Dataset Information

Synthesis and preclinical evaluation of [¹¹C]MTP38 as a novel PET ligand for phosphodiesterase 7 in the brain.

ABSTRACT:

Purpose

Phosphodiesterase (PDE) 7 is a potential therapeutic target for neurological and inflammatory diseases, although in vivo visualization of PDE7 has not been successful. In this study, we aimed to develop [¹¹C]MTP38 as a novel positron emission tomography (PET) ligand for PDE7.

Methods

[¹¹C]MTP38 was radiosynthesized by ¹¹C-cyanation of a bromo precursor with [¹¹C]HCN. PET scans of rat and rhesus monkey brains and in vitro autoradiography of brain sections derived from these species were conducted with [¹¹C]MTP38. In monkeys, dynamic PET data were analyzed with an arterial input function to calculate the total distribution volume (V_T). The non-displaceable binding potential (BP_ND) in the striatum was also determined by a reference tissue model with cerebellar reference. Finally, striatal occupancy of PDE7 by an inhibitor was calculated in monkeys according to changes in BP_ND.

Results

[¹¹C]MTP38 was synthesized with radiochemical purity ≥99.4% and molar activity of 38.6 ± 12.6 GBq/μmol. Autoradiography revealed high radioactivity in the striatum and its reduction by non-radiolabeled ligands, in contrast with unaltered autoradiographic signals in other regions. In vivo PET after radioligand injection to rats and monkeys demonstrated that radioactivity was rapidly distributed to the brain and intensely accumulated in the striatum relative to the cerebellum. Correspondingly, estimated V_T values in the monkey striatum and cerebellum were 3.59 and 2.69 mL/cm³, respectively. The cerebellar V_T value was unchanged by pretreatment with unlabeled MTP38. Striatal BP_ND was reduced in a dose-dependent manner after pretreatment with MTP-X, a PDE7 inhibitor. Relationships between PDE7 occupancy by MTP-X and plasma MTP-X concentration could be described by Hill's sigmoidal function.

Conclusion

We have provided the first successful preclinical demonstration of in vivo PDE7 imaging with a specific PET radioligand. [¹¹C]MTP38 is a feasible radioligand for evaluating PDE7 in the brain and is currently being applied to a first-in-human PET study.

SUBMITTER: Obokata N

PROVIDER: S-EPMC8426238 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Tau aggregates and amyloid-β (Aβ) plaques are key histopathologic features in Alzheimer disease (AD) and are considered targets for therapeutic intervention as well as biomarkers for diagnostic in vivo imaging agents. This article describes the preclinical in vitro and in vivo characterization of 3 novel compounds-RO6958948, RO6931643, and RO6924963-that bind specifically to tau aggregates and have the potential to become PET tracers for future human use. Methods: RO6958948, RO6931643, and RO6924963 were identified as high-affinity competitors at the 3H-T808 binding site on native tau aggregates in human late-stage AD brain tissue. Binding of tritiated compounds to brain tissue sections of AD patients and healthy controls was analyzed by macro- and microautoradiography and by costaining of tau aggregates and Aβ plaques on the same tissue section using specific antibodies. All 3 tracer candidates were radiolabeled with a PET nuclide and tested in vivo in tau-naïve baboons to assess brain uptake, distribution, clearance, and metabolism. Results:3H-RO6958948, 3H-RO6931643, and 3H-RO6924963 bound with high affinity and specificity to tau aggregates, clearly lacking affinity for concomitant Aβ plaques in human AD Braak V tissue sections. The specificity of all 3 radioligands for tau aggregates was supported, first, by binding patterns in AD sections comparable to the tau-specific radioligand 3H-T808; second, by very low nonspecific binding in brain tissue devoid of tau pathology, excluding significant radioligand binding to any other central nervous system target; and third, by macroscopic and microscopic colocalization and quantitative correlation of radioligand binding and tau antibody staining on the same tissue section. RO6958948, RO6931643, and RO6924963 were successfully radiolabeled with a PET nuclide at high specific activity, radiochemical purity, and yield. After intravenous administration of 18F-RO6958948, 11C-RO6931643, and 11C-RO6924963 to baboons, PET scans indicated good brain entry, rapid washout, and a favorable metabolism pattern. Conclusion:18F-RO6958948, 11C-RO6931643, and 11C-RO6924963 are promising PET tracers for visualization of tau aggregates in AD. Head-to-head comparison and validation of these tracer candidates in AD patients and healthy controls will be reported in due course.

