High Throughput Screening for Ligands for Seven Transmembrane-spanning Receptors

National Institute Of Diabetes And Digestive And Kidney Diseases

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Abstract

Seven transmembrane-spanning receptors (7TMRs or G protein-coupled receptors, GPCRs) represent the largest family of signal-transducing molecules known. 7TMRs convey signals for light and many extracellular regulatory molecules, such as, hormones, growth factors and neurotransmitters, that regulate every cell in the body. Dysregulation of 7TMRs has been found in a growing number of human diseases and 7TMRs have been estimated to be the targets of more than 30% of the drugs used in clinical medicine today. Thus, discovery of probes/drugs for 7TMRs is an important goal of biomedical research. We use high throughput screening (HTS) for small molecule ligands (SMLs) for 7TMRs with the receptors for thyroid-stimulating hormone (TSH-R) and thyrotropin-releasing hormone (TRH-R). During this year, we employed cell-based assays that we developed for activation of TSH-R and TRH-R by SML agonists and a complementary assay for SML inhibitors of TSH stimulation of TSH-R for HTS. We identified new antagonists for TSH-R that show excellent selectivity because they do not inhibit the closely related receptors for luteinizing hormone or follicle-stimulating hormone. These are the first SML antagonists for TSH-R reported. We continue to modify these compounds chemically to improve their selectivities, affinities and efficacies. Of particular note, is our observation that the antagonist not only inhibits stimulation of TSH-R by TSH but also by thyroid-stimulating antibodies (TsAbs) from patients with Graves hyperthyroidism. We also identified new, more effective small molecule agonists for TSH-R. These are the first SMLs for TSH-R that have been shown to activate TSH-Rs in normal human thyroid cells and in intact mice. Un fortunately, the HTS failed to identify any agonists for TRH-R.