Synthesis and Evaluation of a Fluorine-18 Radioligand for Imaging Huntingtin Aggregates by Positron Emission Tomographic Imaging.

Mutations in the huntingtin gene (HTT) triggers aggregation of huntingtin protein (HTT), which is the hallmark pathology of neurodegenerative Huntington's disease (HD). Development of a high affinity F radiotracer would enable the study of Huntington's disease pathology using a non-invasive imaging modality, positron emission tomography (PET) imaging. Herein, we report the first synthesis of fluorine-18 imaging agent, 6-(5-((5-(2,2-difluoro-2-(fluoro-F)ethoxy)pyridin-2-yl)methoxy)benzo[]oxazol-2-yl)-2-methylpyridazin-3(2)-one ([F]1), a radioligand for HD and its preclinical evaluation (autoradiography of post-mortem HD brains) and (rodent and non-human primate brain PET).

Identification of AV-1451 as a Weak, Nonselective Inhibitor of Monoamine Oxidase.

[F]AV-1451 is one of the most widely used radiotracers for positron emission tomography (PET) imaging of tau protein aggregates in neurodegenerative disorders. While the radiotracer binds with high affinity to tau neurofibrillary tangles, extensive clinical studies have simultaneously revealed off-target tracer accumulation in areas of low tau burden such as the basal ganglia and choroid plexus. Though there are a number of possible reasons for this accumulation, it is often attributed to off-target binding to monoamine oxidase (MAO).

Evaluating Cholinergic Receptor Expression in Guinea Pig Primary Auditory and Rostral Belt Cortices After Noise Damage Using [H]Scopolamine and [F]Flubatine Autoradiography.

Noise-induced hearing loss leads to anatomic and physiologic changes in primary auditory cortex (A1) and the adjacent dorsal rostral belt (RB). Since acetylcholine is known to modulate plasticity in other cortical areas, changes in A1 and RB following noise damage may be due to changes in cholinergic receptor expression. We used [H]scopolamine and [F]flubatine binding to measure muscarinic acetylcholine receptor (mAChR) and nicotinic acetylcholine receptor (nAChR) expression, respectively, in guinea pig A1 and RB 3 weeks following unilateral, left ear noise exposure, and a temporary threshold shift in hearing.

Futureproofing [F]Fludeoxyglucose manufacture at an Academic Medical Center.

Background: We recently upgraded our [F]fludeoxyglucose (FDG) production capabilities with the goal of futureproofing our FDG clinical supply, expanding the number of batches of FDG we can manufacture each day, and improving patient throughput in our nuclear medicine clinic. In this paper we report upgrade of the synthesis modules to the GE FASTLab 2 platform (Phase 1) and cyclotron updates (Phase 2) from both practical and regulatory perspectives. We summarize our experience manufacturing FDG on the FASTLab 2 module with a high-yielding self-shielded niobium (Nb) fluorine-18 target.

Synthesis and pre-clinical evaluation of a potential radiotracer for PET imaging of the dopamine D receptor.

There is considerable interest in using positron emission tomography (PET) imaging to understand the function of dopamine D receptors. Due to high sequence homology with D receptors, development of D-selective PET radiotracers has been challenging. In an effort to overcome this issue, we report the radiosynthesis of a new selective D ligand with carbon-11 ( ), and its initial preclincial evaluation as a potential PET radiotracer for imaging of D receptors.

Automated synthesis of [Ga]oxine, improved preparation of Ga-labeled erythrocytes for blood-pool imaging, and preclinical evaluation in rodents.

Radiolabeled erythrocytes have multiple applications in nuclear medicine, including blood pool imaging. Historically they have been labeled with SPECT radionuclides. A PET blood pool imaging agent is highly desirable as it would improve clinical applications with better image quality and resolution, higher sensitivity, and dynamic scanning capabilities.

Investigation of Proposed Activity of Clarithromycin at GABAA Receptors Using [(11)C]Flumazenil PET.

