Xanthohumol Isolated from <i>Humulus lupulus</i> Inhibits Menadione-Induced DNA Damage through Induction of Quinone Reductase

Dietz, Birgit M.; Kang, Young Hwa; Li, Xinwei; Eggler, Aimee L.; Yao, Ping; Chadwick, Lucas R.; Pauli, Guido F.; Farnsworth, Norman R.; Mesecar, Andrew D.; Breemen, Richard B. van; Bolton, Judy L.

doi:10.1021/tx050058x

Cited by 184 publications

(188 citation statements)

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“…10-Shogaol was isolated and provided by Dr. Yi Tao of the University of Illinois College of Pharmacy, and xanthohumol was isolated and proScheme 1. Structures of the natural product chemoprevention agents (A) isoliquiritigenin [22]; (B) xanthohumol [28]; and (C) 10-shogaol [29]. The CD values represent the concentration of each compound required to double the intracellular quinone reductase activity in Hepa 1c1c7 murine hepatoma cells [22] and indicate the relative activities of these compounds as chemopreventive reagents.…”

Section: Materials and Reagentsmentioning

confidence: 99%

“…All three of these natural products contain electrophilic unsaturated ketones (Scheme 1). As an indication of their chemopreventive activity through the induction of ARE, the induction of the phase 2 enzyme quinone reductase in Hepa 1c1c7 murine hepatoma cells by xanthohumol, isoliquiritigenin, and 10-shogaol has been determined to be 1.7 Ϯ 0.7, 1.8 Ϯ 0.44, and 42.4 Ϯ 0.9 M, respectively [22,28,29]. In this investigation, the relative reactivities of each of these compounds toward specific cysteine residues of human Keap1 were determined using LC-MS/MS, and the most reactive amino acid residue was identified as C151 for all three compounds.…”

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confidence: 99%

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Sites of alkylation of human Keap1 by natural chemoprevention agents

Luo

Eggler

Liu

et al. 2007

J. Am. Soc. Mass Spectrom.

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Under basal conditions, the interaction of the cytosolic protein Keap1 (Kelch-like ECHassociated protein 1) with the transcription factor nuclear factor-E 2 -related factor 2 (Nrf2) results in a low level of expression of cytoprotective genes whose promoter region contains the antioxidant response element (ARE). Alkylation of one or more of the 27 cysteine sulfhydryl groups of human Keap1 is proposed to lead to Nrf2 nuclear accumulation, to upregulation of cytoprotective gene expression by the ARE, and to prevention of degenerative diseases, such as cancer. Therefore, identification of the most reactive of these cysteine residues toward specific electrophiles should help clarify this mechanism of cancer prevention, also known as chemoprevention. To address this issue, preliminary analyses of tryptic digests of Keap1 alkylated by the model electrophile 1-biotinamido-4-(4=-[maleimidoethyl-cyclohexane]-carboxamido) butane were carried out using liquid chromatographic-tandem mass spectrometry (LC-MS/MS) with a cylindrical ion trap mass spectrometer and also using LC-MS/MS with a hybrid linear ion trap FT ICR mass spectrometer. Because the FT ICR instrument provided more complete peptide sequencing coverage and enabled the identification of more alkylated cysteine residues, only this instrument was used in subsequent studies of Keap1 alkylation by three electrophilic natural products that can upregulate the ARE, xanthohumol, isoliquiritigenin, and 10-shogaol. Among the various cysteine residues of Keap1, C151 was most reactive toward these three electrophiles. These in vitro results agree with evidence from in vivo experiments, and indicate that C151 is the most important site of alkylation on Keap1 by chemoprevention agents that function by activating the ARE through Nrf2. Keap1 has five distinct domains: the N-terminal domain (amino acids 1-60); the BTB (Bric-a-brac, Tramtrack, Broad-complex) domain (amino acids 61-178); a central linker domain (amino acids 179 -321); the Kelch repeat domain (amino acids 322-608); and a C-terminal domain (amino acids 609 -625). The BTB domain mediates the dimerization of Keap1 [9] and also binds the adaptor protein in Cul3-dependent ubiquitination systems [10]. The Kelch repeat domain binds to the Nrf2 directly [1]. Because Keap1 signaling is probably mediated by alkylation of one or more of its cysteine sulfhydryl groups [3,11,12], identification of the cysteine residues that are most reactive toward specific electrophiles should help clarify this mechanism of action of Keap1.However, most of the work to date to identify reactive Keap1 cysteine residues has been carried out with model alkylating agents such as dexamethasone 21-mesylate [2], iodoacetyl-N-biotinyl hexylene diamine (BIA), and 1-biotinamido-4-(4=-[maleimidoethylcyclohexane]-carboxamido) butane (BMCC) [13] instead of biologically relevant ARE inducers that show promise as chemopreventive agents. Unlike ARE inducAddress reprint request to Professor Richard B. van Breemen,

