Inhibition Of Glutathione S-transferase Research Articles

Oral Ezatiostat HCl (Telintra), a Glutathione Analog Prodrug GSTP1-1 Inhibitor, for Treatment of Patients with Myeloid Growth Factor-Resistant Idiopathic Chronic Neutropenia (ICN)

AbstractAbstract 4394 Introduction:Idiopathic chronic neutropenia (ICN) is a group of diseases characterized by low circulating neutrophils, recurrent fevers, mucosal inflammation, and systemic infections. The risk of complications is inversely proportional to the absolute neutrophil count (ANC), with the most severe occurring with ANC of < 0.5 × 109/L. Most patients respond to daily s.c. administration of granulocyte colony stimulating factors (G-CSF); however, some patients do not respond. Patients undergoing G-CSF therapy also often have bone and muscle pain, thrombocytopenia and splenomegaly, complicating therapy. Ezatiostat, a glutathione S-transferase (GST) inhibitor that activates Jun kinase, promoting growth and maturation of hematopoietic progenitors, is an investigational agent in development for treatment of ICN. This report describes 4 patients with longstanding ICN who responded to ezatiostat, all of whom prior to treatment had frequent hospitalizations for sepsis, prolonged courses of antibiotics and poor response to myeloid growth factors. Methods:Patients (pts) with severe ICN and inadequate ANC response to G-CSF were enrolled in this phase 2 trial. After initial starting dose of 2000 mg in divided doses twice daily (b.i.d.) dose-equilibration over 4 weeks, pts were treated with ezatiostat daily for 3 weeks followed by 1 week off. Treatment was given until lack of ANC response or unacceptable toxicity. Clinical benefit was determined by ANC response, infection-free periods, antibiotic use and hospitalizations for infections. Results:Four female pts, age range 23–63, with median ANC of 200 (50–400) were enrolled. Patient 1 is 62 y.o. with longstanding history of infections and treatment with G-CSF. Before entering study, she had recurrent ear, labial, left thigh, pulmonary and sinus infections despite growth factor treatment, to which she had severe reactions. Baseline white blood cell (WBC)/ANC ratio was 2.2/0.7. WBC/ANC improved with ezatiostat for 4 mo to 3.62/1.71 and infections resolved. Patient 2, a 63 y.o. with ICN for 26 years, had a median baseline WBC/ANC on G-CSF treatment of 3.1/.180 and a history of multiple hospital admissions for sepsis, non-healing perineal and decubitus ulcers, and recurrent high fevers within 4 days of cessation of parenteral antibiotics, necessitating resumption. Post-ezatiostat treatment median ANC was 3.1 (range 1.6–3.75) with a persistent infection-free period of over 22 mo with no hospitalizations or antibiotic therapy required. Patient 3, a 23 y.o. with ICN since age 10, initially responded to G-CSF but stopped responding despite injections b.i.d., and ANC never rose above 1000. Her last hospitalization was for methicillin-resistant staphylococcus aureus skin infection, upper respiratory infection with cervical adenopathy, and oral ulcers. She had infections every 3 months and baseline WBC/ANC of 1.4/0.13. She had minimal response over 4 mo of observation, with highest values 2.65/0.92 and median ANC of 0.40, but had no further bacterial infection or use of G-CSF. Patient 4, a 39 y.o. with ICN of 10 years’ duration, had severe bone pain with G-CSF and responses were brief (1–2days). Previously, she had hospital admissions and emergency room visits 4–5 times a year and was ill 2–3 times a week with recurrent urinary tract infections, pneumonias (4–5 times per year), oral ulcers, sinus and gastrointestinal infections, furuncles, and infection after dental work. Baseline WBC/ANC was 1.23/0.20. Currently, her WBC/ANC is 1.50/0.26. While ANC did not increase, infection rate decreased and she had no ER visits or admissions for over 5 mo. She responded to a single 300 mcg dose of of G-CSF with an ANC of 1.0 for a week, suggesting re-sensitization to G-CSF. Most common ezatiostat-related adverse events were grade 1 nausea, abnormal urine/stool odor, and dysgeusia. Conclusions:Ezatiostat, a novel GSTP1-1 inhibitor and jun kinase modulator as treatment of patients with ICN and grade 4 neutropenia not responsive to myeloid growth factors, results in a durable ANC response and clinically significant reductions in serious infections. Results suggest a potential role for ezatiostat as an oral therapy alternative or adjunct to G-CSF in the treatment of ICN in patients who are not responsive to G-CSF. Response to this targeted therapy may also give insight into the pathophysiology of ICN and further study is warranted. Disclosures:Lyons:Telik, Inc.: Research Funding. Wilks:Telik, Inc.: Research Funding. Friedman:Telik, Inc.: Research Funding. Young:Telik, Inc.: Employment, Equity Ownership. Brown:Telik, Inc.: Employment, Equity Ownership.

