Late stage assay provider results from the probe development effort to identify inhibitors of PAFAH2: Fluorescence-based biochemical gel-based Activity-Based Protein Profiling (ABPP) general inhibition and selectivity of serine hydrolases
Name: Late stage assay provider results from the probe development effort to identify inhibitors of PAFAH2: Fluorescence-based biochemical gel-based Activity-Based Protein Profiling (ABPP) general inhibition and selectivity of serine hydrolases. ..more
BioActive Compounds: 2
Source (MLPCN Center Name): The Scripps Research Institute Molecular Screening Center (SRIMSC)
Center Affiliation: The Scripps Research Institute (TSRI)
Assay Provider: Brian Bahnson, Univ. of Delaware, Benjamin Cravatt, TSRI
Network: Molecular Libraries Probe Production Centers Network (MLPCN)
Grant Proposal Number: 1R01HL084366
Grant Proposal PI: Brian Bahnson, Univ. of Delaware, Benjamin Cravatt, TSRI
External Assay ID: PAFAH2_INH_FLUO_GEL_1XINH_SH_SEL
Name: Late stage assay provider results from the probe development effort to identify inhibitors of PAFAH2: Fluorescence-based biochemical gel-based Activity-Based Protein Profiling (ABPP) general inhibition and selectivity of serine hydrolases.
Oxidative stress has been implicated as an underlying inflammatory factor in several disease pathologies, including cancer, atherosclerosis, aging, and various neurodegenerative disorders (1-5). Phospholipids in particular are susceptible to oxidative damage, and (per)oxidized phospholipids can have deleterious effects, including disruption of membrane bilayers and production of toxic byproducts (4, 6-8). One hypothesized pathway for removal of oxidatively damaged species involves hydrolysis by phospholipase A2-type enzymes. Candidate hydrolytic enzymes include the platelet-activating factor acetylhydrolases (PAFAHs) (4,9). The initial role assigned to the PAFAHs was the hydrolysis of platelet activating factor (PAF) (10,11), a potent pro-inflammatory phospholipid signaling molecule (12), which plays a role in myriad physiological processes including inflammation, anaphylaxis, fetal development, and reproduction (4,13). The PAFAHs are subdivided into three classes: plasma (p)PAFAH, and intracellular types 1 and 2. In terms of sequence homology, pPAFAH and PAFAH2 are close homologs and show little similarity to type 1 enzymes. This project aims to develop specific inhibitors for pPAFAH and three counterscreen enzymes: PAFAH2, PAFAH1b2, and PAFAH1b3.
pPAFAH is associated with inflammatory pathways involved in atherosclerosis, asthma, anaphylactic shock, and other allergic reactions (14,15). Numerous studies have also linked increases in pPAFAH concentration and/or activity to an increased risk of various cardiovascular diseases (16,17); however, the biological function of pPAFAH in the development of coronary heart diseases is controversial, with both anti- and proinflammatory roles attributed to it (18,19). Dr. Bahnson and colleagues recently reported the first high-resolution crystal structure of pPAFAH (20), and would like to expand their studies to co-crystallize pPAFAH with substrate-mimetic inhibitors to further define the active site and substrate specificity of pPAFAH. While one selective pPAFAH inhibitor has been reported (21), its properties are not suitable for the proposed studies.
PAFAH2 has also been shown to play a role in inflammatory processes via hydrolysis of oxidized phospholipids. Over-expression of PAFAH2 has been shown to reduce oxidative stress-induced cell death (22,23) and to mediate repair of oxidative-stress induced tissue injury (4). The enzyme also undergoes N-terminal myristoylation and subsequent translocation to the membrane under conditions of oxidative stress (22,23). This evidence suggests that PAFAH2 functions as an important, and perhaps primary, antioxidant enzyme in certain tissues (4); however, its substrate specificity and pathway involvement are far from being fully elucidated. Currently no suitable inhibitors exist for co-crystallization or biochemical studies of PAFAH2.
Given the complex biology of the PAFAH enzymes, chemical tools capable of interrogating enzyme architecture and providing precise temporal control over PAFAH activity are necessary for complete characterization of patho/physiological roles of the PAFAHs in phospholipid metabolism and inflammatory disease processes. Towards that goal, we developed a HTS assay for inhibitor discovery for four PAFAH enzymes: pPAFAH, PAFAH2, PAFAH1b2, and PAFAH1b3, based on their reactivity with the serine-hydrolase-specific fluorophosphonate (FP) (24) activity-based protein profiling (ABPP) probe. This reactivity can be exploited for inhibitor discovery using a competitive-ABPP platform, whereby small molecule enzyme inhibition is assessed by the ability to out-compete ABPP probe labeling (25). Competitive ABPP has also been configured to operate in a high-throughput manner via fluorescence polarization readout, FluoPol-ABPP (26). Following the HTS campaign, top inhibitors for each enzyme will be characterized and medchem optimized with the goal of delivering key reagents for elucidating the biology of the PAFAH enzymes.
