Specific quinone reductase 2 inhibitors reduce metabolic burden and reverse Alzheimer's disease phenotype in mice

Biological aging can be described as accumulative, prolonged metabolic stress and is the major risk factor for cognitive decline and Alzheimer's disease (AD). Recently, we identified and described a quinone reductase 2 (QR2) pathway in the brain, in which QR2 acts as a removable memory constraint and metabolic buffer within neurons. QR2 becomes overexpressed with age, and it is possibly a novel contributing factor to age-related metabolic stress and cognitive deficit. We found that, in human cells, genetic removal of QR2 produced a shift in the proteome opposing that found in AD brains while simultaneously reducing oxidative stress. We therefore created highly specific QR2 inhibitors (QR2is) to enable evaluation of chronic QR2 inhibition as a means to reduce biological age-related metabolic stress and cognitive decline. QR2is replicated results obtained by genetic removal of QR2, while local QR2i microinjection improved hippocampal and cortical-dependent learning in rats and mice. Continuous consumption of QR2is in drinking water improved cognition and reduced pathology in the brains of AD-model mice (5xFAD), with a noticeable between-sex effect on treatment duration. These results demonstrate the importance of QR2 activity and pathway function in the healthy and neurodegenerative brain and what we believe to be the great therapeutic potential of QR2is as first-in-class drugs.

Neuroprotective Properties of Quinone Reductase 2 Inhibitor M-11, a 2-Mercaptobenzimidazole Derivative

The ability of NQO2 to increase the production of free radicals under enhanced generation of quinone derivatives of catecholamines is considered to be a component of neurodegenerative disease pathogenesis. The present study aimed to investigate the neuroprotective mechanisms of original NQO2 inhibitor M-11 (2-[2-(3-oxomorpholin-4-il)-ethylthio]-5-ethoxybenzimidazole hydrochloride) in a cellular damage model using NQO2 endogenous substrate adrenochrome (125 µM) and co-substrate BNAH (100 µM). The effects of M-11 (10-100 µM) on the reactive oxygen species (ROS) generation, apoptosis and lesion of nuclear DNA were evaluated using flow cytometry and single-cell gel electrophoresis assay (comet assay). Results were compared with S29434, the reference inhibitor of NQO2. It was found that treatment of HT-22 cells with M-11 results in a decline of ROS production triggered by incubation of cells with NQO2 substrate and co-substrate. Pre-incubation of HT-22 cells with compounds M-11 or S29434 results in a decrease of DNA damage and late apoptotic cell percentage reduction. The obtained results provide a rationale for further development of the M-11 compound as a potential neuroprotective agent.

Identification and Pharmacokinetics of Quinone Reductase 2 Inhibitors after Oral Administration of Garcinia mangostana L. Extract in Rat by LC-MS/MS

Garcinia mangostana L. (mangosteen) is a famous tropical fruit that contains a large number of xanthones. Regular consumption of mangosteen may confer health benefits and prevent some diseases, such as malaria. Quinone reductase 2 (QR-2) is a cytosolic enzyme found in human red blood cells, and it is becoming a target for chemoprevention because it is involved in the mechanisms of several diseases, including malaria. To understand whether the xanthones present in mangosteen might inhibit the activity of QR-2, blood samples were collected from rat following the oral administration of mangosteen extract and then incubated with QR-2 followed by UF-HPLC-QTOF/MS analysis to rapidly screen for and identify the QR-2-inhibiting xanthones. A total of 16 xanthones were identified, and six of these (α-mangostin, γ-mangostin, 8-deoxyartanin, 1,3,7-trihydroxy-2,8-di(3-methylbut-2-enyl)xanthone, garcinone E, and 9-hydroxycalabaxanthone) were subjected to QR-2 inhibition assay. γ-Mangostin exhibited the strongest inhibition, achieving an IC₅₀ value of 3.82 ± 0.51 μM. Its interaction with QR-2 was found to involve hydrogen bond and arene-arene interaction as revealed by molecular docking. The present study could provide new insight into the potential application of mangosteen as functional food ingredients for inhibiting the activity of QR-2. However, the extent of daily intake of mangosteen required and the exact contribution of mangosteen to the prevention and treatment of malaria remain subjects of further study.

