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) counterscreen assay to assess selectivity against anti-target pPAFAH in vitro
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) inhibition and selectivity to assess carbamate vs. triazole urea scaffold
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) inhibition and selectivity
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
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) assay to assess selectivity against anti-target pPAFAH in situ
Source (MLPCN Center Name): The Scripps Research Institute Molecular Screening Center (SRIMSC) Center Affiliation: The Scripps Research Institute (TSRI) Assay Provider: 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_LCMS_SILAC
Name: Late stage assay provider results from the probe development effort to identify inhibitors of PAFAH2: LC-MS-based cell-based SILAC Activity-Based Protein Profiling (ABPP) for PAFAH2.
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.
1. Ames, B.N., Dietary carcinogens and anticarcinogens. Oxygen radicals and degenerative diseases. Science, 1983. 221(4617): p. 1256-64. 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. 13. Prescott, S.M., et al., Platelet-activating factor and related lipid mediators. Annu. Rev. Biochem., 2000. 69: p. 419-45. 14. Karasawa, K., et al., Plasma platelet activating factor-acetylhydrolase (PAF-AH). Prog. Lipid Res., 2003. 42(2): p. 93-114. 15. Leitinger, N., Oxidized phospholipids as triggers of inflammation in atherosclerosis. Mol. Nutr. Food Res., 2005. 49(11): p. 1063-71. 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. 22. Matsuzawa, A., et al., Protection against oxidative stress-induced cell death by intracellular platelet-activating factor-acetylhydrolase II. J. Biol. Chem., 1997. 272(51): p. 32315-20. 23. Marques, M., et al., Identification of platelet-activating factor acetylhydrolase II in human skin. J. Invest. Dermatol., 2002. 119(4): p. 913-9. 24. Jessani, N., et al., Enzyme activity profiles of the secreted and membrane proteome that depict cancer cell invasiveness. Proc. Natl. Acad. Sci. U. S. A., 2002. 99(16): p. 10335-40. 25. Leung, D., et al., Discovering potent and selective reversible inhibitors of enzymes in complex proteomes. Nat. Biotechnol., 2003. 21(6): p. 687-91. 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, activity-based protein profiling, ABPP, gel-based ABPP, fluorophosphonate rhodamine, FP-Rh, stable isotope labeling with amino acids in cell culture, SILAC, liquid chromatography-tandem mass spectrometry, LC-MS/MS, inhibitor, in situ, cell-based assay, 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 determine the selectivity profile of powder samples of test compounds using stable isotope labeling with amino acids in cell culture (SILAC) ABPP. In this assay, cultured BW5147-derived murine T-cells are metabolically labeled with light or heavy amino acids. Light and heavy cells are treated with inhibitor and DMSO, respectively, in situ. Cells are lysed, proteomes are treated with FP-biotin, and combined in a 1:1 (w/w) ratio. Biotinylated proteins are enriched, trypsinized, and analyzed by LC/LC-MS/MS (MudPIT). Inhibition of target and anti-target activity is quantified by comparing intensities of light and heavy peptide peaks. As designed, compounds that act as inhibitors will block FP-biotin labeling, reducing enrichment in the inhibitor-treated (light) sample relative to the DMSO-treated (heavy) sample, giving a smaller light/heavy ratio for each protein. Proteins not targeted by inhibitors would be expected to have a ratio of 1.
Stable isotope labeling with amino acids in cell culture (SILAC):
BW5147-derived murine T-cell hybridoma cells were initially grown for 6 passages in either light or heavy SILAC RPMI 1640 media supplemented with 10% dialyzed FCS and 1x PenStrep Glutamine. Light media was supplemented with 100 ug/mL L-arginine (Sigma) and 100 ug/mL L-lysine (Sigma). Heavy media was supplemented with 100 ug/mL [13C615N4]-L-Arginine (Isotek) and 100 ug/mL [13C615N2]-L-Lysine (Isotek). Cells were treated with 3 nM test compound (5 uL of a 1000x stock in DMSO) for 4 hours at 37 C. Cells were harvested, washed 4 times with 10 mL DPBS, and homogenized by sonication in DPBS. The soluble and membrane fractions were isolated by centrifugation (100K x g, 45 minutes) and the protein concentration was adjusted to 1 mg/mL with DPBS.
