Decreased defluorination using the novel beta-cell imaging agent [18F]FE-DTBZ-d4 in pigs examined by PET

[18F]FE-DTBZ-d4 was synthesized by alkylation of 9-O-desmethyl-(+)-DTBZ precursor with deuterated [18F]FE bromide ([18F]FCD2CD2Br). Radioligand binding potential [BP] was assessed by an in vitro saturation homogenate binding assay using human endocrine and exocrine pancreatic tissues. In vivo pharmacokinetics and pharmacodynamics [PK/PD] was studied in a porcine model by PET/computed tomography, and the rate of defluorination was quantified by compartmental modeling.[18F]FE-DTBZ-d4 was produced in reproducible good radiochemical yield in 100 ± 20 min. Radiochemical purity of the formulated product was > 98% for up to 5 h with specific radioactivities that ranged from 192 to 529 GBq/μmol at the end of the synthesis. The in vitro BP for VMAT2 in the islet tissue was 27.0 ± 8.8, and for the exocrine tissue, 1.7 ± 1.0. The rate of in vivo defluorination was decreased significantly (kdefluorination = 0.0016 ± 0.0007 min-1) compared to the non-deuterated analogue (kdefluorination = 0.012 ± 0.002 min-1), resulting in a six fold increase in half-life stability.[18F]FE-DTBZ-d4 has similar PK and PD properties for VMAT2 imaging as its non-deuterated analogue [18F]FE-DTBZ in addition to gaining significantly increased stability against defluorination. [18F]FE-DTBZ-d4 is a prime candidate for future preclinical and clinical studies on focal clusters of beta cells, such as in intramuscular islet grafts.Dihydrotetrabenazine [DTBZ], derived from the neuroactive pharmaceutical tetrabenazine, is a ligand for the vesicular monoamine transporter 2 [VMAT2] which is expressed primarily in cells associated with the regulation of neurotransmission. It is especially associated with the dopaminergic system, and [11C]DTBZ has previously been used to study, for example, aspects of dementia [1] and Parkinson's disease [2] in the clinic. High VMAT2 expression has also been found in insulin-producing beta cells in the endocrine islets of Langerhans, but not in the exocrine pancreas [3], and the