Roche´s xCELLigence RTCA HT System: Fully-automated Measurement of Therapeutic Targets` Cellular Activity

Label-free technologies have entered the stage of cellular drug discovery and high-throughput screening (HTS). For the measurement of G protein-coupled receptor (GPCR) activation electrical impedance represents an excellent universal readout technology, since different signaling pathways can be measured in one assay format using recombinant as well as primary cells. The recently developed xCELLigence RTCA HT Instrument from Roche Applied Science now allows to perform fully-automated impedance screens for GPCRs and other targets in the 384-well high-throughput format.

In a recent case study, Urs Lüthi and John Gatfield from Actelion Pharmaceuticals Ltd., Allschwil, Switzerland, integrated 2 RTCA HT (real-time cell analyzer for high-throughput) Instruments on an automated high-throughput screening platform from Agilent Technologies (Santa Clara, US). 263 antagonist hits of the orexin type 1 (Ox1) GPCR that had been identified in a classical calcium flux (FLIPR) HTS were screened for Ox1 inhibition in fully-automated RTCA HT assays. The overall performance, the quality of E-Plates 384 and intra- and inter-assay reproducibility were evaluated. 65% of the 263 antagonist hits were confirmed to be Ox1 receptor antagonists after impedance measurements. According to the researchers, the RTCA HT Instrument could be readily integrated into automated workflows and delivered a highly reproducible data set, making the RTCA HT Instrument a powerful screening technology.

Compared to standard readout technologies one of the major advantages of label-free technologies is that cellular processes are measured in real-time kinetics in a non-invasive manner. The xCELLigence System uses gold electrodes at the bottom surface of microplate wells as sensors to which an alternating current is applied. Cells that are grown as adherent monolayers on top of such electrodes influence the alternating current at the electrodes by changing the electrical resistance (impedance). The degree of this change is primarily determined by the number of cells, strength of the cell-cell interactions, interactions of the cells with the microelectrodes and by the overall morphology of the cells.