Multi-dimensional target profiling of N,4-diaryl-1,3-thiazole-2-amines as potent inhibitors of eicosanoid metabolism

Eicosanoids like leukotrienes and prostaglandins play a considerable role in inflammation. Produced within the arachidonic acid (AA) cascade, these lipid mediators are involved in the pathogenesis of pain as well as acute and chronic inflammatory diseases like rheumatoid arthritis and asthma. With regard to the lipid cross-talk within the AA pathway, a promising approach for an effective anti-inflammatory therapy is the development of inhibitors targeting more than one enzyme of this cascade. Within this study, thirty N-4-diaryl-1,3-thiazole-2-amine based compounds with different substitution patterns were synthesized and tested in various cell-based assays to investigate their activity and selectivity profile concerning five key enzymes involved in eicosanoid metabolism (5-, 12-, 15-lipoxygenase (LO), cyclooxygenase-1 and -2 (COX-1/-2)). With compound 7, 2-(4-phenyl)thiazol-2-ylamino)phenol (ST-1355), a multi-target ligand targeting all tested enzymes is presented, whereas compound 9, 2-(4-(4-chlorophenyl)thiazol-2-ylamino)phenol (ST-1705), represents a potent and selective 5-LO and COX-2 inhibitor with an IC50 value of 0.9 ± 0.2 μM (5-LO) and a residual activity of 9.1 ± 1.1% at 10 μM (COX-2 product formation). The promising characteristics and the additional non-cytotoxic profile of both compounds reveal new lead structures for the treatment of eicosanoid-mediated diseases.

Expression of integrin α3β1 and cyclooxygenase-2 (COX2) are positively correlated in human breast cancer

BACKGROUND

Expression of integrin α3β1 is associated with tumor progression, metastasis, and poor prognosis in several cancers, including breast cancer. Moreover, preclinical studies have revealed important pro-tumorigenic and pro-metastatic functions for this integrin, including tumor growth, survival, invasion, and paracrine induction of angiogenesis. Our previously published work in a preclinical breast cancer model showed that integrin α3β1 promotes expression of cyclooxygenase-2 (COX2/PTGS2), a known driver of breast cancer progression. However, the clinical significance of this regulation was unknown. The objective of the current study was to assess the clinical relevance of the relationship between integrin α3β1 and COX2 by testing for their correlated expression among various forms of human breast cancer.

METHODS

Immunohistochemistry was performed to assess co-expression of α3 and COX2 in specimens of human invasive ductal carcinoma (IDC), either on a commercial tissue microarray (n = 59 samples) or obtained from Albany Medical Center archives (n = 68 samples). Immunostaining intensity for the integrin α3 subunit or COX2 was scored, and Spearman's rank correlation coefficient analysis was performed to assess their co-expression across and within different tumor subtypes or clinicopathologic criteria.

RESULTS

Although expression of integrin α3 or COX2 varied among clinical IDC samples, a statistically significant, positive correlation was detected between α3 and COX2 in both tissue microarrays (r(s) = 0.49, p < 0.001, n = 59) and archived samples (r(s) = 0.59, p < 0.0001, n = 68). In both sample sets, this correlation was independent of hormone receptor status, histological grade, or disease stage.

CONCLUSIONS

COX2 and α3 are correlated in IDC independently of hormone receptor status or other clinicopathologic features, supporting the hypothesis that integrin α3β1 is a determinant of COX2 expression in human breast cancer. These results support the clinical relevance of α3β1-dependent COX2 gene expression that we reported previously in breast cancer cells. The findings also suggest that COX2-positive breast carcinomas of various subtypes might be vulnerable to therapeutic strategies that target α3β1, and that α3 expression might serve as an independent prognostic biomarker.

Oxidative stress: an essential factor in the pathogenesis of gastrointestinal mucosal diseases

Reactive oxygen species (ROS) are generated as by-products of normal cellular metabolic activities. Superoxide dismutase, glutathione peroxidase, and catalase are the enzymes involved in protecting cells from the damaging effects of ROS. ROS are produced in response to ultraviolet radiation, cigarette smoking, alcohol, nonsteroidal anti-inflammatory drugs, ischemia-reperfusion injury, chronic infections, and inflammatory disorders. Disruption of normal cellular homeostasis by redox signaling may result in cardiovascular, neurodegenerative diseases and cancer. ROS are produced within the gastrointestinal (GI) tract, but their roles in pathophysiology and disease pathogenesis have not been well studied. Despite the protective barrier provided by the mucosa, ingested materials and microbial pathogens can induce oxidative injury and GI inflammatory responses involving the epithelium and immune/inflammatory cells. The pathogenesis of various GI diseases including peptic ulcers, gastrointestinal cancers, and inflammatory bowel disease is in part due to oxidative stress. Unraveling the signaling events initiated at the cellular level by oxidative free radicals as well as the physiological responses to such stress is important to better understand disease pathogenesis and to develop new therapies to manage a variety of conditions for which current therapies are not always sufficient.

Conjugates of cisplatin and cyclooxygenase inhibitors as potent antitumor agents overcoming cisplatin resistance

Cyclooxygenase-2 (COX-2) is an enzyme involved in tumorigenesis, and inhibitors of the enzyme are increasingly used as adjuvant modulators in anticancer therapies due to their synergistic effects with traditional chemotherapeutics. COX-2 is also reported to cause resistance towards antitumor agents, such as cisplatin. Here, the first covalently linked conjugates of cisplatin and COX inhibitors are reported. These conjugates exhibit concerted transport of both drugs into tumor cells and simultaneous action upon intracellular cleavage. These platinum(IV) complexes show highly increased cytotoxicity compared with cisplatin and are even able to overcome cisplatin-related resistance of tumor cells. While the results reported show that COX-2 inhibition is not directly responsible for the potent activities of these conjugates, they do represent useful tool compounds for the elucidation of the influence of COX inhibitors on the efficacy of antitumor agents.

2,3-Diaryl-substituted indole based COX-2 inhibitors as leads for imaging tracer development

A series of 2,3-diaryl-substituted indoles containing a fluorine or methoxy group was synthesized via Fischer indole synthesis, McMurry cyclization, or Bischler–Möhlau reaction to identify potential leads for PET radiotracer development.

