxidative stress, and are subject to regulation by a range of structurally unrelated chemicals. In this review, we present a current summary of knockout mouse models in the GST field, discussing some of the issues pertaining to orthologous proteins between mice and humans, the potential confounding issues related to genetic background, and also cover new transgenic models in the increasingly important area of humanization.

Proteomic analyses of Caenorhabditis elegans dauer larvae and long-lived daf-2 mutants implicates a shared detoxification system in longevity assurance

The insulin/insulin-like growth factor-1 (IGF-1) signaling system is a public regulator of aging in the model animals Caenorhabditis elegans, Drosophila melanogaster, and Mus musculus. For the first time, proteomic analyses of the environmentally resistant and 'nonaging' C. elegans dauer stage and long-lived daf-2 mutants has provided a unique insight into the protein changes which mediate survival against endogenously produced toxins. These changes support a diversion of energy consumption away from anabolic processes toward enhanced cellular maintenance and detoxification processes as previously described by the 'Green Theory of Aging'. Important components of this enhanced longevity system identified in this proteomics study include the alpha-crystallin family of small heat shock proteins, anti-ROS defense systems and cellular phase II detoxification (in daf-2 only). Among those proteins involved in phase II cellular detoxification that were significantly upregulated was a Pi-class glutathione transferase (GST) CE00302. Targeting this GST with RNAi revealed compensatory regulation within the Pi-class GSTs. Furthermore, a recombinant form of the GST protein was found to detoxify and/or bind short-chain aldehydic natural toxic products of lipid peroxidation and long-chained fatty-acids at physiologically relevant concentrations, which may indicate a role in longevity.

Chemopreventive and antioxidant efficacy of (6)-paradol in 7,12-dimethylbenz(a)anthracene induced hamster buccal pouch carcinogenesis

The present study evaluated the chemopreventive potential of (6)-paradol, a pungent phenolic constituent of ginger, on 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. The mechanistic pathway for the chemopreventive potential of (6)-paradol was evaluated by measuring the status of tumor incidence, volume and burden as well as by analyzing the status of phase II detoxification agents, lipid peroxidation and antioxidants. Oral squamous cell carcinoma was induced in hamster buccal pouches by painting them with 0.5% DMBA in liquid paraffin three times a week for 14 weeks. We observed 100% tumor formation with marked biochemical abnormalities in tumor-bearing animals compared to control animals. Oral administration of 30 mg/kg b.w. (6)-paradol to DMBA-treated hamsters on alternate days from DMBA painting for 14 weeks, significantly reduced the formation of tumors and improved the status of detoxification agents, lipid peroxidation and antioxidants. Therefore, the present study suggests that (6)-paradol has potent chemopreventive, anti-lipid peroxidative and antioxidant potentials as well as a modulating effect on phase II detoxification enzyme and reduced glutathione (GSH) in DMBA-induced hamster buccal pouch carcinogenesis.