124I-Epidepride: A PET radiotracer for extended imaging of dopamine D2/D3 receptors

Abstract

Objectives A new radiotracer, 124I-epidepride, has been developed for the imaging of dopamine D2/3 receptors (D2/3Rs). 124I-epidepride (half-life of 124I = 4.2days) allows imaging over extended periods compared to 18F-fallypride (half-life of 18F = 0.076days) and may maximize visualization of D2/3Rs in the brain and pancreas (allowing clearance from adjacent organs). D2/3Rs are also present in pancreatic islets where they co-localize with insulin to produce granules and may serve as a surrogate marker for imaging diabetes. Methods 124I-Epidepride was synthesized using N-[[(2S)-1-ethylpyrrolidin-2-yl]methyl]-5-tributyltin-2,3-dimethoxybenzamide and 124I-iodide under no carrier added condition. Rats were used for in vitro and in vivo imaging. Brain slices were incubated with 124I-epidepride (0.75μCi/cc) and nonspecific binding measured with 10 μM haloperidol. Autoradiograms were analyzed by OptiQuant. 124I-Epidepride (0.2 to 0.3 mCi, iv) was administered to rats and brain uptake at 3 hours, 24 hours, and 48 hours post injection was evaluated. Results 124I-Epidepride was synthesized with 50% radiochemical yield and high radiochemical purity (>95%). 124I-Epidepride localized in the striatum with a striatum to cerebellum ratio of 10. Binding was displaced by dopamine and haloperidol. Brain slices demonstrated localization of 124I-epidepride up until 48 hr in the striatum. However, the extent of binding was reduced significantly. Conclusions 124I-Epidepride is a new radiotracer suitable for extended imaging of dopamine D2/3 receptors and may have applications in imaging of receptors in the brain and monitoring pancreatic islet cell grafting.

Development and evaluation of [125I]IPPI for Tau imaging in postmortem human Alzheimer's disease brain

“…6‐[ 125 I]iodo‐3‐(1H‐pyrrolo[2,3‐c]pyridine‐1‐yl)isoquinoline, 15 [ 125 I]IPPI : Radioiodination hood (CBS Scientific, Inc) placed inside a fume hood designated to handle radioactive materials was used to carry out all processes for radioiodination, separation, and purification. Iodine‐125 radiolabeling was carried out by using modification of our previously reported radiolabeling procedures with iodine‐123 and iodine‐124 (Pandey et al., 2012; Pandey, Venugopal, Kant, Coleman, & Mukherjee, 2014). No‐carrier‐added Na 125 I (18.5 MBq, approx 100 µl 0.01 N NaOH, 644 MBq/µg; American Radiolabeled Chemicals, St. Louis) was taken in a V‐vial.…”

The role of iodine-124 positron emission tomography in molecular imaging

“…124 I potentially provides quantification, with its long half-life also permitting delayed imaging [12]. 124 I-Epidepride for extended imaging of dopamine D2/3 receptors may have applications in imaging of receptors in brain and pancreatic islet cells [63]. 124 -I labelled to a small molecule, MIP-1095, that targets prostate specific membrane antigen was used for dosimetry as a guide to therapy with the 131-I labelled molecule [64].…”

Recent Progress of Imaging Agents for Parkinson’s Disease

“…D 2 -like receptors have attracted much attention in the field of nuclear imaging. D 2 - like receptor imaging agents are primarily comprised of [ 11 C]Raclopride [ 86 - 88 ], [ 123 I]IBZM [ 89 - 92 ], [ 18 F] Desmethoxyfallypride ([ 18 F]DMFP) [ 93 , 94 ], [ 11 C]MNPA [ 94 , 95 ], [ 131 I]Epidepride and [ 124 I]Epidepride [ 96 - 99 ], [ 11 C] (+)-PHNO [ 100 , 101 ], [ 11 C]NMSP [ 102 , 103 ], [ 18 F]MCL-524 [ 104 ], etc (Fig. 4 ).…”