Discovery of potent 4-aminoquinoline hydrazone inhibitors of NRH:quinoneoxidoreductase-2 (NQO2)

(NRH):quinone oxidoreductase 2 (NQO2) is associated with various processes involved in cancer initiation and progression probably via the production of ROS during quinone metabolism. Thus, there is a need to develop inhibitors of NQO2 that are active in vitro and in vivo. As part of a strategy to achieve this we have used the 4-aminoquinoline backbone as a starting point and synthesized 21 novel analogues. The syntheses utilised p-anisidine with Meldrum's acid and trimethyl orthoacetate or trimethyl orthobenzoate to give the 4-hydrazin-quinoline scaffold, which was derivatised with aldehydes or acid chlorides to give hydrazone or hydrazide analogues, respectively. The hydrazones were the most potent inhibitors of NQO2 in cell free systems, some with low nano-molar IC50 values. Structure-activity analysis highlighted the importance of a small substituent at the 2-position of the 4-aminoquinoline ring, to reduce steric hindrance and improve engagement of the scaffold within the NQO2 active site. Cytotoxicity and NQO2-inhibitory activity in vitro was evaluated using ovarian cancer SKOV-3 and TOV-112 cells (expressing high and low levels of NQO2, respectively). Generally, the hydrazones were more toxic than hydrazide analogues and further, toxicity is unrelated to cellular NQO2 activity. Pharmacological inhibition of NQO2 in cells was measured using the toxicity of CB1954 as a surrogate end-point. Both the hydrazone and hydrazide derivatives are functionally active as inhibitors of NQO2 in the cells, but at different inhibitory potency levels. In particular, 4-((2-(6-methoxy-2-methylquinolin-4-yl)hydrazono)methyl)phenol has the greatest potency of any compound yet evaluated (53 nM), which is 50-fold lower than its toxicity IC50. This compound and some of its analogues could serve as useful pharmacological probes to determine the functional role of NQO2 in cancer development and response to therapy.

Hydrogen sulfide perturbs mitochondrial bioenergetics and triggers metabolic reprogramming in colon cells

Unlike most other tissues, the colon epithelium is exposed to high levels of H2S derived from gut microbial metabolism. H2S is a signaling molecule that modulates various physiological effects. It is also a respiratory toxin that inhibits complex IV in the electron transfer chain (ETC). Colon epithelial cells are adapted to high environmental H2S exposure as they harbor an efficient mitochondrial H2S oxidation pathway, which is dedicated to its disposal. Herein, we report that the sulfide oxidation pathway enzymes are apically localized in human colonic crypts at the host-microbiome interface, but that the normal apical-to-crypt gradient is lost in colorectal cancer epithelium. We found that sulfide quinone oxidoreductase (SQR), which catalyzes the committing step in the mitochondrial sulfide oxidation pathway and couples to complex III, is a critical respiratory shield against H2S poisoning. H2S at concentrations ≤20 μm stimulated the oxygen consumption rate in colon epithelial cells, but, when SQR expression was ablated, H2S concentrations as low as 5 μm poisoned cells. Mitochondrial H2S oxidation altered cellular bioenergetics, inducing a reductive shift in the NAD+/NADH redox couple. The consequent electron acceptor insufficiency caused uridine and aspartate deficiency and enhanced glutamine-dependent reductive carboxylation. The metabolomic signature of this H2S-induced stress response mapped, in part, to redox-sensitive nodes in central carbon metabolism. Colorectal cancer tissues and cell lines appeared to counter the growth-restricting effects of H2S by overexpressing sulfide oxidation pathway enzymes. Our findings reveal an alternative mechanism for H2S signaling, arising from alterations in mitochondrial bioenergetics that drive metabolic reprogramming.

