Live-cell imaging and GPCRs

Japanese researchers study real-time bioluminescence imaging for monitoring of GPCR activation in living cells in hopes of developing a strategy to even better evaluate drug performance

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That G protein-coupled receptors (GPCRs) are a huge chunk of drug discovery and development and have been for a while would be of little surprise to any but the most sheltered researcher. Also of little surprise to the overwhelmingly majority of life-scientists and other such researchers is that GPCRs, like any other avenue of pharma exploration, lead to a lot of dead ends or unwanted results.
Researchers at the University of Tokyo think they may have a new tool—one relate to live-cell imaging—to help drug discovery and development related to GPCRs go smoother.
In the article “High-throughput Live Cell Imaging and Analysis for Temporal Reaction of G Protein-coupled Receptor Based on Split Luciferase Fragment Complementation,” which appears in the April 25, 2015, issue of Analytical Sciences, the international journal of the Japan Society for Analytical Chemistry, the authors note that for the design of therapeutic drugs, GPCRs are notable targets and that many screening methods have been developed to identify effective agents for GPCR signaling. However, they write, analyses of temporal variations of GPCR activity with specific ligands remain insufficient because of monitoring method limitations and difficulties.
“We previously developed a high-throughput bioluminescence measuring system to detect interactions of GPCR with β-arrestin based on split luciferase fragment complementation,” wrote Hattori Mitsuru and Ozawa Takeaki of the Department of Chemistry in the School of Science at the University of Tokyo. “By newly introducing a bioluminescence imaging technique into the system, we demonstrate a method for the temporal monitoring of GPCR-β-arrestin interactions in living cells during stimulation by different ligands.”
Underlying all this is the fact that in the search for new drugs, particularly for diseases that have no cures, the discovery of unidentified drugs targeting signal transduction in cells is a principal strategy. The largest transmembrane spanning receptor protein family in humans are the GPCRs, and they are related to various physiological functions as a signal converter.
“Each GPCR protein is activated by extracellular stimuli of several types, thereby eliciting intracellular downstream signals,” the authors note. “Because of their fundamental roles in cells, GPCRs have been centrally positioned as a drug discovery target.”
In fact, more than 40 percent of curative drugs being investigated right now are associated with GPCR signal transduction.
“Various strategies to identify GPCR signals are applied to screen effective agents for GPCR from numerous chemical and clinical compound libraries. Most such strategies specialize in high- throughput measurements that simply judge whether the unknown compound activates or inhibits the target GPCR signal or not,” wrote Mitsuru and Takeaki. “However, the reaction profile of GPCR to the specific ligand differs depending on the type of GPCR and the cellular environment. Moreover, information related to the temporal variation of the GPCR signal is intrinsically important for the understanding of physiological drug effects. Therefore, time-course analysis of GPCR in living cells is necessary for drug evaluation, although the data remain insufficient because of methodological difficulties.”
After describing their methods and results in the article, the authors concluded, “We demonstrated real-time bioluminescence imaging for the monitoring of GPCR activation in living cells … These data suggest that the temporal patterns of GPCR activities are sensitive to the concentrations of GPCR agonist and the inhibitor. Time-course information from the imaging strategy is expected to be useful to evaluate the drug performance of GPCRs in living cells.”
To read the scholarly article in full, click here.

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