In vitro pharmacological characterization of ligands of the growth hormone secretagogue receptor (GHSR) using the dynamic mass redistribution and calcium mobilization assays

Ghrelin modulates several biological functions via selective activation of the growth hormone secretagogue receptor (GHSR). GHSR agonists may be useful for the treatment of anorexia and cachexia while antagonists and inverse agonists may represent innovative options for the treatment of drug addiction. Thus, the identification and pharmacodynamic characterization of new GHSR ligands is of high interest. In the present work the label-free dynamic mass redistribution (DMR) assay has been used to evaluate the pharmacological activity of a panel of GHSR ligands, already reported in the scientific or patent literature. This includes ghrelin and PF-05190457, as standard agonist and inverse agonist, respectively, together with the unacetylated form of ghrelin (desacyl-ghrelin), the agonists anamorelin, HM01, HM03, the antagonists HM04 and YIL-781, and R011, and the ghrelin inverse agonist H1498 from patent literature. The DMR results have been compared to those obtained in parallel experiments with the calcium mobilization assay. Ghrelin, anamorelin, HM01, and HM03 behaved as potent full GHSR agonists, with similar potency values in DMR and calcium mobilization assays. YIL-781 behaved as a partial GHSR agonist and R011 as a neutral antagonist in both the assays. Interestingly, PF-05190457, HM04, and H1498 behaved as GHSR inverse agonists in DMR experiments, resulting neutral antagonists in calcium mobilization studies.In conclusion, we demonstrated that the DMR assay can be successfully used to pharmacologically characterize GHSR ligands and particularly to discriminate between neutral antagonists and inverse agonists.