| Assay Method Information | |
| | Homogeneous Time-Resolved Fluorescence (HTRF) Assay for Direct cAMP Measurement |
| Description: | Compounds were screened for agonists of the human prostacyclin (PGI2) receptor using the HTRF assay for direct cAMP measurement (Gabriel et al., ASSAY and Drug Development Technologies, 1:291-303, 2003) and recombinant CHO-K1 cells stably transfected with human prostacyclin receptor. CHO-K1 cells were obtained from ATCC (Manassas, Va.; Catalog # CCL-61). An agonist of the prostacyclin receptor was detected in HTRF assay for direct cAMP measurement as a compound which increased cAMP concentration. HTRF assay also was used to determine EC50 values for prostacyclin receptor agonists.Principle of the Assay:The HTRF assay kit was purchased from Cisbio-US, Inc. (Bedford, Mass.; Catalog #62AM4PEC). The HTRF assay supported by the kit is a competitive immunoassay between endogenous cAMP produced by the CHO-K1 cells and tracer cAMP labeled with the dye d2. The tracer binding is visualized by a monoclonal anti-cAMP antibody labeled with Cryptate. The specific signal (i.e., fluorescence resonance energy transfer, FRET) is inversely proportional to the concentration of unlabeled cAMP in the standard or sample.Standard Curve:The fluorescence ratio (665 nm/620 nm) of the standards (0.17 to 712 nM cAMP) included in the assay was calculated and used to generate a cAMP standard curve according to the kit manufacturer's instructions. The fluorescence ratio of the samples (test compound or compound buffer) was calculated and used to deduce respective cAMP concentrations by reference to the cAMP standard curve.Setup of the Assay:The HTRF assay was carried out using a two-step protocol essentially according to the kit manufacturer's instructions, in 20 μL total volume per well in 384-well plate format (ProxiPlates; PerkinElmer, Fremont, Calif.; catalog #6008280). To each of the experimental wells was transferred 3000 recombinant CHO-K1 cells in 5 μL assay buffer (phosphate buffered saline containing calcium chloride and magnesium chloride (Invitrogen, Carlsbad, Calif.; catalog #14040) supplemented with IBMX (100 μM) and rolipram (10 μM) (phosphodiesterase inhibitors; Sigma-Aldrich, St. Louis, Mo.; catalog #15879 and catalog # R6520, respectively) and 0.1% bovine serum albumin (BSA) fraction V (Sigma-Aldrich; catalog # A3059)), followed by test compound in 5 μL assay buffer or 5 μL assay buffer. The plate was then incubated at room temperature for 1 h. To each well was then added 5 μL cAMP-d2 conjugate in lysis buffer and 5 μL Cryptate conjugate in lysis buffer according to the kit manufacturer's instructions. The plate was then further incubated at room temperature for 1 h, after which the assay plate was read.Assay Readout:The HTRF readout was accomplished using a PHERAstar (BMG LABTECH Inc., Durham, N.C.) or EnVision (PerkinElmer, Fremont Calif.) microplate reader. |
| Affinity data for this assay | |
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