Molinate quantification in environmental water by a glutathione-S-transferase based biosensor

A glutathione-S-transferase (GST) based biosensor was developed to quantify the thiocarbamate herbicide molinate in environmental water. The biosensor construction was based on GST immobilization onto a glassy carbon electrode via aminosilane–glutaraldehyde covalent attachment. The principle supporting the use of this biosensor consists of the GST inhibition process promoted by molinate. Differential pulse voltammetry was used to obtain a calibration curve for molinate concentration, ranging from 0.19 to 7.9mgL−1 and presenting a detection limit of 0.064mgL−1. The developed biosensor is stable, and reusable during 15 days. The GST-based biosensor was successfully applied to quantify molinate in rice paddy field floodwater samples. The results achieved with the developed biosensor were in accordance with those obtained by high performance liquid chromatography. The proposed device is suitable for screening environmental water analysis and, since no sample preparation is required, it can be used in situ and in real-time measurements.

Synthesis and Biological Study of Novel Indole-3-Imine-2-on Derivatives as Src Kinase and Glutathione S-Transferase Inhibitors

The aim of this study is to design and synthesize novel dual inhibitors of Src protein tyrosine kinase (PTK) and Glutathione S-transferases (GSTs), as a potential drug lead with therapeutic efficacy on cancer and immune disorders. The biological activity profiling of small molecule inhibitors via miniaturized biochemical techniques compatible with medium throughput screening and focused screening methodologies were performed. To determining the effects of small molecule inhibitors on Src kinase and Phase II detoxification enzyme GST isozymes in liver homogenates used to verify their roles in drug resistance mechanism for cancer chemotherapeutics. In this study, 14 indole-3-imine-2-on and N-benzyl indole-3-imine-2-on derivatives were synthesized for dual activities against Src and GST. The chemical structures and purities of compounds were verified by IR, 1H NMR, MASS spectroscopy, and elemental analysis. The compounds 2, 3 and 9 are found slightly active against both enzyme Src and GST.

Synthesis and Biological Study of Novel Indole-3-Imine-2-on Derivatives as Src Kinase and Glutathione S-Transferase Inhibitors

The aim of this study is to design and synthesize novel dual inhibitors of Src protein tyrosine kinase (PTK) and Glutathione S-transferases (GSTs), as a potential drug lead with therapeutic efficacy on cancer and immune disorders. The biological activity profiling of small molecule inhibitors via miniaturized biochemical techniques compatible with medium throughput screening and focused screening methodologies were performed. To determining the effects of small molecule inhibitors on Src kinase and Phase II detoxification enzyme GST isozymes in liver homogenates used to verify their roles in drug resistance mechanism for cancer chemotherapeutics. In this study, 14 indole-3-imine-2-on and N-benzyl indole-3-imine-2-on derivatives were synthesized for dual activities against Src and GST. The chemical structures and purities of compounds were verified by IR, 1H NMR, MASS spectroscopy, and elemental analysis. The compounds 2, 3 and 9 are found slightly active against both enzyme Src and GST. Keywords: Cancer, Src tyrosine kinase, Isatine, Glutathion-S-transferase, Drug resistance, Synthesis, tyrosine kinases, PTKs, xenobiotic lipophilic, SFK

151 Andrographolide Induces Cell Cycle Arrest in THP-1 Cancer Cell Line and Inhibits Glutathione S-transferase Enzyme Directly

151 Andrographolide Induces Cell Cycle Arrest in THP-1 Cancer Cell Line and Inhibits Glutathione S-transferase Enzyme Directly

Biochemical response to exposure to six textile dyes in early developmental stages of Xenopus laevis