Clarithromycin is a potential treatment for hypersomnia acting through proposed negative allosteric modulation of GABAA receptors. We were interested whether this therapeutic benefit might extend to Parkinson's disease (PD) patients because GABAergic neurotransmission is implicated in postural control. Prior to initiating clinical studies in PD patients, we wished to better understand clarithromycin's mechanism of action.

Synthesis and Evaluation of [(18)F]RAGER: A First Generation Small-Molecule PET Radioligand Targeting the Receptor for Advanced Glycation Endproducts.

The receptor for advanced glycation endproducts (RAGE) is a 35 kDa transmembrane receptor that belongs to the immunoglobulin superfamily of cell surface molecules. Its role in Alzheimer's disease (AD) is complex, but it is thought to mediate influx of circulating amyloid-β into the brain as well as amplify Aβ-induced pathogenic responses. RAGE is therefore of considerable interest as both a diagnostic and a therapeutic target in AD.

Targeting Metal-Aβ Aggregates with Bifunctional Radioligand [C]L2-b and a Fluorine-18 Analogue [F]FL2-b.

Interest in quantifying metal-Aβ species led to the synthesis and evaluation of [C]L2-b and [F]FL2-b as radiopharmaceuticals for studying the metallobiology of Alzheimer's disease (AD) using positron emission tomography (PET) imaging. [C]L2-b was synthesized in 3.6% radiochemical yield (nondecay corrected, = 3), >95% radiochemical purity, from the corresponding desmethyl precursor.

High affinity radiopharmaceuticals based upon lansoprazole for PET imaging of aggregated tau in Alzheimer's disease and progressive supranuclear palsy: synthesis, preclinical evaluation, and lead selection.

Abnormally aggregated tau is the hallmark pathology of tauopathy neurodegenerative disorders and is a target for development of both diagnostic tools and therapeutic strategies across the tauopathy disease spectrum. Development of carbon-11- or fluorine-18-labeled radiotracers with appropriate affinity and specificity for tau would allow noninvasive quantification of tau burden using positron emission tomography (PET) imaging. We have synthesized [(18)F]lansoprazole, [(11)C]N-methyl lansoprazole, and [(18)F]N-methyl lansoprazole and identified them as high affinity radiotracers for tau with low to subnanomolar binding affinities.

Synthesis and evaluation of [(11)C]PyrATP-1, a novel radiotracer for PET imaging of glycogen synthase kinase-3β (GSK-3β).

Introduction: The dysfunction of glycogen synthase kinase-3β (GSK-3β) has been implicated in a number of diseases, including Alzheimer's disease. The ability to non-invasively quantify GSK-3β activity in vivo is therefore of critical importance, and this work is focused upon development of inhibitors of GSK-3β radiolabeled with carbon-11 to examine quantification of the enzyme using positron emission tomography (PET) imaging.

Methods: (11)C PyrATP-1 was prepared from the corresponding desmethyl-piperazine precursor in an automated synthesis module.

Evaluation of [(11)C]N-Methyl Lansoprazole as a Radiopharmaceutical for PET Imaging of Tau Neurofibrillary Tangles.

[(11)C]N-Methyl lansoprazole ([(11)C]NML, 3) was synthesized and evaluated as a radiopharmaceutical for quantifying tau neurofibrillary tangle (NFT) burden using positron emission tomography (PET) imaging. [(11)C]NML was synthesized from commercially available lansoprazole in 4.6% radiochemical yield (noncorrected RCY, based upon [(11)C]MeI), 99% radiochemical purity, and 16095 Ci/mmol specific activity (n = 5).

Hippocampal inactivation disrupts the acquisition and contextual encoding of fear extinction.

In recent studies, inactivation of the dorsal hippocampus before the retrieval of extinguished fear memories disrupted the context-dependent expression of these memories. In the present experiments, we examined the role of the dorsal hippocampus in the acquisition of extinction. After pairing an auditory conditional stimulus (CS) with an aversive footshock [unconditional stimulus (US)], rats received an extinction session in which the CS was presented without the US.

