Integrated Cell-Based Platform to Study EGFR Activation and Transactivation

Label-free drug screening assay multiplexed with an orthogonal time-resolved fluorescence labeled assay

Cell-based assays against cell surface receptor targets are essential in vitro models of target-based drug discovery. At the lead generation phase large-scale functional screening assays monitoring individual cellular readouts detect interactions between the compounds and the predefined pathways but might lack sufficient sensitivity owing to the complexity of downstream signaling pathways. Cellular label-free assays offer advantages over labeled detection approaches as they reflect whole-cell responses without the prerequisite of detecting only a single cellular analyte and introducing additional genetic manipulations in favor of the chosen detection method. The combination of a label-free assay and labeled assays might integrate the advantageous characteristics of both approaches with regards to added pharmacological information and a bigger pool of chemical starting material. Here we report multiplexing of dynamic mass redistribution label-free technology with HTRF-based cAMP detection on an alpha2c adrenergic receptor expressing cell line. Besides describing the challenging assay development work associated with the set goal, a pilot screening campaign on ca. 1600 compounds is also presented. The combined assay demonstrated the ability to detect relevant activities in both readouts. Interpretation of the results as well as an outlook for further possible opportunities and applications are also discussed.

A novel cell-based duplex high-throughput screening assay combining fluorescent Ca(2+) measurement with homogeneous time-resolved fluorescence technology

Cell-based assays for G-protein-coupled receptor (GPCR) activation applied in high-throughput screening (HTS) monitor various readouts for second messengers or intracellular effectors. Recently, our understanding of diverging signaling pathways downstream of receptor activation and the capability of small molecules to selectively modulate signaling routes has increased substantially, underlining the importance of selecting appropriate readouts in cellular functional screens. To minimize the rate of false negatives in large-scale screening campaigns, it is crucial to maximize the chance of a ligand being detected, and generally applicable methods for detecting multiple analytes from a single well might serve this purpose. The few assays developed so far based on multiplexed GPCR readouts are limited to only certain applications and usually rely on genetic manipulations hindering screening in native or native-like cellular systems. Here we describe a more generally applicable and HTS-compatible homogeneous assay based on the combination of fluorometric detection of [Ca(2+)] with subsequent homogeneous time-resolved fluorescence (HTRF) cAMP readout in the same well. Besides describing development and validation of the assay, using a cell line recombinantly expressing the human PTH1 receptor screening of a small library is also presented, demonstrating the robustness and HTS compatibility of the novel paradigm.