Visualising ligand-receptor interactions in disease
Neurological and neurodegenerative disorders are steadily increasing in prevalence, posing a heavy socioeconomic burden in European countries. Given the expansion of the ageing population, there is considerable worry since there is a lack of therapeutic treatments for these debilitating conditions. Compelling evidence implicates the involvement of cell membrane receptors known as G protein-coupled receptors (GPCRs) in neurodegenerative diseases such as Alzheimer's disease. GPCRs are implicated in the amyloid cascade and amyloid-beta mediated toxicity and neuroinflammation observed in Alzheimer's. The EU-funded FATOKUNEUFP7IIF2010 project focused on the development of fluorescent probes for the visualisation and quantification of GPCRs and their ligands. The idea was to use these molecular tools in drug screening to investigate allosteric interactions. The identification of ligands that pose allosteric effects of GPCRs has been envisaged as a means of eliciting neuroprotection. The researchers investigated adenosine receptors, metabotropic glutamate receptors and the GABAB receptor closely since their modulation is highly relevant to neurodegeneration. Scientists synthesised a series of fluorescent GPCR ligands and screened them on cell lines in vitro. With the serotonin receptor 5-HT as a model system, appropriate functional assays were developed for assessing the quality of nine different fluorescent ligands. One ligand with antagonist properties for the 5-HT receptor was further processed for imaging purposes and is expected to replace the use of radiolabelled ligands in competitive binding experiments. With respect to the inhibitory GABAB receptors, scientists identified one fluorescent ligand with antagonist properties which also had excellent photophysical properties for imaging applications. The binding kinetics of these ligands was evaluated by confocal microscopy. The project has developed molecular tools that promise to be extremely useful in physiological and pharmacological investigations in various pathological conditions. Furthermore, they could be used to understand the kinetics of drugs targeting GPCRs and provide an explanation on the variable behaviour of different drugs at their target receptors.