Ibuprofen: from invention to an OTC therapeutic mainstay

The discovery of ibuprofen's anti-inflammatory activity by Dr (now Professor) Stewart Adams and colleagues (Boots Pure Chemical Company Ltd, Nottingham, UK) 50 years ago represented a milestone in the development of anti-inflammatory analgesics. Subsequent clinical studies were the basis for ibuprofen being widely accepted for treating painful conditions at high anti-rheumatic doses (≤ 2400 mg/d), with lower doses (≤ 1200 mg/d for ≤ 10 days) for mild-moderate acute pain (e.g. dental pain, headache, dysmenorrhoea, respiratory symptoms and acute injury). The early observations have since been verified in studies comparing ibuprofen with newer cyclo-oxygenase-2 selective inhibitors ('coxibs'), paracetamol and other non-steroidal anti-inflammatory drugs (NSAIDs). The use of the low-dose, non-prescription, over-the-counter (OTC) drug was based on marketing approval in 1983 (UK) and 1984 (USA); and it is now available in over 80 countries. The relative safety of OTC ibuprofen has been supported by large-scale controlled studies. It has the same low gastro-intestinal (GI) effects as paracetamol (acetaminophen) and fewer GI effects than aspirin. Ibuprofen is a racemate. Its physicochemical properties and the short plasma-elimination half-life of the R(-) isomer, together with its limited ability to inhibit cyclo-oxygenase-1 (COX-1) and thus prostaglandin (PG) synthesis, compared with that of S(+)-ibuprofen, are responsible for the relatively low GI toxicity. The R(-) isomer is then converted in the body to the S(+) isomer after absorption in the GI tract. Ex vivo inhibition of COX-1 (thromboxane A(2)) and COX-2 (PGE(2)) at the plasma concentrations of S(+)-ibuprofen corresponding to those found in the plasma following ingestion of 400 mg ibuprofen in dental and other inflammatory pain models provides evidence of the anti-inflammatory mechanism at OTC dosages. R(-)-ibuprofen has effects on leucocytes, suggesting that ibuprofen has anti-leucocyte effects, which underlie its anti-inflammatory actions. Future developments include novel gastro-tolerant forms for 'at risk' patients, and uses in the prevention of neuro-inflammatory states and cancers.

Stabilized epoxygenated fatty acids regulate inflammation, pain, angiogenesis and cancer

Epoxygenated fatty acids (EpFAs), which are lipid mediators produced by cytochrome P450 epoxygenases from polyunsaturated fatty acids, are important signaling molecules known to regulate various biological processes including inflammation, pain and angiogenesis. The EpFAs are further metabolized by soluble epoxide hydrolase (sEH) to form fatty acid diols which are usually less-active. Pharmacological inhibitors of sEH that stabilize endogenous EpFAs are being considered for human clinical uses. Here we review the biology of ω-3 and ω-6 EpFAs on inflammation, pain, angiogenesis and tumorigenesis.

Fluorophore-labeled cyclooxygenase-2 inhibitors for the imaging of cyclooxygenase-2 overexpression in cancer: synthesis and biological studies

A group of cyclooxygenase-2 (COX-2)-specific fluorescent cancer biomarkers were synthesized by linking the anti-inflammatory drugs ibuprofen, (S)-naproxen, and celecoxib to the 7-nitrobenzofurazan (NBD) fluorophore. In vitro COX-1/COX-2 inhibition studies indicated that all of these fluorescent conjugates are COX-2 inhibitors (IC₅₀ range: 0.19-23.0 μM) with an appreciable COX-2 selectivity index (SI≥4.3-444). In this study the celecoxib-NBD conjugate N-(2-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)amino)ethyl)-4-(5-(p-tolyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl)benzenesulfonamide, which displayed the highest COX-2 inhibitory potency and selectivity (COX-2 IC₅₀ =0.19 μM; SI=443.6), was identified as an impending COX-2-specific biomarker for the fluorescence imaging of cancer using a COX-2-expressing human colon cancer cell line (HCA-7).

A mechanistic hypothesis for the aspirin-induced switch in lipid mediator production by cyclooxygenase-2

Cyclooxygenase (COX) carries out stereospecific oxygen addition to arachidonic acid to generate prostaglandins, plus smaller amounts of 11- and 15-hydroxyeicosatetraenoic acids. For COX-2, the stereochemistry and relative abundance of generated products is influenced by Ser530 acetylation following aspirin treatment. The molecular bases of the high degree of stereospecificity which characterizes COX-2-catalyzed oxygenations are not yet completely understood, nor are the reasons behind the aspirin-induced shift in lipid mediator production. A mechanistic hypothesis is proposed which identifies steric shielding as the main determinant of oxygenation stereospecificity. This hypothesis is supported by a computational model which accurately reproduces experimental oxygenation patterns on both native and aspirin-inhibited COX-2.

Polyisoprenylated methylated protein methyl esterase is both sensitive to curcumin and overexpressed in colorectal cancer: implications for chemoprevention and treatment

Inhibition of PMPMEase, a key enzyme in the polyisoprenylation pathway, induces cancer cell death. In this study, purified PMPMEase was inhibited by the chemopreventive agent, curcumin, with a K(i) of 0.3 μM (IC50 = 12.4 μM). Preincubation of PMPMEase with 1 mM curcumin followed by gel-filtration chromatography resulted in recovery of the enzyme activity, indicative of reversible inhibition. Kinetics analysis with N-para-nitrobenzoyl-S-trans,trans-farnesylcysteine methyl ester substrate yielded K M values of 23.6 ± 2.7 and 85.3 ± 15.3 μM in the absence or presence of 20 μM curcumin, respectively. Treatment of colorectal cancer (Caco2) cells with curcumin resulted in concentration-dependent cell death with an EC50 of 22.0 μg/mL. PMPMEase activity in the curcumin-treated cell lysate followed a similar concentration-dependent profile with IC50 of 22.6 μg/mL. In colorectal cancer tissue microarray studies, PMPMEase immunoreactivity was significantly higher in 88.6% of cases compared to normal colon tissues (P < 0.0001). The mean scores ± SEM were 91.7 ± 11.4 (normal), 75.0 ± 14.4 (normal adjacent), 294.8 ± 7.8 (adenocarcinoma), and 310.0 ± 22.6 (mucinous adenocarcinoma), respectively. PMPMEase overexpression in colorectal cancer and cancer cell death stemming from its inhibition is an indication of its possible role in cancer progression and a target for chemopreventive agents.

