Biology subjects

Dhaynaut, M.

Publications and source records attributed to Dhaynaut, M..

7 recordsLinked to original sources

bioRxiv2023

Radiosynthesis automation, non-human primate biodistribution and dosimetry of K+ channel tracer 3MeO4AP

Purpose4-Aminopyridine (4AP) is a medication for the symptomatic treatment of multiple sclerosis. Several 4AP-based PET tracers have been developed for imaging demyelination. In preclinical studies, [11C]3MeO4AP has shown promise due to its high brain permeability, high metabolic stability, high plasma availability, and high in vivo binding affinity. To prepare for the translation to human studies, we developed a cGMP-compliant automated radiosynthesis protocol and evaluated the whole-body biodistribution and radiation dosimetry of [11C]3MeO4AP in non-human primates (NHPs). MethodsAutomated radiosynthesis was carried out using a GE TRACERlab FX-C Pro synthesis module. One male and one female adult rhesus macaques were used in the study. A high-resolution CT from cranial vertex to knee was acquired. PET data were collected using a dynamic acquisition protocol with 4 bed positions and 13 passes over a total scan time of [~]150 minutes. Based on the CT and PET images, volumes of interest (VOIs) were manually drawn for selected organs. Non-decay corrected time-activity curves (TACs) were extracted for each VOI. Radiation dosimetry and effective dose were calculated from the integrated TACs using OLINDA software. ResultsFully automated radiosynthesis of [11C]3MeO4AP was achieved with 7.3 {+/-} 1.2 % (n = 4) of non-decay corrected radiochemical yield within 38 min of synthesis and purification time. [11C]3MeO4AP distributed quickly throughout the body and into the brain. The organs with highest dose were the kidneys. The average effective dose of [11C]3MeO4AP was 4.27 {+/-} 0.57 Sv/MBq. No significant changes in vital signs were observed during the scan. ConclusionThe cGMP compliant automated radiosynthesis of [11C]3MeO4AP was developed. The whole-body biodistribution and radiation dosimetry of [11C]3MeO4AP was successfully evaluated in NHPs. [11C]3MeO4AP shows lower average effective dose than [18F]3F4AP and similar average effective dose as other carbon-11 tracers.

neuroscience↗

bioRxiv2022

Radiochemical Synthesis and Evaluation of 3-methyl-4-aminopyridine in Rodents and Non-Human Primates for Imaging Potassium Channels in the CNS

Demyelination, the loss of the insulating sheath of neurons, causes failed or slowed neuronal conduction and contributes to the neurological symptoms in multiple sclerosis, traumatic brain and spinal cord injuries, stroke, and dementia. In demyelinated neurons, the axonal potassium channels Kv1.1 and Kv1.2, generally under the myelin sheath, become exposed and upregulated. Therefore, imaging these channels using positron emission tomography can provide valuable information for disease diagnosis and monitoring. Here, we describe the novel tracer for Kv1 channels [11C]3-methyl-4-aminopyridine ([11C]3Me4AP). [11C]3Me4AP was efficiently synthesized via Pd(0)-Cu(I) co-mediated Stille cross-coupling of a stannyl precursor containing a free amino group. Evaluation of its imaging properties in rats and nonhuman primates showed that [11C]3Me4AP has a moderate brain permeability and slow kinetics. Additional evaluation in monkeys showed that the tracer is metabolically stable and that a 1-tissue compartment model can accurately model the regional brain time-activity curves. Compared to the related tracers [18F]3-fluoro-4-aminopyridine ([18F]3F4AP) and [11C]3-methoxy-4-aminopyridine ([11C]3MeO4AP), [11C]3Me4AP shows lower initial brain uptake, which indicates reduced permeability to the blood-brain-barrier and slower kinetics, suggesting higher binding affinity consistent with in vitro studies. While the slow kinetics and strong binding affinity resulted in a tracer with less favorable properties for imaging the brain than its predecessors, these properties may make 3Me4AP useful as a therapeutic.

