Quinone Reductase Induction Research Articles

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Moringa oleifera leaves extracted with methanol and dichloromethane were screened for antioxidant activity. The in vitro cancer antiproliferative and chemopreventive properties were also investigated. Radical scavenging assays with 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2´-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) were used to determine the antioxidant activity. The antiproliferative assay was evaluated on three types of cancer cell lines: hepatocarcinoma (HepG2), colorectal adenocarcinoma (Caco-2) and breast adenocarcinoma (MCF-7), using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction assay. The in vitro cancer chemoprevention was performed using quinone reductase (QR) induction assay on hepatoma (Hepa-1c1c7). The chemopreventive activity of the extracts was expressed as concentration to double QR activity (CD value). The methanol extract showed higher free radical scavenging activity than the dichloromethane extract (IC50 = 1.60±0.03 mg/ml in DPPH assay and IC50 = 1.02±0.06 mg/ml in ABTS assay). In the antiproliferative assay, the IC50 of dichloromethane extract varied from 112 to 133 µg/ml for HepG2, Caco-2 and MCF-7 cancer cells, but became more than 250 µg/ml for the methanol extract. In the chemopreventive assay, the dichloromethane extract had capacity to induce QR activity significantly (CD value = 91.36±1.26 μg/ml), while the methanol extract had no inductive effect. This study provides evidence that M. oleifera leaves possess antioxidant activity, as well as cytotoxic and chemopreventive properties. Therefore, it might be beneficial as a medicinal plant for alternative novel anticancer drugs and nutraceutical products. Key words: Moringa oleifera, antioxidant activity, quinone reductase, antiproliferation, cancer chemoprevention.

Penicillipyrones A and B, Meroterpenoids from a Marine-Derived Penicillium sp. Fungus

Penicillipyrones A (1) and B (2), two novel meroterpenoids, were isolated from the marine-derived fungus Penicillium sp. On the basis of the results of combined spectroscopic analyses, these compounds were structurally elucidated to be sesquiterpene γ-pyrones from a new skeletal class derived from a unique linkage pattern between the drimane sesquiterpene and pyrone moieties. Compound 2 elicited significant induction of quinone reductase.

Optimization of methyl jasmonate application to broccoli florets to enhance health-promoting phytochemical content

Spray treatment of methyl jasmonate (MeJA) has been shown to increase glucosinolate (GS) concentrations and health-promoting activity in Brassica vegetables. Since there is no reported standardized protocol, several MeJA treatment studies have been conducted to maximize human health bioactivity using the F1 broccoli cultivar 'Green Magic'. Foliar MeJA application 4 days prior to harvest of broccoli at commercial maturity resulted in enhanced total GS concentrations. Although a single application of 250 µmol L(-1) MeJA maximized GS concentrations in broccoli florets, two days of consecutive treatments (4 and 3 days prior to harvest) of 250 µmol L(-1) MeJA further enhanced neoglucobrassicin concentrations and floret extract quinone reductase (QR)-inducing activity. With increasing concentrations of MeJA in spray applications to broccoli florets, concentrations of the glucosinolates glucoraphanin, gluconasturtiin and neoglucobrassicin and the isothiocyanate sulforaphane as well as anticancer and anti-inflammatory bioactivities as measured by QR induction and inhibition of nitric oxide (NO) production respectively were significantly increased. Concentrations of these phytochemicals showed strong positive correlations with QR-inducing and NO-inhibitory activities. These application protocols were found to maximize GS and GS hydrolysis product concentrations and putatively enhance the health-promoting properties of broccoli heads for consumers.

Novel prenylated bichalcone and chalcone from Humulus lupulus and their quinone reductase induction activities

A new prenylated chalcone xanthohumol M (1), a novel prenylated bichalcone humulusol (2) and six known chalcones (3–8) were found from Humulus lupulus. Their structures were determined by spectroscopic methods. All the chalcones' electrophilic abilities were assessed by GSH (glutathione) rapid screening, and their QR (quinone reductase) induction activities were evaluated using hepa 1c1c7 cells. The results of electrophilic assay and QR induction activity assay were quite well. New compounds 1 and 2, along with some known prenylated chalcones, displayed certain QR induction activity.

