Label-free impedance measurements to unravel biomolecular interactions involved in G protein-coupled receptor signaling

G protein-coupled receptors (GPCRs) are among the most heavily addressed drug targets in medicinal chemistry and pharmacology. The screening for new agonists or antagonists has been largely based on genetically engineered cells overexpressing the receptor to study binding of ligands directly or via intracellular signaling events downstream of receptor activation. These approaches are often invasive in nature, need to be conducted as endpoint assays, require isotope- or fluorophore-labeling and significant genetic manipulation. In contrast to that, non-invasive and label-free impedance measurements are capable of monitoring ligand-receptor interactions in target cells with endogenous receptor expression in real time. The cells expressing the receptor are grown on planar gold-film electrodes that are integrated into regular cell culture dishes. This article will highlight several impedance-based assay formats to characterize biomolecular interactions between ligands and their GPCRs in vitro, comprising agonist and antagonist characterization, dose-response relationships, receptor desensitization, and signal transduction profiling.