A New Simple Cell-Based Homogeneous Time-Resolved Fluorescence QRET Technique for Receptor-Ligand Interaction Screening

In this article, a single-label separation-free fluorescence technique is presented as a potential screening method for cell-based receptor antagonists and agonists.The time-resolved fluorescence technique, quenching resonance energy transfer (QRET), relies on a single-labeled binding partner in combination with a soluble quencher. The quencher efficiently suppresses the luminescence of the unbound labeled ligand, whereas the luminescence of the bound fraction is not affected. This approach allows the development of cell-based screening assays in a simple and cost-effective manner. The authors have applied the technique to the screening of β₂-adrenoreceptor (β₂AR) antagonists and agonists in intact human embryonic kidney HEK293_i cells overexpressing human β₂-adrenergic receptors. Two antagonists (propranolol, alprenolol) and 2 agonists (metaproterenol, terbutaline) for β₂AR were investigated in a displacement assay using europium(III)-labeled pindolol ligand. The assay Z′ values ranged from 0.68 to 0.78, the coefficient of variation was less than 10%, and the K_i values were 19 nM for propranolol and alprenolol and 14 and 5.9 µM for metaproterenol and terbutaline, respectively. The QRET technique with β₂AR was also applied to LOPAC compound library screening, yielding nearly error-free recognition of known binders. This simple and cost-effective technique can be readily adapted to laboratory and industrial-scale screening.