PET ligands [ ¹⁸ F]LSN3316612 and [ ¹¹ C]LSN3316612 quantify O -linked-β- N -acetyl-glucosamine hydrolase in the brain

Abstract

<jats:p>We aimed to develop effective radioligands for quantifying brain <jats:italic>O</jats:italic>-linked-β-<jats:italic>N</jats:italic>-acetyl-glucosamine (<jats:italic>O</jats:italic>-GlcNAc) hydrolase (OGA) using positron emission tomography in living subjects as tools for evaluating drug target engagement. Posttranslational modifications of tau, a biomarker of Alzheimer’s disease, by <jats:italic>O</jats:italic>-GlcNAc through the enzyme pair OGA and <jats:italic>O</jats:italic>-GlcNAc transferase (OGT) are inversely related to the amounts of its insoluble hyperphosphorylated form. Increase in tau <jats:italic>O</jats:italic>-GlcNAcylation by OGA inhibition is believed to reduce tau aggregation. LSN3316612, a highly selective and potent OGA ligand [half-maximal inhibitory concentration (IC<jats:sub>50</jats:sub>) = 1.9 nM], emerged as a lead ligand after in silico analysis and in vitro evaluations. [<jats:sup>3</jats:sup>H]LSN3316612 imaged and quantified OGA in postmortem brains of rat, monkey, and human. The presence of fluorine and carbonyl functionality in LSN3316612 enabled labeling with positron-emitting fluorine-18 or carbon-11. Both [<jats:sup>18</jats:sup>F]LSN3316612 and [<jats:sup>11</jats:sup>C]LSN3316612 bound reversibly to OGA in vivo, and such binding was blocked by pharmacological doses of thiamet G, an OGA inhibitor of different chemotype, in monkeys. [<jats:sup>18</jats:sup>F]LSN3316612 entered healthy human brain avidly (~4 SUV) without radiodefluorination or adverse effect from other radiometabolites, as evidenced by stable brain total volume of distribution (V<jats:sub>T</jats:sub>) values by 110 min of scanning. Overall, [<jats:sup>18</jats:sup>F]LSN3316612 is preferred over [<jats:sup>11</jats:sup>C]LSN3316612 for future human studies, whereas either may be an effective positron emission tomography radioligand for quantifying brain OGA in rodent and monkey.</jats:p>

Analytical and Biochemical Perspectives of Protein O-GlcNAcylation

“…In addition, ∼90% of the [ 18 F]LSN3316612 is specifically bound to OGA, on the basis of blocking studies with Thiamet-G and the nonradioactive parent ligand. 333,334 Obviously, PET imaging with [ 18 F]LSN3316612 demonstrates its good brain uptake, a high percentage of specific and reversible binding, selectivity for its target OGA in vivo, and amenability to quantitation with compartmental modeling. Further studies reveal that [ 18 F]LSN3316612 is an excellent PET radioligand for imaging and quantifying OGA in the brain of healthy human participants (Figure 5).…”

“…Further studies reveal that [ 18 F]LSN3316612 is an excellent PET radioligand for imaging and quantifying OGA in the brain of healthy human participants (Figure 5). 334,335 Even though only limited examples have emerged so far, apparently PET imaging with radioactive inhibitors to OGA have already demonstrated its great strength. On one hand, it will assist our understanding of OGA in vivo and aid the exploration of pathophysiology (e.g., the distribution of OGA in subjects at baseline and perturbation, by using whole-body PET scanning).…”

PET Molecular Imaging in Drug Development: The Imaging and Chemistry Perspective

“…Initially, the [ 3 H]LSN3316612 was used to image and quantify OGA in the brains of living subjects like rats, monkeys, and humans, and later the [ 18 F]LSN3316612 was used to image OGA in vivo with the blocking agent thiamet G in monkeys. Furthermore, the research has been extended and reported the PET quantification of O-GlcNAcase in the brain of healthy human volunteers using [ 18 F]LSN3316612, the V T was calculated with two tissue compartment model, and also reported Region-based as well as voxel-based quantification of [ 18 F]LSN3316612 in the human brain for O-GlcNAcase ( 122 , 123 ). Zhang et al have discovered a novel Radioligand PF-06445974 to image preferably Phosphodiesterase (PDE) 4B-isoform using PET, which is this cold ligand had shown promising results with high potency and selectivity over PDE-4D isoform.…”

Insight into the Development of PET Radiopharmaceuticals for Oncology

“…Other animal species are also used to evaluate PET radiopharmaceuticals. For example, rhesus monkeys are commonly used to evaluate neuro-PET radiopharmaceuticals with respect to target engagement, distribution, and dosimetry [235].…”