SAR Analysis of Selective Antagonists of GPR55 using an Image-Based Assay - Set 4
Assay Provider: Dr. Mary Abood, (Temple University, formerly at California Pacific Medical Center Research Institute) ..more
BioActive Compounds: 23
Data Source: Sanford-Burnham Center for Chemical Genomics(SBCCG)
Source Affiliation: Sanford-Burnham Medical Research Institute (SBMRI, San Diego, CA)
Network: NIH Molecular Libraries Probe Production Centers Network (MLPCN)
Grant Number: 1X01 DA026205-01
Assay Provider: Dr. Mary Abood, (Temple University, formerly at California Pacific Medical Center Research Institute)
The cannabinoid and endocannabinoid system has been implicated in the pathophysiology of drug dependence and addiction disorders. GPR55, an orphan G-Protein Coupled Receptor, has been reported to be a cannabinoid receptor, but its status as such remains unresolved due to conflicting results from pharmacological studies. The goal of the project is to identify small molecule antagonists of GPR55, which may aid in the deorphanization efforts of this receptor and ultimately further the understanding of the role of GPR55 in drug addiction.
This high content imaging assay utilizes a cell line permanently expressing a beta-arrestin GFP biosensor and an enhanced GPR55 receptor. Upon agonist-mediated GPR55 activation, the arrestin-GFP redistributes from the cytosolic compartment to the plasma membrane to coated pits and further into endosomal vesicles. This arrestin-GFP redistribution is measured as increased local concentrations of fluorescent arrestins.
This dose response assay is developed and performed to confirm hits originally identified in "Image-based HTS for Selective Antagonists of GPR55" (AID 2013) and to study the structure-activity relationship on analogs of the confirmed hits. Compounds are either acquired from commercial sources or synthesized internally.
1) 384-well plates, black with clear bottom (Greiner# 781091)
2) U2OS (Human Osteosarcoma) cell line stably expressing the Beta-arrestin GFP and GPR55 receptor
3) Culture Media: MEM with L-glutamine, Pen-strep, 10% Fetal Bovine Serum and selection antibiotics - 100ug/ml G418 and 50ug/ml Zeocin
4) Agonist Working Solution: Lysophosphatidylinositol (Avanti Polar #850090P, 5mM stock in DMSO) diluted to 50uM in water.
5) Control Working Solution: 100% DMSO (for positive control wells: no agonist will be added to mimic 100% inhibition of agonist-mediated response; for negative control wells: LPI agonist will be added to mimic 0% inhibition of agonist-mediated response).
6) Test Compounds Working Solution: 10mM in 100% DMSO
7) Fixative Working Solution: 6% Paraformaldehyde (PFA) diluted in PBS.
8) Nuclear Stain Working Solution: DAPI (Invitrogen, D1306) diluted to 150ng/ml in DAPI buffer (10mM TRIS, 10mM EDTA, 100mM NaCl, pH 7.4).
1) 45 ul of cell suspension (200,000 cells/ml in culture medium) was dispensed in each well of the assay plates using a Wellmate bulk dispenser.
2) Plates were incubated overnight or approximately 20 hours at 37 degree C and 5% CO2.
3) Serum was removed by media aspiration and replaced with 45 ul serum-free MEM prior to addition of compounds.
4) Compound addition was done on an ECHO550 Liquid Handler. The "dose response protocol" was used to dispense corresponding volumes of each 10 mM compound on the assay plate.
a. Compounds were added to columns 3 to 22. Final concentration ranged from 62nM to 32uM (ten doses), in duplicate.
b. Control working solution was added to columns 1 and 24 representing positive control wells by using 0 uM agonist to mimick 100% inhibition.
c. Control working solution was added to columns 2 and 23 representing negative control wells.
d. DMSO was back-filled to each well to achieve 0.3% final concentration.
5) Plates were pre-incubated with compounds for 30 minutes at 37 degrees C and 5% CO2.
6) After 30 minutes, 5 ul of the agonist (50 uM LPI) working solution was added to the entire plate except column 1 and 24 for a final agonist concentration of 5 uM.
7) Plates were incubated for 75 minutes at 37 degrees C and 5% CO2.