Celecoxib-loaded PLGA/cyclodextrin microspheres: characterization and evaluation of anti-inflammatory activity on human chondrocyte cultures

PLGA microspheres were prepared as a sustained release system for the intra-articular administration of celecoxib (CCB). The microspheres were prepared in the presence of different concentrations of dimethyl-β-cyclodextrin (DM-β-Cyd), by the simple oil-in-water emulsion/evaporation solvent method. The microspheres were evaluated as to surface morphology, size and technological properties (such as encapsulation efficiency, drug loading capacity and drug release). Ex vivo studies on cultures of human chondrocytes were performed in order to evaluate the influence of the polymeric carriers on the pharmacological activity of CCB. All systems ranged from about 1 to 5 μm in size and had a high encapsulation efficiency percentage ranging from about 80% to 90% (w/w), except for CCB-loaded-PLGA microspheres containing the highest amount of DM-β-Cyd, in which a dramatic drop in the encapsulation efficiency was observed (about 54%, w/w). FIB images evidenced the fact that the microspheres had a porous structure in the presence of the highest amount of DM-β-Cyd. The macrocycle modulated the release profiles of CCB from the microspheres, producing in some cases a zero-order kinetic release. Ex vivo biological studies demonstrated that DM-β-Cyd improved the drug's anti-inflammatory activity. Thus, CCB-loaded PLGA/cyclodextrin microspheres may have a potential therapeutic application in the treatment of osteo- and rheumatoid arthritis.

Radiolabeled COX-2 inhibitors for non-invasive visualization of COX-2 expression and activity--a critical update

Cyclooxygenase-2 (COX-2) is a key player in inflammation. Its overexpression is directly associated with various inflammatory diseases and, additionally, with several processes of carcinogenesis. The development of new selective COX-2 inhibitors (COXIBs) for use in cancer treatment is in the focus of the medicinal chemistry research field. For this purpose, a set of methods is available to determine COX-2 expression and activity in vitro and ex vivo but it is still a problem to functionally characterize COX-2 in vivo. This review focusses on imaging agents targeting COX-2 which have been developed for positron emission tomography (PET) and single photon emission computed tomography (SPECT) since 2005. The literature reveals that different radiochemical methods are available to synthesize COXIBs radiolabeled with fluorine-18, carbon-11, and isotopes of radioiodine. Unfortunately, most of the compounds tested did not show sufficient stability in vivo due to de[¹⁸F]fluorination or de[¹¹C]methylation or they failed to bind specifically in the target region. So, suitable stability in vivo, matching lipophilicity for the target compartment and both high affinity and selectivity for COX-2 were identified as prominent criteria for radiotracer development. Up to now, it is not clear what approach and which model is the most suited to evaluate COX-2 targeting imaging agents in vivo. However, for proof of principle it has been shown that some radiolabeled compounds can bind specifically in COX-2 overexpressing tissue which gives hope for future work in this field.

The 2'-Trifluoromethyl Analogue of Indomethacin Is a Potent and Selective COX-2 Inhibitor

Indomethacin is a potent, time-dependent, nonselective inhibitor of the cyclooxygenase enzymes (COX-1 and COX-2). Deletion of the 2′-methyl group of indomethacin produces a weak, reversible COX inhibitor, leading us to explore functionality at that position. Here, we report that substitution of the 2′-methyl group of indomethacin with trifluoromethyl produces CF₃–indomethacin, a tight-binding inhibitor with kinetic properties similar to those of indomethacin and unexpected COX-2 selectivity (IC₅₀ mCOX-2 = 267 nM; IC₅₀ oCOX-1 > 100 μM). Studies with site-directed mutants reveal that COX-2 selectivity results from insertion of the CF₃ group into a small hydrophobic pocket formed by Ala-527, Val-349, Ser-530, and Leu-531 and projection of the methoxy group toward a side pocket bordered by Val-523. CF₃–indomethacin inhibited COX-2 activity in human head and neck squamous cell carcinoma cells and exhibited in vivo anti-inflammatory activity in the carrageenan-induced rat paw edema model with similar potency to that of indomethacin.

1,4-Diaryl-substituted triazoles as cyclooxygenase-2 inhibitors: Synthesis, biological evaluation and molecular modeling studies

A novel group of 1,4-diaryl-substituted triazoles was designed and synthesized by introducing the cyclooxygenase-2 (COX-2) pharmacophore SO2NH2 attached to one aryl ring and various substituents (H, F, Cl, CH3 or OCH3) attached to the other aryl ring. The effects of size and flexibility of the compounds upon COX-1/COX-2 inhibitory potency and selectivity was studied by increasing the size of an alkyl linker chain [(-CH2)n, where n=0, 1, 2]. In vitro COX-1/COX-2 inhibition studies showed that all compounds (14-18, 21-25 and 28-32) are more potent inhibitors of COX-2 isozyme (IC50=0.17-28.0μM range) compared to COX-1 isozyme (IC50=21.0 to >100μM range). Within the group of 1,4 diaryl-substituted triazoles, 4-{2-[4-(4-chloro-phenyl)-[1,2,3]triazol-1-yl]-ethyl}-benzenesulfonamide (compound 30) displayed highest COX-2 inhibitory potency and selectivity (COX-1: IC50=>100μM, COX-2: IC50=0.17μM, SI >588). Molecular docking studies using the catalytic site of COX-1 and COX-2, respectively, provided complementary theoretical support for the obtained experimental biological structure-activity relationship data. Results of molecular docking studies revealed that COX-2 pharmacophore SO2NH2 in compound 30 is positioned in the secondary pocket of COX-2 active site; with the nitrogen atom of the SO2NH2 group being hydrogen bonded to Q192 (N⋯OC=2.85Å), and one of the oxygen atoms of SO2NH2 group forming a hydrogen bond to H90 (SO⋯N=2.38Å).