Methyl Jasmonate and 1-Methylcyclopropene Treatment Effects on Quinone Reductase Inducing Activity and Post-Harvest Quality of Broccoli

Effect of pre-harvest methyl jasmonate (MeJA) and post-harvest 1-methylcyclopropene (1-MCP) treatments on broccoli floret glucosinolate (GS) concentrations and quinone reductase (QR, an in vitro anti-cancer biomarker) inducing activity were evaluated two days prior to harvest, at harvest and at 10, 20, and 30 days of post-harvest storage at 4 °C. MeJA treatments four days prior to harvest of broccoli heads was observed to significantly increase floret ethylene biosynthesis resulting in chlorophyll catabolism during post-harvest storage and reduced product quality. Post-harvest treatment with 1-methylcyclopropene (1-MCP), which competitively binds to protein ethylene receptors, maintained post-harvest floret chlorophyll concentrations and product visual quality in both control and MeJA-treated broccoli. Transcript abundance of BoPPH, a gene which is responsible for the synthesis of pheophytinase, the primary enzyme associated with chlorophyll catabolism in broccoli, was reduced by 1-MCP treatment and showed a significant, negative correlation with floret chlorophyll concentrations. The GS, glucobrassicin, neoglucobrassicin, and gluconasturtiin were significantly increased by MeJA treatments. The products of some of the GS from endogenous myrosinase hydrolysis [sulforaphane (SF), neoascorbigen (NeoASG), N-methoxyindole-3-carbinol (NI3C), and phenethyl isothiocyanate (PEITC)] were also quantified and found to be significantly correlated with QR. Sulforaphane, the isothiocyanate hydrolysis product of the GS glucoraphanin, was found to be the most potent QR induction agent. Increased sulforaphane formation from the hydrolysis of glucoraphanin was associated with up-regulated gene expression of myrosinase (BoMyo) and the myrosinase enzyme co-factor gene, epithiospecifier modifier1 (BoESM1). This study demonstrates the combined treatment of MeJA and 1-MCP increased QR activity without post-harvest quality loss.

Cancer chemopreventive diterpenes from Salvia corrugata

NMR and NP-HPLC-UV profiling of the exudate of Salvia corrugata revealed that its secondary metabolite composition was largely dominated by α-hydroxy-β-isopropyl-benzoquinone diterpenoids. Among them, four diterpenes not described previously were isolated and identified as fruticulin C (3), 7α-methoxy-19-acetoxy-royleanone (4), 7α,19-diacetoxy-royleanone (5), and 7-dehydroxy-conacytone (7). In addition, the known diterpenes fruticulin A (1), demethyl-fruticulin A (2) and 7α-O-methyl-conacytone (6) were also obtained. The isolated compounds were evaluated for their cancer chemopreventive activity by measuring quinone reductase induction activity and histone deacetylase inhibition. Three compounds (1, 2 and 5) showed promising activity.

Influence of Seasonal Variation and Methyl Jasmonate Mediated Induction of Glucosinolate Biosynthesis on Quinone Reductase Activity in Broccoli Florets