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Section: Materials and Reagentsmentioning

confidence: 99%

mentioning

confidence: 99%

Sites of alkylation of human Keap1 by natural chemoprevention agents

Luo

Eggler

Liu

et al. 2007

J. Am. Soc. Mass Spectrom.

Self Cite

164

145

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“…HepG2-ARE-Luc cells were plated on a six-well plate overnight; treated with DMSO, test samples, or positive control bromoflavone on the second day; and incubated for additional 24 h. The luciferase activity was determined as previously described (27). The data were obtained from three separate experiments and expressed as fold induction over control [treated cells/DMSO-treated cells (F SD)].…”

Section: Are-luciferase Reporter Assaymentioning

confidence: 99%

“…The SERMs were also assayed in the human liver cell line HepG2, which is important because of the availability of HepG2 cells transfected with the ARE-luciferase reporter (27,31). BTC was confirmed as a strong inducer of NQO1 and DMA as a weaker but significant inducer (Fig.…”

Section: Induction Of Nqo1 In Liver Cellsmentioning

confidence: 99%

Structural modulation of reactivity/activity in design of improved benzothiophene selective estrogen receptor modulators: induction of chemopreventive mechanisms

Dietz²,

Dunlap

et al. 2007

Molecular Cancer Therapeutics

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The benzothiophene selective estrogen receptor modulators (SERM) raloxifene and arzoxifene are in clinical use and clinical trials for chemoprevention of breast cancer and other indications. These SERMs are ''oxidatively labile'' and therefore have potential to activate antioxidant responsive element (ARE) transcription of genes for cytoprotective phase II enzymes such as NAD(P)Hdependent quinone oxidoreductase 1 (NQO1). To study this possible mechanism of cancer chemoprevention, a family of benzothiophene SERMs was developed with modulated redox activity, including arzoxifene and its metabolite desmethylarzoxifene (DMA). The relative antioxidant activity of these SERMs was assayed and correlated with induction of NQO1 in murine and human liver cells. DMA was found to induce NQO1 and to activate ARE more strongly than other SERMs, including raloxifene and 4-hydroxytamoxifen. Livers from female, juvenile rats treated for 3 days with estradiol and/or with the benzothiophene SERMs arzoxifene, DMA, and F-DMA showed substantial induction of NQO1 by the benzothiophene SERMs. No persuasive evidence in this assay or in MCF-7 breast cancer cells was obtained of a major role for the estrogen receptor in induction of NQO1 by the benzothiophene SERMs. These results suggest that arzoxifene might provide chemopreventive benefits over raloxifene and other SERMs via metabolism to DMA and stimulation of ARE-mediated induction of phase II enzymes. The correlation of SERM structure with antioxidant activity and NQO1 induction also suggests that oxidative bioactivation of SERMs may be modulated to enhance chemopreventive activity. [Mol Cancer Ther 2007;6(9):2418 -28]

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“…A 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay was conducted as described by Dietz et al, 21) with minor modifications. Reaction mixtures containing 10-mL test samples and 190 mL of a 200 mM DPPH ethanol solution were incubated at room temperature for 30 min in 96-well plates.…”

Section: Methodsmentioning

confidence: 99%