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Assay Method Information

Assay Name:  Radiolabel Binding Studies for Serotonin 5-HT7 Receptors, Method 2
Description:  A solution of the compound of the disclosure to be tested is prepared as a 1-mg/ml stock in Assay Buffer or DMSO according to its solubility. A similar stock of the reference compound chlorpromazine is also prepared as a positive control. Eleven dilutions (5× assay concentration) of the compound of the disclosure and chlorpromazine are prepared in the Assay Buffer by serial dilution to yield final corresponding assay concentrations ranging from 10 pM to 10 μM.A stock concentration of 5 nM [3H]-5-Hydroxytryptamine ([3H]-5HT) is prepared in 50 mM Tris-HCl, 10 mM MgCl2, 1 mM EDTA, pH 7.4 (Assay Buffer). Aliquots (50 μl) of radioligand are dispensed into the wells of a 96-well plate containing 100 μl of Assay Buffer. Duplicate 50-μl aliquots of the compound of the disclosure test and chlorpromazine positive control reference compound serial dilutions are added.Membrane fractions of cells expressing recombinant 5HT7 receptors (50 μL) are dispensed into each well. The membranes are prepared from stably transfected cell lines expressing 5HT7 receptors cultured on 10-cm plates by harvesting PBS-rinsed monolayers, resuspending and lysing in chilled, hypotonic 50 mM Tris-HCl, pH 7.4, centrifuging at 20,000×g, decanting the supernatant and storing at −80° C.; the membrane preparations are resuspended in 3 ml of chilled Assay Buffer and homogenized by several passages through a 26 gauge needle before using in the assay.The 250-μl reactions are incubated at room temperature for 1.5 hours, then harvested by rapid filtration onto 0.3% polyethyleneimine-treated, 96-well filter mats using a 96-well Filtermate harvester. Four rapid 500-μl washes are performed with chilled Assay Buffer to reduce non-specific binding. The filter mats are dried, then scintillant is added to the filters and the radioactivity retained on the filters is counted in a Microbeta scintillation counter.Raw data (dpm) representing total radioligand binding (i.e., specific+non-specific binding) are plotted as a function of the logarithm of the molar concentration of the competitor (i.e., test or reference compound). Non-linear regression of the normalized (i.e., percent radioligand binding compared to that observed in the absence of test or reference compound) raw data is performed in Prism 4.0 (GraphPad Software) using the built-in three parameter logistic model describing ligand competition binding to radioligand-labeled sites: y=bottom+[(top−bottom)/(1+10×−log IC50)] where bottom equals the residual radioligand binding measured in the presence of 10 μM reference compound (i.e., non-specific binding) and top equals the total radioligand binding observed in the absence of competitor. The log IC50 (i.e., the log of the ligand concentration that reduces radioligand binding by 50%) is thus estimated from the data and used to obtain the Ki by applying the Cheng-Prusoff approximation: Ki=IC50/(1+[ligand]/KD) where [ligand] equals the assay radioligand concentration and KD equals the affinity constant of the radioligand for the target receptor.Compounds of the disclosure are also screened at a single concentration of 10 μM using the same method described for the Radiolabel Binding Studies for Serotonin 5HT7 receptors to determine the percent inhibition of [3H]-5HT binding.
Affinity data for this assay
 

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Last update November 1, 2007
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