The xCELLigence System of Roche: A Different Way to Monitor GPCR Functions in Living Cells

A series of research studies have demonstrated the benefit of the xCELLigence System for functional screening of G-protein coupled receptors (GPCRs) activity, based on its ability to modulate the actin cytoskeleton and cell adhesion.

These experiments used cell lines stably expressing human recombinant histamine 1 (H1), vasopressin 1a (V1a), recombinant dopamin 1 (D1), calcitonin, and the 5HT1A receptor (5-HT1A). GPCRs represent the largest family of plasma membrane proteins involved in signal transduction across the plasma membrane. They play a prominent role in regulating a variety of physiological functions such as sight, taste, smell as well as fluid electrolyte balancing, cardiovascular function and neurotransmission. Consequently, these receptors are an important target for pharmaceutical drug development: More than 50 % of the current therapeutic agents on the market are targeted against GPCRs.

The number of assays available to measure the functional activation of endogenous GPCRs in their natural and physiologically relevant settings is limited. Therefore, the important contribution that the technology of the xCELLigence System offers for GPCR cell-based assays is severalfold. First, no pre- or post-labelling of the cells is necessary, saving both expense and time. Since the readout is real-time and non-invasive, cellular destruction is not required. Therefore, the same cells can be stimulated multiple times in the same well to assess desensitization or cross-talk with other receptor types. The detection method is not affected by endogenous compounds, which avoids a major problem encountered in most optical-based assays. Based on the real time technique, the assay provides a comprehensive representation of the entire assay period, allowing the user to make informed decisions about the timing of ligand addition. Furthermore, the real-time kinetic readout provides succinct and valuable information about the pathways being activated.

In addition to the histamine receptor, which is coupled to the Gq subfamily of G-proteins, cells expressing other receptors, coupled to the Gs and Gi families, can also be monitored on the xCELLigence System. Most important, cells expressing endogenous GPCRs including primary cells can also be used with this technique, precluding the need of over-expression of exogenous GPCRs or engineering the cells to express promiscuous G-proteins. This allows the evaluation of the receptors in physiologically appropriate cell types.

The xCELLigence System, whose predecessor Real-Time Cell Electronic Sensing System (RT-CES) was developed by ACEA Biosciences, allows label-free, real-time dynamic monitoring of cell proliferation and viability in real-time. The technique utilizes an electronic readout of impedance to non-invasively quantify cellular status in real-time. Cells are seeded in E-Plate microtiter plates, which are integrated with microelectronic sensor arrays. The interaction of cells with the microelectrode surface generates a cell-electrode impedance response, which not only indicates cell viability but also correlates with the number of the cells seeded in the well.

For more information on the technology of the xCELLigence System, please visit the article webpage.