CHEMBL5734186

scintillation proximity assay (SPA): Test A1 and A2: In order to identify binding to the human MR LBD a scintillation proximity assay (SPA) was adapted to the 384-well format. The MR-LBD (amino acids T729-K985) was expressed as N-terminal fusion with maltose binding protein in Hi5 insect cells by co-infection with recombinant MBP-MR LBD and P23 baculoviruses and crude protein lysate was used in the assay. Tritiated aldosterone is used as the ligand to generate the scintillation signal when brought into proximity of the scintillation (SPA) bead by binding to the MR LBD and test compound affinity (in IC50 values) is defined as the concentration to decrease tritiated aldosterone binding to the MR LBD by 50%.Briefly, in Test A1 the assay was run in 384 well format in 10 mM Tris-HCl, pH 7.5, 0.5 mM EDTA 20 mM NaMoO4, 0.1 mM DTT and 10% glycerol at rt. Compounds were tested in a 7 (Test A1) or 10 (Test A2) concentration response curve ranging from 10 nM to 10 μM (Test A1) or 1 nM to 37 μM (Test A2). Compounds were spotted at the bottom of a well of a 384-well PE Opti-Plate to yield final DMSO concentrations in the assay of 2%. Pre-made MBP-MR/P23 lysate: 3H-aldosterone mix (final assay concentration 7 μg/mL MBP-MR LBD/P23 lysate; 5 nM aldosterone) was added onto the top of the spotted compound and preincubated for 1 h at RT. After 1 h an equal volume anti-rabbit SPA beads (Test A1) or Imaging beads (Test A2) coupled with rabbit anti-MBP were added to the assay mixture and incubated for 3 hrs (Test A1) or >8 h (Test A2) at rt. The inhibition of the scintillation signal by displacement of the bound 3H-aldosterone by test compounds is measured by scintillation counting using a Microbeta Trilux (Wallac) (Test A1) or a by CCD camera detection using a LEADseeker (PerkinElmer) (Test A2).