Antibiotic Korormicin A Kills Bacteria by Producing Reactive Oxygen Species

Korormicin is an antibiotic produced by some pseudoalteromonads which selectively kills Gram-negative bacteria that express the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR.) We show that although korormicin is an inhibitor of Na+-NQR, the antibiotic action is not a direct result of inhibiting enzyme activity. Instead, perturbation of electron transfer inside the enzyme promotes a reaction between O2 and one or more redox cofactors in the enzyme (likely the flavin adenine dinucleotide [FAD] and 2Fe-2S center), leading to the production of reactive oxygen species (ROS). All Pseudoalteromonas contain the nqr operon in their genomes, including Pseudoalteromonas strain J010, which produces korormicin. We present activity data indicating that this strain expresses an active Na+-NQR and that this enzyme is not susceptible to korormicin inhibition. On the basis of our DNA sequence data, we show that the Na+-NQR of Pseudoalteromonas J010 carries an amino acid substitution (NqrB-G141A; Vibrio cholerae numbering) that in other Na+-NQRs confers resistance against korormicin. This is likely the reason that a functional Na+-NQR is able to exist in a bacterium that produces a compound that typically inhibits this enzyme and causes cell death. Korormicin is an effective antibiotic against such pathogens as Vibrio cholerae, Aliivibrio fischeri, and Pseudomonas aeruginosa but has no effect on Bacteroides fragilis and Bacteroides thetaiotaomicron, microorganisms that are important members of the human intestinal microflora.IMPORTANCE As multidrug antibiotic resistance in pathogenic bacteria continues to rise, there is a critical need for novel antimicrobial agents. An essential requirement for a useful antibiotic is that it selectively targets bacteria without significant effects on the eukaryotic hosts. Korormicin is an excellent candidate in this respect because it targets a unique respiratory enzyme found only in prokaryotes, the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR). Korormicin is synthesized by some species of the marine bacterium Pseudoalteromonas and is a potent and specific inhibitor of Na+-NQR, an enzyme that is essential for the survival and proliferation of many Gram-negative human pathogens, including Vibrio cholerae and Pseudomonas aeruginosa, among others. Here, we identified how korormicin selectively kills these bacteria. The binding of korormicin to Na+-NQR promotes the formation of reactive oxygen species generated by the reaction of the FAD and the 2Fe-2S center cofactors with O2.

Structure of the NDH-2 - HQNO inhibited complex provides molecular insight into quinone-binding site inhibitors

Type II NADH:quinone oxidoreductase (NDH-2) is a proposed drug-target of major pathogenic microorganisms such as Mycobacterium tuberculosis and Plasmodium falciparum. Many NDH-2 inhibitors have been identified, but rational drug development is impeded by the lack of information regarding their mode of action and associated inhibitor-bound NDH-2 structure. We have determined the crystal structure of NDH-2 complexed with a quinolone inhibitor 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO). HQNO is nested into the slot-shaped tunnel of the Q-site, in which the quinone-head group is clamped by Q317 and I379 residues, and hydrogen-bonds to FAD. The interaction of HQNO with bacterial NDH-2 is very similar to the native substrate ubiquinone (UQ1) interactions in the yeast Ndi1-UQ1 complex structure, suggesting a conserved mechanism for quinone binding. Further, the structural analysis provided insight how modifications of quinolone scaffolds improve potency (e.g. quinolinyl pyrimidine derivatives) and suggests unexplored target space for the rational design of new NDH-2 inhibitors.

Evaluation of analogues of furan-amidines as inhibitors of NQO2

Inhibitors of the enzyme NQO2 (NRH: quinone oxidoreductase 2) are of potential use in cancer chemotherapy and malaria. We have previously reported that non-symmetrical furan amidines are potent inhibitors of NQO2 and here novel analogues are evaluated. The furan ring has been changed to other heterocycles (imidazole, N-methylimidazole, oxazole, thiophene) and the amidine group has been replaced with imidate, reversed amidine, N-arylamide and amidoxime to probe NQO2 activity, improve solubility and decrease basicity of the lead furan amidine. All compounds were fully characterised spectroscopically and the structure of the unexpected product N-hydroxy-4-(5-methyl-4-phenylfuran-2-yl)benzamidine was established by X-ray crystallography. The analogues were evaluated for inhibition of NQO2, which showed lower activity than the lead furan amidine. The observed structure-activity relationship for the furan-amidine series with NQO2 was rationalized by preliminary molecular docking and binding mode analysis. In addition, the oxazole-amidine analogue inhibited the growth of Plasmodium falciparum with an IC50 value of 0.3 μM.

