¹⁸F-FNDP for PET Imaging of Soluble Epoxide Hydrolase

Abstract

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme located within cytosol and peroxisomes that converts epoxides to the corresponding diols and hydrolyzes phosphate monoesters. It serves to inactivate epoxyeicosatrienoic acids (EETs), which have vasoactive and anti-inflammatory properties. Inhibitors of sEH are pursued as agents to mitigate neuronal damage after stroke. We developed N-(3,3-diphenylpropyl)-6-18F-fluoronicotinamide (18F-FNDP), which proved highly specific for imaging of sEH in the mouse and non-human primate brain with PET. Methods 18F-FNDP was synthesized from the corresponding bromo-precursor. sEH inhibitory activity of 18F-FNDP was measured using the sEH Inhibitor Screening Assay Kit. Biodistribution was undertaken in CD-1 mice. Binding specificity was assayed in CD-1 and sEH knock-out mice and Papio anubis (baboon) through pre-treatment with an sEH inhibitor to block sEH binding. Dynamic PET imaging with arterial blood sampling was performed in three baboons with regional tracer binding quantified using distribution volume (VT). Metabolism of 18F-FNDP in baboon was assessed using high performance liquid chromatography. Results 18F-FNDP (Ki = 1.73 nM) was prepared in one step in radiochemical yield of 14 ± 7%, specific radioactivity in the range of 888 – 3,774 GBq/µmol and in radiochemical purity > 99% using an automatic radiosynthesis module. The time of preparation was about 75 min. In CD-1 mice regional uptake followed the pattern of striatum > cortex > hippocampus > cerebellum, consistent with the known brain distribution of sEH, with 5.2 percent injected dose per gram of tissue at peak uptake. Blockade of 80–90% was demonstrated in all brain regions. Minimal radiotracer uptake was present in sEH-KO mice. PET baboon brain distribution paralleled that seen in mouse with marked blockade (95%) noted in all regions indicating sEH-mediated uptake of 18F-FNDP. Two hydrophilic metabolites were identified with 20% parent compound present at 90 min post-injection in baboon plasma. Conclusion 18F-FNDP can be synthesized in suitable radiochemical yield and high specific radioactivity and purity. In vivo imaging experiments demonstrated that 18F-FNDP targeted sEH in murine and non-human primate brain specifically. 18F-FNDP is a promising PET radiotracer likely to be useful for understanding the role of sEH in a variety of conditions affecting the central nervous system.

An optimized radiosynthesis of [18F]FNDP, a positron emission tomography radiotracer for imaging soluble epoxide hydrolase (sEH)

“…11 Results from that study illustrated the applicability of this tracer for non-invasive in vivo assessment of sEH levels in human brain disorders.…”

“…[6][7][8][9][10] We recently reported the first positron emission tomography (PET) radiotracer, N-(3,3-diphenylpropyl)-6-( 18 F)fluoronicotinamide ([ 18 F]FNDP) ( Figure 1), for in vivo imaging of sEH in rodent and baboon brain. 11 Results from that study illustrated the applicability of this tracer for noninvasive in vivo assessment of sEH levels in human brain disorders.…”

“…N-(3,3-diphenylpropyl)-6-bromonicotinamide (precursor) and 6-fluoro-N-(3,3-dipropyl)nicotinamide (FDNP) (Figure 1) were synthesized and isolated as described previously. 11 …”

“…N-(3,3diphenylpropyl)-6-bromonicotinamide (precursor) and 6fluoro-N-(3,3-dipropyl)nicotinamide (Figure 1) were synthesized and isolated as described previously. 11 The semipreparative HPLC system consisted of an Agilent 1260 Prep pump with a VICI injector, a Knauer 200 UV detector (254 nm), and a Bioscan Hot Cell interface with a diode radioactivity detector. The semipreparative HPLC column was a Waters XBridge Prep C18 10 μm 10 × 150 mm column eluted with a mixture of 40:60 acetonitrile (MeCN): 57mM triethylamine adjusted to pH 7.2 with phosphoric acid buffer at flow rate of 10 mL/min.…”

Oral Presentation Abstracts

“…However, further studies are needed to identify the precise mechanisms of action and pathology of the endocannabinoid system in depression. The hypothesis that depressive-like traits are related to altered CB 1 receptor expression were tested in in-vitro autoradiography experiments, measuring binding of [ 3 H]OMAR, a highly selective CB 1 receptor antagonist (Horti et al, 2006) in the Flinders rodent model of depression. Figure 1).…”