An automated multistep high-throughput screening assay for the identification of lead inhibitors of the inducible enzyme mPGES-1

Engineering 'Enzymelink' for screening lead compounds to inhibit mPGES-1 while maintaining prostacyclin synthase activity

Aim: This study investigated our Enzymelinks, COX-2-10aa-mPGES-1 and COX-2-10aa-PGIS, as cellular cross-screening targets for quick identification of lead compounds to inhibit inflammatory PGE₂ biosynthesis while maintaining prostacyclin synthesis. Methods: We integrated virtual and wet cross-screening using Enzymelinks to rapidly identify lead compounds from a large compound library. Results: From 380,000 compounds virtually cross-screened with the Enzymelinks, 1576 compounds were identified and used for wet cross-screening using HEK293 cells that overexpressed individual Enzymelinks as targets. The top 15 lead compounds that inhibited mPGES-1 activity were identified. The top compound that specifically inhibited inflammatory PGE₂ biosynthesis alone without affecting COX-2 coupled to PGI₂ synthase (PGIS) for PGI₂ biosynthesis was obtained. Conclusion: Enzymelink technology could advance cyclooxygenase pathway-targeted drug discovery to a significant degree.

High-Precision, Room Temperature Screening Assay for Inhibitors of Microsomal Prostaglandin E Synthase-1

Microsomal prostaglandin E synthase-1 (mPGES-1) is the major enzyme catalyzing the isomerization of prostaglandin (PG) H2 to PGE2. Here we report the development of a robust and practical automated assay in a 384-well format for room temperature screening of mPGES-1 inhibitors with high precision and low reagent consumption. The assay should enable precise structure-activity relationship development. It uses acetonitrile as solvent for PGH2, FeCl2/citrate as stop reagent, and a short reaction time. Combined with high-precision liquid transfer and extensive mixing after addition of reactants, these properties let the assay reach Z′ > 0.7 and high reproducibility of inhibitor IC50 values. Thorough investigation of the quality of mixing in all liquid transfer steps proved crucial for reaching high-precision performance.

Abbreviations: mPGES-1 (microsomal prostaglandin E synthase-1); FRET (fluorescence resonance energy transfer); HTRF (homogeneous time-resolved fluorescence); PGH2 (prostaglandin H2); PGE2 (prostaglandin E2); SAR (structure-activity relationship); COX-2 (cyclooxygenase-2); GSH (glutathione); ALP (automated labware positioner)

Lead Discovery for Microsomal Prostaglandin E Synthase Using a Combination of High-Throughput Fluorescent-Based Assays and RapidFire Mass Spectrometry

Microsomal prostaglandin E synthase-1 (mPGES-1) represents an attractive target for the treatment of rheumatoid arthritis and pain, being upregulated in response to inflammatory stimuli. Biochemical assays for prostaglandin E synthase activity are complicated by the instability of the substrate (PGH2) and the challenge of detection of the product (PGE2). A coupled fluorescent assay is described for mPGES-1where PGH2 is generated in situ using the action of cyclooxygenase 2 (Cox-2) on arachidonic acid. PGE2 is detected by coupling through 15-prostaglandin dehydrogenase (15-PGDH) and diaphorase. The overall coupled reaction was miniaturized to 1536-well plates and validated for high-throughput screening. For compound progression, a novel high-throughput mass spectrometry assay was developed using the RapidFire platform. The assay employs the same in situ substrate generation step as the fluorescent assay, after which both PGE2 and a reduced form of the unreacted substrate were detected by mass spectrometry. Pharmacology and assay quality were comparable between both assays, but the mass spectrometry assay was shown to be less susceptible to interference and false positives. Exploiting the throughput of the fluorescent assay and the label-free, direct detection of the RapidFire has proved to be a powerful lead discovery strategy for this challenging target.

Identification and development of mPGES-1 inhibitors: where we are at?

Microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal synthase responsible for the synthesis of the pro-tumorigenic prostaglandin E(2) (PGE(2)). mPGES-1 is overexpressed in a wide variety of cancers. Since its discovery in 1997 by Bengt Samuelsson and collaborators, the enzyme has been the object of over 200 peer-reviewed articles. Although today mPGES-1 is considered a validated and promising therapeutic target for anticancer drug discovery, challenges in inhibitor design and selectivity are such that up to this date there are only a few published records of small-molecule inhibitors targeting the enzyme and exhibiting some in vivo anticancer activity. This review summarizes the structures, and the in vitro and in vivo activities of these novel mPGES-1 inhibitors. Challenges that have been encountered are also discussed.

HTRF-Based Assay for Microsomal Prostaglandin E2 Synthase-1 Activity

Microsomal prostaglandin E2 synthase-1 (mPGES-1) catalyzes the formation of prostaglandin E2 (PGE2) from the endoperoxide prostaglandin H 2 (PGH2). Expression of this enzyme is induced during the inflammatory response, and mouse knockout experiments suggest it may be an attractive target for antiarthritic therapies. Assaying the activity of this enzyme in vitro is challenging because of the unstable nature of the PGH 2 substrate. Here, the authors present an mPGES-1 activity assay suitable for characterization of enzyme preparations and for determining the potency of inhibitor compounds. This plate-based competition assay uses homogenous time-resolved fluorescence to measure PGE2 produced by the enzyme. The assay is insensitive to DMSO concentration up to 10% and does not require extensive washes after the initial enzyme reaction is concluded, making it a simple and convenient way to assess mPGES-1 inhibition. ( Journal of Biomolecular Screening 2008:619-625)