Molecular imaging of cyclooxygenase-2 in canine transitional cell carcinomas in vitro and in vivo

The enzyme COX-2 is induced at high levels in tumors but not in surrounding normal tissues, which makes it an attractive target for molecular imaging of cancer. We evaluated the ability of novel optical imaging agent, fluorocoxib A to detect urinary bladder canine transitional cell carcinomas (K9TCC). Here, we show that fluorocoxib A uptake overlapped with COX-2 expression in primary K9TCC cells in vitro. Using subcutaneously implanted primary K9TCC in athymic mice, we show specific uptake of fluorocoxib A by COX-2-expressing K9TCC xenograft tumors in vivo. Fluorocoxib A uptake by COX-2-expressing xenograft tumors was blocked by 70% (P < 0.005) when pretreated with the COX-2 selective inhibitor, celecoxib (10 mg/kg), 4 hours before intravenous administration of fluorocoxib A (1 mg/kg). Fluorocoxib A was taken up by COX-2-expressing tumors but not by COX-2-negative human UMUC-3 xenograft tumors. UMUC-3 xenograft tumors with no expression of COX-2 showed no uptake of fluorocoxib A. In addition, fluorocoxib A uptake was evaluated in five dogs diagnosed with TCC. Fluorocoxib A specifically detected COX-2-expressing K9TCC during cystoscopy in vivo but was not detected in normal urothelium. Taken together, our findings show that fluorocoxib A selectively bound to COX-2-expressing primary K9TCC cells in vitro, COX-2-expressing K9TCC xenografts tumors in nude mice, and heterogeneous canine TCC during cystoscopy in vivo. Spontaneous cancers in companion animals offer a unique translational model for evaluation of novel imaging and therapeutic agents using primary cancer cells in vitro and in heterogeneous cancers in vivo.

Reciprocal crosstalk between dendritic cells and natural killer cells under the effects of PGE2 in immunity and immunopathology

The reciprocal activating crosstalk between dendritic cells (DCs) and natural killer (NK) cells plays a pivotal role in regulating immune defense against viruses and tumors. The cytokine-producing capacity, Th-cell polarizing ability and chemokine expression, migration and stimulatory functions of DCs are regulated by activated NK cells. Conversely, the innate and effector functions of NK cells require close interactions with activated DCs. Cell membrane-associated molecules and soluble mediators, including cytokines and prostaglandins (PGs), contribute to the bidirectional crosstalk between DCs and NK cells. One of the most well-known and well-studied PGs is PGE2. Produced by many cell types, PGE2 has been shown to affect various aspects of the immune and inflammatory responses by acting on all components of the immune system. There is emerging evidence that PGE2 plays crucial roles in DC and NK cell biology. Several studies have shown that DCs are not only a source of PGE2, but also a target of its immunomodulatory action in normal immune response and during immune disorders. Although NK cells appear to be unable to produce PGE2, they are described as powerful PGE2-responding cells, as they express all PGE2 E-prostanoid (EP) receptors. Several NK cell functions (lysis, migration, proliferation, cytokine production) are influenced by PGE2. This review highlights the effects of PGE2 on DC-NK cell crosstalk and its subsequent impact on immune regulations in normal and immunopathological processes.

Lipids and addiction: how sex steroids, prostaglandins, and cannabinoids interact with drugs of abuse

Lipidomics aims to identify and characterize all endogenous species of lipids and understand their roles in cellular signaling and, ultimately, the functioning of the organism. We are on the cusp of fully understanding the functions of many of the lipid signaling systems that have been identified for decades (e.g., steroids, prostaglandins), whereas our understanding of newer lipid signaling systems (e.g., endocannabinoids, N-acyl amides) still lags considerably behind. With an emphasis on their roles in the neurophysiology of addiction, we will examine three classes of lipids--sex steroids, prostaglandins, and cannabinoids--and how they work synergistically in the neurocircuitry of motivation. We will first give a brief overview of the biosynthesis for each class of lipid and its receptors, and then summarize what is known about the collective roles of the lipids in cocaine and alcohol abuse. This approach provides a novel view of lipid signaling as a class of molecules and their synergistic roles in addiction.

Calcitriol restores renovascular function in estrogen-deficient rats through downregulation of cyclooxygenase-2 and the thromboxane-prostanoid receptor

Cardiovascular risks increase in postmenopausal women. While vitamin D is supplemented for osteoporosis, it is not known whether it protects renal arterial function during estrogen deficiency. Here we measured changes in renovascular reactivity induced by ovariectomy in rats and examined whether calcitriol, the most active form of vitamin D, was able to correct such changes. The impairment of endothelium-dependent relaxation in renal arteries from ovariectomized rats was effectively reversed by long-term calcitriol treatment. It was also corrected by acute exposure to cyclooxygenase-2 (COX-2) inhibitors and a thromboxane-prostanoid receptor antagonist, respectively. Calcitriol normalized the overexpression of COX-2 and thromboxane-prostanoid receptors in intralobal renal artery segments and aortic endothelial cells isolated from ovariectomized rats. In vitro exposure of the arterial segments to calcitriol for 12 h improved relaxation and downregulated thromboxane-prostanoid receptors. The attenuated nitric oxide production in ovariectomized rat aortic endothelial cells was restored following a 12-h treatment with calcitriol, COX-2 inhibition, or thromboxane-prostanoid receptor antagonism. Thus, impaired endothelium-dependent renal artery relaxation in ovariectomized rats is mediated largely through increased activity and expression of COX-2 and the thromboxane-prostanoid receptor. Calcitriol restores endothelial function through downregulating both signaling proteins during estrogen deficiency.

MSK1 and MSK2 inhibit lipopolysaccharide-induced prostaglandin production via an interleukin-10 feedback loop

Prostaglandin production is catalyzed by cyclooxygenase 2 (cox-2). We demonstrate here that MSK1 and MSK2 (MSK1/2) can exert control on the induction of cox-2 mRNA by Toll-like receptor (TLR) agonists. In the initial phase of cox-2 induction, MSK1/2 knockout macrophages confirmed a role for MSK in the positive regulation of transcription. However, at later time points both lipopolysaccharide (LPS)-induced prostaglandin and cox-2 protein levels were increased in MSK1/2 knockout. Further analysis found that while MSKs promoted cox-2 mRNA transcription, following longer LPS stimulation MSKs also promoted degradation of cox-2 mRNA. This was found to be the result of an interleukin 10 (IL-10) feedback mechanism, with endogenously produced IL-10 promoting cox-2 degradation. The ability of IL-10 to do this was dependent on the mRNA binding protein TTP through a p38/MK2-mediated mechanism. As MSKs regulate IL-10 production in response to LPS, MSK1/2 knockout results in reduced IL-10 secretion and therefore reduced feedback from IL-10 on cox-2 mRNA stability. Following LPS stimulation, this increased mRNA stability correlated to an elevated induction of both of cox-2 protein and prostaglandin secretion in MSK1/2 knockout macrophages relative to that in wild-type cells. This was not restricted to isolated macrophages, as a similar effect of MSK1/2 knockout was seen on plasma prostaglandin E2 (PGE2) levels following intraperitoneal injection of LPS.