The two common polymorphic forms of human NRH-quinone oxidoreductase 2 (NQO2) have different biochemical properties

There are two common forms of NRH-quinone oxidoreductase 2 (NQO2) in the human population resulting from SNP rs1143684. One has phenylalanine at position 47 (NQO2-F47) and the other leucine (NQO2-L47). Using recombinant proteins, we show that these variants have similar steady state kinetic parameters, although NQO2-L47 has a slightly lower specificity constant. NQO2-L47 is less stable towards proteolytic digestion and thermal denaturation than NQO2-F47. Both forms are inhibited by resveratrol, but NQO2-F47 shows negative cooperativity with this inhibitor. Thus these data demonstrate, for the first time, clear biochemical differences between the variants which help explain previous biomedical and epidemiological findings.

A secondary mode of action of polymyxins against Gram-negative bacteria involves the inhibition of NADH-quinone oxidoreductase activity

Polymyxin B and colistin were examined for their ability to inhibit the type II NADH-quinone oxidoreductases (NDH-2) of three species of Gram-negative bacteria. Polymyxin B and colistin inhibited the NDH-2 activity in preparations from all of the isolates in a concentration-dependent manner. The mechanism of NDH-2 inhibition by polymyxin B was investigated in detail with Escherichia coli inner membrane preparations and conformed to a mixed inhibition model with respect to ubiquinone-1 and a non-competitive inhibition model with respect to NADH. These suggest that the inhibition of vital respiratory enzymes in the bacterial inner membrane represents one of the secondary modes of action for polymyxins.

Design, synthesis, biological and structural evaluation of functionalized resveratrol analogues as inhibitors of quinone reductase 2

Resveratrol (3,5,4'-trihydroxylstilbene) has been proposed to elicit a variety of positive health effects including protection against cancer and cardiovascular disease. The highest affinity target of resveratrol identified so far is the oxidoreductase enzyme quinone reductase 2 (QR2), which is believed to function in metabolic reduction and detoxification processes; however, evidence exists linking QR2 to the metabolic activation of quinones, which can lead to cell toxicity. Therefore, inhibition of QR2 by resveratrol may protect cells against reactive intermediates and eventually cancer. With the aim of identifying novel inhibitors of QR2, we designed, synthesized, and tested two generations of resveratrol analogue libraries for inhibition of QR2. In addition, X-ray crystal structures of six of the resveratrol analogues in the active site of QR2 were determined. Several novel inhibitors of QR2 were successfully identified as well as a compound that inhibits QR2 with a novel binding orientation.

Antimalarial activity of nepodin isolated from Rumex crispus

The purpose of this study is to define the antimalarial activity of Rumex crispus. To identify an active compound that is isolated from R. crispus, bioassay-based chromatographic fractionation and purification is carried out from 70 % ethanol extract of R. crispus; then, an active compound, nepodin, is identified by spectroscopic analysis. Anitmalarial activity is measured by PfNDH2 assay, cytotoxicity, and animal test. From NADH:quinone oxidoreductase enzyme (PfNDAH2) assay, nepodin exhibited significant IC50 values that were 0.74 ± 0.07 and 0.79 ± 0.06 μg/ml against P. falciparum chloroquine-sensitive (3D7) and P. falciparum chloroquine-resistant (S20), respectively. Nepodin showed a potential selective inhibition (SI index: ratio of 50 % cytotoxic concentration to 50 % effective anti-plasmodial concentration) of 161.6 and 151.4 against P. falciparum 3D7 and P. falciparum S20. In the animal test, all groups of nepodin treatment of 10, 50, and 250 mg/kg were active with a parasitemia suppression of 97.1 ± 3.3, 99.1 ± 3.7, and 99.1 ± 2.6 %, respectively. The survival time with nepodin treatment was increased by 14.6 ± 2.5, 16.2 ± 1.5, and 19.8 ± 1.7 days at each dose, respectively. This study newly identified the plant R. crispus containing nepodin, which is a potential antimalarial compound. It exhibited the inhibitory activity of PfNDH2 and prolonged the survival time on the group of nepodin treatment; moreover, it inhibited the parasitemia in the animal test.

