PET Brain Imaging of Neuropeptide Y2 Receptors Using N-¹¹C-Methyl-JNJ-31020028 in Pigs

Abstract

Neuropeptide Y2 (NPY2) receptors are implicated in diverse brain disorders, but no suitable PET radiotracers are currently available for studying NPY2 receptors in the living brain. We developed a novel positron-emitting radioligand based on the NPY2 receptor antagonist JNJ-31020028 (N-(4-(4-[2-(diethylamino)-2-oxo-1-phenylethyl] piperazin-1-yl)-3-fluorophenyl)-2-pyridin-3-ylbenzamide) and used the radiotracer for PET brain imaging in pigs. Methods: In vitro receptor autoradiography studies were performed to establish the anatomic distribution of NPY2 receptors in the pig brain. In vivo, baseline 90-min PET recordings of N-11 C-methyl-JNJ-31020028 were conducted in anesthetized Yorkshire x Landrace pigs, concurrent with arterial blood sampling. Postchallenge scans were conducted after injection of unlabeled JNJ-31020028 as a pharmacologic intervention. Cyclosporine A was used to enhance levels of the PET radiotracer in the brain. The PET images were manually coregistered to a MR imaging atlas of the pig brain. Maps of the N-11 C-methyl-JNJ-31020028 volume of distribution in the brain were prepared, and regional binding potentials of NPY2 receptors toward the radio-ligand were calculated using the simplified reference tissue method. Results: In autoradiography studies, N-11 C-methyl-JNJ-31020028 receptor binding sites were observed primarily in the hippocampus and were inhibited by unlabeled JNJ-31020028. In PET studies, N-11 C-methyl-JNJ-31020028 was metabolized slowly in the bloodstream , with 25% of the 11 C-labeled parent compound remaining 30 min after injection. PET imaging showed baseline binding potentials of 0.64 ± 0.07 in the thalamus, 0.55 ± 0.02 in the caudate, and 0.49 ± 0.03 in the hippocampus. Graphical reference region analyses demonstrated that N-11 C-methyl-JNJ-31020028 binding was reversible; infusion of unlabeled JNJ-31020028 markedly displaced the PET radioligand from binding sites in the hippocampus, thalamus, caudate nucleus, and cerebellum but not in the corpus callosum, which served as reference region for nonspecific binding. Conclusion: N-11 C-methyl-JNJ-31020028 has several suitable properties for PET neuroimaging of NPY2 receptors. First, it is metabolized slowly in the bloodstream of pigs. Second, using cyclosporine, the target-to-background ratio of N-11 C-methyl-JNJ-31020028 is sufficient for estimating pharmacokinetic parameters. Third, N-11 C-methyl-JNJ-31020028 binds reversibly and competitively to cerebral sites known to contain relatively high numbers of NPY2 receptors, such as the hippocampus, thalamus, caudate nucleus, and cerebellum. Fourth, white matter such as corpus callosum, known to contain negligible numbers of NPY2 receptors, can serve as a reference region for estimating binding potentials in brain regions. To our knowledge, there is no other radioligand with these favorable properties and with this specificity for NPY2 receptors, which makes N-11 C-methyl-JNJ-31020028 the first candidate radioligand for PET investigations of NPY2 receptors in the living brain.

Sex Differences in the Neuropeptide Y System and Implications for Stress Related Disorders

“…More studies assessing NPY and its receptor levels in specific brain regions associated with stress in females are needed to better understand NPY’s involvement in stress-related disorders in a female clinical population. Recent advances in development of PET tracers for neuroimaging of Y1R, Y2R and Y5R show promise for human studies [ 170 , 171 , 172 , 173 ]. Additionally, studies with a focus on time-specific measures in relation to the time of stress are important to establish a temporal relationship between trauma and NPY in females and influence of estrous/menstrual cycle.…”

Less Exploited GPCRs in Precision Medicine: Targets for Molecular Imaging and Theranostics

“…Such a situation, namely the low number of preclinical or clinical assays reported in the literature [67,68,69,70,71], has been partially ascribed to the in vivo instability of the targeting peptides [72,73,74,75]. Although not as extensively as the peptide receptors mentioned above, neuropeptide Y receptor subtypes 1 (NPYR1) and 2 (NPYR2) have also been studied as imaging targets for NPYR1-expressing tumors such as breast cancer, [76,77,78,79,80,81,82,83,84] and for brain imaging [85], respectively.…”

Positron Emission Tomography in the Inflamed Cerebellum: Addressing Novel Targets among G Protein-Coupled Receptors and Immune Receptors

“…NPY2 expression has been described especially during brain development, in neurogenic niches [ 98 , 99 ], and in retinal microglia [ 100 ]. Even if initial reports on the presence of NPY receptors in the cerebellum showed rather low values at 3% of total brain labeling [ 101 ], initial investigations with an NPY2 receptor ligand with PET demonstrated in animal studies cerebellar uptake comparable with that in the frontal cortex [ 102 ].…”

“…In 2014, Winterdahl et al [ 102 ] published PET investigation of York Shire land race pigs using the fluorophenylpiperazine derivative N - 11 C-Methyl-JNJ-31020028 ( Figure 8 : [ 32 ]). Autoradiographic investigations of the brain in vivo revealed a tracer accumulation in the cerebellum of the healthy pig when compared with that in the basal ganglia or frontal cortex.…”

“…The binding of compound 32 in the hippocampus was enhanced three-fold after pretreatment with cyclosporine. This reflected the role of the P-gp transporter in efflux and accumulation of the tracer [ 102 ]. The authors described a similar effect of cyclosporine on the tracer accumulation in corpus callosum.…”