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2. Halliwell, B. and J.M. Gutteridge, Role of free radicals and catalytic metal ions in human disease: an overview. Methods Enzymol., 1990. 186: p. 1-85.
3. Harman, D., The aging process. Proc. Natl. Acad. Sci. U. S. A., 1981. 78(11): p. 7124-8.
4. Kono, N., et al., Protection against oxidative stress-induced hepatic injury by intracellular type II platelet-activating factor acetylhydrolase by metabolism of oxidized phospholipids in vivo. J. Biol. Chem., 2008. 283(3): p. 1628-36.
5. Southorn, P.A. and G. Powis, Free radicals in medicine. II. Involvement in human disease. Mayo. Clin. Proc., 1988. 63(4): p. 390-408.
6. Kinnunen, P.K., On the principles of functional ordering in biological membranes. Chem. Phys. Lipids, 1991. 57(2-3): p. 375-99.
7. Uchida, K., 4-Hydroxy-2-nonenal: a product and mediator of oxidative stress. Prog. Lipid Res., 2003. 42(4): p. 318-43.
8. Fruhwirth, G.O., A. Loidl, and A. Hermetter, Oxidized phospholipids: from molecular properties to disease. Biochim. Et Biophys. Acta, 2007. 1772(7): p. 718-36.
9. Nigam, S. and T. Schewe, Phospholipase A(2)s and lipid peroxidation. Biochim. Et Biophys. Acta, 2000. 1488(1-2): p. 167-81.
10. Blank, M.L., et al., A specific acetylhydrolase for 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (a hypotensive and platelet-activating lipid). J. Biol. Chem., 1981. 256(1): p. 175-8.
11. Farr, R.S., et al., Preliminary studies of an acid-labile factor (ALF) in human sera that inactivates platelet-activating factor (PAF). Clin. Immunol. Immunopathol., 1980. 15(3): p. 318-330.
12. Zimmerman, G.A., et al., The platelet-activating factor signaling system and its regulators in syndromes of inflammation and thrombosis. Crit. Care Med., 2002. 30(5 Suppl): p. S294-301.
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14. Karasawa, K., et al., Plasma platelet activating factor-acetylhydrolase (PAF-AH). Prog. Lipid Res., 2003. 42(2): p. 93-114.
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16. Anderson, J.L., Lipoprotein-associated phospholipase A2: an independent predictor of coronary artery disease events in primary and secondary prevention. Am. J. Cardiol., 2008. 101(12A): p. 23F-33F.
17. Sudhir, K., Clinical review: Lipoprotein-associated phospholipase A2, a novel inflammatory biomarker and independent risk predictor for cardiovascular disease. J. Clin. Endocrinol. Metab., 2005. 90(5): p. 3100-5.
18. Wilensky, R.L. and C.H. Macphee, Lipoprotein-associated phospholipase A(2) and atherosclerosis. Curr. Opin. Lipidol., 2009. 20(5): p. 415-20.
19. Karabina, S.A. and E. Ninio, Plasma PAF-acetylhydrolase: an unfulfilled promise? Biochim. Et Biophys. Acta, 2006. 1761(11): p. 1351-8.
20. Samanta, U. and B.J. Bahnson, Crystal structure of human plasma platelet-activating factor acetylhydrolase: structural implication to lipoprotein binding and catalysis. J. Biol. Chem., 2008. 283(46): p. 31617-24.
21. Blackie, J.A., et al., The identification of clinical candidate SB-480848: a potent inhibitor of lipoprotein-associated phospholipase A2. Bioorg. Med. Chem. Lett., 2003. 13(6): p. 1067-70.
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26. Bachovchin, D.A., et al., Identification of selective inhibitors of uncharacterized enzymes by high-throughput screening with fluorescent activity-based probes. Nat. Biotechnol., 2009. 27(4): p. 387-94.