Indolequinone inhibitors of NRH:quinone oxidoreductase 2. Characterization of the mechanism of inhibition in both cell-free and cellular systems

We describe a series of indolequinones as efficient mechanism-based inhibitors of NRH:quinone oxidoreductase 2 (NQO2) for use either in cellular or cell-free systems. Compounds were designed to be reduced in the active site of the enzyme leading to loss of a substituted phenol leaving group and generation of a reactive iminium electrophile. Inhibition of NQO2 activity was assessed in both cell-free systems and the human leukemia K562 cell line. Inhibition of recombinant human NQO2 by the indolequinones was NRH-dependent, with kinetic parameters characteristic of mechanism-based inhibition and partition ratios as low as 2.0. Indolequinones inhibited NQO2 activity in K562 cells at nanomolar concentrations that did not inhibit NQO1 and were nontoxic to cells. Computation-based molecular modeling simulations demonstrated favorable conformations of indolequinones positioned directly above and in parallel with the isoalloxazine ring of FAD, and mass spectrometry extended our previous finding of adduction of the FAD in the active site of NQO2 by an indolequinone-derived iminium electrophile to the wider series of indolequinone inhibitors. Modeling combined with biochemical testing identified key structural parameters for effective inhibition, including a 5-aminoalkylamino side chain. Hydrogen bonding of the terminal amine nitrogen in the aminoalkylamino side chain was found to be critical for the correct orientation of the inhibitors in the active site. These indolequinones were irreversible inhibitors and were found to be at least 1 order of magnitude more potent than any previously documented competitive inhibitors of NQO2 and represent the first mechanism-based inhibitors of NQO2 to be characterized in cellular systems.

Resveratrol derivatives as promising chemopreventive agents with improved potency and selectivity

SCOPE

Despite scores of investigations, the actual impact of resveratrol (3,5,4'-trihydroxy-trans-stilbene) on human health, as a dietary component or supplement, remains moot. This is due to many factors, such as relatively low potency, pleiotropic mechanisms, and rapid metabolism. Nonetheless, as a promiscuous molecule that interacts with numerous targets, resveratrol can be viewed as a scaffold for designing structural relatives potentially capable of mediating more intense responses with greater mechanistic stringency.

METHODS AND RESULTS

We currently report the synthesis and biological evaluation of 92 stilbene analogs. The compounds were tested with in vitro assays for activation of quinone reductase 1, inhibition of quinone reductase 2, nitric oxide production, aromatase, NFκB, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase, or cyclooxygenase-1 and -2, quenching of 2,2-diphenyl-1-picrylhydrazyl free radical, interaction with estrogen receptors, and as antiproliferative agents. Several compounds were found to mediate responses with much greater potency than resveratrol; some mediated pleiotropic responses, as is the case with the parent molecule, but others were highly specific or totally inactive. When administered to rats, higher serum concentrations and greater stability was demonstrated with prototype lead molecules.

CONCLUSION

Owing to structural simplicity, facile syntheses are available for large-scale production. These data support the promise of more advanced development of novel resveratrol derivatives as drug entities.

Design, synthesis, and biological evaluation of resveratrol analogues as aromatase and quinone reductase 2 inhibitors for chemoprevention of cancer

A series of new resveratrol analogues were designed and synthesized and their inhibitory activities against aromatase were evaluated. The crystal structure of human aromatase (PDB 3eqm) was used to rationalize the mechanism of action of the aromatase inhibitor 32 (IC50 0.59 microM) through docking, molecular mechanics energy minimization, and computer graphics molecular modeling, and the information was utilized to design several very potent inhibitors, including compounds 82 (IC50 70 nM) and 84 (IC50 36 nM). The aromatase inhibitory activities of these compounds are much more potent than that for the lead compound resveratrol, which has an IC50 of 80 microM. In addition to aromatase inhibitory activity, compounds 32 and 44 also displayed potent QR2 inhibitory activity (IC50 1.7 microM and 0.27 microM, respectively) and the high-resolution X-ray structures of QR2 in complex with these two compounds provide insight into their mechanism of QR2 inhibition. The aromatase and quinone reductase inhibitors resulting from these studies have potential value in the treatment and prevention of cancer.