The present study was undertaken to determine the toxic effect of a lethal concentration of six different commercially used textile dyes on the 46th stage of Xenopus laevis tadpoles. The tadpoles were exposed to Astrazon Red FBL, Astrazon Blue FGRL, Remazol Red RR, Remazol Turquoise Blue G-A, Cibacron Red FN-3G, and Cibacron Blue FN-R for 168 h in static test conditions, and thus, 168-h median lethal concentrations (LC(50)s) of each dye were determined to be 0.35, 0.13, 112, 7, 359, and 15.8 mg/L, respectively. Also, to evaluate the sublethal effects of each dye, tadpoles were exposed to different concentrations of dyes (with respect to 168-h LC(50)s) for 24 h. The alteration of selected enzyme activities was tested. For this aim, glutathione S-transferase (GST), carboxylesterase, and lactate dehydrogenase (LDH) were assayed. After dye exposure, the GST induction or inhibition and LDH induction indicated some possible mechanisms of oxidative stress and deterioration in aerobic respiration processes induced by the tested dyes. Findings of the study suggest that selected biomarker enzymes are useful in understanding the toxic mechanisms of these dyes in X. laevis tadpoles as early warning indicators. Therefore, these selected biomarkers may evaluate the effect of environmental factors, such as textile dye effluents and other industrial pollutants, on amphibians in biomonitoring studies.

Calix[4]arene-α-hydroxyphosphonic acids. Synthesis, stereochemistry, and inhibition of glutathione S-transferase

A series of dipropoxy-, tripropoxy- and tetrapropoxycalix(4)arenes bearing one or two fragments of α-hydroxymethylphosphonic acid at the upper rim of the macrocycle was prepared by the reaction of the corresponding mono- and di-formylcalixarenes with sodium salts of dialkyl phosphites or with trialkyl (tristrimethylsilyl)phosphites followed by dealkylation (desilylation) of the ester derivatives. The conformations of the macrocyclic skeleton and the stereoisomeric forms of the compounds obtained were investigated by 1 H NMR. The resulting α- hydroxymethylphosphonic acids were found to be able to inhibit the activity of glutathione S- transferase in vitro.

Variation of acephate susceptibility and correlation with esterase and glutathione S-transferase activities in field populations of the tarnished plant bug, Lygus lineolaris

The tarnished plant bug (TPB) has increasingly become an economically important pest of cotton. Heavy dependence on insecticides, particularly organophosphates and pyrethroids, for TPB control facilitated resistance development to multiple classes of insecticides. To better understand resistance and explore ways to monitor resistance in field populations, this study examined acephate susceptibility and the activities of two major detoxification enzymes in nine field populations collected in the Delta region of Mississippi and Arkansas in 2010. Two Arkansas populations from Reed and Backgate had 3.5- and 4.3-fold resistance to acephate, as compared to a susceptible laboratory strain. Extensive planting of cotton and heavy chemical sprays is a major driving force for resistance development to acephate in Mid-south cotton growing areas. Reduced susceptibility to acephate was highly correlated with elevated esterase activities. The acephate-resistant populations from Backgate, Lula, and Reed consistently had higher (up to 5.3-fold) esterase activities than susceptible populations. Regression analysis of LC50s with kinetic esterase activities revealed a significant polynomial quadratic relationship with R2 up to 0.89. Glutathione S-transferase (GST) also had elevated activity in most populations, but the variations of GST activities were not significantly correlated with changes of acephate susceptibility. Finally, examination of esterase and GST inhibitors indicated that suppression rates (up to 70%) by two esterase inhibitors in 2010 were slightly lower than those detected in 2006, and ethacrynic acid (EA) inhibited GST effectively in both years. Two other GST inhibitors (sulfobromophthalein and diethyl maleate) displayed significantly lower suppression rates in 2010 than those detected in 2006, suggesting a potential genetic shift in pest populations and a necessity of continued monitoring for insecticide resistance with both bioassay and biochemical approaches. Results indicated that using major detoxification enzyme activities for resistance monitoring may provide insight into acephate resistance in field populations of TPB.