Methyl jasmonate spray treatments (250 μM) were utilized to alter glucosinolate composition in the florets of the commercial broccoli F1 hybrids 'Pirate', 'Expo', 'Green Magic', 'Imperial', and 'Gypsy' grown in replicated field plantings in 2009 and 2010. MeJA treatment significantly increased glucoraphanin (11%), gluconasturtiin (59%), and neoglucobrassicin (248%) concentrations and their hydrolysis products including sulforaphane (152%), phenethyl isothiocyanate (318%), N-methoxyindole-3-carbinol (313%), and neoascorbigen (232%) extracted from florets of these genotypes over two seasons. Increased quinone reductase (QR) activity was significantly correlated with increased levels of sulforaphane, N-methoxyindole-3-carbinol, and neoascorbigen. Partitioning experiment-wide trait variances indicated that the variability in concentrations of sulforaphane (29%), neoascorbigen (48%), and QR activity (72%) was influenced by year-associated weather variables, whereas variation in neoglucobrassicin (63%) and N-methoxyindole-3-carbinol (46%) concentrations was primarily attributed to methyl jasmonate treatment. These results suggest that methyl jasmonate treatment can enhance QR inducing activity by increased hydrolysis of glucoraphanin into sulforaphane and the hydrolysis products of neoglucobrassicin.

Bioactive constituents of Indigofera spicata.

Four new flavanones, designated as (+)-5″-deacetylpurpurin (1), (+)-5-methoxypurpurin (2), (2S)-2,3-dihydrotephroglabrin (3), and (2S)-2,3-dihydrotephroapollin C (4), together with two known flavanones (5 and 6), three known rotenoids (7-9), and one known chalcone (10) were isolated from a chloroform-soluble partition of a methanol extract from the combined flowers, fruits, leaves, and twigs of Indigofera spicata, collected in Vietnam. The compounds were obtained by bioactivity-guided isolation using the HT-29 human colon cancer, 697 human acute lymphoblastic leukemia, and Raji human Burkitt's lymphoma cell lines. The structures of 1-4 were established by extensive 1D- and 2D-NMR experiments, and the absolute configurations were determined by the measurement of specific rotations and CD spectra. The cytotoxic activities of the isolated compounds were tested against the HT-29, 697, Raji, and CCD-112CoN human normal colon cells. Also, the quinone reductase induction activities of the isolates were determined using the Hepa 1c1c7 murine hepatoma cell line. In addition, cis-(6aβ,12aβ)-hydroxyrotenone (7) was evaluated in an in vivo hollow fiber bioassay using HT-29, MCF-7 human breast cancer, and MDA-MB-435 human melanoma cells.

Induction of quinone reductase (QR) by withanolides isolated from Physalis pubescens L. (Solanaceae)

In the present study, it was demonstrated that the dichloromethane extract of Physalis pubescens L. (DEPP) had weak potential quinone reductase (QR) inducing activity, but an UPLC–ESI-MS method with glutathione (GSH) as the substrate revealed that the DEPP had electrophiles (with an α,β-unsaturated ketone moiety). These electrophiles could induce quinone reductase (QR) activity, which might be attributed to the modification of the highly reactive cysteine residues in Keap1. Herein, four withanolides, including three new compounds physapubescin B (2), physapubescin C (3), physapubescin D (4), together with one known steroidal compound physapubescin (1) were isolated. Structures of these compounds were determined by spectroscopic analysis and that of physapubescin C (3) was confirmed by a combination of molecular modeling and quantum chemical DFT-GIAO calculations. Evaluation of the QR inducing activities of all withanolides indicated potent activities of compounds 1 and 2, which had a common α,β-unsaturated ketone moiety.

Quinone Reductase Induction Activity of Phlorotannins Derived from Eisenia bicyclis in Hepa1c1c7 Cells

To assess the feasibility of phlorotannins from Eisenia bicyclis as cancer chemopreventative agents, we tested whether they induced quinone reductase (QR) in Hepa1c1c7 cells. The ethyl acetate (EtOAc) soluble fraction obtained from E. bicyclis exhibited a QR induction activity in Hepa1c1c7 cells. Successive column chromatography of the active EtOAc fraction resulted in the isolation of four phlorotannins. Their structures were elucidated using one- and two-dimensional nuclear magnetic resonance spectroscopic techniques and characterized as phloroglucinol (1), dioxinodehydroeckol (2), dieckol (3), and fucofuroeckol-A (4). Among these compounds, fucofuroeckol-A (4) showed moderate QR induction activity, and dioxinodehydroeckol (2) exhibited potent QR induction potency with 2.05 ± 0.04 fold induction at a concentration of 50 µM compared to the dimethyl sulfoxide solvent-treated control cells. However, phloroglucinol (1) and dieckol (3) exerted no detectable QR induction activity in Hepa1c1c7 cells. These results suggest that dioxinodehydroeckol could serve as a useful cancer chemopreventive chemical.

