Functionally biased signalling properties of 7TM receptors - opportunities for drug development for the ghrelin receptor

The ghrelin receptor is a 7 transmembrane (7TM) receptor involved in a variety of physiological functions including growth hormone secretion, increased food intake and fat accumulation as well as modulation of reward and cognitive functions. Because of its important role in metabolism and energy expenditure, the ghrelin receptor has become an important therapeutic target for drug design and the development of anti-obesity compounds. However, none of the compounds developed so far have been approved for commercial use. Interestingly, the ghrelin receptor is able to signal through several different signalling pathways including Gαq , Gαi/o , Gα12/13 and arrestin recruitment. These multiple signalling pathways allow for functionally biased signalling, where one signalling pathway may be favoured over another either by selective ligands or through mutations in the receptor. In the present review, we have described how ligands and mutations in the 7TM receptor may bias the receptors to favour either one G-protein over another or to promote G-protein independent signalling pathways rather than G-protein-dependent pathways. For the ghrelin receptor, both agonist and inverse agonists have been demonstrated to signal more strongly through the Gαq -coupled pathway than the Gα12/13 -coupled pathway. Similarly a ligand that promotes Gαq coupling over Gαi coupling has been described and it has been suggested that several different active conformations of the receptor may exist dependent on the properties of the agonist. Importantly, ligands with such biased signalling properties may allow the development of drugs that selectively modulate only the therapeutically relevant physiological functions, thereby decreasing the risk of side effects.

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This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Multicenter comparison of the Sensititre YeastOne colorimetric antifungal panel with the NCCLS M27-A2 reference method for testing new antifungal agents against clinical isolates of Candida spp

A multicenter (three centers) study compared MICs obtained by the Sensititre YeastOne Colorimetric Antifungal plate to reference microdilution broth (NCCLS M27-A2 document) MICs of three new triazoles (posaconazole, ravuconazole, and voriconazole) and the echinocandin caspofungin acetate for 100 isolates of Candida spp. In addition, amphotericin B and fluconazole were tested as control drugs. Colorimetric MICs of caspofungin and amphotericin B corresponded to the first blue well (no growth), and MICs of the other agents corresponded to the first slightly purple or blue well. Two comparisons of MIC pairs by the two methods were evaluated: 24-h colorimetric MICs were compared to NCCLS MICs at 24 and at 48 h. The interlaboratory reproducibility of YeastOne and reference MICs was also examined. The best performance of the YeastOne plate was with 24-h MICs (overall, 95 to 99% agreement) for all the species and antifungal agents. These results suggest the potential value of the YeastOne plate for use in the clinical laboratory for the four new antifungal agents evaluated.