2-Carbaborane-3-phenyl-1H-indoles--synthesis via McMurry reaction and cyclooxygenase (COX) inhibition activity

Cyclooxygenase-2 (COX-2) inhibitors have been the focus of medicinal chemistry efforts for years, and many compounds that exhibit high selectivity and affinity have been developed. As carbaboranes represent interesting pharmacophores as phenyl mimetics in drug development, this paper presents the synthesis of carbaboranyl derivatives of COX-2-selective 2,3-disubstituted indoles. Despite the lability of carbaboranes under reducing conditions, 2-carbaborane-3-phenyl-1H-indoles could be synthesized by McMurry cyclization of the corresponding amides. Whereas the meta-carbaboranyl-substituted derivatives lacked COX inhibitory activity, an ortho-carbaboranyl analogue was active, but showed a selectivity shift toward COX-1.

Förster resonance energy transfer competitive displacement assay for human soluble epoxide hydrolase

The soluble epoxide hydrolase (sEH), responsible for the hydrolysis of various fatty acid epoxides to their corresponding 1,2-diols, is becoming an attractive pharmaceutical target. These fatty acid epoxides, particularly epoxyeicosatrienoic acids (EETs), play an important role in human homeostatic and inflammation processes. Therefore, inhibition of human sEH, which stabilizes EETs in vivo, brings several beneficial effects to human health. Although there are several catalytic assays available to determine the potency of sEH inhibitors, measuring the in vitro inhibition constant (K(i)) for these inhibitors using catalytic assay is laborious. In addition, k(off), which has been recently suggested to correlate better with the in vivo potency of inhibitors, has never been measured for sEH inhibitors. To better measure the potency of sEH inhibitors, a reporting ligand, 1-(adamantan-1-yl)-3-(1-(2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetyl) piperidin-4-yl)urea (ACPU), was designed and synthesized. With ACPU, we have developed a Förster resonance energy transfer (FRET)-based competitive displacement assay using intrinsic tryptophan fluorescence from sEH. In addition, the resulting assay allows us to measure the K(i) values of very potent compounds to the picomolar level and to obtain relative k(off) values of the inhibitors. This assay provides additional data to evaluate the potency of sEH inhibitors.

Visualization of cyclooxygenase-2 using a 2,3-diarylsubstituted indole-based inhibitor and confocal laser induced cryofluorescence microscopy at 20K in melanoma cells in vitro

This study aimed at visualization of cyclooxygenase-2 (COX-2) protein expression in melanoma cells by confocal laser induced cryofluorescence microscopy using 4-(3-(4-methoxyphenyl)-1H-indol-2-yl)benzene-sulfonamide (C1) representative for a novel class of autofluorescent 2,3-diarylsubstituted indole-based selective COX-2 inhibitors. COX-2 expression was measured in human melanoma cell lines A2058 and MelJuso by immunocytochemistry and immunoblotting. Cellular uptake experiments using varying C1 concentrations down to 0.1 nM (with/without molar excess of celecoxib as control) were performed at 37 °C. Cryofluorescence microscopy was conducted at 20 K. COX-2 protein expression was successfully visualized by C1 in A2058 cells. COX-2-negative MelJuso cells showed no specific accumulation of C1. Control experiments using celecoxib and, additionally, implemented fluorescence spectroscopy confirmed specificity of both cellular uptake and intracellular association of C1. Cryofluorescence microscopy in combination with spectroscopy allowed for visualization of COX-2 protein expression in melanoma cells in vitro using a selective COX-2 inhibitor at very low concentrations.

Single-dose safety and pharmacokinetic evaluation of fluorocoxib A: pilot study of novel cyclooxygenase-2-targeted optical imaging agent in a canine model

We evaluated preclinical single-dose safety, pharmacokinetic properties, and specific uptake of the new optical imaging agent fluorocoxib A in dogs. Fluorocoxib A, N-[(5-carboxy-X-rhodaminyl)but-4-yl]-2-[1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indol-3-yl]acetamide, selectively binds and inhibits the cyclooxygenase-2 (COX-2) enzyme, which is overexpressed in many cancers. Safety pilot studies were performed in research dogs following intravenous (i.v.) administration of 0.1 and 1  mg/kg fluorocoxib A. Blood and urine samples collected three days after administration of each dose of fluorocoxib A revealed no evidence of toxicity, and no clinically relevant adverse events were noted on physical examination of exposed dogs over that time period. Pharmacokinetic parameters were assessed in additional research dogs from plasma collected at several time points after i.v. administration of fluorocoxib A using high-performance liquid chromatography analysis. The pharmacokinetic studies using 1  mg/kg showed a peak of fluorocoxib A (92±28  ng/ml) in plasma collected at 0.5 h. Tumor specific uptake of fluorocoxib A was demonstrated using a dog diagnosed with colorectal cancer expressing COX-2. Our data support the safe single-dose administration and in vivo efficacy of fluorocoxib A, suggesting a high potential for successful translation to clinical use as an imaging agent for improved tumor detection in humans.

Identification and characterization of carprofen as a multitarget fatty acid amide hydrolase/cyclooxygenase inhibitor

Pain and inflammation are major therapeutic areas for drug discovery. Current drugs for these pathologies have limited efficacy, however, and often cause a number of unwanted side effects. In the present study, we identify the nonsteroidal anti-inflammatory drug carprofen as a multitarget-directed ligand that simultaneously inhibits cyclooxygenase-1 (COX-1), COX-2, and fatty acid amide hydrolase (FAAH). Additionally, we synthesized and tested several derivatives of carprofen, sharing this multitarget activity. This may result in improved analgesic efficacy and reduced side effects (Naidu et al. J. Pharmacol. Exp. Ther.2009, 329, 48-56; Fowler, C. J.; et al. J. Enzyme Inhib. Med. Chem.2012, in press; Sasso et al. Pharmacol. Res.2012, 65, 553). The new compounds are among the most potent multitarget FAAH/COX inhibitors reported so far in the literature and thus may represent promising starting points for the discovery of new analgesic and anti-inflammatory drugs.