Sample preparation for ABPP-SILAC:
The light and heavy proteomes were labeled with 7 muM of FP-biotin (500 muL total reaction volume) for 1.5 hours at 25 C. After incubation, light and heavy proteomes were mixed in 1:1 ratio, and the membrane proteomes were additionally solubilized with 1% Triton-X100. The proteomes were desalted over PD-10 desalting columns (GE Healthcare) and FP-labeled proteins were enriched with streptavidin beads. The beads were washed with 1% SDS in PBS (1x), PBS (3x), and H2O (3x), then resuspended in 6 M urea, reduced with DTT for 15 minutes at 60 C, and alkylated with iodoacetamide for 30 minutes at 25 C in the dark. On-bead digestions were performed for 12 hours at 37 C with trypsin (Promega; 4 muL of 0.5 mug/muL) in the presence of 2 mM CaCl2. Peptide samples were acidified to a final concentration of 5% formic acid, pressure-loaded on to a biphasic (strong cation exchange/reverse phase) capillary column and analyzed as described below.
Digested and acidified peptide mixtures were analyzed by two-dimensional liquid chromatography (2D-LC) separation in combination with tandem mass spectrometry using an Agilent 1100-series quaternary pump and Thermo Scientific LTQ Orbitrap ion trap mass spectrometer. Peptides were eluted in a 5-step MudPIT experiment using 0%, 25%, 50%, 80%, and 100% salt bumps of 500 mM aqueous ammonium acetate and data were collected in data-dependent acquisition mode with dynamic exclusion turned on (60 s, repeat of 1). Specifically, one full MS (MS1) scan (400-1800 m/z) was followed by 7 MS2 scans of the most abundant ions. The MS2 spectra data were extracted from the raw file using RAW Xtractor (version 1.9.1; publicly available at http://fields.scripps.edu/?q=content/download). MS2 spectra data were searched using the SEQUEST algorithm (Version 3.0) against the latest version of the mouse IPI database concatenated with the reversed database for assessment of false-discovery rates. SEQUEST searches allowed for variable oxidation of methionine (+16), static modification of cysteine residues (+57 due to alkylation), and no enzyme specificity. The resulting MS2 spectra matches were assembled into protein identifications and filtered using DTASelect (version 2.0.41) using the --trypstat option, which applies different statistical models for the analysis of tryptic, half-tryptic, non-tryptic peptides. DTASelect 2.0 uses a quadratic discriminant analysis to achieve a user-defined maximum peptide false positive rate; the default parameters (maximum false positive rate of 2%) was used for the search; however, the actual false positive rate was much lower (1%). Ratios of Light/Heavy peaks were calculated using in-house software; reported ratios represent the mean of all unique, quantified peptides per protein.
Ratio = Average( AUClight / AUCheavy ) calculated for all unique peptides
AUClight is the area-under-the-curve for the light peptide pair from cells treated with test compound. AUCheavy is the area-under-the-curve for the heavy peptide pair from cells treated with DMSO.
PubChem Activity Outcome and Score:
The following applies to each panel in this assay:
A compound was considered active for a particular target/anti-target with a light/heavy ratio of less than or equal to 0.5. A compound was considered in active for a specified target/anti-target with a light/heavy ratio of greater than 0.5.
Overall Outcome and Score:
A compound was considered active if it was active for PAFAH2 and inactive for all anti-target serine hydrolases tested.
Active compounds were given a score of 100 and inactive compounds were given a score of 0.
The PubChem Activity Score range for active compounds is 100-100. There are no inactive compounds.