Project description:BackgroundMutations in the epidermal growth factor receptor (EGFR) kinase domain are common in non-small cell lung cancer. Conventional tyrosine kinase inhibitors target the mutation site in the ATP binding pocket, thereby inhibiting the receptor's function. However, subsequent treatment resistance mutations in the ATP binding site are common. The EGFR allosteric inhibitor, EAI045, is proposed to have an alternative mechanism of action, disrupting receptor signaling independent of the ATP-binding site. The antibody cetuximab is hypothesized to increase the number of accessible allosteric pockets for EAI045, thus increasing the potency of the inhibitor. This work aimed to gain further knowledge on pharmacokinetics, the EGFR mutation-targeting potential, and the influence of cetuximab on the uptake by radiolabeling EAI045 with carbon-11 and tritium.Results2-(5-fluoro-2-hydroxyphenyl)-2-((2-iodobenzyl)amino)-N-(thiazol-2-yl)acetamide and 2-(5-fluoro-2-hydroxyphenyl)-N-(5-iodothiazol-2-yl)-2-(1-oxoisoindolin-2-yl)acetamide were synthesized as precursors for the carbon-11 and tritium labeling of EAI045, respectively. [11C]EAI045 was synthesized using [11C]CO in a palladium-catalyzed ring closure in a 10 ± 1% radiochemical yield (decay corrected to end of [11C]CO2 production), > 97% radiochemical purity and 26 ± 1 GBq/µmol molar activity (determined at end of synthesis) in 51 min. [3H]EAI045 was synthesized by a tritium-halogen exchange in a 0.2% radiochemical yield, 98% radiochemical purity, and 763 kBq/nmol molar activity. The ability of [11C]EAI045 to differentiate between L858R/T790M mutated EGFR expressing H1975 xenografts and wild-type EGFR expressing A549 xenografts was evaluated in female nu/nu mice. The uptake was statistically significantly higher in H1975 xenografts compared to A549 xenografts (0.45 ± 0.07%ID/g vs. 0.31 ± 0.10%ID/g, P = 0.0166). The synergy in inhibition between EAI045 and cetuximab was evaluated in vivo and in vitro. While there was some indication that cetuximab influenced the uptake of [3H]EAI045 in vitro, this could not be confirmed in vivo when tumor-bearing mice were administered cetuximab (0.5 mg), 24 h prior to injection of [11C]EAI045.ConclusionsEAI045 was successfully labeled with tritium and carbon-11, and the in vivo results indicated [11C]EAI045 may be able to distinguish between mutated and non-mutated EGFR in non-small cell lung cancer mouse models. Cetuximab was hypothesized to increase EAI045 uptake; however, no significant effect was observed on the uptake of [11C]EAI045 in vivo or [3H]EAI045 in vitro in H1975 xenografts and cells.

Project description:UnlabelledThe enzyme phosphodiesterase 2A (PF-05270430) is a potential target for development of novel therapeutic agents for the treatment of cognitive impairments. The goal of the present study was to evaluate the PDE2A ligand (18)F-PF-05270430, 4-(3-fluoroazetidin-1-yl)-7-methyl-5-(1-methyl-5-(4-(trifluoromethyl)phenyl)-1H-pyrazol-4-yl)imidazo[1,5-f][1,2,4]triazine, in nonhuman primates.Methods(18)F-PF-05270430 was radiolabeled by 2 methods via nucleophilic substitution of its tosylate precursor. Tissue metabolite analysis in rodents and PET imaging in nonhuman primates under baseline and blocking conditions were performed to determine the pharmacokinetic and binding characteristics of the new radioligand. Various kinetic modeling approaches were assessed to select the optimal method for analysis of imaging data.Results(18)F-PF-05270430 was synthesized in greater than 98% radiochemical purity and high specific activity. In the nonhuman primate brain, uptake of (18)F-PF-05270430 was fast, with peak concentration (SUVs of 1.5-1.8 in rhesus monkeys) achieved within 7 min after injection. The rank order of uptake was striatum > neocortical regions > cerebellum. Regional time-activity curves were well fitted by the 2-tissue-compartment model and the multilinear analysis-1 (MA1) method to arrive at reliable estimates of regional distribution volume (VT) and binding potential (BPND) with 120 min of scan data. Regional VT values (MA1) ranged from 1.28 mL/cm(3) in the cerebellum to 3.71 mL/cm(3) in the putamen, with a BPND of 0.25 in the temporal cortex and 1.92 in the putamen. Regional BPND values estimated by the simplified reference tissue model (SRTM) were similar to those from MA1. Test-retest variability in high-binding regions (striatum) was 4% ± 6% for MA1 VT, 13% ± 6% for MA1 BPND, and 13% ± 7% SRTM BPND, respectively. Pretreatment of animals with the PDE2A inhibitor PF-05180999 resulted in a dose-dependent reduction of (18)F-PF-05270430 specific binding, with a half maximal effective concentration of 69.4 ng/mL in plasma PF-05180999 concentration.Conclusion(18)F-PF-05270430 displayed fast and reversible kinetics in nonhuman primates, as well as specific binding blockable by a PDE2A inhibitor. This is the first PET tracer with desirable imaging properties and demonstrated ability to image and quantify PDE2A in vivo.

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Synthesis and preclinical evaluation of [¹¹C]MTP38 as a novel PET ligand for phosphodiesterase 7 in the brain.

Purpose

Methods

Results

Conclusion

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Dataset Information

Synthesis and preclinical evaluation of [11C]MTP38 as a novel PET ligand for phosphodiesterase 7 in the brain.

Purpose

Methods

Results

Conclusion

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Synthesis and preclinical evaluation of [¹¹C]MTP38 as a novel PET ligand for phosphodiesterase 7 in the brain.