Impact of soluble epoxide hydrolase and epoxyeicosanoids on human health

The presence of epoxyeicosatrienoic acids (EETs) in tissues and their metabolism by soluble epoxide hydrolase (sEH) to 1,2-diols were first reported 30 years ago. However, appreciation of their importance in cell biology and physiology has greatly accelerated over the past decade with the discovery of metabolically stable inhibitors of sEH, the commercial availability of EETs, and the development of analytical methods for the quantification of EETs and their diols. Numerous roles of EETs in regulatory biology now are clear, and the value of sEH inhibition in various animal models of disease has been demonstrated. Here, we review these results and discuss how the pharmacological stabilization of EETs and other natural epoxy-fatty acids could lead to possible disease therapies.

Synthesis and selective inhibitory activity against human COX-1 of novel 1-(4-substituted-thiazol-2-yl)-3,5-di(hetero)aryl-pyrazoline derivatives

Novel 1-(4-ethyl carboxylate-thiazol-2-yl)-3,5-di(hetero)aryl-2-pyrazoline derivatives were obtained by reacting 3,5-di(hetero)aryl-1-thiocarbamoyl-2-pyrazolines with the ethyl ester of α-bromo-pyruvic acid. The synthesized compounds were confirmed by spectroscopic data and assayed to evaluate their in vitro ability to inhibit both isoforms of human cyclooxygenase (hCOX). Some derivatives (compounds 5, 6, 13, 16, and 17) displayed promising selectivity against hCOX-1 in the micromolar range and were shown to have a selectivity index similar or better than the reference drugs (indometacin, diclofenac). The introduction of a phenyl or a 4-F-phenyl ring on the C5 associated with a 4-substituted phenyl or a heteroaryl group on the C3 of (4-substituted-thiazol-2-yl)pyrazoline derivatives improved the activity against hCOX-1. Thanks to these preliminary results it could be possible to extend our knowledge of the pharmacophoric requirements for the discovery of new pyrazoline-based hCOX-1 inhibitors.

Inflammation and cancer: chemical approaches to mechanisms, imaging, and treatment

The inflammatory response represents a first line of defense against invading pathogens and is important to human health. Chronic inflammation contributes to the etiology of multiple diseases, especially those associated with aging, such as cancer and cardiovascular disease. The chemistry of the inflammatory response is complex and involves the generation of highly reactive oxidants and electrophiles designed to kill the pathogen as well as the release of small molecule and protein mediators of intercellular signaling, chemotaxis, vasoconstriction, and wound-healing. Oxidation of unsaturated fatty acids--either nonenzymatic or enzymatic--contributes to the inflammatory response and associated cellular pathologies. The current perspective summarizes our research on unsaturated fatty acid oxidation in the context of inflammation and cancer. In addition to understanding the consequences of DNA and protein modification by lipid electrophiles, our research has focused on the development of molecularly targeted agents to image and treat cancer.

Investigating substrate promiscuity in cyclooxygenase-2: the role of Arg-120 and residues lining the hydrophobic groove

The cyclooxygenases (COX-1 and COX-2) generate prostaglandin H(2) from arachidonic acid (AA). In its catalytically productive conformation, AA binds within the cyclooxygenase channel with its carboxylate near Arg-120 and Tyr-355 and ω-end located within a hydrophobic groove above Ser-530. Although AA is the preferred substrate for both isoforms, COX-2 can oxygenate a broad spectrum of substrates. Mutational analyses have established that an interaction of the carboxylate of AA with Arg-120 is required for high affinity binding by COX-1 but not COX-2, suggesting that hydrophobic interactions between the ω-end of substrates and cyclooxygenase channel residues play a significant role in COX-2-mediated oxygenation. We used structure-function analyses to investigate the role that Arg-120 and residues lining the hydrophobic groove play in the binding and oxygenation of substrates by murine (mu) COX-2. Mutations to individual amino acids within the hydrophobic groove exhibited decreased rates of oxygenation toward AA with little effect on binding. R120A muCOX-2 oxygenated 18-carbon ω-6 and ω-3 substrates albeit at reduced rates, indicating that an interaction with Arg-120 is not required for catalysis. Structural determinations of Co(3+)-protoporphyrin IX-reconstituted muCOX-2 with α-linolenic acid and G533V muCOX-2 with AA indicate that proper bisallylic carbon alignment is the major determinant for efficient substrate oxygenation by COX-2. Overall, these findings implicate Arg-120 and hydrophobic groove residues as determinants that govern proper alignment of the bisallylic carbon below Tyr-385 for catalysis in COX-2 and confirm nuances between COX isoforms that explain substrate promiscuity.

Cyclooxygenase-2 and gastric cancer

Gastric cancer remains a leading cause of cancer-related deaths worldwide, although its incidence has been steadily declining during recent decades. Expression of cyclooxygenase-2 (COX-2) is elevated in gastric carcinomas and in their precursor lesions. COX-2 expression associates with reduced survival in gastric cancer patients, and it has also been shown to be an independent factor of poor prognosis. Several molecular mechanisms are involved in the regulation of COX-2 expression in gastric cancer cell lines, including signal transduction pathways activated by Helicobacter pylori. In gastric tumor models in vivo the role of COX-2 seems to be predominantly to facilitate tumor promotion and growth.

Observation of two modes of inhibition of human microsomal prostaglandin E synthase 1 by the cyclopentenone 15-deoxy-Δ(12,14)-prostaglandin J(2)

Microsomal prostaglandin E synthase 1 (MPGES1) is an enzyme that produces the pro-inflammatory molecule prostaglandin E(2) (PGE(2)). Effective inhibitors of MPGES1 are of considerable pharmacological interest for the selective control of pain, fever, and inflammation. The isoprostane, 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), a naturally occurring degradation product of prostaglandin D(2), is known to have anti-inflammatory properties. In this paper, we demonstrate that 15d-PGJ(2) can inhibit MPGES1 by covalent modification of residue C59 and by noncovalent inhibition through binding at the substrate (PGH(2)) binding site. The mechanism of inhibition is dissected by analysis of the native enzyme and the MPGES1 C59A mutant in the presence of glutathione (GSH) and glutathione sulfonate. The location of inhibitor adduction and noncovalent binding was determined by triple mass spectrometry sequencing and with backbone amide H/D exchange mass spectrometry. The kinetics, regiochemistry, and stereochemistry of the spontaneous reaction of GSH with 15d-PGJ(2) were determined. The question of whether the anti-inflammatory properties of 15d-PGJ(2) are due to inhibition of MPGES1 is discussed.

