Late stage assay provider results from the extended probe development effort to identify inhibitors of LYPLA1 and LYPLA2: Absorbance-based cell-based dose response assay to determine cytotoxicity of inhibitor compounds
Name: Late stage assay provider results from the extended probe development effort to identify inhibitors of LYPLA1 and LYPLA2: Absorbance-based cell-based dose response assay to determine cytotoxicity of inhibitor compounds. ..more
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: 1 R01 CA132630
Grant Proposal PI: Benjamin Cravatt, TSRI
External Assay ID: HELACYTOX_INH_ABS_3XCC50
Name: Late stage assay provider results from the extended probe development effort to identify inhibitors of LYPLA1 and LYPLA2: Absorbance-based cell-based dose response assay to determine cytotoxicity of inhibitor compounds.
Protein palmitoylation is an essential post-translational modification necessary for trafficking and localization of regulatory proteins that play key roles in cell growth and signaling. Numerous proteins have been identified as targets of palmitoylation, including cytoskeletal proteins, kinases, receptors, and other proteins involved in various aspects of cellular signaling and homeostasis . Using a global chemo-proteomic method for the metabolic incorporation and identification of palmitoylated proteins, we were able to identify hundreds of palmitoylated proteins, revealing palmitoylation as a widespread post-translational modification (PTM) . Palmitoylation involves an acyl-thioester linkage to specific cysteines [3,4]. Given the labile properties of thioesters, palmitoylation is potentially reversible and may be regulated in a manner analogous to other PTMs (e.g., phosphorylation). As such, identification of proteins responsible for the dynamic modulation of palmitoylation is paramount to understanding its patho/physiological roles. For example, multiple oncogenes, including HRAS and SRC, require palmitoylation for malignant transformation , suggesting protein palmitoyl thioesterases may have tumor suppressor activity required to repress aberrant growth signaling. More than a decade ago, the cytosolic serine hydrolase acyl-protein thioesterase 1 (APT1) was identified as an in vitro HRAS palmitoyl thioesterase . Initially classified as lysophospholipase 1 (LYPLA1) , the enzyme has since been demonstrated to have several hundred-fold higher activity as a protein thioesterase. While the in vitro data [6,8] provided an intriguing clue to its possible role in vivo, prior to our studies, little was known about the in vivo thioesterase activity of LYPLA1. Upon retroviral shRNA knockdown of LYPLA1, we found that HRAS was robustly hyper-palmitoylated, providing the first evidence that the endogenous enzyme is a functional protein palmitoyl thioesterase capable of regulating HRAS palmitoylation in mammalian cells. However, shRNA resulted in only an 80% reduction in LYPLA1 expression (unpublished). LYPLA2 (a.k.a. APT2) is 65% identical to LYPLA1, and also exhibits lysophospholipase activity in vitro, but its potential role as a thioesterase is unknown . shRNA knockdown studies of LYPLA2 revealed only partial knockdown of the enzyme, making substrate identification inconclusive (unpublished). A principle goal of post-genomic research is the determination of the molecular and cellular role of uncharacterized enzymes like LYPLA1 and LYPLA2. As such, selective inhibitors of LYPLA1 and/or LYPLA2 would greatly aid investigations into the biological function of these enzymes. Several inhibitors of LYPLA1 have been described [10,11], but none of these agents have proven capable of inhibiting LYPLA1 activity in cells. We recently reported optimization of a covalent dual LYPLA1/LYPLA2 inhibitor ML211 (SID 99445338), and identification of reversible compounds ML348 (SID 160654487) and ML349 (SID 160654496) that act as selective LYPLA1 and LYPLA2 inhibitors, respectively (see Probe Reports on the NIH Bookshelf at http://www.ncbi.nlm.nih.gov/books/NBK47352/). These compounds represent an important advance in chemical tools for investigating the biological function(s) of LYPLA1 and LYPLA2. However, ML211 (SID 99445338), owing to its modest solubility, does not have demonstrated in vivo activity. Irreversible chemical probes have distinct advantages vs. reversible compounds for use in living systems, as confirming target engagement is a comparatively straightforward process, and near-complete and sustained target inhibition can be achieved without extensive optimization of physicochemical and pharmacokinetic properties. The goal of this current investigation is to develop an irreversible, in vivo-active dual LYPLA1/LYPLA2 inhibitor to add to the arsenal of available chemical tools for identification of LYPLA1 and LYPLA2 substrates and evaluating the role of these enzymes in dynamic de-palmitoylation and tumorigenesis.
1. Dekker, F.J., et al., Small-molecule inhibition of APT1 affects Ras localization and signaling. Nat. Chem. Biol., 2010. 6(6): p. 449-56.
