The development of a GPR44 targeting radioligand [11C]AZ12204657 for in vivo assessment of beta cell mass.

Abstract

BACKGROUND:

The G-protein-coupled receptor 44 (GPR44) is a beta cell-restricted target that may serve as a marker for beta cell mass (BCM) given the development of a suitable PET ligand.

METHODS:

The binding characteristics of the selected candidate, AZ12204657, at human GPR44 were determined using in vitro ligand binding assays. AZ12204657 was radiolabeled using 11C- or 3H-labeled methyl iodide ([11C/3H]CH3I) in one step, and the conversion of [11C/3H]CH3I to the radiolabeled product [11C/3H]AZ12204657 was quantitative. The specificity of radioligand binding to GPR44 and the selectivity for beta cells were evaluated by in vitro binding studies on pancreatic sections from human and non-human primates as well as on homogenates from endocrine and exocrine pancreatic compartments.

RESULTS:

The radiochemical purity of the resulting radioligand [11C]AZ12204657 was > 98%, with high molar activity (MA), 1351 ± 575 GBq/μmol (n = 18). The radiochemical purity of [3H]AZ12204657 was > 99% with MA of 2 GBq/μmol. Pancreatic binding of [11C/3H]AZ12204657 was co-localized with insulin-positive islets of Langerhans in non-diabetic individuals and individuals with type 2 diabetes (T2D). The binding of [11C]AZ12204657 to GPR44 was > 10 times higher in islet homogenates compared to exocrine homogenates. In human islets of Langerhans GPR44 was co-expressed with insulin, but not glucagon as assessed by co-staining and confocal microscopy.

CONCLUSION:

We radiolabeled [11C]AZ12204657, a potential PET radioligand for the beta cell-restricted protein GPR44. In vitro evaluation demonstrated that [3H]AZ12204657 and [11C]AZ12204657 selectively target pancreatic beta cells. [11C]AZ12204657 has promising properties as a marker for human BCM.

• Authors: Mahabuba Jahan, Peter Johnström, Ram K Selvaraju, Marie Svedberg, Maria Sörhede Winzell, Jenny Bernström, Lee Kingston, Magnus Schou, Zhisheng Jia, Stanko Skrtic, Lars Johansson, Olle Korsgren, Lars Farde, Christer Halldin, Olof Eriksson
• Journal: EJNMMI research (EJNMMI Res) Vol. 8 Issue 1 Pg. 113 (Dec 27 2018) ISSN: 2191-219X [Print] Germany
• PMID: 30588560 (Publication Type: Journal Article)