late stage, late stage AID, assay provider, powders, platelet-activating factor acetylhydrolase, PAFAH, PAF-AH, plasma platelet-activating factor acetylhydrolase, pPAFAH, platelet-activating factor acetylhydrolase type II, PAFAH2, PAFAHII, cancer, inflammation, atherosclerosis, serine hydrolase, counterscreen, inhibitor, selectivity, activity-based protein profiling, ABPP, gel-based ABPP, fluorophosphonate rhodamine, FP-Rh, Rh-N3, azide, click chemistry, BW5147, murine T cells, T cells, Scripps, Scripps Research Institute Molecular Screening Center, SRIMSC, Molecular Libraries Probe Production Centers Network, MLPCN
The purpose of this assay is to assess the general inhibition profiles of powder samples of test compounds in a complex proteome by competitive activity-based proteomic profiling (ABPP). In Assay 1, a complex proteome is incubated with test compound followed by reaction with a rhodamine-conjugated fluorophosphonate (FP-Rh) activity-based probe. The reaction products are separated by SDS-PAGE and visualized in-gel using a flatbed fluorescence scanner. The percentage activity remaining is determined by measuring the integrated optical density (IOD) of the bands. As designed, test compounds that act as inhibitors will prevent enzyme-probe interactions, thereby decreasing the proportion of bound fluorescent probe, giving lower fluorescence intensity in the band in the gel. Percent inhibition is calculated relative to a DMSO (no compound) control. In Assay 2, the role of competitor and probe is reversed. A complex proteome is incubated with FP-biotin followed by reaction with test compound. Click chemistry is then used to append a fluorophore-azide to the alkyne-functionalized test compounds. As designed, labeling that is successfully competed by the FP-biotin probe is indicative of serine hydrolase targets. Bands that are not competed represent non-serine hydrolase targets of test compounds.
Soluble proteome (1 mg/ml in DPBS) of mouse brain soluble proteome was treated with 20 uM of test compound (1 uL of a 50x stock in DMSO). Test compounds were incubated for 30 minutes at 25 C (50 uL reaction volume). FP-Rh (1 uL of 50x stock in DMSO) was added to a final concentration of 2 uM. The reaction was incubated for 30 minutes at 25 C, quenched with 2x SDS-PAGE loading buffer, separated by SDS-PAGE and visualized by in-gel fluorescent scanning. The percentage activity remaining was determined by measuring the integrated optical density of the bands relative to a DMSO-only (no compound) control.
Mouse brain soluble proteome (1 mg/ml in DPBS) was treated with 20 uM of FP-biotin (1 uL of a 50x stock in DMSO) for 30 minutes at 25 C (50 uL reaction volume). Test compound (1 uL of 50x stock in DMSO) was added to a final concentration of 20 uM for 30 minutes at 25 C. Click chemistry with a rhodamine-azide tag (Rh-N3; 50uM) was carried out under standard conditions (1 mM TCEP, 100 uM TBTA ligand, 1 mM Cu(II)sulfate) to append the rhodamine fluorophore to the alkyne-functionalized test compounds for visualization. Reactions were quenched with 2x SDS-PAGE loading buffer, separated by SDS-PAGE and visualized by in-gel fluorescent scanning. The percentage activity remaining was determined by measuring the integrated optical density of the bands relative to a DMSO-only (no compound) control.
%_Inhibition = ( 1 - ( IOD_Test_Compound - IOD_Low_Control ) / ( IOD_High_Control - IOD_Low_Control ) ) * 100
Test_Compound is defined as protein band in sample treated with competitive agent (test compound in Assay 1 or FP-biotin in Assay 2).
High_Control is defined as protein band in sample treated with DMSO only (no competitive agent).
Low_Control is defined as background in a blank region of the gel.
PubChem Activity Outcome and Score:
Compounds with >= 50% inhibition of two or more bands were considered active. Compounds with >= 50% inhibition of < 2 bands were considered inactive.
The reported PubChem Activity Score has been normalized to 100% observed number of compounds with >= 50% inhibition.
Assay 1 Score: The PubChem Activity Score range for active compounds is 100-62, and for inactive compounds 12-0.
Compounds with >= 50% inhibition by FP-biotin of all target bands were considered active (showing only reactivity within the serine hydrolase enzyme class). Compounds with < 50% inhibition of at least one band were considered inactive (showing undesired reactivity outside serine hydrolase class).
The reported PubChem Activity Score has been normalized to 100% observed number of compounds with >= 50% inhibition by FP-biotin.
Assay 1 Score: The PubChem Activity Score range for active compounds is 100-100, and for inactive compounds 1-1.
Overall Outcome and Score:
Compounds were considered active if they were active in Assay 1 (successful inhibition of protein targets) and active in Assay 2 (showing only reactivity within the serine hydrolase class).
The PubChem Activity Score is assigned a value of 100 for active compounds, and 0 for inactive compounds.
The PubChem Activity Score range for active compounds is 100-100, and for inactive compounds 0-0.
List of Reagents:
Soluble proteome of BW5147-derived murine T-cells
DPBS (Cellgro 20-031-CV)
Rh-N3 (provided by Assay Provider)
TCEP (Sigma-Aldrich 93284)
TBTA Ligand (Sigma-Aldrich 678937)
Copper (II) sulfate (Sigma-Aldrich 451657)
This assay was performed by the assay provider with powder samples of synthetic compounds.
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