Polychlorinated biphenyls and their different level metabolites as inhibitors of glutathione S-transferase isoenzymes

Research on the effects of polychlorinated biphenyl (PCB) toxicity tends to focus on commercial PCB congeners and parent PCBs themselves. However, studies have suggested that PCB metabolites may be more interesting than the parent compounds because of their high reactivity. As a key metabolic enzyme, glutathione S-transferases (GSTs) are responsible for detoxification by catalyzing the conjugation reaction of glutathione (GSH) to xenobiotics. Inhibition of GST activity indicates reduced detoxification ability. We investigated the inhibition of chicken liver GSTs by parent PCBs and their metabolites and observed dose-dependent inhibition in vitro; inhibitory efficiency declined in the order GSH-conjugate>mono-hydroxyl ≈ quinone ≈ hydroquinone>parent PCB. Structure–inhibitory activity relationship studies indicated that with the inhibitory activity greatly increases with the number of GSH moieties or chlorine substituents on the quinone ring. However, no significant linear relationship was observed for chlorine pattern changes on the phenyl ring. The reversibility of PCB metabolite inhibition of GSTs is discussed. PCB mono-hydroxyl, hydroquinone and quinone forms showed irreversible inhibition of GSTs, which suggests a mechanism involving covalent binding to cysteine residues in the GST active site. PCB glutathionyl conjugates showed reversible GST inhibition, implying non-covalent binding. Furthermore, reactive oxygen species did not significantly affect GST activity.

Virtual screening and in vitro assay of potential drug like inhibitors from spices against Glutathione-S-Transferase of Meloidogyne incognita.

Glutathione S-transferases (GSTs) enzymes are critical antioxidant and detoxification system responsible for long-term existence of nematodes in host species. Hence, 16 phytochemicals predicted and reported to have potential nematicidal activity have been docked to GST enzyme of Meloidogyne incognita to assess their binding affinity and inhibitory activity. In vitro effects of these phytochemicals from in silico results have been done for validation of docking studies and efficacy in GST inhibition of following compounds such as alpha- pinene, alpha- terpineol, beta- caryophyllene, capsaicin, cinnamic acid, citronellol, curcumin, eugenol, geraniol, isoeugenol, linalool, myristicin, neral, NVA (N-vanillylnonanamide), piperine, vanillin have been revealed. Nematode inhibition in vitro bioassay for selected compounds could conclude that maximum mortality was observed with highest concentrations of beta- caryophyllene (78%) followed by eugenol (61.6%), cinnamic acid (55%) and N-vanillylnonanamide (49%). These findings thus suggest that the above phytochemicals could be potentially developed as nematicidal molecules against M. incognita infections.

Anti-inflammatory functions of purpurogallin in LPS-activated human endothelial cells

Enzymatic oxidation of commercially available pyrogallol was efficiently transformed to an oxidative product, purpurogallin. Purpurogallin plays an important role in inhibiting glutathione S-transferase, xanthine oxidase, catechol O-methyltransferase activities and is effective in the cell protection of several cell types. However, the anti-inflammatory functions of purpurogallin are not well studied. Here, we determined the effects of purpurogallin on lipopolysaccharide (LPS)-mediated proinflammatory responses. The results showed that purpurogallin inhibited LPS-mediated barrier hyper-permeability, monocyte adhesion and migration and such inhibitory effects were significantly correlated with the inhibitory functions of purpurogallin on LPS-mediated cell adhesion molecules (vascular cell adhesion molecules, intracellular cell adhesion molecule, E-selectin). Furthermore, LPS-mediated nuclear factor-κB (NF-κB) and tumor necrosis factor-α (TNF-α) releases from HUVECs were inhibited by purpurogallin. Given these results, purpurogallin showed its anti-inflammatory activities and could be a candidate as a therapeutic agent for various systemic inflammatory diseases. [BMB reports 2012; 45(3): 200-205].

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 (IC50) 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 (IC50 = 1.26 µM). The inhibition kinetics of this compound followed noncompetitive mechanism versus both glutathione (Ki = 35.9 µM) and CDNB (Ki = 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.

Tributyltin induces oxidative stress and neuronal injury by inhibiting glutathione S-transferase in rat organotypic hippocampal slice cultures

