In Vivo Characterization of Two 18F-Labeled PDE10A PET Radioligands in Nonhuman Primate Brains
摘要:
Positron emission tomography (PET) with phosphodiesterase 10A (PDE10A) specific radioligands provides a noninvasive and quantitative imaging tool to access the expression of this enzyme in vivo under normal and diseased conditions. We recently reported two potent F-18-labeled PDE10A radioligands (F-18-TZ19106B and F-18-TZ8110); initial evaluation in rats and nonhuman primates indicated stable metabolic profiles and excellent target-to-nontarget ratio (striatum/cerebellum) for both tracers. Herein, we focused on in vivo characterization of F-18-TZ19106B and F-18-TZ8110 to identify a suitable radioligand for imaging PDE10A in vivo. We directly compared microPET studies of these two radiotracers in adult male Macaca fascicularis nonhuman primates (NHPs). F-18-TZ19106B had higher striatal uptake and tracer retention in NHP brains than F-18-TZ8110, quantified by either standardized uptake values (SUVs) or nondisplaceable binding potential (BP (ND) ) estimated using reference-based modeling analysis. Blocking and displacement studies using the PDE10A inhibitor MP-10 indicated the binding of F-18-TZ19106B to PDE10A was specific and reversible. We also demonstrated sensitivity of F-18-TZ19106B binding to varying number of specific binding sites using escalating doses of MP-10 blockade (0.3, 0.5, 1.0, 1.5, and 2.0 mg/kg). Pretreatment with a dopamine D2-like receptor antagonist enhanced the striatal uptake of F-18-TZ19106B. Our results indicate that F-18-TZ19106B is a promising radioligand candidate for imaging PDE10A in vivo and it may be used to determine target engagement of PDE10A inhibitors and serve as a tool to evaluate the effect of novel antipsychotic therapies.
Synthesis of Fluorine-Containing Phosphodiesterase 10A (PDE10A) Inhibitors and the In Vivo Evaluation of F-18 Labeled PDE10A PET Tracers in Rodent and Nonhuman Primate
摘要:
A series of fluorine-containing PDE10A inhibitors were designed and synthesized to improve the metabolic stability of [C-11]MP-10. Twenty of the 22 new analogues had high potency and selectivity for PDE10A: 18a-j, 19d-j, 20a-b, and 21b had IC50 values <5 nM for PDE10A. Seven F-18 labeled compounds [F-18](18)a-e, [F-18]18g, and [F-18]20a were radiosynthesized by F-18-introduction onto the quinoline rather than the pyrazole moiety of the MP-10 pharmacophore and performed in vivo evaluation. Biodistribution studies in rats showed similar to 2-fold higher activity in the PDE10A-enriched striatum than nontarget brain regions; this ratio increased from 5 to 30 min postinjection, particularly for [F-18]18a-d and [F-18]20a. Micro-PET studies of [F-18]18d and [F-18]20a in nonhuman primates provided clear visualization of striatum with suitable equilibrium kinetics and favorable metabolic stability. These results suggest this strategy may identify a F-18-labeled PET tracer for quantifying the levels of PDE10A in patients with CNS disorders including Huntington's disease and schizophrenia.
Radiosyntheses and in vivo evaluation of carbon-11 PET tracers for PDE10A in the brain of rodent and nonhuman primate
作者:Jinda Fan、Xiang Zhang、Junfeng Li、Hongjun Jin、Prashanth K. Padakanti、Lynne A. Jones、Hubert P. Flores、Yi Su、Joel S. Perlmutter、Zhude Tu
DOI:10.1016/j.bmc.2014.03.028
日期:2014.5
The radiosyntheses and in vivo evaluation of four carbon-11 labeled quinoline group-containing radioligands are reported here. Radiolabeling of [C-11]1-4 was achieved by alkylation of their corresponding desmethyl precursors with [C-11]CH3I. Preliminary biodistribution evaluation in Sprague-Dawley rats demonstrated that [11C] 1 and [C-11]2 had high striatal accumulation (at peak time) for [C-11]1 and [C-11]2 were 6.0-fold and 4.5-fold at 60 min, respectively. Following MP-10 pretreatment, striatal uptake in rats of [C-11]1 and [C-11]2 was reduced, suggesting that the tracers bind specifically to PDE10A. MicroPET studies of [C-11]1 and [C-11]2 in nonhuman primates (NHP) also showed good tracer retention in the striatum with rapid clearance from non-target brain regions. Striatal uptake (SUV) of [C-11]1 reached 1.8 at 30 min with a 3.5-fold striatum: cerebellum ratio. In addition, HPLC analysis of solvent extracts from NHP plasma samples suggested that [C-11]1 had a very favorable metabolic stability. Our preclinical investigations suggest that [C-11]1 is a promising candidate for quantification of PDE10A in vivo using PET. (C) 2014 Elsevier Ltd. All rights reserved.