Cyclooxygenase-1-selective inhibitors based on the (E)-2'-des-methyl-sulindac sulfide scaffold

Prostaglandins (PGs) are powerful lipid mediators in many physiological and pathophysiological responses. They are produced by oxidation of arachidonic acid (AA) by cyclooxygenases (COX-1 and COX-2) followed by metabolism of endoperoxide intermediates by terminal PG synthases. PG biosynthesis is inhibited by nonsteroidal anti-inflammatory drugs (NSAIDs). Specific inhibition of COX-2 has been extensively investigated, but relatively few COX-1-selective inhibitors have been described. Recent reports of a possible contribution of COX-1 in analgesia, neuroinflammation, or carcinogenesis suggest that COX-1 is a potential therapeutic target. We designed, synthesized, and evaluated a series of (E)-2'-des-methyl-sulindac sulfide (E-DMSS) analogues for inhibition of COX-1. Several potent and selective inhibitors were discovered, and the most promising compounds were active against COX-1 in intact ovarian carcinoma cells (OVCAR-3). The compounds inhibited tumor cell proliferation but only at concentrations >100-fold higher than the concentrations that inhibit COX-1 activity. E-DMSS analogues may be useful probes of COX-1 biology in vivo and promising leads for COX-1-targeted therapeutic agents.

N-1 and C-3 substituted indole Schiff bases as selective COX-2 inhibitors: synthesis and biological evaluation

A group of N-1 and C-3 disubstituted-indole Schiff bases bearing an indole N-1 (R'=H, CH(2)Ph, COPh) substituent in conjunction with a C-3 -C=HN-C(6)H(4)-4-X (X=F, Me, CF(3), Cl) substituent were synthesized and evaluated as inhibitors of cyclooxygenase (COX) isozymes (COX-1/COX-2). Within this group of Schiff bases, compounds 15 (R(1)=CH(2)Ph, X=F), 17 (R(1)=CH(2)Ph, X=CF(3)), 18 (R(1)=COPh, X=F) and 20 (R(1)=COPh, X=CF(3)) were identified as effective and selective COX-2 inhibitors (COX-2 IC(50)'s=0.32-0.84 μM range; COX-2 selectivity index (SI)=113 to >312 range). 1-Benzoyl-3-[(4-trifluoromethylphenylimino)methyl]indole (20) emerged as the most potent (COX-1 IC(50) >100 μM; COX-2 IC(50)=0.32 μM) and selective (SI >312) COX-2 inhibitor. Furthermore, compound 20 is a selective COX-2 inhibitor in contrast to the reference drug indomethacin that is a potent and selective COX-1 inhibitor (COX-1 IC(50)=0.13 μM; COX-2 IC(50)=6.9 μM, COX-2 SI=0.02). Molecular modeling studies employing compound 20 showed that the phenyl CF(3) substituent attached to the CN spacer is positioned near the secondary pocket of the COX-2 active site, the CN nitrogen atom is hydrogen bonded (N···NH=2.85 Å) to the H90 residue, and the indole N-1 benzoyl is positioned in a hydrophobic pocket of the COX-2 active site near W387.

Nitric oxide release is not required to decrease the ulcerogenic profile of nonsteroidal anti-inflammatory drugs

The objective of this work was to evaluate the biological properties of a new series of nitric oxide-releasing nonsteroidal anti-inflammatory drugs (NO-NSAIDs) possessing a tyrosol linker between the NSAID and the NO-releasing moiety (PROLI/NO); however, initial screening of ester intermediates without the PROLI/NO group showed the required (desirable) efficacy/safety ratio, which questioned the need for NO in the design. In this regard, NSAID ester intermediates were potent and selective COX-2 inhibitors in vitro, showed equipotent anti-inflammatory activity compared to the corresponding parent NSAID, but showed a markedly reduced gastric toxicity when administered orally. These results provide complementary evidence to challenge the currently accepted notion that hybrid NO-NSAIDs exert their cytoprotective effects by releasing NO. Results obtained in this work constitute a good body of evidence to initiate a debate about the future replacement of NSAID prodrugs for unprotected NSAIDs (possessing a free carboxylic acid group) currently in clinical use.

Inhibition of cyclooxygenase-2 causes regression of gastric adenomas in trefoil factor 1 deficient mice

Cyclooxygenase-2 (Cox-2) expression is a marker of reduced survival in gastric cancer patients, and inhibition of Cox-2 suppresses gastrointestinal carcinogenesis in experimental animal models. To investigate the role of Cox-2 in gastric carcinogenesis in vivo, we utilized trefoil factor 1 (Tff1) deficient mice, which model the neoplastic process of the stomach by developing gastric adenomas with full penetrance. These tumors express Cox-2 protein and mRNA, and we have now investigated the effects of genetic deletion of the mouse Cox-2 gene [also known as prostaglandin-endoperoxide synthase 2 (Ptgs2)] and a Cox-2 selective drug celecoxib. Our results show that genetic deletion of Cox-2 in the Tff1 deleted background resulted in reduced adenoma size and ulceration with a chronic inflammatory reaction at the site of the adenoma. To characterize the effect of Cox-2 inhibition in more detail, mice that had already developed an adenoma were fed with celecoxib for 8-14 weeks, which resulted in disruption of the adenoma that ranged from superficial erosion to deep ulcerated destruction accompanied with chronic inflammation. Importantly, mice fed with celecoxib for 16 weeks, followed by control food for 9 weeks, redeveloped a complete adenoma with no detectable inflammatory process. Finally, we determined the identity of the Cox-2 expressing cells and found them to be fibroblasts. Our results show that inhibition of Cox-2 is sufficient to reversibly disrupt gastric adenomas in mice.

Binding of ibuprofen, ketorolac, and diclofenac to COX-1 and COX-2 studied by saturation transfer difference NMR

Saturation transfer difference NMR (STD-NMR) spectroscopy has emerged as a powerful screening tool and a straightforward way to study the binding epitopes of active compounds in early stage lead discovery in pharmaceutical research. Here we report the application of STD-NMR to characterize the binding of the anti-inflammatory drugs ibuprofen, diclofenac, and ketorolac to COX-1 and COX-2. Using well-studied COX inhibitors and by comparing STD signals with crystallographic structures, we show that there is a relation between the orientations of ibuprofen and diclofenac in the COX-2 active site and the relative STD responses detected in the NMR experiments. On the basis of this analysis, we propose that ketorolac should bind to the COX-2 active site in an orientation similar to that of diclofenac. We also show that the combination of STD-NMR with competition experiments constitutes a valuable tool to address the recently proposed behavior of COX-2 as functional heterodimers and complements enzyme activity studies in the effort to rationalize COX inhibition mechanisms.