Tributyltin (TBT) has been used as a heat stabilizer, agricultural pesticide and antifouling agents on ships, boats and fish-farming nets; however, the neurotoxicity of TBT has recently become a concern. TBT is suggested to stimulate the generation of reactive oxygen species (ROS) inside cells. The aim of this study was to determine the mechanism of neuronal oxidative injury induced by TBT using rat organotypic hippocampal slice cultures. The treatment of rat hippocampal slices with TBT induced ROS production, lipid peroxidation and cell death. Pretreatment with antioxidants such as superoxide dismutase, catalase or trolox, suppressed the above phenomena induced by TBT, indicating that TBT elicits oxidative stress in hippocampal slices, which causes neuronal cell death. TBT dose-dependently inhibited glutathione S-transferase (GST), but not glutathione peroxidase or glutathione reductase in the cytosol of rat hippocampus. The treatment of hippocampal slices with TBT decreased the GST activity. Pretreatment with reduced glutathione attenuated the reduction of GST activity and cell death induced by TBT, indicating that the decrease in GST activity by TBT is involved in hippocampal cell death. When hippocampal slices were treated with sulforaphane, the expression and activity of GST were increased. Notably, TBT-induced oxidative stress and cell death were significantly suppressed by pretreatment with sulforaphane. These results indicate that GST inhibition could contribute, at least in part, to the neuronal cell death induced by TBT in hippocampal slices. This study is the first report to show the link between neuronal oxidative injury and the GST inhibition elicited by TBT.

Assessment of cellular reduced glutathione content in Pseudokirchneriella subcapitata using monochlorobimane

The green alga Pseudokirchneriella subcapitata has been extensively used for the assessment of adverse impacts of pollutants. Glutathione is involved in antioxidant defence and drug detoxification. Intracellular reduced glutathione (GSH) concentration can be used as an indicator of the health of cells. This work describes a simple and fast fluorescent cell-based assay for the evaluation of intracellular GSH in the alga P. subcapitata, using monochlorobimane (mBCl). Metabolically active algal cells incubated with 50 μmol L−1 mBCl form fluorescent bimane–glutathione (B-SG) adducts that can be measured fluorometrically. The distribution of GSH (B-SG adducts) in whole cells can be observed by epifluorescence microscopy, in the form of blue fluorescent spots. Depletion of cellular GSH with iodoacetamide, inhibition of glutathione S-transferase with ethacrynic acid or heat-induced death of the cells inhibited the formation of fluorescent adducts in the presence of mBCl. The fluorometric assay, using the 96-well microplate format, was able to detect GSH depletion in algal cells. This cell-based assay can be used to evaluate decreases in GSH content due to exposure to toxicants. This assay is amenable to automation and may be useful in high-throughput toxicity screening using the alga P. subcapitata.

JS-K, a glutathione S-transferase-activated nitric oxide donor with antineoplastic activity in malignant gliomas.

Glutathione S-transferases (GSTs) control multidrug resistance and are upregulated in many cancers, including malignant gliomas. The diazeniumdiolate JS-K generates nitric oxide (NO) on enzymatic activation by glutathione and GST, showing promising NO-based anticancer efficacy. To evaluate the role of NO-based antitumor therapy with JS-K in U87 gliomas in vitro and in vivo. U87 glioma cells and primary glioblastoma cell lines were exposed to JS-K and a variety of inhibitors to study cell death by necrosis, apoptosis, and other mechanisms. GST expression was evaluated by immunocytochemistry, polymerase chain reaction, and Western blot, and NO release from JS-K was studied with a NO assay. The growth-inhibitory effect of JS-K was studied in a U87 xenograft model in vivo. Dose-dependent inhibition of cell proliferation was observed in human U87 glioma cells and primary glioblastoma cells in vitro. Cell death was partially induced by caspase-dependent apoptosis, which could be blocked by Z-VAD-FMK and Q-VD-OPH. Inhibition of GST by sulfasalazine, cGMP inhibition by ODQ, and MEK1/2 inhibition by UO126 attenuated the antiproliferative effect of JS-K, suggesting the involvement of various intracellular death signaling pathways. Response to JS-K correlated with mRNA and protein expression of GST and the amount of NO released by the glioma cells. Growth of U87 xenografts was reduced significantly, with immunohistochemical evidence for increased necrosis and apoptosis and reduced proliferation. Our data show for the first time the potent antiproliferative effect of JS-K in gliomas in vitro and in vivo. These findings warrant further investigation of this novel NO-releasing prodrug in gliomas.