2. Duncan, J.A. and A.G. Gilman, A cytoplasmic acyl-protein thioesterase that removes palmitate from G protein alpha subunits and p21(RAS). J. Biol. Chem., 1998. 273(25): p. 15830-7.
3. Sugimoto, H., H. Hayashi, and S. Yamashita, Purification, cDNA cloning, and regulation of lysophospholipase from rat liver. J. Biol. Chem., 1996. 271(13): p. 7705-11.
4. Toyoda, T., H. Sugimoto, and S. Yamashita, Sequence, expression in Escherichia coli, and characterization of lysophospholipase II. Biochim. Biophys. Acta, 1999. 1437(2): p. 182-93.
5. Biel, M., et al., Synthesis and evaluation of acyl protein thioesterase 1 (APT1) inhibitors. Chemistry, 2006. 12(15): p. 4121-43.
6. Deck, P., et al., Development and biological evaluation of acyl protein thioesterase 1 (APT1) inhibitors. Angew. Chem. Int. Ed. Engl., 2005. 44(31): p. 4975-80.
7. 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.
8. Leung, D., et al., Discovering potent and selective reversible inhibitors of enzymes in complex proteomes. Nat. Biotechnol., 2003. 21(6): p. 687-91.
9. 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.
10. Forner, F., et al., Quantitative proteomic comparison of rat mitochondria from muscle, heart, and liver. Mol. Cell. Proteomics, 2006. 5(4): p. 608-19.
11. Schubert, C., The genomic basis of the Williams-Beuren syndrome. Cell. Mol. Life Sci., 2009. 66(7): p. 1178-97.
late stage, late stage AID, assay provider, powders, LYPLA1, lysophospholipase 1, LYPLA2, lysophospholipase 2, APT1, acyl-protein thioesterase 1, APT2, acyl-protein thioesterase 2, serine hydrolase, palmitoylation, counterscreen, dose response, HeLa, cell-based, WST-1, formazan, viability, cytotoxicity, CC50, Scripps, Scripps Research Institute Molecular Screening Center, SRIMSC, Molecular Libraries Probe Production Centers Network, MLPCN
The purpose of this assay is to determine cytotoxicity of powder samples of test compounds. In this assay, HeLa cells in either serum-free medium (Assay 1) or medium containing fetal calf serum (FCS) (Assay 2) are incubated with test compounds, followed by determination of cell viability. The assay utilizes the WST-1 substrate which is converted into colorimetric formazan dye by the metabolic activity of viable cells. The amount of formed formazan directly correlates to the number of metabolically active cells in the culture. As designed, compounds that reduce cell viability will result in decreased absorbance of the dye. Compounds are tested in triplicate in a 5-point 1:10 dilution series starting at a nominal concentration of 100 uM.
This assay was started by seeding HeLa cells in DMEM medium supplemented with 10% FCS and 1X Pen-Strep-Glutamine in a 96-well plate. Cells were incubated at 37 degrees Celsius in a humidified incubator until 80% confluent (24 hours). Medium was removed and 100 uL of fresh medium (serum-free or supplemented with 10% FCS), pre-mixed with DMSO or test compound, was added to each well. Cells were incubated for 48 hours at 37 degrees Celsius in a humidified incubator and cell viability was determined by the WST-1 assay (Roche) according to manufacturer instructions. CC50 values were determined from dose-response curves from three replicates at each inhibitor concentration (100, 10, 1, 0.1, 0.01 uM).
The % cell viability for each well was calculated as follows:
%_Cell_Viability = ( ABS_Test_Compound - MedianABS_Low_Control ) / ( MedianABS_High_Control - MedianABS_Low_Control ) * 100
Test_Compound is defined as wells containing cells in the presence of test compound.
High_Control is defined as wells containing cells treated with media only (no compound).
Low_Control is defined as wells containing no cells (media only).
Compounds with CC50 values less than 10 uM were considered active (cytotoxic). Compounds with CC50 values greater than or equal to 10 uM were considered inactive (non-cytotoxic).
PubChem Activity Outcome:
Compounds active in Assay 1 and/or Assay 2 were considered active (cytotoxic). Compounds inactive in both Assay 1 and Assay 2 were considered inactive (non-cytotoxic).
List of Reagents:
HeLa cells (provided by the Assay Provider)
DMEM Medium (CellGro 10-017-CV)
FCS (Omega Scientific, FB-01)
1x PenStrep Glutamine (CellGro 30-002-CI)
WST-1 reagent (Roche)
96-well plates (Corning)
This assay was performed by the assay provider with powder samples of synthetic test compounds.
* Activity Concentration. ** Test Concentration. § Panel component ID.