5-MCA-NAT does not act through NQO2 to reduce intraocular pressure in New-Zealand white rabbit

Solid data support the idea that the MT(3) melatonin binding site is an enzyme, quinone reductase 2 (NQO2), rather than a membrane melatonin receptor. However, the melatonin analogue, 5-methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT), reduces intraocular pressure (IOP) via MT(3) melatonin receptors. Therefore, the aim of this work was to test whether the melatonin binding site, MT(3), is indeed the enzyme NQO2 in New Zealand rabbit eyes. To investigate this, the action of several substrates and inhibitors for NQO2 was compared to 5-MCA-NAT in their ability to modify IOP. Also, the effect of 5-MCA-NAT on IOP produced after NQO2 silencing by means of a siRNA was determinated. Altogether, the results led us to conclude that the in vivo effect of the MT(3) ligand 5-MCA-NAT on IOP is not mediated by the enzyme NQO2, suggesting the existence of another melatonin receptor.

Antiproliferative effects of resveratrol and the mediating role of resveratrol targeting protein NQO2 in androgen receptor-positive, hormone-non-responsive CWR22Rv1 cells

Trans-resveratrol, a polyphenol present in red wines and various human foods, was first reported to exhibit chemopreventive properties based on studies using a mouse skin cancer model. Our laboratory and others subsequently demonstrated the antiprostate cancer (anti-CaP) activity of resveratrol, as evident in its suppression of cell proliferation, arrest of cell cycle progression, and induction of apoptosis in androgen-responsive LNCaP and androgen-non-responsive DU145 and PC-3 CaP cells. However, the molecular mechanism of action of resveratrol has not been tested in androgen receptor (AR)-positive hormone-non-responsive CWR22Rv1 cells, which mimic the transition stages of prostate carcinoma. In this study, we investigated the antiproliferative effects of resveratrol in the context of modulation of growth suppression and NF-kappaB expression as mediated by resveratrol targeting protein NQO2, using both control and NQO2 siRNA silenced CWR22Rv1 cells. Exposure to resveratrol resulted in a potent, dose-dependent inhibition of CWR22Rv1 proliferation, which was accompanied by a reduction in the expression of NF-kappaB p65. The suppression of NF-kappaB p65 expression was abrogated in NQO2 siRNA silenced CWR22Rv1 cells, suggesting that NQO2 is upstream of and integral to the regulation of NF-kappaB p65. To our knowledge, this study is the first to reveal that resveratrol targeting protein NQO2 plays a mediating role in resveratrol-induced changes of NF-kappaB p65, which may contribute to the anti-CaP activities elicited by resveratrol.

The structure of the leukemia drug imatinib bound to human quinone reductase 2 (NQO2)

BACKGROUND

Imatinib represents the first in a class of drugs targeted against chronic myelogenous leukemia to enter the clinic, showing excellent efficacy and specificity for Abl, Kit, and PDGFR kinases. Recent screens carried out to find off-target proteins that bind to imatinib identified the oxidoreductase NQO2, a flavoprotein that is phosphorylated in a chronic myelogenous leukemia cell line.

RESULTS

We examined the inhibition of NQO2 activity by the Abl kinase inhibitors imatinib, nilotinib, and dasatinib, and obtained IC50 values of 80 nM, 380 nM, and >100 microM, respectively. Using electronic absorption spectroscopy, we show that imatinib binding results in a perturbation of the protein environment around the flavin prosthetic group in NQO2. We have determined the crystal structure of the complex of imatinib with human NQO2 at 1.75 A resolution, which reveals that imatinib binds in the enzyme active site, adjacent to the flavin isoalloxazine ring. We find that phosphorylation of NQO2 has little effect on enzyme activity and is therefore likely to regulate other aspects of NQO2 function.

CONCLUSION

The structure of the imatinib-NQO2 complex demonstrates that imatinib inhibits NQO2 activity by competing with substrate for the active site. The overall conformation of imatinib when bound to NQO2 resembles the folded conformation observed in some kinase complexes. Interactions made by imatinib with residues at the rim of the active site provide an explanation for the binding selectivity of NQO2 for imatinib, nilotinib, and dasatinib. These interactions also provide a rationale for the lack of inhibition of the related oxidoreductase NQO1 by these compounds. Taken together, these studies provide insight into the mechanism of NQO2 inhibition by imatinib, with potential implications for drug design and treatment of chronic myelogenous leukemia in patients.