Cloning and characterization of two glutathione S‐transferases from pyrethroid‐resistant Culex pipiens

The Marin strain of Culex pipiens Say is a pyrethroid-resistant population that was collected in Marin County, California, in 2001 and subsequently maintained in the laboratory under regular permethrin exposure. In this study, two cDNAs, CpGSTd1 and CpGSTd2, encoding glutathione S-transferase (GST) were cloned from Cx. pipiens Marin. Phylogenetic analysis of the deduced amino acid sequences, CpGSTD1 and CpGSTD2, of these genes indicated that they belong to the Delta class of insect GSTs. The nucleotide and deduced amino acid sequences of CpGSTd1 and CpGSTd2 were 59 and 48% identical respectively. CpGSTD1 and CpGSTD2 were expressed in Escherichia coli and purified by affinity chromatography. The recombinant GSTs exhibited unique selectivity towards the general GST substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB), and also differed in their sensitivity to known inhibitors of GSTs. CpGSTD1 exhibited peroxidase activity with cumene hydroperoxide, while CpGSTD2 appeared to lack this activity. CpGSTD1 was able to metabolize 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), while DDT metabolism by CpGSTD2 was not detectable. CpGSTD1 and CpGSTD2 showed no detectable metabolism of permethrin. Gene expression of CpGSTd1 and CpGSTd2 in Marin mosquitoes was elevated about twofold in comparison with that found in a pyrethroid-sensitive mosquito strain. The results indicate that CpGSTD1 and CpGSTD2 have unique biochemical characteristics, but they do not appear to play major roles in permethrin resistance in Marin mosquitoes.

Amitriptyline may have a supportive role in cancer treatment by inhibiting glutathione S-transferase pi (GST-π) and alpha (GST-α)

A tricyclic anti-depressant, amitriptyline, is a highly prescribed drug for cancer patients for mood elevation but there are limited studies about the interaction of amitriptyline with glutathione S-transferases pi (GST-π) and glutathione S-transferases alpha (GST-α). GST isozymes have been implicated in chemotherapeutic drug resistance. We demonstrated that the concentration dependent inhibition of GST-π and GST-α by amitriptyline followed inverse hyperbolic inhibition curves with IC50 values of 5.54 and 8.32 mM, respectively.When the varied substrate was GSH, amitriptyline inhibited both isozymes competitively and similar Ki values were found for GST-π (Ki = 1.61 ± 0.17 mM) and GST-α (Ki = 1.45 ± 0.20 mM). On the other hand, when the varied substrate was CDNB, the inhibition types were non-competitive for GST-π (Ki = 1.98 ± 0.31 mM) and competitive for GST-α (Ki = 1.57 ± 0.16 mM).Amitriptyline, in addition to its antidepressant effect, might also have a minor supportive role on the effectiveness of the anticancer drugs by decreasing their elimination through inhibiting GST-π and GST-α.

Distribution and Mechanism of α-Amanitin Tolerance in Mycophagous Drosophila (Diptera: Drosophilidae)

Many mycophagous species of Drosophila can tolerate the mushroom poison α-amanitin in wild mushrooms and in artificial diet. We conducted feeding assays with sixteen Drosophila species and α-amanitin in artificial diet to better determine the phylogenetic distribution of this tolerance. For eight tolerant and one related susceptible species, we sequenced the gene encoding the large subunit of RNA Polymerase II, which is the target site of α-amanitin. We found no differences in the gene that could account for differences in susceptibility to the toxin. We also conducted feeding assays in which α-amanitin was combined with chemical inhibitors of cytochrome P450s or glutathione S-transferases (GSTs) in artificial diet to determine if either of these enzyme families is involved in tolerance to α-amanitin. We found that an inhibitor of GSTs did not reduce tolerance to α-amanitin, but that an inhibitor of cytochrome P450s reduced tolerance in several species. It is possible that the same cytochrome P450 activity that produces tolerance of α-amanitin might produce tolerance of other mushroom toxins as well. If so, a general detoxification mechanism based on cytochrome P450s might answer the question of how tolerance to α-amanitin arose in mycophagous Drosophila when this toxin is found in relatively few mushrooms.

Gene Expression Studies May Identify Lower Risk Myelodysplastic Syndrome Patients Likely to Respond to Therapy with Ezatiostat Hydrochloride (TLK199)

