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International audience; Cell surface receptors represent a vast majority of drug targets. Efforts have been conducted to develop biosensors reporting their conformational changes in live cells for pharmacological and functional studies. Although Förster resonance energy transfer (FRET) appears to be an ideal approach, its use is limited by the low signal-to-noise ratio. Here we report a toolbox composed of a combination of labeling technologies, specific fluorophores compatible with time-resolved FRET and a novel method to quantify signals. This approach enables the development of receptor biosensors with a large signal-to-noise ratio. We illustrate the usefulness of this toolbox through the development of biosensors for various G-protein-coupled receptors and receptor tyrosine kinases. These receptors include mGlu, GABAB, LH, PTH, EGF and insulin receptors among others. These biosensors can be used for high-throughput studies and also revealed new information on the activation process of these receptors in their cellular environment.

The Na(+)/I(-) symporter (NIS) mediates iodide uptake in the thyroid gland as well as in other NIS-expressing cells. This transport is the basis for an emerging approach to selective cancer cell destruction by using radioiodide after targeted NIS gene transfer. Therapeutic efficacy requires that radioiodide retention be maximized in tumor cells. A first generation of forty imidazo[2,1-b]thiazole derivatives as iodide efflux inhibitors is described along with the evaluation of their biological properties. Structure-activity relationship studies by using radioiodide uptake in rat thyroid-derived cells (FRTL5) revealed that the 5,6-dihydroimidazo[2,1-b]thiazole heterocycle is required for activity. Introduction of electron-donor substituents on the 3-biphenyl moiety led to the discovery of novel potent compounds. A compound was identified with enhanced potency compared to reference 1. These molecules give the possibility to increase the cellular retention of radioiodide in NIS-expressing tumors, leading to higher absorbed doses and killing efficacy.

The Na(+)/I(-) symporter (NIS) mediates iodide uptake into thyroid follicular cells. Although NIS has been cloned and thoroughly studied at the molecular level, the biochemical processes involved in post-translational regulation of NIS are still unknown. The purpose of this study was to identify and characterize inhibitors of NIS function. These small organic molecules represent a starting point in the identification of pharmacological tools for the characterization of NIS trafficking and activation mechanisms. The screening of a collection of 17,020 druglike compounds revealed new chemical inhibitors with potencies down to 40 nM. Fluorescence measurement of membrane potential indicates that these inhibitors do not act by disrupting the sodium gradient. They allow immediate and total iodide discharge from preloaded cells in accord with a specific modification of NIS activity, probably through distinct mechanisms.

A high-throughput screening method based on radioiodide uptake in human embryonic kidney 293 cells expressing the human sodium/iodide symporter was developed. Central to assay development was a homogeneous cell culture in the 96-well microplate coupled with the use of scintillation proximity technology. The assay is fast and highly reproducible with a Z' greater than 0.8. The automated procedure allows the screening of 4,000 compounds per day. Using this methodology, several known substrates of the sodium/iodide symporter were evaluated in a single day. Inhibition of iodide uptake was shown to follow the series PF(6)(-)ClO(4)(-)BF(4)(-)SCN(-)NO(3)(-)IO(4)(-)N(3)(-)Br(-), in accord with the literature. This method represents an initial approach to the search for inhibitors of iodide transport mediated by the sodium/iodide symporter.

In many streptococci, competence for natural DNA transformation is regulated by the Rgg-type regulator ComR and the pheromone ComS, which is sensed intracellularly. We compared the ComRS systems of four model streptococcal species using in vitro and in silico approaches, to determine the mechanism of the ComRS-dependent regulation of competence. In all systems investigated, ComR was shown to be the proximal transcriptional activator of the expression of key competence genes. Efficient binding of ComR to DNA is strictly dependent on the presence of the pheromone (C-terminal ComS octapeptide), in contrast with other streptococcal Rgg-type regulators. The 20 bp palindromic ComR-box is the minimal genetic requirement for binding of ComR, and its sequence directly determines the expression level of genes under its control. Despite the apparent species-specific specialization of the ComR-ComS interaction, mutagenesis of ComS residues from Streptococcus thermophilus highlighted an unexpected permissiveness with respect to its biological activity. In agreement, heterologous ComS, and even primary sequence-unrelated, casein-derived octapeptides, were able to induce competence development in S. thermophilus. The lack of stringency of ComS sequence suggests that competence of a specific Streptococcus species may be modulated by other streptococci or by non-specific nutritive oligopeptides present in its environment.