Label-free biosensor assays in GPCR screening.

About one third of currently marketed drugs target G protein-coupled receptors (GPCRs), which form the largest group of transmembrane proteins in the human proteome. GPCRs are ubiquitously expressed throughout the human body and play a pivotal role in a vast number of physiological and pathophysiological processes. Because of their intriguing complexity, their relevance, and yet unexploited potential in the treatment of diseases, GPCRs are studied intensively by both academic and industrial research labs.Classical biochemical and molecular biology techniques, including traditional second messenger assays, took biomedical research to the next level and represent the fascinating power of in vitro pharmacology. While extremely efficient in capturing one clearly defined cellular readout, those methods do not authentically portray the events taking place in living cells as a whole; hence the process of drug discovery runs the risk to lose sight of a wider context already in early stages. Label-free cell-based assays hold the promise to overcome these shortcomings by considering cellular processes holistically. If combined with diligent assay adjustments, dynamic mass redistribution (DMR) technology is an excellent tool to investigate GPCR signaling. In this article we aim to provide guidance for scientists seeking for information on how to set up and optimize DMR assays with the objective to establish a knowledge base on deciphering integrated cellular readouts. For this reason we focus on a basic DMR protocol for the investigation of the long-chain fatty acid FFA1 receptor as a model family A GPCR and complement it with information that allow a sophisticated approach to more specialized scientific questions with the use of this comparatively novel method.