A Tissue Homogenate Method To Prepare Gram-Scale Allium Thiosulfinates and Their Disulfide Conjugates with Cysteine and Glutathione

The health benefits of Allium vegetables are widely attributed to the enzyme-derived organosulfur compounds called thiosulfinates (TS). However, the lack of a suitable method to prepare TS in good yields has hampered the evaluation of their biological activities. This paper describe a simple enzymatic method using Allium tissue homogenates as a reaction system to prepare gram-scale TS, including those enriched in 1-propenyl groups, which are particularly difficult to obtain. This method is simple, easy to scale up, and requires no column purification step, making it suitable for practical large-scale production of Allium TS. The prepared TS were further utilized to prepare the disulfide conjugates with cysteine and glutathione (CySSR and GSSR, R = methyl, ethyl, propyl, 1-propenyl, and allyl), which are the presumptive metabolites of TS. Among all of the Allium CySSR and GSSR conjugates, the newly prepared glutathione conjugate with 1-propenyl TS, GSSPe, showed the most potent effect to induce quinone reductase (QR, a representative phase II enzyme) in murine hepatoma cells (Hepa 1c1c7) and inhibit nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated macrophage cells (RAW 264.7).

S-Alk(en)ylmercaptocysteine: Chemical Synthesis, Biological Activities, and Redox-Related Mechanism

S-Alk(en)ylmercaptocysteine (CySSR, R = methyl, ethyl, propyl, 1-propenyl, and allyl), which are the putative metabolites of Allium thiosulfinates, were chemically synthesized. CySSR, but not the corresponding monosulfide species S-alk(en)yl cysteine (CySR), were able to induce quinone reductase (QR, a representative phase II enzyme) in Hepa 1c1c7 cells and inhibit nitric oxide (NO, an inflammatory biomarker) formation in lipopolysaccharide (LPS)-activated RAW 264.7 cells. These results indicate the importance of the disulfide bond for the biological activities of CySSR. Glutathione (GSH) and N-acetylcysteine (NAC), but not other types of cellular antioxidants, suppressed multiple biological activities of CySSR in vitro. The inhibitory effects of GSH and NAC on the biological activities of CySSR were correlated with a glutaredoxin (Grx)-dependent intracellular reduction of CySSR to generate cysteine and RSH, which were secreted into the extracellular medium.

Nuclear factor-E2 (Nrf2) is regulated through the differential activation of ERK1/2 and PKC α/βII by Gymnasterkoreayne B

Phytochemicals are well known to have cancer chemopreventive effects by induction of phase II detoxification enzymes including quinone reductase (NQO-1) and glutathione-S-transferases. These detoxification enzymes are commonly regulated by nuclear factor-E2 (Nrf2), which is a representative antioxidant and cytoprotective factor involved in cancer chemoprevention. As one of the known quinone reductase (QR) inducers and Nrf2 activators, Gymnasterkoreayne B (GKB) isolated from Gymnaster (Aster) koraiensis was used to elucidate the upstream signalling pathway for Nrf2 regulation. In this study, we confirmed that GKB significantly increases expression levels of Nrf2 in HCT116 human colon cancer cells. We found the probable mechanism of upstream signalling pathways to activate Nrf2 by GKB. To reveal the pathway that affects Nrf2 translocation by GKB, we examined changes in various kinases in HCT116 cells treated with GKB. We observed that ERK and PKC pathways are particularly involved in the activation of Nrf2 by GKB, followed by translocation of Nrf2 and induction of NQO-1. These results suggest that GKB induces Nrf2 translocation and expression by differential regulation of ERK and PKC pathways in HCT116 cells.