Intratumoral injection of BCNU in ethanol (DTI-015) results in enhanced delivery to tumor--a pharmacokinetic study.

Solvent facilitated perfusion (SFP) has been proposed as a technique to increase the delivery of chemotherapeutic agents to tumors. SFP entails direct injection of the agent into the tumor in a water-miscible organic solvent, and because the solvent moves easily through both aqueous solutions and cellular membranes it drives the penetration of the solubilized anticancer agent throughout the tumor. To test this hypothesis, we compared the pharmacokinetics (PK) of 14C-labeled 1,3-bis-chlorethyl-1-nitrosourea (BCNU) in intra-cerebral 9L rat gliomas after intravenous (IV) infusion in 90% saline--10% ethanol or direct intratumoral (IT) injection of 14C-BCNU in 100% ethanol (DTI-015).

Differential effects of scopolamine on in vivo binding of dopamine transporter and vesicular monoamine transporter radioligands in rat brain.

The in vivo equilibrium specific binding of d-threo-[3H]methylphenidate, a radioligand for the dopamine transporter (DAT), and +-alpha-[3H]dihydrotetrabenazine, a radioligand for the vesicular monoamine transporter (VMAT2), were examined in rat brain with and without prior administration of 5 mg/kg scopolamine. Drug-treated animals exhibited a 30% increase in d-threo-[3H]methylphenidate binding to the DAT in the striatum relative to controls. No changes in specific binding of +-alpha-[3H]dihydrotetrabenazine were observed in any brain region following scopolamine pretreatment.

Protein synthesis in the amygdala, but not the auditory thalamus, is required for consolidation of Pavlovian fear conditioning in rats.

The amygdala is an essential neural substrate for Pavlovian fear conditioning. Nevertheless, long-term synaptic plasticity in amygdaloid afferents, such as the auditory thalamus, may contribute to the formation of fear memories. We therefore compared the influence of protein synthesis inhibition in the amygdala and the auditory thalamus on the consolidation of Pavlovian fear conditioning in Long-Evans rats.

Treatment effects on nigrostriatal projection integrity in partial 6-OHDA lesions: comparison of L-DOPA and pramipexole.

There is controversy over potential effects of dopaminergic replacement therapies on the partially lesioned nigrostriatal dopaminergic projection. We evaluated indirect (levodopa, L-DOPA) versus direct (pramipexole, PRA) dopaminergic treatment effects on nigrostriatal lesion severity as measured with vesicular monoamine transporter type-2 (VMAT2) binding. Prior studies have shown that striatal VMAT2 density provides an objective estimate of dopaminergic neuronal integrity, without confounding effects of compensatory regulation.

Striatal monoaminergic terminals in Lewy body and Alzheimer's dementias.

Vesicular monoamine transporter type 2 and benzodiazepine binding site expressions were examined with quantitative autoradiography in postmortem striata from 19 patients with dementia with Lewy bodies, seven patients with dementia with Lewy bodies and Alzheimer's disease, 12 patients with Alzheimer's disease, and eight neurologically normal subjects. Striatal vesicular monoamine transporter type 2 expression in dementia with Lewy bodies and in dementia with Lewy bodies plus Alzheimer's disease was reduced significantly, indicating degeneration of nigrostriatal projections. Striatal benzodiazepine binding site expression was unchanged, indicating preserved intrinsic striatal neuropil.

Cholinergic vesicular transporters in progressive supranuclear palsy.

Objective: To determine the status of cholinergic and monoaminergic vesicular transporter binding sites in progressive supranuclear palsy (PSP).

Methods: The authors determined autoradiographically the regional expression of acetylcholine vesicular transporter (VAChT) and monoamine vesicular transporter type 2 (VMAT2) binding sites in postmortem basal ganglia samples from subjects with PSP. Comparison neurochemical measures included choline acetyltransferase (ChAT) enzyme activity and benzodiazepine (BZ) binding sites.