Aspirin analogues as dual cyclooxygenase-2/5-lipoxygenase inhibitors: synthesis, nitric oxide release, molecular modeling, and biological evaluation as anti-inflammatory agents

Analogues of aspirin were synthesized through an efficient one-step reaction in which the carboxyl group was replaced by an ethyl ester, and/or the acetoxy group was replaced by an N-substituted sulfonamide (SO(2)NHOR(2):R(2) =H, Me, CH(2)Ph) pharmacophore. These analogues were designed for evaluation as dual cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibitors. In vitro COX-1/COX-2 isozyme inhibition studies identified compounds 11 (CO(2) H, SO(2)NHOH), 12 (CO(2)H, SO(2)NHOCH(2)Ph), and 16 (CO(2)Et, SO(2)NHOH) as highly potent and selective COX-2 inhibitors (IC(50) range: 0.07-0.7 μM), which exhibited appreciable in vivo anti-inflammatory activity (ED(50) range: 23.1-31.4 mg kg(-1)). Moreover, compounds 11 (IC(50) =0.2 μM) and 16 (IC(50) =0.3 μM), with a sulfohydroxamic acid (SO(2)NHOH) moiety showed potent 5-LOX inhibitory activity. Furthermore, the SO(2)NHOH moiety present in compounds 11 and 16 was found to be a good nitric oxide (NO) donor upon incubation in phosphate buffer at pH 7.4. Molecular docking studies in the active binding site of COX-2 and 5-LOX provided complementary theoretical support for the experimental biological structure-activity data acquired.

Hydrogen tunneling steps in cyclooxygenase-2 catalysis

Cyclooxygenases-1 and -2 are tyrosyl radical (Y·)-utilizing hemoproteins responsible for the biosynthesis of lipid-derived autocoids. COX-2, in particular, is a primary mediator of inflammation and believed to be up-regulated in many forms of cancer. Described here are first-of-a-kind studies of COX-2-catalyzed oxidation of the substrate analogue linoleic acid. Very large (≥20) temperature-independent deuterium kinetic isotope effects (KIEs) on the rate constant for enzyme turnover were observed, due to hydrogen atom abstraction from the bisallylic C-H(D) of the fatty acid. The magnitude of the KIE depends on the O(2) concentration, consistent with reversible H/D tunneling mediated by the catalytic Y·. At physiological levels of O(2), retention of the hydrogen initially abstracted by the catalytic tyrosine results in strongly temperature-dependent KIEs on O-H(D) homolysis, also characteristic of nuclear tunneling.

Dynamics of different arachidonic acid orientations bound to prostaglandin endoperoxide synthases

Prostaglandin endoperoxide synthases (PGHSs) catalyze the conversion of arachidonic acid (AA) into prostaglandin endoperoxide H(2). This reaction requires a specific orientation of AA within the active site, but an alternative crystallographic binding orientation for AA also exists. Since the origin of this alternative complex, and its potential relevance, have been neglected so far, we have characterized the dynamics of both orientations of AA, bound to PGHS-1 and -2, in order to obtain new insights for designing PGHSs inhibitors. Our results indicate that AA in the alternative orientation seems to be less stable, moving toward Arg120. Such potentially minor orientation of AA can be related to crystallographic complexes of anti-inflammatory agents, pointing to an alternate SAR on PGHSs inhibitors.

Integrin α3β1 as a breast cancer target

INTRODUCTION

Integrin receptors for cell adhesion to the extracellular matrix have important roles in all stages of cancer progression and metastasis. Since the integrin family was discovered in the early 1980's, many studies have identified critical adhesion and signaling functions for integrins expressed on tumor cells, endothelial cells and other cell types of the tumor microenvironment, in controlling proliferation, survival, migration and angiogenesis. In recent years, the laminin-binding integrin α3β1 has emerged as a potentially promising anti-cancer target on breast cancer cells.

AREAS COVERED

Studies from the past decade that implicate integrins as promising anti-cancer targets and the development of integrin antagonists as anti-cancer therapeutics. Recent preclinical studies that have identified the laminin-binding integrin α3β1 as an appealing anti-cancer target and the knowledge gaps that must be closed to fully exploit this integrin as a therapeutic target for breast cancer.

EXPERT OPINION

Although the tumor-promoting functions of α3β1 implicate this integrin as a promising therapeutic target on breast cancer cells, successful exploitation of this integrin as an anti-cancer target will require a better understanding of the molecular mechanisms whereby it regulates specific tumor cell behaviors and the identification of the most appropriate α3β1 functions to antagonize on breast cancer cells.

Location of inhibitor binding sites in the human inducible prostaglandin E synthase, MPGES1

The inducible microsomal prostaglandin E(2) synthase 1 (MPGES1) is an integral membrane protein coexpressed with and functionally coupled to cyclooxygenase 2 (COX-2) generating the pro-inflammatory molecule PGE(2). The development of effective inhibitors of MPGES1 holds promise as a highly selective route for controlling inflammation. In this paper, we describe the use of backbone amide H/D exchange mass spectrometry to map the binding sites of different types of inhibitors of MPGES1. The results reveal the locations of specific inhibitor binding sites that include the GSH binding site and a hydrophobic cleft in the protein thought to accommodate the prostaglandin H(2) substrate. In the absence of three-dimensional crystal structures of the enzyme-bound inhibitors, the results provide clear physical evidence that three pharmacologically active inhibitors bind in a hydrophobic cleft composed of sections of transmembrane helices Ia, IIb, IIIb, and IVb at the interface of subunits in the trimer. In principle, the H/D exchange behavior of the protein can be used as a preliminary guide for optimization of inhibitor efficacy. Finally, a comparison of the structures and H/D exchange behavior of MPGES1 and the related enzyme MGST1 in the presence of glutathione and the inhibitor glutathione sulfonate confirms the unusual observation that two proteins from the same superfamily harbor GSH binding sites in different locations.