Synthesis and Characterization of a Promising Novel FFAR1/GPR40 Targeting Fluorescent Probe for β-Cell Imaging

Abstract

Diabetes affects an increasing number of patients worldwide and is responsible for a significant rise in healthcare expenses. Imaging of β-cells bears the potential to contribute to an improved understanding, diagnosis, and development of new treatment options for diabetes. Here, we describe the first small molecule fluorescent probe targeting the free fatty acid receptor 1 (FFAR1/GPR40). This receptor is highly expressed on β-cells, and was up to now unexplored for imaging purposes. We designed a novel probe by facile modification of the selective and potent FFAR1 agonist TAK-875. Effective and specific binding of the probe was demonstrated using FFAR1 overexpressing cells. We also successfully labeled FFAR1 on MIN6 and INS1E cells, two widely used β-cell models, by applying an effective amplification protocol. Finally, we showed that the probe is capable of inducing insulin secretion in a glucose-dependent manner, thus demonstrating that functional activity of the probe was maintained. These results suggest that our probe represents a first important step to successful β-cell imaging by targeting FFAR1. The developed probe may prove to be particularly useful for in vitro and ex vivo studies of diabetic cellular and animal models to gain new insights into disease pathogenesis.

Complex Pharmacology of Free Fatty Acid Receptors

“…To overcome this, Bertrand et al utilized an approach in which cells were first labeled with 37 and then the signal was boosted using an antibody directed against the Alexa488 fluorophore present in 37. 218 By contrast, Christiansen et al developed a bioluminescence resonance energy transfer (BRET)-based assay using 38. 220 For this, the small, bright, Nanoluciferase, which can serve as an energy donor to the 4-amino-7-nitrobenzofurazan fluorophore in 38, was introduced into the N-terminal domain of FFA1.…”

Mechanistic investigations of the liver toxicity of the free fatty acid receptor 1 agonist fasiglifam (TAK875) and its primary metabolites

“…Therefore, targeting FFAR1 with selective synthetic agonists has received considerable attention as a potential treatment option for type 2 diabetes averting the risk of hypoglycemia associated with other insulin‐secreting pathways as observed for sulphonyl urea . Numerous novel synthetic FFAR1 agonists have been developed and FFAR1 targeting probes are considered also for functional ß‐cell imaging …”

Molecular imaging of β-cells: diabetes and beyond

“…FFAR1 was found to be expressed in defined human brain areas and in the intestine [142], but the receptor is predominantly expressed in human and rodent β-cells [143,144]. Due to this relatively high expression of FFAR1 in islets, Bertrand et al modified the scaffold of the FFAR1 agonist TAK875 and then conjugated the compound with different fluorophores, of which probe 16 conjugated with Alexa488 maintained its agonistic properties and enhanced insulin secretion in a glucose-stimulated manner [145]. The same group further labeled derivatives of TAK875 with 18 F and yielded good radiochemical results [146].…”