NADPH-dependent coenzyme Q reductase is the main enzyme responsible for the reduction of non-mitochondrial CoQ in cells

We purified an NADPH-dependent coenzyme Q reductase (NADPH-CoQ reductase) in rat liver cytosol and compared its enzymatic properties with those of the other CoQ10 reductases such as NADPH: quinone acceptor oxidoreductase 1 (NQO1), lipoamide dehydrogenase, thioredoxine reductase and glutathione reductase. NADPH-CoQ reductase was the only enzyme that preferred NADPH to NADH as an electron donor and was also different from the other CoQ10 reductases in the sensitivities to its inhibitors and stimulators. Especially, Zn2+ was the most powerful inhibitor for NADPH-CoQ reductase, but CoQ10 reduction by the other CoQ10 reductases could not be inhibited by Zn2+. Furthermore, the reduction of the CoQ9 incorporated into HeLa cells was also inhibited by Zn2+ in the presence of pyrithione, a zinc ionophore. Moreover, NQO1 gene silencing in HeLa cells by transfection of a small interfering RNA resulted in lowering of both the NQO1 protein level and the NQO1 activity by about 75%. However, this transfection did not affect the NADPH-CoQ reductase activity and the reduction of CoQ9 incorporated into the cells. These results suggest that the NADPH-CoQ reductase located in cytosol may be the main enzyme responsible for the reduction of non-mitochondrial CoQ in cells.

Quantitative chemical proteomics reveals mechanisms of action of clinical ABL kinase inhibitors

We describe a chemical proteomics approach to profile the interaction of small molecules with hundreds of endogenously expressed protein kinases and purine-binding proteins. This subproteome is captured by immobilized nonselective kinase inhibitors (kinobeads), and the bound proteins are quantified in parallel by mass spectrometry using isobaric tags for relative and absolute quantification (iTRAQ). By measuring the competition with the affinity matrix, we assess the binding of drugs to their targets in cell lysates and in cells. By mapping drug-induced changes in the phosphorylation state of the captured proteome, we also analyze signaling pathways downstream of target kinases. Quantitative profiling of the drugs imatinib (Gleevec), dasatinib (Sprycel) and bosutinib in K562 cells confirms known targets including ABL and SRC family kinases and identifies the receptor tyrosine kinase DDR1 and the oxidoreductase NQO2 as novel targets of imatinib. The data suggest that our approach is a valuable tool for drug discovery.

Chemical proteomic profiles of the BCR-ABL inhibitors imatinib, nilotinib, and dasatinib reveal novel kinase and nonkinase targets

The BCR-ABL tyrosine kinase inhibitor imatinib represents the current frontline therapy in chronic myeloid leukemia. Because many patients develop imatinib resistance, 2 second-generation drugs, nilotinib and dasatinib, displaying increased potency against BCR-ABL were developed. To predict potential side effects and novel medical uses, we generated comprehensive drug-protein interaction profiles by chemical proteomics for all 3 drugs. Our studies yielded 4 major findings: (1) The interaction profiles of the 3 drugs displayed strong differences and only a small overlap covering the ABL kinases. (2) Dasatinib bound in excess of 30 Tyr and Ser/Thr kinases, including major regulators of the immune system, suggesting that dasatinib might have a particular impact on immune function. (3) Despite the high specificity of nilotinib, the receptor tyrosine kinase DDR1 was identified and validated as an additional major target. (4) The oxidoreductase NQO2 was bound and inhibited by imatinib and nilotinib at physiologically relevant drug concentrations, representing the first nonkinase target of these drugs.