neuroscience↗

bioRxiv2021

Design, synthesis, and characterization of mG2P026 as a high contrast PET imaging ligand for metabotropic glutamate receptor 2

An array of triazolopyridines based on JNJ-46356479 (6) were synthesized as potential PET imaging ligands for metabotropic glutamate receptor 2 (mGluR2) in the brain. The selected candidates 8-11 featured an enhanced positive allosteric modulator (PAM) activity (37-fold max.) and an apparent mGluR2 agonist activity (25-fold max.) compared to compound 6. Radiolabeling of compounds 8 and 9 (also named mG2P026) was achieved via the Cu(I)-mediated radiofluorination in the automated TRACERLabTM FXF-N platform. Both [18F]8 and [18F]9 were obtained with satisfactory radiochemical yields (> 5%, non-decay corrected), high molar activity (> 180 GBq/mol), and excellent chemical and radiochemical purities (> 98%). Preliminary characterization of [18F]8 and [18F]9 in rats confirmed their excellent brain permeability with [18F]9 showing better brain heterogeneity and favorable binding kinetics. Pretreatment with different classes of PAMs enhanced the radioactivity uptake for both [18F]8 and [18F]9 at the regions of interest by 20.3-40.9% and 16.7-81.6%, respectively, due to their pharmacological effects. Further evaluation of [18F]9 in a nonhuman primate confirmed its superior brain heterogeneity in mapping mGlu2 receptors and its higher specific binding than [18F]6. Pretreatment with 0.5 mg/kg BINA led (2) to an enhanced brain uptake of [18F]9 by 3% in high tracer uptake regions that was consistent with the rat studies. Therefore, [18F]9 has the potential to be translated for human studies.

neuroscience↗

bioRxiv2021

PET imaging studies to investigate functional expression of mGluR2 using mG2P001

Metabotropic glutamate receptor 2 (mGluR2) has been extensively studied for the treatment of various neurological and psychiatric disorders. Understanding of the mGluR2 function is pivotal in supporting the drug discovery targeting mGluR2. Herein, the positive allosteric modulation of mGluR2 was investigated via the in vivo positron emission tomography (PET) imaging using 2-((4-(2-[11C]methoxy-4-(trifluoromethyl)phenyl)piperidin-1-yl)methyl)-1-methyl-1H-imidazo[4,5-b]pyridine ([11C]mG2P001).Distinct from the orthosteric compounds, pretreatment with the unlabeled mG2P001, a potent mGluR2 positive allosteric modulator (PAM), resulted in a significant increase instead of decrease of the [11C]mG2P001 accumulation in rat brain detected by PET imaging. Subsequent in vitro studies with [3H]mG2P001 revealed the cooperative binding mechanism of mG2P001 with glutamate and its pharmacological effect that contributed to the enhanced binding of [3H]mG2P001 in transfected CHO cells expressing mGluR2. The in vivo PET imaging and quantitative analysis of [11C]mG2P001 in non-human primates (NHPs) further validated the characteristics of [11C]mG2P001 as an imaging ligand for mGluR2. Self-blocking studies in primates enhanced accumulation of [11C]mG2P001 dose- and delivery-dependently. Altogether, these studies show that [11C]mG2P001 is a sensitive biomarker for mGluR2 expression and the binding is affected by the tissue glutamate concentration.

neuroscience↗

bioRxiv2021

Synthesis and characterization of 5-(2-fluoro-4-pyridine-7-carboxamide as a PET imaging ligand for metabotropic glutamate receptor 2