Abstract 2779Interpretation of gene expression studies in MDS have been especially challenging due to the heterogeneity of the cell lineages that comprise the malignant clone. In attempting to overcome these difficulties we have used a bedside-to-bench approach to define an expression signature that may identify patients likely to respond. Ezatiostat hydrochloride (TLK199) is an inhibitor of glutathione S-transferase, an enzyme that is over expressed in many cancers, and has been shown in vitro to stimulate growth and differentiation of hematopoietic progenitor cells and to induce apoptosis in leukemia cells. Based on multilineage responses in low-Int1 MDS patients in our phase 2 study of oral TLK199, a multi institutional phase 2 study was conducted in low-Int1 patients. Response was evaluated by International Working Group (IWG 2006) criteria. Pre-therapy bone marrow mononuclear cells of patients treated with TLK199 were analyzed for gene expression on the Illumina HT12v4 whole genome array with IRB approval. RNA isolated from the marrow mononuclear cells was available on 9 responders (R) and 21 non-responders (NR). Five R and 13 NR were randomly chosen to create a training set with the intent to later use the remaining samples for model testing. We identified the top 100 differentially expressed genes using a sensitive metric based on the normalized mutual information. We also performed single-sample Gene Set Enrichment Analysis to find the most salient differences in terms of pathways and biological processes between R/NR. Of special note are the 4 microRNA s differentially expressed between R/NR. Three miRNAs are under-expressed (miR-129, 802 and 548e) and one (miR-155) is over-expressed in R. Reduced expression of miR-129 has been reported in solid tumors when over-expressed has been shown to have anti-proliferative activity in cell lines. SOX4 is a target gene for miR129 and reduced expression of miR-129 results in concomitant up-regulation of SOX4 mRNA which can function as both an oncogene and a tumor suppressor gene depending on tumor lineage. Over-expression of SOX4 inhibited cytokine induced granulocyte maturation in the myeloid 32Dcl3 cell line suggesting a possible role in MDS. MiR-802 targets the receptor for angiotensin II and when expression is decreased there is increased angiotensin II activity. It has recently been shown that angiotensin is a pro-inflammatory mediator that participates in apoptosis, angiogenesis and promotes mitochondrial dysfunction, all characteristics of MDS. In addition, the transcription factor ZFHX3, a predicted target of miR-802, is a negative regulator of c-MYB which has been shown to be up-regulated in all subtypes of MDS. Similarly, c-MYB is a predicted target of miR-155, which is over-expressed in TLK199 responders. MiR-155 was shown to be over-expressed in marrow cells of a subset of human AML patients. Of particular note are the studies showing that sustained expression of miR-155 in mouse hematopoietic stem cells cause a myeloproliferative/myelodysplastic disorder.Subsequent pathway analysis of this expression data revealed that a JNK gene set as defined from the GEO dataset GDSS8081 was consistently under-expressed in responders and over-expressed in non-responders. TLK199 has been shown to induce JUN/JNK by binding to glutathione S-transferase, a key inhibitor of this pathway. The expression data confirms that patients whose pre-therapy marrow shows under-expression of the JNK gene set are precisely those who benefit from this drug therapy and those patients who already over-express these genes are unlikely to respond. This study highlights two important points: 1) Using a bedside-to-bench strategy yielded a signature that distinguished responders from non-responders 2) The signature identified genes and signaling pathways that shed light on both the biology of the disease and the mechanism of action of the drug. In conclusion, if these results are confirmed in the test set, we will use the signature in a future prospective study to preselect MDS patients for therapy with this promising drug. Disclosures:Brown:Telik, Inc.: Employment, Equity Ownership.

Binding properties of ferrocene–glutathione conjugates as inhibitors and sensors for glutathione S-transferases

The binding properties of two electroactive glutathione–ferrocene conjugates that consist in glutathione attached to one or both of the cyclopentadienyl rings of ferrocene (GSFc and GSFcSG), to Schistosoma japonica glutathione S-transferase (SjGST) were studied by spectroscopy fluorescence, isothermal titration calorimetry (ITC) and differential pulse voltammetry (DPV). Such ferrocene conjugates resulted to be competitive inhibitors of glutathione S-transferase with an increased binding affinity relative to the natural substrate glutathione (GSH). We found that the conjugate having two glutathione units (GSFcSG) exhibits an affinity for SjGST approximately two orders of magnitude higher than GSH. Furthermore, it shows negative cooperativity with the affinity for the second binding site two orders of magnitude lower than that for the first one. We propose that the reason for such negative cooperativity is steric since, i) the obtained thermodynamic parameters do not indicate profound conformational changes upon GSFcSG binding and ii) docking studies have shown that, when bound, part of the first bound ligand invades the second site due to its large size. In addition, voltammetric measurements show a strong decrease of the peak current upon binding of ferrocene–glutathione conjugates to SjGST and provide very similar K values than those obtained by ITC. Moreover, the sensing ability, expressed by the sensitivity parameter shows that GSFcSG is much more sensitive than GSFc, for the detection of SjGST.