NRH:quinone oxidoreductase 2 and NAD(P)H:quinone oxidoreductase 1 protect tumor suppressor p53 against 20s proteasomal degradation leading to stabilization and activation of p53

Tumor suppressor p53 is either lost or mutated in several types of cancer. MDM2 interaction with p53 results in ubiquitination and 26S proteasomal degradation of p53. Chronic DNA damage leads to inactivation of MDM2, stabilization of p53, and apoptotic cell death. Here, we present a novel MDM2/ubiquitination-independent mechanism of stabilization and transient activation of p53. The present studies show that 20S proteasomes degrade p53. The 20S degradation of p53 was observed in ubiquitin-efficient and -deficient cells, indicating that this pathway of degradation did not require ubiquitination of p53. The cytosolic quinone oxidoreductases [NRH:quinone oxidoreductase 2 (NQO2) and NAD(P)H:quinone oxidoreductase 1 (NQO1)] interacted with p53 and protected p53 against 20S proteasomal degradation. Further studies revealed that acute exposure to radiation or chemical leads to induction of NQO1 and NQO2 that stabilizes and transiently activates p53 and downstream genes. These results suggest that stress-induced NQO1 and NQO2 transiently stabilize p53, which leads to protection against adverse effects of stressors.

Reduction of mitomycin C is catalysed by human recombinant NRH:quinone oxidoreductase 2 using reduced nicotinamide adenine dinucleotide as an electron donating co-factor

NRH:Quinone Oxidoreductase 2 (NQO2) has been described as having no enzymatic activity with nicotinamide adenine dinucleotide (NADH) or NADPH as electron donating cosubstrates. Mitomycin C (MMC) is both a substrate for and a mechanistic inhibitor of the NQO2 homologue NQO1. NRH:quinone oxidoreductase 2 catalysed the reduction of MMC at pH 5.8 with NADH as a co-factor. This reaction results in species that inhibit the NQO2-mediated metabolism of CB1954. In addition, MMC caused an increase in DNA cross-links in a cell line transfected to overexpress NQO2 to an extent comparable to that observed with an isogenic NQO1-expressing cell line. These data indicate that NQO2 may contribute to the metabolism of MMC to cytotoxic species.

Steady-state kinetics and inhibitory action of antitubercular phenothiazines on mycobacterium tuberculosis type-II NADH-menaquinone oxidoreductase (NDH-2)

Type-II NADH-menaquinone oxidoreductase (NDH-2) is an essential respiratory enzyme of the pathogenic bacterium Mycobacterium tuberculosis (Mtb) that plays a pivotal role in its growth. In the present study, we expressed and purified highly active Mtb NDH-2 using a Mycobacterium smegmatis expression system, and the steady-state kinetics and inhibitory actions of phenothiazines were characterized. Purified NDH-2 contains a non-covalently bound flavin adenine dinucleotide cofactor and oxidizes NADH with quinones but does not react with either NADPH or oxygen. Ubiquinone-2 (Q2) and decylubiquinone showed high electron-accepting activity, and the steady-state kinetics and the NADH-Q2 oxidoreductase reaction were found to operate by a ping-pong reaction mechanism. Phenothiazine analogues, trifluoperazine, Compound 1, and Compound 2 inhibit the NADH-Q2 reductase activity with IC50 = 12, 11, and 13 microm, respectively. Trifluoperazine inhibition is non-competitive for NADH, whereas the inhibition kinetics is found to be uncompetitive in terms of Q2.

Inhibitor studies on non-photochemical plastoquinone reduction and H(2) photoproduction in Chlamydomonas reinhardtii

In the absence of PSII, non-photochemical reduction of plastoquinones (PQs) occurs following NADH or NADPH addition in thylakoid membranes of the green alga Chlamydomonas reinhardtii. The nature of the enzyme involved in this reaction has been investigated in vitro by measuring chlorophyll fluorescence increase in anoxia and light-dependent O(2) uptake in the presence of methyl viologen. Based on the insensitivity of these reactions to rotenone, a type-I NADH dehydrogenase (NDH-1) inhibitor, and their sensitivity to flavoenzyme inhibitors and thiol blocking agents, we conclude to the involvement of a type-II NADH dehydrogenase (NDH-2) in PQ reduction. Intact Chlamydomonas cells placed in anoxia have the property to produce H(2) in the light by a Fe-hydrogenase which uses reduced ferredoxin as an electron donor. H(2) production also occurs in the absence of PSII thanks to the existence of a non-photochemical pathway of PQ reduction. From inhibitors effects, we suggest the involvement of a plastidial NDH-2 in PSII-independent H(2) production in Chlamydomonas. These results are discussed in relation to the absence of ndh genes in Chlamydomonas plastid genome and to the existence of 7 ORFs homologous to type-II NDHs in its nuclear genome.