Metabotropic glutamate receptor 2 (mGluR2) is a therapeutic target for the treatment of several neuropsychiatric disorders and conditions. The role of mGluR2 function in etiology could be unveiled by in vivo imaging using positron emission tomography (PET). In this regard, 5-(2- fluoro-4-[11C]methoxyphenyl)-2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]pyridine-7- carboxamide ([11C]13), a potent negative allosteric modulator (NAM), was developed to support this endeavor. Radioligand [11C]13 was synthesized via the O-[11C]methylation of phenol 24 with a high molar activity of 212 {+/-} 76 GBq/{micro}mol (n = 5) and excellent radiochemical purity (> 99%). PET imaging of [11C]13 in rats demonstrated its superior brain heterogeneity, particularly in the regions of striatum, thalamus, hippocampus, and cortex. Accumulation of [11C]13 in these regions of interest (ROIs) was reduced with pretreatment of mGluR2 NAMs, VU6001966 (9) and MNI-137 (26), the extent of which revealed a time-dependent drug effect of the blocking agents. In a nonhuman primate, [11C]13 selectively accumulated in mGluR2-rich regions, especially in different cortical areas, putamen, thalamus, and hippocampus, and resulted in high-contrast brain images. The regional total volume of distribution (VT) estimates of [11C]13 decreased by 14% after the pretreatment with 9. Therefore, [11C]13 is a potential candidate for translational PET imaging studies of mGluR2 function.

neuroscience↗

bioRxiv2020

Radiochemical synthesis and evaluation in nonhuman primates of 3-methoxy-4-aminopyridine: a novel PET tracer for imaging potassium channels in the CNS

Demyelination, the loss of the protecting sheath of neurons, contributes to disability in many neurological diseases. In order to fully understand its role in different diseases and to monitor treatments aiming at reversing this process, it would be valuable to have PET radiotracers that can detect and quantify molecular changes involved in demyelination such as the uncovering and upregulation of the axonal potassium channels Kv1.1 and Kv1.2. Carbon-11 labeled radiotracers present the advantage of allowing for multiple scans on the same subject in the same day. Here, we describe [11C|3MeO4AP, a novel 11C-labeled version of the K+ channel tracer [18F]3F4AP, and characterize its imaging properties in two nonhuman primates including a monkey with a focal brain injury sustained during a surgical procedure three years prior to imaging. Our findings show that [11C]3MeO4AP is brain permeable, metabolically stable and has high plasma availability. When compared with [18F]3F4AP, [11C]3MeO4AP shows very high correlation in volumes of distribution (VT) confirming a common target. [11C]3MeO4AP shows slower washout than [18F]3F4AP suggesting stronger binding. Finally, similar to [18F]3F4AP, [11C]3MeO4AP is highly sensitive to the focal brain injury. All these features make it a promising radioligand for imaging demyelinated lesions.

neuroscience↗

bioRxiv2020

Evaluation of the potassium channel tracer 3F4AP in rhesus macaques

Demyelination causes slowed or failed neuronal conduction and is a driver of disability in multiple sclerosis and other neurological diseases. Currently, the gold standard for imaging demyelination is MRI, but despite its high spatial resolution and sensitivity to demyelinated lesions, it remains challenging to obtain specific and quantitative measures of demyelination. To understand the contribution of demyelination in different diseases and to assess the efficacy of myelin-repair therapies, it is critical to develop new in vivo imaging tools sensitive to changes induced by demyelination. Upon demyelination, axonal K+ channels, normally located underneath the myelin sheath, become exposed and increase in expression, causing impaired conduction. Here, we investigate the properties of the K+ channel PET tracer [18F]3F4AP in primates and its sensitivity to a focal brain injury that occurred three years prior to imaging. [18F]3F4AP exhibited favorable properties for brain imaging including high brain penetration, high metabolic stability, high plasma availability, high reproducibility, high specificity, and fast kinetics. [18F]3F4AP showed preferential binding in areas of low myelin content as well as in the previously injured area. Sensitivity of [18F]3F4AP for the focal brain injury was higher than [18F]FDG, [11C]PiB and [11C]PBR28, and compared favorably to currently used MRI methods.

neuroscience↗