Preliminary evaluation for cancer chemopreventive and cytotoxic potential of naturally growing ethnobotanically selected plants of Pakistan

Context: Natural products are a very productive source of leads for the development of medicines. Six Pakistani plants were chosen for study based on ethnobotanical data.Objective: Exploration of important medicinal plants of Pakistan for cancer treatment.Materials and methods: The crude extracts of the six plants and their fractions were tested for inhibition of nuclear factor κB (NFκB), aromatase, and nitric oxide (NO) production in lipopolysaccharide (LPS)-activated murine macrophage RAW 264.7 cells, induction of quinone reductase 1 (QR1), agonism of retinoid X receptor, and growth inhibition with MCF-7, LU-1 and MDA-MB-231 cancer cells.Results: Two samples of Withania coagulans (Stocks) Dunal (Solanaceae) demonstrated inhibition of TNF-α induced activity of NFκB with IC50 values of 2.6 and 4.3 µg/mL, respectively. Two fractions from W. coagulans and Euphorbia wallichii Hook F. (Euphorbiaceae) aerial parts inhibited aromatase with IC50 values of 17.0 and 17.7 µg/mL, respectively. A total of 13 samples (five from E. wallichii, one from Acer oblongifolium Hort. ex Dippel (Aceraceae), one from Aster thomsonii C. B. Clarke (Asteraceae) and six from W. coagulans aerial parts with fruits) inhibited NO production with IC50 values ranging from 1.3 to 15.6 µg/mL. Fourteen samples demonstrated induction of QR1 with CD ranging from 1.0 to 20.6 µg/mL, and a total of eight extracts and fractions inhibited the proliferation of cancer cells in culture with IC50 values ranging from 1.2 to 7.8 µg/mL.Discussion and conclusion: Selected plants can be a valuable source of chemopreventive and anticancer products. W. coagulans aerial parts showed the strongest activity.

Quinone reductase (QR) inducers from Andrographis paniculata and identification of molecular target of andrographolide

In the present study, it was demonstrated that the petroleum extract of Andrographis paniculata (AP) had quinone reductase (QR) inducing activity, which might be attributed to the modification of key cysteine residues in Keap1 by Michael addition acceptors (MAAs) in it. To screen MAAs in AP, glutathione (GSH) was employed, and a LC/MS/MS method was implied. Three compounds, andrographoside, andrographolide, 14-deoxy-14,15-dehydroandrographolide were revealed could well conjugated with GSH. Then, andrographolide along with 4 new and 14 known compounds were isolated to conduct QR induction evaluation, and the CD (the concentration required to double the activity of QR) value of andrographolide is 1.43μM. The QR induce activity of andrographolide might be attributed to its targeting multiple cysteine residues in Keap1, therefore, the alkylation of Keap1 by andrographolide was further studied and the result showed that four cysteine residues: Cys77, Cys151, Cys273 and Cys368 were alkylated, which indicated that Keap1 is a potential target for the QR induce activity of andrographolide.

Neoflavonoids and Tetrahydroquinolones as Possible Cancer Chemopreventive Agents

Several lactone- and lactam-based neoflavonoids and tetrahydroquinolones were synthesized and evaluated for cancer chemopreventive studies using cell and molecular target-based in vitro bioassays, namely NFκB, aromatase, and quinone reductase 1. These analogs blocked TNF-α-induced NFκB activation in a dose-dependent manner with IC₅₀ values in the range of 0.11-3.2 μM. In addition, compound 8 inhibited aromatase activity with an IC₅₀ value of 12.12 μM, and compound 10 affected quinone reductase 1 induction (IR, 3.6; CD, 19.57 μM). Neoflavonoids 8 and 10 exhibiting good results can further be optimized for improved therapeutic profiles. However, investigations into the actions of neoflavonoids and tetrahydroquinolones, especially those related to the NFκB signaling pathway, aromatase inhibition, induction of quinone reductase 1 expression, and in vivo studies could provide new insights into the cancer chemopreventive ability of these molecules.

