Hellström-Lindahl E, Åberg O, Ericsson C, O'Mahony G, Johnström P, Skrtic S, Eriksson O
Acta diabetologica 54 (7) 663-668 [2017-07-00; online 2017-04-13]
Molecular imaging of the free fatty acid receptor 1 (FFAR1) would be a valuable tool for drug development by enabling in vivo target engagement studies in human. It has also been suggested as a putative target for beta cell imaging, but the inherent lipophilicity of most FFAR1 binders produces high off-target binding, which has hampered progress in this area. The aim of this study was to generate a suitable lead compound for further PET labeling. In order to identify a lead compound for future PET labeling for quantitative imaging of FFAR1 in human, we evaluated tritiated small molecule FFAR1 binding probes ([ 3H]AZ1, [3H]AZ2 and [3H]TAK-875) for their off-target binding, receptor density and affinity in human pancreatic tissue (islets and exocrine) and rodent insulinoma. [ 3H]AZ1 showed improved specificity to FFAR1, with decreased off-target binding compared to [3H]AZ2 and [3H]TAK-875, while retaining high affinity in the nanomolar range. FFAR1 density in human islets was approximately 50% higher than in exocrine tissue. AZ1 is a suitable lead compound for PET labeling for molecular imaging of FFAR1 in humans, due to high affinity and reduced off-target binding.