Cellular Uptake of a Fluorescent Ligand Reveals Ghrelin -Acyltransferase Interacts with Extracellular Peptides and Exhibits Unexpected Localization for a Secretory Pathway Enzyme.

Ghrelin acyltransferase (GOAT) plays a central role in the maturation and activation of the peptide hormone ghrelin, which performs a wide range of endocrinological signaling roles. Using a tight-binding fluorescent ghrelin-derived peptide designed for high selectivity for GOAT over the ghrelin receptor GHSR, we demonstrate that GOAT interacts with extracellular ghrelin and facilitates ligand cell internalization in both transfected cells and prostate cancer cells endogenously expressing GOAT. Coupled with enzyme mutagenesis, ligand uptake studies support the interaction of the putative histidine general base within GOAT with the ghrelin peptide acylation site.

Discovery of Ghrelin(1-8) Analogues with Improved Stability and Functional Activity for PET Imaging.

The highest affinity ghrelin-based analogue for fluorine-18 positron emission tomography, [Inp,Dpr(6-FN),1Nal,Thr]ghrelin(1-8) amide (), has remarkable subnanomolar receptor affinity (IC = 0.11 nM) toward the growth hormone secretagogue receptor 1a (GHSR). However, initial PET imaging and biodistribution of in mice demonstrated an unfavorable pharmacokinetic profile with rapid clearance and accumulation in liver and intestinal tissue, prompting concerns about the metabolic stability of this probe.

Protease-activated receptor 2 (PAR2)-targeting peptide derivatives for positron emission tomography (PET) imaging.

The proteolytically-activated G protein-coupled receptor (GPCR) protease-activated receptor 2 (PAR2), is implicated in various cancers and inflammatory diseases. Synthetic ligands and in vitro imaging probes targeting this receptor have been developed with low nanomolar affinity, however, no in vivo imaging probes exist for PAR2. Here, we report the strategic design, synthesis, and biological evaluation of a series of novel 4-fluorobenzoylated PAR2-targeting peptides derived from 2f-LIGRLO-NH (2f-LI-) and Isox-Cha-Chg-Xaa-NH (Isox-) peptide families, where the 4-fluorobenzoyl moiety acts as the F-standard of an F-labeled probe for potential use in in vivo imaging.

Radiofluorination of non-activated aromatic prosthetic groups for synthesis and evaluation of fluorine-18 labelled ghrelin(1-8) analogues.

The growth hormone secretagogue receptor 1a (GHSR) is differentially expressed in various disease states compared to healthy tissues and thus is a target for molecular imaging. The endogenous ligand for the GHSR is ghrelin, a 28 amino acid peptide with a unique octanoyl group on the serine-3 residue. A recently reported ghrelin analogue revealed the successful use of fluorine-containing, polycyclic aromatic groups in place of the octanoyl side chain, thereby providing potential access to new F-PET imaging probes.

A Decade's Progress in the Development of Molecular Imaging Agents Targeting the Growth Hormone Secretagogue Receptor.

The growth hormone secretagogue receptor 1a (GHSR), also called the ghrelin receptor, is a G protein-coupled receptor known to play an important metabolic role in the regulation of various physiological processes, including energy expenditure, growth hormone secretion, and cell proliferation. This receptor has been implicated in numerous health issues including obesity, gastrointestinal disorders, type II diabetes, and regulation of body weight in patients with Prader-Willi syndrome, and there has been growing interest in studying its mechanism of behavior to unlock further applications of GHSR-targeted therapeutics. In addition, the GHSR is expressed in various types of cancer including prostate, breast, and testicular cancers, while aberrant expression has been reported in cardiac disease.