Bioactivity-guided isolation of antioxidant and quinone reductase-inducing constituents from Maqui berry

Aristotelia chilensis (Mol.) Stuntz (Elaeocarpaceae), Maqui berry, is a native South American evergreen shrub that produces small edible purple or black berries. In a search for naturally occurring cancer chemopreventive agents, the ethyl acetate-soluble extract of A. chilensis showed significant hydroxyl-radical (·OH) scavenging activity, and thus was fractionated via bioactivity-guided isolation. Fifteen known compounds (1-15) were isolated, with phloroglucinaldehyde 2-O-s-D-glucopyranoside (12) being isolated as a new natural product, and eleven compounds (1, 3, and 7-15) obtained from A. chilensis for the first time. The structures of these compounds were identified on the basis of spectroscopic methods. All pure isolates were evaluated for their hydroxyl-radical scavenging and quinone reductase (QR) induction activities. Twelve compounds (1-12) showed potent antioxidant activity in the hydroxyl-radical scavenging assay, with cyanidin 3-O-s-D-glucopyranoside (2, ED50=0.13µM) being of the greatest potency. Four compounds (3, 7, 9, and 11) exhibited relatively high QR-inducing activity, with protocatechuic acid (9, CD=4.1µM) found to be the most potent. Thus, A. chilensis seems worthy of further investigation for the discovery of cancer chemopreventive agents.

Induction of quinone reductase by tamoxifen or DPN protects against mammary tumorigenesis

We have previously shown that estrogen receptor β (ERβ)-mediated up-regulation of quinone reductase (QR) is involved in the protection against estrogen-induced mammary tumorigenesis. Our present study provides evidence that the ERβ agonist, 2,3-bis-(4-hydroxy-phenyl)-propionitrile (DPN), and the selective estrogen receptor modulator tamoxifen (Tam), inhibit estrogen-induced DNA damage and mammary tumorigenesis in the aromatase transgenic (Arom) mouse model. We also show that either DPN or Tam treatment increases QR levels and results in a decrease in ductal hyperplasia, proliferation, oxidative DNA damage (ODD), and an increase in apoptosis. To corroborate the role of QR, we provide additional evidence in triple transgenic MMTV/QR/Arom mice, wherein the QR expression is induced in the mammary glands via doxycycline, causing a decrease in ductal hyperplasia and ODD. Overall, we provide evidence that up-regulation of QR through induction by Tam or DPN can inhibit estrogen-induced ODD and mammary cell tumorigenesis, representing a novel mechanism of prevention against breast cancer. Thus, our data have important clinical implications in the management of breast cancer; our findings bring forth potentially new therapeutic strategies involving ERβ agonists.