8) Media was aspirated leaving 20 ul liquid in each well using a Titertek plate washer.
9) 40ul of fixative working solution was added to each well using a Wellmate bulk dispenser (Matrix) for a final concentration of 4% PFA.
10) Plates were incubated for 40 minutes at room temperature.
11) Fixative was aspirated and plates were washed twice with 50 ul PBS leaving 20 ul liquid in each well using a Titertek plate washer.
12) 40ul of DAPI working solution was added using a Wellmate bulk dispenser for a final DAPI concentration of 100 ng/ml. Aluminum plate sealers were applied to each plate.
Image Acquisition and Analysis:
1) Image acquisition was performed on an Opera QEHS (Perkin Elmer) with 45 plate capacity loader/stacker and the following settings:
20x 0.45 NA air objective
Acquisition camera set to 2-by-2 binning for an image size of 688 by 512 pixels
2 channels acquired sequentially: Exp1Cam1 = Beta-arrestin GFP using 488 nm laser excitation and 540/70 nm emission filters, Exp2Cam2 = DAPI (nuclei) using 365 nm Xenon lamp excitation and 450/50 nm emission filters
4 fields per well
2) Image analysis was performed using the Acapella Spot Detection Algorithm with the following analysis settings:
Threshold Adjustment: 1.5
Nuclear Splitting Adjustment: 7
Minimum Nuclear Area: 0
Minimum Nuclear Contrast: 0.1
Cytoplasm Threshold Adjustment: 0.45
Cytoplasm Individual Threshold Adjustment: 0.15
Spot Minimum Distance 3
Spot Peak Radius 0
Spot Reference Radius 2
Spot Minimum Contrast 0.25
Spot Minimum to Cell Intensity 1
3) Metrics calculated from
NUCLEI IMAGES: Cell Count (NumberofCellsAnalyzed), Nuclei Area (AreaoftheNucleus), Integrated Intensity of the Nuclei (TotalIntegratedIntensityoftheNucleus), Average Intensity of the Nuclei (AverageIntensityoftheNucleus)
GFP IMAGES: Integrated Intensity of the Cytoplasm (TotalCytoplasmIntensity), Integrated Intensity of the Detected Spots (TotalSpotIntensity), Ratio of the Integrated Spot to Integrated Cytoplasm Intensities (RatioofSpotIntensitytoCytoplasmintensity), Number of Spots per Cell (AverageSpotsPerCell), Percentage of Cells Positive for Spot Formation (PercentagePositiveCells)
4) The "AverageSpotsPerCell" metric was used to calculate the dose response curves and parameters. IC50 values were calculated using CBIS (ChemInnovations) software employing a sigmoidal dose-response equation through non-linear regression.
Compounds with an IC50 < 10 uM are defined as actives in the dose response confirmation.
To simplify the distinction between the inactives of the primary screen and of the confirmatory screening stage, the Tiered Activity Scoring System was developed and implemented. Its utilization for the assay is described below.
Activity scoring rules were devised to take into consideration compound efficacy, its potential interference with the assay and the screening stage that the data was obtained. Details of the Scoring System will be published elsewhere. Briefly, the outline of the scoring system utilized for the assay is as follows:
1) First tier (0-40 range) is reserved for primary screening data and is not applicable to this assay
2) Second tier (41-80 range) is reserved for dose-response confirmation data and is not applicable to this assay
3) Third tier (81-100 range) is reserved for resynthesized true positives and their analogues.
a. Inactive compounds of the confirmatory stage are assigned a score value equal 81.
b. For the remaining compounds the score is linearly correlated with a compound's inhibitory potency and, in addition, provides a measure of the likelihood that the compound is not an artifact based on the available information.
c. Summary equation that takes into account the items discussed above is
Score = 82 + 3*(pIC50 - 3),
where pIC50 is a negative log(10) of the IC50 value expressed in mole/L concentration units. This equation results in the Score values above 85 for compounds that demonstrate high potency and predictable behavior. Compounds that are inactive in the assay or whose concentration-dependent behavior are likely to be an artifact of that assay will generally have lower score values.
Categorized Comment - additional comments and annotations
* Activity Concentration. ** Test Concentration.
Data Table (Concise)