Acylated pregnane glycosides from Caralluma sinaica

Caralluma sinaica is sold on local markets of Saudi Arabia for various health benefits however no phytochemical study has specifically been performed on this species. NMR and UHPLC-ESI-TOF-MS profilings of the ethanolic extract of the whole plant reveal a very complex phytochemical composition dominated by pregnanes. Detailed information on its constituents was obtained after isolation. Six pregnane glycosides were obtained and characterized based on the extensive spectroscopic analysis (including IR, 1H NMR, 13C NMR and MS data), in addition to ten known compounds (seven pregnanes and three flavonoids). The compounds were identified as 12β-O-benzoyl-20-O-acetyl boucerin-3-O-6-deoxy-3-O-methyl-β-d-glucopyranosyl-(1→4)-β-d-cymaropyranosyl-(1→4)-β-d-cymaropyranoside, 12β-O-tigloyl-20-O-acetyl boucerin-3-O-β-d-glucopyranosyl-(1→4)-β-d-cymaropyranoside, 12β-O-benzoyl-20-O-acetyl boucerin-3-O-β-d-glucopyranosyl-(1→4)-β-d-digitalopyranosyl-(1→4)-β-d-cymaropyranosyl-(1→4)-β-d-cymaropyranoside, 12β-O-benzoyl-20-O-acetyl boucerin-3-O-β-d-glucopyranosyl-(1→4)-thevetopyranosyl-(1→4)-β-d-cymaropyranosyl-(1→4)-β-d-cymaropyranoside, 12β-O-benzoyl-20-O-tigloyl boucerin-3-O-β-d-glucopyranosyl-(1→4)-β-d-cymaropyranoside, 12β-20-O-dibenzoyl boucerin-3-O-β-d-glucopyranosyl-(1→4)-β-d-cymaropyranosyl-(1→4)-β-d-cymaropyranoside. Finally, the isolated compounds were evaluated for their quinone reductase induction.

Abstract 1609: Oxidation products of green tea polyphenols induce inactivation of PKC isoenzymes and induce cell death via modulation of selenoprotein thioredoxin reductase and quinone reductase

Abstract Autooxidation of green tea polyphenols generates H2O2 and quinones which have been implicated in cell death induced by these polyphenols. While autooxidation of epigallocatechin-3-gallate (EGCG), the major green tea polyphenol, has been shown in vitro where oxygen tension is high, the role of reactive oxygen species in the action of EGCG in vivo is currently gaining attention. When DU145 prostate cancer cells were treated in vitro with EGCG, PKC isoenzymes were inactivated. This inactivation was strongly correlated with EGCG-induced cell death. Cell-permeable catalase partially blocked EGCG-induced inactivation of PKC and cell death suggesting the involvement of H2O2 in these processes. EGCG-induced cell death was enhanced by 3-amino-1,2,4-triazole, a catalase inhibitor, suggesting an inhibitory role for intracellular catalase in this process. Furthermore, the inactivated PKC isoenzymes were regenerated to their active form by thiol agents in the test tube or by the thioredoxin reductase (TR) system in cells. This suggests sulfhydryl oxidation of PKC is induced by EGCG-mediated ROS generation. Previously, others have demonstrated inactivation of TR by a quinone generated by autooxidation of EGCG. We found that EGCG treatment of intact DU145 cells inactivated TR, presumably by generation of quinone. Such inactivation of TR enhanced the net increase in inactivation of PKC due to a decrease in reversal of PKC oxidative modification. Thus, the combined actions of H2O2 and quinones induce more inactivation of PKC and cell death than either agent alone. Cotreatment of cells with auranofin, a specific inhibitor of TR, enhanced EGCG-induced inactivation of PKC and cell death. Conversely, a three-fold increase in the induction of TR, by pretreatment of DU145 cells with selenite for 48 h, completely abolished both EGCG-induced inactivation of PKC and induction of cell death. This suggests a possible antagonistic interaction between selenium and EGCG. Dicumarol, an inhibitor of phase II enzyme quinone reductase, enhanced inactivation of TR, presumably by accumulation of quinones. Conversely, an induction of quinone reductase by tertiary butylhydroquinone, decreased EGCG-induced inactivation of TR, presumably due to less accumulation of EGCG-derived quinones. This decreased inactivation of TR subsequently led to a net decrease in inactivation of PKC isoenzymes and cell death. This suggests that QR is a negative regulator of EGCG-induced inactivation of PKC and cell death. Thus, EGCG oxidation products H2O2 and quinone appear to mediate EGCG-induced cell death via inactivation of PKC isoenzymes and TR respectively. Furthermore, the data suggests that both EGCG-induced PKC inactivation and cell death are antagonized by an increase in TR and QR. This study was supported by the National Cancer Institute grant CA099216. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1609. doi:1538-7445.AM2012-1609